Design, synthesis, structure-activity relationship, and in vivo activity of azabicyclic aryl amides as α7 nicotinic acetylcholine receptor agonists

Article abstract of DOI:10.1016/j.bmc.2006.09.019

A novel set of azabicyclic aryl amides have been identified as potent and selective agonists of the α7 nAChR. A two-pronged approach was taken to improve the potential hERG liability of previously disclosed α7 nAChR agonist, PNU-282,987, while maintaining the compound's other desirable pharmacological properties. The first approach involved further exploration of the aryl carboxylic acid fragment of PNU-282,987, while the second approach focused on modification of the azabicyclic amine portion of PNU-282,987. The best compounds from each series are characterized by rapid brain penetration, good oral bioavailability in rat, and demonstrate in vivo efficacy in a rat P50 auditory sensory gating assay. At least one analog from each series (1h, 1o, 2a, 9a, and 18a) shows an improved hERG safety profile over PNU-282,987.

Full text of DOI:10.1016/j.bmc.2006.09.019

Bioorganic & Medicinal Chemistry 14 (2006) 8219–8248
Design, synthesis, structure–activity relationship, and in vivo
activity of azabicyclic aryl amides as a7 nicotinic
acetylcholine receptor agonists
Daniel P. Walker, Donn G. Wishka, David W. Piotrowski, Shaojuan Jia,ꢀ Steven C. Reitz,
Karen M. Yates, Jason K. Myers,ꢀ Tatiana N. Vetman,ꢀ Brandon J. Margolis,ꢀ
E. Jon Jacobsen, Brad A. Acker, Vincent E. Groppi, Mark L. Wolfe,ꢁ
Bruce A. Thornburgh, Paula M. Tinholt, Luz A. Cortes-Burgos, Rodney R. Walters,
Matthew R. Hester, Eric P. Seest,ꢀ Lester A. Dolak, Fusen Han,§ Barbara A. Olson,
Laura Fitzgerald, Brian A. Staton,ꢀ Thomas J. Raub,ꢀ Mihaly Hajos,
William E. Hoffmann, Kai S. Li, Nicole R. Higdon,ꢁ Theron M. Wall,ꢁ
Raymond S. Hurst, Erik H. F. Wong and Bruce N. Rogers*
Neuroscience Research, Pfizer Global Research and Development, Eastern Point Rd., Groton, CT 06340, USA
Received 22 July 2006; revised 11 September 2006; accepted 11 September 2006
Available online 2 October 2006
Abstract—A novel set of azabicyclic aryl amides have been identified as potent and selective agonists of the a7 nAChR. A two-
pronged approach was taken to improve the potential hERG liability of previously disclosed a7 nAChR agonist, PNU-282,987,
while maintaining the compound’s other desirable pharmacological properties. The first approach involved further exploration
of the aryl carboxylic acid fragment of PNU-282,987, while the second approach focused on modification of the azabicyclic amine
portion of PNU-282,987. The best compounds from each series are characterized by rapid brain penetration, good oral bioavail-
ability in rat, and demonstrate in vivo efficacy in a rat P50 auditory sensory gating assay. At least one analog from each series
(1h, 1o, 2a, 9a, and 18a) shows an improved hERG safety profile over PNU-282,987.
ꢀ 2006 Elsevier Ltd. All rights reserved.
1. Introduction
gated ion channels that are formed by combinations of
a and b subunits, or as homopentamers in the case of
a7, a8, and a9. To date, 10 a and 4 b isoforms have been
discovered, resulting in a huge diversity of possible com-
positions, though only a small subset of combinations
have been shown to give rise to functionally and physi-
ologically relevant channels.2
Nicotinic acetylcholine receptors (nAChRs) are found
throughout the central and peripheral nervous systems,
as well as in the neuromuscular junction.1 Numerous
studies have established the importance of nAChRs
within the CNS, in particular their link to higher pro-
cesses such as memory, cognition, reward, and sensory
processing.1 Neuronal nAChRs are pentameric ligand-
The homomeric a7 subtype is highly permeable to calci-
um and has been proposed to modulate a variety of
attention and cognitive processes.3 These receptors are
prevalent in the hippocampus, where they modulate
inhibitory GABAergic synaptic transmission involved
in sensory processing. Deficits in auditory sensory pro-
cessing are thought to lead to a state of sensory overload
and are hypothesized to contribute to the attention and
cognitive symptoms in a variety of CNS diseases, most
convincingly in schizophrenia.
Keywords: a7; Nicotinic; nAChR; PHA-543613.
Corresponding author. Tel.: +1 860 686 0545; fax: +1 860 686
5403; e-mail: bruce.n.rogers@pfizer.com
*
ꢀ
Present address: The Lilly Research Laboratories, Lilly Corporate
Center, Indianapolis, IN 46285, USA.
ꢁ
Present address: MPI Pharmaceuticals, Mattawan, MI, USA.
Present address: Department of Material Sciences, University of
Oregon, Eugene, OR, USA.
§
0968-0896/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2006.09.019

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D. P. Walker et al. / Bioorg. Med. Chem. 14 (2006) 8219–8248
Interest in the a7 nAChR as a medicinal chemistry tar-
get has greatly expanded over the past decade, with a fo-
cus on the identification of new and selective chemical
entities.4 Most ligands described in the primary litera-
ture as a7 nAChR agonists are derived from the quinu-
clidine scaffold, and include such structures as
spirooxazolidinone AR-R17779,5 quinuclidine carba-
mates,6 amides,7 and ethers.8 Reports in the primary lit-
erature describing additional structural diversity in the
amine portion of a7 nAChR ligands have been limited.
One significant departure from the quinuclidine tem-
plate is the partial agonist GTS-21, which is an anabase-
ine analog.9
SAR Strategy
Amine
Portion
N
O
N
H
Acid
Portion
R
Figure 1. Strategy for the quinuclidine amide series structure–activity
relationship.
While further evaluation of PHA-543,613 was under-
way, we sought to identify additional novel, potent
(<50 nM), and selective a7 nAChR agonists that, like
PHA-543,613, possess reduced hERG activity and low
first pass metabolism. We detail below the synthesis
and biological profiles of an expanded set of novel
nAChR ligands. To expand the SAR on the quinucli-
dine amide template and gain a broader understanding
of the overlap with other nicotinic pharmacophores,
two parallel approaches were utilized. The first focused
on the acid portion of the quinuclidine template and in-
volved preparing an expanded set of 6,5- and 6,6-fused
aryl rings. The second approach investigated modifica-
tions to the azabicyclic ring system (Fig. 1).
O
H
O
H
O
N
N
Ar
N
N
NH
Ar
N
O
O
Quinuclidine
carbamates
AR-R17779
Quinuclidine
amides
MeO
N
OMe
S
O
N
N
GTS-21
Quinuclidine
ethers
Within the nAChR field, alternative azabicyclic amines
are prevalent among ligands for other subtypes of recep-
tors. An example is epibatidine,10 a non-selective
nAChR agonist containing the 7-azabicyclo[2.2.1] ring
system. This compound has served as a lead for fruitful
exploration of selective a4b2 ligands and has inspired
alterations such as the ABT-594 template.11 The recent
disclosure of varenicline,12 possessing a benzo-fused 3-
azabicyclo[3.2.1] ring system, also highlights the diversi-
ty of nAChR ligands.
2. Chemistry
According to Scheme 1, treatment of 3-(R)-aminoquinu-
clidine dihydrochloride with an aryl carboxylic acid,
using O-(7-azabenzotriazole-1-yl)-N,N,N0,N0-tetrameth-
yluronium hexafluorophosphate (HATU), diphenyl
phosphoryl azide (DPPA), diphenyl phosphinic chloride
(DPPCl) or benzotriazol-1-yl-oxytripyrrolidino phos-
phonium hexafluorophosphate (PyBOP), followed by
salt formation gave rise to quinuclidine benzamides
(1a–v).15 In general, the HATU conditions afforded
cleaner products in higher yields. The custom aryl car-
boxylic acid fragments were either prepared via multi-
step synthesis,15 or were available commercially.
Cl
NH
H
Cl
N
O
N
N
N
N
H
N
H
Epibatidine
ABT-594
varenicline
Carboxamides 2a–e were prepared by HATU coupling
of enantiomerically pure (2S,3R)-2-methyl-3-aminoqui-
nuclidine dihydrochloride [(+)-3] with aryl carboxylic
acids (Scheme 2).16 The known racemic ketone 4,17 pre-
pared in high yield from 2-(hydroxymethyl)-1-azabicy-
clo[2.2.2]octane-3,3-diol hydrochloride (5), served as
the starting material for the preparation of (+)-3. Treat-
ment of ketone 4 with hydroxylamine gave the corre-
sponding oxime as a mixture of geometric isomers.
Exposure of the oxime to dissolving metal conditions
afforded a 5:1 mixture of isomers favoring the desired
trans-configuration [( )-3]. Workup with ethanol al-
lowed clean isolation of the trans-isomer. Enantiomeri-
cally pure amide 7 was obtained via coupling amine
( )-3 with 4-chlorobenzoic acid followed by subsequent
chromatographic resolution. Hydrolysis of carboxamide
7 gave rise (67%) to amine (+)-3. The absolute configu-
ration of (+)-3 was unambiguously established as
(2S,3R) by single crystal X-ray analysis of thienyl amide
Our initial efforts in the a7 nAChR area have focused on
the quinuclidine amide template, exemplified by PNU-
282,987,7 and PHA-543,613.13 Chlorobenzamide PNU-
282,987 was identified as a potent and selective agonist
of the a7 nAChR with robust in vivo activity in a vali-
dated rat model of impaired sensory gating.14 This com-
pound was later found however to significantly inhibit
the human Ether-a-go-go (hERG) potassium channel.
Subsequent lead optimization of PNU-282,987 led to
the discovery of PHA-543,613,13 a potent, selective,
and in vivo efficacious a7 agonist with reduced hERG
activity.
N
N
O
O
N
N
H
H
N
O
Cl
18
PHA-543,613
PNU-282,987
8 (Chart 1).

D. P. Walker et al. / Bioorg. Med. Chem. 14 (2006) 8219–8248
8221
H
NO2
EtO2C
CO2Et
NH2
+
N
Ar
a or b or c or d
24-86%
NO2
OBz
a
b, c
ArCO2H
+
O
N
N
N
67%
65%
HX
1a-v
NH
2HCl
Ph
Ph
11
12
10
HN
Scheme 1. General synthetic route for quinuclidine amide analogs.
Reagents and conditions: (a) i—HATU, i-Pr2NEt, DMF, 0 ꢁC ! rt,
ii—HX, methanol; (b) i—DPPA, Et3N, DMF, H2O, rt, ii—HX,
methanol; (c) i—DPPCl, Et3N, THF, rt, ii—HX, methanol; (d) i—
PyBOP, i-Pr2NEt, DMF, rt, ii—HX, methanol.15
HO
HN
BOC
EtO2C
BOC
f, g, h
86%
d, e
N
N
47%
Ph
Ph
13
(+)-14
OH
O
Me
c, d, e
64%
a, b
H
N
OH
Ar
NH2
2TsOH
i, j
90%
N
N
N
N
H
O
H
63-84%
HCl
OH
fumarate
4
9a-e
5
15
Cl
NH2
NH2
H
N
f, g
Scheme 3. General synthetic route for 1-azabicyclo[2.2.1]heptan-3-yl
carboxamide analogs. Reagents and conditions: (a) EtOH, rt; (b) H2,
RaNi, EtOH, 50 psi, rt; (c) BOC2O, CH2Cl2, rt; (d) LiAlH4, THF,
ꢀ5 ꢁC; (e) chromatographic separation of enantiomers; (f) MsCl,
Et3N, CH2Cl2, 0 ꢁC ! rt; (g) H2, 10% Pd/C, EtOH, rt; (h) 2.2 equiv
TsOH, EtOH, reflux; (i) ArCO2H, HATU, i-Pr2NEt, DMF, 0 ꢁC ! rt;
(j) fumaric acid, MeOH.15
+
40%
N
N
O
2HCl
2HCl
N
6
( )-3
NH2
1:5
(+)-7
H
i or j, k
N
Ar
h
O
67%
36-74%
N
2HCl
N
HCl
aluminum hydride followed by chromatographic resolu-
tion. Reaction of the alcohol with methanesulfonyl
chloride effected ring closure to give a quaternary
ammonium salt. Hydrogenolysis of the benzyl group
and cleavage of the BOC group generated diamine 15.
Amide coupling of 15 with aryl carboxylic acids gave
rise to carboxamides 9a–e. The absolute configuration
of diamine 15 was unambiguously established by single
crystal X-ray analysis of thienyl amide 16 (Chart 1).21
2a-e
(+)-3
Scheme 2. General synthetic route for 2-methylquinuclidine amide
analogs. Reagents and conditions: (a) K2CO3, CH2Cl2–H2O, rt; (b)
H2, 10% Pd/C, 45 psi; (c) NH2OHÆHCl, EtOH, rt; (d) Naꢁ, n-PrOH,
reflux; (e) concd HCl, EtOH; (f) 4-chlorobenzoic acid, HATU, i-
Pr2NEt, DMF, 0 ꢁC ! rt; (g) chromatographic resolution; (h) concd
HCl, EtOH, reflux; (i) ArCO2H, HATU, i-Pr2NEt, DMF, 0 ꢁC ! rt;
(j) ArCO2H, DPPCl, Et3N, THF, rt; (k) HCl, MeOH.15
H
H
Br
3
N
Br
N
3
S
BOC
4N
S
2
CO2Me
O
N
O
H
N
8
a, b
c
16
fumarate
HCl
+
N
BOC
H
58%
70%
BOC
N
4
Br
CO2Me
H
Br
2
17
N
S
1
BOC
N
BOC
N
H
O
22
d, e
f
H
N
CO2H
Chart 1. Bromothiophene analogs utilized to establish stereochemical
proof via single crystal X-ray analysis.
20%
CBZ
96%
H
H
(+)-20
19
BOC
N
H
N
HCl
The (3R,4S)-1-Azabicyclo[2.2.1]heptan-3-yl carboxa-
mides of type 9 were prepared as shown in Scheme 3.16
The synthesis began with pyrrolidine 10,19 recognized
in 1997 as a logical starting point for the preparation
of exo-3-amino-1-azabicyclo[2.2.1] heptanes.20 Pyrroli-
dine 10 was conveniently prepared in 65% yield via tan-
dem Michael addition reaction of amine 11 with
nitroethene precursor 12.19 Reduction of the nitro group
and subsequent BOC protection led to carbamate 13.
Enantiomerically pure alcohol 14 was obtained in two
steps by reduction of the ester function with lithium
g or h, i
52-90%
H
N
Ar
NH2
H
H
O
21
18a-d
Scheme 4. General synthetic route for 7-azabicyclo[2.2.1]heptan-2-yl
carboxamides. Reagents and conditions: (a) 90–95 ꢁC, 30 h; (b) H2,
10% Pd/C, NaHCO3, EtOH; (c) NaOMe, MeOH, reflux; aq workup;
(d) (PhO)2P(O)N3, Et3N, PhCH3, reflux; BnOH, reflux; (e) chroma-
tographic resolution; (f) H2, 10% Pd/C, EtOH; (g) ArCO2H, HATU,
i-Pr2NEt, DMF; (h) BOPCl, Et3N, CH2Cl2, rt; (i) HCl, MeOH.15

8222
D. P. Walker et al. / Bioorg. Med. Chem. 14 (2006) 8219–8248
The known azabicyclic ester 17,22 prepared in 58% yield
(Scheme 4), served as a rational starting point for the
synthesis of (1S,2R,4R)-7-azabicyclo[2.2.1]heptan-2-yl
carboxamides of type 18.16 Toward this end, treatment
of endo-ester 17 with sodium methoxide, followed by
careful aqueous workup, led to a 20:1 mixture of exo:
endo carboxylic acids.23 Curtius rearrangement of
carboxylic acid 19 and benzyl alcohol trapping of the
resulting isocyanate gave rise to the corresponding
CBZ-protected amine ( )-20 (94%), which was
chromatographically resolved to afford (+)-20. Amine
21 was obtained in 96% yield by hydrogenolysis of the
CBZ-group. Carboxamides of type 18 were obtained in
two steps by amide bond formation followed by subse-
quent exposure to methanolic hydrogen chloride. Single
crystal X-ray analysis of bromothienyl amide derivative
22 unambiguously established the absolute configuration
of type 18 amides as (1S,2R,4R) (Chart 1).24
FLIPR assay and good activity in the a7 nAChR bind-
ing assay.
Reasonable a7 nAChR binding and potency is demon-
strated by benzoxazole 1e and its regioisomer 1f; unfortu-
nately, neither analog is stable in RLM. While 5-
substituted benzothiazole 1g did not meet our potency cri-
teria, 6-substituted benzothiazole 1h shows good potency
and affinity in the FLIPR and binding assays, respective-
ly, and possesses good stability in RLM. Indazole 1i
shows similar a7-5HT3 potency, a7 receptor binding,
and RLM stability to that of benzothiazole 1h. Regioiso-
meric indazole 1j is five times less potent in the FLIPR as-
say than 1i; consequently, it did not meet our potency
requirement. Pyrrolopyrimidine 1k possess excellent a7
nAChR binding and a7-5HT3 potency. Despite its mod-
est stability in RLM, analog 1k was retained for further
evaluation. Excellent binding and potency are demon-
strated by indolizine 1l and pyrrolo–pyrazine 1m. Howev-
er, based on the low RLM stability shown by 1l and 1m,
further profiling of these two analogs was not justified.
Interestingly, imidazopyridine 1n is 55 times less potent
in the chimera assay than indolizine 1l; consequently, it
was dropped from consideration.
3. Results and discussion
Over 100 analogs of type 1 possessing either a 6,5- or
6,6-fused aryl ring were prepared; subsets of these com-
pounds are shown in Tables 1 and 2, respectively, with
PNU-282,987 and PHA-543,613 being shown for com-
parative purposes. A prior study on mono-substituted
quinuclidine benzamides, such as PNU-282,987, estab-
lished that the 3(R)-configuration on the quinuclidine
ring is the preferred stereochemistry, and that para-sub-
stitution is favored over meta- and ortho-substitution.7
A subsequent study found that analogs possessing a
5-membered ring fused to the parent benzamide, such
as PHA-543,613, generally show enhanced a7 nAChR
activity.13 Accordingly, the analogs in Tables 1 and 2 re-
flect application of this knowledge. Newly prepared
compounds were first evaluated in a FLIPR-based func-
tional assay that utilizes SH-EP1 cells expressing an a7-
5HT3 chimeric receptor.25 This chimera combines the li-
gand binding domain of the a7 nAChR and the pore
forming region of the 5-HT3 receptor.26 Compounds
possessing an a7-5HT3 EC50 of less than 500 nM were
subsequently evaluated in an a7 nAChR binding assay
and a rat liver microsomes (RLM) stability assay. The
RLM assay was chosen as an initial predictor of in vivo
rat clearance within this series of analogs.
Benzodioxane 1o displays reasonable a7-5HT3 potency
in the FLIPR assay, good binding to the a7 nAChR,
and shows modest stability in the RLM assay (Table
2). Replacing the oxygen atom meta to the carboxamide
function in 1o with saturated carbon gave rise to chro-
man 1p. While chroman 1p demonstrates similar poten-
cy and binding to that of benzodioxane 1o, it lacks
sufficient stability in RLM. Both the corresponding
7-substituted chroman derivative 1q and tetralin 1r pos-
sess weak activity in the a7-5HT3 functional assay.
Interestingly, naphthalene 1s is 14 times more potent
than tetralin 1r and shows high affinity toward the a7
nAChR in a binding assay. Unfortunately, analog 1s
has low stability in RLM. Dioxanopyridine 1t is about
four times less potent than benzodioxane 1o, consistent
with the decrease in activity seen in the corresponding
benzodioxole/dioxolopyridine series. Neither of the ben-
zoxazines 1u or 1v showed sufficient potency in the
FLIPR assay to justify further evaluation. In general,
it was found that 6,5-fused aryl analogs of type 1 are
more potent in the a7-5HT3 assay than 6,6-fused type
1 analogs. Analogs containing a fused ring capable of
supplying additional electron density via resonance to
the amide carbonyl show enhanced a7-5HT3 activity
(compare 1a and 1b). Compounds possessing a hydro-
gen bond donating atom in the fused ring, such as 1c,
1j, and 1v, regardless of ring size, show diminished
a7-5HT3 activity; one exception is indazole 1i. Based
on the data shown in Tables 1 and 2, four compounds
were identified for further evaluation, namely benzo-
thiazole 1h, indazole 1i, pyrrolopyrimidine 1k, and
benzodioxane 1o.
Benzodioxole 1a is more potent than both PNU-282,987
and PHA-543,613 in the a7-5HT3 chimera assay and
demonstrates tight binding to the a7 nAChR; however,
its excellent activity is offset by its poor stability in
RLM. Replacing the oxygen atoms in the dioxole ring
of compound 1a with saturated carbon atoms produced
indan 1b, which is an order of magnitude less potent
than 1a. Benzimidazole 1c is two orders of magnitude
less potent than benzodioxole 1a. The large differences
in potencies for compounds 1a–c are not surprising
based on previously tested compounds in this series.7,13
Replacing the carbon atom at the 6-position of benzodi-
oxole 1a with nitrogen afforded dioxolopyridine 1d.
While 1d is somewhat less potent than the correspond-
ing benzodioxole 1a, it still shows good potency in the
Although many analogs in Table 1 met our potency
requirement, a good percentage of those analogs showed
low stability in the RLM assay. Additional metabolic
data on some of the compounds in Table 1 revealed that
the primary bioactivation pathway in rats involves

D. P. Walker et al. / Bioorg. Med. Chem. 14 (2006) 8219–8248
Table 1. Quinuclidine amine 6,5-fused heterocyclic analogs
8223
N
O
Ar
N
H
1a-n
Compound
Ar
a7-5HT3 chimera
EC50 (nM)
a7 Kib (nM)
In vitro RLM %
remainc
a
PNU-282987
128 31 (n = 16)
24 8 (n = 13)
96
Cl
O
PHA-543613
65 11 (n = 12)
37, 75
330
9
1 (n = 5)
55
<1
2
N
O
O
1a
1b
1c
1d
1e
1f
24
60, 160
NT
H
N
3800
NT
NT
3
N
O
O
130
34 11 (n = 4)
32 11 (n = 4)
260, 380
61, 92
N
N
O
130
O
N
290
4
N
S
1g
1h
1i
720
NT
59
47
NT
10
2
S
N
170, 260
190, 220
1500
20, 40
H
N
64, 40
N
N
1j
NT
N
H
1k
1l
130, 90
140
10, 14
N
N
N
13
N
N
1m
1n
130
13, 21
4
N
7500
NT
NT
N
a Cell based FLIPR assay using SH-EP1 cells expressing the a7-5HT3 chimera. Numbers indicate EC50 values generated from individual 7-point
concentration–response relationships; means SEM is shown when P3 determinations were made.
b [3H]MLA rat brain homogenate binding assay. Numbers indicate individual Ki values or means SEM are shown when P3 determinations were
made.
c In vitro metabolism in rat liver microsomes, expressed as % remaining at 1 h.

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D. P. Walker et al. / Bioorg. Med. Chem. 14 (2006) 8219–8248
Table 2. Quinuclidine amine 6,6-fused heterocyclic analogs
N
O
Ar
N
H
1o-v
a
Compound
Ar
a7-5HT3chimera EC50 (nM)
a7 Kib (nM)
In vitro RLM %
remainc
O
O
1o
258 26 (n = 4)
44 7 (n = 7)
12
1p
1q
1r
1s
350, 460
28, 29
NT
2
O
O
1300, 1300
1700, 1100
140, 62
NT
NT
1
NT
16
O
O
1t
900
299 68 (n = 4)
NT
NT
N
H
N
1u
1000
NT
O
O
1v
1800
NT
NT
N
H
a Cell based FLIPR assay using SH-EP1 cells expressing the a7-5HT3 chimera. Numbers indicate EC50 values generated from individual 7-point
concentration–response relationships; means SEM are shown when P3 determinations were made.
b [3H]MLA rat brain homogenate binding assay. Numbers indicate individual Ki values or means SEM are shown when P3 determinations were
made.
c In vitro metabolism in rat liver microsomes, expressed as % remaining at 1 h.
N-oxide formation on the quinuclidine nitrogen (i.e.,
23).27 Furthermore, it was found that type 23 com-
pounds are inactive in the a7-5HT3 chimera assay (data
not shown). At this time, it is unclear why analogs in Ta-
ble 1 are more susceptible to N-oxide formation in the
rat than mono-substituted quinuclidine benzamides like
PNU-282,987. Nevertheless, it was hypothesized that
placing a small alkyl substituent on one of the carbon
atoms adjacent to the bridgehead nitrogen in 1 would
attenuate N-oxide formation and may lead to com-
pounds with greater stability in the RLM assay. After
a brief survey of the literature, it appeared that placing
a methyl group at C-2 on the quinuclidine ring would
be the most synthetically straightforward approach.28
After extensive investigation, it was determined that
within the 2-methyl-3-arylamido quinuclidine series,
the (2S,3R) stereochemistry is the biologically most rel-
evant configuration based on potency in the a7-5HT3
chimera assay.16 Aryl amides based on (2S,3R)-3-ami-
no-2-methylquinuclidine are shown in Table 3. We were
pleased to discover that, when compared to quinuclidine
analogs of type 1, not only do the corresponding
2-methylquinuclidine analogs of type 2 possess very
similar a7-5HT3 potencies and a7 nAChR binding affin-
ities, but they also show enhanced stability in the RLM
assay. Because of this increased stability, additional type
2 analogs were prepared using acid fragments that orig-
inally gave rise to low stability in type 1 analogs. For in-
stance, while naphthalene 1q was too unstable in RLM
to be considered further, naphthalene 2e demonstrated
good stability in RLM. Except for benzothiazole 2b
and benzodioxane 2d, which did other not meet the a7
nAChR binding requirement of <50 nM, all 2-methyl-
quinulclidine analogs in Table 3 were advanced for fur-
ther profiling.
H
H
N
Ar
N
Ar
N
N
O
O
+
O
24
23
-
Early in the program, it was found that aryl amides
derived from a rigid diamine like 3-aminoquinuclidine
(i.e., 1) are potent a7 nAChR agonists, while other aryl
amides derived from a conformationally more flexible
diamine (e.g., 24) are, at best, weak a7 nAChR
agonists.7 The rigid quinuclidine framework enforces

D. P. Walker et al. / Bioorg. Med. Chem. 14 (2006) 8219–8248
Table 3. Alternative azabicyclic amine templates
8225
H
H
H
N
Ar
N
N
Ar
H
N
O
H
O
N
Ar
N
H
18a-d
O
2a-e
9a-e
a
Compound
Ar
a7-5HT3 chimera EC50 (nM)
a7 Kib (nM)
In vitro RLM % remainingc
2a
91
15 2 (n = 3)
69
72
11
71
<1
75
79
84
1
N
N
N
O
9a
92 6 (n = 3)
20 4 (n = 5)
O
O
18a
9b
130, 69
9
1 (n = 4)
O
O
330
63
NT
O
O
18b
2b
490
S
N
200
62, 92
2c
129 5 (n = 3)
23 6 (n = 4)
43 14 (n = 4)
14 4 (n = 2)
340, 350
NT
N
N
N
N
N
N
9c
160
220
570
790
1800
140
360
18c
2d
O
64
NT
NT
44
30
O
O
9d
O
O
18d
2e
NT
O
22, 25
9e
64
a Cell based FLIPR assay using SH-EP1 cells expressing the a7-5HT3 chimera. Numbers indicate EC50 values generated from individual 7-point
concentration–response relationships; means SEM are shown when P3 determinations were made.
b [3H]MLA rat brain homogenate binding assay. Numbers indicate individual Ki values or means SEM are shown when P3 determinations were
made.
c In vitro metabolism in rat liver microsomes, expressed as % remaining at 1 h.
an orientation of the bridgehead nitrogen lone pair that
is orthogonal to the amide carbonyl. Presumably this
orientation is important for optimal binding to the a7
nAChR. Hence, maintaining this relative orientation
of the basic nitrogen lone pair and the amide carbonyl
became a key element in the design of new a7 nAChR
agonists possessing modified quinuclidine rings. We first
considered amides derived from 3-amino-1-azanorborn-
ane 15. Indeed, it is well precedented in the muscarinic
and 5-HT3 literature that azanorbornane can serve as
an effective replacement for quinuclidine.29,30
After determining that type 9 amides possessing the
(3R,4S) stereochemistry are the most potent in the
a7-5HT3 assay (data not shown), additional amides of
type 9 were prepared and tested (Table 3). Generally,

8226
D. P. Walker et al. / Bioorg. Med. Chem. 14 (2006) 8219–8248
azanorbornane amides 9 are 2- to 6-fold less potent
against the a7-5HT3 chimera than the corresponding
quinuclidine amides 1. However, many type 9 amides
do show potent a7-5HT3 activity similar to that of
PNU-282,987. Interestingly, compared to the corre-
sponding quinuclidine analogs, the azanorbornane ana-
logs (9) display greatly enhanced stability in RLM.
Although the increased RLM stability of the azanor-
bornane analogs may in part be due to their increased
hydrophilicity,31 the magnitude of the increased stability
is somewhat surprising. Based on their favorable biolog-
ical activities and RLM stability, azanorbornane ana-
logs 9a and 9c were profiled further.
The 10 compounds identified above were submitted to a
set of ligand-gated ion channel selectivity screens,
including the 5-hydroxytryptamine 3 (5-HT3) receptor,
the predominate ganglionic nAChR (a3b4), and the
neuromuscular nAChR (a1b1kd) (Table 4). All com-
pounds show excellent selectivity against the a3b4
nAChR. While the high selectivity shown for 7-azanor-
bornane 18a against the a3b4 receptor was desirable, the
magnitude of the selectivity was somewhat surprising
given the compound’s structural similarity to epibati-
dine. Most compounds in Table 4 also show excellent
selectivity against the a1b1cd nAChR. Although a few
compounds, such as benzothiazole 1h and naphthalene
2e, display weak a1b1cd nAChR activity, selectivities
toward the a7-5HT3 chimera are still 75- and 225-fold,
respectively. The compounds of highest interest were
evaluated in an a4b2 nAChR binding assay at a single
concentration. 7-Azanorbornane 18a shows weak affini-
ty toward the a4b2 nAChR, which is surprising given its
structural similarity to epibatidine. All other analogs
tested in this assay show little or no affinity for a4b2.
Cross-receptor activity against the 5-HT3 receptor was
observed, which was not unexpected given the high de-
gree of homology between orthosteric sites in a7 and
5-HT3.34 Still, selectivity against the 5-HT3 receptor ran-
ged from a low of 4-fold for pyrrolopyrimidine 1k to
>100-fold for benzothiazole 1h, suggesting there are
structure–activity relationships for this endpoint within
these series. It was further demonstrated that all com-
pounds in Table 4 behave functionally as 5-HT3
antagonists.35
Combining the saturated bicyclic ring of epibatidine
with the aryl carboxamide of type 1 molecules afforded
7-azanorbornane analogs of type 18 (Table 3). ( )-Epi-
batidine is a known a7 nAChR agonist and shows po-
tent binding to the a7 receptor (rat a7 Ki = 21 nM).32
However, epibatidine is non-selective and possesses
exquisite affinity at other nicotinic receptors, such as
a4b2 and a3b2.33 We reasoned that replacing the pyridyl
ring of epibatidine with an N-linked aryl carboxamide
may give rise to analogs with improved selectivity for
the a7 receptor. Thus, we were pleased to discover that
aryl amides of type 18 are active against the a7-5HT3
chimera with the (1S,2R,4R) diastereomers having the
best potency (data not shown).16 Although, type 18
compounds containing either a 6,5- or a 6,6-fused aryl
ring are typically somewhat less potent than similarly
substituted type 1 analogs, several compounds possess-
ing a 6,5-fused aryl ring proved to be equipotent to
the corresponding type 1 analogs, for example, 18a
and 18c, which also show tight binding to the a7
nAChR. 7-Azanorbornane analogs of type 18 generally
show low stability in RLM. Despite this, furopyridine
18a, with an RLM stability of 11%, was retained for fur-
ther profiling as the only representative from the 7-aza-
norbornane series.
To meet program objectives for identifying additional
potent a7 nAChR agonists suitable for development, it
was important that in vitro cardiovascular safety be as-
sessed. Compounds were evaluated in a patch clamp
hERG K+ channel assay (Table 4).36 Prolongation of
the QT interval is believed to increase the risk of cardiac
arrhythmia in humans and could potentially lead to
Table 4. In vitro selectivity for selected compounds
Compound
5-HT3 binding Ki (nM)
Nicotinic selectivity data
a3b4a,b IC50 (lM)
a1b1cda,c IC50 (lM)
a4b2d % inhib
hERGe % inhib
PNU-282987
PHA-543613
1700
630
14%f
990
63
>60
>60
>100
16
14
13
57
29
2
>100
>100
>100
>100
>100
46
1h
1i
3
>100
>100
>100
>100
>100
32
NT
NT
<1
NT
NT
NT
16
<1
71
5
1k
1o
2a
2c
2e
9a
9c
18a
2800
830
430
400
8
18
35
60
16
41
19
64
80
>100
>100
>100
>100
>100
50
690
530
NT
<1
a FLIPR cell based functional assays, numbers indicate EC50 values generated from individual 7-point concentration–response relationships.
b SH-SY5Y cells, a3b4 containing.
c TE671 cells, native a1b1cd.
d Rat brain homogenate binding assay, [3H]cytisine, % block, 1 lM.
e In vitro effect on hERG current (IKr), HEK cells expressed as a percent inhibition at a concentration of 20 lM.
f Percent inhibition at a single concentration of 10 lM.

D. P. Walker et al. / Bioorg. Med. Chem. 14 (2006) 8219–8248
8227
ventricular fibrillation.37 Measuring the ability of a com-
pound to block the hERG potassium channel is an
important preclinical assay to assess the compound’s
proarrhythmic potential.38 Based on the estimated effi-
cacious free drug concentration of PNU-282,987 in rat
(ꢁ190 nM),7,13,39 our goal was to identify compounds
with no greater than 30% inhibition of hERG at
20 lM. Fortunately, over half of the new compounds
in Table 4 meet this criterion. The compounds that did
not meet the hERG selectivity criteria, including pyrrol-
opyrimidines 1k, 2c, 9c, and naphthalene 2e, were re-
moved from further consideration.
determined that compounds 9a, 1o, 18a, and 2a similarly
activate endogenous a7 nAChRs of cultured rat hippo-
campal neurons as measured by patch-clamp electro-
physiology. All four compounds activate desensitizing
a7 nAChR-mediated currents in a concentration-depen-
dent fashion between the tested concentrations of 0.30
and 30 lM (Fig. 2). The evoked responses are normal-
ized to the current evoked by 100 lM (ꢀ)-nicotine to
compare response between cells with different a7
nAChR expression levels. The response evoked by
30 lM of each test compound is completely blocked
by the selective antagonist methyllycaconitine (10 nM),
suggesting that the compounds are acting on a7-con-
taining nAChRs (data not shown).
In an effort to assess blood–brain barrier penetration,
the six compounds were evaluated in a multi-drug resis-
tant (MDR) P-glycoprotein (PgP) assay (Table 5).40
Compounds that show PgP efflux, as evidenced by an
MDR ratio of greater than three, tend to show hindered
brain penetration. Benzothiazole 1h shows significant
PgP efflux and benzodioxane 1o shows slight PgP efflux;
otherwise, the remaining compounds, 2a, 9a, and 18a,
show no PgP efflux.41 CNS penetration was further as-
sessed in a mouse brain uptake assay (MBUA).42 Com-
pounds 1o, 2a, 9a, and 18a show good to excellent brain
penetration in this model. Benzothiazole 1h shows hin-
dered brain penetration in the MBUA, which is consis-
tent with the MDR efflux data. The remaining
compounds were also evaluated in a constant infusion
rat in vivo pharmacokinetic (PK) model (Table 5). In vi-
tro human liver microsome (HLM) extraction ratios
range from low to moderate and are consistent with
the corresponding rat in vitro and in vivo clearance val-
ues; indazole 1i was an exception. Rat oral bioavailabil-
ities range from a high of 82% for furopyridine 2a to a
low of 3% for indazole 1i. With the exception of inda-
zole 1i, in vitro human liver microsome (HLM) extrac-
tion ratios range from low to moderate, consistent
with the corresponding rat in vitro and in vivo clearance
values. Based on the data presented in Table 5, benzo-
thiazole 1h and indazole 1i were dropped from further
consideration.
The in vivo pharmacological activity of a7 nAChR ago-
nists was tested in a rat model of impaired sensory gat-
ing. It was shown previously that amphetamine-induced
auditory gating deficit in rats is restored by nicotine, and
partial or full a7 nAChR agonists,43,44 including PNU-
282,98714 and PHA-543,613.13 In the present study,
PNU-282,987 was used as a positive control and shows
significant reversal of amphetamine-induced gating def-
icit, in line with previous observations (Fig. 3).7,14 Com-
pounds 1o and 9a also show significant in vivo activity
Figure 2. Concentration–response relationships for endogenous a7
nAChRs of rat hippocampal neurons. Peak current evoked by 1o, 2a,
9a, 18a, PNU-282,987, and PHA-543,613 expressed as a percent of the
current evoked by 100 lM nicotine.
We have reported that PNU-282,987 and PHA-543,613
activate a7 nAChRs endogenously expressed by rat hip-
pocampal neurons.7,13,14 In the present study, it was
Table 5. In vitro and in vivo PK profiles for select compounds
Compound
MDRa
(B > A)/(A > B)
MBUAb
Brain/plasma at 5, 60 min
HLMc
Eh
HLM
t1/2 (min)
Rat CLd
(mL/min/kg)
Rat
% F
PNU-282987
PHA-543613
NT
1.2
13
0.8, 5.0
1.5, 1.5
0.08, 0.54
NT
<0.26
<0.26
0.57
>120
>120
32
30
34
68
55
58
28
21
44
74
65
38
3
1h
1i
NT
3.2
1.5
1.0
1.0
<0.26
0.36
0.40
>120
78
65
1o
2a
9a
18a
0.24, 1.31
0.94, 0.84
2.8, 3.4
2.8, 6.4
18
82
72
7
0.33
<0.26
87
>120
a MDR, multidrug-resistant P-glycoprotein assay; (B > A)/(A > B), basel to apical Papp divided by apical to basel Papp or efflux ratio.
b MBUA, mouse brain uptake assay, brain to plasma = concentration in brain divided by concentration in plasma.
c HLM, human liver microsomes; in vitro compound stabilities (Eh) are reported as the fraction of compound remaining as compared with the
concentration at t0.
d Clearance and oral bioavailability determined in constant infusion model.

8228
D. P. Walker et al. / Bioorg. Med. Chem. 14 (2006) 8219–8248
each series (i.e., 2a, 9a, and 18a) shows an improved
100
80
60
40
20
0
*
*
hERG safety profile over PNU-282,987. The same three
analogs show acceptable oral bioavailability in rats and
demonstrate excellent brain penetration in the MBUA.
Furthermore, 1-azanorbornane 9a is active in a P50
auditory gating assay.
*
5. Experimental
5.1. Chemistry
5.1.1. General. Proton (1H) and carbon (13C) nuclear
magnetic resonance (NMR) spectra were recorded on
a Bruker 400 spectrometer. Chemical shifts are reported
in parts per million (d) relative to tetramethylsilane (d
0.0). Infrared (IR) spectra, high-resolution mass spectra,
and combustion analyses were performed in-house by
Structural, Analytical, and Medicinal Chemistry
Department personnel, Kalamazoo, MI. Melting points
were obtained on a Thomas-Hoover melting point appa-
ratus and are uncorrected. Reactions were monitored by
thin-layer chromatography (TLC) using Analtech silica
gel GF 250 micron plates. The plates were visualized
either by UV inspection or I2 stain. Flash chromatogra-
phy was performed as described by Still45 using EM
Science silica gel 60 (230–400 mesh). All reagents were
purchased from either the Aldrich Chemical Co. or
The Lancaster Synthesis Co. and used without further
purification unless otherwise stated. HATU46 was pur-
chased from Biosystems, Warrington, UK. All solvents
were of HPLC grade unless otherwise stated. Anhy-
drous solvents were purchased from the Aldrich Chem-
ical Co. and used without further drying.
PNU-
282,987
V
1o
18a
9a
Figure 3. Average reversal of amphetamine-induced gating deficit in
the hippocampus CA3 region after administration of vehicle (V, n = 5),
PNU-282987 (282, 1 mg/kg, iv, n = 5), and compounds 1o (1 mg/kg, iv,
*
n = 6), 18a (1 mg/kg, IV, n = 4) and 9a (1 mg/kg, iv, n = 8). Indicates
significant difference in auditory gating between degree of gating after
amphetamine administration and after subsequent administration of
the agonist (p < 0.05; two-tailed paired Student’s t-test).
at 1 mg/kg, iv in this assay. In contrast, compound 18a
fails to restore amphetamine-induced gating deficit; gat-
ing is similar in rats treated with 18a to controls rats
treated with vehicle. Presently, it is unclear why this
compound does not show activity in auditory sensory
gating experiments. Further in vitro and in vivo charac-
terization of these agonists is warranted to understand
the in vivo pharmacological diversity of a7 nAChR
agonists.
4. Conclusions
Note: We have observed that some quinuclidine-con-
taining compounds (1) and 1-azanorbornane-containing
compounds (9) react with methylene chloride, forming a
quaternary salt.47
The synthesis and SAR of several new analogs possess-
ing modifications to the acid portion of PNU-282,987
have been described. Generally, quinuclidine analogs
containing a 6,5-fused aryl carboxamide are more po-
tent a7 nAChR agonists than similarly substituted
quinuclidine analogs containing a 6,6-fused aryl carbox-
amide. Several 6,5- and 6,6-fused quinuclidine analogs
were prepared that are potent, high affinity a7 nAChR
agonists and show good to excellent selectivity and rat
in vitro profiles. Of these, benzothiazole 1h and benzodi-
oxane 1o show a significant improvement in hERG
activity compared to PNU-282,987 and are orally bio-
available in a rat PK model. Furthermore, benzodiox-
ane 1o shows good brain penetration and is highly
efficacious at 1 mg/kg in a validated in vivo model, the
reversal of an amphetamine-induced P50 gating deficit.
5.1.2. N-[(3R)-1-Azabicyclo[2.2.2]oct-3-yl]-1,3-benzodi-
oxole-5-carboxamide-4-methyl-benzenesulfonate (1a). To
a stirred suspension of 1,3-benzodioxole-5-carboxylic
acid (380 mg, 2.3 mmol) in dry methylene chloride
(5.0 mL) was added triethylamine (320 lL, 2.3 mmol),
followed by diphenylphosphoryl azide (405 lL,
2.0 mmol). In a separate flask, to a stirred suspension
of 3-(R)-aminoquinuclidine dihydrochloride (300 mg,
1.5 mmol) in methylene chloride (5.0 mL) was added
triethylamine (530 lL, 3.8 mmol). After 10 min, the
aminoquinuclidine solution was rapidly added to the
benzodioxole
solution.
N,N-Dimethylformamide
(1.0 mL) was added, and the combined mixture was stir-
red for 24 h at room temperature. The reaction mixture
was partitioned between saturated aqueous potassium
carbonate solution and methylene chloride. The aque-
ous layer was extracted with methylene chloride, and
the combined organic layers were washed with brine,
dried over anhydrous magnesium sulfate, filtered and
concentrated in vacuo to a clear residue. The crude
product was purified by flash chromatography on silica
gel. Elution with chloroform–methanol–ammonium
hydroxide (90:9:1) gave 130 mg (31%) of a white foam.
The design, synthesis, and SAR of several new analogs
possessing modifications to the quinuclidine portion of
PNU-282,987 have been described. Generally, all three
series, the 2-methylquinuclidines (2), the 1-azanorborn-
anes (9), and the 7-azanorbornanes (18), show good to
excellent potency and affinity toward the a7 nAChR
and possess good to excellent selectivity over other nic-
otinic receptors. Analogs based on the 2-methylquinucli-
dine, and the 1-azanorbornane series generally show
enhanced stabilities in RLM. At least one analog from

D. P. Walker et al. / Bioorg. Med. Chem. 14 (2006) 8219–8248
8229
The foam from above (125 mg, 0.46 mmol) was dis-
solved in ethyl acetate (1.0 mL) and a solution of p-tol-
uenesulfonic acid monohydrate (90 mg, 0.48 mmol) in
methyl alcohol (0.5 mL) was added. The solution was al-
lowed to stand overnight. The resulting precipitate was
filtered and dried under high vacuum at 50 ꢁC for 48 h
fumaric acid (320 mg, 2.8 mmol) in isopropyl alcohol
(2.0 mL) was added. The solution was heated in a
45 ꢁC water bath for 15 min, followed by removal of
the solvent in vacuo. The remaining residue was triturat-
ed in acetone (10 mL) containing a few drops of water.
The resulting solid was filtered, washed with acetone,
to afford 160 mg (76%) of 1a as a white solid: mp 233–
and dried in vacuo to afford 510 mg (45%) of 1b as a
25
D
1654, 1534, 1504, 1484, 1261, 1213, 1186, 1154, 1120,
25
D
235 ꢁC; ½aꢂ 7 (c 0.35, MeOH); IR (diffuse reflectance)
white solid: mp 140–143 ꢁC (loss of H2O); ½aꢂ 7 (c
0.73, MeOH); IR (diffuse reflectance) 3430, 3341, 3306,
3225, 3062, 3029, 2965, 2959, 2923, 1710, 1706, 1701,
1039, 1029, 1005, 820, 763, 683 cmꢀ1
;
1H NMR
1
(400 MHz, methanol-d4) d 7.72 (d, 2.5H, J = 8.19 Hz),
7.47 (dd, 1H, J = 8.12 Hz, 1.80 Hz), 7.36 (d, 1H,
J = 1.70 Hz), 7.25 (d, 2.5H, J = 7.90 Hz), 6.90 (d, 1H,
J = 8.14 Hz), 6.06 (s, 2H), 4.44–4.38 (m, 1H), 4.10–
3.79 (m, 1H), 3.50–3.32 (m, 4H), 2.27 (ddd, 1H,
J = 13.38, 5.72, 2.26 Hz), 2.39 (s, 3.75H), 2.36–2.33 (m,
1H), 2.29–2.20 (m, 1H), 2.11–2.08 (m, 2H), 1.97–1.90
(m, 1H); 13C NMR (100 MHz, methanol-d4) d 170.4,
152.7, 149.8, 143.9, 142.2, 130.3, 129.3, 127.3, 124.2,
109.3, 109.1, 103.7, 53.89, 48.08, 47.63, 47.08, 26.03,
23.20, 21.70, 18.87; high-resolution MS (FAB) Calcd
for C15H19N2O3 [M+H] m/e 275.1396. Found
275.1397. % Water (KF): 2.28. Anal. Calcd for
C15H18N2O3Æ1.25C7H8O3SÆ2.28% H2O: C, 56.93; H,
5.89; N, 5.59. Found: C, 57.14; H, 5.98; N, 5.83.
1663, 1627, 1551 cmꢀ1; H NMR (400 MHz, MeOH-
d4) d 7.72 (s, 1H), 7.64 (d, 1H, J = 7.82 Hz), 7.32 (d,
1H, J = 7.83 Hz), 6.70 (s, 2H), 4.48–4.41 (m, 1H),
3.85–3.78 (m, 1H), 3.45–3.31 (m, 4H), 3.25 (ddd, 1H,
J = 13.45, 5.63, 2.04 Hz), 2.95 (t, 4H, J = 7.42 Hz),
2.36–2.32 (m, 1H), 2.30–2.20 (m, 1H), 2.18–2.09 (m,
4H), 1.98–1.90 (m, 1H); 13C NMR (100 MHz, MeOH-
d4) d 173.4, 173.3, 152.0, 147.8, 138.2, 135.2, 128.9,
127.3, 126.4, 55.30, 49.52, 49.08, 48.67, 35.75, 35.55,
28.53, 27.81, 24.91, 20.56; high-resolution MS (FAB)
Calcd for C17H23N2O [M+H] m/e 271.1810. Found
271.1804. % Water (KF): 4.47. Anal. Calcd for
C17H22N2OÆC4H4O4Æ4.47% H2O: C, 62.35; H, 6.97; N,
6.93. Found: C, 62.19; H, 6.96; N, 6.91.
5.1.5. N-[(3R)-1-Azabicyclo[2.2.2]oct-3-yl]-1H-benzimid-
azole-5-carboxamidebis(4-ethylbenzenesulfonate)ÆH2O
(1c). To a stirred solution of 1H-benzimidazole-5-car-
boxylic acid (500 mg, 3.09 mmol) in anhydrous
N,N-dimethylformamide (20 mL) were added diiso-
propylethylamine (2.15 mL, 12.4 mmol), 3-(R)-amin-
oquinuclidine dihydrochloride (614 mg, 3.09 mmol),
and PyBOP (1.88 g, 3.55 mmol) at room temperature.
The reaction mixture was stirred for 4 days. The sol-
vent was removed in vacuo and the residue was parti-
tioned between saturated aqueous potassium
carbonate solution and chloroform–methanol (95:5).
The aqueous layer was extracted with 95:5 chloro-
form–methanol (3·). The combined organic layers
were dried over anhydrous magnesium sulfate, fil-
tered, and concentrated in vacuo. The crude product
was purified by flash chromatography on silica gel.
5.1.3. Indan-5-carboxylic acid. To a stirred 6% aqueous
sodium hypochlorite solution in an oil bath at 55 ꢁC
was added 1-indane-5-yl-ethanone48 (1.0 g, 6.2 mmol).
The mixture was stirred at 55 ꢁC for 2 h, followed by
cooling to room temperature. Solid sodium bisulfite
was added until the solution became clear. The mixture
was diluted with water, followed by aqueous hydrochlo-
ric acid (6.0 M). The resulting precipitate was filtered
and washed several times with water. The solid was
dried under high vacuum at 60 ꢁC for 5 h to afford
0.96 g (95%) of indan-5-carboxylic acid as a white solid:
Rf 0.05–0.2 (hexanes–ethyl acetate, 75:25); IR (diffuse
reflectance) 2962, 2920, 2838, 2665, 2557, 1676, 1611,
1576, 1435, 1414, 1335, 1311, 1300, 1272, 766 cmꢀ1
;
1H NMR (400 MHz, CDCl3) d 11.0–10.0 (br s, 1H),
8.00 (s, 1H), 7.96 (d, 1H, J = 7.79 Hz), 7.35 (d, 1H,
J = 7.92 Hz), 3.01 (t, 4H, J = 7.44 Hz), 2.21–2.14 (m,
2H); 13C NMR (100 MHz, CDCl3) d 170.7, 149.4,
143.0, 126.9, 125.6, 124.4, 122.6, 31.42, 30.81, 23.69.
Elution
with
chloroform–methanol–ammonium
hydroxide (86:13:1) gave 683 mg (82%) of the corre-
sponding amide as a white solid.
5.1.4. N-[(3R)-1-Azabicyclo[2.2.2]oct-3-yl]indane-5-car-
boxamideÆfumarate (1b). To a stirred solution of indan-
5-carboxylic acid (500 mg, 3.1 mmol) in dry N,N-di-
methylformamide (30 mL) was added diisopropylethyl-
amine (1.6 mL, 9.3 mmol), followed by 3-(R)-
aminoquinuclidine dihydrochloride (580 mg, 2.9 mmol).
The solution was cooled to 0 ꢁC before 1.0 g (2.9 mmol)
of HATU was added. The solution was allowed to warm
to room temperature and stir for 16 h. The solvent was
removed in vacuo, and the remaining residue was parti-
tioned between half saturated aqueous potassium car-
bonate solution and chloroform–methanol (9:1). The
aqueous layer was extracted with 9:1 chloroform–meth-
anol, and the combined organic layers were washed with
brine, dried over anhydrous magnesium sulfate, filtered
and concentrated in vacuo to a clear oil. The oil was dis-
solved in methanol (2.0 mL) and a hot solution of
To a stirred solution of the above amide (564 mg,
2.09 mmol) in methanol (10 mL) was added a warm
solution of 4-methylbenzenesulfonic acid monohydrate
(793 mg, 4.18 mmol) in methanol (5 mL). The mixture
was warmed to 40 ꢁC for 10 min. The solvent was re-
moved in vacuo and the remaining residue was diluted
with acetone (10 mL) and water (0.5 mL). The mixture
was stirred at room temperature for 3 days. The result-
ing solid was collected by filtration, washed with ace-
tone, and dried under high vacuum to afford 1.00 g
(76%) of 1c as an off-white solid: mp 145–148 ꢁC (loss
25
of H2O); ½aꢂ 5 (c 0.77, MeOH); IR (diffuse reflectance)
D
3235, 3098, 3023, 2958, 2832, 2701, 1221, 1199, 1176,
1158, 1121, 1032, 1010, 815, 681 cmꢀ1 1H NMR
;
(400 MHz, MeOH-d4) d 9.50 (s, 1H), 8.41 (d,
J = 1.5 Hz, 1H), 8.16 (dd, J = 8.6, 1.5 Hz, 1H), 7.92 (d,
J = 8.5 Hz, 1H), 7.69 (d, J = 8.3 Hz, 4H), 7.22 (d,

8230
D. P. Walker et al. / Bioorg. Med. Chem. 14 (2006) 8219–8248
J = 8.3 Hz, 4H), 4.54–4.50 (m, 1H), 3.89–3.83 (m, 1H),
3.56–3.49 (m, 1H), 3.44–3.35 (m, 4H), 2.42–2.39 (m,
1H), 2.37 (s, 6H), 2.33–2.28 (m, 1H), 2.14–2.08 (m,
2H), 1.98–1.89 (m, 1H); 13C NMR (100 MHz, MeOH-
d4) d 166.0, 145.2, 142.7, 137.9, 132.8, 131.6, 130.8,
128.1, 125.4, 125.1, 114.3, 114.2, 51.02, 45.67, 45.18,
44.89, 24.11, 21.38, 20.74, 17.09; high-resolution MS
(FAB) Calcd for C15H19N4O [M+H] m/e 271.1559.
Found 271.1567. % Water (KF): 2.93. Anal. Calcd for
C15H18N4OÆ2C7H8O3SÆ2.93% H2O: C, 55.00; H, 5.74;
N, 8.85. Found: C, 55.06; H, 5.76; N, 8.78.
tance) 3158, 2986, 2949, 2909, 2781, 2599, 1711, 1430,
1
1290, 1273, 1259, 1103, 916, 767, 746 cmꢀ1; H NMR
(400 MHz, DMSO-d6) d 13.10 (br s, 1H), 8.89 (s, 1H),
8.32 (d, J = 1.4 Hz, 1H), 8.06 (dd, J = 8.6, 1.6 Hz, 1H),
7.89 (d, J = 8.6 Hz, 1H); 13C NMR (100 MHz,
DMSO-d6) d 166.5, 155.2, 151.8, 139.4, 127.3, 126.8,
121.1, 110.9; high-resolution MS (FAB) Calcd for
C8H6NO3 [M+H] m/e 164.0348. Found 164.0349. Anal.
Calcd for C8H5NO3: C, 58.90; H, 3.09; N, 8.59. Found:
C, 58.82; H, 3.12; N, 8.56.
5.1.9. N-[(3R)-1-Azabicyclo[2.2.2]oct-3-yl]-1,3-benzoxaz-
ole-5-carboxamideÆfumarate (1e). The compound 1e
(180 mg, 62%) was prepared from 1,3-benzoxazole-
5-carboxylic acid (124 mg, 0.76 mmol) and 3-(R)-amino-
quinuclidine dihydrochloride (151 mg, 0.76 mmol),
followed by subsequent treatment with fumaric acid
(73.6 mg, 0.63 mmol) in a manner similar to that
5.1.6. [1,3]Dioxolo[4,5-c]pyridine-6-carboxylic acid. To a
stirred solution of ethyl[1,3]dioxolo[4,5-c]pyridine-6-car-
boxylate49,50 (462 mg, 2.37 mmol) in ethyl alcohol
(5.0 mL) was added sodium hydroxide (10 mL of a 5%
aqueous solution). The mixture was heated to reflux
for 1.5 h, followed by cooling to room temperature.
The ethanol was removed in vacuo, and the remaining
aqueous layer was acidified to pH 4 with 1 N hydrochlo-
ric acid. The aqueous layer was continuously extracted
with methylene chloride for 48 h. The organic layer
was concentrated to afford 315 mg (80%) of [1,3]dioxol-
described for the preparation of 1b. Off-white solid:
25
D
reflectance) 3362, 3338, 3116, 2598, 1710, 1694, 1651,
mp 179–180 ꢁC; ½aꢂ 8 (c 0.71, MeOH); IR (diffuse
1
1618, 1541, 1532, 1281, 1058, 1053, 800, 755 cmꢀ1; H
NMR (400 MHz, MeOH-d4) d 8.60 (s, 1H), 8.32 (d,
J = 1.6 Hz, 1H), 8.01 (dd, J = 8.6, 1.7 Hz, 1H), 7.80 (d,
J = 8.6 Hz, 1H), 6.70 (s, 2H), 4.50–4.46 (m, 1H), 3.89–
3.83 (m, 1H), 3.49–3.26 (m, 5H), 2.41–2.39 (m, 1H),
2.31–2.23 (m, 1H), 2.14–2.09 (m, 2H), 1.99–1.91 (m,
1H); 13C NMR (100 MHz, MeOH-d4) d 171.8, 170.5,
156.9, 153.8, 141.5, 136.6, 132.8, 127.3, 121.2, 112.6,
53.83, 47.96, 47.51, 47.33, 26.13, 23.34, 18.98; high-reso-
lution MS (FAB) Calcd for C15H18N3O2 [M+H] m/z
272.1399. Found 272.1399. Anal. Calcd for
C15H17N3O2ÆC4H4O4: C, 58.91; H, 5.46; N, 10.85.
Found: C, 58.74; H, 5.52; N, 10.75.
1
o[4,5-c]pyridine-6-carboxylic acid as a white solid: H
NMR (400 MHz, DMSO-d6) d 13.5 (br s, 1H), 8.12 (s,
1H), 7.52 (s, 1H), 6.21 (s, 2H); IR (diffuse reflectance)
3133, 2919, 2882, 2864, 2778, 2569, 2512, 2468, 1507,
1341, 1285, 1273, 1173, 1030, 910 cmꢀ1; high-resolution
MS (ESI) Calcd for C7H6NO4 168.0297. Found
168.0304.
5.1.7. N-[(3R)-1-Azabicyclo[2.2.2]oct-3-yl][1,3]dioxolo-
[4,5-c]pyridine-6-carboxamideÆfumarate (1d). The com-
pound 1d (285 mg, 87%) was prepared from [1,3]dioxol-
o[4,5-c]pyridine-6-carboxylic acid (140 mg, 0.840 mmol)
and 3-(R)-aminoquinuclidine dihydro chloride (167 mg,
0.840 mmol), followed by subsequent treatment with
fumaric acid (97.0 mg, 0.836 mmol) in a manner similar
5.1.10. 1,3-Benzoxazole-6-carboxylic acid. A mixture of
4-amino-3-hydroxybenzoic acid (250 mg, 1.63 mmol)
and trimethyl orthoformate (500 lL, 4.57 mmol) was
heated at 100 ꢁC for 2 h. The mixture was cooled to
room temperature and diluted with methanol, and the
resulting solution was filtered through a pad of Celite.
The filtrate was concentrated in vacuo to give 237 mg
(89%) of 1,3-benzoxazole-6-carboxylic acid as a brown
solid: IR (diffuse reflectance) 3224, 3194, 3135, 3103,
3077, 3061, 3008, 2975, 2965, 1693, 1676, 1601, 1312,
to that described for the preparation of 1b. White solid:
25
D
reflectance) 3362, 2588, 2578, 1728, 1662, 1569, 1528,
mp 204–205 ꢁC; ½aꢂ ꢀ1 (c, 0.99, methanol); IR (diffuse
1501, 1480, 1429, 1367, 1330, 1308, 1276, 1175 cmꢀ1
;
1H NMR (400 MHz, methanol-d4) d 8.09 (s, 1H), 7.57
(s, 1H), 6.67 (s, 2H), 6.19 (s, 2H), 4.28–4.20 (m, 1H),
3.81–3.74 (m, 1H), 3.50–3.40 (m, 1H), 3.40–3.24 (m,
4H), 2.35 (m, 1H), 2.20 (m, 1H), 2.08 (m, 2H), 1.95–
1.83 (m, 1H); 13C NMR (100 MHz, methanol-d4) d
170.2, 165.2, 156.3, 148.8, 145.5, 135.0, 127.7, 103.7,
103.4, 51.73, 46.28, 45.86, 44.94, 24.88, 21.66, 17.27;
high-resolution MS (ESI) Calcd for C14H18N3O3
[M+H] m/e 276.1348. Found 276.1345. Anal. Calcd for
C14H17N3O3ÆC4H4O4: C, 55.24; H, 5.41; N, 10.74.
Found: C, 55.11; H, 5.35; N, 10.70.
1293, 1248 cmꢀ1 1H NMR (400 MHz, DMSO-d6) d
;
13.20 (br s, 1H), 8.94 (s, 1H), 8.29 (d, J = 1.5 Hz, 1H),
8.02 (dd, J = 8.4, 1.5 Hz, 1H), 7.90 (d, J = 8.4 Hz, 1H);
low-resolution MS (ESI) m/z 162 (MꢀH).
5.1.11. N-[(3R)-1-Azabicyclo[2.2.2]oct-3-yl]-1,3-benzox-
azole-6-carboxamideÆfumarate (1f). The compound 1f
(150 mg, 35%) was prepared from 1,3-benzoxazole-6-
carboxylic acid (194 mg, 1.19 mmol) and 3-(R)-amin-
oquinuclidine dihydrochloride (225, 1.13 mmol), fol-
lowed by subsequent treatment with fumaric acid
(66.0 mg, 0.58 mmol) in a manner similar to that de-
scribed for the preparation of 1b. Light yellow solid:
5.1.8. 1,3-Benzoxazole-5-carboxylic acid. A mixture of
3-amino-4-hydroxybenzoic acid (5.00 g, 32.7 mmol)
and trimethyl orthoformate (10 mL, 91.5 mmol) was
heated at 100 ꢁC for 5 h. The mixture was cooled to
room temperature and diluted with ethyl acetate. The
resulting solution was filtered through a pad of silica
gel, and the filtrate was concentrated in vacuo to afford
3.0 g (56%) of 1,3-benzoxazole-5-carboxylic acid as a
light orange solid: mp 241–242 ꢁC; IR (diffuse reflec-
mp 194–195 ꢁC; ½aꢂ25 5 (c, 0.9, MeOH); IR (diffuse reflec-
D
tance) 3091, 3058, 3002, 2987, 1726, 1710, 1699, 1656,
1532, 841, 796, 772, 751, 738, 646 cmꢀ1 1H NMR
;
(400 MHz, MeOH-d4) d 8.64 (s, 1H), 8.23 (d,
J = 1.6 Hz, 1H), 7.98 (dd, J = 8.4, 1.6 Hz, 1H), 7.87 (d,

D. P. Walker et al. / Bioorg. Med. Chem. 14 (2006) 8219–8248
8231
J = 8.4 Hz, 1H), 6.7 (s, 2H), 4.49–4.45 (m, 1H), 3.89–
3.83 (m, 1H), 3.47–3.25 (m, 5H), 2.41–2.38 (m, 1H),
2.31–2.23 (m, 1H), 2.14–2.09 (m, 2H), 2.00–1.91 (m,
1H); 13C NMR (100 MHz, MeOH-d4) d 171.8, 170.3,
157.8, 151.5, 144.2, 136.6, 133.6, 126.0, 121.4, 112.3,
53.77, 47.94, 47.49, 47.37, 26.14, 23.33, 18.97; high-reso-
lution MS (FAB) Calcd for C15H18N3O2 [M+H] m/z
272.1399. Found 272.1400. Anal. Calcd for
C15H17N3O2ÆC4H4O4: C, 58.91; H, 5.46; N, 10.85.
Found: C, 58.71; H, 5.55; N, 10.73.
(400 MHz, CDCl3) d 9.10 ( s, 1H), 8.84 (d, 1H,
J = 1.3 Hz), 8.15 (d, 1H, J = 8.43, 1.52 Hz), 8.04 (d,
1H, J= 8.42 Hz), 4.00 (s, 3H); 13C NMR (100 MHz,
CDCl3) d 167.2, 155.7, 153.5, 138.8, 129.1, 126.6,
125.6, 122.2, 52.83. Anal. Calcd for C9H7NO2S: C,
55.95; H, 3.65; N, 7.25. Found: C, 55.90; H, 3.66; N,
7.27.
5.1.14. 1,3-Benzothiazole-5-carboxylic acid. To a stirred
solution of methyl 1,3-benzothiazole-5-carboxylate
(290 mg, 1.5 mmol) in methyl alcohol (20 mL) was add-
ed sodium hydroxide (10 mL of a 5% aqueous solution).
The mixture was heated in a 65 ꢁC oil bath for 30 min,
followed by cooling to room temperature. The mixture
was diluted with water and extracted with hexanes–ether
(1:1). The organic layer was discarded and the aqueous
layer was acidified with concentrated hydrochloric acid
to pH 1. The aqueous layer was extracted with ether.
The ethereal layer was dried over anhydrous magnesium
sulfate, filtered, and concentrated in vacuo to give
260 mg (98%) of 1,3-benzothiazole-5-carboxylic acid as
a white powder (260 mg, 98%): 1H NMR (400 MHz,
DMSO-d6) d 13–12.5 (br s, 1H), 9.5 (s, 1H), 8.58 (d,
1H, J = 1.48 Hz), 8.31 (d, 1H, J = 8.40), 8.03 (dd, 1H,
J = 8.40, 1.56); low-resolution MS (ESI) m/e 178
[MꢀH].
5.1.12. Dimethyl 4,40-dithio-bis-(3-nitrobenzoate).
A
solution of sodium sulfideÆnonahydrate (1.15 g,
4.9 mmol) in methanol–water (ca. 10 mL, 1:1) was
warmed on a hot plate. To this solution was added ele-
mental sulfur (150 mg, 4.6 mmol). Heating was contin-
ued for 15 min before the solution was poured into a
separate solution of 1.0 g (4.6 mmol) of methyl 4-chlo-
ro-3-nitrobenzoate in methanol (5.0 mL). The mixture
was stirred for 30 min, followed by cooling in a refriger-
ator overnight. The solid precipitate was filtered, washed
with water and methanol, and dried in vacuo at 50 ꢁC to
afford 650 mg (65%) of dimethyl 4,40-dithio-bis-(3-nitro-
benzoate) as a yellow solid: mp 164–165 ꢁC; Rf 0.29
(hexanes–ethyl acetate, 75:25); IR (diffuse reflectance)
1720, 1606, 1524, 1438, 1389, 1338, 1294, 1240, 1230,
1158, 1131, 821, 772, 749, 738 cmꢀ1
;
1H NMR
(400 MHz, CDCl3) d 8.97 (d, 2H, J = 1.80 Hz), 8.17
(dd, 2H, J = 8.50, 1.81 Hz), 7.92 (d, 2H, J = 8.50 Hz),
4.01 (s, 6H); 13C NMR (100 MHz, CDCl3) d 164.4,
145.9, 139.6, 134.6, 129.7, 127.6, 127.4, 52.91; high-reso-
lution MS (EI) Calcd for C16H12N2O8S2 [M]+ m/e
424.0035. Found 424.0042. Anal. Calcd for
C16H12N2O8S2: C, 45.28; H, 2.85; N, 6.60. Found: C,
45.35; H, 2.76; N, 6.58.
5.1.15. N-[(3R)-1-Azabicyclo[2.2.2]oct-3-yl]-1,3-benzo-
thiazole-5-carboxamideÆfumarate (1g). The compound
1g (300 mg, 57%) was prepared from 1,3-benzoxazole-
5-carboxylic acid (250 mg, 1.40 mmol) and 3-(R)-amin-
oquinuclidine dihydrochloride (260 mg, 1.30 mmol),
followed by subsequent treatment with fumaric acid
(100 mg, 0.86 mmol) in a manner similar to that
described for the preparation of 1b. White solid: mp
25
D
tance) 3273, 3057, 3038, 2963, 2888, 2691, 2595, 1725,
160–164 ꢁC; ½aꢂ 7 (c 0.63, MeOH); IR (diffuse reflec-
5.1.13. Methyl 1,3-benzothiazole-5-carboxylate. To a
stirred solution of dimethyl 4,40-dithio-bis-(3-nitro-
benzoate) (1.0 g, 2.4 mmol) in ethanol was added tin
powder (2.1 g, 19.2 mmol). The mixture was heated in
a 70 ꢁC oil bath for 30 min before 3.1 mL of concentrat-
ed hydrochloric acid was added dropwise. After com-
plete addition, the mixture was stirred for an
additional 10 min, followed by cooling to room temper-
ature. The reaction mixture was filtered and the filtrate
was concentrated in vacuo to a yellow solid. The solid
was washed with 1.0 M aqueous hydrochloric acid and
dried in vacuo to afford 1.7 g of a yellow solid.
1655, 1630, 1562, 1537, 1368, 1338, 1312 cmꢀ1 1H
;
NMR (MeOH-d4) d 9.40 (s, 1H), 8.60 (s, 1H), 8.21 (d,
1H, J = 8.45 Hz), 8.00 (d, 1H, J = 8.41 Hz), 6.70 (s,
2H), 4.53–4.47 (m, 1H), 3.89–3.82 (m, 1H), 3.50–3.26
(m, 5H), 2.44–2.40 (m, 1H), 2.36–2.22 (m,1H), 2.17–
2.10 (m, 2H), 2.02–1.90 (m, 1H); 13C NMR (100 MHz,
MeOH-d4) d 171.4, 170.3, 158.8, 154.1, 138.7, 136.2,
133.8, 125.7, 123.6, 123.3, 53.35, 47.57, 47.12, 46.95,
25.81, 22.95, 18.61; high-resolution MS (FAB) Calcd
for C15H18N3OS [M+H] m/e 288.1170. Found
288.1154. Anal. Calcd for C15H17N3OSÆC4H4O4ÆH2O:
C, 54.14; H, 5.50; N, 9.97. Found: C, 53.97; H, 5.54;
N, 9.75.
To a stirred suspension of the above solid (1.5 g) in for-
mic acid (8 mL) in a 100 ꢁC oil bath was added zinc dust
(50 mg). The mixture was stirred for 1 h, followed by
cooling to room temperature. The mixture was diluted
with water and extracted with ethyl acetate. The organic
layer was dried over anhydrous magnesium sulfate, fil-
tered, and concentrated in vacuo to yellow solid. The
crude product was purified by flash chromatography
on silica gel. Elution with hexanes–ethyl acetate
(60:40) gave 410 mg (50%) of methyl 1,3-benzothiaz-
ole-5-carboxylate as a light yellow solid: mp 96–97 ꢁC;
Rf 0.55 (hexanes–ethyl acetate, 1:1); IR (diffuse reflec-
tance) 3041, 1722, 1429, 1307, 1282, 1248, 1194, 1182,
5.1.16. N-[(3R)-1-Azabicyclo[2.2.2]oct-3-yl]-1,3-benzo-
thiazole-6-carboxamideÆfumarate (1h). The compound
1h (4.37 g, 85%) was prepared from 1,3-benzothiazole-
6-carboxylic acid (2.18 g, 12.0 mmol) and 3-(R)-amin-
oquinuclidine dihydrochloride (2.42 g, 12.1 mmol), fol-
lowed by subsequent treatment with fumaric acid
(1.38 g, 11.9 mmol) in a manner similar to that described
for the preparation of 1b. White solid: mp 181–184 ꢁC,
25
½aꢂ 5 (c 0.96, MeOH); IR (diffuse reflectance) 3382,
D
3257, 3252, 3243, 3054, 3029, 3017, 3009, 2904, 1715,
1710, 1699, 1646, 1627, 1535 cmꢀ1
;
1H NMR
1148, 1089, 963, 910, 844, 839, 760 cmꢀ1
;
1H NMR
(400 MHz, MeOH-d4) d 9.40 (s, 1H), 8.65 (d, 1H,

8232
D. P. Walker et al. / Bioorg. Med. Chem. 14 (2006) 8219–8248
J = 1.50 Hz), 8.17 (d, 1H, J = 8.60 Hz), 8.06 (dd, 1H,
J = 8.58, 1.73 Hz), 6.73 (s, 2H), 4.53–4.47 (m, 1H),
3.90–3.83 (m, 1H), 3.50–3.30 (m, 5H), 2.44–2.40 (m,
1H), 2.35–2.27 (m, 1H), 2.16–2.09 (m, 2H), 2.02–1.90
(m, 1H); 13C NMR (100 MHz, MeOH-d4) d 170.5,
170.4, 160.4, 156.7, 136.2, 135.6, 133.1, 127.2, 124.3,
123.8, 53.76, 47.96, 47.51, 47.30, 26.13, 23.27, 18.94;
high-resolution MS (FAB) Calcd for C15H18N3OS
[M+H] m/e 288.1170. Found 288.1173. % Water (KF)
4.31. Anal. Calcd for C15H17N3OSÆC4H4O4Æ4.31%
H2O: C, 54.15; H, 5.50; N, 9.97. Found: C, 54.15; H,
5.54; N, 9.96.
quent treatment with fumaric acid (95 mg, 0.82 mmol)
in a manner similar to that described for the preparation
of 1b. White solid: mp 105–108 ꢁC (loss of H2O); IR
(diffuse reflectance) 3428, 3307, 3295, 3289, 3224, 3039,
1701, 1663, 1638, 1559, 1292, 1260, 1238, 860,
784 cmꢀ1 1H NMR (400 MHz, MeOH-d4) d 8.15 (s,
;
1H), 8.11 (s, 1H), 7.88 (d, 1H, J = 8.47 Hz), 7.63 (dd,
1H, J = 8.48, 1.29 Hz), 6.71 (s, 2H), 4.52–4.45 (m, 1H),
3.90–3.82 (m, 1H), 3.50–3.29 (m, 5H), 3.45–3.40 (m,
1H), 2.33–2.20 (m, 1H), 2.16–2.09 (m, 2H), 2.02–1.90
(m, 1H); 13C NMR (100 MHz, MeOH-d4) d 171.8,
171.6, 141.5, 136.6, 135.3, 134.1, 126.6, 122.4, 121.1,
111.8, 53.68, 47.92, 47.49, 47.28, 26.21, 23.32, 18.98;
high-resolution MS (FAB) Calcd for C15H19N4O
[M+H] m/e 271.1559. Found 271.1562. Anal. Calcd for
C15H18N4OÆC4H4O42H2O: C, 54.02; H, 6.20; N, 13.27.
Found: C, 53.99; H, 6.17; N, 13.14.
5.1.17. 3-(tert-Butylthio)diazenyl-4-methylbenzoic acid.
To a stirred solution of aqueous hydrochloric acid
(15 mL of concentrated hydrochloric acid and 50 mL
of water) was added 3-amino-4-methyl benzoic acid
(5.0 g, 33 mmol). The mixture was cooled in an ace-
tone-ice water bath, followed by the slow addition of a
solution of sodium nitrite (2.28 g, 33 mmol) in water
(12 mL). The mixture was allowed to stir for 10 min at
which point the mixture becomes homogeneous. A satu-
rated aqueous solution of sodium acetate was added un-
til pH 6. 2-Methylpropane-2-thiol (1.8 mL, 16 mmol)
was added and the mixture was stirred for 1 h. The
resulting precipitate was collected by filtration, washed
with water, and dried in vacuo to give 3.85 g (96%) of
3-(tert-butylthio)diazenyl-4-methylbenzoic acid as a tan
solid: IR (diffuse reflectance) 3067, 2979, 2959, 2922,
2895, 2862, 1679, 1484, 1427, 1364, 1283, 1268, 922,
5.1.20. 1H-Indazole-5-carboxylic acid. To a stirred solu-
tion of methyl 1H-indazole-5-carboxylate51 (500 mg,
2.84 mmol) in methanol (15 mL) was added sodium
hydroxide (20 mL of 2.5% aqueous solution). The
mixture was heated at reflux for 1 h, followed by
removal of the methanol in vacuo. The remaining
aqueous solution was washed with ethyl acetate
(5 mL), acidified with 1 N aqueous hydrochloric acid
to pH 5–6. The resulting precipitate was collected by
filtration, washed with water, and dried in vacuo to
afford 410 mg (89%) of 1H-indazole-5-carboxylic acid
as a tan solid: mp >250 ꢁC; IR (diffuse reflectance)
3290, 3115, 2964, 2954, 2813, 2606, 2557, 2505,
851, 763 cmꢀ1
;
1H NMR (400 MHz, DMSO-d6) d
13.15 (s, 1H), 7.84 (dd, J = 8.0, 1.6 Hz, 1H), 7.49 (d,
J = 8.0 Hz, 1H), 7.28 (d, J = 1.6 Hz, 1H), 2.10 (s, 3H),
1.56 (s, 9H); 13C NMR (100 MHz, DMSO-d6) d 166.3,
155.1, 131.7, 131.4, 129.7, 129.3, 116.6, 48.94, 29.58,
16.16.
1687, 1627, 1321, 1274, 948, 937, 769 cmꢀ1 1H
;
NMR (400 MHz, DMSO-d6) d 13.36 (s, 1H), 12.74
(br s, 1H), 8.46 (s, 1H), 8.24 (d, 1H, J = 1.5 Hz),
7.91 (dd, 1H, J = 8.8, 1.5 Hz), 7.59 (d, 1H,
J = 8.8 Hz); 13C NMR (100 MHz, DMSO-d6)
d
167.6, 141.5, 135.1, 126.5, 123.7, 122.9, 122.5, 109.9;
Anal. Calcd for C8H6N2O2: C, 59.26; H, 3.73; N,
17.28. Found: C, 58.92; H, 3.72; N, 17.16.
5.1.18. 1H-Indazole-6-carboxylic acid. To a stirred solu-
tion of potassium tert-butoxide (8.14 g, 72.7 mmol) in
dimethylsulfoxide (30 mL) was added a solution of
3-(tert-butylthio)diazenyl-4-methylbenzoic acid (1.85 g,
7.34 mmol) in dimethylsulfoxide (20 mL). The mixture
was stirred overnight at room temperature. The mix-
ture was diluted with ice-water, acidified with 1 N
aqueous hydrochloric acid to pH 5–6, and extracted
with ethyl acetate (3·). The combined organic layers
were washed sequentially with water and brine, dried
over anhydrous magnesium sulfate, and concentrated
in vacuo to afford 1.17 g (98%) of 1H-indazole-6-car-
boxylic acid as a tan solid: IR (diffuse reflectance)
3171, 3135, 3067, 3014, 2950, 2889, 2865, 1685,
5.1.21. N-[(3R)-1-Azabicyclo[2.2.2]oct-3-yl]-1H-indazole-
5-carboxamideÆfumarate (1j). The compound 1j (230 mg,
63%) was prepared from 1H-indazole-5-carboxylic acid
(162 g, 1.00 mmol) and 3-(R)-aminoquinuclidine dihy-
drochloride (190 mg, 0.95 mmol), followed by subse-
quent treatment with fumaric acid (90 mg, 0.78 mmol)
in a manner similar to that described for the preparation
of 1b. White solid: mp 105–108 ꢁC (loss of H2O); ½aꢂ
25
D
5
(c, 0.78, methanol); IR (diffuse reflectance) 3408, 3225,
3159, 3074, 3047, 3015, 2981, 2958, 2950, 1666, 1631,
1618, 1550, 1279, 784 cmꢀ1
;
1H NMR (400 MHz,
1
1326, 1308, 1240, 960, 945, 762, 740 cmꢀ1; H NMR
MeOH-d4) d 8.40 (s, 1H), 8.20 (s, 1H), 7.92 (d, 1H,
J = 8.78 Hz), 7.63 (d, 1H, J = 8.83 Hz), 6.71 (s, 2H),
4.50–4.46 (m, H), 3.90–3.81 (m, 1H), 3.50–3.25 (m,
5H), 2.42–2.37 (m, 1H), 2.35–2.21 (m, 1H), 2.15–2.08
(m, 2H), 2.01–1.90 (m, 1H); 13C NMR (100 MHz,
MeOH-d4) d 171.4, 171.1, 142.9, 136.2, 128.0, 127.0,
123.9, 122.6, 111.2, 53.35, 47.51, 47.06, 46.79, 25.86,
22.92, 18.57; high-resolution MS (FAB) Calcd for
C15H19N4O [M+H] m/e 271.1559. Found 271.1564. %
Water (KF): 4.84. Anal. Calcd for C15H18N4OÆ-
C4H4O4Æ4.84% H2O: C, 56.20; H, 6.00; N, 13.80. Found:
C, 56.02; H, 6.03; N, 13.73.
(400 MHz, DMSO-d6) d 13.41 (s, 1H), 13.01 (br s,
1H), 8.18 (s, 1H), 8.15 (d, 1H, J = 1.1 Hz), 7.86 (d,
1H, J = 8.4 Hz), 7.67 (dd, 1H, J = 8.4, 1.1 Hz); 13C
NMR (100 MHz, DMSO-d6) d 167.6, 139.3, 133.5,
128.2, 125.1, 120.5, 120.4, 112.1.
5.1.19. N-[(3R)-1-Azabicyclo[2.2.2]oct-3-yl]-1H-indazole-
6-carboxamideÆfumarate (1i). The compound 1i (235 mg,
64%) was prepared from 1H-indazole-6-carboxylic acid
(162 g, 1.00 mmol) and 3-(R)-aminoquinuclidine dihy-
drochloride (190 mg, 0.95 mmol), followed by subse-

D. P. Walker et al. / Bioorg. Med. Chem. 14 (2006) 8219–8248
8233
5.1.22. N-[(3R)-1-Azabicyclo[2.2.2]oct-3-yl]pyrrolo[1,2-
c]pyrimidine-3-carboxamide (1k). To a stirred solution
of pyrrolo[1,2-c]pyrimidine-3-carboxylic acid hydro-
chloride52 (330 mg, 1.66 mmol) and triethylamine
(2.0 mL, 14.4 mmol) in tetrahydrofuran (15 mL) was
added dropwise diphenylphosphinic chloride (470 mg,
1.99 mmol). The mixture was stirred for 1 h before 3-
at 130 ꢁC with protection from light for 11 h. The reac-
tion mixture was cooled to room temperature, diluted
with methylene chloride, and passed through a plug of
Celite. The filtrate was extracted with saturated aqueous
ammonium chloride solution. The organic layer was
concentrated in vacuo. The remaining residue was puri-
fied by flash chromatography on silica gel. Elution with
hexanes–ethyl acetate (80:20) gave 547 mg (35%) of eth-
yl indolizine-6-carboxylate as a solid: IR (diffuse reflec-
tance) 2495 (w), 2469 (w), 2411 (w), 2397 (w), 2351
(w), 1704 (s), 1366, 1345, 1303 (s), 1261, 1233 (s), 1212
(s), 772 (s), 745 (s), 718 (s), cmꢀ1; MS (EI) m/z (rel.
intensity) 189 (M+, 56), 189 (56), 161 (99), 144 (14),
117 (14), 116 (39), 115 (25), 89 (33), 86 (26), 84 (54),
51 (18); 1H NMR (400 MHz, CDCl3) d 8.78 (d,
J = 1 Hz, 1H), 7.43 (d, J = 2 Hz, 1H), 7.40 (d,
J = 10 Hz, 1H), 7.22 (dd, J = 1, 9 Hz, 1H), 6.91–6.93
(m, 1H), 6.51 (d, J = 4 Hz, 1H), 4.42 (q, J = 7 Hz, 2H),
1.43 (t, J = 7 Hz, 3H); 13C NMR (CDCl3) d 166.0,
133.0, 130.3, 118.4, 116.2, 116.0, 114.5, 114.2, 100.3,
60.9, 14.4; high-resolution MS (FAB) Calcd for
C11H12NO2 [M+H] m/e 190.0868. Found 190.0860;
Anal. Calcd for C11H11NO2: C, 69.83; H, 5.86; N,
7.40. Found: C, 69.69; H, 6.03; N, 7.26.
(R)-aminoquinuclidine
dihydrochloride
(330 mg,
1.66 mmol) was added. The mixture was stirred for
24 h, followed by the addition of sodium hydroxide
(10 mL of a 5% aqueous solution). The mixture was
extracted with chloroform, and the organic layer was
dried over anhydrous magnesium sulfate, filtered, and
concentrated in vacuo. The crude product was purified
by flash chromatography on silica gel using a Biotage
40S apparatus. Elution with chloroform–methanol–am-
monium hydroxide (90:9:1) gave 450 mg (99%) of 1k as
a solid: IR (diffuse reflectance) 3384, 3128, 3104, 1653,
1610, 1547, 1528, 1504, 1355, 1269, 1229, 1056, 773,
1
734 cmꢀ1; H NMR (400 MHz, methanol-d4) d 9.01 (s,
1H), 8.08 (s, 1H), 7.22 (d, 1H, J = 2.90 Hz), 6.99 (dd,
1H, J = 4.15, 2.90 Hz), 6.76 (d, 1H, J = 3.73 Hz), 4.18–
4.10 (m, 1H), 3.40–3.30 (m, 1H), 3.04–2.92 (m, 1H),
2.91–2.74 (m, 4H), 2.01 (m, 1H), 1.96–1.86 (m, 1H),
1.81–1.76 (m, 2H), 1.62–1.50 (m, 1H); 13C NMR
(100 MHz, methanol-d4) d 165.5, 138.4, 132.2, 130.9,
117.4, 114.1, 113.4, 104.4, 54.12, 46.82, 46.66, 46.14,
25.88, 25.04, 19.50; high-resolution MS (ESI) Calcd
for C15H19N4O [M+H] m/e 271.1559. Found 271.1555.
% Water (KF): 0.26. Anal. Calcd for C15H18N4OÆ0.26%
H2O: C, 66.47; H, 6.72; N, 20.68. Found: C, 66.25; H,
6.85; N, 20.51.
5.1.25. Indolizine-6-carboxylic acid. To ethyl indolizine-
6-carboxylate (0.5 g, 2.7 mmol) in ethanol (8.0 mL)
and water (1.0 mL) were added potassium hydroxide
pellets (1.5 g, 2.7 mmol). The mixture was stirred at
room temperature for 1 h. The reaction mixture was
diluted with water (10 mL) and extracted with methy-
lene chloride (2· 15 mL). The organic layer was discard-
ed. The aqueous layer was acidified with 5 N aqueous
hydrochloric acid and extracted with methylene chloride
(2· 15 mL). The organic layer was dried over anhydrous
magnesium sulfate, filtered, and concentrated in vacuo
to afford 0.40 g (93%) of indolizine-6-carboxylic acid
as a yellow solid: IR (diffuse reflectance) 2351, 2339,
2044 (w), 2015 (w), 1990 (w), 1709 (s), 1678 (s), 1428
(s), 1314 (s), 1258, 1216, 817, 768 (s), 711 (s), 682,
5.1.23. Ethyl 6-prop-1-ynylnicotinate. To a sealed tube
containing ethyl 6-chloronicotinate (2.0 g, 10.8 mmol),
CuI (0.3 g, 1.6 mmol, 15 mol%), and Pd(PPh3)2Cl2
(0.4 g, 0.5 mmol, 5 mol%), anhydrous Et3N (60 mL)
was added prop-1-yne (7.0 mL, 129 mmol). The mixture
was allowed to stir at 60 ꢁC for 3 h. The mixture was fil-
tered through a pad of Celite and solvent was removed
in vacuum. The resulting solid was purified by silica
gel chromatography (30% EtOAc–hexanes) to give ethyl
cmꢀ1
; d 8.84 (d,
1H NMR (400 MHz, CDCl3)
J = 1 Hz, 1H), 7.43 (d, J = 2 Hz, 1H), 7.40 (d,
J = 9 Hz, 1H), 7.20 (dd, J = 1, 9 Hz, 1H), 6.91 (dd,
J = 3, 4 Hz, 1H), 6.50 (d, J = 4 Hz, 1H); 13C NMR
(100 MHz, CDCl3) d 171.3, 133.0, 131.6, 118.5, 116.5,
115.9, 114.5, 113.2, 100.8; high-resolution MS (EI)
Calcd for C9H7NO2 [M]+ m/e 161.0477. Found
161.0477. Anal. Calcd for C9H7NO2: C, 67.08; H,
4.38; N, 8.69. Found: C, 66.78; H, 4.43; N, 8.50.
6-prop-1-ynylnicotinate as
a
yellow solid (1.3 g,
6.8 mmol, 63%): IR (diffuse reflectance) 3051, 2478
(w), 2410 (w), 2388 (w), 2365 (w), 2226, 1716 (s), 1592,
1296 (s), 1269 (s), 1144, 1121, 1107, 1027, 781 (s),
cmꢀ1; MS (EI ) m/z (rel. intensity) 189 (M+, 83), 189
(83), 161 (85), 145 (25), 144 (99), 116 (62), 89 (67), 86
(28), 84 (40), 63 (54), 51 (29); 1H NMR (400 MHz,
CDCl3) d 9.17 (dd, J = 1, 2 Hz, 1H), 8.26 (dd, J = 2,
8 Hz, 1H), 7.46 (dd, J = 1, 8 Hz, 1H), 4.45 (q,
J = 7 Hz, 2H), 2.2 (s, 3H), 1.50 (t, J = 7 Hz, 3H); 13C
NMR (CDCl3) d 165.4, 151.4, 147.8, 137.5, 126.5,
124.9, 90.6, 79.9, 61.9, 14.7, 4.9; high-resolution MS
(EI) Calcd for C11H11NO2 [M]+ m/e 189.0790. Found
189.0787. Anal. Calcd for C11H11NO2: C, 69.83; H,
5.86; N, 7.40. Found: C, 69.68; H, 5.84; N, 7.30.
5.1.26. N-[(3R)-1-Azabicyclo[2.2.2]oct-3-yl]indolizine-6-
carboxamideÆD-tartrate (1l). A round-bottomed flask
was charged with indolizine-6-carboxylic acid (400 mg,
2.5 mmol), 3-(R)-1-azabicyclo[2.2.2]octan-3-amine dihy-
drochloride (498 mg, 2.5 mmol), DIEA (1.50 mL,
7.5 mmol), and N,N-dimethylformamide (20 mL). The
reaction mixture was cooled to 0 ꢁC and HATU
(970 mg, 2.5 mmol) was added. The mixture was al-
lowed to stir at room temperature for 3 h. The reaction
mixture was diluted with 1 N aqueous sodium hydroxide
(20 mL) and extracted with methylene chloride (3·
30 mL). The organic layer was dried over anhydrous
magnesium sulfate, filtered, and concentrated in vacuo.
5.1.24. Ethyl indolizine-6-carboxylate. To a stirred solut
ion of ethyl 6-prop-1-ynylnicotinate (1.58 g, 8.36 mmol)
and triethylamine (10 mL) in N,N-dimethylacetamide
(50 mL) under argon atmosphere was added copper(I)
chloride (828 mg, 8.36 mmol). The mixture was heated

8234
D. P. Walker et al. / Bioorg. Med. Chem. 14 (2006) 8219–8248
The crude product was purified by flash chromatogra-
phy on silica gel. Elution with methylene chloride–meth-
anol–ammonium hydroxide (89:10:1) afforded 400 mg
(59%) of an off-white solid.
in vacuo afforded a clear residue, which crystallized on
standing. The crystals were filtered and washed with
methylene chloride to afford 240 mg (42%) of 1n as a
white solid: IR (diffuse reflectance) 3238 (b), 3144,
3094, 3064, 3045 (b), 2944, 2427 (w), 2350 (w), 2295
(w), 1940 (w), 1652 (s), 1617, 1561, 1331, 1313 (s),
To a stirred solution of the above solid (200 mg,
0.70 mmol) in methanol (2 mL) were added a solution
of D-tartaric acid (100 mg, 0.7 mmol) in methanol
(2 mL). The solvent was removed in vacuo and resulting
solid was recrystallized from ether–methanol to afford
100 mg (29%) of 1l as an off-white solid: IR (diffuse
reflectance) 2333 (w), 1645 (s), 1622, 1545, 1526, 1320
(s), 1135 (s), 832, 826, 815 (s), 785, 726 (s), 706, 681,
1
cmꢀ1; H NMR (400 MHz, DMSO-d6) d 9.11 (s, 1H),
8.40 (d, J = 7 Hz, 1H), 8.07 (s, 1H), 7.66–7.68 (m, 2H),
7.59–7.62 (m, 1H), 3.95 (d, J = 7 Hz, 1H), 3.09–3.15
(m, 1H), 2.85–2.90 (m, 1H), 2.66–2.76 (m, 4H), 1.86–
1.88 (m, 1H), 1.82–1.83 (m, 1H), 1.58 (m, 2H), 1.32
(m, 1H); 13C NMR (100 MHz, DMSO-d6) d 165.0,
145.0, 134.7, 128.6, 123.7, 120.3, 114.5, 116.3, 54.0,
47.6, 47.2, 46.7, 26.2, 26.0, 20.3; high-resolution MS
(FAB) Calcd for C15H19N4O [M+H] m/e 271.1559.
Found 271.1562. Anal. Calcd for C15H18N4OÆ1.5H2O:
C, 60.59; H, 7.12; N, 18.84. Found: C, 60.39; H, 7.33;
N, 19.03.
1
607 (s), cmꢀ1; H NMR (400 MHz, CDCl3) d 8.88 (s,
1H), 8.42 (d, J = 6 Hz, 1H), 7.69 (s, 1H), 7.46 (d,
J = 9 Hz, 1H), 7.11 (dd, J = 1, 9 Hz, 1H), 6.85 (dd,
J = 3, 4 Hz, 1H), 6.46 (d, J = 4 Hz, 1H), 4.20 (m, 1H),
3.93 (s, 2H), 3.52 (m, 1H), 3.16 (m, 1H), 3.08 (m, 4H),
2.10 (m, 2H), 1.83 (m, 2H), 1.62 (m, 1H); 13C NMR
(CDCl3) d 174.3, 165.5, 131.8, 127.9, 117.8, 117.4,
115.4, 115.3, 114.5, 99.7, 71.5, 51.5, 45.7, 45.2 (d,
J = 6 Hz), 24.6, 22.4, 17.7; high-resolution MS (FAB)
Calcd for C16H20N3O [M+H] m/e 270.1606. Found
270.1604. % Water (KF): 5.77. Anal. Calcd for
C16H19N3OC4H6O61.5H2O: C, 57.27; H, 6.01; N,
10.02. Found: C, 53.46; H, 6.41; N, 9.37.
5.1.29. 2,3-Dihydro-1,4-benzodioxane-6-carboxylic acid.
To a stirred solution of 2,3-dihydro-1,4-benzodioxane-
6-carboxaldehyde (1.0 g, 6.1 mmol) in tert-butyl alcohol
(120 mL) and 2-methyl-2-butene (29 mL, 270 mmol)
were added a solution of sodium dihydrogen phosphate
(4.6 g, 38 mmol) and sodium chlorite (4.4 g, 49 mmol) in
water (44 mL). The solution was stirred at room temper-
ature for 45 min, then concentrated in vacuo. The
remaining residue was partitioned between 0.1 N aque-
ous hydrochloric acid and ether. The aqueous layer
was extracted with ether, and the combined ethereal lay-
ers were washed sequentially with saturated aqueous
sodium thiosulfate solution and brine. The ethereal layer
was dried over anhydrous magnesium sulfate, filtered,
and concentrated in vacuo to afford 1.1 g (99%) of 2,3-
dihydro-1,4-benzodioxane-6-carboxylic acid as a white
5.1.27. N-[(3R)-1-Azabicyclo[2.2.2]oct-3-yl]pyrrolo[1,2-
a]pyrazine-3-carboxamideÆD-tartrate (1m). The com-
pound 1m (130 mg, 43%) was prepared from pyr-
rolo[1,2-a]pyrazine-3-carboxylic acid hydrochloride53
(120 mg, 0.72 mmol) and 3-(R)-aminoquinuclidine dihy-
drochloride (140 mg, 0.72 mmol), followed by subse-
quent treatment with fumaric acid (64 mg, 0.42 mmol)
in a manner similar to that described for the preparation
of 1l. White powder: IR (diffuse reflectance) 3356, 3331,
2954, 2338, 1916, 1663, 1608, 1541, 1516, 1447, 1431,
1
solid: H NMR (400 MHz, CDCl3) d 11.3–10.7 (br s,
1H), 7.67–7.64 (m, 2H), 6.93 (d, 1H, J = 8.98 Hz),
4.36–4.34 (m, 2H), 4.32–4.30 (m, 2H); 13C NMR
(100 MHz, CDCl3) d 171.9, 148.9, 143.6, 124.6, 122.9,
120.0, 117.7, 65.08, 64.44; low-resolution MS (ESI)
m/e 179 [MꢀH].
1379, 1342, 1308, 1211, cmꢀ1 1H NMR (400 MHz,
;
DMSO-d6) d 9.00 (s, 1H), 8.70 (s, 1H), 8.81 (d,
J = 7 Hz, 1H), 7.98 (s, 1H), 7.05–6.99 (m, 2H), 4.30
(dd, J = 7, 1 Hz, 1H), 3.91 (s, 2 H), 3.50 (t, J = 12 Hz,
1H), 3.30–3.21 (m, 2H), 3.12–3.04 (m, 3H), 2.10 (d,
J = 3 Hz, 1H), 1.96 (dd, J = 10, 15 Hz, 1H), 1.84 (t,
J = 6 Hz, 2H) 1.68–1.61 (m, 1H); 13C NMR
(100 MHz, DMSO-d6) d 173.9, 163.9, 143.0, 129.7,
127.4, 120.5, 117.7, 116.5, 104.9, 71.2, 51.1, 45.7, 45.3,
44.5, 24.9, 22.4, 17.7; high-resolution MS Calcd for
C15H19N4O1 [M+H] m/e 271.1559. Found 271.1547.
Anal. Calcd for C15H18N4OÆC4H6O6Æ0.7H2O: C, 52.70;
H, 5.91; N, 12.94. Found: C, 53.08; H, 6.08; N, 12.74.
5.1.30. N-[3-(R)-1-Azabicyclo[2.2.2]oct-3-yl]-1,4-benzodi-
oxane-6-carboxamidefumarate (1o, PHA-568487). The
compound 1o (550 mg, 43%) was prepared from 2,3-
dihydro-1,4-benzodioxane-6-carboxylic acid (590 mg,
3.30 mmol) and 3-(R)-aminoquinuclidine dihydrochlo-
ride (620 mg, 3.11 mmol), followed by subsequent treat-
ment with fumaric acid (268 mg, 2.40 mmol) in a
manner similar to that described for the preparation of
25
D
1b. White solid: mp 198–200 ꢁC; ½aꢂ 4 (c 0.90, MeOH);
5.1.28. N-[(3R)-1-Azabicyclo[2.2.2]oct-3-yl]imidazo[1,2-
a]pyridine-7-carboxamide (1n). A round-bottomed flask
was charged with imidazo[1,2-a]pyridine-6-carboxylic
acid54 (63 mg, 0.39 mmol), 3-(R)-1-azabicyclo[2.2.2]oc-
tan-3-amine dihydrochloride (77 mg, 0.39 mmol), DIEA
(234 lL, 1.2 mmol), and N,N-dimethylformamide
(5 mL). The reaction mixture was cooled to 0 ꢁC and
HATU (151 mg, 0.39 mmol) was added. The mixture
was allowed to stir at room temperature for 3 h. The
mixture was concentrated in vacuo. The resulting brown
oil was purified by DOWEX 50WX2-400 ion-exchange
resin. Concentration of the fractions containing product
IR (diffuse reflectance) 3395, 2990, 2955, 2892, 2625,
1715, 1703, 1646, 1579, 1549, 1500, 1292, 1275, 1259,
1
1249 cmꢀ1; H NMR (400 MHz, MeOH-d4) d 7.42 (d,
1H, J = 2.04 Hz), 7.39 (dd, 1H, J = 8.35, 2.16 Hz), 6.92
(d, 1H, J = 8.34 Hz), 6.74 (s, 4H), 4.47–4.40 (m, 1H),
4.37–4.28 (m, 4H), 3.85–3.80 (m, 1H), 3.50–3.30 (m,
4H), 3.25 (ddd, 1H, J = 13.34, 5.63, 2.16 Hz), 2.38–
2.34 (m, 1H), 2.30–2.19 (m, 1H), 2.15–2.05 (m, 2H),
1.98–1.89 (m, 1H); 13C NMR (100 MHz, MeOH-d4) d
170.5, 170.2, 148.9, 145.2, 136.1, 128.3, 122.5, 118.6,
118.3, 66.32, 65.94, 53.74, 47.93, 47.49, 47.05, 26.14,
23.25, 18.91; high-resolution MS (FAB) Calcd for

D. P. Walker et al. / Bioorg. Med. Chem. 14 (2006) 8219–8248
8235
C16H21N2O3 m/e 289.1552. Found 289.1548. Anal.
Calcd for C16H20N2O3Æ2C4H4O4: C, 55.38; H, 5.42; N,
5.38. Found: C, 55.40; H, 5.50; N, 5.60
3224, 2997, 2957, 2938, 1701, 1660, 1610, 1530, 1494,
1466, 1317, 1289, 1259, 1239 cmꢀ1 1H NMR
;
(400 MHz, MeOH-d4) d 7.63–7.60 (m, 2H), 6.80 (d,
1H, J = 8.38 Hz), 6.70 (s, 2H), 4.46–4.40 (m, 1H), 4.23
(t, 2H, J = 5.12 Hz), 3.85–3.79 (m, 1H), 3.50–3.32 (m,
4H), 3.30–3.23 (m, 1H), 2.85 (t, 2H, J = 6.39 Hz),
2.37–2.34 (m, 1H), 2.27–2.19 (m, 1H), 2.12–2.05 (m,
2H), 2.05–1.99 (m, 2H), 1.98–1.89 (m, 1H); 13C NMR
(100 MHz, MeOH-d4) d 171.8, 171.0, 160.1, 136.6,
131.2, 128.4, 126.8, 124.0, 118.0, 68.35, 53.66, 47.88,
47.44, 47.00, 26.26, 26.24, 23.55, 23.28, 18.93; high-reso-
lution MS (FAB) Calcd for C17H23N2O2 [M+H] m/e
287.1759. Found 287.1774. % Water (KF): 1.73. Anal.
Calcd for C17H22N2O2ÆC4H4O4Æ1.73% H2O: C, 61.58;
H, 6.59; N, 6.84. Found: C, 61.46; H, 6.62; N, 6.79.
5.1.31. 1-(3,4-Dihydro-2H-chromen-6-yl)ethanone. To a
stirred solution of acetyl chloride (4.78 mL, 67.1 mmol)
in dry methylene chloride (20 mL) at ꢀ10 ꢁC was added
aluminum trichloride (4.76 g, 35.7 mmol) in small por-
tions. The mixture was stirred for 15 min until the solu-
tion became homogeneous. The solution was added via
canula to a separate solution of chromane55 (4.79 g,
35.7 mmol) in methylene chloride (30 mL) all at
ꢀ10 ꢁC. After complete addition, the solution was stir-
red at ꢀ10 ꢁC for 30 min. The solution was poured over
a mixture of crushed ice and concentrated hydrochloric
acid. The mixture was extracted with methylene chlo-
ride. The combined organic layers were washed with
brine, dried over anhydrous magnesium sulfate, filtered,
and concentrated in vacuo. The remaining residue was
purified via crystallization from hexanes to give 4.0 g
(64%) of 1-(3,4-dihydro-2H-chromen-6-yl)ethanone as
a white solid: Rf 0.31 (hexanes–ethyl acetate, 75:25);
IR (chloroform) 3048, 2928, 2853, 1672, 1598, 1571,
5.1.34. Chromane-7-carboxylic acid. To a stirred solu-
tion of methyl chromane-7-carboxylate56 (140 mg,
0.73 mmol) in methanol (5.0 mL) was added sodium
hydroxide (5.0 mL of a 5% aqueous solution). The mix-
ture was heated to 85 ꢁC for 3 h, followed by cooling to
room temperature. The methanol was removed in vac-
uo, and the remaining aqueous layer was acidified to
pH 1 with concentrated hydrochloric acid. The aqueous
layer was extracted with ethyl acetate. The organic layer
was dried over anhydrous magnesium sulfate, filtered,
and concentrated in vacuo to afford 130 mg (99%) of
1497, 1430, 1355, 1259, 827 cmꢀ1
;
1H NMR
(400 MHz, CDCl3) d7.76–7.73 (m, 2H), 6.75 (d, 1H,
J = 8.42 Hz), 4.27 (t, 2H, J = 5.16 Hz), 2.86 (t, 2H,
J = 6.43 Hz), 2.57 (s, 3H), 2.09–2.03 (m, 2H); 13C
NMR (100 MHz, CDCl3) d 195.1, 157.3, 128.9, 127.8,
126.4, 120.1, 114.8, 62.21, 24.42, 22.94, 20.06.
1
chromane-7-carboxylic acid as a white solid: H NMR
(400 MHz, DMSO-d6) d 13.0–12.0 (br s, 1H), 7.37 (dd,
1H, J = 7.9, 1.6 Hz); 7.24 (d, 1H, J = 1.6 Hz), 7.16 (d,
1H, J = 7.9 Hz); 4.16 (t, 2H, J = 5.4 Hz), 2.79 (t, 2H,
J = 6.6 Hz), 1.94–1.90 (m, 2H).
5.1.32. Chromane-6-carboxylic acid. A mixture of 1-(3,4-
dihydro-2H-chromen-6-yl)ethanone (3.80 g, 22.0 mmol)
and sodium hypochlorite [150 mL of a 6.0% aqueous
solution (Clorox brand of bleach)] at 55 ꢁC was stirred
for 2 h. The mixture (now homogeneous) was cooled
to room temperature and solid sodium bisulfite was add-
ed until a clear color persisted. Hydrochloric acid (ca.
15 mL of a 6.0 M aqueous solution) was added, fol-
lowed by extraction with ethyl acetate. The organic layer
was washed with brine, dried over anhydrous magne-
sium sulfate, filtered, and concentrated in vacuo to af-
ford 3.10 g (82%) of chromane-6-carboxylic acid as a
white solid: mp 148–150 ꢁC, IR (diffuse reflectance)
2972, 2949, 2926, 2900, 2856, 2364, 2342, 2317, 2215,
5.1.35. N-[(3R)-1-Azabicyclo[2.2.2]oct-3-yl]chromane-7-
carboxamideÆfumarate (1q). The compound 1q (114 mg,
64%) was prepared from chromane-7-carboxylic acid
(80 mg, 0.45 mmol) and 3-(R)-aminoquinuclidine dihy-
drochloride (89 mg, 0.45 mmol), followed by subsequent
treatment with fumaric acid (50 mg, 0.43 mmol) in a
manner similar to that described for the preparation of
25
D
1b. White solid: mp 140–150 ꢁC (loss of H2O); ½aꢂ
6
(c 0.75, methanol); IR (diffuse reflectance) 3429, 3226,
2960, 2487, 2350, 2338, 1940, 1921, 1626, 1551, 1314,
1278, 1231, 1134, 1063 cmꢀ1 1H NMR (400 MHz,
;
2162, 1686, 1329, 1295, 1256, 1190 cmꢀ1
;
1H NMR
methanol-d4) d 7.30 (dd, 1H, J= 7.88, 1.66 Hz), 7.22
(d, 1H, J = 1.66 Hz), 7.12 (d, 1H, J = 7.88 Hz), 6.67 (s,
2H), 4.42–4.37 (m, 1H), 4.19 (t, 2H, J = 5.39 Hz),
3.81–3.75 (m, 1H), 3.42–3.20 (m, 5H), 2.81 (t, 2H,
J = 6.64 Hz), 2.15 (m, 1H), 2.22–2.17 (m, 1H), 2.10–
1.92 (m, 4H), 1.91–1.80 (m, 1H); 13C NMR (100 MHz,
methanol-d4) d 170.2, 169.4, 155.1, 135.0, 132.9, 129.9,
126.9, 118.8, 115.6, 66.53, 51.94, 45.87, 45.84, 45.44,
24.71, 21.99, 21.70, 17.36; high-resolution MS Calcd
for C17H23N2O2 [M+H] m/e 287.1759. Found
287.1758. Anal. Calcd for C17H22N2O2ÆC4H4O4ÆH2O:
C, 59.99; H, 6.71; N, 6.66. Found: C, 59.79; H, 6.80;
N, 6.57.
(400 MHz, DMSO-d6) d 12.55 (s, 1H), 7.67 (s, 1H),
7.64 (dd, 1H, J = 8.46, 1.93 Hz), 6.79 (d, 1H,
J = 8.45 Hz), 4.20 (t, 2H, J = 5.09 Hz), 2.77 (t, 2H,
J = 6.37 Hz), 1.96–1.90 (m, 2H); 13C NMR (100 MHz,
DMSO-d6) d 166.5, 157.8, 131.0, 128.1, 121.6, 121.5,
115.7, 63.79, 23.42, 20.73; low-resolution MS (ESI)
m/e 177 [MꢀH]. Anal. Calcd for C10H10O3: C, 67.41;
H, 5.66. Found: C, 67.25; H, 5.73; N, 0.22.
5.1.33. N-[(3R)-1-Azabicyclo[2.2.2]oct-3-yl]chromane-6-
carboxamidefumarate (1p). The compound 1p (300 mg,
70%) was prepared from chromane-6-carboxylic acid
(200 mg, 1.12 mmol) and 3-(R)-aminoquinuclidine dihy-
drochloride (213 mg, 1.06 mmol), followed by subse-
quent treatment with fumaric acid (115 mg,
0.99 mmol) in a manner similar to that described for
5.1.36. N-[(3R)-1-Azabicyclo[2.2.2]oct-3-yl]-5,6,7,8-tetra-
hydronaphthalene-2-carboxamidefumarate (1r). The
compound 1r (257 mg, 69%) was prepared from 1,2,3,
4-tetrahydronaphthalene-6-carboxylic acid (163 mg,
0.93 mmol) and 3-(R)-aminoquinuclidine dihydrochlo-
the preparation of 1b. White solid: mp 194–195 ꢁC;
25
½aꢂ 5 (c 0.98, MeOH); IR (diffuse reflectance) 3363,
D

8236
D. P. Walker et al. / Bioorg. Med. Chem. 14 (2006) 8219–8248
ride (184 mg, 0.93 mmol), followed by subsequent treat-
ment with fumaric acid (97 mg, 0.84 mmol) in a manner
similar to that described for the preparation of 1b.
and the remaining residue was partitioned between
water and ethyl acetate. The aqueous layer was extract-
ed with ethyl acetate. The combined organic layers were
dried over anhydrous magnesium sulfate, filtered, and
concentrated in vacuo to afford 348 mg (86%) of methyl
2,3-dihydro-1,4-dioxino[2,3-c]pyridine-7-carboxylate as
a yellow solid: H NMR (400 MHz, CDCl3) d 8.29 (s,
1H), 7.71 (s, 1H), 4.39 (m, 2H), 4.00 (s, 3H), 3.98 (m,
2H).
25
White solid: mp 119–125ꢁC (loss of H2O); ½aꢂ 6 (c
D
0.83, MeOH); IR (diffuse reflectance) 3425, 3352, 3230,
3111, 3059, 3038, 3023, 2938, 2885, 2857, 2836, 1627,
1
1
1550, 1537, 1281 cmꢀ1; H NMR (400 MHz, CD3OD)
d 7.58–7.56 (m, 2H), 7.17 (d, J = 7.7Hz, 1H), 6.70 (s,
2H), 4.45–4.41 (m, 1H), 3.85–3.79 (m, 1H), 3.47–3.36
(m, 4H), 3.28–3.22 (m, 1H), 2.84–2.83 (m, 4H), 2.37–
2.34 (m, 1H), 2.27–2.19 (m, 1H), 2.12–2.07 (m, 2H),
1.97–1.89 (m, 1H), 1.87–1.83 (m, 4H); 13C NMR
(100 MHz, methanol-d4) d 171.4, 171.1, 142.9, 138.5,
136.2, 132.2, 130.3, 129.3, 125.7, 53.38, 50.93, 47.59,
47.15, 46.69, 30.44, 25.83, 24.22, 24.12, 22.96, 18.60;
high-resolution MS (FAB) Calcd for C18H25N2O
[M+H] m/e 285.1967. Found 285.1981. % Water (KF):
3.88. Anal. Calcd for C18H24N2OÆC4H4O4Æ3.88% H2O:
C, 63.41; H, 7.21; N, 6.99. Found: C, 63.76; H, 7.21;
N, 6.78.
To a stirred solution of methyl 2,3-dihydro-1,4-dioxi-
no[2,3-c]pyridine-7-carboxylate (300 mg, 1.54 mmol) in
methanol (10 mL) was added sodium hydroxide
(10 mL of a 5% aqueous solution). The mixture was
heated to reflux for 3 h, followed by cooling to room
temperature. The methanol was removed in vacuo,
and the remaining aqueous layer was acidified to pH 5
with 1 N aqueous hydrochloric acid. The aqueous layer
was continuously extracted with methylene chloride for
48 h. The organic layer was concentrated in vacuo to af-
ford 245 mg (88%) of 2,3-dihydro[1,4]dioxino[2,3-c]pyr-
idine-7-carboxylic acid as a white solid: mp 223–225 ꢁC;
IR (diffuse reflectance) 2483, 2453, 2401, 2334, 2259,
1741, 1428, 1357, 1325, 1313, 1295, 1051, 940, 907,
5.1.37. N-[(3R)-1-azabicyclo[2.2.2]oct-3-yl]-2-naphthami-
dehydrochloride (1s). The compound 1s (1.01 g, 63%)
was prepared from 2-naphthoic acid (1.00 g, 5.81 mmol)
and 3-(R)-aminoquinuclidine dihydrochloride (1.00 g,
5.02 mmol), followed by subsequent treatment with
ethereal hydrogen chloride (30 mL of a 2.0 M solution)
1
880 cmꢀ1; H NMR (400 MHz, DMSO-d6) d 13.1–12.7
(br s, 1H), 8.19 (s, 1H), 7.49 (s, 1H), 4.40–4.33 (m,
4H); 13C NMR (100 MHz, DMSO-d6) d 166.2, 150.4,
144.4, 142.6, 139.3, 114.4, 65.50, 64.98; high-resolution
MS (ESI) Calcd for C8H8NO4 [M+H] m/e 182.0453.
Found 182.0462. Anal. Calcd for C8H7NO4: C, 53.04;
H, 3.90; N, 7.73. Found: C, 52.93; H, 3.81; N, 7.70.
in a manner similar to that described for the preparation
25
D
reflectance) 3235, 2657, 2633, 2596, 2555, 2484, 1652,
of 1b. White solid: ½aꢂ 12 (c 0.93, methanol); IR (diffuse
1526, 1503, 1330, 1313, 829, 781, 760, 623 cmꢀ1 1H
;
NMR (400 MHz, D2O) d 7.86 (s, 1H), 7.70 (d, 2H,
J = 7.88 Hz), 7.65 (d, 1H, J = 8.71 Hz), 7.48–7.34 (m,
3H), 3.98–3.90 (m, 1H), 3.50 (t, 1H, J = 11.62 Hz),
3.21–3.00 (4H), 2.99–2.90 (m, 1H), 2.00–1.60 (m, 5H);
13C NMR (100 MHz, D2O) d 170.8, 134.7, 132.1,
130.1, 129.1, 128.4, 128.3, 128.1, 127.8, 127.2, 123.6,
51.96, 46.55, 46.17, 45.37, 23.95, 21.24, 17.00; high-reso-
lution MS (ESI) Calcd for C18H21N2O [M+H] m/e
281.1654. Found 281.1657. % Water (KF): 0.51. Anal.
Calcd for C18H20N2OÆHClÆ0.51% H2O: C, 67.89; H,
6.71; N, 8.80. Found: C, 67.81; H, 6.73; N, 8.79.
5.1.40.
N-[(3R)-1-Azabicyclo[2.2.2]oct-3-yl]-2,3-dihy-
dro[1,4]dioxino[2,3-c]pyridine-7-carboxamide (1t). The
compound 1t (116 mg, 40%) was prepared from 2,3-
dihydro[1,4]dioxino[2,3-c]pyridine-7-carboxylic
(130 mg, 0.72 mmol) and 3-(R)-aminoquinuclidine dihy-
drochloride (143 mg, 0.72 mmol), followed by subse-
quent treatment with fumaric acid (51 mg, 0.44 mmol)
acid
in a manner similar to that described for the preparation
25
D
of 1b. White solid: mp 204–205 ꢁC; ½aꢂ ꢀ2 (c, 0.58
methanol); IR (diffuse reflectance) 3359, 2992, 2962,
2887, 1728, 1663, 1578, 1568, 1513, 1484, 1461, 1439,
5.1.38. Methyl 4,5-dihydroxypyridine-2-carboxylate. To
a stirred solution of 4,5-dihydroxypyridine-2-carboxylic
acid49,57 (800 mg, 4.18 mmol) in methanol (30 mL) was
added concentrated sulfuric acid (1.0 mL). The mixture
was heated to reflux for 48 h, followed by cooling to
room temperature. Solid sodium bicarbonate was add-
ed, followed by dilution with water. The resulting pre-
cipitate was filtered, washed with water, and dried in
vacuo to afford 527 mg (75%) of methyl 4,5-dihydroxy-
pyridine-2-carboxylate as a white solid: 1H NMR
(400 MHz, methanol-d4) d 7.68 (s, 1H), 7.24 (s, 1H),
3.97 (s, 3H).
1378, 1371, 1315 cmꢀ1 1H NMR (400 MHz, metha-
;
nol-d4) d 8.13 (s, 1H), 7.55 (s, 1H), 6.67 (s, 2H), 4.45–
4.38 (m, 1H), 4.40–4.32 (m, 4H), 3.81–3.72 (m, 1H),
3.50–3.39 (m, 1H), 3.40–3.25 (m, 4H), 2.31 (m, 1H),
2.25–2.15 (m, 1H), 2.10–2.02 (m, 2H), 1.95–1.85 (m,
1H); 13C NMR (100 MHz, methanol-d4) d 170.3,
166.0, 151.0, 144.3, 143.8, 138.2, 135.0, 65.20, 64.59,
51.80, 46.22, 45.85, 44.89, 24.89, 21.68, 17.27; high-reso-
lution MS (FAB) Calcd for C15H20N3O3 [M+H] m/e
290.1505. Found 290.1510. Anal. Calcd for
C15H19N3O3ÆC4H4O4: C, 56.29; H, 5.72; N, 10.37.
Found: C, 56.20; H, 5.72; N, 10.31.
5.1.39. 2,3-Dihydro[1,4]dioxino[2,3-c]pyridine-7-carbox-
ylic acid. To a stirred solution of methyl 4,5-dihydroxy-
pyridine-2-carboxylate (348 mg, 2.06 mmol) in N,N-
dimethylformamide (20 mL) were added anhydrous
potassium carbonate (3.10 g, 22 mmol) and 1,2-dib-
romoethane (386 lL, 4.5 mmol). The mixture was heat-
ed to 115 ꢁC for 2 h. The solvent was removed in vacuo,
5.1.41. Methyl 4-hydroxy-3-nitrobenzoate. To a stirred
solution of 4-hydroxy-3-nitrobenzoic acid (5.0 g,
27.3 mmol) in methanol (100 mL) was added concen-
trated sulfuric acid (0.3 mL). The solution was heated
to reflux for 16 h, followed by cooling to room temper-
ature. The solvent was removed in vacuo, and the
remaining residue was partitioned between water and

D. P. Walker et al. / Bioorg. Med. Chem. 14 (2006) 8219–8248
8237
ethyl acetate. The organic layer was washed with brine,
dried over anhydrous sodium sulfate, filtered and con-
centrated in vacuo to afford methyl 4-hydroxy-3-nitro-
benzoate as a yellow solid (5 g, 93%): Rf 0.31
(hexanes–ethyl acetate, 3:1); IR (diffuse reflectance)
1720, 1627, 1538, 1439, 1423, 1332, 1291, 1259, 1191,
5.1.43. Methyl 3,4-dihydro-2H-1,4-benzoxazine-6-car-
boxylate. To a stirred mixture of methyl 3-oxo-3,4-
dihydro-2H-1,4-benzoxazine-6-carboxylate
(350 mg,
1.69 mmol) in anhydrous tetrahydrofuran (7 mL) was
added boron trifluoride diethyl etherate (450 lL,
3.55 mmol) slowly. The mixture was stirred for 20 min,
sodium borohydride (135 mg, 3.55 mmol) was added in
small portions. The resulting mixture was stirred for
2 h, followed by careful dilution with ethyl acetate
(1 mL) and hydrochloric acid (2 mL of a 1.0 M aqueous
solution). The mixture was poured into saturated aque-
ous potassium carbonate and extracted with ethyl ace-
tate (2·). The organic layer was washed with brine,
dried over anhydrous sodium sulfate, filtered, and con-
centrated in vacuo. The residue was purified by flash
chromatography on silica gel. Elution with hexanes–eth-
yl acetate (60:40) afforded methyl 3,4-dihydro-2H-1,4-
benzoxazine-6-carboxylate as a white solid (285 mg,
87%): mp 73–74 ꢁC; Rf 0.50 (hexanes–ethyl acetate,
3:2); IR (diffuse reflectance) 2412, 2335, 2251, 2121,
2063, 1697, 1588, 1502, 1316, 1277, 1252, 1228, 1209,
1169, 1145, 912, 760, 707, 686 cmꢀ1
;
1H NMR
(400 MHz, CDCl3) d 10.94 (s, 1H), 8.87 (d, J = 2.1 Hz,
1H), 8.28 (dd, J = 8.8, 2.1 Hz, 1H), 7.26 (d, J = 8.8 Hz,
1H), 3.99 (s, 3H); low-resolution MS (ESI-) m/z 196
(MꢀH). Anal. Calcd for C8H7NO5: C, 48.74; H, 3.58;
N, 7.11. Found: C, 48.66; H, 3.58; N, 7.08.
5.1.42. Methyl 3-oxo-3,4-dihydro-2H-1,4-benzoxazine-6-
carboxylate. To a stirred solution of methyl 4-hydroxy-
3-nitrobenzoate (1.0 g, 5.08 mmol) in acetone (50 mL)
were added methyl bromoacetate (504 lL, 5.33 mmol)
and anhydrous sodium bicarbonate (640 mg,
7.62 mmol). The mixture was heated to reflux for
16 h, followed by cooling to room temperature. The
mixture was diluted with ethyl acetate and washed
sequentially with water, saturated sodium bicarbonate,
saturated potassium carbonate, and brine. The organic
layer was dried over anhydrous magnesium sulfate, fil-
tered, and concentrated in vacuo. The residue was
purified by flash chromatography on silica gel. Elution
with hexanes–ethyl acetate (1:1) gave 1.05 g (77%) of
methyl 4-(2-methoxy-2-oxoethoxy)-3-nitrobenzoate as
a white solid: mp 123–134 ꢁC; Rf 0.17 (hexanes–ethyl
acetate, 3:1); IR (diffuse reflectance) 1763, 1710,
1618, 1532, 1441, 1398, 1346, 1311, 1290, 1229, 1167,
1
1106, 766 cmꢀ1; H NMR (300 MHz, CDCl3) d 7.42–
7.41 (m, 2H), 6.83 (d, J = 8.3 Hz, 1H), 4.36 (t,
J = 4.4 Hz, 2H), 3.88 (s, 3H), 3.49 (t, J = 4.4 Hz, 2H);
13C NMR (100 MHz, CDCl3) d 167.5, 148.6, 133.7,
123.4, 121.5, 117.2, 116.9, 65.99, 60.85, 52.28, 40.92;
low-resolution MS (ESI+) m/z 194 (M+H). Anal. Calcd
for C10H11NO3: C, 62.17; H, 5.74; N, 7.25. Found: C,
61.84; H, 5.70; N, 7.19.
5.1.44.
3,4-Dihydro-2H-1,4-benzoxazine-6-carboxylic
1134, 1082, 758, 727 cmꢀ1
;
1H NMR (400 MHz,
acid. A mixture of methyl 3,4-dihydro-2H-1,4-benzox-
azine-6-carboxylate (285 mg, 1.48 mmol) in 2% aqueous
sodium hydroxide (16 mL) and methanol (5 mL) was
heated to reflux for 30 min. The reaction mixture was al-
lowed to cool to room temperature, diluted with water,
and washed with ethyl acetate (2·). The aqueous layer
was acidified to pH 5–6 with concentrated hydrochloric
acid. The aqueous layer was extracted with chloroform
(5·). The organic layer was washed with brine, dried
over anhydrous magnesium sulfate, filtered, and concen-
trated in vacuo to give 191 mg (72%) of 3,4-dihydro-2H-
1,4-benzoxazine-6-carboxylic acid as a light yellow solid:
mp 150–151 ꢁC; IR (diffuse reflectance) 2970, 2944,
2885, 1676, 1607, 1582, 1491, 1420, 1328, 1302, 1225,
CDCl3) d 8.56 (d, J = 2.1 Hz, 1H), 8.21 (dd, J = 8.8,
2.1 Hz, 1H), 7.02 (d, J = 8.8 Hz, 1H), 4.88 (s, 2H),
3.96 (s, 3H), 3.84 (s, 3H); low-resolution MS (ESI)
m/z 268 (MꢀH). Anal. Calcd for C11H11NO7: C,
49.08; H, 4.12; N, 5.20. Found: C, 48.90; H, 4.14;
N, 5.18.
A mixture of the above solid (1.0 g, 3.72 mmol) and
5% palladium on activated carbon (100 mg) in meth-
anol–tetrahydrofuran (5:2, 70 mL) was placed in a
Parr bottle. The mixture was shaken at room temper-
ature for 16 h under an atmosphere of hydrogen
(45 psi). The mixture was filtered through a pad of
Celite, and to the filtrate was added acetic acid
(10 mL). The resulting solution was heated to reflux
for 30 min, followed by cooling to room temperature.
The mixture was concentrated in vacuo. The residue
was triturated in hexanes, which produced a white
precipitate. The precipitate was filtered and dried in
vacuo to give 700 mg (91%) of methyl 3-oxo-3,4-dihy-
dro-2H-1,4-benzoxazine-6-carboxylate as a white sol-
id: mp 191.5–193 ꢁC; Rf 0.56 (hexanes–ethyl acetate,
1:1); IR (diffuse reflectance) 3063, 3009, 2981, 2958,
1721, 1698, 1606, 1499, 1402, 1303, 1280, 1213,
;
1216, 1129, 923, 766 cmꢀ1 1H NMR (400 MHz,
DMSO-d6) d 12.30 (s, 1H), 7.19 (d, J = 2.0 Hz, 1H),
7.10 (dd, J = 8.3, 2.0 Hz, 1H), 6.70 (d, J = 8.3 Hz, 1H),
6.02 (s, 1H), 4.17 (t, J = 4.3 Hz, 2H), 3.28 (t,
J = 4.3 Hz, 2H); high-resolution MS (FAB) Calcd for
C9H9NO3 [M+H] m/z 180.0661. Found 180.0663. Anal.
Calcd for C9H9NO3: C, 60.33; H, 5.06; N, 7.82. Found:
C, 59.92; H, 5.12; N, 7.75.
5.1.45. N-[(3R)-1-Azabicyclo[2.2.2]oct-3-yl]-3,4-dihydro-
2H-1,4-benzoxazine-6-carboxamideÆfumarate (1u). The
compound 1u (300 mg, 86%) was prepared from 3,4-
dihydro-2H-1,4-benzoxazine-6-carboxylic acid (152 mg,
0.85 mmol) and 3-(R)-aminoquinuclidine dihydrochlo-
ride (169 mg, 0.85 mmol), followed by subsequent treat-
ment with fumaric acid (99 mg, 0.86 mmol) in a manner
1103, 1039, 765 cmꢀ1 1H NMR (400 MHz, DMSO-
;
d6) d 10.90 (s, 1H), 7.54 (d, J = 2.0 Hz, 1H), 7.52
(dd, J = 8.3, 2.0 Hz, 1H), 7.05 (d, J = 8.3 Hz, 1H),
4.69 (s, 2H), 3.82 (s, 3H); low-resolution MS (ESI)
m/z 206 (MꢀH). Anal. Calcd for C10H9NO4: C,
57.97; H, 4.38; N, 6.76. Found: C, 57.83; H, 4.42;
N, 6.72.
similar to that described for the preparation of 1b.
25
D
White solid: mp 183–184 ꢁC; ½aꢂ 5 (c 0.71, MeOH);

8238
D. P. Walker et al. / Bioorg. Med. Chem. 14 (2006) 8219–8248
IR (diffuse reflectance) 3331, 3271, 2974, 2964, 2937,
1695, 1653, 1608, 1551, 1500, 1406, 1324, 1305, 1212,
acetic acid (10 mL). The solution was heated to reflux
for 30 min, followed by cooling to room temperature.
The mixture was concentrated in vacuo and the resulting
residue was triturated in hexanes for 30 min. The solid
precipitate was filtered and dried in vacuo to give 1.8 g
(88%) of methyl 3-oxo-3,4-dihydro-2H-1,4-benzox-
azine-7-carboxylate as an off-white solid: mp 253–
255 ꢁC; Rf 0.38 (chloroform–methanol, 95:5); IR (diffuse
reflectance) 3068, 1720, 1701, 1610, 1440, 1423, 1402,
1
980 cmꢀ1; H NMR (400 MHz, MeOH-d4) d 7.13 (dd,
J = 8.3, 2.0 Hz, 1H), 7.10 (d, J = 2.0 Hz, 1H), 6.74 (d,
J = 8.3 Hz, 1H), 6.7 (s, 2H), 4.41–4.37 (m, 1H), 4.25 (t,
J = 4.4 Hz, 2H), 3.83–3.77 (m, 1H), 3.46–3.28 (m, 4H),
3.38 (t, J = 4.4 Hz, 2H), 3.25–3.20 (m, 1H), 2.34–2.32
(m, 1H), 2.26–2.19 (m, 1H), 2.11–2.06 (m, 2H), 1.96–
1.88 (m, 1H); 13C NMR (100 MHz, DMSO-d6) d
171.8, 171.5, 149.0, 136.6, 136.2, 128.1, 118.9, 117.5,
116.3, 67.07, 53.82, 47.94, 47.49, 47.00, 41.83, 26.18,
23.31, 18.95; high-resolution MS (FAB) Calcd
for C16H21N3O2 [M+H] m/z 288.1712. Found
288.1709. Anal. Calcd for C16H21N3O2ÆC4H4O4: C,
59.54; H, 6.25; N, 10.41. Found: C, 59.37; H, 6.26; N,
10.35.
1
1317, 1294, 1246, 1218, 1099, 1048, 830, 761 cmꢀ1; H
NMR (400 MHz, DMSO-d6) d 11.1 (s, 1H), 7.58 (dd,
1H, J = 8.06, 1.37 Hz), 7.44 (s, 1H), 6.98 (d, 1H,
J = 8.07 Hz), 4.65 (s, 2H), 3.81 (s, 3H); 13C NMR
(100 MHz, DMSO-d6) d 165.9, 165.3, 143.2, 132.2,
124.5, 124.4, 117.0, 116.1, 66.99, 52.42.
5.1.48. Methyl 3,4-dihydro-2H-1,4-benzoxazine-7-car-
boxylate. To a stirred solution of methyl 3-oxo-3,4-
dihydro-2H-1,4-benzoxazine-7-carboxylate (585 mg,
2.82 mmol) in dry tetrahydrofuran (8.0 mL) at ꢀ5 ꢁC
under argon was added borontrifluoride etherate
(751 lL, 5.92 mmol). The solution was stirred at ꢀ5 ꢁC
for 20 min, followed by the addition of sodium borohy-
dride (224 mg, 5.92 mmol). The mixture was stirred for
5 h at ꢀ5 ꢁC. Ethyl acetate (ca. 1 mL) was added, fol-
lowed by hydrochloric acid (1.8 mL of a 1.0 M aqueous
solution). The mixture was poured into saturated aque-
ous potassium carbonate solution and extracted with
ethyl acetate. The organic layer was washed with brine,
dried over anhydrous magnesium sulfate, filtered, and
concentrated in vacuo to give 400 mg (73%) of methyl
3,4-dihydro-2H-1,4-benzoxazine-7-carboxylate as a yel-
low solid: mp 82–83 ꢁC, Rf 0.52 (chloroform–methanol,
95:5); IR (diffuse reflectance) 3406, 1691, 1605, 1582,
1534, 1439, 1330, 1286, 1251, 1221, 1087, 1033, 897,
5.1.46. Methyl 3-hydroxy-4-nitrobenzoate. To a stirred
solution of 3-hydroxy-4-nitrobenzoic acid (5.0 g,
30 mmol) in methyl alcohol (100 mL) was added con-
centrated sulfuric acid (0.9 mL). The mixture was heated
to reflux for 5 h, followed by cooling to room tempera-
ture. Solid sodium bicarbonate (ca. 3 g) was added and
the mixture was stirred for 30 min. The mixture was con-
centrated in vacuo and the remaining residue was parti-
tioned between 0.1 M aqueous hydrochloric acid
solution and ethyl acetate. The organic layer was sepa-
rated, washed with brine, dried over anhydrous magne-
sium sulfate, filtered, and concentrated in vacuo to
afford 5.4 g (99%) of methyl 3-hydroxy-4-nitrobenzoate
as a yellow solid: mp 86–88 ꢁC; Rf 0.69 (hexanes–ethyl
acetate, 1:1); IR (chloroform) 3267, 3015, 2958, 1737,
1590, 1482, 1324, 1281, 1212, 753 cmꢀ1 1H NMR
;
(400 MHz, CDCl3) d 10.52 (s, 1H), 8.22 (d, 1H,
J = 8.80 Hz), 7.87 (d, 1H, J = 1.76 Hz), 7.65 (dd, 1H,
J = 8.82, 1.80 Hz), 4.00 (s, 3H); 13C NMR (100 MHz,
CDCl3) d 165.3, 155.1, 138.4, 137.1, 125.7, 122.1,
121.0, 53.37.
825, 766 cmꢀ1 1H NMR (300 MHz, CDCl3) d 7.50
;
(dd, 1H, J = 8.15, 1.90 Hz), 7.47 (d, 1H, J = 1.80 Hz),
6.55 (d, 1H, J = 8.15 Hz); 4.27–4.24 (m, 2H), 3.86 (s,
3H), 3.51–3.48 (m, 2H); 13C NMR (75 MHz, CDCl3) d
167.1, 142.7, 138.3, 124.0, 119.6, 118.2, 113.8, 64.57,
51.70, 40.66; low-resolution MS (ESI) m/e 194 [M+H].
Anal. Calcd for C10H11NO3: C, 62.17; H, 5.74; N,
7.25. Found: C, 61.90; H, 5.80; N, 7.03.
5.1.47. Methyl 3-oxo-3,4-dihydro-2H-1,4-benzoxazine-7-
carboxylate. To a stirred solution of methyl 3-hydroxy-
4-nitrobenzoate (2.0 g, 10 mmol) in acetone (100 mL)
were added methyl bromoacetate (1.2 mL, 12 mmol)
and anhydrous potassium carbonate (2.1 g, 15 mmol).
The mixture was heated to reflux for 4 h, followed by
cooling to room temperature. The mixture was parti-
tioned between dilute aqueous potassium carbonate
solution and ethyl acetate. The organic layer was
washed with brine, dried over anhydrous magnesium
sulfate, filtered, and concentrated in vacuo to afford
2.67 g (99%) of methyl 3-(2-methoxy-2-oxoethoxy)-4-
nitrobenzoate as a yellow solid: Rf 0.73 (hexanes–ethyl
5.1.49.
3,4-Dihydro-2H-1,4-benzoxazine-7-carboxylic
acid. To a stirred solution of methyl 3,4-dihydro-2H-
1,4-benzoxazine-7-carboxylate (390 mg, 2.02 mmol) in
methanol (25 mL) was added sodium hydroxide
(15 mL of a 5% aqueous solution). The mixture was
heated to 65 ꢁC for 5 h, followed by cooling to room
temperature. The mixture was diluted with water and
the pH was adjusted to 5–6 with concentrated hydro-
chloric acid. The mixture was extracted with chloroform
(6X). The organic layer was dried over anhydrous mag-
nesium sulfate, filtered, and concentrated in vacuo to af-
ford 355 mg (98%) of 3,4-dihydro-2H-1,4-benzoxazine-
7-carboxylic acid as an off-white solid: 1H NMR
(400 MHz, CDCl3) d 7.57 (dd, 1H, J = 8.26, 1.90 Hz),
7.53 (d, 1H, J = 1.88 Hz), 6.57 (d, 1H, J = 8.26 Hz),
4.28–4.26 (m, 2H), 3.53–3.50 (m, 2H); 13C NMR
(100 MHz, CDCl3) d 171.6, 143.0, 139.4, 125.2, 119.1,
118.8, 114.1, 64.83, 41.02; low-resolution MS (ESI) m/e
178 [MꢀH].
1
acetate, 1:1); H NMR (400 MHz, CDCl3) d 7.89 (d,
1H, J = 8.36 Hz), 7.78 (dd, 1H, J = 8.38, 1.54 Hz), 7.66
(d, 1H, J = 1.52 Hz), 4.90 (s, 2H), 3.97 (s, 3H), 3.83 (s,
3H).
A mixture of methyl 3-(2-methoxy-2-oxoethoxy)-4-
nitrobenzoate (2.67 g, 9.9 mmol) and 10% palladium
on activated carbon (200 mg) in methyl alcohol
(100 mL) was placed in a Parr bottle and shaken under
an atmosphere of hydrogen (45 psi) overnight. The cat-
alyst was filtered and to the filtrate was added glacial

D. P. Walker et al. / Bioorg. Med. Chem. 14 (2006) 8219–8248
8239
5.1.50. N-[(3R)-1-Azabicyclo[2.2.2]oct-3-yl]-3,4-dihydro-
2H-1,4-benzoxazine-7-carboxamide (1v). To a stirred
solution of 3,4-dihydro-2H-1,4-benzoxazine-7-carboxyl-
ic acid (390 mg, 2.18 mmol) in anhydrous N,N-dimethyl-
formamide (21 mL) in an ice bath were added
sequentially diisopropylethylamine (1.10 mL,
6.33 mmol), 3(R)-aminoquinuclidine dihydrochloride
(412 mg, 2.08 mmol), and HATU (789 mg, 2.08 mmol).
The mixture was stirred at 0 ꢁC for 1 h, followed by
warming to room temperature and stirring overnight.
The mixture was concentrated in vacuo to a yellow res-
idue. The residue was partitioned between chloroform–
methanol (90:10) and half saturated aqueous potassium
carbonate solution. The aqueous layer was extracted
with chloroform–methanol (90:10), and the combined
organic layers were washed with brine, dried over anhy-
drous magnesium sulfate, filtered, and concentrated in
vacuo. The crude product was purified by flash chroma-
tography on silica gel. Elution with chloroform–metha-
nol–ammonium hydroxide (90:9:1) gave 400 mg (67%)
0.24 mol) and 100 mL n-propanol) was added dropwise
to a suspension of the (3E/3Z)-2-methyl-1-azabicy-
clo[2.2.2]octan-3-one oxime hydrochloride (45.8 g,
0.24 mol) in 150 mL n-propanol. After complete addi-
tion, 250 mL of n-propanol was added and the mixture
was heated under reflux. Sodium (55.2 g, 2.40 mol) was
added in portions to the refluxing mixture. The mixture
was heated under reflux overnight. After about 14 h, the
mixture was cooled, water (ca. 100 mL) was added, and
the layers were separated. The n-propanol layer was
washed 1· brine and dried over anhydrous magnesium
sulfate. The combined aqueous layers were extracted
with chloroform (5·) and dried over anhydrous magne-
sium sulfate. The combined, dried organic layers were
treated with about 70 mL concentrated hydrochloric
acid. The solvent was removed in vacuo. Absolute etha-
nol was added and the solvent was removed. The se-
quence was repeated 2–3 times with fresh ethanol until
precipitation of a white solid occurred. The precipitate
was filtered, washed with ethanol, and dried (vacuum
oven, 60ꢁC) to afford 36.5 g (71%) of ( )-3. Additional
material was obtained from the mother liquor; 7.8 g
(2nd crop) and 1.5 g (3rd crop), both as a trans/cis mix-
ture of isomers. The combined 2nd and 3rd crops were
recrystallized from methanol–ethanol to provide 1.7 g
(3.3%) of 6.
of 1v as
Rf 0.10 (chloroform–methanol–ammonium hydroxide,
a
light yellow solid: mp 213–214 ꢁC;
25
D
3350, 2946, 2874, 1627, 1610, 1582, 1518, 1354, 1318,
80:19:1); ½aꢂ 33 (c 0.96, MeOH); IR (diffuse reflectance)
1297, 1285, 1253, 1209, 815, 624 cmꢀ1
;
1H NMR
(400 MHz, MeOH-d4)
d 7.28 (dd, 1H, J = 8.25,
2.06 Hz), 7.25 (d, 1H, J = 2.02 Hz), 6.60 (d, 1H,
J = 8.25 Hz), 4.21–4.18 (m, 2H), 4.15–4.08 (m, 1H),
3.43–3.41 (m, 2H), 3.32–3.25 (m, 1H), 3.05–2.95 (m,
1H), 2.90–2.75 (m, 5H), 2.03–1.98 (m, 1H), 1.97–1.83
(m, 1H), 1.81–1.75 (m, 2H), 1.60–1.50 (m, 1H); 13C
NMR (75 MHz, MeOH-d4) d 170.7, 144.0, 139.8,
123.6, 122.5, 116.7, 114.8, 65.93, 54.54, 48.58, 47.82,
47.48, 41.49, 27.05, 26.33, 20.78; low-resolution MS
(ESI) m/e 288 [M+H]. % Water (KF): 0.21%. Anal.
Calcd for C16H21N3O2Æ0.21% H2O: C, 66.74; H, 7.38;
N, 14.59. Found: C, 66.51; H, 7.38; N, 14.22.
trans-Isomer ( )-3. 1H NMR (400 MHz, DMSO) d
10.90 (br s, 1H), 8.94 (br s, 3H), 3.57–3.48 (dq, 1H,
J = 6.5, 6.5 Hz), 3.40–3.05 (m, 4H), 2.53–2.49 (m, 1H),
2.33–2.27 (m, 1H), 2.24–2.13 (m, 1H), 1.91–1.82 (m,
2H), 1.80–1.70 (m, 1H), 1.52 (d, 3H, J = 6.8 Hz); MS
(ESI) for C8H16N2 m/z 141.3 (M+).
1
cis-Isomer (6). H NMR (400 MHz, DMSO) d 8.85 (br
s, 3H), 8.20 (br s, 1H), 3.95–3.84 (dq, 1H, J = 7.4,
8.1 Hz), 3.70 (dd, 1H, J = 3.2, 9.4 Hz), 3.54–3.43 (m,
1H), 3.28–3.17 (m, 2H), 3.14–3.05 (dt, 1H, J = 3.5,
12.6 Hz), 2.35–2.29 (m, 1H), 2.11–2.00 (m, 1H), 1.94–
1.82 (m, 2H), 1.80–1.68 (m, 1H), 1.52 (d, 3H,
J = 7.2 Hz).
5.1.51. (3E/3Z)-2-Methyl-1-azabicyclo[2.2.2]octan-3-one
417
oxime.
2-Methylquinuclidin-3-one
(39.6 g,
0.284 mol) and hydroxylamine hydrochloride (20.0 g,
0.288 mol) were dissolved in 170 mL absolute EtOH.
The mixture was heated under reflux until a clear solu-
tion developed (about 20 min), after which was immedi-
ately followed by formation of a white precipitate. The
reaction mixture was cooled and allowed to stand over-
night. The mixture was cooled in an ice bath, the solids
were filtered and dried in vacuo to provide 46.4 g of 2-
methyl-1-azabicyclo[2.2.2]octan-3-one oxime hydrochlo-
ride as a 3.5:1 mixture of geometric isomers. A second
crop of 2.4 g was also obtained. Overall yield 48.8 g
(90%): 1H NMR (400 MHz, DMSO) d 11.26 (br s,
1H), 11.17 (s, 0.8H), 11.05 (s, 0.2H), 4.39 (q, 0.2H),
4.29 (q, 0.8H), 3.54–3.38 (m, 1H), 3.34–3.14 (m, 3H),
2.73–2.68 (m, 0.2H), 2.53–2.48 (m, 0.8H), 2.04–1.72
(m, 4H), 1.57 (d, 0.6H, J = 6.9 Hz), 1.47 (d, 2.4H,
J = 6.7 Hz); low-resolution MS (ESI) for C8H14N2O
m/z 154.8 (M+).
5.1.53.
4-Chloro-N-[(2S,3R)-2-methyl-1-azabicy-
clo[2.2.2]oct-3-yl]benzamide [(+)-7] and 4-chloro-N-
[(2R,3S)-2-methyl-1-azabicyclo[2.2.2]oct-3-yl]benzamide
[(ꢀ)-7]. 4-Chlorobenzoic acid (26.3 g, 0.168 mol,
1.1 equiv) and triethylamine (106 mL, 0.764 mol,
5 equiv) were dissolved in 300 mL tetrahydrofuran.
Diphenylphosphinic chloride (32.0 mL, 0.168 mol) was
added dropwise. After 1 h, ( )-3 (32.6 g, 0.153 mol)
was added. The mixture was allowed to stir at room
temperature overnight. Aqueous sodium hydroxide
(100 mL of 1.0 N solution) was added, followed by
adjusting the pH of the solution and to 11 with 50%
aqueous sodium hydroxide and ꢁ50 g of potassium car-
bonate. The layers were separated. The aqueous layer
was extracted with chloroform (4·). The combined
organic layers were dried over anhydrous magnesium
sulfate, filtered, and concentrated. The residue was trit-
urated in heptane, followed by removal of the solvent in
vacuo to afford 35.1 g (82%) of racemic 4-chloro-N-
(2-methyl-1-azabicyclo[2.2.2]oct-3-yl)phenyl-2-carboxamide
[( )-7] as a light yellow solid. Reverse-phase HPLC
5.1.52. trans-2-Methyl-1-azabicyclo[2.2.2]octan-3-amine
dihydrochloride [( )-3] and cis-2-Methyl-1-azabicy-
clo[2.2.2]octan-3-amine dihydrochloride (6). A solution
of sodium n-propoxide (prepared from sodium (5.5 g,

8240
D. P. Walker et al. / Bioorg. Med. Chem. 14 (2006) 8219–8248
(ZORBAX Eclipse XDB-C8, 4.6 mm · 15 cm, 80:12:8
H2O–CH3CN–IPA) revealed >98% of the trans-isomer.
was allowed to warm to room temperature and stir for
16 h. The solvent was removed in vacuo, and the
remaining residue was partitioned between 1 N aqueous
sodium hydroxide solution and chloroform. The aque-
ous layer was extracted with chloroform (5·), and the
combined organic layers were washed with brine, dried
over anhydrous magnesium sulfate, filtered, and concen-
trated in vacuo to a clear oil. The crude product was
purified by silica gel chromatography using a Biotage
40S apparatus. Elution with chloroform–methanol–am-
monium hydroxide (90:9:1) afforded 861 mg (99%) of a
solid.
The compound ( )-7 was resolved by preparative chiral
HPLC using closed-loop steady-state recycling,58
5 · 50 cm Chiralcel OD column (30 ꢁC column tempera-
ture, 90 mL/min flow rate, 249 nm detection). Elution
with
heptane–iso-propyl
alcohol–diethyl
amine
(85:14.9:0.1, v/v/v) afforded 17.4 g (49%) of (+)-7 (reten-
tion time 9.9 min, 97% ee) and 17.2 g (49%) of (ꢀ)-7
(retention time 12.9 min, 99% ee).
The compound (+)-7 was characterized as the corre-
25
sponding mono 4-methylbenzenesulfonic acid salt: ½aꢂ
The above solid was dissolved in methanol (3 mL) and an
ethereal hydrogen chloride solution was added (10 mL of
a 2.0 M solution, 20 mmol). The mixture was briefly
heated, followed by removal of the solvent in vacuo.
Re-crystallization of the crude product from ethyl ace-
tate–methanol afforded 790 mg (73%) of 2a as a white
D
+3 (c 0.96, methanol); IR (diffuse reflectance) 2592,
2470, 2351, 2335, 2237, 2151, 1661, 1531, 1485, 1234,
1
1150, 1116, 1004, 820, 681, cmꢀ1; H NMR (400 MHz,
DMSO) d 9.18 (br s, 1H), 8.59 (d, 1H, J = 7.2 Hz),
7.89 (d, 2H, J = 8.7 Hz), 7.57 (d, 2H, J = 8.7 Hz), 7.48
(d, 2H, J = 8.0 Hz), 7.13 (d, 2H, J = 7.8 Hz), 3.97–3.91
(m, 1H), 3.57–3.48 (dq, 1H, J = 6.7, 6.7 Hz), 3.45–3.25
(m, 3H), 3.24–3.12 (m 1H), 2.16–2.05 (m, 2H), 1.98–
1.79 (m, 2H), 1.75–1.64 (m, 1H), 1.40 (d, 3H,
J = 6.8 Hz); high-resolution MS (FAB) Calcd for
C15H20ClN2O [M+H] m/e 279.1264. Found 279.1272;
Anal. Calcd for C15H19ClN2OÆC7H8O3S: C, 58.59; H,
6.03; N, 6.21. Found: C, 58.33; H, 6.11; N, 6.17.
1
solid: H NMR (400 MHz, methanol-d4) d 9.31 (s, 1H),
9.12 (s, 1H), 8.61 (d, 1H, J = 2.07 Hz), 7.48 (d, 1H,
J = 2.07 Hz), 4.21 (d, 1H, J = 6.64 Hz), 3.95–3.86 (m,
1H), 3.68–3.39 (m, 3H), 3.33–3.25 (m, 1H), 2.42–2.30
(m, 2H), 2.18–2.02 (m, 2H), 1.99–1.88 (m, 1H), 1.58 (d,
3H, J = 6.64 Hz); 13C NMR (100 MHz, methanol-d4) d
161.8, 156.8, 152.8, 141.7, 138.0, 129.2, 117.9, 108.5,
58.68, 53.94, 40.66, 26.74, 21.84, 17.16, 15.37; IR (diffuse
reflectance) 3052, 3002, 2984, 2956, 2886, 2835, 2817,
The compound (ꢀ)-7 was characterized as the corre-
2791, 2664, 2357, 2353, 2341, 2334, 2007, 1674 cmꢀ1
;
25
D
sponding mono 4-methylbenzenesulfonic acid salt: ½aꢂ
high-resolution MS (ESI) Calcd for C16H20N3O2
[M+H] m/e 286.1555. Found 286.1567. Anal. Calcd for
C16H19N3O2Æ2HClÆ0.75 H2O: C, 51.69; H, 6.10; N,
11.30. Found: C, 51.58; H, 6.21; N, 11.32.
ꢀ3 (c 0.89, methanol). Anal. Calcd for C15H19ClN2OÆ-
C7H8O3S: C, 58.59; H, 6.03; N, 6.21. Found: C, 58.36;
H, 6.08; N, 6.18.
5.1.54.
(2S,3R)-2-Methyl-1-azabicyclo[2.2.2]octan-3-
5.1.56. N-[(2S,3R)-2-Methyl-1-azabicyclo[2.2.2]oct-3-yl]-
1,3-benzothiazole-6-carboxamidehydrochloride (2b). The
compound 2b (123 mg, 36%) was prepared from 1,3-
benzothiazole-6-carboxylic acid (180 mg, 1.00 mmol)
and (+)-3 (215 mg, 1.00 mmol), followed by subsequent
treatment with ethereal hydrogen chloride (5.0 mL of a
2.0 M solution, 10.0 mmol) in a manner similar to that
described for the preparation of 2a. White solid: 1H
NMR (400 MHz, methanol-d4) d 9.41 (s, 1H), 8.74 (br
d, 1H, J = 7.05 Hz), 8.66 (d, 1H, J = 1.66 Hz), 8.15 (d,
1H, J = 8.30 Hz), 8.06 (dd, 1H, J = 8.30, 1.66 Hz),
4.18–4.11 (m, 1H), 3.70–3.61 (m, 1H), 3.59–3.38 (m,
3H), 3.30–3.24 (m, 1H), 2.32–2.22 (m, 2H), 2.18–2.00
(m, 2H), 1.98–1.87 (m, 1H), 1.58 (d, 3H, J = 6.64 Hz);
13C NMR (100 MHz, methanol-d4) d 169.0 158.9,
155.3, 134.1, 131.8, 125.7, 122.7, 122.2, 59.32, 53.54,
40.67, 26.71, 21.88, 17.11, 15.44; IR (diffuse reflectance)
3291, 2932, 2581, 2530, 2524, 2489, 2489, 2453, 2358,
2328, 1921, 1649, 1535, 1468, 1298 cmꢀ1; high-resolu-
tion MS (ESI) Calcd for C16H20N3OS [M+H] m/e
302.1327. Found 302.1311. Anal. Calcd for C16H19N3O-
SÆHClÆH2O: C, 54.00; H, 6.23; N, 11.81. Found: C,
53.96; H, 6.14; N, 11.88.
amine dihydrochloride [(+)-3]. A solution of (+)-7
(17.2 g, 61.7 mmol) in absolute ethanol (70 mL) and
concentrated hydrochloric acid (70 mL) was heated un-
der reflux for about 64 h. The reaction was monitored
for disappearance of starting amide by reverse phase
HPLC (ZORBAX Eclipse XDB-C8, 4.6 mm · 15 cm,
80:12:8 H2O–CH3CN–IPA). The solvent was removed
in vacuo, the residue was suspended in ethanol, and
the solvent was removed (twice). The solid was suspend-
ed in boiling ethanol, filtered, and dried (vacuum oven,
60 ꢁC) to provide 8.8 g (67%) of (+)-3 as a white solid:
25
½aꢂ 36 (c 0.93, methanol); 1H NMR (400 MHz, DMSO)
D
d 10.95 (br s, 1H), 8.97 (br s, 3H), 3.57–3.48 (dq, 1H,
J = 6.5,6.5 Hz), 3.40–3.05 (m, 5H), 2.33–2.27 (m, 1H),
2.24–2.13 (m, 1H), 1.91–1.82 (m, 2H), 1.80–1.70 (m,
1H), 1.52 (d, 3H, J = 6.8 Hz); high-resolution MS
(ESI) Calcd for C8H17N2 [M+H] m/e 141.1392. Found
141.1394. Anal. Calcd for C8H16N2Æ2HCl: C, 45.08; H,
8.51; N, 13.14. Found: C, 45.10; H, 8.40; N, 12.85.
5.1.55.
N-[(2S,3R)-2-Methyl-1-azabicyclo[2.2.2]oct-3-
yl]furo[2,3-c]pyridine-5-carboxamidedihydrochloride (2a).
To a stirred solution of furo[2,3-c]pyridine-5-carboxylic
acid hydrochloride (602 mg, 3.02 mmol) in dry acetoni-
trile (20 mL) was added diisopropylethylamine
(4.20 mL, 24.2 mmol), followed by (+)-3 (656 mg,
3.08 mmol). The solution was cooled to 0 ꢁC before
1.37 g (3.62 mmol) of HATU was added. The solution
5.1.57.
N-[(2S,3R)-2-Methyl-1-azabicyclo[2.2.2]oct-3-
yl]pyrrolo[1,2-c]pyrimidine-3-carboxamide dihydrochlo-
ride (2c). The compound 2c (415 mg, 58%) was prepared
from pyrrolo[1,2-c]pyrimidine-3-carboxylic acidhydro-
chloride (397 mg, 2.00 mmol) and (+)-3 (426 mg,

D. P. Walker et al. / Bioorg. Med. Chem. 14 (2006) 8219–8248
8241
2.00 mmol), followed by subsequent treatment with
ethereal hydrogen chloride (5.0 mL of a 2.0 M solution,
10.0 mmol) in a manner similar to that described for the
(m, 2H), 4.16 (d, 1H, J = 7.05 Hz), 3.73–3.66 (m, 1H),
3.58–3.49 (m, 2H), 3.48–3.37 (m, 1H), 3.30–3.23 (m,
1H), 2.34–2.22 (m, 2H), 2.16–2.00 (m, 2H), 1.98–1.87
(m, 1H), 1.58 (d, 3H, J = 6.64 Hz); 13C NMR
(100 MHz, methanol-d4) d 169.6, 135.3, 132.8, 131.1,
128.9, 128.2, 128.0, 127.9, 127.6, 126.8, 123.9, 59.23,
53.47, 40.67, 26.80, 21.91, 17.14, 15.43; IR (diffuse reflec-
tance) 3215, 2634, 2597, 2578, 2568, 2547, 2492, 2351,
2320, 2214, 1950, 1649, 1525, 1311, 1305 cmꢀ1; high-res-
olution MS (ESI) Calcd for C19H23N2O [M+H] m/e
295.1810. Found 295.1815. Anal. Calcd for
C19H22N2OÆHCl: C, 68.97; H, 7.01; N, 8.47. Found: C,
68.58; H, 7.08; N, 8.38.
1
preparation of 2a. Off-white solid: H NMR (400 MHz,
methanol-d4) d 9.67 (s, 1H), 8.58 (s, 1H), 8.00 (d, 1H,
J = 2.91 Hz), 7.27 (t, 1H, J = 7.27 Hz), 7.09 (d, 1H,
J = 3.73 Hz), 4.13 (d, 1H, J = 6.64 Hz), 3.84–3.76 (m,
1H), 3.62–3.37 (m, 3H), 3.30–3.24 (m, 1H), 2.36–2.25
(m, 2H), 2.18–2.00 (m, 2H), 1.98–1.86 (m, 1H), 1.55
(d, 3H, J = 7.05 Hz); 13C NMR (100 MHz, methanol-
d4) d 163.0, 141.0, 129.9, 126.8, 121.0, 117.4, 114.6,
108.0, 58.94, 53.37, 40.63, 26.89, 21.86, 17.12, 15.32;
IR (diffuse reflectance) 2933, 2610, 2580, 2558, 2350,
2328, 2147, 1657, 1544, 1506, 1433, 1350, 1269, 736,
730 cmꢀ1
;
high-resolution MS (ESI) Calcd for
5.1.60. Ethyl E-4-(benzylamino)-2-butenoate (11). The ti-
tle compound was prepared according to the established
procedure19b with slight modification:
C16H21N4O [M+H] m/e 285.1715. Found 285.1717.
Anal. Calcd for C16H20N4OÆ2HCl: C, 53.79; H, 6.21;
N, 15.68. Found: C, 53.62; H, 6.27; N, 15.59.
To a stirred solution of benzylamine (111 mL, 1.04 mol)
in dry methylene chloride (1.3 L) at room temperature
was added ethyl 4-bromo-2-butenaote (100 g,
0.518 mol, Aldrich 75% tech grade). The reaction mix-
ture was stirred for 4 h, followed by concentration in
vacuo. The remaining residue was triturated in hexanes
(1.2 L) for 1 h. The precipitate was filtered and washed
with hexanes. The filtrate was concentrated in vacuo
to afford 125 g of crude 11 as a brown oil. The 1H
NMR spectrum indicated this material was at least
90% pure and was used without further purification.
Rf 0.52 (hexanes–ethyl acetate, 75:25); 1H NMR
(300 MHz, CDCl3) d 7.38–7.20 (m, 5H), 6.99 (dt,
J = 15.75, 5.54 Hz, 1H), 6.03 (dt, J = 15.75, 1.78 Hz,
1H), 4.20 (q, J = 7.14 Hz, 2H), 3.83 (s, 2H), 3.44 (dd,
J = 5.52, 0.96 Hz, 1H), 2.05–1.75 (br s, 1H), 1.29 (t,
J = 7.14 Hz, 3H); 13C NMR (75 MHz, CDCl3) d 166.4,
146.3, 139.5, 128.5, 128.2, 127.2, 121.9, 60.37, 53.18,
49.40, 14.26.
5.1.58. N-[(2S,3R)-2-Methyl-1-azabicyclo[2.2.2]oct-3-yl]-
2,3-dihydro-1,4-benzodioxine-6-carboxamide hydrochlo-
ride (2d). The compound 2d (225 mg, 64%) was prepared
from 2,3-dihydro-1,4-benzodioxine-6-carboxylic acid
(187 mg, 1.04 mmol) and (+)-3 (215 mg, 1.00 mmol), fol-
lowed by subsequent treatment with ethereal hydrogen
chloride (5.0 mL of a 2.0 M solution, 10.0 mmol) in a
manner similar to that described for the preparation of
1
2a. White solid: H NMR (400 MHz, methanol-d4) d
8.40 (br d, 1H, J = 6.64 Hz), 7.41–7.38 (m, 2H), 6.90
(d, 1H, J = 9.12 Hz), 4.31–4.24 (m, 4H), 4.06 (t, 1H,
J = 7.05 Hz), 3.62–3.56 (m, 1H), 3.55–3.35 (m, 3H),
3.31–3.20 (m, 1H), 2.25–2.14 (m, 2H), 2.12–1.95 (m,
2H), 1.94–1.84 (m, 1H), 1.54 (d, 3H, J = 7.05 Hz); 13C
NMR (100 MHz, methanol-d4) d 169.0, 147.5, 143.8,
126.6, 120.9, 117.0, 116.7, 64.74, 64.36, 59.18, 53.30,
40.64, 26.78, 21.87, 17.08, 15.35; IR (diffuse reflectance)
2936, 2458, 2327, 1653, 1581, 1535, 1500, 1466, 1319,
1306, 1287, 1262, 1252, 1062, 886 cmꢀ1; high-resolution
MS (ESI) Calcd for C17H23N2O3 [M+H] m/e 303.1708.
Found 303.1697. Anal. Calcd for C17H22N2O3ÆHClÆ0.40-
H2O: C, 59.01; H, 6.93; N, 8.10. Found: C, 58.93; H,
6.95; N, 8.20.
5.1.61. 2-(Benzoyloxy)-1-nitroethane (12). The title com-
pound was prepared according to the established proce-
dure19b with slight modification:
To a stirred solution of nitroethanol (79 mL, 1.1 mol) in
dry benzene (1 L) was added benzoyl chloride (155 g,
1.1 mmol). The solution was heated at reflux for 24 h
and then concentrated in vacuo. The crude product was
dissolved in 300 mL of methyl tert-butyl ether with warm-
ing, followed by cooling to ꢀ15 ꢁC in a freezer overnight.
The resulting crystals were filtered and washed with cold
hexanes to afford 110 g (56%) of 12 as colorless crystals:
Rf 0.20 (hexanes–ethyl acetate, 80:20); 1H NMR
(300 MHz, CDCl3) d 8.00 (dd, J = 7.12, 1.45 Hz, 2H),
7.59 (td, J = 7.40, 1.20 Hz, 1H), 7.45 (t, J = 7.85 Hz,
2H), 4.85 (dd, J = 6.70, 4.28 Hz, 2H), 4.75 (dd, J = 6.69,
4.22 Hz, 2H); 13C NMR (75 MHz, CDCl3) d 165.9,
133.6, 129.8, 128.9, 128.6, 73.83, 59.94; low-resolution
MS (ESI+) m/z 220 (M+H).
5.1.59. N-[(2S,3R)-2-Methyl-1-azabicyclo[2.2.2]oct-3-yl]-
2-naphthamidehydrochloride (2e). To a stirred solution of
2-naphthoic acid (189 mg, 1.10 mmol) and triethylamine
(1.0 mL, 7.17 mmol) in tetrahydrofuran (10 mL) was
added dropwise diphenylphosphinic chloride (260 mg,
1.10 mmol). The mixture was stirred for 1 h before
213 mg (1.00 mmol) of (+)-3 was added. The mixture
was stirred for 24 h, followed by the addition of sodium
hydroxide (10 mL of a 5% aqueous solution). The mix-
ture was extracted with chloroform, and the organic
layer was dried over anhydrous magnesium sulfate, fil-
tered and concentrated in vacuo to a white solid. The
solid was dissolved in methanol (1 mL) and an ethereal
hydrogen chloride solution was added (5.0 mL of a
2.0 M solution, 10 mmol). The mixture was briefly heat-
ed, followed by removal of the solvent in vacuo. The
crude product was re-crystallized from ethyl acetate–
methanol to afford 246 mg (74%) of 2e as a white solid:
1H NMR (400 MHz, methanol-d4) d 8.47 (s, 1H), 8.01
(d, 1H, J = 7.05 Hz), 7.99–7.90 (m, 3H), 7.62–7.56
5.1.62. trans-4-Nitro-1-(phenylmethyl)-3-pyrrolidineace-
tic acid ethyl ester (10). To a stirred solution of 11
(125 g, 0.518 mol) in ethyl alcohol (1 L) at room temper-
ature was added 12 (101 g, 0.518 mol). The mixture was
stirred at room temperature overnight, then concentrat-

8242
D. P. Walker et al. / Bioorg. Med. Chem. 14 (2006) 8219–8248
ed in vacuo. The residue was diluted with ether (1 L) and
saturated aqueous sodium bicarbonate solution (1 L).
The ethereal layer was separated and dried over anhy-
drous magnesium sulfate, filtered, and concentrated in
vacuo. The crude product was purified by flash chroma-
tography on silica gel. Elution with hexanes–ethyl ace-
tate (85:15) afforded 10 as a yellow oil (97 g, 65%): Rf
0.60 (hexanes–ethyl acetate, 75:25); IR (neat) 3050,
acetate: mp 99.5–100.5 ꢁC. Anal. Calcd for
C20H30N2O4: C, 66.27; H, 8.34; N, 7.73. Found: C,
66.26; H, 8.18; N, 7.69.
5.1.64. tert-Butyl (3R,4S)-1-benzyl-4-(2-hydroxyethyl)
pyrrolidin-3-ylcarbamate [(+)-14] and tert-butyl (3S,4R)-
1-benzyl-4-(2-hydroxyethyl)
pyrrolidin-3-ylcarbamate
[(ꢀ)-14]. To a stirred solution of 13 (51 g, 0.14 mol) in
anhydrous tetrahydrofuran (1 L) at ꢀ5ꢁ C was added
lithium aluminum hydride powder (12 g, 0.30 mol) in
small portions over 30 min. The mixture was stirred
for 40 min at ꢀ5 ꢁC. The reaction was quenched by
the sequential addition of water (10 mL), 15% aqueous
NaOH (10 mL), and water (20 mL). The mixture was
diluted with ether (1 L), followed by the addition of ex-
cess anhydrous potassium carbonate and the mixture
was stirred for 1 h. The mixture was filtered, and the fil-
trate was concentrated in vacuo to afford 44 g (97%) of
( )-14 as a white solid: Rf 0.07 (hexanes–ethyl acetate,
1:1); IR (diffuse reflectance) 3492, 3458, 3202, 3027,
2975, 2945, 2910, 2820, 1682, 1538, 1366, 1290, 1251,
2800, 1730, 1550, 1030, 770 cmꢀ1
;
1H NMR
(300 MHz, CDCl3) d 7.33–7.26 (m, 5H), 4.82–4.72 (m,
2H), 4.13 (q, J = 7.14 Hz, 2H), 3.75–3.60 (m, 2H),
3.30–3.00 (m, 4 H), 2.69–2.57 (m, 2H), 2.37–2.27 (m,
1H), 1.24 (t, J = 7.14 Hz, 3H); 13C NMR (100 MHz,
CDCl3) d 170.3, 141.7, 127.7, 127.6, 126.5, 87.32,
60.06, 58.13, 57.46, 56.66, 39.20, 36.21, 13.2; low-resolu-
tion MS (ESI+) m/z 293 [M+H]. Anal. Calcd for
C15H20N2O4: C, 61.63; H, 6.89; N, 9.58. Found: C,
61.54; H, 6.96; N, 9.96.
5.1.63.
trans-4-(1,1-Dimethylethoxycarbonylamido)-1-
(phenylmethyl)-3-pyrrolidineacetic acid ethyl ester (13).
A mixture of 10 (64 g, 0.22 mol) and RaNi (35 g) in ethyl
alcohol (1 L) was placed in a Parr bottle and hydroge-
nated at room temperature for 4 h under an atmosphere
of hydrogen (40 psi). The mixture was filtered through a
pad of Celite, and the solvent was removed in vacuo to
give trans-4-amino-1-(phenylmethyl)-3-pyrrolidineacetic
acid ethyl ester as a clear oil (48 g, 84%): Rf 0.15 (chlo-
roform–methanol–ammonium hydroxide, 95:4.5:0.5);
IR (liquid) 3354, 3304, 3030, 2978, 2907, 2804, 1730,
1
1170, 1075 cmꢀ1; H NMR (300 MHz, CDCl3) d 7.40–
7.30 (m, 5H), 5.30–5.15 (br s, 1 H), 4.05–3.97 (m, 1H),
3.85–3.65 (m, 5H), 3.25–3.15 (m, 1H), 2.78–2.70 (m,
2H), 2.30–2.05 (m, 2H), 1.67 (m, 2H), 1.45 (s, 9H); 13C
NMR (75 MHz, CDCl3) d 156.0, 129.1, 128.6, 127.7,
79.92, 60.95, 59.84, 59.62, 59.26, 54.35, 44.20, 36.19,
28.40; high-resolution MS (FAB) Calcd for
C18H29N2O3 [M+H] m/z 321.2178. Found 321.2183.
An analytical sample was prepared via re-crystallization
from hexanes–ethyl acetate: mp 68–70ꢁC; Anal. Calcd
for C18H28N2O3: C, 67.47; H, 8.81; N, 8.74. Found: C,
67.43; H, 8.86; N, 8.65.
1
1448, 1368, 1255, 1147, 870, 744, 654 cmꢀ1; H NMR
(300 MHz, CDCl3) d 7.32–7.20 (m, 5H), 4.12 (q,
J = 7.14 Hz, 2H), 3.61 (AB quartet, JAB = 12.94 Hz,
DmAB=15.84 Hz, 2H), 3.20–3.15 (m, 1H), 2.99–2.91 (m,
1H), 2.81 (dd, J = 9.63, 6.80 Hz, 1H), 2.85–2.60 (br s,
2H), 2.60–2.35 (m, 3H), 2.30–2.23 (m, 2H), 1.24 (t,
J = 7.13 Hz, 3H); 13C NMR (75 MHz, CDCl3) d 172.9,
138.7, 128.8, 128.3, 127.2, 62.15, 60.56, 59.97, 58.86,
57.03, 44.11, 38.15, 14.22; low-resolution MS (ESI+)
m/z 263 [M+H].
The compound ( )-14 was resolved by preparative
chiral HPLC using closed-loop steady-state recy-
cling,58 5 · 50 cm Chiralpak AD column (30 ꢁC col-
umn temperature). Elution with heptane–iso-propyl
alcohol–diethyl amine (85:14.9:0.1, v/v/v) afforded
21.9 g (49%) of (+)-14 as an oil and 21.7 (48%) of
(ꢀ)-14 as an oil.
To a stirred solution of trans-4-amino-1-(phenylmethyl)-
3-pyrrolidineacetic acid ethyl ester (48 g, 0.18 mol) in
methylene chloride (0.5 L) at 0 ꢁC was added di-tert-bu-
tyl dicarbonate (47 g, 0.22 mol). The reaction mixture
was allowed to warm to room temperature and stirred
overnight. The mixture was concentrated in vacuo and
the crude product was purified by flash chromatography
on silica gel. Elution with hexanes–ethyl acetate (80:20)
afforded 13 as a white solid (53 g, 80%): Rf 0.15 (hex-
anes–ethyl acetate, 75:25); IR (diffuse reflectance) 2995,
2962, 2828, 1728, 1698, 1544, 1369, 1312, 1278, 1251,
Analytical data for (+)-14: Elution time 14.1 min, >95%
25
D
ee; ½aꢂ 35 (c 1.0, MeOH).
Analytical data for (ꢀ)-14: Elution time 13.1 min, >95%
25
ee; ½aꢂ ꢀ34 (c 0.98, MeOH).
D
5.1.65. (3R,4S)-1-Azabicyclo[2.2.1]heptan-3-amine bis(4-
methylbenzenesulfonate) (15). To a stirred solution of
(+)-14 (23.1 g, 72.2 mmol) in methylene chloride
(430 mL)
was
added
triethylamine
(11.7 mL,
1
1188, 1171, 1003, 762, 707 cmꢀ1; H NMR (300 MHz,
79.4 mmol). The reaction was cooled to 0 ꢁC before
methanesulfonyl chloride (5.58 mL, 72.2 mmol) was
added dropwise. The mixture was stirred for 2 h at
0 ꢁC. After 2 h, additional methanesulfonyl chloride
(1.0 mL, 13 mmol) and triethylamine (2 mL, 14 mmol)
were added, followed by warming to room temperature.
The mixture was concentrated in vacuo to afford a white
syrup (39 g).
CDCl3) d 7.38–7.20 (m, 5H), 5.1–4.9 (br s, 1H), 4.13
(q, J = 7.16 Hz, 2H), 3.95–3.83 (m, 1H), 3.65 (br s,
2H), 3.19–3.03 (m, 1H), 2.84–2.60 (m, 3H), 2.50–2.35
(m, 2H), 2.25–2.14 (m, 1H), 1.44 (s, 9H), 1.25 (t,
J = 7.14 Hz, 3H); 13C NMR (100 MHz, CDCl3) d
172.6, 155.9, 129.3, 128.8, 127.8, 79.82, 60.93, 60.40,
60.23, 59.02, 55.55, 42.94, 38.16, 28.78, 14.57; high-reso-
lution MS (FAB) Calcd for C20H31N2O4 [M+H] m/z
363.2284. Found 363.2281. An analytical sample was
prepared via re-crystallization from hexanes–ethyl
A mixture of the above residue (39 g) and 10% Pd/C
(15 g) in ethyl alcohol (600 mL) was placed in a Parr

D. P. Walker et al. / Bioorg. Med. Chem. 14 (2006) 8219–8248
8243
bottle and hydrogenated at 50 psi for 48 h. The mixture
was filtered through Celite and concentrated in vacuo to
afford 15.1 g (99%) of (3R,4S)-3-(tert-butoxycarbonyla-
mino)-1-azabicyclo[2.2.1]heptane as a white solid: Rf
C14H15N3O2ÆC4H4O4: C, 57.91; H, 5.13; N, 11.25.
Found: C, 57.80; H, 5.19; N, 11.17.
5.1.67. N-[(3R,4S)-1-Azabicyclo[2.2.1]hept-3-yl]-1,3-ben-
zodioxole-5-carboxamideÆ4-methylbenzenesulfonate (9b).
The compound 9b (191 mg, 64%) was prepared from
1,3-benzodioxole-5-carboxylic acid (166 mg, 1.0 mmol)
and 15 (456 mg, 1.0 mmol), followed by subsequent
treatment with para-toluenesulfonic acid monohydrate
(133 mg, 0.70 mmol) in a manner similar to that de-
0.16 (chloroform–methanol–ammonium hydroxide,
25
D
tance) 2975, 2942, 2885, 1711, 1551, 1364, 1292, 1277,
90:9.5:0.5); ½aꢂ 20 (c 1.0, CHCl3); IR (diffuse reflec-
1
1270, 1248, 1171, 1078, 1005, 979, 827 cmꢀ1; H NMR
(300 MHz, CDCl3) d 5.60–5.50 (br s, 1H), 3.82–3.72
(m, 1 H), 3.33–3.15 (m, 4H), 2.82–2.70 (m, 2H), 2.00–
1.84 (m, 1H), 1.65–1.50 (m, 1H), 1.46 (s, 9H); 13C
NMR (75 MHz, CDCl3) d 155.3, 79.59, 63.34, 57.41,
53.91, 53.22, 42.84, 28.41, 27.20; high-resolution MS
(FAB) Calcd for C11H21N2O2 [M+H] m/z 213.1603.
Found 213.1611. An analytical sample was prepared
via silica gel column chromatography (chloroform–
methanol–ammonium hydroxide, 95:4:1), followed by
crystallization from ethyl acetate: mp 165–166 ꢁC.
scribed for the preparation of 1b. White solid: mp
25
D
tance) 1650, 1539, 1485, 1350, 1303, 1259, 1240, 1217,
147–149 ꢁC; ½aꢂ 6 (c 0.74, methanol); IR (diffuse reflec-
1199, 1187, 1172, 1123, 1034, 1011, 682 cmꢀ1 1H
;
NMR (400 MHz, methanol-d4)
d
7.69 (d, 2H,
J = 8.30 Hz), 7.45 (dd, 1H, J = 7.88, 1.66 Hz), 7.32 (d,
1H, J = 1.66 Hz), 7.21 (d, 2H, J = 7.88 Hz), 6.85 (d,
1H, J = 8.30 Hz), 6.02 (s, 2H), 4.22–4.16 (m, 1H),
3.74–3.66 (m, 1H), 3.49 (d, 1H, J = 9.12 Hz), 3.41–3.37
(m, 2H), 3.29–3.20 (m, 2H), 3.01 (d, 1H, J = 4.56 Hz),
2.35 (s, 3H), 2.20–2.10 (m, 1H), 1.86–1.76 (m, 1H);13C
NMR (100 MHz, methanol-d4) d 168.3, 151.1, 148.2,
142.2, 140.6, 128.7, 127.4, 125.8, 122.6, 107.7, 107.4,
102.1, 60.00, 57.14, 52.09, 51.90, 40.93, 24.40, 20.12;
high-resolution MS (ESI) Calcd for C14H17N2O3
[M+H] m/e 261.1239. Found 261.1244. Anal. Calcd for
C14H16N2O3ÆC7H8O3S : C, 58.32; H, 5.59; N, 6.48.
Found: C, 57.99; H, 5.65; N, 6.44.
To a stirred solution of (3R,4S)-3-(tert-butoxycarbon-
ylamino)-1-azabicyclo[2.2.1]heptane (22.0 g, 104 mmol)
in ethyl alcohol (700 mL) was added p-toluenesulfonic
acid monohydrate (42.7 g, 224 mmol). The reaction
mixture was heated to reflux for 10 h, followed by
cooling to room temperature. The white solid that
formed was collected by vacuum filtration and washed
with cold ethyl alcohol to give 15 as a white, crystal-
25
D
line solid (40.7 g, 87%): ½aꢂ 2.4 (c 0.90, MeOH); IR
(diffuse reflectance) 3028, 2979, 2971, 2958, 2926,
2817, 2782, 1210, 1194, 1170, 1125, 1036, 1013, 813,
5.1.68.
N-[(3R,4S)-1-Azabicyclo[2.2.1]hept-3-yl]pyr-
686 cmꢀ1
;
1H NMR (400 MHz, D2O) d 7.54 (d,
rolo[1,2-c]pyrimidine-3-carboxamide sesquifumarate (9c).
The compound 9c (273 mg, 63%) was prepared from
pyrrolo[1,2-c]pyrimidine-3-carboxylic acid hydrochlo-
ride (202 mg, 1.01 mmol) and 15 (456 mg, 1.00 mmol),
followed by subsequent treatment with fumaric acid
(102 mg, 0.88 mmol) in a manner similar to that de-
J = 8.25 Hz, 2H), 7.22 (d, J = 8.09 Hz, 2H), 3.73–3.68
(m, 1H), 3.62 (dd, 1H, J = 7.70, 2.28 Hz), 3.45–3.33
(m, 3H), 3.22 (d, 1H, J = 10.26 Hz), 3.20–3.12 (m,
1H), 3.11 (d, 1H, J = 4.42 Hz), 2.25 (s, 6H), 2.20–
2.10 (m, 1H), 1.78–1.67 (m, 1H); 13C NMR
(100 MHz, CD3OD) d 143.1, 141.6, 129.6, 126.7,
58.29, 57.48, 52.89, 51.93, 40.85, 25.47, 21.03; high-res-
olution MS (FAB) Calcd for C6H13N2 [M+H] m/z
113.1079. Found 113.1078. An analytical sample was
prepared via re-crystallization from ethyl alcohol: mp
232–233 ꢁC. Anal. Calcd for C6H12N2. 2C7H8O3S: C,
52.61; H, 6.18; N, 6.14. Found: C, 52.62; H, 6.15;
N, 6.14.
scribed for the preparation of 1b. White solid: mp
25
D
tance) 3380, 3366, 2977, 2961, 1738, 1698, 1662, 1545,
140–145 ꢁC; ½aꢂ 0 (c 0.61, methanol); IR (diffuse reflec-
1491, 1428, 1421, 1354, 1318, 1299, 1270 cmꢀ1 1H
;
NMR (400 MHz, methanol-d4) d 9.01 (s, 1H), 8.10 (s,
1H), 7.72 (d, 1H, J = 3.32 Hz), 6.99 (dd, 1H, J = 3.73,
2.90 Hz), 6.78 (d, 1H, J = 3.73 Hz), 6.71 (s, 3H), 4.30–
4.25 (m, 1H), 3.72–3.68 (m, 1H), 3.55–3.38 (m, 3H),
3.30–3.20 (m, 2H), 3.03 (d, 1H, J 4.56 Hz), 2.22–2.12
(m, 1H), 1.90–1.80 (m, 1H); 13C NMR (100 MHz, meth-
anol-d4) d 169.0, 166.0, 138.3, 134.5, 132.0, 130.5, 117.5,
114.2, 113.9, 104.6, 59.51, 56.94, 51.97, 51.46, 41.41,
24.46; high-resolution MS (ESI) Calcd for C14H17N4O
[M+H] m/e 257.1402. Found 257.1393. Anal. Calcd for
C14H16N4OÆ1.5C4H4O4: C, 55.81; H, 5.15; N, 13.02.
Found: C, 55.51; H, 5.23; N, 12.81.
5.1.66. N-[(3R,4S)-1-Azabicyclo[2.2.1]hept-3-yl]furo[2,3-
c]pyridine-5-carboxamideÆfumarate (9a). The compound
9a (1.88 g, 85%) was prepared from furo[2,3-c]pyri-
dine-5-carboxylic acid (965 mg, 5.92 mmol) and 15
(2.70 g, 5.92 mmol), followed by subsequent treatment
with fumaric acid (615 mg, 5.30 mmol) in a manner sim-
ilar to that described for the preparation of 1b. White
25
D
(mull) 1683, 1673, 1659, 1605, 1579, 1527, 1516, 1492,
solid: mp 170–172 ꢁC; ½aꢂ 0 (c 0.98, methanol); IR
5.1.69.
N-[(3R,4S)-1-Azabicyclo[2.2.1]hept-3-yl]-2,3-
1
1349, 1337, 1291, 1277, 1172, 790, 640 cmꢀ1; H NMR
dihydro-1,4-benzodioxine-6-carboxamideÆ0.5fumarateÆ0.5
hydrate (9d). The compound 9d (200 mg, 65%) was pre-
pared from 2,3-dihydro-1,4-benzodioxine-6-carboxylic
acid (180 mg, 0.89 mmol) and 15 (400 mg, 0.89 mmol),
followed by subsequent treatment with fumaric acid
(101 mg, 0.88 mmol) in a manner similar to that de-
(400 MHz, methanol-d4) d 8.88 (s, 1H), 8.42 (s, 1H),
8.09 (d, 1H, J = 2.07 Hz), 7.09 (d, 1H, J = 1.66 Hz),
6.69 (s, 2H), 4.36–4.28 (m, 1H), 3.76–3.68 (m, 1H),
3.57–3.45 (m, 2H), 3.44–3.39 (m, 1H), 3.28–3.20 (m,
2H), 3.05 (d, 1H, J = 4.98 Hz), 2.22–2.13 (m, 1H),
1.90–1.80 (m, 1H); 13C NMR (100 MHz, methanol-d4)
d; high-resolution MS (API) Calcd for C14H16N3O2
[M+H] m/e 258.1242. Found 258.1249. Anal. Calcd for
scribed for the preparation of 1b. White solid: 185–
25
D
3236, 3060, 2991, 1644, 1609, 1583, 1550, 1499, 1372,
188 ꢁC; ½aꢂ 9 (c 0.57, methanol); IR (diffuse reflectance)

8244
D. P. Walker et al. / Bioorg. Med. Chem. 14 (2006) 8219–8248
1347, 1337, 1308, 1300, 1255, 666 cmꢀ1
;
1H NMR
4.10 (m, 1H), 2.56 (m, 1H), 2.05 (m, 1H), 1.46–1.70
(m, 5H), 1.35 (s, 9H); high-resolution MS (FAB) Calcd
for C12H20NO4 [M+H] m/e 242.1392. Found 242.1390.
(400 MHz, methanol-d4) d 7.39 (d, 1H, J = 2.08 Hz),
7.37 (dd, 1H, J = 8.30, 2.08), 6.88 (d, 1H, J = 8.30),
6.66 (s, 1.5H), 4.30–4.23 (m, 4H), 4.15–4.10 (m, 1H),
3.61–3.52 (m, 1H), 3.37–3.24 (m, 3H), 3.15–3.07 (m,
2H), 2.94 (d, 1H, J = 4.56 Hz), 2.14–2.04 (m, 1H),
1.79–1.70 (m, 1H); 13C NMR (100 MHz, methanol-d4)
d 172.1, 168.2, 147.7, 143.6, 135.6, 126.6, 120.9, 117.0,
116.7, 64.72, 64.34, 59.98, 56.90, 52.20, 52.01, 41.29,
24.89; high-resolution MS (ESI) Calcd for
C15H19N2O3 [M+H] m/e 275.1396. Found 275.1392.
Anal. Calcd for C15H18N2O3Æ0.5C4H4O4Æ0.5H2O: C,
59.81; H, 6.20; N, 8.21. Found: C, 60.23; H, 6.09; N,
8.28.
%
Water
(KF):
0.30%.
Anal.
Calcd
for
C12H19NO4Æ0.30% H2O: C, 59.56; H, 7.95; N, 5.79.
Found: C, 59.16; H, 7.87; N, 5.75.
5.1.72. tert-Butyl (1S,2R,4R)-2-{[(benzyloxy)carbon-
yl]amino}-7-azabicyclo[2.2.1]heptane-7-carboxylate [(+)-
20] and tert-butyl (1R,2S,4S)-2-{[(benzyloxy)carbonyl]
amino}-7-azabicyclo[2.2.1]heptane-7-carboxylate
[(ꢀ)-
20]. To a stirred solution of 19 (32.5 g, 0.135 mol) and tri-
ethylamine (24.4 mL, 0.175 mol) in dry toluene (0.56 L)
in a flame fried 1 L three-neck round-bottomed flask un-
der nitrogen at 0 ꢁC was added diphenylphosphoryl
azide (37.7 mL, 0.175 mol). After complete addition,
the mixture was slowly warmed to 90 ꢁC over 1 h. The
mixture was stirred at 90 ꢁC for 1 h, followed by the
addition of benzyl alcohol (18.1 mL, 0.175 mol). Heating
at 90 ꢁC was continued for another 16 h, followed by
cooling to room temperature. The mixture was extracted
successively with 2· 250 mL of 5% citric acid, 2· 200 mL
water, 2· 200 mL saturated sodium bicarbonate, and 2·
100 mL saturated sodium chloride. The organic layer
was dried over anhydrous magnesium sulfate, filtered,
and concentrated in vacuo to an amber oil. The crude
material was purified by flash chromatography on silica
gel. Gradient elution with hexanes–ethyl acetate
(85:15 ! 1:1) afforded 44 g (94%) of ( )-20 as a pale yel-
low oil that crystallized on standing: IR (diffuse reflec-
tance) 2483, 2292, 2201, 1990, 1965, 1715, 1679, 1532,
1392, 1368, 1299, 1250, 1173, 1152, 748 cmꢀ1; H NMR
(400 MHz, CDCl3) d 7.36 (m, 5H), 5.10 (br s, 2H), 4.24
(m, 1H), 4.10 (m, 1H), 3.88–3.76 (m, 1H), 1.62–2.01
(m, 3H), 1.44 (s, 9H), 1.60–1.29 (m, 4H).
5.1.70. N-[(3R,4S)-1-Azabicyclo[2.2.1]hept-3-yl]-2-naph-
thamidefumaratehydrate (9e). The compound 9e
(343 mg, 84%) was prepared from 2-naphthoic acid
(172 mg, 1.00 mmol) and 15 (456 mg, 1.00 mmol), fol-
lowed by subsequent treatment with fumaric acid
(112 mg, 0.98 mmol) in a manner similar to that de-
scribed for the preparation of 1b. White solid: mp
25
D
120–127 ꢁC (loss of H2O); ½aꢂ 4 (c 0.40, methanol);
IR (diffuse reflectance) 3460, 3243, 1637, 1621, 1551,
1316, 1303, 1017, 1011, 1005, 992, 979, 875, 829,
1
787 cmꢀ1; H NMR (400 MHz, methanol-d4) d 8.41 (s,
1H), 8.00–7.86 (m, 4H), 7.61–7.52 (m, 2H), 6.69 (s,
2H), 4.31–4.26 (m, 1H), 3.76–3.69 (m, 1H), 3.53–3.37
(m, 3H), 3.28–3.20 (m, 2H), 3.06 (d, 1H, J = 4.56 Hz),
2.22–2.12 (m, 1H), 1.90–1.80 (m, 1H); 13C NMR
(100 MHz, methanol-d4) d 170.0, 169.2, 135.25, 135.0,
132.8, 131.0, 128.9, 128.2, 128.0, 127.9, 127.6, 126.8,
123.8, 59.80, 56.98, 52.07, 51.95, 41.14, 24.56; high-reso-
lution MS (ESI) Calcd for C17H19N2O [M+H] m/e
267.1497. Found 267.1491. Anal. Calcd for
C17H18N2OÆC4H4O4ÆH2O: C, 62.99; H, 6.04; N, 7.00.
Found: C, 62.89; H, 6.07; N, 6.96.
The compound ( )-20 (44 g, 127 mmol) was resolved by
preparative chiral HPLC using closed-loop steady-state
recycling.58 5 · 50 cm Chiralcel OJ column (30 ꢁC col-
umn temperature). Elution with heptane-iso-propyl
alcohol (9:1, v/v) afforded 9.5 g (22%) of (+)-20 as a
white solid and (32%) of (ꢀ)-20 as a white solid.
5.1.71. exo-tert-Butyl 2-{[(benzyloxy)carbonyl]amino}-7-
azabicyclo[2.2.1]heptane-7-carboxylate (19). To a stirred
solution of endo-7-tert-butyl 2-methyl 7-azabicy-
clo[2.2.1]heptane-2,7-dicarboxylate22b
(17)
(72.8 g,
0.285 mol) in dry methanol (1 L) in a flame dried 2 L
three-neck round-bottomed flask under nitrogen was
added solid sodium methoxide (38.5 g, 0.713 mol) in a
single lot. The reaction mixture was heated to reflux
for 4 h. The mixture was cooled to room temperature
before 400 mL of water was added. The mixture was
stirred for 1 h at room temperature. The mixture was
concentrated under reduced pressure to a volume of
ca. 400 mL, and the pH was adjusted to 4.5 with concen-
trated hydrochloric acid. The resulting precipitate was
collected and dried in vacuo. The tan, slightly tacky sol-
id was washed with 2· 100 mL portions of 60% diethyl
ether in hexane and dried in vacuo to afford 47 g
(68%) of 19 as an off-white powder. The 1H NMR spec-
trum of 19 showed it to be at least 95% pure, containing
<5% of the corresponding endo-carboxylic acid.
Analytical data for first eluting enantiomer (+)-20:
25
D
>98% ee; ½aꢂ 22, (c 0.42, chloroform); Anal. Calcd
for C19H26N2O4: C, 65.87; H, 7.56; N, 8.09. Found: C,
65.77; H, 7.51; N, 8.05.
Analytical data for second eluting eantiomer (ꢀ)-20:
25
>99% ee; ½aꢂ ꢀ23, (c 0.39, chloroform). Anal. Calcd
D
for C19H26N2O4: C, 65.87; H, 7.56; N, 8.09. Found: C,
65.77; H, 7.64; N, 8.02.
5.1.73.
tert-Butyl
(1S,2R,4R)-2-amino-7-azabicy-
clo[2.2.1]heptane-7-carboxylate (21). The compound
(+)-20 (9.5 g, 27.4 mmol) was combined with 950 mg
10% palladium on activated carbon (Engelhard,
C3645) in absolute ethyl alcohol (75 mL) in a 500 mL
PARR shaker bottle. The reaction mixture was hydro-
genated at 50 psi for 3 h. The catalyst was removed by
filtration through Celite, and the filter cake was washed
carefully with methanol using extreme care to avoid dry-
ing the cake. The filtrate was concentrated in vacuo to
exo-Carboxylic acid 19. Mp 176–178 ꢁC; IR (diffuse
reflectance) 3131, 2985, 2975, 2958, 2350, 1734, 1663,
1
1393, 1370, 1265, 1182, 1153, 1147, 901, 792 cmꢀ1; H
NMR (DMSO-d6) d 12.28 (br s, 1 H), 4.31 (m, 1H),

D. P. Walker et al. / Bioorg. Med. Chem. 14 (2006) 8219–8248
8245
give 6.4 g of an oil. The crude product was purified by
flash chromatography on silica gel. Elution with chloro-
form–methanol–ammonium hydroxide (92:7:1) afforded
(140 mg, 0.55 mmol). The mixture was stirred for
30 min, followed by the addition of a solution of 21
(106 mg, 0.50 mmol) in methylene chloride (2.0 mL).
The mixture was stirred at room temperature for 3 h.
The reaction mixture was washed with a saturated solu-
tion of sodium bicarbonate. The organic layer was dried
over anhydrous potassium carbonate, filtered, and con-
centrated in vacuo. The crude product was purified by
flash chromatography on silica gel. Elution with hex-
anes–ethyl acetate (65:35) afforded a clear residue.
25
5.61 g (96%) of 21 as a pale oil: ½aꢂ 9 (c 0.67, chloro-
D
form); IR (liq.) 2974, 2168, 1996, 1954, 1698, 1455,
1391, 1367, 1321, 1257, 1177, 1145, 1108, 1087, 903
cmꢀ1 1H NMR (400 MHz, CDCl3) d 4.20 (m, 1H),
;
3.89 (m, 1H), 2.95 (dd, J = 3, 8 Hz, 1H), 1.81 (dd, J =
8, 13 Hz, 1H), 1.68 (m, 1H), 1.53 (br s, 2H), 1.46 (s,
9H), 1.37 (m, 3H), 1.29 (dd, J = 2, 8 Hz, 1H); MS (EI
) m/z (rel. intensity): 212 (M+, 39), 139 (84), 113 (91),
94 (75), 86 (92), 84 (99), 69 (95), 68 (94), 57 (91), 56
(74), 51 (77). Anal. Calcd for C11H20N2O2: C, 62.24;
H, 9.49; N, 13.20. Found: C, 61.89; H, 9.39; N, 13.18.
The above residue was dissolved in a 1 N methanolic
hydrogen chloride solution and stirred at room temper-
ature for 16 h. The solvent was removed in vacuo. The
remaining residue was triturated in ether–isopropyl
alcohol (3.0 mL, 2:1). The resulting precipitate was fil-
tered, washed with isopropyl alcohol, and dried in vacuo
to afford 50 mg (35%) of 18b as a white solid: IR (diffuse
reflectance) 2883, 2386, 2293, 2241, 2155, 2123, 1661,
5.1.74. N-[(1S,2R,4R)-7-Azabicyclo[2.2.1]hept-2-yl]furo[2,3-
c]pyridine-5-carboxamidehydrochloride (18a). To a stirred
solution of furo[2,3-c]pyridine-5-carboxylic acid hydro-
chloride (2.10 g, 10.5 mmol) in dry N,N-dimethylform-
amide (45 mL) were added diisopropylethylamine
(5.5 mL, 31.5 mmol) and 21 (2.12 g, 10.0 mmol). The
solution was cooled to 0 ꢁC before 3.99 g (10.5 mmol)
of HATU was added. The solution was allowed to warm
to room temperature and stirred for 48 h. The solvent
was removed in vacuo, and the remaining residue was
partitioned between brine–30% ammonia water (1:1)
and chloroform–methanol (9:1). The aqueous layer
was extracted with 9:1 chloroform–methanol, and the
combined organic layers were washed with brine, dried
over anhydrous magnesium sulfate, filtered, and concen-
trated in vacuo to a clear oil. The crude product was
purified by flash chromatography on silica gel. Elution
with hexanes–ethyl acetate (60:40) afforded 2.98 g
(84%) of a white solid.
1525, 1501, 1483, 1310, 1264, 1248, 1032, 760 cmꢀ1
;
1H NMR (DMSO-d6) d 1.61 (m, 1H), 1.72 (m, 1H),
1.81 (m, 2H), 1.99 (m, 1H), 2.16 (m, 1H), 4.08 (m,
1H), 4.19 (m, 1H), 4.24 (m, 1H), 6.10 (s, 2H), 7.00 (d,
J = 8 Hz, 1H), 7.48 (m, 1H), 7.54 (m, 1H), 8.52 (d,
J = 7 Hz, 1H); 13C NMR (DMSO-d6) d 24.15, 25.92,
36.25, 51.06, 57.23, 63.24, 102.09, 107.80, 108.23,
122.90, 128.04, 147.66, 150.30, 165.39; high-resolution
MS (FAB) Calcd for C14H17N2O3 [M+H] m/e
261.1239. Found 261.1245.
5.1.76. N-[(1S,2R,4R)-7-Azabicyclo[2.2.1]hept-2-yl]pyr-
rolo[1,2-c]pyrimidine-3-carboxamide hydrochloride (18c).
The compound 18c (297 mg, 90%) was prepared from
pyrrolo[1,2-c]pyrimidine-3-carboxylic acid hydrochlo-
ride (198 mg, 1.00 mmol) and 21 (233 mg, 1.10 mmol),
followed by subsequent treatment with methanolic
hydrogen chloride (10 mL of a 1.0 M solution, 10 mmol)
in a manner similar to that described for the preparation
of 18a. Yellow solid: IR (diffuse reflectance) 3040, 2951,
2939, 2902, 2885, 2826, 2804, 2405, 2354, 2338, 2145,
To a stirred solution of the above solid in methanol
(10 mL) was added methanolic hydrogen chloride
(20 mL of a 3.0 N solution, 60 mmol). The mixture
was warmed to 60 ꢁC for 2 h. The mixture was cooled
to 0 ꢁC and diluted with ether (10 mL). The resulting
precipitate was filtered, washed with ether, and dried
2106, 1664, 1517, 1350 cmꢀ1 1H NMR (400 MHz,
;
in vacuo to afford 2.28 g (83%) of 18a as a white solid:
mp 199–200 ꢁC; ½aꢂ ꢀ8 (c 0.93, DMSO); IR (mull)
;
1531, 1487, 1355, 1342, 1178, 886 cmꢀ1 1H NMR
DMSO-d6) d 9.26 (s, 2H), 9.07 (s, 1H), 8.76 (d,
J = 8 Hz, 1H), 8.11 (s, 1H), 7.86 (s, 1H), 7.03 (t,
J = 4 Hz, 1H), 6.81 (d, J = 4 Hz, 1H), 4.23 (m, 2H),
4.08 (m, 1H), 2.23 (m, 1H), 1.85 (m, 3H), 1.71 (m,
1H), 1.62 (m, 1H); 13C NMR (100 MHz, DMSO-d6) d
163.4, 138.4, 132.0, 130.1, 117.2, 114.3, 113.3, 104.1,
62.84, 56.75, 49.99, 36.43, 25.22, 24.12; high-resolution
MS (FAB) Calcd for C14H17N4O [M+H] m/e 257.1402.
Found 257.1417.
25
D
3253, 3238, 3159, 3103, 2668, 1669, 1638, 1619, 1556,
(400 MHz, methanol-d4) d 9.32 (s, 1H), 9.03 (s, 1H),
8.62 (d, 1H, J = 2.08 Hz), 7.48 (d, 1H, J = 2.07 Hz),
4.41–4.34 (m, 3H), 2.40 (dd, 1H, J = 14.11, 8.71),
2.34–2.27 (m, 1H), 2.11–1.95 (m, 2H), 1.94–1.77 (m,
2H); 13C NMR (100 MHz, methanol-d4) d 161.0,
156.9, 152.5, 141.2, 137.9, 129.2, 117.7, 108.5, 63.51,
58.30, 52.28, 35.53, 25.70, 23.93; high-resolution MS
Calcd for C14H16N3O2 [M+H] m/e 258.1242. Found
257.1244. % Water (KF): 6.12. Anal. Calcd for
C14H15N3O2Æ2HClÆ6.12% H2O: C, 47.80; H, 5.53; N,
11.95. Found: C, 47.81; H, 5.58; N, 11.89.
5.1.77. N-[(1S,2R,4R)-7-Azabicyclo[2.2.1]hept-2-yl]-2,3-
dihydro-1,4-benzodioxine-6-carboxamidefumarate (18d).
To a stirred solution of 2,3-dihydro-1,4-benzodioxine-
6-carboxylic acid (212 mg, 1.20 mmol) in dry N,N-di-
methylformamide (4.0 mL) were added diisopropyleth-
ylamine (416 lL, 2.4 mmol) and 21 (240 mg,
1.1 mmol). The solution was cooled to 0 ꢁC before
437 mg (1.2 mmol) of HATU was added. The solution
was allowed to warm to room temperature and stir for
24 h. The solvent was removed in vacuo, and the
remaining residue was partitioned between brine–30%
ammonia water (1:1) and ethyl acetate. The aqueous
5.1.75. N-[(1S,2R,4R)-7-azabicyclo[2.2.1]hept-2-yl]-1,3-
benzodioxole-5-carboxamidehydrochloride (18b). To a
stirred solution of 1,3-benzodioxole-5-carboxylic acid
(91 mg, 0.55 mmol) and triethylamine (76 lL,
0.55 mmol) in methylene chloride (3.0 mL) was added
bis(2-oxo-3-oxazolidinyl)-phosphinic chloride (BOPCl)

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D. P. Walker et al. / Bioorg. Med. Chem. 14 (2006) 8219–8248
layer was extracted with ethyl acetate, and the combined
organic layers were washed with brine, dried over anhy-
drous potassium carbonate, filtered, and concentrated in
vacuo to a pale oil. The crude product was purified by
flash chromatography on silica gel. Elution with hex-
anes–ethyl acetate (70:30) afforded 422 mg (99%) of a
white solid.
days thereafter. Patch pipettes were pulled from borosil-
icate capillary glass using a Flaming/Brown micropi-
pette puller (P97, Sutter Instrument, Novato, CA) and
filled with an internal pipette solution composed of:
CsCH3SO3 (126 mM), CsCl (10 mM), NaCl (4 mM),
MgCl2 (1 mM), CaCl2 (0.5 mM), EGTA (5 mM),
HEPES (10 mM), ATP-Mg (3 mM), GTP-Na
(0.3 mM), and phosphocreatine (4 mM), pH 7.2. The
resistances of the patch pipettes when filled with internal
solution ranged between 3 and 6 MX. All experiments
were conducted at room temperature. Cultured cells
were continuously superfused with an external bath
solution containing: NaCl (140 mM), KCl (5 mM),
CaCl2 (2 mM), MgCl2 (1 mM), HEPES (10 mM), glu-
cose (10 mM), bicuculline (10 lM), CNQX (5 lM), D-
AP-5 (5 lM), and tetrodotoxin (0.5 lM), pH 7.4. Com-
pounds were dissolved in water or DMSO and diluted
into the external bath solution containing a final DMSO
concentration of 0.1% and delivered via a multibarrel
fast perfusion system (Warner Instrument, Hamden,
CT). Compounds were applied for one second once
every 30 s for at least three applications and the
whole-cell currents were recorded using an Axopatch
200B amplifier (Molecular Devices, Union City, CA).
Analog signals were filtered at 1/5 the sampling frequen-
cy, digitized, stored, and measured using pCLAMP soft-
ware (Molecular Devices). All data are reported as
means SEM. Cell culture reagents were purchased
from Invitrogen Corp. (Carlsbad, CA).
To a stirred solution of the above solid in methanol
(3.0 mL) was added methanolic hydrogen chloride
(3 mL of a 3.0 N solution, 9.0 mmol). The mixture was
warmed to 60 ꢁC for 2 h. The mixture was cooled to
room temperature and treated with pre-washed Amber-
jet 4400 resin. The mixture was agitated for 20 min, fol-
lowed by removal of the resin by filtration and removal
of the solvent in vacuo. The remaining residue was dis-
solved in methanol (1.0 mL) and treated with fumaric
acid (116 mg, 1.0 mmol), followed by dilution with ethyl
acetate (10 mL). The resulting precipitate was filtered,
washed with ethyl acetate, and dried in vacuo to afford
360 mg (83%) of 18d as a white solid: mp 117–118 ꢁC;
IR (diffuse reflectance) 3302, 3268, 3254, 3025, 2994,
2950, 2925, 2878, 1650, 1578, 1498, 1323, 1305, 1297,
1
1281 cmꢀ1; H NMR (400 MHz, methanol-d4) d 7.38
(d, 1H, J = 2.08 Hz), 7.35 (dd, 1H, J = 8.30, 2.07 Hz),
6.86 (d, 1H, J = 8.71 Hz), 6.68 (s, 2H), 4.31–4.21 (m,
5H), 4.20 (d, 1H, J = 4.56 Hz), 4.11 (dd, 1H, J = 8.71,
4.15 Hz), 2.25 (dd, 1H, J = 13.7, 8.71 Hz), 2.21–2.13
(m, 1H), 2.04–1.90 (m, 2H), 1.87–1.70 (m, 2H); 13C
NMR (100 MHz, methanol-d4) d 170.1, 168.3, 147.4,
143.6, 135.1, 126.1, 120.8, 117.0, 116.7, 64.70, 64.31,
63.31, 58.02, 52.28, 35.57, 25.83, 24.12; high-resolution
MS Calcd for C15H19N2O3 [M+H] m/e 275.1396. Found
275.1398. Anal. Calcd for C15H18N2O3ÆC4H4O4ÆH2O: C,
55.88; H, 5.92; N, 6.86. Found: C, 55.76; H, 6.18; N,
6.61.
5.3. In vivo assays
5.3.1. Auditory gating. Auditory gating experiments
were performed on male Sprague–Dawley rats, as de-
scribed in detail previously.14,60 Briefly, rats were anes-
thetized with chloral hydrate, the femoral artery and
vein were cannulated for monitoring arterial blood pres-
sure and administration of drugs or additional doses of
anaesthetic, respectively. Unilateral hippocampal field
potential (EEG) was recorded by a metal monopolar
macroelectrode placed into the CA3 region (Paxinos
and Watson, 1986).61 Field potentials were amplified, fil-
tered, displayed, and recorded for on-line and off-line
analysis (Spike3 programme). The auditory stimulus
consisted of a pair of 10 ms, 5 kHz tone bursts with a
0.5 s delay between the first ‘conditioning’ stimulus
and second ‘test’ stimulus. Auditory evoked responses
were computed by averaging of responses to 50 pairs
of stimuli presented with an interstimulus interval of
10 s. Percentage of gating was determined by the formu-
la: (1 ꢀ test amplitude/conditioning amplitude) · 100.
Amphetamine (D-amphetamine sulfate, 1 mg/kg, IV)
was administered in order to disrupt sensory gating.
Recordings of evoke potentials commenced 5 min after
amphetamine administration, and only rats showing
gating deficit exceeding 20% were used for subsequent
evaluation of a7 nAChR agonists or vehicle.
5.2. In vitro assays
For detailed procedures for the functional and binding
assays, see references 7 and 13.
5.2.1. Patch-clamp electrophysiology. Cultured neurons
were prepared from Sprague–Dawley rats (postnatal
day 3) according to the methods of Brewer.59 Rats were
killed by decapitation and their brains were removed
and placed in ice-cold Hibernate-A medium. Hippocam-
pal regions were gently removed, cut into small pieces,
and placed in Hibernate-A medium with 1 mg/mL papa-
in for 60 min at 35 ꢁC. After digestion, the tissues were
washed several times in Hibernate-A media and trans-
ferred to a 50 mL conical tube containing 6 mL Hiber-
nate-A medium with 2% B-27 supplement. Neurons
were dissociated by gentle trituration and plated onto
poly-D-lysine/laminin coated coverslips at a density of
300–700 cells/mm2, and transferred to 24-well tissue cul-
ture plates containing warmed culture medium com-
posed of Neurobasal-A medium, B-27 supplement
(2%), L-glutamine (0.5 mM), 100 U/mL penicillin,
100 mg/mL streptomycin, and 0.25 mg/mL fungizone.
Cells were maintained in a humidified incubator at
37 ꢁC and 6% CO2 for 1–2 weeks. The medium was
changed after 24 h and then approximately every three
Acknowledgments
We thank Jon Bordner, Ivan Samardjiev, and Gerald
Bryant for determining absolute stereochemistry via

D. P. Walker et al. / Bioorg. Med. Chem. 14 (2006) 8219–8248
8247
H.; Porsolt, R. D.; Williams, M.; Arneric, S. P. Science
1998, 279, 77.
X-ray crystallography of 8, 16, and 22; Mike Mao and
Dan Dukesherer for Process Chemistry support; Antho-
ny Bahinski and Kipp Erickson for coordinating hERG
data collection; the SAM-Chem group for analytical
data; the ATG group for in vitro ADME data; Mike
Zawistoski for analytical support and K. Birrell and
M. Black for in vivo PK support.
12. Coe, J. W.; Brooks, P. R.; Vetelino, M. G.; Wirtz, M.
C.; Arnold, E. P.; Huang, J.; Sands, S. B.; Davis, T. I.;
Lebel, L. A.; Fox, C. B.; Shrikhande, A.; Heym, J. H.;
Schaeffer, E.; Rollema, H.; Lu, Y.; Mansbach, R. S.;
Chambers, L. K.; Rovetti, C. C.; Schulz, D. W.;
Tingley, F. D.; O’Neill, B. T. J. Med. Chem. 2005, 48,
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13. Wishka, D. G.; Walker, D. P.; Yates, K. M.; Reitz, S. C.;
Jia, S.; Myers, J. K.; Olson, K. L.; Jacobsen, E. J.; Wolfe,
M. L.; Groppi, V. E.; Hanchar, A. J.; Thornburgh, B. A.;
Cortes-Burgos, L. A.; Wong, E.; Staton, B. A.; Raub, T.
J.; Higdon, N. R.; Wall, T. M.; Hurst, R. S.; Walters, R.
R.; Hoffmann, W. E.; Hajos, M.; Franklin, S.; Carey, G.;
Gold, L. H.; Cook, K. K.; Sands, S. B.; Zhao, S. X.;
Soglia, J. R.; Kalgutkar, A. S.; Arneric, S. P.; Rogers, B.
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NH2
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HN
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