Structure-activity studies on 2-methyl-3-(2(S)- pyrrolidinylmethoxy)pyridine (ABT-089): An orally bioavailable 3-pyridyl ether nicotinic acetylcholine receptor ligand with cognition-enhancing properties

Article abstract of DOI:10.1021/jm960233u

2-Methyl-3-(2(S)-pyrrolidinylmethoxy)pyridine, ABT-089 (S-4), a member of the 3-pyridyl ether class of nicotinic acetylcholine receptor (nAChR) ligands, shows positive effects in rodent and primate models of cognitive enhancement and a rodent model of anxiolytic activity and possesses a reduced propensity to activate peripheral ganglionic type receptors. The profiles of S-4, its N-methyl analogue, and the corresponding enantiomers across several measures of cholinergic channel function in vitro and in vivo are presented, together with in vitro metabolism and in vivo bioavailability data. On the basis of its biological activities and favorable oral bioavailability, S-4 is an attractive candidate for further evaluation as a treatment for cognitive disorders.

Full text of DOI:10.1021/jm960233u

J . Med. Chem. 1997, 40, 385-390
385
Notes
Str u ctu r e-Activity Stu d ies on 2-Meth yl-3-(2(S)-p yr r olid in ylm eth oxy)p yr id in e
(
ABT-089): An Or a lly Bioa va ila ble 3-P yr id yl Eth er Nicotin ic Acetylch olin e
Recep tor Liga n d w ith Cogn ition -En h a n cin g P r op er ties
†
Nan-Horng Lin,* David E. Gunn, Keith B. Ryther, David S. Garvey, Diana L. Donnelly-Roberts,
‡
§
Michael W. Decker, J orge D. Brioni, Michael J . Buckley, A. David Rodrigues, Kennan G. Marsh,
|
|
David J . Anderson, J erry J . Buccafusco, Mark A. Prendergast, J ames P. Sullivan, Michael Williams,
Stephen P. Arneric, and Mark W. Holladay
Neuroscience Research, D-47W, Biotransformation, D-46V, and Drug Analysis, D-46W, Pharmaceutical Products Division,
Abbott Laboratories, AP-10, 100 Abbott Park Road, Abbott Park, Illinois 60064-3500
X
Received March 25, 1996
2
-Methyl-3-(2(S)-pyrrolidinylmethoxy)pyridine, ABT-089 (S-4), a member of the 3-pyridyl ether
class of nicotinic acetylcholine receptor (nAChR) ligands, shows positive effects in rodent and
primate models of cognitive enhancement and a rodent model of anxiolytic activity and possesses
a reduced propensity to activate peripheral ganglionic type receptors. The profiles of S-4, its
N-methyl analogue, and the corresponding enantiomers across several measures of cholinergic
channel function in vitro and in vivo are presented, together with in vitro metabolism and in
vivo bioavailability data. On the basis of its biological activities and favorable oral bioavail-
ability, S-4 is an attractive candidate for further evaluation as a treatment for cognitive
disorders.
In tr od u ction
The potential ability for compounds acting at neu-
ronal nicotinic acetylcholine receptors (nAChRs) to exert
beneficial effects in central nervous system disorders
has prompted a search for agents having improved
safety and pharmacokinetic profiles relative to those of
S)-nicotine.1
-3
ABT-418 (1, Figure 1), an analogue of
(
(
F igu r e 1. Structures of ABT-418 1 and analogs 2, 3, and S-4.
S)-nicotine in which the pyridine ring is replaced by
the 3-methyl-5-isoxazole moiety, has been shown to
possess cognitive-enhancing and anxiolytic-like activi-
ties in animal models with an improved safety profile
compared to that of nicotine.4 Key objectives for ongoing
efforts in this area have been to achieve further im-
provements in the margin of safety and to identify
compounds with oral bioavailability.
models of anxiolytic-like action and cognition-enhancing
properties. On the basis of the hypothesis that ion flux
in IMR-32 cells would serve as a model for activity at
peripheral ganglionic receptors, and hence of potential
cardiovascular and gastrointestinal liabilities,6 it was
of particular interest to identify compounds which
elicited improvements in measures of cognitive enhance-
ment and anxiolytic-like activity but showed reduced
ability relative to 1-3 to stimulate ion flux in this cell
line. Here we report that this strategy has led to the
identification of S-4 (ABT-089), a member of the 3-py-
ridyl ether series. The properties of S-4 in in vitro
binding and functional assays and in several behavioral
tests are compared with those of 1, 2, 3, and several
close analogs of S-4. Further characterization in an
aged primate model of cognitive enhancement demon-
strates that S-4 elicits favorable effects in this model.
Moreover, S-4 is shown to be orally bioavailable. Taken
together, these data indicate that S-4 is an orally
bioavailable nAChR ligand with cognitive-enhancing
properties and diminished potential for side effects
mediated by peripheral ganglionic receptors.
,7
Recently, we disclosed a novel series of 3-pyridyl ether
5
compounds, including A-84543 (2) and A-85380 (3),
which possess subnanomolar affinity for nAChRs and
stimulate ion flux at human nAChRs with efficacies
similar to the efficacy of nicotine. A particularly at-
tractive feature of this series was the opportunity for
ready preparation of enantiomerically pure analogues
from the commercially available chiral pool. During the
course of structure-activity studies, numerous ana-
logues of 2 and 3 were prepared and screened for
binding affinity to central nAChRs, for activity in in
vitro functional assays (ion flux), for effects on temper-
ature and activity in vivo, and in rodent behavioral
*
Author to whom correspondence should be addressed.
Present address: NitroMed Research Laboratories, 801 Albany St.,
†
Ch em istr y. New compounds S-4, its N-methyl ana-
logue [2-methyl-3-[[((S)-1-methyl-2-pyrrolidyl)methyl]-
oxy]pyridine, S-5], and the corresponding enantiomers
Boston, MA 02118.
‡
Biotranformation.
Drug analysis.
Department of Pharmacology and Toxicology, Medical College of
§
|
[2-methyl-3-[((R)-2-pyrrolidylmethyl)oxy]pyridine, R-4]
Georgia, Augusta, GA.
X
Abstract published in Advance ACS Abstracts, December 1, 1996.
and [2-methyl-3-[[((R)-1-methyl-2-pyrrolidyl)methyl]-
S0022-2623(96)00233-6 CCC: $14.00 © 1997 American Chemical Society

3
86 J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 3
Notes
Sch em e 1a
a
(
a) 2-Methyl-3-pyridinol, diethyl azodicarboxylate, triphen-
ylphosphine, THF; (b) TFA, CH2Cl2; (c) (HCHO)n, HCO2H, 70 °C.
Ta ble 1. Radioligand Binding and Functional Properties of
Cholinergic Channel Ligands
a
F igu r e 2. The effects of 2, S-4, S-5, and R-4 on elevated plus-
maze exploration in mice. Shown are the mean times spent in
the open arms in seconds ((SEM). Significant improvement
in retention test performance was observed for S-4 [F(5,69) )
86Rb+ flux,
human R3âx
(IMR-32 cells)
K
i
(nM)
3
.21; p < 0.05]. *Significantly different from appropriate saline
[3
H]cytisine
binding
[125I]-R-Bgt
binding (K28 cells)
EC50
(µM)
%
max
group, p < 0.05.
b
compound
S-4 (ABT-089) 16.7 ( 3
>10000
>10000
>10000
150 ( 20
25 ( 6
50 ( 11
NT
63 ( 9
64 ( 12
21 ( 3
8 ( 4
29 ( 11
11 ( 5
NT
100 ( 10
85 ( 4
(100)
those from the previous report5 that the 2-methyl
S-5
R-4
R-5
27.7 ( 2
39 ( 4
substituent on the pyridine ring of S-4, R-4, and S-5 is
principally responsible for the reduced activity at gan-
glionic-type receptors. Thus, compound S-5 shows only
29% of the response in IMR-32 cells compared to 2.
Similarly, the 2-desmethyl analogues of S-4 and R-4
possessed efficacy comparable to that of (S)-nicotine in
3000 ( 360 >10000
2
1
(A-84543)
(ABT-418)
0.28 ( 0.05 1530 ( 320
4.2 ( 0.6
1 ( 0.1
4050 ( 795
1610 ( 220
S)-nicotinec
(
a
Values represent mean ( SEM; n ) 3-5. b % max represents
the maximal efficacy of the compounds relative to 100 µM nicotine.
NT ) not tested. Data from refs 5 and 17.
5
c
IMR-32 assay, whereas S-4 and R-4 stimulated only
8
% and 11% of the nicotine response, respectively. A
separate report describes more detailed in vitro char-
acterization of S-4 and R-4, including evidence that
several effects of S-4 (dopamine release, ion flux in
TE671 cells and neuroprotective properties) are medi-
oxy]pyridine, R-5] were synthesized by employing the
Mitsunobu reaction as a key step as described previ-
ously (Scheme 1).5 Following Mitsunobu couplings,
N-Boc-protected derivatives (S-7 or R-7) were depro-
tected by trifluoroacetic acid to give N-H products (S-4
or R-4). N-Methylpyrrolidines were prepared by reduc-
tive methylation of the N-Boc-protected secondary amines
with formaldehyde and formic acid. Final compounds
were isolated and characterized as dihydrochlorides.
8
ated by cholinergic channels. Interestingly, S-4 is not
a potent activator of ion flux mediated by human R4â2
8
receptors.
In Vivo P h a r m a cology. Compounds 2, S-4, R -4,
and S-5 were evaluated in the elevated plus maze as a
screen for anxiolytic-like activity (Figure 2). Compound
S-4 showed a significant effect in this assay at 1.9 µmol/
kg, whereas 2, R-4, and S-5 did not show a significant
effect at the doses tested. By comparison, 1 and (S)-
nicotine showed activity in this assay at 0.19 and 0.62
Resu lts a n d Discu ssion
3
In Vitr o P h a r m a cology. Binding affinities to [ H]-
(-)-cytisine sites and to R7 homomeric receptors are
shown in Table 1 for S-4, R-4, S-5, R-5, and reference
compounds 1 and 2, together with functional data
measured at peripheral ganglionic-type receptors in
IMR-32 cells. Compounds S-4, R-4, and S-5 are all in
9
µmol/kg, respectively. Compounds 2, S-4, R-4, and S-5
also were evaluated for their effects on locomotor
activity in mice (Figure 3). None of S-4, R-4, or S-5
showed significant reduction in locomotor activity at
doses up to 190 µmol/kg. In contrast, compound 2
caused significantly reduced locomotor activity at 6.2
and 19 µmol/kg, doses similar to those at which (S)-
3
a similar potency range for binding to [ H]-(-)-cytisine
sites, whereas R-5 possesses much lower affinity. This
pattern of affinities with respect to stereochemistry and
N-methylation is similar to that observed for the cor-
9
responding 2-desmethyl series,5 although the com-
nicotine had a significant effect.
pounds of the present series are consistently 100-300-
fold weaker than those lacking the 2-methyl substituent.
None of analogues S-4, R-4, S-5, and R-5 showed
detectable affinity for human R7 receptors at up to 10
µM.
With respect to functional activity, whereas 1 and 2
elicited maximal responses at the ganglionic subtype
comparable to that of (S)-nicotine, S-4, R -4, and S-5
showed comparatively low efficacy at this subtype. It
is apparent by comparison of the functional data with
Compound S-4 was further characterized in the
inhibitory avoidance assay as a preliminary screen for
possible cognitive enhancing activity, as well as for
hypothermic effects and ability to elicit seizures. Data
comparing S-4 in these measures with 1 and (S)-nicotine
are presented in Table 2. Compound S-4 elicited a
significant effect in the inhibitory avoidance assay at
0.62 µmol/kg, whereas (S)-nicotine and 1 produced
similar effects at the same and at a 10-fold lower dose,
respectively. Compound S-4 did not elicit a hypothermic

Notes
J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 3 387
Ta ble 2. In Vivo Pharmacological Properties of S-4 Compared
to Those of 1 and (S)-Nicotine
EDmin, µmol/kg, ipa
assay
1
S-4
(S)-nicotine
mouse inhibitory 0.062b
avoidance
0.62
NSc
0.62b
locomotor activity NSc
0.62b
(
19
0.0062-6.2) (1.9-19)
b
b
hypothermia
seizure
>62
6.2
d
d
d
62 [51-75] 774 [670-894] 41 [34-49]
a
EDmin is defined as the minimum dose of the drug that elicited
b
c
a statistically significant response. Data from ref 9. NS ) no
d
significant effect in indicated dose range. (ED50, µmol/kg [95%
CI].
F igu r e 4. The effects of S-4 on delayed matching-to-sample
DMTS) in monkeys. Shown are the mean correct in percent-
(
age (( SEM). Significant improvement in DMTS test pe-
formance was observed for S-4 [F(1,2) ) 35.00; p ) 0.027] at
medium delay. *Significantly different from appropriate saline
group, p ) 0.027.
Ta ble 3. Half-Lives of Compounds S-4, 1, and S-5-R-5 in
Vitro and in Vivo and Their Oral Bioavailabilities
t1/2 (h) in
dog liver slices
t1/2 (h)
following iv
administration
to dogs
oral
bioavailability
(
% remaining
a,c
compound
after 24 h)b
in dog (%)
S-4
S-5
R-4
R-5
1
>24 (77)
9 (32)
>24 (72)
8.5 (32)
3 (2.9)
1.6
0.31
1.4
0.61
0.21
61.5 ( 27.5d
5.8 ( 3.6
66.0 ( 14.3
4.9 ( 0.4
1.2 ( 1.2
a
Data provided as the mean ( SEM following a single 500 nmol/
kg oral or intravenous dose in dog. b Half-life from in vitro dog
liver slice experiments (% remaining after 24 h incubation).
F igu r e 3. The effects of 2, S-4, S-5, and R-4 on locomotor
activity measured for 15 min in an open field beginning
approximately 2 min after injection. Shown are mean percent
of saline control activity counts (infrared beam breaks) ( SEM.
Significant effects were noted for 2 [F(5,42) ) 6.65; p < 0.0001],
but not for S-4, S-5, and R -4. *Significantly different from
appropriate saline group, p < 0.05.
c
Values are mean of three dogs, unless otherwise indicated.
Values are mean of six dogs.
d
a stabilizing influence on the pyrrolidine ring relative
to the effect of the isoxazole substituent.
The in vivo half-lives and the oral bioavailabilities of
S-4, R-4, S-5, and R-5 reflect their stabilities in vitro.
Thus, the N-desmethyl compounds S-4 and R-4 have
half-lives approximately 2.5-5-fold longer than those
of the corresponding N-methyl analogs S-5 and R-5, and
oral bioavailabilities of S-4 and R-4 are 62% and 66%,
respectively, compared to less than 10% for compounds
S-5 and R-5. As was found in in vitro studies, the effect
of stereochemistry is minimal, although for the N-
methyl analogues, R-5 has a somewhat longer half-life
than S-5. A possible interpretation of the data is that
first pass metabolism could play a substantial role in
reducing the in vivo half-lives and bioavailabilities of
1, S-5, and R-5.
effect at doses up to 62 µmol/kg, compared to significant
effects elicited by 1 and (S)-nicotine at 19 and 6.2 µmol/
kg, respectively. Moreover, compound S-4 was >10-fold
less potent to elicit seizure activity than either 1 or (S)-
nicotine.
The effect of S-4 in the delayed matching-to-sample
task is shown in Figure 4. The data are normalized to
the actual percent correct for each delay interval. In
aged monkeys, S-4 given orally 90 min prior to behav-
ioral evaluation (average “best dose” ) 38 ( 14 nmol/
kg) improves impaired performance of the task,with a
robust enhancement seen primarily at the medium
delay interval. Broader behavioral assessment of S-4
1
0
in rats and monkeys is the subject of a separate report.
Su m m a r y
Meta bolism a n d P h a r m a cok in etics
Compound S-4 is a member of the 3-pyridyl ether
class of nAChR ligands that exhibits positive effects in
rodent and primate models of cognitive enhancement
and in a rodent model of anxiolytic-like activity. In
addition, S-4 has a reduced propensity compared to (S)-
nicotine to activate peripheral ganglionic-like nAChRs
and to elicit seizures or effects on temperature and
locomotor activity. On the basis of its biological activi-
ties and favorable oral bioavailability, S-4 is an attrac-
tive candidate for further evaluation as an orally active
agent for treatment of cognitive deficits.
The half-lives of compounds 1, S-4, R-4, S-5, and R-5
in the presence of dog liver slices in vitro and in dogs
in vivo are shown in Table 3. The N-desmethyl com-
pounds are more stable than the corresponding N-
methyl compounds, whereas the effect of stereochem-
istry is minimal under the conditions examined.
Compound 1 is substantially less stable than S-5 or R-5.
Since it has been established that the primary sites of
1
1,12
metabolism of 1 occur on the pyrrolidine ring,
appears that the pyridyloxymethyl appendage confers
it

3
88 J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 3
Notes
Exp er im en ta l Section
DEAD (4.7 mL, 30 mmol) dropwise. The mixture was stirred
at 0 °C for 30 min and then brought to room temperature. (R)-
Gen er a l Ch em istr y Meth od s. Proton magnetic resonance
spectra were obtained on a Nicolet QE-300 (300 MHz) or a
General Electric GN-300 (300 MHz) instrument. Chemical
1
3
-BOC-2-pyrrolidinemethanol (4.03 g, 20 mmol) and 2-methyl-
-hydroxypyridine (3.27 g, 30 mmol) were added to the reaction
vessel, and the mixture was stirred for 16 h. Solvent was
removed in vacuo, and the residue was diluted with hexane
and sonicated for 30 min. The resulting precipitate was
filtered and washed with hexane. The hexane was removed
in vacuo. The residue was purified by silica gel flash chro-
matography (hexane/ethyl acetate, 9:1 to 7:3) to give 1.8 g (31%
4
shifts are reported as δ values (ppm) relative to Me Si as an
internal standard unless otherwise indicated. Mass spectra
were obtained with a Hewlett-Packard HP5965 spectrometer.
The above determinations were performed by the Analytical
Research Department, Abbott Laboratories, and elemental
analyses were performed by Robertson Microlit Laboratiories,
Inc., Madison, NJ . Analytical results indicated by elemental
symbols were within (0.4% of the theoretical values.
yield) of the title compound as a pale yellow oil: TLC R
)
f
+
0
.50 (EtOAc); MS (DCI/NH
To a solution of the product from above (0.40 g, 1.35 mmol)
in CH Cl (3 mL) at 0 °C was added TFA (3 mL). The reaction
3
) m/e 293 (M + H) .
Thin-layer chromatography (TLC) was carried out by using
E. Merck precoated silica gel F-254 plates (thickness 0.25 mm).
Flash chromatography was carried out using Merck silica gel
2
2
mixture was stirred at this temperature for 40 min. The
temperature was raised to room temperature, and the reaction
mixture was stirred for an additional 30 min. Once the
6
0, 200-400 mesh.
Melting points are uncorrected and were determined on a
starting material was consumed, saturated K
and the product was extracted from the aqueous phase with
CH Cl
(3×). The organic layer was then dried over MgSO
The resulting crude material was purified by silica gel flash
chromatography (100% CHCl to MeOH/CHCl , 1:9) to give
3
.196 g (55%) of product as a pale yellow oil: MS (DCI/NH )
2 3
CO was added
Buchi melting point apparatus. Optical rotation data were
obtained on a Perkin-Elmer Model 241 polarimeter. All
reactions were performed under anhydrous conditions unless
otherwise noted.
2
2
4
.
3
3
The following abbreviations are used in the Experimental
0
Section: THF for tetrahydrofuran, D
CDCl for deuteriochloroform, DMSO-d
2
O for deuterium oxide,
+ 1
m/e 193 (M + H) ; H NMR (CDCl , 300 MHz) δ 8.07 (t, J )
3
3
6
for deuteriodimethyl
3
2
1
Hz, 1H), 7.07 (m, 2H), 3.95-3.85 (m, 2H), 3.58 (m, 1H), 3.10-
.97 (m, 2H), 2.48 (s, 3H), 2.23 (br s, 1H), 1.99 (m, 1H), 1.90-
.78 (m, 2H), 1.63 (m, 1H).
sulfoxide, BOC for tert-butoxycarbonyl, TFA for trifluoroacetic
acid, and DEAD for diethyl azodicarboxylate.
(S)-1-(tert-Butoxycarbonyl)-2-pyrrolidinemethanol and (R)-
The free base from above was dissolved in diethyl ether and
1
-(tert-butoxycarbonyl)-2-pyrrolidinemethanol were prepared
brought to 0 °C with stirring. The solution was treated with
diethyl ether saturated with hydrogen chloride gas. The
solvent was removed in vacuo. The resulting salt was tritu-
rated with diethyl ether (2×) and dried under vacuum to give
a beige powder: mp > 250 °C (decomposition occurs at 250 °C
1
3,14
according to the literature procedure
mercially available L-proline and D-proline, which were pur-
chased from Aldrich.
starting from com-
2
-Meth yl-3-(2(S)-p yr r olid in ylm eth oxy)p yr id in e Dih y-
2
5
d r och lor id e (S-4). To a solution of triphenylphosphine (3.83
g, 14.6 mmol) in 40 mL of anhydrous THF at 0 °C was added
diethyl azodicarboxylate (2.30 mL, 14.6 mmol) dropwise. The
mixture was stirred at 0 °C for 30 min and then brought to
room temperature. (S)-1-BOC-2-pyrrolidinemethanol (1.96 g,
and higher); [R] ) -25.5° (c ) 1, MeOH); MS (DCI/NH ) m/e
D
3
+
1
193 (M + H) ; H NMR (D O, 300 MHz) δ 8.17 (d, J ) 5.5 Hz,
2
1H), 7.86 (d, J ) 7.5 Hz, 1H), 7.67 (dd, J ) 8.50, 5.50 Hz, 1H),
4.58 (dd, J ) 11, 3 Hz, 1H), 4.34 (dd, J ) 11, 8 Hz, 1H), 4.22
(m, 1H), 3.46-3.42 (m, 2H), 2.62 (s, 3H), 2.32 (m, 1H), 2.22-
196 (m, 3H). Anal. Calcd for (C H N O‚2HCl) C, H, N.
9
.75 mmol) and 2-methyl-3-hydroxypyridine (1.60 g, 14.6
1
1
16
2
mmol) were added to the reaction vessel, and the mixture was
stirred for 16 h. Solvent was removed in vacuo, and the
residue was diluted with hexane and sonicated for 30 min. The
resulting precipitate was filtered and washed with hexane. The
hexane was removed in vacuo, and the residue was purified
by silica gel flash chromatography (ethyl acetate) to give 1.42
2-Meth yl-3-(1-m eth yl-2(S)-p yr r olid in ylm eth oxy)p yr i-
d in e Dih yd r och lor id e (S-5). To a sample of S-4 from above
(658 mg, 2.25 mmol) were added formic acid (1 mL) and
formaldehyde (2 mL), and the reaction mixture was stirred at
80 °C for 3 h. The reaction was quenched with water and
saturated K CO , and the mixture was extracted with meth-
2
3
g (50% yield) of the title compound as a pale yellow oil: TLC
ylene chloride. The extract was dried over MgSO and reduced
4
+
R
f
) 0.50 (EtOAc); MS (DCI/NH
3
) m/e 293 (M + H) .
in volume, and the residue was purified by chromatography
To a solution of the compound from above (0.407 g, 1.39
mmol) in methylene chloride (2 mL) at 0 °C was added TFA
2 mL). The mixture was stirred at this temperature for 40
min, allowed to reach room temperature, and stirred for an
additional 30 min. Saturated K CO was added, and the
product was extracted with CH Cl
(3×). The organic layer
was dried over MgSO , and the crude product was purified by
silica gel flash chromatography (100% CHCl to 1:9 MeOH/
CHCl and finally 0.1:1:9 NH OH/MeOH/CHCl ) to give 0.236
g (88%) of the title compound as a pale yellow oil: MS (DCI/
on silica gel (MeOH/ CHCl , 1:19 to 1:9). Removal of the
3
solvent and conversion of the residue into the salt with HCl
2
5
(
in ether gave the title compound: mp 202-205 °C; [R]
)
D
+
+6.38° (c ) 0.02, MeOH); MS (DCI/NH ) m/e 193 (M + H) ;
H NMR (D O, 300 MHz) δ 2.08-2.27 (m, 3H), 2.45 (m, 1H),
3
1
2
3
2
2
2
2.55 (s, 3H), 3.09 (s, 3H), 3.31 (br s, 1H), 3.76 (br s, 1H), 4.04
(br s, 1H), 4.36 (dd, J ) 7, 11 Hz, 1H), 4.58 (dd, J ) 3, 11 Hz,
1H), 7.50 (dd, J ) 5, 8.5 Hz, 1H), 7.65 (dd, J ) 1, 8.5 Hz, 1H),
8.12 (d, J ) 1, 5 Hz, 1H). Anal. (C H N O‚2HCl) C, H, N.
4
3
3
4
3
1
2
18
2
2-Meth yl-3-[[(1-m eth yl-2(R)-p yr r olid in yl)m eth yl]oxy]-
p yr id in e Dih yd r och lor id e (R-5). 2-Methyl-3-[[(1-BOC-2(R)-
pyrrolidinyl)methyl]oxy]pyridine (1.4 g, 4.7 mmol) was dis-
solved in formic acid (5 mL) and formalin (10 mL), heated at
reflux for 2 h, and cooled to room temperature. The reaction
mixture was poured into water (60 mL) and extracted with
+
1
NH
3
) m/e 193 (M + H) ; H NMR (CDCl , 300 MHz) δ 8.07 (t,
3
J ) 3 Hz, 1H), 7.07 (m, 2H), 3.95-3.85 (m, 2H), 3.58 (m, 1H),
3
1
.10-2.97 (m, 2H), 2.48 (s, 3H), 2.23 (br s, 1H), 1.99 (m, 1H),
.90-1.78 (m, 2H), 1.67-1.58 (m, 1H).
The free base from above was dissolved in diethyl ether and
brought to 0 °C with stirring. The solution was treated with
diethyl ether saturated with hydrogen chloride gas. The
solvent was removed in vacuo. The resulting salt was tritu-
rated with diethyl ether (2×) and dried under vacuum to give
a beige powder: mp >250 °C (decomposition occurs at 250 °C
CH
The aqueous mixture was extracted with CH
the combined extracts were dried over MgSO
was removed. The residue was chromatographed on silica gel
(CHCl /MeOH, 95:5), and the HCl salt was formed in Et O/
EtOH to yield 0.78 g (60%) of a hygroscopic solid: mp 203-
2
Cl
2
(3 × 10 mL). The pH was adjusted to 10 with K
Cl
(3 × 10 mL),
, and the solvent
2 3
CO .
2
2
4
3
2
2
5
and higher); [R]
D
+
3
) +25.50° (c ) 1, MeOH); MS (DCI/NH )
1
25
m/e 193 (M + H) ; H NMR (D
2
O, 300 MHz) δ 2.22-1.96 (m,
207 °C; [R]
D
) -5.73° (c ) 1, MeOH); MS (DCI/NH
3
) m/z 207
+
3
1
7
H), 2.32 (m, 1H), 2.62 (s, 3H), 3.46-3.42 (m, 2H), 4.22 (m,
H), 4.34 (dd, J ) 11, 8 Hz, 1H), 4.58 (dd, J ) 11, 3 Hz, 1H),
(M + H) ; NMR (D O, 300 MHz) δ 2.26 (m, 1H), 2.35 (m, 1H),
2
2.45 (m, 1H), 2.6 (s, 3H), 3.09 (s, 3H), 3.9 (m, 1H), 3.77 (m,
1H), 4.03 (m, 1H) 4.47 (m, 1H) 4.46 (m, 1H), 4.65 (m, 1H), 7.76
(dd, J ) 5.5, 8.4 Hz, 1H), 7.97 (d, J ) 8.4 Hz, 1H), 8.21 (dd, J
.67 (dd, J ) 8.50, 5.50 Hz, 1H), 7.86 (d, J ) 7.5 Hz, 1H),8.17
.
(d, J ) 5.5 Hz, 1H). Anal. (C11
H
16
N
2
O 2 HCl) C, H, N.
2
-Meth yl-3-(2(R)-p yr r olid in ylm eth oxy)p yr id in e Dih y-
) 1.1, 5.9 Hz, 1H). Anal. Calcd (C12
C, H, N.
H
18
N
2
O
4
2
‚2HCl‚0.4H O)
d r och lor id e (R-4). To a solution of triphenylphosphine (7.87
g, 30 mmol) in 120 mL of anhydrous THF at 0 °C was added
Biology. Interaction with high-affinity nicotine binding

Notes
J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 3 389
1
5
sites, mainly composed of R4 and â2 subunits, was measured
free access to water. Groups of dogs (n ) 3-6) received a 500
nmol/kg dose administered as either an oral dose (by gavage)
or as a slow bolus intravenous dose in the saphenous vein.
Blood samples were obtained from the jugular vein of each
animal at selected time points for the 8 h postdosing interval.
Plasma concentrations of parent drug were determined by
reverse phase HPLC with either electrochemical detection
3
by displacement of [ H]-(-)-cytisine from a preparation of
1
6
whole rat brain.
Interaction with the R7 subtype was
125
assessed by displacement of [ I]-R-bungarotoxin from K28
1
7
cells, which stably express human R7 homooligomers. In-
teraction with ganglionic-type receptors, thought to contain
1
8
R3 subunits in combination with â2 or â4 and possibly R5,
was measured using a Rb flux functional assay in a human
neuroblastoma-derived IMR-32 cell line, as described previ-
8
6
+
(
compounds 1, S-5, and R-5) or fluorescence detection following
23
derivatization with 7-fluoro-4-nitro-2-oxa-1,3-diazole (com-
1
9
ously.
pounds S-4 and R-4).
All animal studies were conducted in accord with AALAC
procedures as approved by the Institutional Animal Care and
Use Committee at Abbott Laboratories. Body temperature and
open field locomotor activity were measured in the same mice.
Beginning 4 min after an ip injection of compounds, horizontal
and vertical activity counts were recorded for 15 min in an
open field (41 × 41 cm) using photobeam activity monitors (San
Diego Instrument, San Diego, CA). Body temperature was
measured immediately after the mice were removed from the
open field (approximately 20 min after drug injection) using a
rectal probe (YSI TeleThermometer, Yellow Spring Instrument
Co., Yellow Spring, OH) inserted 3 cm.
Refer en ces
(1) Holladay, M. W.; Lebold, S. A.; Lin, N.-H. Structure-Activity
Relationships of Nicotinic Acetylcholine Receptor Agonists as
Potential Treatments for Dementia. Drug Dev. Res. 1995, 35,
1
91-213.
(
2) Williams, M.; Sullivan, J . P.; Arneric, S. P. Neuronal Nicotinic
Acetylcholine Receptors. Drug News Perspect. 1994, 7, 205-223.
3) McDonald, I. A.; Cosford, N.; Vernier, J .-M. Nicotinic Acetyl-
choline Receptors: Molecular Biology, Chemistry and Pharma-
cology. Ann. Rep. Med. Chem. 1995, 30, 41-50.
(
(4) Arneric, S. P.; Anderson, D. J .; Bannon, A. W.; Briggs, C. A.;
Buccafusco, J . J .; Brioni, J . D.; Decker, M. W.; Donnelly-Roberts,
D.; Gopalakrishnan, M.; Holladay, M. W.; Kyncl, J .; Marsh, K.
C.; Pauly, J .; Radek, R. J .; Rodrigues, D.; Sullivan, J . P.
Preclinical Pharmacology of ABT-418: A Prototypical Cholin-
ergic Channel Activator for the Potential Treatment of Alzhe-
imer’s Disease. CNS Drug Rev. 1995, 1, 1-26.
Anxiolytic-like activity was evaluated in mice using the
elevated plus-maze as previously described.9
,20
Briefly, the
maze consists of two open arms, to which rodents are naturally
averse, and two closed arms. The extent to which exploration
of the open arms is increased as a result of drug administration
(ip, 30 min prior to the test) is taken as a reflection of
(5) Abreo, M. A.; Lin, N.-H.; Garvey, D. S.; Gunn, D. E.; Hettinger,
A.-M.; Wasicak, J . T.; Pavlik, P. A.; Martin, Y. C.; Donnelly-
Roberts, D. L.; Anderson, D. J .; Sullivan, J . P.; Williams, M.;
Arneric, S. P.; Holladay, M. W. Novel 3-Pyridyl Ethers With
Subnanomolar Affinity for Central Nicotic Acetylcholine Recep-
tors. J . Med. Chem. 1996, 39, 817-825.
anxiolytic-like action of the drug. Inhibitory avoidance testing
9
was conducted as described previously. Briefly, mice were
trained to avoid the dark side of a dark-light chamber by
administration of a mild foot shock. The latency to enter the
dark chamber during a subsequent test session was used as
the index of memory of the training experience. Test com-
pounds were administered (ip) 15 min before the beginning of
the training session.
(6) McBride, P. E. The Health Consequences of Smoking. Med. Clin.
N. Am. 1992, 76, 333-353.
(7) Carlson, G. M.; Ruddon, R. W.; Hug, C. C., J r.; Schmiege, S. K.;
Bass, P. Analysis of the Site of Nicotine Action on Gastric Antral
and Duodenal Contractile Activity. J . Pharmacol. Exp. Ther.
1970, 173, 377-383.
Delayed matching-to-sample (DMTS) was evaluated in
2
1
monkeys as previously described. Stimuli on the test panels
were 2.54 cm diameter colored disks (red, yellow, or green).
Each trial began with the illumination of the sample key by
one of three colored stimuli. A key-press extinguished the
sample light and initiated one of four preprogrammed delay
intervals, during which no disks were illuminated. Following
the delay interval, two choice lights located below the sample
key were illuminated. One of the choice stimuli matched the
hue of the sample light. Key-presses of choice stimuli that
matched the hue of the sample stimulus were rewarded by a
(
8) Sullivan, J . P.; Donnelly-Roberts, D.; Briggs, C. A.; Gopalakrish-
nan, M.; Hu, I.; Campbell, J . E.; Anderson, D. J .; Piattoni-
Kaplan, M.; Molinari, E.; McKenna, D. G.; Gunn, D. E.; Lin, N.-
H.; Ryther, K. B.; He, Y.; Holladay, M. W.; Williams, M.; Arneric,
S. P. ABT-089 [2-Methyl-3-(2-(S)-pyrrolidinylmethoxy)pyridine
dihydrochloride]: A Potent and Selective Cholinergic Channel
Modulator with Cytoprotective Properties. J . Pharmacol. Exp.
Ther., submitted for publication.
(
9) Garvey, D. S.; Wasicak, J . T.; Decker, M. W.; Brioni, J . D.;
Buckley, M. J .; Sullivan, J . P.; Carrera, G. M.; Holladay, M. W.;
Arneric, S. P.; Williams, M. Novel Isoxazoles Which Interact with
Brain Cholinergic Channel Receptors Have Intrinsic Cognitive
Enhancing and Anxiolytic Activities. J . Med. Chem. 1994, 37,
1055-1059.
3
0 mg banana-flavored pellet. Monkeys completed 96 trials
on each day of testing. Four possible delay intervals between
a monkey’s response to the sample light and the presentation
of the two choice lights were employed. Short, medium, and
long delay intervals were individually adjusted for each
monkey to produce stable performance approximating the
following performance levels: short (75-84% correct), medium
(
10) Decker, M. W.; Bannon, A. W.; Curzon, P.; Gunther, K. L.; Brioni,
J . D.; Holladay, M. W.; Lin, N.-H.; Li, Y.; Daanen, J . F.;
Buccafusco, J . F.; Prendergast, M. A.; J ackson, W. J .; Arneric,
S. P. Effects of ABT-089, a Novel Cholinergic Channel Modula-
tor, on Cognitive Performance in Rats and Monkeys. J . Phar-
macol. Exp. Ther., submitted for publication.
(65-74% correct), and long (55-64% correct). The duration of
the short, medium, and long delay intervals in this experiment
were 5, 10, and 15 s, respectively, for the first monkey; 5, 10,
and 20 s for the second monkey; and 5, 15, and 30 s for the
third monkey. Performance for 0 s delay trials averaged 85-
(11) Rodrigues, A. D.; Ferrero, J . L.; Amann, M. T.; Rotert, G. A.;
Cepa, S. P.; Surber, B. W.; Machinist, J . M.; Tich, N. R.; Sullivan,
J . P.; Garvey, D. S.; Fitzgerald, M.; Arneric, S. P. The In Vitro
Hepatic Metabolism of ABT-418, A Cholinergic Channel Activa-
tor, In Rats, Dogs, Cynomolgus Monkeys, and Humans. Drug
Metab. Dispos. 1994, 22, 788-798.
1
00% correct. ABT-089 was dissolved in saline and placed on
a sugar cube which was fed to each monkey 90 min prior to
the start of DMTS testing. Monkeys were tested 5 days per
week with drug being administered on a maximum of two of
these days.
(
12) Lin, N.-H.; He, Y.; Anderson, D. J .; Wasicak, J . T.; Kasson, R.;
Sweeny, D.; Sullivan, J . P. Synthesis and Structure-Activity
Relationships of Pyrrolidine-Modified Analogs of the Potent
Cholinergic Channel Activator, ABT 418. Bioorg. Med. Chem.
Lett. 1994, 4, 2389-2394.
13) Evans, D. A.; Takacs, J . M.; Hurst, K. M. Phosphonamide
Stabilized Allylic Carbanions. New Homoenolate Anion Equiva-
lents. J . Am. Chem. Soc. 1979, 101, 371-378.
Meta bolism a n d P h a r m a cok in etics. The stability of
compounds in the presence of dog liver slices in vitro was
carried out by employing a previously published procedure.11
Compounds at a final concentration of 12 µg/mL were incu-
bated with liver tissue at 37 °C for various times up to 24 h.
At the required time, the medium was removed, transferred
to separate tubes, and immediately frozen in a 2-propanol/
dry ice bath. The samples were stored frozen until required
(
(
(
14) Harris, B. D.; Bhat, K. L.; J oullie, M. M. Synthetic Studies of
Detoxin Complex II: Synthesis of Detoxin B1 and B3. Hetero-
cycles 1986, 24, 1045-1060.
15) Flores, C. M.; Rogers, S. W.; Pabreza, L. A.; Wolfe, B. B.; Kellar,
K. J . A Subtype of Nicotinic Cholinergic Receptor in Rat Brain
is Composed of R4 and â2 Subunits and Is Up-regulated by
Chronic Nicotine Treatment. Mol. Pharmacol. 1991, 41, 31-37.
2
2
for assay by HPLC.
The pharmacokinetic behavior of each compound was evalu-
ated in beagle dog, fasted overnight prior to dosing and
throughout the duration of the study; animals were permitted
3
(
16) Pabreza, L. A.; Dhawan, S.; Kellar, K. J . [ H] Cytisine Binding
to Nicotinic Cholinergic Receptors in Brain. Mol. Pharmacol.
1990, 39, 9-12.

3
90 J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 3
Notes
(
17) Gopalakrishnan, M.; Buisson, B.; Touma, E.; Giordano, T.;
Campbell, J . E.; Hu, I. C.; Donnelly-Roberts, D.; Arneric, S. P.;
Bertrand, D.; Sullivan, J . P. Stable Expression and Pharmaco-
logical Properties of the Human R7 Nicotinic Acetylcholine
Receptor. Eur. J . Pharmacol. 1995, 290, 237-246.
(21) Buccafusco, J . J .; J ackson, W. J . Beneficial Effects of Nicotine
Administered Prior to a Delayed Matching-to-Sample Task in
Young and Aged Monkeys. Neurobiol. Aging 1991, 12, 233-238.
(22) The compounds of interest were separated from components of
the reaction medium on either a 15 cm × 4.6 mm 5 µm ODS-
AQ column (compounds S-4 and R-4) or a 15 cm × 4.6 mm 5
µm YMC-basic column (compounds 1, S-5, and R-5) (YMC, Inc.)
with an acetonitrile/methanol/buffer mobile phase at a flow rate
of 1.0 mL/min using electrochemical detection (ESA, Inc.) in the
oxidation mode for quantitation; the mobile phase buffer con-
tained 0.01 M tetramethylammonium hydroxide in 0.05 M KH2-
PO4 adjusted to pH 6.9.
(
18) Lukas, R. J . Expression of Ganglia-Type Nicotinic Acetylcholine
Receptors and Nicotinic Binding Sites by Cells of the IMR-32
Human Neuroblastoma Clonal Line. J . Pharmacol. Exp. Ther.
1
993, 265, 294-302.
(
19) Sullivan, J . P.; Decker, M. W.; Brioni, J . D.; Donnelly-Roberts,
D.; Anderson, D. J .; Bannon, A. W.; Kang, C.-H.; Adams, P.;
Piattoni-Kaplan, M.; Buckley, M.; Gopalakrishnan, M.; Williams,
M.; Arneric, S. P. (()-Epibatidine Elicits a Diversity of In Vitro
and In Vivo Effects Mediated by Nicotinic Acetylcholine Recep-
tors. J . Pharmacol. Exp. Ther. 1994, 271, 624-631.
(23) Hui, Y. H.; Marsh, K. C. Sensitive Detection of Selected
Cholinergic Channel Activators Derivatized with 7-Fluoro-4-
Nitrobenzo-2-Oxa-1,3-Diazole. J . Pharm. Biomed. Anal. 1996,
14, in press.
(
20) Brioni, J . D.; O’Neill, A. B.; Kim, D. J . B.; Decker, M. W. Nicotinic
Receptor Agonists Exhibit Anxiolytic-like Effects on the Elevated
Plus-Maze Test. Eur. J . Pharmacol. 1993, 238, 1-8.
J M960233U