Further structural optimization of cis-(6-benzhydryl-piperidin-3-yl)-benzylamine and 1,4-diazabicyclo[3.3.1]nonane derivatives by introducing an exocyclic hydroxyl group: Interaction with dopamine, serotonin, and norepinephrine transporters

Article abstract of DOI:10.1016/j.bmc.2008.01.009

Our earlier effort to develop constrained analogues of flexible piperidine derivatives for monoamine transporters led to the development of a series of 3,6-disubstituted piperidine derivatives, and a series of 4,8-disubstituted 1,4-diazabicyclo[3.3.1]nonane derivatives. In further structure-activity relationship (SAR) studies on these constrained derivatives, several novel analogues were developed where an exocyclic hydroxyl group was introduced on the N-alkyl-aryl side chain. All synthesized derivatives were tested for their affinities for the dopamine transporter (DAT), serotonin (5-HT) transporter (SERT), and norepinephrine transporter (NET) in the brain by measuring their potency in inhibiting the uptake of [³H]DA, [³H]5-HT, and [³H]NE, respectively. Compounds were also tested for their binding potency at the DAT by their ability to inhibit binding of [³H]WIN 35,428. The results indicated that position of the hydroxyl group on the N-alkyl side chain is important along with the length of the side chain. In general, hydroxyl derivatives derived from more constrained bicyclic diamines exhibited greater selectivity for interaction with DAT compared to the corresponding 3,6-disubstituted diamines. In the current series of molecules, compound 11b with N-propyl side chain with the hydroxyl group attached in the benzylic position was the most potent and selective for DAT (K_i = 8.63 nM; SERT/DAT = 172 and NET/DAT = 48.4).

Full text of DOI:10.1016/j.bmc.2008.01.009

Available online at www.sciencedirect.com
Bioorganic & Medicinal Chemistry 16 (2008) 2769–2778
Further structural optimization of cis-(6-benzhydryl-piperidin-3-yl)-
benzylamine and 1,4-diazabicyclo[3.3.1]nonane derivatives by
introducing an exocyclic hydroxyl group: Interaction
with dopamine, serotonin, and norepinephrine transporters
Manoj Mishra,a Rohit Kolhatkar,a Juan Zhen,b Ingrid Parrington,b
Maarten E. A. Reithb and Aloke K. Duttaa,*
aDepartment of Pharmaceutical Sciences, Wayne State University, Applebaum College of Pharmacy & Health Sciences,
Room# 3128, Detroit, MI 48202, USA
bNew York University, Department of Psychiatry, New York, NY 10016, USA
Received 24 November 2007; revised 31 December 2007; accepted 7 January 2008
Available online 11 January 2008
Abstract—Our earlier effort to develop constrained analogues of flexible piperidine derivatives for monoamine transporters led to
the development of a series of 3,6-disubstituted piperidine derivatives, and a series of 4,8-disubstituted 1,4-diazabicyclo[3.3.1]nonane
derivatives. In further structure–activity relationship (SAR) studies on these constrained derivatives, several novel analogues were
developed where an exocyclic hydroxyl group was introduced on the N-alkyl-aryl side chain. All synthesized derivatives were tested
for their affinities for the dopamine transporter (DAT), serotonin (5-HT) transporter (SERT), and norepinephrine transporter
(NET) in the brain by measuring their potency in inhibiting the uptake of [3H]DA, [3H]5-HT, and [3H]NE, respectively. Compounds
were also tested for their binding potency at the DAT by their ability to inhibit binding of [3H]WIN 35,428. The results indicated
that position of the hydroxyl group on the N-alkyl side chain is important along with the length of the side chain. In general, hydro-
xyl derivatives derived from more constrained bicyclic diamines exhibited greater selectivity for interaction with DAT compared to
the corresponding 3,6-disubstituted diamines. In the current series of molecules, compound 11b with N-propyl side chain with the
hydroxyl group attached in the benzylic position was the most potent and selective for DAT (Ki = 8.63 nM; SERT/DAT = 172 and
NET/DAT = 48.4).
ꢀ 2008 Elsevier Ltd. All rights reserved.
1. Introduction
The dopamine hypothesis of cocaine addiction received
further support from a series of in vivo experiments and
also from molecular biological studies involving DAT
knockout mice.3,4 Furthermore, in a recent experiment
with knock-in mouse model it was demonstrated that
binding to DAT is mainly responsible for its reinforcing
effect.5 This recent evidence further validates DAT as a
target for drug development for cocaine addiction. DAT
has been targeted for the development of pharmacother-
apy for cocaine addiction for number of years. How-
ever, it is also important to mention that other studies
have indicated the additional involvement of the seroto-
nergic system in some of the subjective effects of co-
Cocaine binds to several binding sites in the brain
including those on monoamine transporter proteins.
These proteins transport dopamine (DA), serotonin (5-
HT), and norepinephrine (NE) (DAT, SERT, and
NET, respectively).1,2 However, binding of cocaine to
DAT is believed to be responsible for production of its
powerful reinforcing effect. As no effective medication
is currently available to treat cocaine dependence, the
development of an effective pharmacotherapy for this
disorder is urgently needed.
caine.6 The validity of DAT as
a target for
development of cocaine pharmacotherapy is evident
from preclinical results in animal behavior studies which
indicated that GBR 12909, a DAT blocker, could atten-
uate self-administration of cocaine without modulating
Keywords: Dopamine transporter; Serotonin transporter; Norepineph-
rine transporter; Cocaine.
*
Corresponding author. Tel.: +1 313 577 1064; fax: +1 313 577
2033; e-mail: adutta@wayne.edu
0968-0896/$ - see front matter ꢀ 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2008.01.009

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M. Mishra et al. / Bioorg. Med. Chem. 16 (2008) 2769–2778
food reinforcement in monkeys.7 In a human clinical
trial GBR 12909 was a non-stimulant.8 However, the
clinical trial of GBR 12909 was discontinued due to
problems of QTc prolongation. In another ongoing
study with a different DAT blocker, the phenyl tropane
analogue RTI-336 is being evaluated preclinically as a
pharmacotherapy for cocaine abuse.9 Finally, a recent
study on the mechanism of interaction of benztropine-
like compounds with DAT suggests a link between con-
formational effects at DAT and their ability to serve in
psychostimulant substitution therapy.10,11
ally constrained 3,6-disubstituted piperidine derivatives.
The cis isomeric derivative from this novel series exhib-
ited preferential affinity at the DAT over the trans deriv-
ative.16 Further SAR exploration based on the novel cis-
structure yielded more potent molecules for the DAT
(compounds II and III in Figure 1), thus, confirming
preferential affinity of this novel cis-template for the
DAT.17 In our efforts to further expand our SAR studies
in searching for suitable pharmacotherapeutic agents for
cocaine addiction, the design of more structurally con-
strained molecules of 3,6-disubstituted derivatives was
undertaken. Thus, a further structural rigidification on
this template was carried out by linking the two nitrogen
atoms in the molecule by a bis-methylene-chain linker
which yielded a novel series of 4,8-disubstituted 1,4-
diazabicyclo[3,3,1]nonane derivatives where the pipera-
zine and the piperidine rings were fused into each other.
A brief SAR study was conducted which led to the dis-
covery of lead molecules exhibiting high affinity and
selectivity for the DAT, paralleling the results obtained
from the corresponding lesser constrained 3,6-disubsti-
tuted versions.17 However, the more rigid 1,4-diazabicy-
clo[3,3,1]nonane compounds exhibited greater selectivity
for the DAT indicating enhanced effect of rigidity on
selectivity (compound IV in Figure 1).18 Furthermore,
in vivo locomotor and drug discrimination experiments
demonstrated more activity in these constrained deriva-
tives compared to their flexible counterparts, indicating
Structurally diverse molecules have been developed for
DAT. These molecules are broadly categorized into four
main classes depending on their chemical structure,
known as the tropane, GBR, methylphenidate, and
mazindol class of derivatives. Detailed structure–activity
relationship (SAR) studies of these different categories
of molecules have been described in a recent review
paper.12
In our earlier studies for development of novel mole-
cules for DAT, we have developed a large number of
flexible piperidine analogues of GBR 12909 exhibiting
potent affinity at the DAT.13–15 In order to address poor
in vivo activity in these flexible molecules, we modified
one of our lead flexible DAT-selective piperidine ana-
logues, compound I in Figure 1, into a series of structur-
CH3
N
F
F
(S)
(S)
CO2CH3
N
N
(S)
(S)
H
O
N
NH
N
NH
O
O
N
N
(-)-II. R=F
(-)-III. R=CN
OCH3
R
(-)-IV
I
Cocaine
GBR 12909
Figure 1. Molecular structure of dopamine transporter blockers.
N
H
N
a
H
+
NH
NH
N
O
O
H
NH2
O
O
2a
2b
O
O
cis-( )-1
(S)
N
(S)
H
NH
OH
R-(-)-4a, R= -Ph-4F
S-(-)-4b, R=-Ph-4F
O
F
R
R or S
(S)
(S)
N
c
(S)
b
N
H
2b
(S)
H
NH
OH
NH2
O
R-(-)-4c, R=-Ph
S-(-)-4d, R=-Ph
R or S
cis-(-)-3
R
Scheme 1. Reagents and condition: (a) 1S-(ꢀ)camphanic chloride, Et3N, CH2Cl2; (b). HCl/MeOH, reflux, 72 h; (c) R- or S-epoxide, EtOH, 65 ꢁC,
overnight.

M. Mishra et al. / Bioorg. Med. Chem. 16 (2008) 2769–2778
2771
(S)
(S)
N
N
(S)
(S)
O
(S)
N
N
N
(S)
+
(R)
(S)
a
HN
OH
OH
(-)-6a
(-)-6b
cis-(-)-5
(S)
N
(S)
R-(-)-7a, R= -Ph
S-(-)-7b, R=-Ph
a
cis-(-)-5
N
R
R-(-)-7c, R=-Ph-4F
S-(-)-7d, R=-Ph-4F
O
*
R
OH
Scheme 2. Reagents and condition: (a) epoxide, EtOH, 65 ꢁC, overnight.
(S)
(S)
N
N
(S)
(S)
(S)
a
b
N
N
(S)
N
HN
HO
O
9
cis-(-)-5
8
F
F
(S)
N
(S)
Fraction I
d
N
HO
(R)
(S)
N
(S)
11a
O
O
N
O
F
HPLC
Separation
c
9
F
O
(S)
N
(S)
N
Fraction II
d
10a, 10b
HO
(S)
11b
F
Scheme 3. Reagents and conditions: (a) 3-chloro-40-fluoro propiophenone, K2CO3, KI, MeCN, reflux, 3 h; (b) NaBH4, THF, H2O, 3 h, rt; (c) (1S)-
(ꢀ)-camphanic chloride, Et3N, DMAP, CH2Cl2, 3 h; (d) K2CO3, MeOH, 12 h, rt.
an effect of the constrained structure in efficient penetra-
tion of blood–brain barrier. In this regard, more con-
strained 1,4-diazabicyclo[3,3,1]nonane seemed to
exhibit higher in vivo potency.
piperidine ring of our earlier flexible piperidine ana-
logue produced highly potent and selective molecule
for DAT.19 In the present study we also determine
the influence of chirality of the newly introduced hy-
droxyl center on interaction with monoamine
transporters.
In the present SAR study we examine the effect of
introduction of an exocyclic hydroxyl group in the
above–constrained derivatives on affinity and selectiv-
ity for monoamine transporters. Specifically, we
wanted to observe the effect of introduction of an
exocyclic hydroxyl functionality in both optically pure
(ꢀ)-cis-3,6-disubstituted monocyclic diamine and (ꢀ)-
cis-bicyclic diamine structures to understand the influ-
ence of such a hydroxyl group on binding interac-
2. Chemistry
Synthesis of target compounds is shown in Schemes 1–3.
Scheme 1 describes the synthesis of targets 4a to 4d. As
described in our earlier publication,17 optically active
cis-amine was synthesized from racemic 1 by converting
the amine into diastereoisomeric intermediates followed
tion. Introduction of
a hydroxyl group in the

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M. Mishra et al. / Bioorg. Med. Chem. 16 (2008) 2769–2778
by separation and hydrolysis of the desired isomers to
the corresponding amine cis-(ꢀ)-3. Treatment of (ꢀ)-3
with optically active epoxides furnished the final hydro-
xy targets 4a–4d in good yield. The optically active epox-
ides were synthesized by following the published
procedure.20
droxyl group to 3,6-disubstituted template. Between
compounds 4a and 4b, compound 4b has the hydroxyl
group in a S-configuration as it was synthesized from
S-epoxide. Compound 4b was more potent in inhibiting
uptake of radiolabeled DA and NE by DAT and NET,
respectively, compared to 4a (Ki (DAT) = 236 nM vs
152 nM for 4a and 4b, respectively, and Ki
(NET) = 1435 vs 306 nM for 4a and 4b, respectively).
Thus, the difference in NE uptake inhibitory activity be-
tween the two compounds was much greater than the
DA uptake inhibitory activity.
Scheme 2 describes the synthesis of targets 7a–7d. Here
optically active amine (ꢀ)-5 was synthesized by follow-
ing our earlier procedure.18 This amine was treated with
racemic 2,3-epoxypropyl benzene, which produced two
diastereomers 6a and 6b, which were separated by col-
umn chromatography. Amine cis-(ꢀ)-5 was further trea-
ted with enantiomeric (R and S) 2-phenyloxirane and 2-
(4-fluorophenyl)oxirane separately in ethanol to yield
the target compounds 7a–7d in reasonably good yield.
In designing the next two compounds, an additional
methylene unit was introduced between the phenyl moi-
ety and the hydroxyl center. This transformation made
4c–d more potent DAT uptake inhibitors compared to
4a–b (Table 1). Both 4c and 4d exhibited low nanomolar
activity for inhibition of DA uptake activity (Ki
(DAT) = 25 nM and 25.3 nM for 4c and 4d, respec-
tively) and also the same relative potency was exhibited
in the binding assay with the radiolabeled tropane li-
gand CFT. It is interesting to note that both compounds
exhibited comparable inhibition activity, thus, not
exhibiting any preference for chirality of the hydroxyl
center. Thus, a minor change in molecular structure
resulted in almost 10-fold increase of DAT inhibition
potency in 4c–d compared to 4a–b.
Scheme 3 describes the synthesis of targets 11a and 11b.
N-alkylation of amine cis-(ꢀ)-5 with 3-chloro-40-fluoro
propiophenone under basic condition produced 8 which
was reduced by sodium borohydride to produce mixture
of both R- and S-alcohols 9. Alcohol 9 was next con-
verted into diastereomeric caphanic esters, which were
separated by semi-preparative HPLC process. The final
targets, 11a and 11b, were produced after hydrolyzing
the esters.
3. Results and discussion
In designing our next analogues, the bicyclic (ꢀ)-diamine
template was chosen for introduction of exocyclic hydro-
xyl group. Thus in compounds 6a and 6b, which represent
bicyclic versions of 4c and 4d, a hydroxyl functionality was
introduced with R- and S-stereo-centers. These molecules
exhibited differential potencies for inhibition of DA uptake
with the S-hydroxyl stereo-center exhibiting greater
potency than the R stereo-center (Ki (DAT) = 16.8 nM
vs 82.9 nM for 6b and 6a, respectively). Thus, this result
was somewhat different compared to their 3,6-disubsti-
tuted counterparts 4c–d. Compound 6b was 5 times more
potent in inhibiting DA uptake than 6a (Table 1). This
might indicate an effect of a more constrained bicyclic
Our previous study with 3,6-disubstituted constrained
piperidine derivatives produced high-affinity ligands
for DAT.17,18 In the current study, we wanted to explore
whether introduction of an exocyclic hydroxyl group
can further increase affinity of these compounds for
DAT or for other monoamine transporters. We had
established earlier that (ꢀ)-enantiomeric (S,S) versions
of disubstituted diamines exhibited the highest potency.
Thus, in our design we selectively wanted to synthesize
only the (ꢀ)-isomeric versions. Design of compounds
4a–b and 4c–d involved introduction of an exocyclic hy-
Table 1. Affinity of drugs at DAT, SERT, and NET in rat brain
Compound
DAT binding, Ki, nM,
[3H]WIN 35, 428a
DAT uptake, Ki, nM,
[3H]DAa
SERT uptake, Ki, nM,
[3H]5-HTa
NET uptake, Ki, nM
[3H]NEa
GBR 12909b
10.6 1.9
11.3 0.9
22.5 2.1
10.6 2.2
9.10 1.86
18.4 0.9
236 41
91.1 12.8
102 32
IIIb
IVb
D-228, 4a (S,S,R)
D-227, 4b (S,S,S)
D-254, 4c (S,S,R)
D-272, 4d (S,S,S)
D-169, 6a (S,S,R)
D-170, 6b (S,S,S)
D-250, 7a (S,S,R)
D-251, 7b (S,S,S)
D-252, 7c (S,S,R)
D-253, 7d (S,S,S)
D-273 (11a)
2895 755
3117 757
1391 298
1435 495
306 89
170 32
231 50
730 79
259 20
954 138
1730 387
319 58
728 142
388 76
418 27
152 46
31.8 6.0
28.9 2.3
148 48
25.1 2.5
25.3 6.9
82.9 7.2
16.8 1.3
204 34
2596 718
11,216 231
10,336 539
12,904 1440
9508 1748
7414 978
47.0 5.6
228 45
1039 179
142 22
266 31
66.5 5.7
160 12
649 100
19.9 0.9
13.5 2.9
7344 1437
11,884 4136
1484 366
41.8 6.9
8.63 1.36
D-274 (11b)
a For binding, the DAT was labeled with [3H]WIN 35, 428. For uptake by DAT, SERT and NET, [3H]DA, [3H]5-HT and [3H]NE accumulation
were measured. Results are average SEM of three to eight independent experiments assayed in triplicate.
b Results from Refs. 1 and 2.

M. Mishra et al. / Bioorg. Med. Chem. 16 (2008) 2769–2778
Table 2. Selectivity ratio for uptake inhibition
2773
that an N-propyl linker length was optimal for interac-
tion with DAT. Position of an exo-cyclic hydroxyl
group in the benzylic position of the N-propyl terminus
produced the most active and selective DAT compound
11b in the current series. In most cases a stereochemical
preference was exhibited for the hydroxyl stereo center.
In general, as expected from earlier findings, hydroxyl
compound derived from more constrained bicyclic
amine produced greater selectivity for DAT than 3,6-
disubstituted amine derivatives.
Compound
SERT
uptake/DAT
uptakea
NET
uptake/DAT
uptakea
DAT
uptake/DAT
bindinga
GBR 12909
8.5
9.6
6.0
2.0
6.7
9.1
8.8
15.4
4.6
6.5
4.7
4.5
9.2
48.4
1.0
4a
4b
4c
12.2
20.5
55.4
103
0.78
0.87
0.56
0.35
0.89
0.25
0.46
0.24
2.1
4d
6a
6b
7a
7b
7c
135
615
63.2
35.7
111
5. Experimental
7d
11a
11b
45.9
284.3
171.9
Analytical silica gel-coated TLC plates (Si 250F) were
purchased from Baker, Inc and were visualized with
UV light or by treatment with phosphomolybdic acid
(PMA). Flash chromatography was carried out on Ba-
0.63
a Ratio of Ki values.
1
ker Silica Gel 40 mM. H NMR spectra were routinely
structure on greater selectivity and affinity for DAT as we
observed earlier.18 The next series of compounds 7a–d,
which represents more constrained bicyclic versions of
4a–b, yielded results from weak to strong potency for the
DAT. However, these molecules, contrary to previous
derivatives, produced preferential interaction with DAT
with an exocyclic hydroxyl group in the R-stereo-center.
The most potent compound identified in the 7-series was
fluoro derivative 7c, exhibiting the highest potency for
DAT (Ki = 66.5 nM). In general, fluoro derivatives were
more potent compared to unsubstituted versions. In gen-
eral, compounds 7a–d were much less potent than 6a–b,
indicating the importance of N-alkyl chain length in trans-
porter interaction.
obtained at Varian 400 MHz FT NMR. The NMR sol-
vent used was CDCl3 as indicated. TMS was used as an
internal standard. Elemental analyses were performed
by Atlantic Microlab, Inc. and were within 0.4% of
the theoretical value. Optical rotations were measured
on Perkin-Elmer 241 polarimeter.
[3H]WIN 35,428 (83.6 Ci/mmol), [3H]dopamine (55.1 Ci/
mmol), [3H]serotonin (30.0 Ci/mmol), and [3H]norepi-
nephrine (54.6 Ci/mmol) were obtained from Dupont-
New England Nuclear (Boston, MA, U.S.A). WIN
35,428 naphthalene sulfonate was purchased from
Research Biochemicals, Inc. (Natick, MA, USA). (ꢀ)-
Cocaine HCl was obtained from the National Institute
on Drug Abuse. GBR 12909 Dihydrochloride (1-[2-[bis(4-
Fluorophenyl)methoxy]ethyl]-4-[3-phenylpropyl]piper-
azine) was purchased from SIGMA-ALDRICH (#D-
052; St. Louis, MO).
In the design of next two bicyclic amine analogues, 11a
and 11b, the hydroxyl group was introduced in the ben-
zyl position at the terminus of the propyl chain. Thus, in
these two compounds the hydroxyl group was located
furthest from the N-atom as compared to previous ana-
logues. It is evident from uptake inhibition data that
such location of the hydroxyl group produced maximal
inhibition of DA uptake in one of the diastereomers, 11b
(Ki = 8.63 nM). Thus, compound 11b exhibited maxi-
mum potency and selectivity for inhibition of dopamine
uptake compared to inhibition of both serotonin and
norepinephrine (SERT/DAT and NET/DAT; 172 and
48.4, Table 2). In fact, compound 11b turned out to be
the most potent and selective compound in this current
series of molecules. The diastereomer 11a, on the other
hand, was less potent compared to 11b even though its
potency was comparable to that of the third best com-
pound 4d in the series (Ki (DAT) = 41.8 nM and
25.3 nM, respectively, for 11a and 4d). It is evident from
this result that the location of the hydroxyl group with
respect to the aromatic ring and the N-atom played an
important role in uptake inhibition activity.
5.1. Synthesis of N-(6-benzhydrylpiperidin-3-yl)-4,7,7-
trimethyl-3-oxo-2-oxa-bicyclo [2.2.1]heptane-1-carbox-
amide (2a and 2b)
To a stirring solution of racemic cis-6-benzhydrylpiperi-
din-3-ylamine 1 (1.10 g, 4.12 mmol) in anhydrous
CH2Cl2 (50 ml), triethylamine (2.08 g, 20.64 mmol) was
added dropwise (1S)-(ꢀ)-camphanic chloride (1.07 g,
4.95 mmol) dissolved in 10 ml anhydrous CH2Cl2 under
nitrogen. The reaction mixture was stirred at 0 ꢁC for
30 min and at room temperature for another 3 h under
nitrogen atmosphere. The reaction mixture was then
diluted with CH2Cl2 (50 ml) and washed with water
(20 ml), dried over Na2SO4 and the solvent was evapo-
rated in vacuo to afford a mixture of two diastereomers
2a and 2b. Each diastereoisomer was separated by flash
column chromatography over silica gel using hexanes/
diethyl ether (12:88) as a mobile phase.
1
Eluting first was 2a (0.51 g, 55%) H NMR (400 MHz,
4. Conclusion
CDCl3): d 0.89 (3H, s, CH3), 1.09 (3H, s, CH3), 1.11
(3H, s, CH3), 1.37–1.41 (1H, m, H-5), 1.48–1.56 (1H, m,
H-5), 1.65–1.72 (2H, m, CCH2C), 1.82–1.97 (3H, m,
CCH2C and H-4), 2.48–2.56 (1H, m, H-4), 2.78–2.84
(2H, m, H-2), 3.23 (1H, dt, J = 2.4 Hz, J = 10.4 Hz,
The positional effect of the exo-cyclic hydroxyl group on
N-alkyl side chain and the importance of the optimum
length of N-alkyl side chain were evaluated for interac-
tion with monoamine transporters. The results indicated

2774
M. Mishra et al. / Bioorg. Med. Chem. 16 (2008) 2769–2778
1
dure A) to yield 4b (0.029 g, 25%). H NMR (400 MHz,
H-6), 3.79 (1H, d, J = 10.0 Hz, (Ph)2CH), 4.09–4.12 (1H,
m, H-3), 7.13–7.37 (8H, m, ArH), 7.39–7.41 (2H, m, ArH).
CDCl3): d 1.25–1.38 (2H, m, H-5), 1.47–1.53 (1H, m, H-
4ax), 1.79–1.83 (1H, m, H-4eq), 2.43–2.53 (1H, dd,
J = 2.8 Hz, J = 12.0 Hz, NHCH2), 2.71–2.74 (2H, m, H-
2), 2.87–2.97 (2H, m, NHCH2 and H-3eq), 3.25 (1H, dt,
J = 3.2 Hz, J = 9.6 Hz, H-6ax), 3.74 (1H, d, J = 10 Hz,
(Ph)2CH), 4.60–4.63 (1H, dd, J = 2.8 Hz, J = 8.8 Hz,
Eluting second was 2b (0.45 g, 49%) 1H NMR (400 MHz,
CDCl3): d 0.82 (3H, s, CH3), 1.02 (3H, s, CH3), 1.05 (3H, s,
CH3), 1.32–1.35 (1H, m, H-5), 1.43–1.52 (1H, m, H-5),
1.57–1.64 (2H, m, CCH2C), 1.71–1.90 (3H, m, CCH2C
and H-4), 2.41–2.50 (1H, m, H-4), 2.71–2.80 (2H, m, H-
2), 3.16 (1H, dt, J = 2.0 Hz, J = 10.4 Hz, H-6), 3.71 (1H,
d, J = 10.0 Hz, (Ph)2CH), 4.01–4.07 (1 H, m, H-3),
7.07–7.30 (8H, m, ArH), 7.33–7.35 (2H, m, ArH).
CH-OH), 7.01 (2H, t, J = 8.8 Hz, ArH), 7.16–7.37 (12H,
25
D
m, ArH). ½aꢁ (oxalate salt) = (+)19.2ꢁ (c 0.38, MeOH).
Free base was converted into oxalate salt 203–205 ꢁC.
Analysis calculated for (C26H29FN2O. 2(COOH)2,
0.9H2O) C, H, N.
5.2. Synthesis of (ꢀ)-cis-6-benzhydrylpiperidin-3-ylamine
(3)
5.5. Synthesis of (R)-1-[(3S,6S)-6-benzhydrylpiperidin-3-
ylamino)-3-phenylpropan-2-ol (4c)
A solution of 2b (0.55 g, 1.23 mmol) in conc. HCl/MeOH
(50 ml, 1:4 ratio v/v) was refluxed for 72 h. Methanol was
then evaporated under reduced pressure at 50 ꢁC and the
remaining aqueous solution was neutralized by saturated
NaHCO3 solution. The solution was extracted with
CH2Cl2 (3 · 50 ml). All organic layers were combined,
washed with brine (50 ml) and dried over Na2SO4, con-
centrated, and purified by flash column chromatography
over silica gel using ethyl acetate/MeOH/Et3N (80:15:5)
to afford 3 as a white solid (0.26 g, 79%). 1H NMR
(400 MHz, CDCl3): d 1.35–1.43 (2H, m, H-5), 1.59–1.64
(2H, m, H-4), 2.18 (2H, broad singlet, NH), 2.79–2.81
(2H, m, H-2), 2.98–3.04 (1H, m, H-3), 3.25 (1H, dt,
Compound 3 (0.076 g, 0.285 mmol) was reacted with R-
(+)-2,3-epoxypropyl benzene (0.057 g, 0.427 mmol)
(Procedure A). The crude product was purified by flash
column chromatography using diethyl ether/MeOH/
1
Et3N (90:10:0.2) to give 4c (0.035 g, 30%). H NMR
(400 MHz, CDCl3): d 1.25–1.34 (2H, m, H-5), 1.44–
1.52 (1H, m, H-4ax), 1.72–1.75 (1H, m, H-4eq), 2.32–
2.38 (1H, dd, J = 2.8 Hz, J = 9.6 Hz, NHCH2), 2.64–
2.83 (5H, m, H-2, NHCH2, Ph–CH2), 2.90–2.93 (1H,
m, H-3eq), 3.23 (1H, dt, J = 3.2 Hz, J = 10.0 Hz, H-
6ax), 3.73–3.83 (2H, m, (Ph)2CH and CH–OH), 7.12–
J = 4 Hz, J = 10 Hz, H-6ax), 3.80 (1H, d, J = 10.2 Hz,
7.31 (13H, m, ArH), 7.35–7.36 (2H, m, ArH). Optical
25
D
25
D
(Ph)2CH), 7.12–7.40 (10H, m, ArH). ½aꢁ ¼ ðꢀÞ41:9ꢂ (c
rotation of free base, ½aꢁ ¼ ðꢀÞ38:9ꢂ (c 0.57, MeOH).
1, MeOH).
Free base was converted into oxalate salt 205–207 ꢁC.
5.3. Procedure A. Synthesis of (R)-2-[(3S,6S)-6-ben-
zhydrylpiperidin-3-ylamino)-1-(4-fluorophenyl)ethanol
(4a)
Analysis calculated for (C27H32N2O. 2(COOH)2,
0.5H2O) C, H, N.
5.6. Synthesis of (S)-1-[(3S,6S)-6-benzhydrylpiperidin-3-
ylamino)-3-phenylpropan-2-ol (4d)
To a stirring solution of (ꢀ)-cis-6-benzhydrylpiperidin-3-
ylamine 3 (0.058 g, 0.217 mmol) in dry ethanol (20 ml)
was added R-(ꢀ)-4-fluoro styrene oxide (0.045 g,
0.326 mmol). The reaction mixture was refluxed overnight
under nitrogen atmosphere. The solvent was evaporated
and the product was purified by flash column chromatog-
raphy over silica gel using diethyl ether/MeOH/Et3N
(92:8:0.2) to give 4a (0.023 g, 26%). 1H NMR (400 MHz,
CDCl3): d 1.30–1.38 (2H, m, H-5), 1.48–1.55 (1H, m, H-
4ax), 1.75–1.79 (1H, m, H-4eq), 2.44–2.54 (1H, dd,
J = 2.0 Hz, J = 10.0 Hz, NHCH2), 2.71–2.78 (2H, m, H-
2), 2.86–2.90 (1H, dd, J = 3.2 Hz, J = 12.4 Hz, NHCH2),
2.97–3.00 (1H, m, H-3eq), 3.25 (1H, dt, J = 3.2 Hz,
J = 9.6 Hz, H-6ax), 3.75 (1H, d, J = 10 Hz, (Ph)2CH),
4.60–4.64 (1H, dd, J = 3.2 Hz, J = 9.6 Hz, CH–OH), 7.01
Compound 3 (0.075 g, 0.281 mmol) was reacted with
S-(ꢀ)-2,3-epoxypropyl benzene (0.056 g, 0.422 mmol)
(Procedure A) and was purified by flash column chroma-
tography over silica gel using diethyl ether/MeOH/Et3N
(90:10:0.2) to yield 4d (0.037 g, 33%). 1H NMR
(400 MHz, CDCl3): d 1.23–1.35 (2H, m, H-5), 1.41–1.49
(1H, m, H-4ax), 1.75–1.78 (1H, m, H-4eq), 2.36–2.41
(1H, dd, J = 3.2 Hz, J = 8.8 Hz, NHCH2), 2.66–2.84
(5H, m, H-2, NHCH2, Ph-CH2), 2.89–2.92 (1H, m, H-
3eq), 3.23 (1H, dt, J = 2.4 Hz, J = 10.0 Hz, H-6ax), 3.75
(1H, d, J = 10.0 Hz, (Ph)2CH) 3.78–3.85 (1H, m, and
CH–OH), 7.12–7.31 (13H, m, ArH), 7.35–7.36 (2H, m,
25
D
ArH). Optical rotation, ½aꢁ ¼ ðꢀÞ49:3ꢂ (c 0.96, MeOH).
(2H, t, J = 8.4 Hz, ArH), 7.13–7.37 (12H, m, ArH). Free
base converted into oxalate salt, m.p. 202–204 ꢁC. ½aꢁ
Free base was converted into oxalate salt 206–209 ꢁC.
25
D
(oxalate salt) = (ꢀ)21.5ꢁ (c 0.26, MeOH).
Analysis calculated for (C27H32N2O. 2(COOH)2, 0.3
H2O) C, H, N.
Analysis calculated for (C26H29FN2O. 2(COOH)2,
0.5H2O) C, H, N.
5.7. Synthesis of 1-((5S,8S)-8-benzhydryl-1,4-diazabicy-
clo [3.3.1]nonane-2-yl)-3-phenylpropan-2-ol (6a and 6b)
5.4. Synthesis of (S)-2-[(3S,6S)-6-benzhydrylpiperidin-3-
ylamino)-1-(4-fluorophenyl) ethanol (4b)
To a stirring solution of cis-(ꢀ)-8-benzydryl-1,4-diazabi-
cyclo[3.3.1]nonane 5 (0.100 g, 0.341 mmol) in dry etha-
nol was added 2,3-epoxypropyl benzene (0.068 g,
0.512 mmol). The reaction mixture was stirred overnight
Compound 3 (0.076 g, 0.285 mmol) was refluxed with S-
(+)-4-fluoro styrene oxide (0.059 g, 0.427 mmol) (Proce-

M. Mishra et al. / Bioorg. Med. Chem. 16 (2008) 2769–2778
2775
at 65 ꢁC (Procedure A). The diastereomers were sepa-
rated by preparative TLC using acetone/diethyl ether
(20:80) as mobile phase to afford 6a and 6b. Upper Frac-
tion gave 6a (0.026 g, 18%). 1H NMR (400 MHz,
CDCl3): d 1.24–1.43 (2H, m, H-7), 1.54–1.66 (1H, m,
H-6ax), 2.03–2.06 (1H, m, H-6eq), 2.28 (1H, t,
J = 12.4 Hz, NCH2CH), 2.39 (1H, bs, H-5), 2.57–2.87
(6H, m, NCH2CH, NCH2CH2N, Ph–CH2), 2.98–3.01
(1H, m, H-9ax), 3.10 (1H, bd, J = 11.8 Hz,
NCH2CH2N), 3.22–3.25 (1H, m, H-9eq) 3.77 (1H, dt,
J = 4.8 Hz, J = 11.2 Hz, H-8ax), 3.84–3.91 (2H, m, CH-
H-7eq), 1.54–1.65 (1H, m, H-6ax), 2.22–2.27 (1H, m,
H-6eq), 2.34 (1H, dd, J = 2.8 Hz, J = 10.4 Hz,
NCH2CH), 2.46–2.49 (1H, m, NCH2CH2N), 2.64 (1H,
bs, H-5), 2.91–3.11 (6H, m, NCH2CH2N, NCH2CH,
H-9ax), 3.24–3.27 (1H, m, H-9eq) 3.72–3.83 (1H, m, H-
8ax), 3.88 (1H, d, J = 11.6 Hz, (Ph)2CH), 4.67 (1H, dd,
J = 3.6 Hz, J = 10.0 Hz, CHOH), 7.10–7.37 (15H, m,
25
D
ArH). ½aꢁ ¼ ðꢀÞ45:8ꢂ (c 0.52, MeOH). Free base was
converted into oxalate salt 193–195 ꢁC.
Analysis calculated for (C28H32N2O. 2(COOH)2,
0.3H2O) C, H, N.
OH, (Ph)2CH), 7.11–7.15 (2H, m, ArH), 7.19–7.31
25
D
(11H, m, ArH), 7.35–7.38 (2H, m, ArH). ½aꢁ (oxalate
salt) = (ꢀ)24.7ꢁ (c 0.42, MeOH).
5.10. Synthesis of (R)-2-((5S,8S)-8-benzhydryl-1,4-diaza-
bicyclo[3.3.1]nonane-2-yl)-1-4-fluorophenyl)ethanol (7c)
Analysis calculated for (C29H34N2O. 2(COOH)2) C, H,
N.
Compound 5 (0.060 g, 0.205 mmol) was reacted with
R-(ꢀ)-2-(4-fluorophenyl)oxirane (0.042 g, 0.307 mmol)
(Procedure A) to yield 7c (0.034 g, 39%). 1H NMR
(400 MHz, CDCl3): d 1.25–1.32 (1H, m, H-7ax), 1.35–
1.47 (1H, m, H-7eq), 1.54–1.64 (1H, m, H-6ax), 2.00–2.03
(2H, m, H-6eq), 2.32–2.38(1H, dd, J = 11.2 Hz,
J = 0.8 Hz, NCH2CH), 2.44 (1H, bs, H-5), 2.73 (1H, dd,
J = 3.6 Hz, J = 12.8 Hz, NCH2CH), 2.79–2.96 (3H, m,
NCH2CH2N), 3.02–3.06 (1H, m, H-9ax), 3.16–3.19 (1H,
bm, NCH2CH2N), 3.27–3.31 (1H, m, H-9eq), 3.75–3.86
(1H, m, H-8ax), 3.90 (1H, d, J = 11.2 Hz, (Ph)2CH), 4.66
Lower fraction gave 6b (0.024 g, 16%). 1H NMR
(400 MHz, CDCl3): d 1.22–1.29 (1H, m, H-7ax), 1.34–
1.42 (1H, m, H-7eq), 1.47–1.56 (1H, m, H-6ax), 2.02–
2.07 (1H, m, H-6eq), 2.20 (1H, dd, J = 10.8 Hz,
J = 2.4 Hz, NCH2CH), 2.48 (1H, bm, H-5), 2.67 (1H,
dd, J = 8.0 Hz, J = 5.6 Hz, NCH2CH), 2.75–3.10 (7H,
m, NCH2CH2N, Ph–CH2, H-9ax), 3.17–3.20 (1H, m,
H-9eq) 3.75 (1H, dt, J = 4.8 Hz, J = 11.3 Hz, H-8ax),
3.83–3.90 (2H, m, CH–OH, (Ph)2CH), 7.12–7.15 (2H,
m, ArH), 7.19–7.30 (11H, m, ArH), 7.33–7.38 (2H, m,
ArH). ½aꢁ (oxalate salt) = (ꢀ)31.2ꢁ (c 0.40, MeOH).
(1H, dd, J = 3.2 Hz, J = 10.8 Hz, CHOH), 7.03 (2H, t,
25
D
25
D
J = 8.4 Hz, ArH), 7.10–7.38 (12H, m, ArH). ½aꢁ (free
base) = (ꢀ)45.5ꢁ (c 0.57, MeOH). Free base was con-
verted into oxalate salt 189–191 ꢁC.
Analysis calculated for (C29H34N2O. 2(COOH)2) C, H,
N.
Analysis calculated for (C28H31FN2O. 2(COOH)2,
0.2H2O) C, H, N.
5.8. Synthesis of (R)-2-((5S,8S)-8-benzhydryl-1,4-diaza-
bicyclo[3.3.1]nonane-2-yl)-1-phenylethanol (7a)
5.11. Synthesis of (S)-2-((5S,8S)-8-benzhydryl-1,4-diaza-
bicyclo[3.3.1]nonane-2-yl)-1-4-fluorophenyl)ethanol (7d)
To a stirring solution of cis-(ꢀ)-8-benzydryl-1,4-diazabi-
cyclo[3.3.1]nonane 5 (0.065 g, 0.222 mmol) in dry etha-
nol was added R-(+)-2-phenyloxirane (0.04 g,
0.333 mmol) (Procedure A). The compound was purified
by flash column chromatography by using diethyl ether/
MeOH (9:1) to afford 7a (0.051 g, 56%). 1H NMR
(400 MHz, CDCl3): d 1.26–1.33 (1H, m, H-7ax), 1.38–
1.47 (1H, m, H-7eq), 1.54–1.63 (1H, m, H-6ax), 2.00–
2.03 (1H, m, H-6eq), 2.38–2.47 (2H, m, NCH2CH,
H-5), 2.77 (1H, dd, J = 3.6 Hz, J = 12.4 Hz, NCH2CH),
2.82–2.99 (3H, m, NCH2CH2N) 3.03–3.06 (1H, m, H-
9ax), 3.17–3.19 (1H, m, NCH2CH2N), 3.29–3.33 (1H,
m, H-9eq) 3.80 (1H, dt, J = 4.4 Hz, J = 10.8 Hz, H-8ax),
3.91 (1H, d, J = 11.6 Hz, (Ph)2CH), 4.69 (1H, dd,
Compound 5(0.070 g, 0.239 mmol)wasreactedwithS-(+)-
2-(4-fluorophenyl)oxirane (0.049 g, 0.358 mmol) (Proce-
1
dure A) to yield 7d (0.040 g, 39%). H NMR (400 MHz,
CDCl3): d 1.27–1.34 (1H, m, H-7ax), 1.37–1.49 (1H, m, H-
7eq), 1.59–1.68 (1H, m, H-6ax), 2.20–2.32 (2H, m, H-6eq,
NCH2CH), 2.45–2.49 (1H, m, NCH2CH2N), 2.62 (1H,
bs, H-5), 2.91–3.11 (5H, m, NCH2CH2N, NCH2CH, H-
9ax), 3.23–3.28 (1H, m, H-9eq), 3.75–3.82 (1H, m, H-8ax),
3.88 (1H, d, J = 11.2 Hz, (Ph)2CH), 4.64 (1H, dd,
J = 3.2 Hz, J = 10.0 Hz, CHOH), 6.99–7.04 (2H, m,
25
D
ArH), 7.10–7.37 (12H, m, ArH). ½aꢁ (free base) = (ꢀ)44.0ꢁ
(c 0.56, MeOH). Free base was converted into oxalate salt
191–193 ꢁC.
J = 3.2 Hz, J = 11.2 Hz, CHOH), 7.10–7.38 (15H, m,
25
D
ArH). ½aꢁ ¼ ðꢀÞ52:3ꢂ (c 0.52, MeOH). Free base was
converted into oxalate salt 194–197 ꢁC.
Analysis calculated for (C28H31FN2O. 2(COOH)2,
0.3H2O) C, H, N.
Analysis calculated for (C28H32N2O. 2(COOH)2) C, H, N.
5.12. Synthesis of 3-((1S,6S)-6-benzhydryl-2,5-diazabicy-
clo[3.3.1]nonane-2-yl)-1-(4-fluorophenyl)propan-1-one (8)
5.9. Synthesis of (S)-2-((5S,8S)-8-benzhydryl-1,4-diaza-
bicyclo[3.3.1]nonane-2-yl)-1-phenylethanol (7b)
Into a stirred solution of cis-(-)-8-benzydryl-1,4-diazabicy-
clo[3.3.1] nonane 5 (0.250 g, 0.854 mmol) in dry acetoni-
trile was added K2CO3 (0.354 g, 2.56 mmol) followed by
3-chloro-40-fluoro propiophenone (0.207 g, 1.11 mmol).
Catalytic amount of potassium iodide was added and the
Compound 5 (0.060 g, 0.205 mmol) was reacted with
S-(ꢀ)-2-phenyloxirane (0.036 g, 0.307 mmol) (Procedure
A) to yield 7b (0.045 g, 53%). 1H NMR (400 MHz,
CDCl3): d 1.25–1.34 (1H, m, H-7ax), 1.38–1.49 (1H, m,

2776
M. Mishra et al. / Bioorg. Med. Chem. 16 (2008) 2769–2778
reaction mixture was refluxed for 3 h under nitrogen atmo-
sphere. After evaporation of solvent, the residue was dis-
solved in water and extracted with CH2Cl2 (2 · 100 ml),
dried over Na2SO4, and evaporated. The compound was
purified by flash column chromatography using diethyl
ether/MeOH/Et3N (93:7:0.2) to afford 8 (0.260 g, 68%).
1H NMR (400 MHz, CDCl3): d 1.25–1.34 (1 H, m, H-
7ax), 1.34–1.45 (1H, m, H-7eq), 1.48–1.58 (1H, m, H-6ax),
2.20–2.23 (1H, m, H-6eq), 2.52 (1H, bs, H-5), 2.62–2.65
(1H, m, NCH2CH2), 2.80–3.16 (8H, m, NCH2CH2N,
NCH2CH2, CH2CO, H-9ax), 3.20–3.23 (1H, m, H-9eq)
3.77 (1H, dt, J = 4.4 Hz, J = 11.2 Hz, H-8ax), 3.89 (1H, d,
J = 11.8 Hz, (Ph)2CH), 7.08–7.15 (2H, m, ArH), 7.20–
7.28 (6H, m, ArH), 7.36 (2H, d, J = 7.2 Hz, ArH), 7.95–
7.99 (2H, dt, J = 2.0 Hz, J = 5.2 Hz, ArH).
HPLC using a normal phase column (Nova-pack silica
6 lm). Hexanes/2-propanol/Et3N (92:8:0.3) was used as
a mobile phase with a flow rate of 12 mL/min. The
two fractions were eluted with retention time 2.83 min
and 3.30 min for 10a and 10b, respectively.
Eluting first was 10a (0.115 g, 42%). 1H NMR (400 MHz,
CDCl3): d 0.79 (3H, s, CH3), 0.97 (3H, s, CH3), 1.07 (3H,
s, CH3), 1.24–1.49 (2H, m, H-7ax, H-7eq), 1.62–1.68 (1H,
m, H-6ax), 1.84–2.07 (3H, m, CH2CHO, H-6eq), 2.16–
2.49 (5H, m, H-5, CCH2C, NCH2CH2N), 2.59–2.63
(1H, m, NCH2CH2N), 2.68–2.75 (1H, m, NCH2CH2),
2.86–2.98 (2H, m, NCH2CH2, H-9ax), 3.09–3.12 (1H,
m, NCH2CH2N), 3.18–3.21 (1H, m, H-9eq), 3.75 (1H,
dt, J = 4.4 Hz, J = 11.2 Hz, H-8ax), 3.87 (1H, d,
J = 11.2 Hz, (Ph)2CH), 5.94 (1H, t, J = 7.2 Hz, CHO-
CO), 6.97–7.03 (2H, m, ArH), 7.09–7.14 (2H, m, ArH),
7.19–7.27 (6H, m, ArH), 7.30–7.37 (4H, m, ArH).
5.13. Synthesis of 3-((1S,6S)-6-benzhydryl-2,5-diazabicy-
clo[3.3.1]nonane-2-yl)-1-(4-fluorophenyl)propan-1(R&S)-
ol (9)
Eluting second was 10b (0.105 g, 38%). 1H NMR
(400 MHz, CDCl3): d 0.88 (3H, s, CH3), 0.98 (3H, s,
CH3), 1.09 (3H, s, CH3), 1.23–1.52 (2H, m, H-7ax, H-
7eq), 1.62–1.68 (1H, m, H-6ax), 1.84–1.99 (2H, m,
CH2CHO), 2.04–2.07 (1H, m, H-6eq), 2.12–2.52 (5H, m,
H-5, CCH2C, NCH2CH2N), 2.68–2.75 (1H, m,
NCH2CH2), 2.84–2.92 (1H, m, NCH2CH2), 2.95–2.99
(1H, m, H-9ax), 3.08–3.11 (1H, m, NCH2CH2N), 3.18–
3.22 (1H, m, H-9eq), 3.76 (1H, dt, J = 4.8 Hz,
J = 11.2 Hz, H-8ax), 3.87 (1H, d, J = 11.6 Hz, (Ph)2CH),
5.92 (1H, t, J = 6.8 Hz, CHOCO), 6.98–7.03 (2H, m,
ArH), 7.09–7.15 (2H, m, ArH), 7.19–7.37 (10H, m, ArH).
To
a stirred solution of compound 8 (0.250 g,
0.564 mmol) dissolved in 25 ml of THF was added
NaBH4 (0.025 g, 0.677 mmol) followed by addition of
0.5 ml of water. The reaction mixture was stirred for 3 h
under nitrogen atmosphere at RT. Water (5 ml) was
added next into the reaction mixture. The solvent was
evaporated and the residue was dissolved in water and ex-
tracted with CH2Cl2 (2 · 50 ml), dried over Na2SO4, and
evaporated in vacuo. The crude product was purified by
flash column chromatography using diethyl ether/
1
MeOH/Et3N (93:8:0.2) to afford 9 (0.195 g, 79%). H
NMR (400 MHz, CDCl3): d 1.25–1.41 (2H, m, H-7ax,
H-7eq), 1.47–1.95 (3H, m, CH2CHOH, H-6ax), 2.09–2.18
(1H, m, H-6eq), 2.59–2.96 (6H, m, H-5, NCH2CH2,
NCH2CH2N), 3.04 (1H, d, J = 13.2 Hz, H-9ax), 3.12–
3.25 (2H, m, NCH2CH2N, H-9eq), 3.73–3.82 (1H, m, H-
8ax), 3.88 (1H, dd, J = 1.6 Hz, J = 11.6 Hz, (Ph)2CH),
4.84–4.95 (1H, m, CHOH), 7.00 (2H, dt, J = 1.6 Hz,
J = 8.4 Hz, ArH), 7.10–7.16 (2H, m, ArH), 7.19–7.37
(10H, m, ArH).
5.15. Procedure B. Synthesis of (ꢀ)11a
The first eluting camphanic ester fraction 10a (0.075 g,
0.120 mmol) was hydrolyzed with K2CO3 (20 mg) in
methanol (20 ml) at room temperature for 12 h. Methanol
was evaporated, water (20 ml) was added, and the prod-
uct was extracted with ethyl acetate (2 · 50 ml). Organic
layer was dried over Na2SO4 and evaporated under re-
duced pressure. The crude product was purified by flash
column chromatography over silica using diethyl ether/
5.14. Synthesis of 3-((1S,6S)-6-benzhydryl-2,5-diazabi-
cyclo[3.3.1]nonane-2-yl)-1-(4-fluorophenyl)propyl-4,7,7-
trimethyl-3-oxo-2-oxabicyclo[2.2.1]heptane-1-carboxyl-
ate (10a and 10b)
1
MeOH/Et3N (93:8:0.2) to afford 11a (0.048 g, 90%). H
NMR (400 MHz, CDCl3): d 1.25–1.44 (2H, m, H-7ax,
H-7eq), 1.54–1.69 (2H, m, CH2CHOH, H-6ax), 1.80–1.90
(1H, m, CH2CHOH), 2.15–2.18 (1H, m, H-6eq), 2.63
(1H, bs, H-5), 2.67–2.974 (1H, m, NCH2CH2), 2.79–
2.95 (4H, m, NCH2CH2, NCH2CH2N), 3.04 (1H, d,
J = 13.2 Hz, H-9ax), 3.13–3.18 (1H, m, NCH2CH2N),
3.22–3.25 (1H, m, H-9eq), 3.79 (1H, dt, J = 4.8 Hz,
J = 11.6 Hz, H-8ax), 3.88 (1H, d, J = 11.6 Hz, (Ph)2CH),
4.86 (1H, dd, J = 2.4 Hz, J = 9.6 Hz, CHOH), 7.00 (2H,
To a stirred solution of 3-((1S,6S)-6-benzhydryl-2,5-
diazabicyclo [3.3.1]nonane-2-yl)-1-(4-fluorophenyl)pro-
pan-1 (R&S)-ol 9 (0.195 g, 0.438 mmol), Et3N (0.088 g,
0.876 mmol), and DMAP (10 mg) in 100 ml of dry
CH2Cl2 under nitrogen atmosphere at 0 ꢁC was added
(1S)-(ꢀ)-camphanic chloride (0.123 g, 0.569 mmol) dis-
solved in 10 ml dry CH2Cl2. The reaction mixture was
stirred at 0 ꢁC for 30 min and at room temperature for
3 h under nitrogen. The reaction mixture was quenched
with water (20 ml) and then diluted with CH2Cl2
(50 ml). Organic layer was separated and the aqueous
layer was extracted with CH2Cl2 (2 · 50 ml), dried over
Na2SO4, and evaporated in vacuo. The crude product
was purified by flash column chromatography over silica
gel using diethyl ether/MeOH (95:5) to afford mixture of
two diastereoisomers 10a and 10b (0.250 g, 91%). The
diastereoisomers were separated by semipreparative
t, J = 8.8 Hz, ArH), 7.11–7.16 (2H, m, ArH), 7.19–7.37
25
D
(10H, m, ArH). ½aꢁ ¼ ðꢀÞ38:7ꢂ (c 1.08, MeOH). Free
base was converted into oxalate salt 191–193 ꢁC.
Analysis calculated for (C29H33FN2O. 2(COOH)2,
1.5H2O) C, H, N.
5.16. Synthesis of (ꢀ)11b
The second eluting fraction 10b (0.105 g, 0.168 mmol)
was hydrolyzed with K2CO3 (20 mg) in methanol

M. Mishra et al. / Bioorg. Med. Chem. 16 (2008) 2769–2778
2777
1
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(20 ml) to afford 11b (0.071 g, 94%) (Procedure B). H
NMR (400 MHz, CDCl3): d 1.24–1.43 (2H, m, H-7ax,
H-7eq), 1.48–1.54 (1H, m, H-6ax), 1.71–1.79 (1H, m,
CH2CHOH), 1.88–1.95 (1H, m, CH2CHOH), 2.09–
2.12 (1H, m, H-6eq), 2.60–2.66 (2H, m, H-5, NCH2CH2),
2.76–2.97 (4H, m, NCH2CH2, NCH2CH2N), 3.04 (1H,
d, J = 13.2 Hz, H-9ax), 3.12–3.15 (1H, m, NCH2CH2N),
3.21–3.24 (1H, m, H-9eq), 3.78 (1H, dt, J = 4.8 Hz,
J = 11.6 Hz, H-8ax), 3.88 (1H, d, J = 11.6 Hz, (Ph)2CH),
4.94 (1H, dd, J = 3.2 Hz, J = 7.6 Hz, CHOH), 7.00 (2H,
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25
D
(10H, m, ArH). ½aꢁ ¼ ðꢀÞ56:8ꢂ (c 1.0, MeOH). Free
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5.17. Transporter assays
The affinity of test compounds in binding to rat DAT and
in inhibiting monoamine uptake was monitored as de-
scribed by us previously.21 Briefly, rat striatum was used
for measuring binding of [3H]WIN 35,428 by DAT and
uptake of [3H]DA by DAT. Rat cerebral cortex was used
for assessing uptake of [3H]serotonin by SERT and hip-
pocampus for uptake of [3H]NE by NET. Nonspecific
binding at DAT was defined with 100 lM cocaine; non-
specific uptake at DAT, SERT, and NET with 100 lM co-
caine, 10 lM citalopram, and 10 lM desipramine,
respectively. Test compounds were dissolved in dimethyl-
sulfoxide (DMSO), diluted out in 10% (v/v) DMSO, and
added to assays resulting in a final DMSO concentration
of 0.5% which by itself did not interfere with the assays. At
lease five triplicate concentrations of each test compound
were studied, spaced evenly around the IC50 value. The
latter was estimated by nonlinear computer curve-fitting
procedures and converted to Ki with the Cheng–Prusoff
equation as described previously.16
8. Sogaard, U.; Michalow, J.; Butler, B.; Lund Laursen,
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Dopamine transporter as target for drug development of
cocaine dependence medications. Eur. J. Pharmacol. 2003,
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13. Dutta, A. K.; Xu, C.; Reith, M. E. Structure–activity
Acknowledgment
relationship
studies
of
novel
4-[2-[bis(4-fluoro-
phenyl)methoxy]ethyl]-1-(3-phenylpropyl)piperidine ana-
logs: synthesis and biological evaluation at the dopamine
and serotonin transporter sites. J. Med. Chem. 1996, 39,
749–756.
This work was supported by the National Institute on
Drug Abuse, Grant No. DA 12449 (AKD).
14. Dutta, A. K.; Coffey, L. L.; Reith, M. E. Highly selective,
novel analogs of 4-[2-(diphenylmethoxy)ethyl]-1-benzylpi-
peridine for the dopamine transporter: effect of different
aromatic substitutions on their affinity and selectivity. J.
Med. Chem. 1997, 40, 35–43.
15. Dutta, A. K.; Fei, X. S.; Beardsley, P. M.; Newman, J. L.;
Reith, M. E. Structure–activity relationship studies of 4-
[2-(diphenylmethoxy)ethyl]-1-benzylpiperidine derivatives
and their N-analogues: evaluation of O- and N-analogues
and their binding to monoamine transporters. J. Med.
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Supplementary data
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/
j.bmc.2008.01.009.
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