Interaction of cis-(6-benzhydrylpiperidin-3-yl)benzylamine analogues with monoamine transporters: Structure-activity relationship study of structurally constrained 3,6-disubstituted piperidine analogues of (2,2-diphenylethyl)-[1-(4-fluorobenzyl)piperidin-

Article abstract of DOI:10.1021/jm020561w

To explore structure-activity relationships (SAR) of a novel conformationally constrained lead cis-3,6-disubstituted piperidine derivative derived from (2,2-diphenylethyl)-[1-(4-fluorobenzyl)-piperidine-4-ylmethyl]amine (I), a series of compounds was synt

Full text of DOI:10.1021/jm020561w

J . Med. Chem. 2003, 46, 2205-2215
2205
In ter a ction of cis-(6-Ben zh yd r ylp ip er id in -3-yl)ben zyla m in e An a logu es w ith
Mon oa m in e Tr a n sp or ter s: Str u ctu r e-Activity Rela tion sh ip Stu d y of
Str u ctu r a lly Con str a in ed 3,6-Disu bstitu ted P ip er id in e An a logu es of
(2,2-Dip h en yleth yl)-[1-(4-flu or oben zyl)p ip er id in -4-ylm eth yl]a m in e
Rohit B. Kolhatkar,† Sujit K. Ghorai,† Clifford George,‡ Maarten E. A. Reith,§ and Aloke K. Dutta*,†
Wayne State University, Department of Pharmaceutical Sciences, Detroit, Michigan 48202, Laboratory for the Structure of
Matter, Code 6030, Naval Research Laboratory, Washington, D. C. 20735, and University of Illinois, College of Medicine,
Department of Biomedical and Therapeutic Sciences, Peoria, Illinois 61656
Received December 20, 2002
To explore structure-activity relationships (SAR) of a novel conformationally constrained lead
cis-3,6-disubstituted piperidine derivative derived from (2,2-diphenylethyl)-[1-(4-fluorobenzyl)-
piperidine-4-ylmethyl]amine (I), a series of compounds was synthesized by derivatizing the
exocyclic N-atom at the 3-position of the lead. This study led to the formation of substituted
phenyl and heterocyclic derivatives. All novel compounds were tested for their affinity at the
dopamine transporter (DAT), serotonin transporter (SERT), and norepinephrine transporter
(NET) in the brain by measuring their potency in competing for the binding of [3H]WIN 35
428, [3H]citalopram, and [3H]nisoxetine, respectively. Selected compounds were also evaluated
for their activity in inhibiting the uptake of [3H]DA. The SAR results demonstrated that the
nature of substitutions on the phenyl ring is important in activity at the DAT with the presence
of an electron-withdrawing group having the maximum effect on potency. Replacement of the
phenyl ring in the benzyl group by heterocyclic moieties resulted in the development of
compounds with moderate activity for the DAT. Two most potent racemic compounds were
separated by a diastereoisomeric separation procedure, and differential affinities were observed
for the enantiomers. Absolute configuration of the enantiomers was obtained unambiguously
by X-ray crystal structural study. One of the enantiomers, compound S,S-(-)-19a , exhibited
the highest potency for the DAT (IC50 ) 11.3 nM) among all the compounds tested and was as
potent as GBR 12909 (1-[2-[bis(4-fluorophenyl)methoxy]ethyl]-4-(3-phenylpropyl)piperazine).
However, the compound (-)-19a was more selective than GBR 12909 in binding to the DAT
compared with binding to the SERT and NET. The present results establish the newly developed
3,6-disubstituted piperidine derivatives as a novel template for high-affinity inhibitors of DAT.
Structurally these molecules are more constrained compared to our earlier flexible piperidine
molecules and, thus, should provide more insights about their bioactive conformations.
In tr od u ction
mice and behavioral intervention experiments indicated
that the serotonergic system might also play a role in
(-)-Cocaine is a naturally occurring alkaloid isolated
from Erythroxylon coca and has been around in our
society for over a century.1,2 Harmful addictive effect of
cocaine was first recognized by Sigmund Freud almost
a century ago. Early medicinal application of cocaine
was mainly restricted in its use as a local anesthetic
for minor surgery. Cocaine has continued to be abused
through out the world due to its powerful reinforcing
effect and has impacted the public health system to a
significant extent.3 The results of many biochemical and
pharmacological experiments demonstrated cocaine’s
interaction with the three monoamine neurotransporter
systems in the brain while the generation of cocaine’s
powerful reinforcing effect is thought to be mediated by
binding to the dopamine transporter (DAT) system in
the CNS.4-7 However, recent results from knock out
the reinforcing effect of cocaine.8,9
DAT has been a target for the development of
medications for cocaine addiction for some time.10 DAT
was cloned a decade ago and was shown to contain a
putative 12-transmembrane (TM) domain protein.11
DAT is a presynaptically located protein which trans-
locates extracellular DA into nerve endings of DA
neurons. Molecular biological studies on DAT with the
help of site-directed mutagenesis demonstrated the
potential of developing a cocaine antagonist.12,13 A large
number of studies have been carried out with various
DAT mutants and cocaine analogues. These studies
indicated that DAT portions of TM domains involved
in binding DA and cocaine analogues are not exactly
identical raising the possibility of developing a cocaine
antagonist.12-14 However, no single amino acid residue
has yet been shown to be differentially involved in
cocaine and dopamine binding. So far no such studies
have been carried out systematically with other classes
of nontropane DAT blockers which might shed more
light into this aspect. Finally, there is yet a compound
* Correspondence address: Aloke K. Dutta, Ph.D., Department of
Pharmaceutical Sciences, Applebaum College of Pharmacy & Health
Sciences, Rm# 3128, Detroit, MI 48202, Tel: 1-313-577-1064, Fax:
1-313-577-2033, e-mail: adutta@ea.cphs.wayne.edu.
† Wayne State University.
‡ Naval Research Laboratory.
§ University of Illinois.
10.1021/jm020561w CCC: $25.00 © 2003 American Chemical Society
Published on Web 04/19/2003

2206 J ournal of Medicinal Chemistry, 2003, Vol. 46, No. 11
Kolhatkar et al.
to be found which exhibits the property of interfering
with cocaine binding while sparing the interaction
between DA and DAT. A potential application of an
antagonist against cocaine binding is the treatment of
cocaine overdose toxicity. On the other hand, a partial
agonist with slower onset and longer duration of action
than cocaine might find application in a substitution
maintenance treatment program for cocaine depen-
dence. Currently both cocaine antagonists and partial
agonists are being pursued as probable pharmacothera-
peutic treatment agents.
F igu r e 1. Molecular structure of dopamine transporter
blockers.
Various molecules belonging to diverse chemical
structures have been developed for the DAT. They can
be classified as tropane, benztropine, mazindol, or
methylphenidate derivatives, and as either piperazine
or piperidine derivatives of GBR 12935.15-26 This wide
variety of molecular classes might indicate the presence
of flexible binding pockets in the receptor which can
accommodate the different molecular templates. This
should increase the likelihood of developing a cocaine
antagonist.
exhibited more activity and selectivity for the DAT.35
The active cis version represents a considerable struc-
tural rigidity compared to our original piperidine ana-
logue I, Figure 1. Moreover, this molecule also repre-
sents a novel molecular template as a 3,6-disubstituted
piperidine derivative for the first time was shown to
have affinity for DAT.
In our current study, further structural variations of
our initial lead compound (()-11 (Figure 1) were un-
dertaken to develop a biological receptor binding profile
of this novel 3,6-disubstituted piperidine template. In
particular, experiments were aimed at exploring the
effect of different substitutions with the variations of
steric and electronic effects on the exocyclic N-atom of
the cis compound.
In our effort to develop potent and selective blockers
for the DAT, a large number of potent piperidine
analogues of GBR 12935 was synthesized and biologi-
cally characterized.27-31 Most of these molecules have
a high degree of structural flexibility, and consequently,
it is rather difficult to elucidate their biologically active
conformational structure(s) which might interact with
the target receptor. It is quite possible that these flexible
piperidine analogues might interact with the trans-
porter molecule via an induced-fit conformational change
conforming them to a right orientation for their interac-
tion with the DAT.32 Previous studies in conformation-
ally constrained molecular structures indicated that
rigidification of ligand molecules can potentially influ-
ence their biological activity either by decreasing or
increasing their potencies and selectivities for the target
receptors. From the thermodynamic point of view, a
conformationally constrained molecule with correct bio-
active conformation should exhibit enhanced affinity as
the reduction in flexibilities reduces loss of entropy upon
binding normally occurring when a rotationally free
compound becomes more restricted upon alignment with
the binding site.33 In addition, such transformation is
also a powerful tool to illustrate possible bioactive
conformation of a flexible parent molecule. In the opioid
area, conformational constrained versions of opioid
peptides led to high degree of receptor selectivity and
potency.34 GBR 12935 and related molecules are known
for the flexibility in their molecular structures. Struc-
turally constrained versions of these molecules might
produce interesting properties as they might display
altered pharmacological and pharmacokinetic proper-
ties. As a result of such transformations, it might
improve their overall pharmacological properties which
may include their blood-brain barrier crossing ability.
Ch em istr y
The synthesis of our target molecules is shown in
Schemes 1-4 which describe mostly a linear step
synthesis process. In Scheme 1, the starting 2-chloro-
5-nitropyridine was reacted with diphenylacetonitrile
under phase-transfer conditions consisting of toluene,
tetrabutylammonium fluoride, and 50% NaOH to fur-
nish (5-nitro-pyridin-2-yl)diphenylacetonitrile 2 in very
good yield.35 Acidic hydrolysis of nitrile 2 by brief
treatment with aqueous sulfuric acid produced amide
intermediate 3 in good yield.36 The nitro group of 3 was
first reduced by hydrogenation in the presence of 10%
Pd-C as a catalyst producing amino-amide 4 in almost
quantitative yield. Then 4 was hydrolyzed and decar-
boxylated to 5 by refluxing with 37% HCl in excellent
yield. Compound 5 was next transformed into acetyl
derivative by reacting with acetyl chloride in excellent
yield, and the acetyl derivative 6 was next hydrogenated
in the presence of platinum oxide catalyst into cis and
trans derivatives of 3,6-disubstituted piperidine mol-
ecules 7a and 7b which were separated by column
chromatography. As described in Supporting Informa-
1
tion, H NMR spectra of 7a and 7b clearly indicate cis
and trans orientation of these two compounds.
Racemic cis-7a was next used as a starting precursor
for the synthesis of various other analogues by deriva-
tizing the exocyclic N-atom in 7a as shown in Scheme
3. Compounds 13a -i were produced by initial hydroly-
sis of cis-7a to liberate cis-diamine 12 which on reduc-
tive amination with appropriate aldehyde produced the
targets 13a -i. The precursor for 13f, 2-substituted
indole aldehyde 17, was synthesized from the starting
material 15 via Weinreb amide intermediate 16 by
following a published procedure.38 Synthesis of 13j was
carried out by first acylation of 12 followed by reduction
of the intermediate 14 with borane-THF complex.
In our effort to design structurally constrained pip-
eridine analogues of GBR 12935, we embarked on a
molecular design which transformed one of our flexible
analogues into a more structurally constrained novel
3,6-piperidine derivative (Figure 2). Thus, in our earlier
reported study, the synthesis of two isomeric 3,6-
disubstituted cis and trans piperidine derivatives was
reported, from which cis-3,6-disubstituted compound

Structurally Constrained Inhibitors of Monoamine Transporters J ournal of Medicinal Chemistry, 2003, Vol. 46, No. 11 2207
F igu r e 2. Rationale for structural transformation of flexible piperidine analogue I to relatively more constrained cis- and trans-
derivatives.
Sch em e 1
Sch em e 2
Subsequently, resolution of one of the lead compounds
(()-11 was carried out which is shown in Scheme 2. The
resolution was complicated due to the presence of the
two basic N-atoms in the molecule. In our initial attempt
of reaction of (()-11 with an optically active acid a
complex diastereomeric reaction mixture resulted which
was difficult to separate. On the other hand, treatment
with optically active tartaric acid did not yield any good
results either. At that point, it was decided to go ahead
with the racemic compound cis-(()-7a for enantiomeric
separation. Reaction of (()-7a with R -(-)-methoxy-
phenylacetyl chloride produced two diastereomeric com-
pounds 8a and 8b which were separated by column
chromatography. Next each one of these two diastere-
omers was treated separately to produce the optically
active target compounds. Thus, treatment of 8a with
HCl (2 N) liberated amine 9a which on reductive
amination with p-fluorobenzaldehyde under standard

2208 J ournal of Medicinal Chemistry, 2003, Vol. 46, No. 11
Kolhatkar et al.
Sch em e 3
condition produced N-benzylated 10. Final hydrolysis
of the mandalate moiety was carried out in two steps
which involved first basic hydrolysis with potassium
tert-butoxide followed by acidic hydrolysis of the inter-
mediate aldehyde to produce the final optically active
amine (-)-11.39a,b Similarly the other diastereomer 8b
was subjected to the same sequence of reactions to
produce (+)-11. Separation of racemic (()-13a , however,
was carried out in a slightly modified way and is shown
in Scheme 4. In this modified procedure optically active
diamine 18a was first produced from 9a by hydrolysis
of the mandalate moiety as described above. The
compound 18a was then subjected to reductive amina-
tion with p-cyanobenzaldehyde to produce optically pure
target (-)-19a . The other enantiomer (+)-19b was
produced in the similar fashion. This modified procedure
was adopted to avoid any unwanted hydrolysis of the
cyano group during the hydrolysis of the mandalate
group.
lography. For this purpose, one of the diastereomeric
intermediates formed in the separation of (()-11 and
(()-13a was crystallized for X-ray study. Thus, the more
polar diastereomer 8b was first hydrolyzed with HCl
(2 N) to hydrolyze selectively the exocyclic N-acetyl
moiety to liberate amine 9b which was then crystallized
from methanol/water (2:1) mixture for X-ray structure
evaluation. The absolute configuration assignment from
this X-ray structure determination corresponded to a
designation of R,R at the 3 and 6 carbon centers in the
piperidine ring of the compound 9b, Figure 3. Conse-
quently, (+)-11 and (+)-19b which are derived directly
from the functionalization of the exocyclic amine of 9b,
have also the R,R-configuration at the 3 and 6 carbon
centers. The corresponding enantiomers (-)-11 and (-)-
19a must then have S,S-configurations at their asym-
metric 3,6-centers.
Resu lt a n d Discu ssion
The absolute configurations of the enantiomers of the
compounds 11 and 13a was evaluated by X-ray crystal-
Our attempt to derive conformationally constrained
versions of piperidine analogues of GBR 12935 led us
Sch em e 4

Structurally Constrained Inhibitors of Monoamine Transporters J ournal of Medicinal Chemistry, 2003, Vol. 46, No. 11 2209
Ta ble 1. Affinity of Drugs at the Dopamine, Serotonin, and Norepinephrine Transporters in Rat Striatum and in Inhibition of DA
Reuptake
DAT binding, IC50
,
SERT binding, IC50
,
NET binding, IC50
,
DAT uptake, IC50
nM, [3H]DA a
,
compd
cocaine
GBR 12909
I
(()-11
(-)S,S-11
(+)R,R-11
13a
13b
13c
13d
13e
13f
13g
13h
13i
13j
(-)S,S-19a
(+)R,R-19b
nM, [3H]WIN 35, 428a
nM, [3H]citaloprama
nM, [3H]nisoxetinea
266 ( 37b
10.6 ( 1.9b
19.7 ( 1.4b
32.5 ( 12.6
33.8 ( 5
737 ( 160
132 ( 0
3530 ( 550
496 ( 22
6.63 ( 0.43
49.6 ( 7.2
45.7 ( 5.1
53.8 ( 7.4
142 ( 25
30.2 ( 5.2
77.0 ( 9.7
137 ( 46
1110 ( 120
1020 ( 70
1420 ( 560
2290 ( 230
3200 ( 940
1590 ( 140
4730 ( 1080
1050 ( 460
3790 ( 1170
1010 ( 490
612 ( 130
1110 ( 60
201 ( 13
2220 ( 590
1330 ( 120
3540 ( 640
1130 ( 250
2250 ( 490
3650 ( 1110
2770 ( 680
3010 ( 950
1800 ( 280
2130 ( 110
1040 ( 110
862 ( 57
229 ( 17
31.5 ( 5.3
63.5 ( 3.2
267 ( 91
515 ( 130
834 ( 70
95.4 ( 20.2
114 ( 10.6
47.5 ( 6.2
65.9 ( 8.2
173 ( 4
11.3 ( 0.9
109.0 ( 16.7
51.0 ( 21.9
40.5 ( 21.8
2190 ( 80
434 ( 27
1550 ( 420
1740 ( 100
1670 ( 90
16600 ( 410
9.10 ( 1.86
152 ( 41
a
For binding, the DAT was labeled with [3H]WIN 35, 428, the SERT with [3H]citalopram and the NET with [3H]nisoxetine. For uptake
by DAT, [3H]DA accumulation was measured. Results are average ( SEM of three to eight independent experiments assayed in triplicate.
bSee reference 30.
piperidine analogues, similar 4-cyanophenyl and 3,4-
difluorophenyl substitutions resulted in generation of
potent compounds for the DAT.28,30 In fact, a cyano-
substituted derivative, thus produced from our earlier
study, was turned out to be one of the most potent and
selective compounds for the DAT.30 In the present study,
racemic cyano 13a exhibited the highest activity (IC50
) 31.5 nM, Table 1), and thus, indicated a similar SAR
result. As cyano is a strong electron-withdrawing group,
the effect of this group on the aromatic ring might have
positively influenced the interaction with DAT. On the
other hand, the presence of an electron-donating meth-
oxy group in compound 13h also produced a potent
compound for the DAT (IC50 ) 47.5 nM). The same
relative decrease in potency for the DAT from changing
an electron-withdrawing to an electron-donating groups
was also maintained in our flexible analogues. However,
F igu r e 3. The molecular structure and numbering scheme
as opposed to our earlier results, the present data
for compound 9b with displacement ellipsoids drawn at the
indicate that the presence of either electron-withdraw-
30% probability level.
ing or electron-donating groups improve activity for
DAT in these molecules compared to the unsubstituted
to design and synthesize two preliminary molecules as
reported earlier.35 Further SAR exploration on our
initial lead structure was taken up to better understand
its structural and functional properties in interacting
with monoamine transporter systems. In this report,
results of an SAR study conducted through derivatiza-
tion of the exocyclic N-atom at the 3-position of the cis-
isomer is presented. Differently substituted benzyl
derivatives along with bioisosteric heterocyclic replace-
ment were introduced on the N-atom. The effect of these
different substitutions on biological activity will enable
us to understand the roles of steric and electronic factors
and the role of bioisosteric heterocyclic moieties at this
molecular center in interacting with the DAT. Also
comparison of these results with our previously devel-
oped more flexible piperidine analogues will enable us
to better understand the mode of binding interactions.
Replacement of the 4-fluorophenyl ring by 4-cy-
anophenyl, 3,4-difluorophenyl, 4-methoxyphenyl, and
unsubstituted phenyl groups resulted in the production
of potently active to moderately active compounds in
interacting with DAT. In our earlier study with flexible
phenyl ring 13g. An interesting observation was made
when the methoxy group in compound 13h was con-
verted into a hydroxyl functionality in 13i. This trans-
formation resulted in 5.5-fold increase in NET activity
for 13i compared to 13h (IC50 of 201 vs 1110 nM),
indicating the possible involvement of an H-bond inter-
action emanating from the hydroxyl functionality in 13i
with the NET. Overall rank order of DAT activity of the
substituted benzyl derivatives is as follows: 4-Ph-CN
(13a ) > 4-Ph-F (11) > 4-Ph-OCH3 (13h ) > 3,4-bis-Ph-F
(13b) > 4-Ph-OH (13i) > Ph (13g).
Replacement of the phenyl group by bioisosteric
heterocyclic moieties resulted in 13c-f. In our previous
study with the flexible piperidine analogues, thiophene
and benzothiophene moieties were introduced as the
bioisosteric replacement for the phenyl ring. In that
study, the thiophene ring turned out to be the most
potent bioisostere. In the current study, in addition to
thiophene and benzothiophene rings, an indole moiety
was also included for such bioisosteric replacement.
Such replacement mostly produced weakly active to

2210 J ournal of Medicinal Chemistry, 2003, Vol. 46, No. 11
Kolhatkar et al.
Ta ble 2. Selectivity of Various Ligands for Their Activity at
Monoamine Transporters
nM and 109 nM, respectively, for the (+)-isomers). Thus,
appreciable separation of DAT activity was observed
between the two enantiomers which might be indicative
of structural rigidity resulting in a better fit selectively
for one of the enantiomers. The enantiomer (-)-S,S-19a
turned out to be the most potent compound developed
in the current series.
Selected compounds showing relatively higher po-
tency for the DAT were tested in the DA uptake
inhibition assay. For the most part, binding and uptake
activity correlated very well with compound (-)-19a
exhibiting the highest DA uptake inhibitory activity
(IC50 ) 9.10 nM). No significant differential uptake and
binding activity was observed for any one of these
compounds, providing no indication for potential cocaine
antagonist activity.
SERT binding/ NET binding/ [3H]DA uptake/
compound
DAT binding
DAT binding
DAT binding
GBR 12909
I
11
(-)-11
(+)-11
13a
13b
13c
13d
13e
13f
13g
13h
13i
13j
12
7
47
56
31
42
10
100
25
18
2
4.5
11
5.4
23
3
0.62
2.5
1.4
68
39
15
36
35
14
5.4
3.6
19
19
22
13
13
38
14
1.6
0.62
0.95
1.2
0.53
0.85
10
148
15
(-)-S,S-19a
(+)-R,R-19b
0.8
1.4
Con clu sion
In this SAR study, 3,6-disubstituted piperidine de-
rivatives were further established as a novel template
for DAT. Exploration of various substituents on the
exocyclic N-atom produced potent and selective com-
pounds for the DAT. The optically active (-)-S,S-19a
with an electron-withdrawing cyano substituent turned
out to be the most potent DAT compound with a potency
comparable to that of GBR 12909. However, it was more
selective than GBR 12909 for binding to the DAT when
compared with SERT and NET (Table 2). These novel
molecules are structurally constrained versions of our
earlier flexible compounds and, thus, reflect more closely
to their bioactive conformers. Our ongoing studies to
probe and identify further active molecular determi-
nants will shed more light on their mode of interactions
with the DAT in comparison to that of the flexible
piperidine analogues. In this regard, our photoaffinity
ligand binding study with a flexible piperidine deriva-
tive demonstrated dual incorporation into two regions
that are distal in the primary sequence of DAT.41
Similar experiments will be carried out with a suitable
photoaffinity ligand derived from the current structur-
ally constrained series allowing comparison of sites of
incorporation.
moderately active compounds for the DAT. Unlike our
earlier thiophene derivative, in the current series the
thiophene version was much less potent. Interestingly,
compounds 13f and 13e which are the positional iso-
mers of 2- and 3-substituted indole derivatives, exhib-
ited differential activities. Thus, the compound 13f
exhibited approximately 9-fold more activity for the
DAT compared to 13e (95.4 nM vs 834 nM, Table 1).
This differential activity can probably be attributed to
the generation of different electronic effects arising from
substitutions at the two different positions in the indole
ring since molecular orbital calculation demonstrated
that the C-3 of the indole ring carries a greater
π-electron density than the C-2 position.40 Altenatively,
it may be due to steric or positional effects which
produced unfavorable interactions with the DAT in the
case of the 3-substituted derivative 13e. All heterocyclic
analogues showed moderate to appreciable selectivity
for the DAT when their binding was compared with that
to SERT and NET (Table 2).
A drop in DAT activity was observed in compound 13j
compared to 11 when 4-fluorobenzyl was replaced by
4-fluorophenylethyl moiety (32.5 nM vs 173 nM). This
result was somewhat surprising and contrasted to
earlier results found in our flexible piperidine analogues
where no such drop in activity was observed.27 In fact,
replacement of the methylene linker in the N-benzyl
moiety by either ethyl or propyl linker produced some
of the most potent DAT blockers in structurally flexible
piperidine derivatives.29 As it was eluded earlier, this
might be an indication of the role of an induced-fit
mechanism in the binding interaction, resulting in
production of receptor bound conformation for our
flexible analogues which might be more restricted in our
current molecules due to structural rigidity. Another
possibility is that with the current structural modifica-
tions, these new molecules might bind to different sites
on the DAT. This is a possibility our future experiments
will address.
Exp er im en ta l Section
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 Baker Silica Gel 40 mM.
1H NMR spectra were routinely obtained at GE-300 and 400
MHz FT NMR. The NMR solvent 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.
[3H]WIN 35,428 (86.0 Ci/mmol), [3H]nisoxetine (80.0 Ci/
mmol), and [3H]dopamine (48.2 Ci/mmol) were obtained from
Dupont-New England Nuclear (Boston, MA). [3H]Citalopram
(85.0 Ci/mmol) was from Amersham Pharmacia Biotech Inc.
(Piscataway, NJ ). Cocaine hydrochloride was purchased from
Mallinckrodt Chemical Corp. (St. Louis, MO). WIN 35,428
naphthalene sulfonate was purchased from Research Bio-
chemicals, Inc. (Natick, MA). (-)-Cocaine HCl was obtained
from the National Institute on Drug Abuse. GBR 12909
dihydrochloride (1-[2-[bis(4-fluorophenyl)methoxy]ethyl]-4-[3-
phenylpropyl]piperazine) was purchased from SIGMA-Aldrich
(#D-052; St. Louis, MO).
Our previous report describes the activity of the
racemic version of compound 11.35 Here, enantiomeric
separation of the racemic 11 and the most potent cyano
derivative 13a was carried out. Higher activity at DAT
was found in the (-)-S,S-isomer of both 11 and 13a (33.8
nM for (-)-S,S-11 and 11.3 nM for (-)-S,S-19a vs. 229

Structurally Constrained Inhibitors of Monoamine Transporters J ournal of Medicinal Chemistry, 2003, Vol. 46, No. 11 2211
Syn th esis of (5-Nitr op yr id in -2-yl)d ip h en yla ceton itr ile
(2). To a mixture of 2-chloro-5-nitropyridine (1.0 g, 6.3 mmol),
diphenylacetonitrile (1.33 g, 6.9 mmol, 1.1 equiv), and tet-
rabutylammonium fluoride (0.70 g, 3.15 mmol, 0.5 equiv) in
10 mL of toluene was added dropwise 1.5 mL 50% aqueous
NaOH. After 30 min the mixture was filtered through a short
plug of silica to remove tars, and solvent was evaporated to
get a slightly yellow oil. The crude oil was purified by flash
chromatography over a silica gel column using hexane:EtOAc
(3:1), to get the title compound (1.7 g, 86%) as colorless plates.
broad singlet, NH), 8.05 (1H, dd, J ) 2.4 Hz J ) 8.7 Hz, ArH),
8.45 (1H, d, J ) 2.4 Hz, ArH).
Syn th esis of cis- a n d tr a n s-N-(6-Ben zh yd r ylp ip er id in -
3-yl)a cet a m id e (7a a n d 7b ). To a solution of N-(6-benz-
hydrylpyridin-3-yl)acetamide dihydrochloride salt (1.11 g, 3.28
mmol) in 20 mL of methanol was added platinum(IV) oxide
(0.11 g, 10%), and the mixture was shaken on Parr hydroge-
nator at room temperature under H2 atmosphere (60 psi) for
12 h. The reaction mixture was then filtered through Celite,
and the methanol was evaporated. The residue was basified
with saturated solution of NaHCO3 and extracted with CH2-
Cl2 (5×). The extracts were pooled, washed with brine, and
dried over Na2SO4, and the solvent was evaporated in vacuo
to give crude product which was purified by flash chromatog-
raphy over a silica gel column using hexane/EtOAc/MeOH/
Et3N (52:40:4:4). 7a cis-N-(6-Benzhydrylpiperidin-3-yl)aceta-
mide was eluted first (0.4865 g, 48%). 1H NMR (CDCl3 400
MHz): δ 1.17-1.27 (1H, m, H-5), 1.38-1.53 (2H, m, H-5,H-
1
mp 94-9 °C. H NMR (CDCl3; 300 MHz) δ 7.20-7.29 (5H, m,
ArH), 7.35-7.42 (5H, m, ArH), 7.54 (1H, d, J ) 8.7 Hz, H-3),
8.49 (1H, dd, J ) 3 and 9 Hz, H-4), 9.48 (1H, d, J ) 2.4 Hz,
H-6). Anal. (C19H13N3O2): C, H, N.
Syn th esis of 2-(5-Nitr op yr id in -2-yl)2,2-d ip h en yla ceta -
m id e(3). A mixture of (5-nitropyridin-2-yl)diphenylacetonitrile
(5.0 g, 15.8 mmol) was added to a magnetically stirred, room-
temperature solution of 40 mL of concentrated H2SO4 diluted
with 10 mL of H2O. The mixture was then stirred for 24 h at
90 °C. The dark solution was then poured onto crushed ice
and water and stirred for 1 h. The mixture was extracted thrice
with EtOAc. All organic extracts were pooled, washed with
brine, and dried over MgSO4, and solvent was evaporated. The
crude product was purified by flash chromatography over a
silica gel column using hexane:EtOAc (2:1) to furnish the title
compound (4.74 g, 90%) as an amorphous tan solid. mp 160-4
4
ax), 1.81-1.88 (1H, m, H-4eq), 2.0 (3H, s, COCH3), 2.81-2.84
(2H, m, H-2), 3.24 (1H, dt, J ) 2.4 Hz J ) 10.4 Hz, H-6), 3.71
(1H, d, J ) 10.8 Hz, Ph2CH), 4.03-4.09 (1H, m, H-3eq), 6.42-
6.53 (1H, broad doublet, CONH), 7.15-7.39 (10H, m, ArH).
Eluting second was 7b trans-N-(6-Benzhydrylpiperidin-3-yl)-
acetamide (0.27 g, 27%). 1H NMR (CDCl3, 400 MHz): δ 1.11-
1.31 (3H, m, H-5, H-4), 1.56-1.63 (1H, m, H-4), 1.92 (3H, s,
COCH3), 2.30 (1H, t, J ) 10.4 Hz, H-2ax), 3.17-3.24 (2H, m,
H-6, H-2eq), 3.76 (1H, d, J ) 10.4 Hz,Ph2CH), 3.80-3.90 (1H,
m, H-3ax), 5.25-5.42 (1H, broad doublet, NHCO), 7.15-7.39
(10 H, m, ArH).
1
°C. H NMR (CDCl3; 300 MHz) δ 5.9 (1H, bs, NH), 7.05-7.1
(4H, m, ArH), 7.26 (1H, d, J ) 8.4 Hz, H-3), 7.3-7.4 (6H, m,
ArH), 8.19 (1H, bs, NH), 8.36 (1H, dd, J ) 2.4 and 6.3 Hz,
H-4), 9.43 (1H, d, J ) 1.8 Hz, H-6). Anal. (C19H15N3O3) C, H,
N.
P r oced u r e A. Syn th esis of N-[6-Ben zh yd r yl-1-(m eth -
oxyp h en yla cetyl)p ip er id in -3-yl]a ceta m id e (8a a n d 8b).
Racemic cis-N-(6-benzhydrylpiperidin-3-yl)acetamide 7a (1 g,
3.2 mmol) was dissolved in dry CH2Cl2 and into it was added
Et3N (1.63 g, 16.23 mmol). The solution was stirred for few
minutes (5 min) and into it was added (-)-R-mandelic acid
chloride freshly prepared from (-)-R-mandelic acid (1.07 g,
6.49 mmol) and oxalyl chloride (3.29 g, 25.9 mmol). The
mixture was stirred overnight under N2 atmosphere. After 12
h the solution was diluted with CH2Cl2 and washed with water
and brine. The organic layer was then separated and dried
over Na2SO4 . The solvent was evaporated in vacuo to give a
crude mixture of two diastereomers which was separated by
flash chromatography over a silica gel column using hexane/
EtOAc/MeOH/Et3N (52:40:4:4).
Syn t h esis of 2-(5-Am in op yr id in -2-yl)-2,2-d ip h en yl-
a cet a m id e (4). A mixture of 2-(5-nitropyridin-2-yl)-2,2-di-
phenylacetamide (8.86 g, 26.5 mmol) in 50% EtOH/glacial
AcOH with Pd/C (10%) was stirred for 24 h. The mixture was
then filtered through
a bed of Celite, and ethanol was
evaporated under reduced pressure. The aquous portion was
then basified with K2CO3 and extracted with EtOAc (4×). All
organic portions were pooled, washed with brine, dried over
MgSO4, and the solvent was evaporated. Obtained crude
product was purified by flash chromatography over a silica gel
column using hexane:EtOAc (2:1) to furnish the title compound-
1
(7.9 g, 98%) as a tan crystal. mp 215-20 °C. H NMR (CDCl3;
300 MHz) δ 3.85 (2H, broad singlet, NH2), 5.88 (1H, broad
singlet, CONH), 6.54 (1H, d, J ) 8.4 Hz, H-3), 6.84 (1H, dd, J
) 3 and 8.7 Hz, H-4), 7.01-7.06 (4H, m, ArH), 7.24-7.32 (6H,
m, ArH), 8.11 (1H, d, J ) 2.4 Hz, H-6), 9.57 (1H, bs, CONH).
Anal. (C19H17N3O‚0.25 H2O) C, H, N.
Eluting first 8a (0.5393 g, 36%). 1H NMR (CDCl3 , 300
MHz): δ 1.52-1.84 (4H, m, H-5, H-4), 1.92 (3H, s, COCH3),
2.62-2.74 (1H, m,H-2ax), 3.32 (3H, s, OCH3), 3.42-3.61(1H,
m, H-3), 3.95(1H, dd, J ) 13.5 Hz J ) 3.6 Hz, H-2eq), 4.32
(1H, d, J ) 12.3 Hz, Ph2CH), 4.86 (1H, s, Ar-CH), 5.38 (1H,
broad doublet, NH), 5.75 (1H, d, J ) 12.3 Hz, H-6), 6.99 (2H,
d, J ) 6.9 Hz, ArH), 7.12-7.48 (13H, m, ArH). Eluting second
8b (0.640 g, 43%) 1H NMR (CDCl3 400 MHz): δ 1.55-1.76
(4H, m, H-5,H-4), 1.92 (3H, s, COCH3), 2.54-2.66 (1H, m,H-
Syn th esis of 6-Ben zh yd r ylp yr id in -3-yla m in e (5). A
mixture of 2-(5-aminopyridin-2-yl)-2,2-diphenylacetamide (5.28
g, 17.4 mmol) and 150 mL of 37% HCl under a N2 atmosphere
was refluxed for 24 h. The mixture was then cooled and poured
over/onto 300 g of ice and H2O and basified with K2CO3. The
mixture was then extracted thrice with EtOAc (150 mL). All
organic portions were pooled, washed with brine, and dried
over MgSO4, and the solvent was evaporated to yield a green
oil that solidified. This crude oil was purified by flash chro-
matography over a silica gel column using hexane:EtOAc
(1:1), to furnish the title compound (4.09 g, 90%) as a tan
2
ax), 3.13 (3H, s, OCH3), 3.30-3.47 (1H, m, H-3), 3.90 (1H, dd,
J ) 14.1 Hz, J ) 3.6 Hz, H-2eq), 4.25 (1H, d, J ) 12.3, Ph2-
CH), 4.95 (1H, s, Ar-CH), 5.54 (1H, broad doublet, NH), 5.75
(1H, d, J ) 11.1 Hz, H-6), 6.96 (2H, d, J ) 7.2 Hz, ArH), 7.1-
7.44 (13H, m, ArH).
P r oced u r e B. Syn th esis of 1-(5-Am in o-2-ben zh yd r yl-
p ip er id in -1-yl)-2-m eth oxy-2-p h en yleth a n on e (9a ). N-[6-
Ben zh ydr yl-1-(m et h oxyph en yla cet yl)piper idin -3-yl]a cet -
amide 8a (0.200 g, 0.43 mmol) was dissolved in 2 N HCl in
MeOH (10 mL), and the solution was refluxed for 24 h.
Methanol was then evaporated, and the residue was neutral-
ized using soild NaHCO3. It was then extracted with EtOAc
(3×). The extracts were pooled, washed with brine, and dried
over Na2SO4. Removing the solvent in vacuo gave a crude
mixture, which was purified by flash chromatography over a
silica gel column with hexane/EtOAc/MeOH/Et3N (52:40:4:4)
to yield 9a (0.131 g, yield 72%). 1H NMR (CDCl3 300 MHz): δ
1.32-1.68 (6H, m, H-5, H-4, NH2), 2.22-2.32 (1H, m, H-3),
2.49 (1H, t, J ) 13.2 Hz, H-2), 3.38 (3H, s, OCH3), 3.52 (1H,
dd, J ) 13.6 Hz, J ) 3 Hz, H-2), 4.31 (1H, d, J ) 12.4 Hz,
1
crystalline solid. mp 130-4 °C. H NMR (CDCl3; 300 MHz) δ
3.52 (2H, broad singlet, NH), 5.61 (1H, s, CH(Ph)2), 6.83-6.91
(2H, m, ArH), 7.15-7.32 (10H, m, ArH), 8.08 (1H, d, J ) 2.4
Hz, H-2). Anal. (C18H16N2) C, H, N.
Syn th esis of N-(6-Ben zh yd r ylp yr id in -3-yl)a ceta m id e
(6). To a solution of 6-benzhydrylpyridin-3-ylamine (0.100 g,
0.38 mmol) in dry CH2Cl2 (20 mL) were added acetyl chloride
(0.033 g, 0.42 mmol) and Et3N (0.76 g, 0.76 mmol). The solution
was stirred for 3 h after which the solution was diluted with
CH2Cl2 and the organic layer was washed three times with
water and finally with brine. It was then dried over Na2SO4,
and the solvent was evaporated in vacuo to give 6 (0.1053 g,
90.77%). 1H NMR (CDCl3 300 MHz): δ 2.10 (3H, s, COCH3),
5.64 (1H, s, (Ph)2CH), 7.01-7.30 (11H, m, ArH), 7.91 (1H,

2212 J ournal of Medicinal Chemistry, 2003, Vol. 46, No. 11
Kolhatkar et al.
Ph2CH), 4.75 (1H, s, Ar-CH), 5.68-5.74 (1H, m, H-6), 6.91
(2H, d, J ) 10 Hz, ArH), 7.12-7.5 (13H, m, ArH).
was converted into hydrochloride salt. mp 244-257 °C. Anal.
(C25H27FN2‚2HCl‚0.9 H2O) C, H, N.
Syn th esis of Ra cem ic cis-6-Ben zh yd r ylp ip er id in -3-
yla m in e (12). A solution of racemic cis-N-(6-benzhydrylpip-
eridin-3-yl)acetamide 7a (0.4 g, 1.29 mmol) in 2 N HCl/
methanol (25 mL) was refluxed for 48 h. Methanol was then
evaporated under vacuum, and the aqueous solution was
neutralized by using saturated NaHCO3 solution. The mixture
was then extracted using EtOAc (3×). All organic extracts were
combined, washed with brine and dried over Na2SO4. The
solvent was then evaporated in vacuo to give 12 (0.324 g, 94%).
This was used without further purification in the next step.
1H NMR (CDCl3, 400 MHz): δ 1.36-1.42 (2H, m, H-5), 1.59-
1.62 (2H, m, H-4), 2.08 (2H, broad singlet, NH), 2.79-2.80 (2H,
m, H-2), 2.97-3.02 (1H, m, H-3), 3.25 (1H, dt, J ) 4 Hz, J )
10 Hz, H-6), 3.80 (1H, d, J ) 10.4, (Ph)2CH), 7.13-7.40 (10H,
m, ArH).
P r oced u r e E. Syn th esis of Ra cem ic cis-4-[(6-Ben zh y-
dr ylpiper idin -3-ylam in o)m eth yl]ben zon itr ile (13a). A mix-
ture of racemic cis-6-benzhydrylpiperidin-3-ylamine 12 (0.080
g, 0.31 mmol), 4-cyanobenzaldehyde (0.032 g, 0.25 mmol), and
acetic acid (0.018 g, 0.31 mmol) in 1,2 dichloroethane (5 mL)
was stirred at room temperature under N2 atmosphere for 15-
20 min. Sodium cyanoborohydride (0.029 g, 0.46 mmol) and
methanol (1 mL) were added next, and the mixture was stirred
for 3-4 h. Water (5 mL) was added followed by few drops of
HCl. Excess HCl was then neutralized with saturated NaHCO3
solution. The mixture was then extracted with CH2Cl2 (3×).
All organic extracts were combined and washed with brine and
dried over Na2SO4. The solvent was then evaporated in vacuo
to give crude product which was purified by flash chromatog-
raphy over a silica gel column using hexane/EtOAc/MeOH (50:
40:10) to furnish the title compound 13a (0.058 g, 63%). 1H
NMR (CDCl3, 400 MHz): δ 1.29-1.44 (2H, m, H-5), 1.50 (1H,
tt, J ) 13.2 Hz, J ) 3.6 Hz, H-4ax), 1.81-1.88 (3H, m, 2NH,
H-4eq), 2.65-2.76 (2H, m, H-3, H-2), 2.99 (1H, td, J ) 2.4 Hz,
J ) 11.2 Hz, H-2eq), 3.28 (1H, dt, J ) 3.2 Hz, J ) 9.6 Hz, H-6ax),
3.77-3.84 (3H, m, ArCH2, (Ph)2CH),7.14-7.35(8H, m, ArH),
7.36-7.42(2H, m, ArH), 7.44-7.50(2H, m, ArH), 7.56-7.62-
(2H, m, ArH). The free base was converted into oxalate salt
mp 226-228 °C. Anal. (C26H27N3‚(COOH)2‚0.7H2O) C, H, N.
P r oced u r e C. Syn th esis of 1-[2-Ben zh yd r yl-5-(4-flu o-
r oben zyla m in o)p ip er id in -1-yl]-2-m eth oxy-2-p h en yleth a -
n on e (10). 1-(5-Amino-2-benzhydrylpiperidin-1-yl)-2-methoxy-
2-phenylethanone 9a (0.2908 g, 0.7024 mmol) was dissolved
in 1,2 dichloroethane (10 mL), and into it was added p-
fluorobenzaldehyde (0.1741 g, 1.404 mmol) followed by acetic
acid (0.08424 g, 1.4 mmol). After 15-20 min of stirring under
N2 sodium cyanoborohydride (0.1323 g, 2.107 mmol) was added
followed by 1 mL of methanol. The mixture was stirred for
3-4 h. Into the solution was then added 3-4 mL of water
followed by few drops of HCl. Excess HCl was then neutralized
with NaHCO3, and the mixture was extracted with CH2Cl2
(3x). All extracts were pooled, washed with brine, and dried
over Na2SO4, and the solvent was evaporated in vacuo to
give crude product which was purified by flash chromatogra-
phy over a silica gel column using hexane:EtOAc:MeOH
(50:40:10) to yield 10 (0.3212 g, 88%). 1H NMR (CDCl3, 400
MHz): δ 1.50-1.70 (4H, m, H-5, H-4), 2.15-2.22 (1H, m, H-3),
2.47-2.55(1H, m, H-2), 3.33(3H, s, OCH3), 3.38-3.54 (2H, m,
ArCH2), 3.71(1H, dd, J ) 14 Hz, J ) 4 Hz, H-2), 4.33 (1H, d,
J ) 12 Hz, Ph2CH), 4.75 (1H, s, (CO)CH), 5.74 (1H, m, H-6),
6.90-7.01 (4H, m, ArH), 7.13-7.29 (11H, m, ArH), 7.39-7.47
(4H, m, ArH).
P r oced u r e D. Syn th esis of (-)-cis-(6-Ben zh yd r ylp ip -
er id in -3-yl)(4-flu or oben zyl)a m in e (11). 1-[2-Benzhydryl-5-
(4-fluorobenzylamino)piperidin-1-yl]-2-methoxy-2-phenyleth-
anone 10 (0.100 g, 0.195 mmol) was dissolved in dry THF, into
it was added potassium tert-butoxide (0.171 g, 1.56 mmol), and
the mixture was stirred overnight under N2 atmosphere.
Stirring was stopped after 24 h, and into the solution was
added water. THF was evaporated, and the mixture was
extracted with CH2Cl2 (3×). All organic extracts were pooled,
washed with brine, and dried over Na2SO4. Solvent was then
evaporated in vacuo to obtain a crude mixture which was used
without any further purification in the next step.
The crude mixture was dissolved in HCl (6 N, 5 mL) and 1
mL of methanol. The solution was refluxed for 3-4 h.
Methanol was then evaporated in vacuo, and the solution was
neutralized with saturated solution of NaHCO3. The mixture
was then extracted with EtOAc (3×). All organic extracts were
pooled, washed with brine, and dried over Na2SO4. The solvent
was removed in vacuo gave a crude mixture which was purified
by flash chromatography over a silica gel column using hexane:
EtOAc:MeOH (50:40:10) to give (-)-11 (0.036 g, 51%). 1H NMR
(CDCl3 400 MHz): δ 1.30-1.42 (2H, m, H-5), 1.49 (1H, tt, J )
4 Hz, J ) 12.8 Hz, H-4ax), 1.80-1.89 (2H, m, H-4eq, NH), 2.67-
2.74 (2H, m, H-3eq, H-2ax), 2.96-3.02 (1H, m, H-2eq), 3.28 (1H,
dt, J ) 3.2 Hz, J ) 9.6 Hz, H-6ax), 3.72 (2H, s, ArCH2), 3.81-
(1H, d, (J ) 10.4 Hz), Ph2CH), 6.96-7.02 (2H, m, ArH), 7.15-
7.38 (12H, m, ArH). The optical rotation was measured in
Syn th esis of Ra cem ic cis-(6-Ben zh yd r ylp ip er id in -3-
yl)(3,4-d iflu or ob en zyl)a m in e (13b ). Racemic cis-6-benz-
hydrylpiperidin-3-ylamine 12 (0.040 g, 0.15 mmol) was reacted
with 3,4-diflurobenzaldehyde (0.017 g, 0.11 mmol) (Procedure
E) to yield 13b (0.019 g, 41%). 1H NMR (CDCl3, 400 MHz):
δ1.29-1.43 (2H, m, H-5), 1.49 (1H, tt, J ) 12.8 Hz, J ) 4.0
Hz, H-4ax), 1.79-1.87 (1H, m, H-4eq), 2.65-2.75 (2H, m, H-2ax
,
H-3eq), 2.99 (1H, td, J ) 2.4 Hz, J ) 11.2 Hz, H-2eq), 3.28 (1H,
dt, J ) 2.8 Hz, J ) 10.0 Hz, H-6ax), 3.71 (2H, s, ArCH2), 3.80
(1H, d, J ) 10.4 Hz, (Ph)2CH), 7.00-7.42 (13H, m, ArH). The
free base was converted into oxalate salt. mp 114-130 °C.
Anal. (C25H36N2F2‚2(COOH)2‚1.1H2O) C, H, N.
Perkin-Elmer 241 polarimeter, [R]25 ) -27 ° (c 1, MeOH).
D
Syn th esis of Ra cem ic cis-(6-Ben zh yd r ylp ip er id in -3-
yl)t h iop h en -2-ylm et h yla m in e (13c). Racemic cis-6-benz-
hydrylpiperidin-3-ylamine 12 (0.080 g, 0.30 mmol) was reacted
with thiophene-2-carbaldehyde (0.028 g, 0.25 mmol) (Procedure
The free base was converted into a hydrochloride salt. mp 246-
265 °C. Anal. (C25H27FN2‚2HCl‚H2O) C, H, N.
Syn th esis of (+)-cis-(6-Ben zh yd r ylp ip er id in -3-yl)(4-
flu or oben zyl)a m in e (11). Compound 8b was refluxed with
2 N HCl in methanol (Procedure B) to produce 1-(5-amino-2-
benzhydrylpiperidin-1-yl)-2-methoxy-2-phenylethanone) (70%)
which was then reacted with 4-fluorobenzaldehyde (Procedure
C) to yield 1-[2-benzhydryl-5-(4-fluorobenzylamino)piperidin-
1-yl]-2-methoxy-2-phenylethanone (89%). This compound was
then hydrolyzed using potassium tert-butoxide followed by
treatment with (6 N) HCl (Procedure D) to give (+)cis-(6-
benzhydrylpiperidin-3-yl)(4-fluorobenzyl)amine, (+)-11 (54%)
1
E) to give 13c (0.037 g, 41.11%). H NMR (CDCl3, 400 MHz):
δ 1.31-1.42 (2H, m, H-5), 1.50 (1H, tt, J ) 12 Hz, J ) 4.0 Hz,
H-4ax), 1.78-1.88 (2H, m, NH, H-4), 2.71 (1H, dd, J ) 2.4 Hz,
J ) 12.4 Hz, H-2ax), 2.74-2.80(1H, m, H-3eq), 2.99 (1H, td, J
) 2.4 Hz, J ) 11.2 Hz, H-2eq), 3.27 (1H, dt, J ) 3.6 Hz, J )
10.0 Hz, H-6ax), 3.80 (1H, d, J ) 9.6 Hz, (Ph)2CH), 3.97 (2H, s,
(2-thiophene)CH2(NH)), 6.90-6.97 (2H, m, ArH), 7.13-7.42
(11H, m, ArH). The free base was converted into hydrochloride
salt. mp 247-255 °C. Anal. (C23H26N2S‚2HCl‚1.1H2O) C, H,
N.
1
(overall yield 33%). H NMR (CDCl3 400 MHz): δ 1.30-1.42
(2H, m, H-5), 1.49 (1H, tt, J ) 4 Hz, J ) 12.8 Hz, H-4ax), 1.80-
1.90 (2H, m, H-4eq, NH), 2.68-2.74 (2H, m, H-3eq, H-2ax), 2.96-
3.02 (1H, m, H-2eq), 3.28 (1H, dt, J ) 3.2 Hz, J ) 9.6 Hz, H-6ax),
3.72 (2H, s, ArCH2), 3.81(1H, d, (J ) 9.6 Hz), Ph2CH), 6.96-
7.02 (2H, m, ArH), 7.13-7.33 (10H, m, ArH), 7.35-7.40 (2H,
m, ArH). The optical rotation was measured in Perkin-Elmer
Syn th esis of Ra cem ic cis-(6-Ben zh yd r ylp ip er id in -3-
yl)ben zo[b]th iop h en -3-ylm eth yla m in e (13d ). Racemic cis-
6-benzhydrylpiperidin-3-ylamine 12 (0.080 g, 0.30 mmol) was
reacted with benzo[b]thiophene-3-carbaldehyde (0.040 g, 0.25
mmol) (Procedure E) to give 13d (0.067 g, 66%). 1H NMR
(CDCl3, 400 MHz): δ 1.34-1.44 (2H, m, H-5), 1.55 (1H, tt, J
) 11.2 Hz, J ) 4.0 Hz, H-4ax), 1.87-1.95 (1H, m, H-4eq), 2.76
241 polarimeter, [R]25 ) +28 ° (c 1, MeOH). The free amine
D

Structurally Constrained Inhibitors of Monoamine Transporters J ournal of Medicinal Chemistry, 2003, Vol. 46, No. 11 2213
(1H, dd, J ) 2.4 Hz, J ) 11.2 Hz, H-2ax), 2.80-2.85 (1H, m,
H-3eq), 3.04-3.11 (1H, m, H-2eq), 3.31 (1H, dt, J ) 4 Hz, J )
9.6 Hz, H-6ax), 3.83 (1H, d, J ) 10.4 Hz, (Ph)2CH), 4.02 (2H, s,
(2-benzthiophene) CH2), 7.14-7.42 (13H, m, ArH) 7.83-7.88
(2H, m, ArH). The free base was converted into hydrochloride
salt. mp 227-240 °C. Anal. (C27H28N2S‚2HCl‚1.1H2O) C, H,
N.
Syn th esis of Ra cem ic cis-(6-Ben zh yd r ylp ip er id in -3-
yl)(1H-in d ol-3-ylm eth yl)a m in e (13e). Racemic cis-6-benz-
hydrylpiperidin-3-ylamine 12 (0.080 g, 0.30 mmol) was reacted
with 1H-indole-3-carbaldehyde (0.036 g, 0.25 mmol) (Procedure
E) to give 13e (0.045 g, 46%). 1H NMR (CDCl3, 400 MHz):
δ1.39-1.46 (2H, m, H-5), 1.51-1.62 (1H, m, H-4ax), 1.87-1.96
(1H, m, H-4eq), 2.77 (1H, dd, J ) 2.4 Hz, J ) 11.2 Hz, H-2ax),
2.84-2.89 (1H, m, H-3eq), 3.06-3.12 (1H, m, H-2eq), 3.31-3.38
(1H, m, H-6ax), 3.86 (1H, d, J ) 10.8 Hz, (Ph)2CH), 3.98 (2H,
s, (3-indole)CH2), 7.04-7.42 (14H, m, ArH) 7.68 (1H, d, J ) 8
Hz, ArH), 8.69 (1H, broad singlet, indole-NH). The free base
was converted into oxalate salt. mp 100-113 °C. Anal.
(C27H39N3‚(COOH)2‚1.9H2O) C, H, N.
Syn th esis of r a cem ic cis-(6-Ben zh yd r ylp ip er id in -3-yl)-
ben zyla m in e (13g). Racemic cis-6-benzhydrylpiperidin-3-
ylamine 12 (0.023 g, 0.089 mmol) was reacted with benzalde-
hyde (0.0076 g, 0.07 mmol) (Procedure E) to give 13g (0.012
g, yield 48%). 1H NMR (CDCl3, 300 MHz) δ 1.30-1.39 (2H, m,
H-5), 1.44-1.56 (1H, m, H-4ax), 1.68 (2H, broad singlet, NH),
1.80-1.91(1H, m, H-4eq), 2.70-2.76 (2H, m, H-3eq, H-2ax), 3.00
(1H, bd, J ) 10.5 Hz, H-2eq) 3.21-3.39 (1H, m, H-6ax), 3.76(2H,
s, CH2Ph), 3.82 (1H, d, J ) 10.2 Hz, CH(Ph)2), 7.13-7.38 (15H,
m, ArH). Free base was converted into its hydrochloride salt,
mp 267-268 °C. Anal. (C25H30Cl2N2‚1.3H2O) C, H, N.
was added into the residue, and the solution was refluxed for
1 h. Solid NaHCO3 was added, and the methanol was removed
in vacuo. The mixture was extracted with EtOAc. The com-
bined organic phase was washed with brine and dried over
Na2SO4, and the solvent was evaporated to give the crude
product which was purified by flash chromatography over a
silica gel column using hexane:acetone:Et3N (7:2:0.2) to give
a colorless oil 13j (0.025 g, 70%); 1H NMR (CDCl3, 400 MHz):
δ 1.03-1.13 (1H, m, H-5ax), 1.28-1.38 (1H, m, H-5eq), 1.48 (1H,
tt, J ) 4 Hz, J ) 13.2 Hz, H-4ax), 1.87 (1H, td, J ) 2.8 Hz, J
) 14 Hz, H-4eq), 2.69 (1H, dd, J ) 12 Hz, J ) 2.4 Hz, H-2ax),
2.82-2.88 (5H, m, CH2CH2C6H4F, H-3eq), 2.98 (1H, td, J ) 2.4
Hz, J ) 12 Hz, H-2eq), 3.24 (1H, dt, J ) 9.6 Hz, J ) 2.4 Hz,
H-6ax), 3.63 (1H, d, J ) 10.8 Hz, CH(Ph)2), 4.02 (1H, broad
singlet, NH), 7.00 (2H, t, J ) 8.8 Hz, ArH), 7.12-7.33 (12H,
m, ArH).
Free base was converted into its hydrochloride salt, mp
228-230°C. Anal. (C26H31Cl2FN2‚1.9H2O) C, H, N.
Syn th esis of N-Meth oxy-N-m eth yl-1H-in d ole-2-ca r box-
a m id e (16). A solution of indole-2-carboxylic acid 15 (0.500
g, 3.1 mmol), 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimi-
dehydrochloride (EDCI) (1.19 g, 6.2 mmol) in Et3N(1.5 mL),
and dry CH2Cl2 (20 mL) was stirred at room temperature for
1 h. N,O-Dimethylhydroxylamine hydrochloride (0.331 g, 3.4
mmol) dissolved in dry CH2Cl2 (5 mL) was added to the above
reaction mixture. The solution was stirred at room tempera-
ture for overnight. The solution was then diluted with CH2-
Cl2, and the organic phase was washed with water and brine
and finally dried over Na2SO4. The solvent was removed in
vacuo to give a crude product which was purified by flash
chromatography over a silica gel column using EtOAc:hexane
1
(1:1) to collect 16 (0.510 g, 81%). H NMR (CDCl3, 300 MHz):
Syn th esis of Ra cem ic cis-(6-Ben zh yd r ylp ip er id in -3-
yl)(4-m eth oxyben zyl)a m in e (13h ). Racemic cis-6-benzhy-
drylpiperidin-3-ylamine 12 (0.100 g, 0.39 mmol) was reacted
with 4-methoxybenzaldehyde (0.042 g, 0.31 mmol) (Procedure
δ 3.45 (3H, s, NCH3), 3.83 (3H, s, OCH3), 7.12 (1H, t, J ) 7.9
Hz, ArH), 7.23-7.33 (2H, m, ArH), 7.45 (1H, d, J ) 8.4 Hz,
ArH), 7.69 (1H, d, J ) 8.7 Hz, ArH), 9.89 (1H, broad singlet,
NH).
1
E) to give 13h (0.039 g, 32%). H NMR (CDCl3 400 MHz): δ
1.30-1.42 (2H, m, H-5), 1.44-1.54 (1H, m, H-4ax), 1.78-1.92
(2H, m, H-4eq, NH), 2.68-2.74 (2H, m, H-3eq, H-2ax), 2.96-
3.02 (1H, m, H-2eq), 3.25-3.32 (1H, m, H-6ax), 3.69 (2H, s,
ArCH2), 3.79 (3H, s, OCH3), 3.82 (1H, d, J ) 9.6 Hz, Ph2CH),
6.84-6.88 (2H, m, ArH), 7.13-7.34 (10H, m, ArH), 7.35-7.40
(2H, m, ArH). Anal. (C26H30N2O‚(COOH)2‚1.1H2O) C, H, N.
Syn th esis of Ra cem ic cis-4-[(6-Ben zh yd r ylp ip er id in -
3-yla m in o)m eth yl]p h en ol (13i). Racemic cis-6-benzhydrylpi-
peridin-3-ylamine 12 (0.075 g, 0.28 mmol) was reacted with
4-hydroxybenzaldehyde (0.027 g, 0.22 mmol) (Procedure E) to
furnish the title compound 13i (0.035 g, 42%). 1H NMR (CDCl3,
400 MHz): δ 1.34-1.84 (5H, m, H-5, H-4ax, 2NH), 1.86-1.98
(1H, m, H-4eq), 2.68-2.76 (1H, m, H-2ax), 2.78-2.84 (1H, m,
H-3), 3.00-3.08 (1H, m, H-2eq), 3.35 (1H, dt, J ) 2.0 Hz, J )
8.8 Hz, H-6ax), 3.58-3.68 (2H, m, ArCH2), 3.90 (1H, d, J )
10.4 Hz, (Ph)2CH), 6.49-6.54 (2H, m, ArH), 7.01-7.05 (2H,
m, ArH), 7.11-7.33 (8H, m, ArH), 7.35-7.38 (2H, m, ArH).
Anal. (C27H30N2O‚2.1H2O) C, H, N.
Syn th esis of Ra cem ic cis-N-(6-Ben zh yd r ylp ip er id in -
3-yl)-2-(4-flu or op h en yl)a cet a m id e (14). Racemic cis-6-
benzhydrylpiperidin-3-ylamine,12 (0.085 g, 0.332 mmol) was
reacted with (4-fluorophenyl)acetyl chloride (0.0515 g, 0.29
mmol) in the presence of excess Et3N in CH2Cl2 to give a crude
product, which was purified using flash chromatography
(hexane:EtOAc:MeOH 70:30:2) to yield 14 (0.040 g, 48%). mp:
105-106 °C.1H NMR (CDCl3, 300 MHz) δ 0.90-1.08 (1H, m,
H-5ax), 1.30-1.42 (1H, m, H-5eq), 1.46 (1H, td, J ) 3.6 Hz, J )
13 Hz, H-4ax), 1.74-1.86 (2H, m, H-4eq, NH), 2.75 (2H, m, H-2),
3.14-3.25 (1H, m, H-6ax), 3.48-3.56 (3H, m, ArCH2, (Ph)2CH),
3.87-4.05 (1H, m, H-3eq), 6.50-6.58 (1H, m, CONH), 7.07 (2H,
t, J ) 8.7 Hz, ArH), 7.14-7.34 (12H, m, ArH).
Syn th esis of Ra cem ic cis-(6-Ben zh yd r ylp ip er id in -3-
yl)-[2-(4-flu or op h en yl)eth yl]a m in e (13j). Into the solution
of 14 (0.035 g, 0.087 mmol) in 5 mL of dry THF was added 1
M BH3/THF (0.5 mL, 5 mmol). The reaction mixture was
refluxed for 6 h. After the solution was cooled to room
temperature, methanol (2 mL) was added slowly. The solvent
was removed under reduced pressure, 10% HCl/MeOH (5 mL)
Syn th esis of 1H-In d ole-2-ca r ba ld eh yd e (17). Into a
solution of N-methoxy-N-methyl-1H-indole-2-carboxamide 16
(0.200 g, 0.98 mmol) in anhydrous THF (10 mL) at -30 °C
was added dropwise 5 mL suspension of LAH in THF (2 g in
100 mL refluxed overnight) under nitrogen atmosphere. The
reaction mixture was stirred for 2 h, and ice-water was then
added to destroy excess hydride. The reaction mixture was
then evaporated in vacuo until most of the THF was removed,
and the aqueous residue was extracted with CH2Cl2 (3×). All
organic fractions were combined, washed with brine, and dried
over Na2SO4. The solvent removed in vacuo leaving to obtain
1
17 (0.091 g, 64%). H NMR (CDCl3, 300 MHz): δ 7.19 (1H, t,
J ) 7.8 Hz, ArH), 7.29 (1H, s, ArH), 7.40 (1H, t, J ) 8.1 Hz,
ArH), 7.50 (1H, d, J ) 8.1 Hz, ArH), 7.76 (1H, d, J ) 8.7 Hz,
ArH), 9.60 (1H, broad singlet, NH), 9.87 (1H, s, CHO).
Syn th esis of Ra cem ic cis-(6-Ben zh yd r ylp ip er id in -3-
yl)(1H-in d ol-2-ylm eth yl)a m in e (13f). Racemic cis-6-benz-
hydrylpiperidin-3-ylamine 12 (0.145 g, 0.54 mmol) was reacted
with 1H-indole-2-carbaldehyde 17 (0.055 g, 0.38 mmol) (Pro-
cedure E) to give 13f (0.093 g, 62%). 1H NMR (CDCl3, 300
MHz): δ 1.29-1.60 (3H, m, H-5, H-4ax), 1.82-1.92 (1H, m,
H-4eq), 2.72 (1H, dd, J ) 2.4 Hz, J ) 11.7 Hz, H-2ax), 2.75-
2.82 (1H, m, H-3eq), 3.03 (1H, td, J ) 2.4 Hz, J ) 11.7 Hz,
H-2eq), 3.27-3.38 (1H, m, H-6ax), 3.81 (1H, d, J ) 10.2 Hz,
(Ph)2CH), 3.88-4.10 (2H, m, (2-indole)CH2), 6.32 (1H, s, ArH),
7.02-7.42 (13H, m, ArH) 7.57 (1H, d, J ) 7.5 Hz, ArH), 9.36
(1H, broad singlet, indole-NH). The free base was converted
into oxalate salt, mp 215-217 °C. Anal. (C27H29N3‚(COOH)2‚
1.9H2O) C, H, N.
Syn th esis of (-)-cis-6-Ben zh yd r ylp ip er id in -3-yla m in e
(18a ). Compound 8a was refluxed with 2 N HCl in methanol
(procedure B) to produce 9a (70%). Compound 9a (0.336 g,
0.811 mmol) was dissolved in dry THF, into it was added
potassium tert-butoxide (0.728 g, 6.48 mmol), and the mixture
was stirred overnight under N2 atmosphere. After 24 h,
stirring was stopped, and into the solution water was added.
THF was evaporated in vacuo, and the mixture was extracted
with CH2Cl2 (3×). All extracts were pooled, washed with brine

2214 J ournal of Medicinal Chemistry, 2003, Vol. 46, No. 11
Kolhatkar et al.
and dried over Na2SO4. The solvent was removed in vacuo to
give a crude mixture which was used without any purification
in the next step. The crude mixture was dissolved in HCl (6
N, 10 mL), 2 mL of methanol was added to dissolve the mixture
completely, and the solution was refluxed for 3-4 h. Methanol
was then evaporated in vacuo, and the solution was neutral-
ized with NaHCO3. The mixture was then extracted with CH2-
CL2 (3×). All extracts were pooled, washed with brine, and
dried over Na2SO4. The solvent was removed in vacuo to give
a crude mixture, which was purified using flash chromatog-
raphy over a silica gel column using EtOAc:MeOH:Et3N
(60:35:5) to furnish the title compound 18a (0.109 g, 50%). 1H
NMR (CDCl3, 400 MHz): δ 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, J ) 4 Hz, J ) 10
Hz, H-6ax), 3.80 (1H, d, (J ) 10.2), (Ph)2CH), 7.12-7.40 (10H,
m, ArH). The optical rotation was measured in Perkin-Elmer
Biology. The affinity of test compounds in binding to rat
DAT, SERT, and NET was assessed by measuring inhibition
of binding of [3H]WIN 35,428, [3H]citalopram, and [3H]nis-
oxetine, respectively, exactly as described by us previously.31
Briefly, rat striatum was the source for DAT, and cerebral
cortex for SERT and NET. Final [Na+] was 30 mM for DAT
and SERT assays, and 225 mM for NET assays. All binding
assays were conducted at 0-4°C, for a period of 2 h for [3H]-
WIN 35,428 and [3H]citalopram binding, and 3 h for [3H]-
nisoxetine binding. Nonspecific binding of [3H]WIN 35,428 and
[3H]citalopram binding was defined with 100 µM cocaine, and
that of [3H]nisoxetine binding with 1 µM desipramine. Test
compounds were dissolved in dimethyl sulfoxide (DMSO) and
diluted out in 10% (v/v) DMSO. Additions from the latter
stocks resulted in a final concentration of DMSO of 0.5%,
which by itself did not interfere with radioligand binding. At
least five triplicate concentrations of each test compound were
studied, spaced evenly around the IC50 value. For DAT uptake
assays, uptake of [3H]DA into rat striatal synaptosomes was
measured exactly as described by us previously.31 Briefly, rat
striatal P2 membrane fractions were incubated with test drug
for 8 min followed by the additional presence of [3H]DA for 4
min at 25°C. Nonspecific uptake was defined with 100 µM
cocaine. Construction of inhibition curves and dissolvement
of test compounds were as described above.
241 polarimeter, [R]25 ) -43° (c 1, MeOH).
D
Syn th esis of (-)-cis-4-[(6-Ben zh ydr ylpiper idin -3-ylam i-
n o)m eth yl]ben zon itr ile (19a ). (-)-cis-6-benzhydrylpiperi-
din-3-ylamine 18a (0.075 g, 0.28 mmol) was reacted with
4-cyanobenzaldehyde (0.029 g, 0.22 mmol) (Procedure E) to
yield 19a (0.057 g, 68%). 1H NMR (CDCl3, 400 MHz): δ 1.24-
1.42 (2H, m, H-5), 1.50 (1H, tt, J ) 4 Hz, J ) 12.8 Hz, H-4ax),
1.80-1.96 (3H, m, H-4eq, 2NH), 2.66-2.76 (2H, m, H-3eq,
H-2ax), 3.00 (1H, td, J ) 2.4 Hz, J ) 11.2 Hz, H-2eq), 3.28 (1H,
dt, J ) 3.2 Hz, J ) 9.6 Hz, H-6ax), 3.77-3.83 (3H, m, ArCH2,
(Ph)2CH), 7.14-7.34 (8H, m, ArH), 7.36-7.40 (2H, m, ArH),
7.44-7.49 (2H, m, ArH), 7.57-7.62 (2H, m, ArH). The optical
Sin gle-cr ysta l X-r a y Diffr a ction An a lysis of 9b. C27H30
-
N2O2‚0.187(H2O), FW ) 417.91, orthorhombic space group
P212121, a ) 12.0787(5), b ) 13.6177(5), c ) 14.6543(5) Å, V )
2410.40(16) Å3, Z ) 4, _calc ) 1.152 mg mm-3, _(Cu KR) )
1.54178 Å, _ ) 0.574 mm-1, F(000) ) 896, T ) 293 K.
rotation was measured in Perkin-Elmer 241 polarimeter, [R]25
D
A clear colorless 0.63 × 0.08 × 0.08 mm crystal was used
for data collection with a Bruker SMART1 6K CCD detector
on a Platform goniometer. The Rigaku rotating Cu anode
source was equipped with an incident beam Gobel mirrors.
Lattice parameters were determined using SAINT42 from 5759
reflections within 7.3< 2σ < 125.6. Data were collected to
2_ ) 135.5°. A set of 11938 reflections was collected in the ω
scan mode. There were 4119 unique reflections. Corrections
were applied for Lorentz, polarization, and absorption effects.
The structure was solved with SHELXTL43 and refined with
the aid of the SHELX97 system of programs. The full-matrix
least-squares refinement on F2 used three restraints and
varied 297 parameters: atom coordinates and anisotropic
thermal parameters for all non-H atoms except the lower
occupancy solvate atoms. H atoms were included using a riding
model [coordinate shifts of C applied to attached H atoms,
) -32° (c 1, MeOH). The free base was converted into oxalate
salt, mp 226-228 °C. Anal. (C26H27N3,(COOH)2‚0.5H2O) C, H, N.
Syn th esis of (+)-cis-6-Ben zh yd r ylp ip er id in -3-yla m in e
(18b). 1-(5-Amino-2-benzhydrylpiperidin-1-yl)-2-methoxy-2-
phenylethanone 9b (0.172 g, 0.415 mmol) was dissolved in dry
THF, into it was added potassium tert-butoxide (0.372 g, 3.32
mmol), and the mixture was stirred overnight under N2
atmosphere. Stirring was stopped after 24 h, and into the
solution was added water. THF was evaporated in vacuo, and
the mixture was extracted with CH2Cl2 (3×). All extracts were
pooled, washed with brine, and dried over Na2SO4. The solvent
was then evaporated in vacuo to obtain a crude mixture which
was used without any further purification in the next step.
The crude mixture was dissolved in HCl (6 N, 10 mL), 2 mL
of methanol was added to dissolve the mixture completely, and
the solution was refluxed for 3-4 h. Methanol was then
evaporated under vacuum, and the solution was neutralized
with saturated solution of NaHCO3. The mixture was then
extracted with CH2CL2 (3×). All extracts were pooled, washed
with brine, and dried over Na2SO4. The solvent was evaporated
in vacuo to give a crude mixture which was purified by flash
chromatography using EtOAc:MeOH:Et3N (60:35:5) to give
C-H distances set to 0.96 to 0.93 Å, H_angles idealized, Uiso
-
(H) were set to 1.2 to 1.5 Ueq(C). Final residuals were R1 )
0.050 for the 3069 observed data with Fo > 4_(Fo) and 0.067
for all data. Final difference Fourier excursions of 0.15 and
-0.13 eÅ-3. The asymmetric unit contains a molecule of the
title compound and water at the partial occupancy of 0.187.
Tables of coordinates, bond distances and bond angles, and
anisotropic thermal parameters have been deposited with the
Crystallographic Data Centre, Cambridge, CB2, and 1EW,
England.
1
18b (0.082 g, 48%). H NMR (CDCl3, 400 MHz): δ 1.36-1.42
(2H, m, H-5), 1.59-1.62 (2H, m, H-4), 2.08 (2H, broad singlet,
NH), 2.79-2.80 (2H, m, H-2), 2.97-3.02 (1H, m, H-3), 3.25
(1H, dt, J ) 4 Hz, J ) 10 Hz, H-6), 3.80 (1H, d, (J ) 10.4),
(Ph)2CH), 7.13-7.40 (10H, m, ArH). The optical rotation was
Ack n ow led gm en t. This work was supported by the
National Institute on Drug Abuse, Grant No. DA 12449
(A.K.D.). We thank J anet Berfield and Li J uan Wang
for conducting the binding and uptake assays.
measured in Perkin-Elmer 241 polarimeter, [R]25 ) + 39° (c
D
1, MeOH).
Syn th esis of (+)-cis-4-[(6-Ben zh ydr ylpiper idin -3-ylam i-
n o)m eth yl]ben zon itr ile (19b). (+)-cis-6-Benzhydrylpiperi-
din-3-ylamine 18 (0.053 g, 0.28 mmol) was reacted with
4-cynobenzaldehyde (0.020 g, 0.22 mmol) (Procedure E) to yield
Su p p or tin g In for m a tion Ava ila ble: Crystal Structure
data and additional 1H NMR data interpretation are available
free of charge via the Internet at http://pubs.acs.org.
1
0.025 g (yield 43%) of 19b. H NMR (CDCl3, 400 MHz): δ 1.
30-1.44 (2H, m, H-5), 1.50(1H, tt, J ) 12.8 Hz, J ) 3.2 Hz,
H-4ax) 1.70-1.90 (3H, m, H-4eq, 2NH), 2.66-2.76 (2H, m, H-3eq,
H-2ax), 2.97-3.04 (1H, m, H-2eq), 3.27 (1H, dt, J ) 3.6 Hz, J )
9.6 Hz, H-6ax), 3.76-3.84 (3H, m, ArCH2, (Ph)2CH), 7.14-7.34
(8H, m, ArH), 7.35-7.41 (2H, m, ArH), 7.44-7.50 (2H, m,
ArH), 7.57-7.62 (2H, m, ArH). The optical rotation was
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