Structure-activity studies of 3′-4′-dichloro-meperidine analogues at dopamine and serotonin transporters

Article abstract of DOI:10.1016/j.bmc.2005.05.025

The structure-activity relationships of 3′,4′-dichloro- meperidine were investigated at dopamine (DAT) and serotonin transporters (SERT). Large ester substituents and lipophilic groups at the 4-position favored molecular recognition at the SERT. The benzy

Full text of DOI:10.1016/j.bmc.2005.05.025

Bioorganic & Medicinal Chemistry 13 (2005) 5623–5634
Structure–activity studies of 30-40-dichloro-meperidine analogues
at dopamine and serotonin transporters
Jill B. Rhoden,a Maud Bouvet,a Sari Izenwasser,b Dean Wade,b
Stacey A. Lomenzoa and Mark L. Trudella,*
aDepartment of Chemistry, University of New Orleans, New Orleans, LA 70148, USA
bDepartment of Psychiatry and Behavioral Sciences, University of Miami School of Medicine, Miami, FL 33136, USA
Received 30 March 2005; revised 18 May 2005; accepted 18 May 2005
Available online 1 July 2005
Abstract—The structure–activity relationships of 30,40-dichloro-meperidine were investigated at dopamine (DAT) and serotonin
transporters (SERT). Large ester substituents and lipophilic groups at the 4-position favored molecular recognition at the SERT.
The benzyl ester of 30,40-dichloro-meperidine exhibited high potency and high selectivity for the SERT (DAT/SERT = 760). Chem-
ical modification of the ester group and N-substitution generally led to compounds with decreased DAT affinity. Only small esters
and alkyl groups were tolerated at the 4-position of the meperidine ring system by the DAT. Overall, the meperidine analogues were
generally more selective for the SERT than for the DAT.
ꢀ 2005 Elsevier Ltd. All rights reserved.
1. Introduction
SERT(Ki = 19 nM) and was slightly SERT-selective
(DAT/SERT = 6.7) (see Fig. 1).
Recent studies in our laboratory have focused upon the
structure–activity relationships (SAR) of meperidine, 1,
an atypical l-opioid agonist, at monoamine transport-
ers.1,2 Meperidine was initially found to be selective
for the serotonin transporter (SERT) over the dopamine
transporter (DAT) (SERT/DAT = 43).1 Further explo-
ration of various aryl-substituted meperidine analogues
2 revealed that although the DAT affinity of these com-
pounds could be enhanced, high SERT affinity and
selectivity predominated throughout the series.2 Effects
of the aryl substituent on the DAT affinity of meperidine
analogues paralleled the SAR previously reported for
2b-carbomethoxy-3b-aryl tropanes 3,3–5 and cis-3-car-
bomethoxy-4-aryl piperidines, 4.6,7 From the SAR of
the meperidine analogues, the 3,4-dichlorophenyl group
was identified as an important moiety for molecular
recognition at the DAT. Similar effects of the 3,4-
dichlorophenyl group on DAT affinity have been re-
ported for other tropane derivatives,8–10 non-nitrogen
tropane analogues,11,12 and piperidine derivatives.13
However, unlike these tropane, tropane-related,
and piperidine ligands that are DAT selective, 30,40-
dichloromeperidine, 5, exhibited high potency at the
The inherent SERT selectivity of the meperidine ana-
logues 2 warranted an investigation of the SAR at
monoamine transporters to elucidate further the phar-
macophore requirements at both the DAT and the
SERT. To this end, it was of interest to explore the
structural modification of meperidine and evaluate the
effects on DAT and SERT affinities. The modestly
SERT selective ligand 5 was selected as a molecular scaf-
fold for these studies since it exhibited good affinity at
Keywords: Meperidine; Dopamine transporter; Serotonin transporter.
*
Corresponding author. Tel.: +1 504 280 7337; fax: +1 504 280
6860; e-mail: mtrudell@uno.edu
Figure 1.
0968-0896/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2005.05.025

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J. B. Rhoden et al. / Bioorg. Med. Chem. 13 (2005) 5623–5634
both the DAT and the SERT. Herein, we report the syn-
thesis and biological evaluation of a series of modified
ester and N-substituted analogues of 30,40-dichlorome-
peridine, 5, at the dopamine and serotonin transporters.
acetal moieties, followed by reductive amination with
the corresponding arylaldehyde. Subsequent transforma-
tion of the nitrile group of 9a–c into the desired ethyl es-
ters 10a–c took place with a one-pot hydrolysis/ ethanol
esterification process. Alternatively, the remaining N-
alkylaryl (10d–f), N-alkyl, N-alkenyl, and N-alkynyl
congeners (10g–p) were prepared from 5 via a demethyla-
tion/N-alkylation sequence. The N-3-chloropropyl deriv-
ative 10n was prepared from the hydroxy derivative 10m
via the corresponding mesylate. Attempts to directly pre-
pare 10n from the 1,3-dichloropropane or 1-bromo-3-
chloropropane afforded an intractable mixture. Finally,
the N-(E)-3-iodo-2-propenyl analogue 10p was prepared
from the corresponding stannane 10o.15
2. Results
In an attempt to specifically increase potency and selec-
tivity for either the DAT or the SERT, various substitu-
tions on the ester group and on the nitrogen atom as
well as modifications of the ester moiety were consid-
ered. As illustrated in Scheme 1, ester analogues of 5
were prepared from the diacetal 6 using a synthetic
approach that was previously developed in our labora-
tories.2 Hydrolysis of 6 and concomitant reductive ami-
nation with methylamine furnished the piperidine nitrile
7. The ester derivatives 8 were then obtained using a
one-pot hydrolysis/esterification process. Hydrolysis of
the nitrile 7 with aqueous sulfuric acid at 120 ꢁC was
followed by the addition of an appropriate alcohol in
excess. Azeotropic distillation of the alcohol/water
afforded the desired ester substitutions 8a–g in good
overall yield. However, this process was not amenable
to high boiling alcohols. To this end, the benzyl ester
8h was obtained in 51% yield from the methyl ester 8a
using the 1,3-bis(mesityl)imidazol-2-ylidene (IMes)
carbene catalyzed transesterification method.14
As illustrated in Scheme 2, functional group transforma-
tion at the 4-position took place in a straightforward
fashion. Treatment of 5 or 7 with 1 equiv of a Grignard
reagent (methyl magnesium bromide and phenyl magne-
sium bromide) afforded the corresponding ketones 11
and 12, respectively. Sodium borohydride reduction of
11 gave the alcohol 13 in 90% yield. Lithium aluminum
hydride reduction of 5 furnished the alcohol 14 in 95%
yield. Subsequent conversion of 14 into the acetate 15,
the vinyl derivative 16, and ethyl analogue 17 was
effected using standard synthetic methods.
The transporter binding affinities were determined for the
30,40-dichloro meperidine analogues by their ability to dis-
place bound radiolabeled ligands from rat caudate-puta-
men tissue.2 The Ki values that are reported in Tables 1–3
are inhibition constants derived for the unlabeled ligands.
The binding affinities of the meperidine analogues were
determined at DAT by inhibition of [3H]WIN 35,428
binding. For compounds that were equipotent with 5 at
the DAT, the SERT affinity was also determined by inhi-
The N-substituted 30,40-dichloro meperidine derivatives
were synthesized using two different methods (Scheme
1). The N-alkylaryl congeners 10a–c were synthesized by
a reductive amination sequence in which the N-alkylaryl
group was introduced during construction of the piper-
idne ring system. The diacetal 6 was converted into the
N-alkylaryl piperidine nitriles 9a–c by hydrolysis of the
Scheme 1. Reagents and conditions: (i) 3 N HCl, 50 ꢁC, then CH3NH2ÆHCl, CH3OH, NaBH3CN; (ii) H2SO4/H2O, 120 ꢁC, then R1OH, azeotropic
distillation; (iii) BnOH, IMesÆHCl, t-BuOK, THF; (iv) 3 N HCl, 50 ꢁC, then R2NH2ÆHCl, CH3OH, NaBH3CN; (v) H2SO4/H2O, 120 ꢁC, then EtOH,
azeotropic distillation; (vi) ACE-Cl, ClCH2CH2Cl, reflux; then CH3OH; (vii) R2X (X=Cl or Br), KI, Et3N, EtOH, reflux; (viii) H2, 10% Pd/C, EtOH;
(ix) MsCl, Et3N, CH2Cl2, 48 h; (x) I2, CHCl3, 0 ꢁC.

J. B. Rhoden et al. / Bioorg. Med. Chem. 13 (2005) 5623–5634
5625
worthy that the benzyl ester 8h exhibited very high affinity
for the SERT (Ki = 3.9 nM) and was the most potent ana-
logue of the series. In addition, the transporter selectivity
(DAT/SERT = 760) was nearly 3 orders of magnitude
greater for the SERT than the DAT.
For the N-substituted series (Table 2), the esters (10a–c)
were more potent than the corresponding nitriles (9a–c).
This was consistent with the previous SAR of the aryl-
substituted meperidine derivatives.2 Overall, the N-alkyl
substituted meperidine analogues were less potent at the
DAT than the corresponding N-methyl derivative 5. The
most potent compounds of the N-substituted series were
the N-propargyl 10j (Ki = 504 nM) and the N-phenyl-
propyl ester 10c (Ki = 515 nM) and N-propylchloro
10n (Ki = 573 nM) derivatives, whereas the least potent
compounds were the N-benzyl 10a and the N-iodo-
propenyl 10n derivatives.
The binding affinities of the modified ester derivatives
11–17 at the DAT and SERT are summarized in Table
3. Conversion of the ester moiety of 5 into the ketones
11 (Ki = 367 nM) and 12 (Ki = 253 nM) resulted in a
slightly decreased affinity for both the DAT and the
SERT. The alcohol derivatives 13 and 14 exhibited sig-
nificant decreases in DAT affinity, while the SERT affin-
ity was only modestly affected. As a result, the SERT
selectivity of 13 and 14 increased significantly (DAT/
SERT ꢀ 40). Conversion of the alcohol 14 into the ace-
tate 15 improved the DAT affinity (Ki = 633 nM) but re-
mained SERT selective (Ki = 38 nM, DAT/SERT = 17).
The 4-vinyl (16, Ki = 9 nM) and 4-ethyl (17, Ki = 11 nM)
analogues exhibited potent SERT affinity and were
nearly equipotent with 5 at the DAT but exhibited en-
hanced selectivity for the SERT (DAT/SERT ꢀ 18).
Scheme 2. Reagents and conditions: (i) CH3MgBr, Et2O, 0 ꢁC; (ii)
PhMgBr, Et2O, 0 ꢁC; (iii) NaBH4, CH3OH; (iv) LiAlH4, Et2O; (v)
CH3COCl, DMAP, ET3N, CH2Cl2; (vi) (COCl)2, DMSO, i-Pr2NEt,
CH2Cl2, then CH3PPh3Br, BuLi, THF; (vii) H2, 10% Pd/C, CH3OH.
bition of [3H]paroxetine binding using assay methods pre-
viously reported.2
3. Discussion
Despite similarities between the substituted aryltropanes
and the aryl-substituted meperidine analogues relative
to SAR trends at the DAT, the SAR of the ester moiety
of the two classes of compounds was significantly differ-
ent. Unlike the phenyltropanes that can tolerate a wide
variety of esters and functionality at the 2-position of
the tropane system and maintain high DAT affinity,16–21
a slight modification of the ester group at the 4-position
of the piperidine ring of 5 resulted in significant loss of
In general, the ester analogues 8a–h (Table 1) exhibited
equipotent-binding affinity at the SERT relative to 5. In
addition, all of the esters 8a–h were more selective for
the SERT than the DAT. Only the branched short-chain
esters 8c (i-Pr, Ki = 271 nM) and 8e (sec-Bu, Ki = 283 nM)
exhibited similar DAT potency. Once the ester chain ex-
ceeded four carbon atoms in length, the binding affinity
at the DAT dropped into the micromolar range, while
the SERT affinity was not significantly affected. It is note-
Table 1. In vitro binding data at the DAT and the SERT for the 30,40-dichloro meperidine ester derivatives 8
Compounda
R1
[3H]WIN 35,428 (DAT) Ki (nM)b
[3H]Paroxetine (SERT) Ki (nM)b
DAT/SERT
5
–CH2CH3
–CH3
125 15
383 32
449 94
18.7 2.6
15.4 1.1
16.4 0.7
43.3 7.0
16.0 2.5
44.3 4.7
ND
6.7
25
8a
8b
8c
8d
8e
8f
8g
8h
–CH2CH2CH3
–CH(CH3)2
27
271 51
864 110
283 11
6.3
–CH2(CH2)2CH3
–CH(CH3)CH2CH3
–(CH2)4CH3
–CH2CH2CH(CH3)2
–CH2C6H5
54
6.4
1580 190
1810 230
2970 300
ND
ND
760
ND
3.9 0.5
ND, not determined.
a All compounds were tested as the HCl salt.
b All values are means SEM of three experiments performed in triplicate.

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J. B. Rhoden et al. / Bioorg. Med. Chem. 13 (2005) 5623–5634
Table 2. In vitro binding data at DAT for the N-substituted 30,40-
dichloro meperidine derivatives 9 and 10
Substitution of the N-methyl group of 5 led to a greatly
diminished affinity, of the ester analogues 10 at the
DAT. Since N-substitution among the cis-3-carbome-
thoxy-4-arylpiperidines and 2b-carbomethoxy-3b-aryl-
tropanes does not generally lead to increased SERT
binding affinity these compounds were not evaluated
in SERT assays.23,24 In general, the various N-substi-
tuted derivatives 10 exhibited DAT affinity that was
much less than the N-methyl analogue 5. The N-alkyl-
aryl analogues 10a–c exhibited reduced affinity, relative
to the N-methyl ester 5, similar to that reported for the
3-carbomethoxy-4-arylpiperidines.24 Likewise, N-alkyl
(10g, 10i, 10k, 10l, and 10m), N-alkenyl (10d, 10h, and
10n), and N-alkynyl (10j) substitution led to decreased
affinity of 5 at the DAT. Similar substitution effects have
been reported for the 2b-carbomethoxy-3b-aryltropanes
on DAT affinity with mixed effects on DAT/SERT
selectivity.15,23
Compounda R2
[3H]WIN 35,428 (DAT) Ki (nM)
4
9a
2670 240
4180 990
1790 120
1500 300
1860 230
1100 370
514 30
CH2Ph
9b
9c
CH2CH2Ph
CH2(CH2)2Ph
CH2Ph
10a
10b
10c
10d
10e
10f
10g
10h
10i
10j
10k
10l
10m
10n
CH2CH2Ph
CH2(CH2)2Ph
t-CH2CH@CHPh 1500 110
CH2(CH2)3Ph
CH2(CH2)4Ph
CH2CH3
1110 130
625 110
894 460
1140 130
1170 150
504 46
CH2CH@CH2
CH2CH2CH3
CH2C„CH
CH2-cycloPr
CH2CH2CH2F
CH2CH2CH2Cl
t-CH2CH@CHI
1510 180
825 160
573 84
2000 250
In general, the ester-modified derivatives 11–17 exhi-
bited similar potency at SERT to that of the ester 5.
The 4-vinyl (16) and 4-ethyl (17) analogues were the
most potent ligands of this series at the SERT and
were equipotent with benzyl ester 8h. However, the
SERT selectivity of 16 and 17 over the DAT was only
modestly increased, relative to 5, due to only slightly
diminished DAT affinities of the compounds. It is note-
worthy that the electronic character of the functional
group at the 4-position of the meperidine ring system
did not significantly affect the binding affinity at the
SERT. Only the alcohol 14 exhibited a significant
reduction in affinity for the DAT relative to 5. This
is similar to the SAR of the 2b-substituted-3b-aryl-
tropanes and cis-3-substituted 4-arylpiperidines in that
an ester moiety is not required for high affinity binding
and that a variety of functional groups can be tolerated
at this position.16–21,24,25
All values are means SEM of three experiments performed in
triplicate.
a All compounds were tested as the HCl salt.
Table 3. In vitro binding data at DAT and SERT for the 30,40-dichloro
meperidine derivatives 11–17
Compounda
Ki (nM)
DAT/SERT
DAT
SERT
5
125 15
367 35
253 21
670 39
19 2.6
35 13
200 18
6.7
10
11
12
13
14
15
16
17
1.3
36
17
83
38
9
1
3
6
2
1
3310 210
633 91
192 31
163 38
40
17
17
18
11
All values are means SEM of three experiments performed in
triplicate.
a All compounds were tested as the HCl salt.
In conclusion, the results of this study clearly demon-
strate that meperidine and its analogues are selective
ligands for the SERT over the DAT. Chemical modifica-
tion of the ester group generally led to compounds with
increased SERT affinity. The long-chain ester substitu-
ents and lipophilic groups at the 4-position favored
molecular recognition at the SERT. In addition, hydro-
philic groups did not affect SERT affinity but greatly re-
duced DAT affinity and led to enhanced SERT
selectivity. The benzyl ester 8h was found to be the most
potent and most selective ligand of this study. Despite
some structural similarities and common trends in
SAR to the cis-3-substituted-4-arylpiperidines and 2-
substituted-3b-aryltropanes, the meperidine derivatives
exhibited more potent affinity for the SERT and were
significantly less potent at the DAT than the corre-
sponding cis-3-substituted-4-arylpiperidines and 2b-
substituted-3b-aryltropanes. Overall, this investigation
suggests that the ester moiety at the 4-position is a key
structural feature of the meperidine-related compounds
for molecular recognition at the SERT as well as differ-
entiation between the SERT and the DAT. This suggests
that analogues of meperidine could be developed as po-
tential selective serotonin reuptake inhibitors (SSRIs).
Structure–activity studies directed toward the optimiz-
affinity at the DAT. While small-branched esters (8c and
8e) exhibited comparable affinity to the ethyl ester 5,
long-chain esters (8d and 8f), as well as more sterically
demanding esters (8g and 8h), were not tolerated at
the binding site on the DAT. Alternatly, an increase in
the size of the ester chain of 5 led to increased affinity
at the SERT. Most notably, the benzyl ester 8h was
the most potent ligand of the series at the SERT. In
addition, 8h exhibited high selectivity for the SERT over
the DAT and is the most SERT selective meperidine
analogue reported to date. From these data, it appears
that it is the position of the ester moiety in the meperi-
dine system, relative to that of the 2b-carbomethoxy-
3b-aryltropanes, that leads to an observed reversal of
transporter selectivity favoring the SERT. While the
SERT can tolerate fairly large lipophilic ester residues
at the 4-position, the DAT can only accommodate the
small-ester chains. In addition, the hydroxyl group at
the 4-position led to a greatly reduced affinity for the
DAT, while the SERT affinity was unaffected. This rep-
resents a significant divergence in the SAR of the
meperidines from the cis-3-substituted-4-arylpiperi-
dines22 and 2-substituted-3b-aryltropanes.

J. B. Rhoden et al. / Bioorg. Med. Chem. 13 (2005) 5623–5634
5627
ation of SERT selectivity are currently under investi-
gation and will be reported in due course.
(dd, 1H, J = 2.4, 8.4 Hz), 3.67 (s, 3H), 2.81 (br s, 2H),
2.55 (d, 2H, J = 12.8 Hz), 2.30 (s, 3H), 2.18 (t, 2H,
J = 10.8 Hz), 1.98 (t, 2H, J = 10.8 Hz). 13C NMR (free
base): d 173.8, 142.9, 132.5, 131.1, 130.3, 128.1, 125.3,
53.2, 52.3, 48.3, 46.1, 33.7. Anal. Calcd for C14H17
NO2Cl2ÆHClÆ0.5H2O: C, 48.36; H, 5.51; N, 4.03. Found:
C, 48.28; H, 5.46; N, 4.09.
4. Experimental
All chemicals were purchased from Aldrich Chemical
Co., Milwaukee, WI, unless otherwise noted. THF,
CH2Cl2, and CH3OH were dried under the argon system.
Toluene and Et2O were dried by distillation over Na/
benzophenone. Chromatography refers to column chro-
matography on silica gel (Silica Gel 60, 230–400 mesh).
Petroleum ether refers to pentanes with a boiling point
range of 30–60 ꢁC. Reported melting points are uncor-
rected. NMR spectra were recorded on a Varian-Gemini
400 MHz spectrometer. Chemical shifts are reported as d
values with tetramethylsilane (TMS), employed as the
internal standard. Elemental analyses were obtained
from Atlantic Microlabs, Inc., Norcross, GA.
4.4. 4-(3,4-Dichlorophenyl)-1-methyl-piperidine-4-
carboxylic acid propyl ester (8b)
General procedure B. This compound was obtained as an
orange oil (210 mg, 58% yield) and converted into a
hydrochloride salt (Section 4.1), which was obtained as
1
a white solid, mp 202–204 ꢁC. H NMR (free base): d
7.47 (d, J = 2.4 Hz, 1H), 7.39 (d, J = 8.4 Hz, 1H), 7.23
(dd, J = 2.0 Hz, J = 8.4 Hz, 1H), 4.04 (t, J = 6.6 Hz,
2H), 2.79 (br s, 2H), 2.56 (d, J = 13.2 Hz, 2H), 2.28 (s,
3H), 2.16 (m, 2H), 1.96 (m, 2H), 1.59 (m, 2H), 0.86 (t,
J = 7.6 Hz, 3H). 13C NMR (free base): d 173.5, 136.6,
131.2, 130.4, 128.2, 125.4, 66.8, 53.2, 48.3, 46.1, 33.6,
21.8, 10.3. Anal. Calcd for C16H21NO2Cl2ÆHClÆH2O: C,
49.95; H, 6.29; N, 3.64. Found: C, 50.19; H, 6.00; N, 3.70.
4.1. General procedure A. Preparation of hydrochloride
salts
All of the compounds were converted into the hydro-
chloride salts for biological testing, as well as for storage
and handling purposes. The base (50–100 mg) was dis-
solved in a minimum amount of Et2O (1–2 mL) and
added to a saturated ethereal solution (10 mL) of anhy-
drous hydrogen chloride. The hydrochloride salts crys-
tallized and were washed with Et2O (3· 2 mL) and
purified by titration with Et2O and ethyl acetate. Frac-
tional moles of water could not be prevented, despite vig-
orous drying (110 ꢁC, 1 h) under vacuum (0.01 mmHg).
All compounds were homogeneous by thin-layer chro-
matography (CHCl3/CH3OH/NH4OH, 90:9:1).
4.5. 4-(3,4-Dichlorophenyl)-1-methyl-piperidine-4-
carboxylic acid isopropyl ester (8c)
General procedure B. This compound was obtained as an
orange oil (134 mg, 39% yield) and converted into a
hydrochloride salt (Section 4.1), which was obtained as
1
a white solid, mp 221–223 ꢁC. H NMR (free base): d
7.47 (d, J = 2.0 Hz, 1H), 7.40 (d, J = 8.8 Hz, 1H), 7.22
(dd, J = 2.0 Hz, J = 8.2 Hz, 1H), 5.02 (m, 1H), 2.82 (br
s, 2H), 2.54 (d, J = 12.8 Hz, 2H), 2.30 (s, 3H), 2.16 (m,
2H), 1.96 (m, 2H), 1.17 (d, J = 6.0 Hz, 6H). 13C NMR
(free base): d 172.8, 132.6, 131.2, 130.4, 128.2, 125.3,
66.7, 53.2, 48.2, 46.0, 33.5, 21.5. Anal. Calcd for
C16H21NO2Cl2ÆHClÆH2O: C, 49.95; H, 6.29; N, 3.64.
Found: C, 49.81; H, 6.20; N, 3.65.
4.2. General procedure B. Esterification of nitriles
The nitrile 7 or 9 (5.2 mmol) in an aqueous solution of
sulfuric acid (6.5 mL H2SO4/H2O, 1:1) was heated in
an oil bath at 120 ꢁC for 1.5 h. The flask was then
equipped with a Dean Stark Trap and excess alcohol
was added. The water was azeotropically removed over
4 h and alcohol was added as needed. The reaction was
heated to reflux overnight, then the reaction mixture was
allowed to come to room temperature and excess alco-
hol was removed under reduced pressure. The flask
was then cooled in an ice bath and the acid was neutral-
ized to a pH of 10 with 1 N NaOH. The aqueous layer
was extracted with Et2O (3· 75 mL). The combined or-
ganic fractions were dried (Na2SO4) and the solvent was
removed under reduced pressure. The residue was puri-
fied by flash chromatography (CHCl3/CH3OH/NH4OH,
90:9:1) to afford the esters 8a–g and 10a–c.
4.6. 4-(3,4-Dichlorophenyl)-1-methyl-piperidine-4-
carboxylic acid butyl ester (8d)
General procedure B. This compound was obtained as an
orange oil (200 mg, 54% yield) and converted into a
hydrochloride salt (Section 4.1), which was obtained as
1
a white solid, mp 177–179 ꢁC. H NMR (free base): d
7.47 (d, J = 2.0 Hz, 1H), 7.39 (d, J = 8.8 Hz, 1H), 7.22
(dd, J = 2.4, 8.8 Hz, 1H), 4.07 (t, J = 6.4 Hz, 1H), 2.77
(br s, 2H), 2.54 (d, J = 13.2 Hz, 2H), 2.27 (s, 3H), 2.15
(t, J = 10.8 Hz, 2H), 1.94 (t, J = 11.2 Hz, 2H), 1.55 (m,
J = 6.8 Hz, 2H), 1.28 (m, J = 7.2 Hz, 2H), 0.878 (t,
J = 7.6 Hz, 3H). 13C NMR (free base): d 173.4, 143.1,
132.6, 131.1, 130.3, 128.2, 125.3, 65.0, 53.2, 48.3, 46.1,
33.6, 30.4, 19.0, 13.5. Anal. Calcd for C17H23 NO2Cl2Æ
HClÆH2O: C, 51.20; H, 6.57; N, 3.51. Found: C, 51.23;
H, 6.54; N, 3.52.
4.3. 4-(3,4-Dichlorophenyl)-1-methyl-piperidine-4-
carboxylic acid methyl ester (8a)
General procedure B. This compound was obtained as a
yellow solid (150 mg, 56% yield) and converted into a
hydrochloride salt (Section 4.1), which was obtained as
a white solid, mp 196–198 ꢁC. H NMR (free base): d
7.45 (d, 1H, J = 2.4 Hz), 7.40 (d, 1H, J = 8.4 Hz), 7.21
4.7. 4-(3,4-Dichlorophenyl)-1-methyl-piperidine-4-
carboxylic acid sec-butyl ester (8e)
1
General procedure B. This compound was obtained as
an orange oil (140 mg, 35% yield) and converted into

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J. B. Rhoden et al. / Bioorg. Med. Chem. 13 (2005) 5623–5634
a hydrochloride salt (Section 4.1), which was obtained
as a white solid, mp 198–200 ꢁC. H NMR (free base):
verted into a hydrochloride salt (Section 4.1), which
was obtained as a white solid, mp 186–188 ꢁC. 1H
NMR (free base): d 7.43 (d, J = 2.4 Hz, 1H), 7.36 (d,
J = 8.4 Hz, 1H), 7.30 (m, 3H), 7.19 (m, 2H), 7.18
(dd, J = 2.4, 8.4 Hz, 1H), 5.10 (s, 2H), 2.76 (d,
J = 8.8 Hz, 2H), 2.56 (d, J = 12.4 Hz, 2H), 2.24 (s, 3H),
2.12 (t, J = 10.8 Hz, 2H), 1.95 (t, J = 10.8 Hz, 2H). 13C
NMR (free base): d 173.3, 135.4, 132.7, 131.3, 130.4,
128.5, 128.3, 128.1, 125.4, 67.0, 53.1, 48.4, 46.1, 33.6.
Anal. Calcd for C20H21NO2Cl2ÆHClÆ 0.5H2O: C, 56.68;
H, 5.47; N, 3.31. Found: C, 56.54; H, 5.53; N, 3.29.
1
d 7.48 (d, J = 2.0 Hz, 1H), 7.39 (d, J = 8.4 Hz, 1H),
7.23 (dd, J = 2.4, 8.4 Hz, 1H), 4.84 (m, 1H), 2.80 (br
s, 2H), 2.56 (d, J = 12.8 Hz, 2H), 2.30 (s, 3H), 2.21
(m, 2H), 1.96 (m, 2H), 1.50 (m, 2H), 1.13 (d,
J = 6.4 Hz, 3H), 0.78 (t, J = 7.6 Hz, 3H). 13C NMR
(free base): d 173.0, 132.6, 131.1, 130.3, 128.2, 125.3,
53.2, 48.2, 46.1, 33.5, 28.6, 19.2, 9.6. Anal. Calcd for
C17H23NO2Cl2ÆHCl: C, 53.63; H, 6.35; N, 3.68. Found:
C, 53.51; H, 6.27; N, 3.68.
4.8. 4-(3,4-Dichlorophenyl)-1-methyl-piperidine-4-
carboxylic acid pentyl ester (8f)
4.11. General procedure C. Reductive amination of 6 with
alkylaryl amines
General procedure B. This compound was obtained
(CHCl3/CH3OH, 19:1) as an orange oil (56 mg, 17% yield)
and converted into a hydrochloride salt (Section 4.1),
which was obtained as a white solid, mp 158–160 ꢁC. 1H
NMR (free base): d 7.30 (d, J = 2.8 Hz, 1H), 7.35 (d,
J = 11.6 Hz, 1H), 7.18 (dd, J = 2.8, 11.4 Hz, 1H), 4.03
(t, J = 8.8 Hz, 2H), 2.76 (d, J = 14.4 Hz, 2H), 2.51 (d,
J = 16.8 Hz, 2H), 2.24 (s, 3H), 2.13 (t, J = 15.2 Hz, 2H),
1.91 (t, J = 14 Hz, 2H), 1.52 (m, J = 9.2 Hz, 2H), 1.21
(m, 4H), 0.82 (t, J = 9.2 Hz, 3H). 13C NMR (free base):
d 173.1, 142.4, 132.6, 131.3, 130.3, 128.1, 125.2, 65.4,
53.0, 48.1, 45.6, 33.0, 28.1, 28.0, 22.1, 13.9. Anal. Calcd
for C18H25NO2Cl2Æ HClÆH2O: C, 52.37; H, 6.84; N, 3.39.
Found: C, 51.95; H, 6.52; N, 3.21.
To a three-necked round-bottomed flask containing 3 N
HCl (160 mL) at 50 ꢁC was added the diacetal 6
(10 mmol) and the mixture was allowed to stir over-
night. The acid mixture was allowed to cool to room
temperature and then extracted with Et2O (300 mL).
The ethereal layer was washed with saturated NaHCO3
(150 mL) and dried (Na2SO4). The Et2O was removed
under reduced pressure. The resulting residue was dis-
solved in dry methanol (52 mL), and then the alkylaryl
amine hydrochloride (21 mmol) was added, followed
by the addition of NaBH3CN (9.4 mmol), and the mix-
ture was allowed to stir for 48 h under an atmosphere of
nitrogen. The methanol was removed under reduced
pressure and the residue was treated with saturated
NaHCO3 (160 mL) and extracted with Et2O (3·
100 mL). The combined organic fractions were dried
(Na2SO4) and the solvent was removed under reduced
pressure. The residue was purified by chromatography
(CHCl3/CH3OH, 39:1) to afford 9a–c, respectively.
4.9. 4-(3,4-Dichlorophenyl)-1-methyl-piperidine-4-
carboxylic acid 3-methyl-butyl ester (8g)
General procedure B. This compound was obtained as an
orange oil (250 mg, 70% yield) and converted into a
hydrochloride salt (Section 4.1), which was obtained as
4.12. 1-Benzyl-4-(3,4-dichlorophenyl)-piperidine-4-
carbonitrile (9a)
1
a white solid, mp 176–178 ꢁC. H NMR (free base): d
7.47 (d, J = 2.8 Hz, 1H), 7.39 (d, J = 8.4 Hz, 1H), 7.22
(dd, J = 2.2 Hz, J = 8.6 Hz, 1H), 4.10 (t, J = 6.6 Hz,
2H), 2.76 (br s, 2H), 2.54 (d, J = 12.8 Hz, 2H), 2.26 (s,
3H), 2.13 (m, 2H), 1.93 (m, 2H), 1.45 (m, 2H), 0.90
(m, 1H), 0.86 (d, J = 8.6 Hz, 6H). 13C NMR (free base):
d 173.6, 132.6, 131.2, 130.3, 128.3, 125.4, 63.8, 53.2,
48.3, 46.1, 37.1, 33.7, 25.0, 22.3. Anal. Calcd for
C18H25NO2Cl2ÆHCl: C, 54.77; H, 6.64; N, 3.55. Found:
C, 54.83; H, 6.65; N, 3.59.
General procedure C. This compound was obtained as a
yellow oil (2.0 g, 56% yield) and converted into the
hydrochloride salt (Section 4.1), which was obtained as
a white solid, mp 271–274 ꢁC (dec.). 1H NMR (free
base): d 7.59 (d, J = 2.0 Hz, 1H), 7.47 (d, J = 8.0 Hz,
1H), 7.36 (d, J = 2.4 Hz, 1H), 7.34 (m, 4H), 7.29 (t,
J = 4.4 Hz, 1H), 3.61 (s, 2H), 3.02 (d, J = 10.8 Hz,
2H), 2.51 (s, 2H), 2.08 (s, 4H). 13C NMR (free base): d
140.4, 137.7, 133.1, 132.2, 130.8, 128.9, 128.2, 127.8,
127.2, 125.1, 121.1, 62.6, 50.3, 42.2, 36.3. Anal. Calcd
for C19H18N2Cl2ÆHClÆ0.5H2O: C, 58.40; H, 5.16; N,
7.17. Found: C, 58.24; H, 4.94; N, 7.08.
4.10. 4-(3,4-Dichlorophenyl)-1-methyl-piperidine-4-
carboxylic acid benzyl ester (8h)
A flask containing oven-dried 4 A molecular sieves
(500 mg) was charged with IMesHCl (10 mol %), potas-
sium t-butoxide (9.5 mol %), and THF (1 mL). The mix-
ture was allowed to stir under an atmosphere of nitrogen
for 15 min. The methyl ester (1 mmol) and benzyl alco-
hol (1.5 mmol) were dissolved in THF (0.5 mL) and
added to the reaction mixture via cannula. The reaction
was allowed to stir at room temperature and was moni-
tored by TLC (CHCl3/CH3OH, 19:1). The mixture was
filtered and the solvent was removed under reduced pres-
sure. The crude product was purified using column chro-
matography (CHCl3/CH3OH, 19:1) and obtained as a
pale yellow solid (97 mg, 51% yield). The base was con-
4.13. 4-(3,4-Dichlorophenyl)-1-phenethyl-piperidine-4-
carbonitrile (9b)
General procedure C. This compound was obtained
(CHCl3) as a white solid (320 mg, 32% yield) and con-
verted into the hydrochloride salt (Section 4.1), which
was obtained as a white solid, mp 244–250 ꢁC (dec.).
1H NMR (free base): d 7.60 (d, J = 2.4 Hz, 1H), 7.47
(d, J = 8.4 Hz, 1H), 7.35 (dd, J = 2.4, 8.6 Hz, 1H), 7.30
(m, 2H), 7.21 (m, 1H), 3.11 (d, J = 12.8 Hz, 2H), 2.83
(m, 2H), 2.71 (m, 2H), 2.55 (m, 2H), 2.10 (d,
J = 8.6 Hz, 2H), 2.08 (m, 2H). 13C NMR (free base): d

J. B. Rhoden et al. / Bioorg. Med. Chem. 13 (2005) 5623–5634
5629
140.2, 139.8, 133.2, 132.4, 130.9, 128.5, 128.4, 127.8,
126.1, 125.0, 121.0, 60.0, 50.5, 42.3, 36.4, 33.6. Anal.
Calcd for C20H20N2Cl2ÆHCl: C, 60.70; H, 5.35; N,
7.08. Found: C, 60.66; H, 5.45; N, 6.99.
the hydrochloride salt (Section 4.1), which was obtained
as a white solid, mp 179–180 ꢁC. 1H NMR (free base): d
7.47 (d, J = 2.4 Hz, 1H), 7.37 (d, J = 8.4 Hz, 1H), 7.27
(m, 2H), 7.21 (dd, J = 2.4, 8.6 Hz, 1H), 7.17 (m, 3H),
4.12 (m, J = 7.2 Hz, 2H), 2.83 (d, J = 10.4 Hz, 2H),
2.62 (t, J = 7.6 Hz, 2H), 2.53 (d, J = 13.2 Hz, 2H), 2.34
(t, J = 7.2 Hz, 2H), 2.12 (t, J = 10.8 Hz, 2H), 1.91 (t,
J = 10.8 Hz, 2H), 1.81 (m, J = 7.6 Hz, 2H), 1.18 (t,
J = 7.2 Hz, 3H). 13C NMR (free base): d 173.5, 143.2,
142.0, 132.5, 131.0, 130.3, 128.3, 128.2, 128.2, 128.1,
125.7, 125.4, 61.1, 57.9, 51.2, 48.8, 33.7, 33.6, 28.6,
14.0. Anal. Calcd for C23H27NO2Cl2ÆHCl: C, 60.47; H,
6.18; N, 3.07. Found: C, 60.36; H, 6.14; N, 3.09.
4.14. 4-(3,4-Dichlorophenyl)-1-(3-phenyl-propyl)-
piperidine-4-carbonitrile (9c)
General procedure C. This compound was obtained
(CHCl3) as an orange oil (370 mg, 36% yield) and con-
verted into the hydrochloride salt (Section 4.1), which
was obtained as a white solid, mp 230–234 ꢁC (dec.).
1H NMR (free base): d 7.60 (d, J = 2.0 Hz, 1H), 7.48
(d, J = 8.8 Hz, 1H), 7.35 (dd, J 2.4, 8.8 Hz, 1H), 7.29
(m, 2H), 7.20 (m, 3H), 3.05 (d, J = 12.0 Hz, 1H), 2.66
(t, J = 7.6 Hz, 2H), 2.49 (t, J = 7.6 Hz, 2H), 2.45 (d,
J = 7.6 Hz, 2H), 2.09 (d, J = 4.0 Hz, 4H), 1.87 (m,
J = 8.0 Hz, 2H); 13C NMR (free base): d 141.8, 140.4,
133.1, 132.3, 130.8, 128.3, 128.3, 127.8, 125.8, 125.0,
121.1, 57.5, 50.4, 42.3, 36.4, 33.5, 28.5. Anal. Calcd for
C21H22N2Cl2ÆHCl: C, 61.55; H, 5.66; N, 6.84. Found:
C, 61.67; H, 5.64; N, 6.82.
4.18. General procedure D. N-Demethylation
N-alkylation of 5
A solution of 5 (6.1 mmol), sodium bicarbonate
(9.1 mmol) and 1-chloro-ethylchloroformate (52 mmol)
in 1,2-dichloroethane (27 mL) was heated to reflux under
an atmosphere of nitrogen for 48 h. The product was fil-
tered to remove the sodium bicarbonate and the solvent
was removed under reduced pressure. Methanol
(155 mL) was added and the mixture was heated to reflux
for 3 h. The solvent was removed under reduced pressure.
Chloroform was added, washed with 1.8 N NaOH
(30 mL) and water (30 mL), and then dried (Na2SO4).
The crude product was purified by column chromato-
graphy (SiO2, CHCl3/CH3OH, 12:1) to afford the norme-
peridine analogue. To the N–H compound (0.33 mmol)
and potassium iodide (0.1 mol %) in triethylamine
(140 lL/mmol) and ethanol (10 mL/mmol), the appropri-
ate alkylbromide oralkylchloride(0.50 mmol) wasadded.
The mixture was heated to reflux under an atmosphere of
nitrogen for 16 h. The solvent was removed underreduced
pressure and the crude products were purified by column
chromatography to afford the products 10d–p.
4.15. 1-Benzyl-4-(3,4-dichlorophenyl)-piperidine-4-
carboxylic acid ethyl ester (10a)
General procedure B. This compound was obtained as a
pale yellow solid (1.2 g, 55% yield) and converted into
the hydrochloride salt (Section 4.1), which was obtained
as a white solid, mp 246–249 ꢁC. 1H NMR (free base): d
7.47 (d, J = 2.0 Hz, 1H), 7.36 (d, J = 8.4 Hz, 1H), 7.28
(m, 3H), 7.23 (m, 2H), 7.21 (dd, J = 2.0, 8.6 Hz, 1H),
4.12 (m, J = 7.2 Hz, 2H), 3.46 (s, 2H), 2.80 (d,
J = 11.6 Hz, 2H), 2.51 (d, J = 12.8 Hz, 2H), 2.17
(t, J = 11.6 Hz, 2H), 1.90 (t, J = 11.2 Hz, 2H), 1.17
(t, J = 6.8 Hz, 3H). 13C NMR (free base): d 173.5,
143.3, 138.2, 132.5, 131.0, 130.3, 129.0, 128.1, 127.0,
125.4, 63.0, 61.1, 51.1, 48.7, 33.7, 14.0. Anal. Calcd for
C21H23NO2Cl2ÆHCl: C, 58.82; H, 5.64; N, 3.27. Found:
C, 58.78; H, 5.67; N, 3.23.
4.19. 4-(3,4-Dichlorophenyl)-1-(cinnamyl)-piperidine-4-
carboxylic acid ethyl ester (10d)
General procedure D. This compound was obtained as
an orange solid (39 mg, 38% yield) and converted into
the hydrochloride salt (Section 4.1), which was obtained
as a white solid, mp 217–219 ꢁC (dec.). H NMR (free
4.16. 4-(3,4-Dichlorophenyl)-1-phenethyl-piperidine-4-
carboxylic acid ethyl ester (10b)
1
General procedure B. This compound was obtained as a
light yellow solid (180 g, 50% yield) and converted into
the hydrochloride salt (Section 4.1), which was obtained
as a white solid, mp 206–208 ꢁC. 1H NMR (free base): d
7.48 (d, J = 2.0 Hz, 1H), 7.39 (d, J = 8.8 Hz, 1H), 7.27
(m, 2H), 7.23 (dd, J = 2.0, 8.6 Hz, 1H), 7.19 (m, 3H),
4.14 (m, J = 7.2 Hz, 2H), 2.92 (d, J = 11.2 Hz, 2H),
2.80 (m, 2H), 2.58 (m, 4H), 2.22 (t, J = 10.8 Hz, 2H),
1.94 (m, 2H), 1.19 (t, J = 6.8 Hz, 3H). 13C NMR (free
base): d 173.5, 143.1, 140.2, 132.6, 131.1, 130.3, 128.6,
128.3, 128.2, 126.0, 125.4, 61.2, 60.5, 51.2, 48.8, 33.7,
14.0. Anal. Calcd for C22H25NO2Cl2ÆHCl: C, 59.67; H,
5.92; N, 3.16. Found: C, 59.76; H, 5.96; N, 3.17.
base): d 7.47 (d, J = 2.4 Hz, 1H), 7.38 (d, J = 8.4 Hz,
1H), 7.37 (d, J = 6.8 Hz, 2H), 7.30 (t, J = 7.2 Hz, 2H),
7.23 (m, 1H), 7.22 (dd, J = 2.4, 8.6 Hz, 1H), 6.51 (d,
J = 16.0 Hz, 1H), 6.26 (tt, J = 6.8 15.6 Hz, 1H), 4.14
(q, J = 6.8 Hz, 2H), 3.13 (d, J = 6.8 Hz, 2H), 2.91 (d,
J = 9.6 Hz, 2H), 2.55 (d, J = 12.8 Hz, 2H), 2.19 (t,
J = 10.8 Hz, 2H), 1.94 (t, J = 10.8 Hz, 2H), 1.19 (t,
J = 6.8 Hz, 3H). 13C NMR (free base): d 173.5, 143.1,
136.8, 133.1, 132.6, 131.1, 130.3, 128.5, 128.2, 127.5,
126.5, 126.3, 125.4, 95.4, 61.2, 61.1, 51.2, 48.7, 33.7,
14.0. Anal. Calcd for C23H25NO2Cl2ÆHCl: C, 60.74; H,
5.76; N, 3.08. Found: C, 60.61; H, 5.62; N, 3.05.
4.17. 4-(3,4-Dichlorophenyl)-1-(3-phenylpropyl)-piperi-
dine-4-carboxylic acid ethyl ester (10c)
4.20. 4-(3,4-Dichlorophenyl)-1-(4-phenylbutyl)-piperidine-
4-carboxylic acid ethyl ester (10e)
General procedure B. This compound was obtained as a
light yellow oil (140 mg, 47% yield) and converted into
General procedure D. This compound was obtained as a
yellow solid (97 mg, 67%) and converted into the hydro-

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J. B. Rhoden et al. / Bioorg. Med. Chem. 13 (2005) 5623–5634
chloride salt (Section 4.1), which was obtained as a
white solid, mp 148–150 ꢁC (HCl salt). H NMR (free
2.55 (d, J = 12.8 Hz, 2H), 2.14 (t, J = 11.2 Hz, 2H),
1.92 (t, J = 10.8 Hz, 2H), 1.19 (t, J = 7.2 Hz, 3H). 13C
NMR (free base): d 173.4, 143.2, 134.9, 132.5, 131.1,
130.3, 128.1, 125.3, 118.0, 61.7, 61.1, 51.0, 48.7, 33.6,
13.9. Anal. Calcd for C17H21NO2Cl2ÆHCl: C, 53.91; H,
5.86; N, 3.70. Found: C, 54.13; H, 5.85; N, 3.69.
1
base): d 7.46 (d, J = 2.0 Hz, 1H), 7.37 (d, J = 8.8 Hz,
1H), 7.26 (m, 2H), 7.21 (dd, J = 2.4, 8.2 Hz, 1H), 7.16
(m, 3H), 4.12 (q, J = 7.2 Hz, 2H), 2.83 (d, J = 10.4 Hz,
2H), 2.62 (t, J = 6.8 Hz, 2H), 2.53 (d, J = 12.8 Hz,
2H), 2.33 (t, J = 7.2 Hz, 2H), 2.12 (t, J = 10.8 Hz, 2H),
1.92 (t, J = 10.4 Hz, 2H), 1.63 (m, J = 8.4 Hz, 2H),
1.53 (m, J = 6.8 Hz, 2H), 1.18 (t, J = 7.2 Hz, 3H). 13C
NMR (free base): d 173.4, 143.1, 142.3, 132.5, 131.2,
130.3, 128.3, 128.2, 128.1, 125.6, 125.3, 61.1, 58.4,
51.2, 48.7, 35.7, 33.5, 29.7, 26.5, 14.0. Anal. Calcd for
C24H29NO2Cl2ÆHClÆ0.5H2O: C, 60.64; H, 6.46; N, 2.95.
Found: C, 60.95; H, 6.36; N, 2.92.
4.24. 4-(3,4-Dichlorophenyl)-1-propyl-piperidine-4-
carboxylic acid ethyl ester (10i)
To a slurry of 10% Pd/C (4 mg) in ethanol (3.1 mL) un-
der an atmosphere of nitrogen was added a solution of
the alkene 10h (39 mg, 0.11 mmol) in ethanol (3.1 mL).
The mixture was hydrogenated at 1 atm overnight.
The catalyst was removed by filtration through a pad
of Celite. The filter cake was rinsed with methanol
(25 mL) and the filtrate was concentrated under reduced
pressure. The crude product was purified using column
chromatography (CHCl3/CH3OH, 13:1) to furnish 10i
as an orange oil (22 mg, 56% yield) and converted into
the hydrochloride salt (Section 4.1), which was obtained
as a white solid, mp 205–208 ꢁC. 1H NMR (free base): d
7.47 (d, J = 1.6 Hz, 1H), 7.39 (d, J = 8.8 Hz, 1H), 7.22
(dd, J = 2.0, 8.8 Hz, 1H), 4.14 (q, J = 7.2 Hz, 2H), 2.90
(d, 10.0 Hz, 2H), 2.55 (d, J = 13.2 Hz, 2H), 2.31 (m,
2H), 2.18 (t, J = 11.2 Hz, 2H), 1.97 (t, J = 10.8 Hz,
2H), 1.53 (m, J = 7.2 Hz, 2H), 1.20 (t, J = 6.8 Hz, 3H),
0.90 (t, J = 7.6 Hz, 3H). 13C NMR (free base): d 173.5,
143.0, 132.6, 131.2, 130.4, 128.2, 125.4, 61.2, 60.5,
51.1, 48.7, 33.4, 19.9, 14.0, 11.9. Anal. Calcd for
C17H23NO2Cl2ÆHCl: C, 53.63; H, 6.35; N, 3.68. Found:
C, 53.45; H, 6.28; N, 3.62.
4.21. 4-(3,4-Dichlorophenyl)-1-(5-phenylpentyl)-
piperidine-4-carboxylic acid ethyl ester (10f)
General procedure D. This compound was obtained as
an orange oil (55 mg, 37% yield) and converted into
the hydrochloride salt (Section 4.1), which was obtained
as a white solid, mp 157–158 ꢁC. 1H NMR (free base): d
7.46 (d, J = 2.0 Hz, 1H), 7.39 (d, J = 8.8 Hz, 1H), 7.27
(m, 2H), 7.22 (dd, J = 2.4, 8.4 Hz, 1H), 7.17 (m, 3H),
4.13 (q, J = 6.8 Hz, 2H), 2.84 (d, J = 10.0 Hz, 2H),
2.61 (t, J = 7.6 Hz, 2H), 2.54 (d, J = 12.8 Hz, 2H), 2.32
(t, J = 7.6 Hz, 2H), 2.14 (t, J = 9.6 Hz, 2H), 1.94 (t,
J = 10.4 Hz, 2H), 1.64 (m, J = 7.2 Hz, 2H), 1.54 (m,
J = 7.6 Hz, 2H), 1.34 (m, J = 7.6 Hz, 2H), 1.19 (t,
J = 7.2 Hz, 3H). 13C NMR (free base): d 173.5, 143.2,
142.5, 132.5, 131.1, 130.3, 128.3, 128.2, 128.2, 125.6,
125.4, 61.1, 58.6, 51.2, 48.8, 35.8, 33.6, 31.3, 27.2, 26.8,
14.0. Anal. Calcd for C25H31NO2Cl2ÆHCl: C, 61.93; H,
6.65; N, 2.89. Found: C, 61.87; H, 6.65; N, 2.88.
4.25. 4-(3,4-Dichlorophenyl)-1-prop-2-ynyl-piperidine-4-
carboxylic acid ethyl ester (10j)
4.22. 4-(3,4-Dichlorophenyl)-1-ethyl-piperidine-4-
carboxylic acid ethyl ester (10g)
General procedure D. This compound was obtained as a
yellow solid (104 mg, 90% yield) and converted into the
hydrochloride salt (Section 4.1), which was obtained as
a white solid, mp 193–195 ꢁC (dec.). 1H NMR (free
base): d 7.46 (d, J = 1.6 Hz, 1H), 7.38 (d, J = 8.4 Hz,
1H), 7.21 (dd, J = 2.0, 8.6 Hz, 1H), 4.14 (q, J = 6.8 Hz,
2H), 3.27 (d, J = 2.4 Hz, 2H), 2.85 (d, J = 11.2 Hz,
2H), 2.57 (d, J = 12.4 Hz, 2H), 2.37 (t, J = 12.0, 2H),
2.23 (t, J = 2.4 Hz, 1H), 1.92 (t, J = 10.4 Hz, 2H), 1.19
(t, J = 6.8 Hz, 3H). 13C NMR (free base): d 173.3,
143.1, 132.6, 131.2, 130.4, 128.1, 125.3, 78.7, 73.1,
61.2, 50.0, 48.4, 46.9, 33.6, 14.0. Anal. Calcd for
C17H19NO2Cl2ÆHCl: C, 54.20; H, 5.35; N, 3.72. Found:
C, 54.17; H, 5.29; N, 3.69.
General procedure D. This compound was obtained
(CHCl3/CH3OH, 19:1) as an off-white solid (95 mg,
87% yield) and converted into the hydrochloride salt
(Section 4.1), which was obtained as a white solid, mp
203–205 ꢁC. 1H NMR (free base):
d
7.45 (d,
J = 2.0 Hz, 1H), 7.41 (d, J = 8.0 Hz, 1H), 7.23 (dd,
J = 2.0, 8.6 Hz, 1H), 4.16 (q, J = 6.8 Hz, 2H), 3.11 (br
s, 2H), 2.65 (q, J = 7.2 Hz, 2H), 2.62 (d, J = 8.8 Hz,
2H), 2.41 (t, J = 11.2 Hz, 2H), 2.22 (t, J = 10.8 Hz,
2H), 1.24 (t, J = 7.2 Hz, 3H), 1.20 (t, J = 6.8 Hz, 3H).
13C NMR (free base): d 172.7, 141.8, 132.5, 131.3,
130.3, 127.8, 125.1, 61.4, 52.1, 50.1, 48.1, 32.0, 13.7,
10.7.
4.26. 1-Cyclopropylmethyl-4-(3,4-dichlorophenyl)-
piperidine-4-carboxylic acid ethyl ester (10k)
4.23. 1-(Prop-2-enyl)-4-(3,4-dichlorophenyl)-piperidine-4-
carboxylic acid ethyl ester (10h)
General procedure D. This compound was obtained as a
yellow solid (96 mg, 81% yield by NMR) and converted
into the hydrochloride salt (Section 4.1), which was ob-
tained as a white solid, mp 199–201 ꢁC (dec.). 1H NMR
(free base): d 7.47 (d, J = 2.0 Hz, 1H), 7.40 (d,
J = 8.0 Hz, 1H), 7.23 (dd, J = 2.4, 8.6 Hz, 1H), 4.14 (q,
J = 7.2 Hz, 2H), 3.05 (br s, 2H), 2.57 (d, J = 12.4 Hz,
2H), 2.29 (d, J = 6.8 Hz, 2H), 2.23 (t, J = 11.2 Hz,
2H), 2.02 (t, J = 10.8 Hz, 2H), 1.20 (t, J = 6.8 Hz, 3H),
General procedure D. This compound was obtained as
an orange oil (136 mg, 60% yield) and converted into
the hydrochloride salt (Section 4.1), which was obtained
as a white solid, mp 217–220 ꢁC (dec.). H NMR (free
base): d 7.47 (d, J = 2.4 Hz, 1H), 7.39 (d, J = 8.4 Hz,
1H), 7.23 (dd, J = 2.0, 8.4 Hz, 1H), 5.85 (m, 1H), 5.16
(d, J = 25.6, 1H), 5.16 (s, 1H), 4.14 (q, J = 6.8 Hz,
2H), 2.97 (d, J = 6.0 Hz, 2H), 2.85 (d, J = 9.6 Hz, 2H),
1

J. B. Rhoden et al. / Bioorg. Med. Chem. 13 (2005) 5623–5634
5631
0.90 (m, 1H), 0.54 (m, 2H), 0.13 (m, 2H). 13C NMR (free
base): d 173.5, 143.0, 132.6, 131.2, 130.4, 128.1, 125.3,
63.6, 61.2, 51.1, 48.7, 33.3, 14.0, 8.1, 4.0 (2C). Anal.
Calcd for C18H23NO2Cl2ÆHClÆ1/4H2O: C, 54.42; H,
6.22; N, 3.53. Found: C, 54.12; H, 6.03; N, 3.51.
d 173.5, 143.2, 132.6, 131.1, 130.3, 128.2, 125.4, 95.4,
61.1, 55.4, 51.3, 48.7, 43.1, 33.7, 30.0, 14.0. Anal. Calcd
for C17H22NO2Cl3ÆHCl: C, 49.18; H, 5.58; N, 3.37.
Found: C, 49.21; H, 5.56; N, 3.35.
4.30. 4-(3,4-Dichlorophenyl)-1-[(3-tri-n-butylstannanyl)-
prop-(2E)-enyl]-piperidine-4-carboxylic acid ethyl ester
(10o)
4.27. 4-(3,4-Dichlorophenyl)-1-(3-fluoropropyl)-
piperidine-4-carboxylic acid ethyl ester (10l)
General procedure D. This compound was obtained as
an orange/brown solid (95 mg, 79% yield) and converted
into the hydrochloride salt (Section 4.1), which was ob-
tained as a white solid, mp 209–211 ꢁC. H NMR (free
General procedure D with 3-(tri-n-butylstannyl)prop-
(2E)-enyl chloride.15,26 This compound was obtained
(SiO2, CHCl3) as a yellow oil (85 mg, 54% yield). H
1
1
NMR: d 7.48 (d, J = 2.4 Hz, 1H), 7.38 (d, J = 8.0 Hz,
1H), 7.22 (dd, J = 2.4, 8.6 Hz, 1H), 6.11 (d,
J = 19.2 Hz, 1H), 5.99 (dt, J = 18.8, 6.0 Hz, 1H), 4.13
(q, J = 6.8 Hz, 2H), 3.03 (d, J = 5.6 Hz, 2H), 2.85 (d,
J = 8.8 Hz, 2H), 2.55 (d, J = 13.2 Hz, 2H), 2.12 (t, J =
10.8 Hz, 2H), 1.93 (t, J = 11.2 Hz, 2H), 1.50 (m, 6H),
1.30 (m, 6H), 1.19 (t, J = 7.2 Hz, 3H), 0.910–0.866 (m,
15H). 13C NMR: d 173.5, 145.0, 143.2, 132.6, 132.3,
131.1, 130.3, 128.2, 125.3, 65.5, 61.1, 51.0, 48.7, 33.7,
29.0, 27.2, 13.9, 13.6, 9.4.
base): d 7.47 (d, J = 2.0 Hz, 1H), 7.39 (d, J = 8.8 Hz,
1H), 7.22 (dd, J = 2.0, 8.4 Hz, 1H), 4.50 (dt,
JCꢁF = 47.6 Hz, J = 6.0 Hz, 2H), 4.14 (q, J = 7.6 Hz,
2H), 2.85 (d, 10.8 Hz, 2H), 2.55 (d, J = 13.2 Hz, 2H),
2.47 (t, J = 7.6 Hz, 2H), 2.18 (t, J = 11.2 Hz, 2H), 1.90
(m, 4H), 1.20 (t, J = 7.6 Hz, 3H). 13C NMR (free base):
d 173.4, 143.1, 132.5, 131.0, 130.3, 128.1, 125.3, 82.3
(JCꢁF = 652 Hz), 61.1, 54.2, 54.1, 51.1, 48.6, 33.5, 28.0,
27.8, 13.9. Anal. Calcd for C17H22NO2Cl2FÆHClÆ
0.5H2O: C, 50.64; H, 5.87; N, 3.47. Found: C, 50.62;
H, 5.84; N, 3.44.
4.31. 4-(3,4-Dichlorophenyl)-1-[(3-tri-n-butylstanna-
nyl)prop-(2E)-enyl]-piperidine-4-carboxylic acid ethyl
ester (10p)
4.28. 4-(3,4-Dichlorophenyl)-1-(3-hydroxypropyl)-
piperidine-4-carboxylic acid ethyl ester (10m)
The stannyl derivative 10o (60 mg, 0.10 mmol) was dis-
solved in CHCl3 (0.6 mL) and the resulting mixture
was cooled to 0 ꢁC. A solution of iodine in CHCl3
(0.1 N) was then added dropwise to the stirred mixture
until a color change resulted. The solution was allowed
to come to room temperature and stirred for an addi-
tional 4 h. The reaction mixture was washed with brine
(5 mL) and dried (Na2SO4). The solvent was removed
under reduced pressure and the crude product was puri-
fied by column chromatography (Et2O/hexanes, 1:1) to
give the product as a yellow oil (21 mg, 44% yield). This
compound was converted into the hydrochloride salt
(Section 4.1), which was obtained as a white solid, mp
219–221 ꢁC (dec.). 1H NMR (free base): d 7.46 (d,
J = 2.4 Hz, 1H), 7.39 (d, J = 8.8 Hz, 1H), 7.21 (dd,
J = 2.8, 8.4 Hz, 1H), 6.57 (dt, J = 6.8, 14.8 Hz, 1H),
6.25 (d, J = 14.4 Hz, 1H), 4.13 (q, J = 6.8 Hz, 2H),
2.93 (dd, J = 1.6, 6.8 Hz, 2H), 2.81 (d, J = 11.2 Hz,
2H), 2.54 (d, J = 13.2 Hz, 2H), 2.15 (t, J = 11.2 Hz,
2H), 1.90 (m, 2H), 1.19 (t, J = 7.6 Hz, 3H). 13C NMR
(free base): d 173.4, 142.8, 132.7, 131.2, 130.4, 128.2,
125.3, 78.6, 62.7, 61.2, 50.9, 48.6, 33.6, 14.0. Anal. Calcd
for C17H20NO2Cl2IÆHCl: C, 40.26; H, 4.19; N, 2.78.
Found: C, 40.42; H, 4.18; N, 2.75.
General procedure D. This compound was obtained as a
yellow oil (120 mg, 79%) and was converted into the
hydrochloride salt (Section 4.1), which was obtained as
an orange solid, mp 184–186 ꢁC. H NMR (free base):
d 7.45 (d, J = 2.4 Hz, 1H), 7.40 (d, J = 8.4 Hz, 1H),
7.21 (dd, J = 2.4, 8.8 Hz, 1H), 4.36 (s, 1H), 4.14 (q,
J = 6.8 Hz, 2H), 3.81 (t, J = 5.2 Hz, 2H), 3.06 (br s,
2H), 2.67 (t, J = 6.0 Hz, 2H), 2.57 (d, J = 13.2 Hz,
2H), 2.27 (m, 2H), 1.95 (t, J = 9.2 Hz, 2H), 1.77 (m,
J = 7.2 Hz, 2H), 1.19 (t, J = 6.8 Hz, 3H). 13C NMR (free
base): d 173.2, 142.7, 132.7, 131.4, 130.5, 128.1, 125.3,
64.0, 61.4, 58.6, 51.3, 48.6, 33.3, 27.0, 14.0. Anal. Calcd
for C17H23NO3Cl2ÆHCl: C, 51.47; H, 6.10; N, 3.53.
Found: C, 51.31; H, 6.15; N, 3.56.
1
4.29. 1-(3-Chloropropyl)-4-(3,4-dichlorophenyl)-
piperidine-4-carboxylic acid ethyl ester (10n)
The alcohol 10m (150 mg, 0.42 mmol) was dissolved in
CH2Cl2 (3.2 mL) and cooled to 0 ꢁC under an atmo-
sphere of nitrogen. Methanesulfonyl chloride (30 lL,
0.44 mmol) was added, followed by the addition of tri-
ethylamine (90 lL, 0.62 mmol). The reaction mixture
was allowed to stir for 2 h. The mixture was then allowed
to warm to room temperature and stirred for an addi-
tional 48 h. The crude product was purified using column
chromatography (CHCl3/CH3OH, 13:1) to afford a yel-
low oil (97 mg, 61%). This compound was converted to
the hydrochloride salt to afford a white solid, mp 205–
207 ꢁC. 1H NMR (free base): d 7.47 (d, J = 1.6 Hz,
1H), 7.39 (d, J = 8.8 Hz, 1H), 7.22 (dd, J = 2.0, 8.4 Hz,
1H), 4.13 (q, J = 7.6 Hz, 2H), 3.59 (t, J = 6.4 Hz, 2H),
2.81 (d, J = 11.2 Hz, 2H), 2.53 (d, J = 12.8 Hz, 2H),
2.45 (t, J = 6.8 Hz, 2H), 2.16 (t, J = 11.2 Hz, 2H), 1.92
(m, 4H), 1.19 (t, J = 7.2 Hz, 3H). 13C NMR (free base):
4.32. 1-[4-(3,4-Dichlorophenyl)-1-methyl-piperidin-4-yl]-
ethanone (11)
To a solution of methyl magnesium bromide (0.37 mL,
1.1 mmol) in dry ether (0.21 mL) stirring under an atmo-
sphere of nitrogen at 0 ꢁC was added a solution ofthe ester
5 (120 mg, 0.37 mmol) in dry ether that had been cooled to
0 ꢁC under an atmosphere of nitrogen. The mixture was
allowed to stir for 20 min, and then allowed to return to
room temperature and continue to stir overnight. Wet
ether was added to the solution, followed by a deionized

5632
J. B. Rhoden et al. / Bioorg. Med. Chem. 13 (2005) 5623–5634
water wash. The organic layer was dried (Na2SO4), and
the solvent was removed under reduced pressure. The res-
idue was purified by chromatography (CHCl3/CH3OH,
12:1) to give a yellow oil (68 mg, 65% yield) and converted
into the hydrochloride salt (Section 4.1), which was ob-
tained as a white solid, mp 254–256 ꢁC (dec.). 1H NMR
(free base): d 7.43 (d, J = 8.4 Hz, 1H), 7.40 (d,
J = 2.4 Hz, 1H), 7.15 (dd, J = 2.4, 8.4 Hz, 1H), 2.66 (br
s, 2H), 2.45 (d, J = 12.8 Hz, 2H), 2.25 (s, 3H), 2.21 (t,
J = 10.8 Hz, 2H), 1.95 (s, 3H). 13C NMR (free base): d
208.1, 141.9, 133.0, 131.3, 130.7, 128.4, 125.7, 53.7, 52.6,
46.0, 32.7, 25.6. Anal. Calcd for C14H17NOCl2ÆHClÆ
3H2O: C, 44.64; H, 6.15; N, 3.72. Found: C, 44.94; H,
5.78; N, 3.68.
31.3, 30.9, 18.0. Anal. Calcd for C14H18NOCl2ÆHClÆ
0.5H2O: C, 50.54; H, 6.06; N, 4.21. Found: C, 50.35;
H, 6.32; N, 4.26.
4.35. 4-(3,4-Dichlorophenyl)-1-methyl-piperidin-4-yl-
methanol (14)
To a suspension of LiAlH4 (250 mg, 6.5 mmol) in dry
Et2O (33 mL) under an atmosphere of nitrogen was
added a solution of the ethyl ester 5 (1.0 g, 3.3 mmol)
in dry Et2O (33 mL). The reaction mixture was stirred
at room temperature for 3 h. Wet ether (33 mL) and
1 M NaOH (0.2 mL) were added slowly. A white precip-
itate began to form and the mixture was allowed to stir
for 1 h. The resulting suspension was filtered through
Celite washing with Et2O and EtOAc. The filtrate was
filtered and dried to give a white solid (740 mg, 83%
yield). This compound was converted to the hydrochlo-
ride salt (Section 4.1) to afford a white solid, mp 224–
226 ꢁC. 1H NMR (free base): d 7.44 (d, J = 10 Hz,
1H), 7.43 (d, J = 0.4 Hz, 1H), 7.19 (dd, J = 2.4, 8.6 Hz,
1H), 3.57 (s, 2H), 2.58 (m, 2H), 2.18 (s, 3H), 2.12 (t,
J = 14.0 Hz, 2H), 1.96 (m, 2H), 1.81 (s, 2H). 13C
NMR (free base): d 144.0, 132.5, 130.3, 130.2, 129.6,
126.8, 71.1, 51.5, 45.9, 41.5, 31.4. Anal. Calcd for
C13H17NOCl2ÆHCl: C, 50.26; H, 5.84; N, 4.51. Found:
C, 50.01; H, 5.83; N, 4.46.
4.33. 4-(3,4-Dichlorophenyl)-1-methyl-piperidin-4-yl]-
phenylmethanone (12)
To a stirred solution of phenyl magnesium bromide
(0.39 mL, 1.2 mmol) in dry ether (0.19 mL) under an
atmosphere of nitrogen at 0 ꢁC was added a solution
of the nitrile 7 (160 mg, 0.59 mmol) in dry ether that
had been cooled to 0 ꢁC under an atmosphere of nitro-
gen. The mixture was allowed to stir for 20 min, and
then allowed to return to room temperature and stirred
overnight. Wet ether was added to the solution, fol-
lowed by a deionized water wash. The organic layer
was dried (Na2SO4), and the solvent was removed under
reduced pressure. The residue was purified by chromat-
ography (CHCl3/CH3OH, 24:1) to give a yellow oil
(114 mg, 56% yield). This compound was converted to
the hydrochloride salt (Section 4.1), which was obtained
4.36. Acetic acid 4-(3,4-dichlorophenyl)-1-methyl-piperi-
din-4-yl methyl ester (15)
The alcohol 14 (190 mg, 0.700 mmol) was dried under
vacuum and 4-(dimethylamino) pyridine (9 mg,
0.0697 mmol) was added to the flask and flushed with
nitrogen. Dry CH2Cl2 (12 mL), fresh triethylamine
(370 lL, 2.7 mmol), and acetyl chloride (70 lL,
1.04 mmol) were added dropwise at 0 ꢁC. The mixture
was allowed to stir on ice for 30 min, and then overnight
at room temperature. To the mixture 1 N NaOH was
added dropwise to adjust the pH to 10–11, followed
by the addition of deionized water (10 mL). The mixture
was extracted with CH2Cl2 (3· 15 mL) and the organic
layers were dried (Na2SO4). The crude product was puri-
fied using chromatography (CHCl3/CH3OH, 13:1) to
give a white solid (140 mg, 65% yield). This compound
was converted into the hydrochloride salt (Section 4.1)
1
as a white solid mp 244–246 ꢁC (dec.). H NMR (free
base, 300 MHz): d 7.51 (d, J = 2.1 Hz, 1H), 7.46 (d,
J = 8.4 Hz, 1H), 7.44–7.22 (m, 5H), 7.25 (dd, J = 2.1,
8.6 Hz, 1H), 2.72 (m, 2H), 2.55 (m, J = 2.7, 8.9 Hz,
2H), 2.25 (s, 3H), 2.15–2.07 (m, 4H). 13C NMR (free
base): d 203.0, 143.5, 137.4, 133.4, 131.7, 131.5, 131.0,
128.7, 128.3, 128.2, 125.6, 52.9, 52.8, 46.0, 35.1. Anal.
Calcd for C19H19NOCl2ÆHClÆ1/2H2O: C, 57.95; H,
5.38; N, 3.55. Found: C, 57.98; H, 5.34; N, 3.47.
4.34. 1-[4-(3,4-Dichlorophenyl)-1-methyl-piperidin-4-yl]-
ethanol (13)
To a stirred solution of the ketone 8 (100 mg,
0.35 mmol) in methanol (1.7 mL) was added sodium
borohydride (13 mg, 0.35 mmol). The mixture was stir-
red at room temperature under an atmosphere of nitro-
gen for 2 h. The solvent was removed under reduced
pressure, and water was added to the resulting residue,
followed by extraction with Et2O (3· 5 mL), and the or-
ganic extracts were dried (Na2SO4). The crude product
was purified using chromatography (CHCl3/CH3OH,
13:1) to give an off-white solid (80 mg, 80% yield) and
converted into the hydrochloride salt (Section 4.1),
which was obtained as a white solid, mp 185–187 ꢁC.
1H NMR (free base): d 7.44 (d, J = 8.4 Hz, 1H), 7.42
(d, J = 2.4 Hz, 1H), 7.18 (dd, J = 2.4, 8.4 Hz, 1H), 3.70
(m, J = 6.8 Hz, 1H), 2.86 (d, J = 7.6 Hz, 2H), 2.45 (m,
1H), 2.28 (s, 3H), 2.15 (m, 2H), 2.05 (m, 4H), 0.925 (d,
J = 6.4 Hz, 3H). 13C NMR (free base): d 140.6, 132.6,
130.7, 130.6, 130.1, 128.1, 55.6, 51.7, 51.5, 45.4, 44.7,
1
to afford a white foam. H NMR (free base): d 7.43
(d, J = 2.4 Hz, 1H), 7.41 (d, J = 6.0 Hz, 1H), 7.18 (dd,
J = 3.2, 11.4 Hz, 1H), 4.03 (s, 2H), 2.60 (m, 2H), 2.24
(s, 3H), 2.17 (m, 4H), 1.97 (m, 2H), 1.97 (s, 3H). 13C
NMR (free base): d 170.5, 143.3, 132.4, 130.4, 130.2,
129.4, 126.5, 71.2, 51.4, 46.0, 39.6, 32.0, 20.7. Anal.
Calcd for C15H19NO2Cl2ÆHClÆ1.5H2O: C, 47.44; H,
6.11; N, 3.69. Found: C, 47.11; H, 5.72; N, 3.35.
4.37. 4-(3,4-Dichlorophenyl)-1-methyl-4-vinyl-piperidine
(16)
To a two-necked round-bottom-flask under an atmo-
sphere of nitrogen was added a solution of oxalyl chlo-
ride (280 lL, 3.2 mmol) in dichloromethane (4.9 mL).
The solution was cooled to ꢁ78 ꢁC. A solution of
dimethylsulfoxide (450 lL, 6.3 mmol) in dichlorometh-

J. B. Rhoden et al. / Bioorg. Med. Chem. 13 (2005) 5623–5634
5633
ane (0.58 mL) was then added dropwise for over 5 min.
The temperature rose to ꢁ70 ꢁC and was allowed to
continue to rise to ꢁ60 ꢁC for over 10 min. The alcohol
14 (580 mg, 2.10 mmol) was dissolved in dichlorometh-
ane (3.5 mL) and added dropwise to the reaction mix-
ture for over a 10 min period. The temperature rose to
ꢁ55 ꢁC and was allowed to continue to rise to ꢁ45 ꢁC
at which time diisopropylethyl amine (2.1 mL, 12 mmol)
dissolved in dichloromethane (0.29 mL) was added and
the solution was allowed to warm to 0 ꢁC. The reaction
mixture was added to ice-cold 1 M HCl and extracted
with dichloromethane (3· 5 mL). The combined organic
layers were washed with a pH 7 aqueous phosphate buf-
fer (3· 5 mL) and dried over Na2SO4. The solvent was
concentrated under reduced pressure and the crude
product was purified by chromatography (CHCl3/
CH3OH, 40:1) to give the aldehyde as a yellow oil
pressure to give the product in sufficient purity as an or-
ange oil (71 mg, 81% yield). This compound was con-
verted into the hydrochloride salt (Section 4.1), which
was obtained as a white solid, mp 200–204 ꢁC (dec.).
1H NMR (free base): d 7.38 (d, J = 8.4 Hz, 1H), 7.34
(d, J = 2.0 Hz, 1H), 7.10 (dd, J = 2.0, 8.6 Hz, 1H), 2.55
(br s, 2H), 2.22 (s, 3H), 2.19–2.10 (m, 4H), 1.81 (m,
2H), 1.57 (q, J = 7.6 Hz, 2H), 0.563 (t, J = 7.6 Hz,
3H). 13C NMR (free base): d 146.3, 132.2, 130.0,
129.4, 129.2, 126.5, 51.8, 45.9, 39.2, 34.7, 29.6, 7.67.
Anal. Calcd for C14H19NCl2ÆHCl: C, 54.48; H, 6.53;
N, 4.54. Found: C, 54.45; H, 6.47; N, 4.55.
4.39. [3H]WIN 35,428 binding assay
Male Sprague–Dawley rats (200–250 g, Taconic,
Germantown, NY) were decapitated and their brains
were removed to an ice-cooled dish for dissection of
the caudate putamen. The tissue was homogenized in
30 volumes of ice-cold modified Krebs–HEPES buffer
(15 mM HEPES, 127 mM NaCl, 5 mM KCl, 1.2 mM
MgSO4, 2.5 mM CaCl2, 1.3 mM NaH2PO4, and
10 mM glucose, pH adjusted to 7.4) using a Teflon/glass
homogenizer and centrifuged at 20,000g for 10 min at
4 ꢁC. The resulting pellet was then washed two more
times by resuspension in ice-cold buffer and centrifuga-
tion at 20,000g for 10 min at 4 ꢁC. Fresh homogenates
were used in all experiments. Binding assays were con-
ducted in modified Krebs–HEPES buffer on ice, essen-
tially as previously described.27 The total volume in
each tube was 0.5 mL and the final concentration of
membrane after all additions was approximately 0.3%
(w/v) corresponding to 150–300 lg protein/sample.
Increasing concentrations of the drug being tested were
added to triplicate samples of the membrane suspension.
Five minutes later, [3H]WIN 35,428 (final concentration
of 1.5 nM) was added and the incubation was continued
for 1 h on ice. The incubation was terminated by the
addition of 3 mL ice-cold buffer and rapid filtration
through Whatman GF/B glass fiber filter paper (presoa-
ked in 0.1% BSA in water to reduce non-specific bind-
ing) using a Brandel Cell Harvester (Gaithersburg,
MD). After filtration, the filters were washed with three
additional 3 mL washes and transferred to scintillation
vials. Absolute ethanol (0.5 mL) and Beckman Ready
Value Scintillation Cocktail (2.75 mL) were added to
the vials, which were counted the next day at an effi-
ciency of about 36%. Under these assay conditions, an
average experiment yielded approximately 6000 dpm to-
tal binding per sample and approximately 250 dpm non-
specific binding. Non-specific binding was defined as
binding in the presence of 100 lM cocaine. Ki values
were derived from 14 point competition assays using
increasing concentrations of unlabeled compounds
(0.05 nM to 100 lM) against 1.5 nM [3H]WIN 35,428.
Data were analyzed with GraphPad Prism software
(San Diego, California).
1
(330 mg, 57% yield). H NMR: d 9.37 (s, 1H), 7.45 (d,
J = 8.4 Hz, 1H), 7.38 (d, J = 2.4 Hz, 1H), 7.13 (dd,
J = 2.0, 8.6, Hz, 1H), 2.72 (d, J = 11.2 Hz, 2H), 2.43
(d, J = 13.6 Hz, 2H), 2.27 (s, 3H), 2.20 (t, J = 2.2, 2H),
2.05 (m, 2H). A solution of 1.6 M n-butyl lithium
(2.0 mL, 3.2 mmol) dissolved in THF (5.5 mL) was
cooled to 0 ꢁC with stirring under nitrogen. Methyl tri-
phenyl phosphonium bromide (1.1 g, 3.2 mmol) was
slowly added to the mixture. The resulting orange mix-
ture was allowed to stir at 0 ꢁC for 30 min and became
milky in consistency. The reaction mixture was removed
from the ice and the aldehyde (290 mg, 1.1 mmol) dis-
solved in THF (1.2 mL) was added and allowed to stir
overnight at room temperature. The mixture was diluted
with ethyl acetate (10 mL) and washed with saturated
ammonium chloride (2· 15 mL). The organic phase
was extracted with 10% HCl (3· 5 mL). The combined
aqueous layers were washed with EtOAc (15 mL), neu-
tralized with saturated NaHCO3, and extracted with
CH2Cl2 (3· 15 mL). The combined organic layers were
dried over Na2SO4 and the solvent was removed under
reduced pressure. The mixture was purified by chromat-
ography (CHCl3/CH3OH, 13:1) to give a yellow oil
(130 mg, 44% yield) and converted into the hydrochlo-
ride salt (Section 4.1), which was obtained as a white so-
1
lid, mp 211–214 ꢁC (dec.). H NMR (free base): d 7.40
(d, J = 2.4 Hz, 1H), 7.37 (d, J = 8.8 Hz, 1H), 7.16 (dd,
J = 2.0, 8.4 Hz, 1H), 5.77 (dd, J = 10.8, 17.6 Hz, 1H),
5.17 (d, J = 10.4 Hz, 1H), 4.91 (d, J = 17.6 Hz, 1H),
2.46 (br s, 4H), 2.25 (s, 3H), 2.13 (m, 2H), 2.01 (dt,
J = 4.4, 14.0 Hz, 2H). 13C NMR (free base): d 146.8,
144.9, 132.3, 130.1, 129.9, 129.1, 126.3, 114.7, 51.9,
46.1, 42.3, 35.2. Anal. Calcd for C14H17NCl2ÆHClÆ
1.5H2O: C, 54.04; H, 5.99; N, 4.50. Found: C, 54.15;
H, 5.94; N, 4.47.
4.38. 4-(3,4-Dichlorophenyl)-4-ethyl-1-methyl-piperidine
(17)
To a slurry of 10% Pd/C (10 mg) in methanol (10 mL)
under an atmosphere of nitrogen was added a solution
of the alkene 16 (100 mg, 0.37 mmol) in methanol
(10 mL). The mixture was hydrogenated at 1 atm over-
night. The catalyst was removed by filtration through
a pad of Celite. The filter cake was rinsed with methanol
(30 mL) and the filtrate was concentrated under reduced
4.40. [3H]Paroxeting binding assay
Brains from male Sprague–Dawley rats weighing
200–225 g (Taconic Labs) were removed, and midbrain
was dissected and rapidly frozen. Membranes were

5634
J. B. Rhoden et al. / Bioorg. Med. Chem. 13 (2005) 5623–5634
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prepared by homogenizing tissues in 20 volumes (w/v) of
50 mM Tris containing 120 mM NaCl and 5 mM KCl
(pH7.4 at 25 ꢁC), using a Brinkman Polytron (setting 6
for 20 s), and centrifuged at 50,000g for 10 min at
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Acknowledgment
We are grateful to the National Institute on Drug Abuse
(DA11528) for the financial support of this research.
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