Synthesis of 8-thiabicyclo[3.2.1]octanes and their binding affinity for the dopamine and serotonin transporters

Article abstract of DOI:10.1016/j.bmc.2006.10.016

Cocaine is a potent stimulant of the central nervous system. Its reinforcing and stimulant properties have been associated with inhibition of the dopamine transporter (DAT) on presynaptic neurons. In the search for medications for cocaine abuse, we have p

Full text of DOI:10.1016/j.bmc.2006.10.016

Bioorganic & Medicinal Chemistry 15 (2007) 1067–1082
Synthesis of 8-thiabicyclo[3.2.1]octanes and their binding
affinity for the dopamine and serotonin transporters
Duy-Phong Pham-Huu,a Jeffrey R. Deschamps,b Shanghao Liu,a
Bertha K. Madrasc and Peter C. Meltzera,*
aOrganix Inc., 240 Salem Street, Woburn, MA 01801, USA
bNaval Research Laboratory, Washington D.C. 20375, USA
cHarvard Medical School and New England Regional Primate Research Center, Southborough, MA 01772, USA
Received 5 September 2006; revised 9 October 2006; accepted 11 October 2006
Available online 13 October 2006
Abstract—Cocaine is a potent stimulant of the central nervous system. Its reinforcing and stimulant properties have been associated
with inhibition of the dopamine transporter (DAT) on presynaptic neurons. In the search for medications for cocaine abuse, we have
prepared 2-carbomethoxy-3-aryl-8-thiabicyclo[3.2.1]octane analogues of cocaine. We report that this class of compounds provides
potent and selective inhibitors of the DAT and SERT. The selectivity resulted from reduced activity at the SERT. The 3b-(3,4-
dichlorophenyl) analogue inhibits the DAT and SERT with a potency of IC50 = 5.7 nM and 8.0 nM, respectively. The 3-(3,4-
dichlorophenyl)-2,3-unsaturated analogue inhibits the DAT potently (IC50 = 4.5 nM) and selectively (>800-fold vs SERT).
Biological enantioselectivity of DAT inhibition was limited for both the 3-aryl-2,3-unsaturated and the 3a-aryl analogues (2-fold),
but more robust (>10-fold) for the 3b-aryl analogues. The (1R)-configuration provided the eutomers.
ꢀ 2006 Elsevier Ltd. All rights reserved.
1. Introduction
of the synaptic dopamine concentration, with the conse-
quence of increased activation of postsynaptic dopamine
receptors. This hyperstimulation of postsynaptic recep-
tors is responsible for cocaine’s stimulant activity. The
reinforcing and addictive properties of cocaine are
thought to be related to its pharmacokinetic profile.
The addict gains almost immediate effect (<15 s) with
short duration of action (10–15 min), and only the lack
of continuous availability of drug appears to terminate
the addict’s binge. Therefore, in the search for a safe
replacement therapeutic agent, many researchers have
focused their efforts on the design of compounds that
bind with selectivity to the DAT and manifest slow on-
set of action and long duration of action.7
Cocaine abuse continues to present a societal problem of
monumental proportions. The search for suitable medi-
cations has not yet yielded a clinically proven candidate,
and physicians presented with addicted patients do not
yet have the tools with which to deal with this challeng-
ing problem.
Cocaine is a potent stimulant of the central nervous sys-
tem. Its reinforcing and stimulant properties have been
primarily associated with its ability to inhibit the dopa-
mine transporter (DAT) on presynaptic neurons in the
striatum.1–3 While the DAT has been considered a prime
target of cocaine, and therefore of potential medications
designed to inhibit the activity of cocaine, the serotonin
transporter (SERT) may also play a substantial role in
the pharmacological activity of cocaine.4–6 Inhibition
of the monoamine uptake systems by cocaine effectively
incapacitates the system that removes excess dopamine
from the synapse. This, in turn, results in an increase
The focus of much attention in the design of prospective
medications for cocaine abuse has been the class of bicy-
clo[3.2.1]octanes.8–23 This focus has its historic origins in
the structure of cocaine itself (Fig. 1) as well as the met-
abolically more stable lead tropane, WIN 35,428, a
3b-aryl-2b-carbomethoxy-8-azabicyclo[3.2.1]octane ana-
logue of cocaine disclosed by Clarke et al. in 1973.24
Keywords: Thiatropanes; Monoamine transporter ligands; Cocaine
medications.
Until 1997 when we presented evidence14 that the 8-aza
functionality within the bicyclo[3.2.1]octane (tropane)
series is not a prerequisite for potent inhibition of
*
Corresponding author. Tel.: +1 781 932 4142; fax: +1 781 933
6695; e-mail: meltzer@organixinc.com
0968-0896/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2006.10.016

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D.-P. Pham-Huu et al. / Bioorg. Med. Chem. 15 (2007) 1067–1082
H3C
H3C
N
N
CO2CH3
CO2CH3
O
F
Cocaine
WIN 35,428
O
Figure 1. Cocaine and WIN35,428 are the lead compounds.
monoamine uptake systems, it was assumed that the
presence of an amine nitrogen was essential for binding
to these systems.25,26 We later demonstrated that the
topological properties of tropane-like ligands (bicy-
clo[3.2.1]octanes) that bind to monoamine uptake sys-
tems were possibly more important than the presence,
or absence, of specific functionality.14 Indeed, 8-oxabi-
cyclo[3.2.1]octanes (8-oxatropanes)14 and 8-carbabicy-
clo[3.2.1]octanes (8-carbatropanes)27 also manifested
substantial binding potency at the DAT as well as selec-
tivity versus SERT inhibition.
enol triflate that is then subjected to palladium catalyzed
Suzuki coupling with a suitably substituted arylboronic
acid.14,37 In this synthesis of 8-thia analogues, this sem-
inal intermediate is 5 (Scheme 1). Thus, tropinone 1 was
quaternized with methyl iodide to obtain the dimethy-
lammonium iodide intermediate 2 in 90% yield. Treat-
ment with sodium sulfide, as described by Parr et al.,38
then provided the 3-ketobicyclooctane 3 in 78% yield.
Introduction of the 2-carbomethoxy group was effect-
ed14,36 with methylcyanoformate, and the keto ester 4
was obtained in 69% yield. It is important to note that
the racemic ketoester 4 exists in an equilibrium mixture
of three tautomeric forms: the 2a-carbomethoxy keto es-
ter, the 2b-carbomethoxy keto ester, and the enol ester.
This tautomerism is of no stereochemical significance
since all centers are lost in the ensuing conversion to
the enol triflate 5. However the existence of the three
The concept of replacement of an amine nitrogen by an
ether oxygen or a methylene carbon was then extended
to methylphenidate where we showed that, once again,
binding potency was maintained in methylphenidate
analogues that are topologically similar, but functionally
different.28
1
tautomers complicates the H NMR spectrum of 4 sig-
nificantly. Introduction of the triflate was effected with
In this report, we again explore the functional role of the
8-heteroatom in the bicyclo[3.2.1]octane skeletal nucle-
us. We were particularly interested in the effect of a sul-
fur for nitrogen exchange because sulfur is similar to
oxygen in that it has two lone pairs of electrons. Howev-
er, it does not favor hydrogen bonding and therefore has
some attributes that are more similar to the 8-methylene
group of our 8-carbatropanes29 with respect to interac-
tion with a biological macromolecule. This exchange
of S for N has been reported for unrelated D2 ligands
previously.30–34 However, although the resultant thia
compounds manifested potency, their potency was much
reduced compared with their aza counterparts. Majew-
ski et al. have explored enolate chemistry of 8-thiabicy-
clo[3.2.1]octane-3-one and have used enantioselective
deprotonation to prepare 2-substituted-8-thiabicy-
clo[3.2.1]octane-3-ones as an entry to sulfur analogues
of tropanes.35,36 However, no 3-aryl-8-thiabicy-
clo[3.2.1]octanes were reported.
N-phenyltriflimide and sodium bis(trimethylsilyl)amide
in 75% yield. H NMR of the triflate 5 is unequivocal.
The H1 proton at d 4.39 appears as a double doublet
(J = 0.9, 3.6 Hz), while the H4b proton at d 2.99 appears
as a double double doublet [J = 2.1 (H4b–H6b), 4.3 (H4b–
H5), 18.6 Hz (H4b–H4a)].
1
Suzuki coupling of the appropriately substituted boron-
ic acids with enol triflate 5 under palladium tetrakis
triphenylphosphine catalysis provided the products 6
(74–96%). Samarium iodide reduction14,39 then provided
the saturated compounds as a mixture of 7 and 8 in 60–
90% yields. In general, a 4:1 ratio of the 3a-aryl (7) to
3b-aryl (8) analogues was obtained from this samarium
iodide reduction. Compounds 7 and 8 were initially sep-
arated by laborious sequential column chromatography
in order to obtain the pure 3a-aryl (7f,g,i,j) and 3b-aryl
(8f,g,i,j) esters in 30–40% and 20–35% yields, respective-
ly. Subsequently, a two-step procedure was utilized to
obtain configurationally pure 3a-aryl and 3b-aryl com-
pounds for those compound mixtures that could not
be purified effectively by column chromatography. Thus
the mixed esters 7 and 8, obtained directly from the
samarium iodide reduction, were de-esterified (50–76%
yield) under nonhydrolytic conditions with aluminum
trichloride and dimethyl sulfide under an argon atmo-
sphere40,41 to provide their carboxylic acids (50–80%
yields). The acids were separated by flash column chro-
matography and then re-esterified with trimethylsilyldi-
azomethane to obtain pure 7 and 8 (77–94% yields).
The combined yields via the two step procedure were
similar to those of the direct chromatographic separa-
tion of the samarium iodide products (see 7 and 8
f,g,i,j), and were in the range of 35–51% for the 3a-aryl
We have previously published a preliminary report con-
cerning 3-aryl-2-carbomethoxy-8-thiabicyclo[3.2.1]oct-
2-enes.37 We now report the synthesis and biological
evaluation of a family of 2-carbomethoxy-8-thiabicy-
clo[3.2.1]octanes and oct-2-enes that provide examples
of compounds that are potent inhibitors of the DAT
while manifesting substantial selectivity versus inhibi-
tion of the SERT.
2. Chemistry
The general approach that we have adopted for the syn-
thesis of bicyclo[3.2.1]octanes has pivoted around an

D.-P. Pham-Huu et al. / Bioorg. Med. Chem. 15 (2007) 1067–1082
1069
(CH3)2N+ I-
S
CH3N
(i)
(ii)
(iii)
O
O
O
S
1
2
3
S
CO2CH3
CO2CH3
OTf
(v)
S
(iv)
4
O
5
S
S
CO2CH3
Ar
CO2CH3
Ar
CO2CH3
Ar
(vi) (vii)
(viii) (ix)
and
6
7
8
(x)
(x)
CO2CH3
Ar
(x)
O
S
O
O
S
S
CO2CH3
Ar
CO2CH3
Ar
9
11
10
Scheme 1. Synthesis of 8-thiabicyclo[3.2.1]octanes and 8-thiabicyclo[3.2.1]octenes. Reagents and conditions: (i) CH3I, 90%; (ii) Na2S, 78%; (iii) LDA,
NCCOOCH3, 69%; (iv) NaN(TMS)2, PhN(Tf)2, 75%; (v) ArB(OH)2, Pd(PPh3), LiCl, Na2CO3, 74–96%; (vi) SmI2, THF, MeOH, ꢀ60 ꢁC, 60–90%;
(vii) AlCl3, (CH3)2S, 50–80%; (viii) column chromatography; (ix) TMSCHN2, 77–94%; (x) KO2, TMSCl, CH3CN, 49–94%.
(7) and 11–18% for the 3b-aryl (8) compounds. However,
the two-step procedure allowed facile separation of 7
and 8, whereas the direct column chromatography of
compounds obtained from samarium iodide reduction
did not.
Since biological enantioselectivity had already been
demonstrated for the 8-oxabicyclooctanes14 as well as
for 8-azatropanes,16 it was important to explore biolog-
ical selectivity in this new class of 8-thiabicyclooctanes.
The 3,4-dichlorophenyl analogues were selected for
determination of biological enantioselectivity because
the racemic 3,4-dichlorophenyl substituted 6f, 7f, and
8f manifested substantial potency at the dopamine
transporter. Intermediate ketoester 4 served as the
springboard for resolution (Scheme 2).
Oxidation of 6, 7, and 8 was carried out with potassi-
um superoxide and trimethylsilyl chloride in acetoni-
trile to provide 9a, 10a–f, and 11a,b in 49–94%
yields. The sulfoxide 10f was crystallized from ethyl
acetate/heptane to obtain monoclinic crystals, and the
exo orientation of the oxygen was established by X-
ray crystallography.
Thus the enolate of 4 obtained by treatment with sodi-
um bis(trimethylsilyl)amide in THF was functionalized
S
H
S
CO2CH3
(R)
CO2CH3
(iv)
O
(S)
O
O
O
O
(1R)-4
(1R,1'S)-4a
S
CO2CH3
O
(i), (ii), (iii)
S
4
CO2CH3
S
(iv)
CO2CH3
O
O
(R)
H(S)
O
O
O
(1S,1'R)-4b
4
(1S)-
Scheme 2. Resolution of keto ester reagents and conditions. Reagents: (i) NaN(TMS)2; (ii) (1R) or (1S)-camphanyl chloride; (iii) recrystallization
from THF/hexanes, 64%; (iv) NaOCH3, MeOH, 90%.

1070
D.-P. Pham-Huu et al. / Bioorg. Med. Chem. 15 (2007) 1067–1082
with (1S)-camphanyl chloride to provide the (1R,10S)-
camphanyl enol ester 4a. Crystallization from THF/hex-
anes provided a pure diastereomer. The absolute stereo-
chemistry of the ester derived from (1S)-camphanyl
chloride was established as (1R,10S)-4a by X-ray crystal-
lography. (1R,10S)-4a was then hydrolyzed with sodium
methoxide in methanol to provide enantiomerically pure
intermediate keto ester (1R)-4. Enantiomer (1S)-4 was
obtained similarly by the use of the (1R)-camphanyl
chloride. The enantiomeric excess of (1R)-4 and (1S)-4
octane(ene)s (Table 1). The most potent DAT and
SERT inhibitors among these compounds possessed
3,4-dichloro substitution at the 3-aryl ring. These 3,4-
dichlorophenyl analogues were obtained enantiomeri-
cally pure and their binding data, in comparison with
data from the (1R)- and (1S)-8-oxa-,14 (1R)- and (1S)-
8-aza-,9 7b-hydroxy-(1R)- and (1S)-8-aza-,20 and race-
mic 8-carba-29 bicyclo[3.2.1]octane(ene)s, are presented
in Table 2.
1
was established by H NMR. The methyl resonances
Among this class of 8-thia compounds, inhibitory
potency at the DAT was not markedly different between
the 2,3-enes 6, the 3a-aryl 7, (boat configured) and 3b-
aryl 8 (chair configured) compounds. This was especially
true for the more potent compounds (Table 1): 4-Cl
(IC50 for 6c, 7c, 8c: 13 nM, 11 nM, 9.6 nM, respective-
ly), 4-Br (IC50 for 6d, 7d, 8d: 9.1 nM, 6 nM, 6 nM,
respectively), 4-I (IC50 for 6e, 7e, 8e: 6.7 nM, 9 nM,
14 nM, respectively), 3,4-Cl2 (IC50 for 6f, 7f, 8f:
4.5 nM, 6.9 nM, 5.7 nM, respectively) and 3-(2-naph-
thyl) (IC50 for 6h, 7h, 8h: 8 nM, 8 nM, 16 nM, respec-
tively). However, inhibitory potency at the SERT, and
therefore selectivity for the DAT, was quite different
among these three classes. Thus the 3b-aryl analogues
8 were most potent at the SERT followed by the 3a-aryl
compounds 7. The unsaturated analogues 6 were the
least potent inhibitors of the SERT, and were therefore
the most selective for the DAT. Therefore the selectivity
exhibited by 8-thia-2,3-unsaturated 3a-aryl and 3b-aryl
compounds did not derive from enhanced activity at
DAT, but rather from reduced activity at SERT. This
DAT selectivity as a consequence of diminishing
inhibitory potency at SERT was also evident in other
8-heterobicyclo[3.2.1]octanes. Thus in a comparison of
3,4-dichlorophenyl substituted tropanes (Table 2),
SERT inhibition for the racemic 8-oxatropane ana-
logues ranged from an IC50 = 6 lM (R/S-12) to
IC50 = 64.5 nM (R/S-13) to the SERT potent R/S-14a
with IC50 = 6.5 nM. This relative selectivity was also evi-
dent in the 8-carbatropane series with the 2,3-unsaturat-
ed R/S-21 manifesting SERT IC50 = 5.1 lM, 3a-aryl
R/S-22 IC50 = 166 nM, and the least DAT selective 3b-
aryl R/S-23 with a SERT IC50 = 33 nM.
for the camphanyl methyl group of the esters (1R,10S)-
4a and (1S,10S)-4a (or (1S,10S)-4b and (1S,10R)-4b) were
baseline differentiated for the diastereomeric pairs
(d = 0.970 and 0.928 ppm) and could therefore be quan-
titated within the experimental error of NMR integra-
tion. Diastereomeric excess (de) was thus calculated as
97% for the (1R,10S)-4a and 88% for (1S,10R)-4b. This
optical purity of (1R,10S)-4a and (1S,10R)-4b then gov-
erned the optical purity of the keto esters (1R)-4 and
(1S)-4 generated upon ester hydrolysis (Scheme 2), as
well as the purity of all subsequent products in the syn-
thetic sequence (Scheme 1) since there were no transfor-
mations that could effect ring opening and closing thus
altering the chirality at the bridgehead. Subsequent con-
version of (1R)-4 and (1S)-4 was effected, as for racemic
4 above, to provide the 2,3-enes (1R)-6f and (1S)-6f.
Samarium iodide reduction then gave the 3a-(3,4-
dichlorophenyl) compounds (1R)-7f and (1S)-7f and
the 3b-(3,4-dichlorophenyl) compounds (1R)-8f and
(1S)-8f.
3. Biology
The affinities (IC50) of the 8-thia-2-carbomethoxybicy-
clo[3.2.1]octane(ene)s for the dopamine (DAT) and
serotonin (SERT) transporters were determined in
competition studies using [3H]-3b-(4-fluorophenyl)tro-
pane-2b-carboxylic acid methyl ester ([3H]WIN 35,428)
to label the dopamine transporter and [3H]citalopram
to label the serotonin transporter.20,42,43 Studies were
conducted in cynomolgous or rhesus monkey striata
since these compounds are part of an ongoing investiga-
tion of structure–activity relationships at the dopamine
transporter in these tissues, and meaningful compari-
sons with an extensive database and in vivo imaging
data can be made. Competition studies were conducted
with a fixed concentration of radioligand and a range of
concentrations of the test drug. All drugs inhibited
[3H]WIN 35,428 and [3H]citalopram binding in a con-
centration-dependent manner. Binding constants are
presented in Tables 1 and 2.
It is quite interesting that for the most potent DAT inhib-
itors, the differences between the DAT inhibitory poten-
cies are less marked within this class of 8-thiatropane
analogues, than they are for 8-aza or 8-oxatopane ana-
logues. Therefore, SAR interpretations are less robust
for these 8-thiatropane analogues. However, the relative
binding potencies at the DAT of the 3-aryl-4-substituted
analogues: 4-H, 4-F, 4-Cl, 4-Br, 4-I, 4-(2-naphthyl), and
3,4-dichlorophenyl in the three classes of 2,3-ene, (6),
3a-aryl (7), and 3b-aryl, (8) appear similar to that evi-
denced in all other 8-heterobicyclo[3.2.1]octanes ex-
plored.14,20,27,29,37 Therefore, the structure–activity
relationships (SAR) of the 2-carbomethoxy-3-arylbicy-
clo[3.2.1]octane(ene)s are consistent, thus supporting
the hypothesis that these 8-hetero-tropanes likely bind
in very similar, if not identical, domains on the DAT.
4. Discussion
The affinities (IC50) for the dopamine (DAT) and
serotonin (SERT) transporters determined in competi-
tion studies using [3H]WIN 35,428 to label the dopa-
mine transporter and [3H]citalopram to label the
serotonin transporter are presented for a family of
It is noteworthy that exchange of either the 3- or 4-chlo-
ro substituent in 6f for a 3-fluoro (6i) or a 4-fluoro (6j)
racemic
3-aryl-2-carbomethoxy-8-thiabicyclo[3.2.1]-

Table 1. Inhibition of [3H]WIN 35,428 binding to the dopamine transporter (DAT) and [3H]citalopram binding to the serotonin transporter (SERT) in rhesus (Macaca mulatta) or cynomolgus monkey
(Macaca fascicularis) caudate-putamen for 6–11a,b
S
S
S
CO2CH3
CO2CH3
CO2CH3
R
7
6
8
R
R
Compound Compound # R 8-S
IC50 (nM)
DAT SERT
SERT/DATb Compound Compound #
IC50 (nM)
SERT/DATb Compound Compound #
IC50 (nM)
SERT/DATb
DAT SERT
DAT SERT
WIN35,428c
11
96
160
270
(ꢀ)-Cocainec
6a
6b
6c
6d
6e
6f
O-2682
O-2643
O-2683
O-2752
O-2838
O-2642
O-2890
O-2795
O-3244
O-2837
H
910
220
13
>10 lM >11
>30 lM >127
>10 lM >770
>25 lM >2,747
>8 lM
>3 lM
>10 lM >133
>1 lM >163
> 50 lM >5,000
>6 lM >789
7a
7b
7c
7d
7e
7f
O-3767
O-3856
O-3768
O-2878
O-2859
O-2751
O-2891
O-2876
O-3325
O-2879
140
59
>8 lM >57
>11 lM >186
8a
8b
8c
8d
8e
8f
O-3808
O-3876
O-3806
O-3807
O-3878
O-2793
O-2940
O-3877
O-3387
O-2858
117
38
>3 lM >29
F
Cl
494
33
13
3.4
2.3
0.7
1.5
7
11
1 lM
342
70
91
57
8
9.6
6.0
14
Br
I
9.1
6.7
4.5
75
6.0
9.0
6.9
14
10
>1,300
>800
3,4-Cl2
3,4-F2
99
14
88
4.5
100
68
5.7
32
8.0
235
13
6g
6h
6i
7g
7h
7i
11.3 1 lM
8g
8h
8i
2-Naphthyl 8.0
4-Cl–3-F
3-Cl–4-F
8.0
7.0
7.1
36
16
0.8
3
10
7.6
702
480
6.0
6.7
17
370
6j
7j
8j
55
8-S@O
H
Br
9a
O-2938
6 lM >10 lM >1.6
10a
10b
10c
10d
10e
10f
O-2915
O-3384
O-3243
O-2939
O-3388
O-2916
1 lM 100 lM 100
14
7.8
23
17
89
>24 lM >1,714
>3 lM >346
>31 lM >1,348
>14 lM >824
>69 lM >775
3,4-Cl2
3-Cl–4-F
4-Cl–3-F
3,4-F2
11a
11b
O-3264
O-3385
5.3
14
120
23
>4 lM >286
a These compounds are racemic. Each value is the mean of two or more independent experiments each conducted in different brains and in triplicate. Errors generally do not exceed 10% between replicate
experiments.
b Preference for DAT inhibition over SERT inhibition.
c Data from Ref. 9.

Table 2. Inhibition of [3H]WIN 35,428 binding to the dopamine transporter (DAT) and [3H]citalopram binding to the serotonin transporter (SERT) in rhesus (Macaca mulatta) or cynomolgus monkey
(Macaca fascicularis) caudate-putamena,c
X
X
X
CO2CH3
CO2CH3
CO2CH3
Cl
Cl
Cl
Cl
Cl
6f: X=S
12: X=O
8f: X=S
14: X=O
7f: X=
S
Cl
13: X=O
15: X=NCH3, 7β -OH
β
17: X=NCH3, 7β -OH
16: X=NCH3, 7 -OH
19: X=NCH3
18: X=NCH3
20: X=NCH3
21: X=CH2
23: X=CH2
22: X=CH2
Compound Enantiomer Compound #
X = S
IC50 (nM)
SERT/DATb Compound Compound #
IC50 (nM)
SERT/DATb Compound Compound #
IC50 (nM)
DAT SERT
SERT/DATb
DAT SERT
DAT SERT
6f
(1R/1S)
(1R)
(1S)
O-2642
O-3513
O-3514
4.5
2.5
5.0
2.0
3600
2600
4000
800
1,040
800
7f
7f
7f
O-2751
O-3635
O-3636
6.9
4.9
99
39
14
8
8f
8f
8f
O-2793
O-3516
O-3520
5.7
2.0
8.0
3.0
1.4
1.5
4
6f
6f
10
139
14
22
11
90
30
Bioenantd
1.5
2.0
3.6
X = O
(1R/1S)
(1R)
12a
12b
O-1014
O-1059
O-1108
10
4.6
58
12.6
6000
2120
46,700
22
600
460
805
13a
13b
13c
O-913
O-1066
O-1113
3.1
2.3
64.5
31.0
21
13
51
14a
14b
14c
O-914
O-1072
O-1114
3.3
3.3
47
6.5
4.7
58
2
1.4
1.2
12c
Bioenantd
(1S)
56
24
2860
92
14
12
7b-OH
X = NCH3
(1R)
15a
15b
Bioenantd
O-1677
O-1923
265
1590
5370
6
730
16a
16b
O-1676
O-1924
482
5300
11
1,610
17a
17b
O-1675
O-1945
2,690
139
0.05
50
(1S)
7.4
35.8
0.76 1220
634 4.3
0.3 15
897 9.3
3.3
X = NCH3
(1R)
(1S)
18a
18b
O-1109
O-1120
1.2
867
1900
723
4
19a
19b
O-1157
NA
0.4
27
68
13
20a
20b
O-401
NA
1.1
2.5
2.2
3.4
490
408
Bioenantd
2.2
X = CH2
(1R/1S)
21
O-1231
7.1
5160
727
22
O-1442
13
166
23
O-1414
9.6 33
a Each value is the mean of two or more independent experiments each conducted in different brains and in triplicate.
b Preference for DAT inhibition over SERT inhibition.
c Where X = NCH3, data taken from Ref. 9; where X = NCH3 and 7-OH, data are taken from Ref. 20; where X = O, data are from Ref. 14; where X = CH2, data are for the racemic compounds only and
are taken from Ref. 27. NA, not available
d Biological enantioselectivity ‘Bioenant’ is given as the ratio of IC50 distomer/IC50 eutomer.

D.-P. Pham-Huu et al. / Bioorg. Med. Chem. 15 (2007) 1067–1082
1073
had very little impact on DAT inhibitory potency. In
contrast, introduction of two fluorines (6g, 7g, and 8g)
reduced DAT potency most for the 2,3-ene 6g (17-fold)
followed by the 3b-difluorophenyl analogue 8g (6-fold).
The least affected analogue was the 3a-difluorophenyl
analogue 7g (2-fold). SERT inhibitory potency was also
much reduced for the 3,4-difluorophenyl compounds.
1S-18b. The 8-aza bridge hydroxylated (7b-OH) com-
pounds (15–17) manifested greatest DAT selectivity, with
the 2,3-ene eutomer 15a about 35-fold selective, followed
by the 3a-aryl eutomer 16a with 635-fold selectivity, and
then the 3b-aryl eutomers in which the 1R isomer was
effectively inactive at DAT (1R/1S ꢁ9000-fold). [Note
that the stereochemical designator (R vs S) in the 7b-hy-
droxy series is reversed as a consequence of naming rules
and the presence of an oxygen functionality adjacent to
the chiral center. The relative absolute structure of the
7b-hydroxy 1S-compounds is the same as that within
the 1R series of 8-hetero analogues lacking a bridge
hydroxyl group.] Therefore 3,4-dichlorophenyl-8-thiabi-
cyclo[3.2.1]octanes are less biologically enantioselective
than are their 8-oxa or 8-aza10,20,46 counterparts. The
biological availability of these compounds may rest, at
least partially, on their lipophilicities. In that regard, it
is promising that the clogP values for the 8-thia, 8-aza,
and 8-oxa analogues range from 2.7 to 4.5. Therefore,
any of these compounds can meet lipophilicity require-
ments for biological availability.
Oxidation of the 8-S to provide the 8-sulfoxides proved
interesting. In the case of the inherently weak inhibitor
(6a: 4-H), potency was essentially absent for both the
2,3-ene 9a as well as for the 3a-aryl compound 10a.
When halogens were present in the aromatic ring,
DAT potency was evident (IC50 DAT = 5.3–89 nM),
however all analogues tested were inactive at SERT with
the exception of the 3,4-dichlorophenyl compound 11a
that possessed the SERT-favoring 3b-aryl (chair) config-
uration (IC50 = 120 nM). Again, the 3,4-dichlorophenyl
compounds proved interesting. Here the 3a-boat 10c re-
tained similar DAT inhibitory potency (IC50 = 7.8 nM)
as the unoxidized 7f (DAT IC50 = 6.9 nM). However
all potency was absent for the sulfoxide 10c at the SERT
(IC50 = >3 lM). Thus the DAT selectivity manifested by
the sulfoxide 10c was considerably greater (>346-fold)
than that manifested by the thioether 7f (14-fold). This
enhancement of selectivity by reduction of SERT poten-
cy was also evident in the 3b-chair configured com-
pounds. Thus the thioether 8f showed almost no DAT
versus SERT selectivity (1.5-fold), whereas the sulfoxide
11a was about 23-fold DAT selective. It was not unex-
pected that bulk at the 8-position can reduce SERT
potency because, in the class of 8-azatropanes, Carroll
et al. have demonstrated that the nitrogen unsubstituted
8-NH analogues were more potent SERT inhibitors
than were their 8-NCH3 counterparts.44,45
6. Conclusion
The functional role of the 8-thia in the bicyclo[3.2.1]oc-
tane skeletal nucleus is the focus of this report. In this
class, inhibitory potency at the dopamine transporter
was not markedly different between the 2,3-enes 6, the
3a-aryl 7, and 3b-aryl 8 compounds. For example, the
3,4-dichlorophenyl compounds manifested IC50 values
for the 2,3-ene 6f, the 3a-aryl 7f, and the 3b-aryl 8f of
4.5 nM, 6.9 nM, 5.7 nM, respectively. In contrast, the
selectivity exhibited by 8-thia-2,3-unsaturated, 3a-aryl,
and 3b-aryl compounds for inhibition of both the dopa-
mine and serotonin transporters derived specifically from
reduced activity at the SERT. The unsaturated analogues
6 were the least potent inhibitors of the SERT and there-
fore most selective for the DAT. The 3a-(3,4-dichlorophe-
nyl)-8-sulfoxide 10c retained DAT inhibitory potency
(IC50 = 7.8 nM), however all SERT potency was absent.
Biological enantioselectivity of DAT inhibition was limit-
ed in the 8-thia series. The (1R)-configuration provided
the eutomers in the 2,3-ene (6f-1R; 2-fold over 1S), 3a-aryl
(7f-1R; 2-fold over 1S), and 3b-aryl (8f-1R, 11-fold over
1S) series. In general, molecular topology appeared to
be more important for SERT binding than it was for
DAT inhibition. This may imply that the SERT offers a
more rigid binding site than does the DAT and that there
is only one binding site on the SERT for tropane-like li-
gands. In contrast, there are either multiple binding sites
on the DAT, or it is more accommodating than the SERT.
5. Stereospecific binding
Biological enantioselectivity for inhibition of mono-
amine uptake systems has been demonstrated for 8-aza
and 8-oxa tropanes.16,19,20 We selected the 3,4-dichloro-
phenyl analogues to explore biological enantioselectiv-
ity of these 8-thia compounds. Table 2 presents
comparative data for the enantiomers of the analogous
3,4-dichlorophenyl-sustituted 8-oxa- (12–14),14 7b-hy-
droxy-8-aza- (15–17),20 and 8-aza- (18–20)9 bicy-
clo[3.2.1]octane(ene)s. It was evident that biological
enantioselectivity of DAT inhibition was limited in the
8-thia series. The (1R)-configuration provided the more
active enantiomers in the 2,3-ene (6f-1R; 2-fold over
1S), 3a-aryl (7f-1R; 2-fold over 1S), and 3b-aryl (8f-1R,
11-fold over 1S) analogues. Notwithstanding, the 1S iso-
mers in this series remained potent DAT inhibitors
(IC50 = 5–22 nM). Biological enantioselectivity was
much more pronounced in the 8-oxa series where again
the 1R isomers were the eutomers. However, there was
over an order of magnitude decrease in potency manifest-
ed by the 1S enantiomers in the 8-oxa series. The presence
of a nitrogen in the 8-position resulted in compounds that
possessed the greatest biological enantioselectivity. Data
from our laboratories for the 2,3-ene showed that the 1
R-18a was about 400-fold selective for DAT over the
7. Supplementary information
Atomic coordinates for (1R,10S)-4a (deposition number
617590) and 10f (deposition number 617808) have been
deposited with the Cambridge Crystallographic Data
Centre. Copies of the data can be obtained, free of
charge, on application to CCDC, 12 Union Road,
Cambridge, CB21EZ, UK [fax: +44(0) 1223 336033;
e-mail: deposit@ccdec.cam.ac.uk.]

1074
D.-P. Pham-Huu et al. / Bioorg. Med. Chem. 15 (2007) 1067–1082
8. Experimental
phase separated. The aqueous phase was extracted with
ether and the combined extracts were washed with satu-
rated aq NaHCO3, brine and dried (Na2SO4). Organic
solvents were removed under reduced pressure. The
crude product was recrystallized from ether/hexanes to
provide the camphanyl ester (9.78 g) as a 10:1 mixture
of the 1R,10S: 1S,10S isomers. The camphanyl ester
was then recrystallized repeatedly from THF/hexanes
NMR spectra were recorded on a Jeol 300 NMR spec-
trometer with tetramethylsilane (TMS) as internal stan-
dard and CDCl3 as solvent. Melting points are
uncorrected and were measured on a Mel-Temp melting
point apparatus. Optical rotations were measured with a
JASCO DIP 320 polarimeter at the sodium D line at
room temperature. Room temperature (t) is
22 ꢁC 1 ꢁC. Thin layer chromatography (TLC) was
carried out on Baker Si 250F plates. Visualization was
accomplished with iodine vapor, UV exposure or treat-
ment with phosphomolybdic acid (PMA). Flash chro-
matography was carried out on Baker Silica Gel
40 lM (Silica gel). All reactions were conducted under
an atmosphere of dry nitrogen. Yields have not been
optimized. Elemental analyses were performed by
Atlantic Microlab, Norcross, GA. HPLC and MS data
were obtained on an Agilent 1100 LC/MSD system. A
Beckman 1801 Scintillation Counter was used for scin-
tillation spectrometry. 0.1% Bovine serum albumin
and (ꢀ)-cocaine were purchased from Sigma Chemicals.
1
and monitored by H NMR. Recrystallization was ter-
minated when the ratio of diastereomer (1R,10S-4a) to
diastereomer (1S,10S-4a) was >100:1 (ee = 98%) as evi-
denced by the methyl resonances at d 0.970 and d
0.928. X-ray structural analysis confirmed the structure
as (1R,10S-4a). Lithium hydroxide (0.68 g, 16.2 mmol)
was added to the camphanyl ester (1R,10S-4a) (4.14 g,
10.9 mmol) in THF/H2O (40:10 mL) at 0 ꢁC. After 1 h
the solution was neutralized with 1 N HCl; ether
(200 mL) was added and the organic phase separated.
The aqueous phase was extracted with ether and the
combined extracts were washed with brine, dried
(Na2SO4), and solvent was evaporated in vacuo. The
residue was recrystallized from ethyl acetate/hexanes.
Purification by flash column chromatography (5% ethyl
acetate/hexanes) provided the desired enantiomer (1R)-4
(1.72 g, 79%). All other spectral data were identical to
those for racemic 4. Anal. (C15H14O2SCl2) C, H, S, Cl.
([3H]WIN35,428,
2b-carbomethoxy-3b-(4-fluorophe-
nyl)-N-[3H]methyltropane, 79.4–87.0 Ci/mmol) and
[3H]citalopram (86.8 Ci/mmol) were purchased from
Perkin Elmer (Boston, MA). (ꢀ)-Cocaine hydrochloride
for the pharmacological studies was donated by the
National Institute on Drug Abuse. Fluoxetine was
donated by E. Lilly & Co.
8.3. (1S)-2-Carbomethoxy-8-thiabicyclo[3.2.1]octan-3-one
(1S-4)
8.1. 2-Carbomethoxy-8-thiabicyclo[3.2.1]octan-3-one (4)
Racemic keto ester 4 was treated as described above for
(1R-4) with sodium bis(trimethylsilyl)amide followed by
(1R)-camphanyl chloride to provide the camphanyl es-
ter. The camphanyl ester was recrystallized repeatedly
from THF/hexanes and monitored by 1H NMR. Recrys-
tallization was terminated when the ratio of diastereo-
mer (1S,10R-4b) to diastereomer (1S,10S-4b) was
>100:1 (ee = 98%) as evidenced by the methyl resonanc-
es at d0.970 and d 0.928. Lithium hydroxide was added
to the camphanyl ester (1S,10R-4b) in THF/H2O
(40:10 mL) at 0 ꢁC. After 1 h the solution was neutral-
ized with 1 N HCl; ether was added, and the organic
phase separated. The aqueous phase was extracted with
ether and the combined extracts were washed with brine,
dried (Na2SO4), and solvent was evaporated in vacuo.
The residue was recrystallized from ethyl acetate/hex-
anes. Purification by flash column chromatography
(5% ethyl acetate/hexanes) provided the desired enantio-
mer (1S)-4. All other spectral data were identical to
those for racemic 4. Anal. (C15H14O2SCl2) C, H, S, Cl.
A solution of 8-thiatropinone 338 (15.5 g, 109 mmol) in
THF (300 mL) was stirred at ꢀ78 ꢁC under nitrogen,
then LDA (2 M, 60 mL) was added dropwise. After stir-
ring for 2 h, methyl cyanoformate (10.4 mL, 131 mmol)
was added. The reaction was quenched after 1 h with
saturated aqueous NaHCO3 (100 mL) and allowed to
warm to room temperature. Water was added and the
mixture was extracted with ether (3· 100 mL). The com-
bined organic phase was washed with saturated aqueous
NaHCO3, brine and dried (Na2SO4). The solvents were
removed on a rotary evaporator and the residue was
purified by flash chromatography (5% EtOAc/hexanes)
to afford 15.0 g (69%) of 4, which was comprised of
three tautomers: the 2a-carbomethoxy keto ester, the
2b-carbomethoxy keto ester, and the enol ester. Since
these compounds could not be separated, characteriza-
tion was conducted on the triflate derivative 5.
8.2. Resolution of 4. (1R)-2-Carbomethoxy-8-thiabicy-
clo[3.2.1]octan-3-one (1R-4)
8.4. 2-Carbomethoxy-3[(trifluoromethanesulfonyl)oxy]-8-
thiabicyclo[3.2.1]-2-octene (5)
Racemic keto ester 4 (8.0 g, 40 mmol) was dissolved in
THF (150 mL) and cooled to ꢀ78 ꢁC. A solution of
sodium bis(trimethylsilyl)amide (1 M in THF, 44 mL,
44 mmol) was added under nitrogen over a period of
30 min. After stirring for 1 h, (1S)-camphanyl chloride
(8.68 g, 40 mmol) was added in one portion and the
resulting mixture was stirred for 1 h. The cooling bath
was removed and a saturated solution of NaHCO3
was added. The reaction mixture was allowed to warm
to room temperature, ether was added and the organic
Sodium bis(trimethylsilyl)amide (1.0 M in THF, 67 mL)
was added drop wise at ꢀ78 ꢁC under nitrogen to a solu-
tion of 4 (10.1 g, 50.5 mmol) in anhydrous THF (200 mL).
After stirring for 1 h at ꢀ78 ꢁC, N-phenyltrifluorome-
thanesulfonimide (19.9 g, 55.6 mmol) was added. The
reaction mixture was allowed to warm to room tempera-
ture and was stirred overnight. The reaction mixture was
concentrated and the residue was dissolved in CH2Cl2
(200 mL). The organic phase was washed with H2O (2·

D.-P. Pham-Huu et al. / Bioorg. Med. Chem. 15 (2007) 1067–1082
1075
100 mL), brine (50 mL) and dried (Na2SO4). The solvent
was removed on a rotary evaporator and the residue was
purified by flash chromatography (5% EtOAc/hexanes) to
give 12.6 g (75%) of 5 as a pale yellow oil: 1H NMR: d 4.39
(dd, J = 0.9, 3.6 Hz, 1H), 3.94 (m, 1H), 3.84 (s, 3H), 2.99
(ddd, J = 2.1, 4.3, 18.6 Hz, 1H), 2.53–2.42 (m, 2H), 2.36–
2.14 (m, 2H), 1.95 (m, 1H).
6d was obtained (85%) as white solid: mp 70–71 ꢁC; Rf
0.20 (5% EtOAc/hexanes). 1H NMR: d 7.42 (d,
J = 8.5 Hz, 2H), 6.94 (d, 2H), 4.31 (d, J = 5.2 Hz, 1H),
3.89 (m, 1H), 3.49 (s, 3H), 2.91 (ddd, J = 1.9, 4.2,
19.2 Hz, 1H), 2.48 (m, 1H), 2.41 (dd, J = 2.2, 19.2,
1H), 2.33–2.17 (m, 2H), 1.99 (m, 1H); MS (CI, m/z):
339, 341 [M+]. Anal. (C15H15O2SBr) C, H, S, Br.
8.5. General procedure for synthesis of 2-carbomethoxy-
3-aryl-8-thiabicyclo[3.2.1]-2-octenes. 2-Carbomethoxy-3-
phenyl-8-thiabicyclo[3.2.1]-2-octene (6a)
8.9. 2-Carbomethoxy-3-(4-iodophenyl)-8-thiabicyclo-
[3.2.1]-2-octene (6e)
Compound 6e was prepared from
5
with 4-
Pd(PPh3)4 (0.31 g, 0.27 mmol), LiCl (0.76 g, 18 mmol),
and Na2CO3 (2 M solution, 9 mL) were added to a solu-
tion of 5 (3.0 g, 9.0 mmol) in diethoxymethane (30 mL).
The mixture was stirred vigorously and phenylboronic
acid (1.32 g, 10.8 mmol) was added. The resulting mix-
ture was heated at reflux for 3 h and cooled to room
temperature, filtered through celite, and washed with
ether. Water was added and the mixture was basified
to pH 10 with NH4OH. The aqueous phase was extract-
ed with chloroform (2· 30 mL). The chloroform and
ether layers were combined, dried (Na2SO4), and con-
centrated on a rotary evaporator. The residue was puri-
fied by flash column chromatography (10% EtOAc/
hexanes) to afford 2.17 g (92%) of 6a as a white solid:
iodophenylboronic acid as described for 6a. Compound
6e was obtained (74%) as white solid: mp 111–112 ꢁC; Rf
0.31 (10% EtOAc/hexanes). 1H NMR: d 7.63 (d,
J = 8.5 Hz, 2H), 6.82 (d, 2H), 4.31 (d, J = 5.3 Hz, 1H),
3.89 (m, 1H), 3.49 (s, 3H), 2.89 (ddd, J = 1.9, 4.1,
19.2 Hz, 1H), 2.48 (m, 1H), 2.40 (dd, J = 2.3, 19.1,
1H), 2.33–2.15 (m, 2H), 2.01 (m, 1H); MS (CI, m/z):
387 [(M+H)+]. Anal. (C15H15O2SI) C, H, S, I.
8.10. 2-Carbomethoxy-3-(3,4-dichlorophenyl)-8-thiabicy-
clo[3.2.1]-2-octene (6f)
Compound 6f was prepared from 5 with 3,4-dic-
hlorophenylboronic acid as described for 6a. Compound
6f was obtained (96%) as white solid: mp 94–95 ꢁC; Rf
0.27 (10% EtOAc/hexanes). 1H NMR: d 7.37 (d,
J = 8.3 Hz, 1H), 7.17 (d, J = 2.0 Hz, 1H), 6.90 (dd,
1H), 4.32 (d, J = 5.0 Hz, 1H), 3.89 (m, 1H), 3.52 (s,
3H), 2.90 (ddd, J = 1.9, 4.1, 19.2 Hz, 1H), 2.50–2.15
(m, 4H), 2.02 (m, 1H); MS (CI, m/z): 329 [M+]. Anal.
(C15H14O2SCl2) C, H, S, Cl.
1
mp 81–82 ꢁC; Rf 0.25 (5% EtOAc/hexanes). H NMR:
d 7.32–7.25 (m, 3H), 7.06 (dd, J = 8.0, 1.9 Hz, 2 H),
4.30 (d, J = 5.1 Hz, 1H), 3.89 (m, 1H), 3.44 (s, 3H),
2.95 (ddd, J = 2.1, 4.4, 18.9 Hz, 1H), 2.54–2.43 (m,
2H), 2.37–2.16 (m, 2H), 2.01 (m, 1H);. MS (CI, m/z):
261 [(M+H)+]. Anal. (C15H16O2S) C, H, S.
8.6. 2-Carbomethoxy-3-(4-fluorophenyl)-8-thiabicyclo-
[3.2.1]-2-octene (6b)
8.10.1. (1R)-2-Carbomethoxy-3-(3,4-dichlorophenyl)-8-
21
thiabicyclo[3.2.1]-2-octene 1R-6f). ½aꢂ ꢀ52ꢁ (c 0.25,
D
MeOH). All other spectral data were identical to those
for racemic 6f. Anal. (C15H14O2SCl2) C, H, S, Cl.
Compound 6b was prepared from 5 with 4-fluor-
ophenylboronic acid as described for 6a. Compound
6b was obtained (94%) as white solid: mp 60–61 ꢁC; Rf
1
0.28 (5% EtOAc/hexanes). H NMR: d 7.06–6.94 (m,
8.10.2. (1S)-2-Carbomethoxy-3-(3,4-dichlorophenyl)-8-
21
4H), 4.30 (d, J = 5.3 Hz, 1H), 3.89 (m, 1H), 3.47 (s,
3H), 2.91 (ddd, J = 2.0, 4.2, 19.0 Hz, 1H), 2.51–2.40
(m, 2H), 2.32–2.12 (m, 2H), 2.01 (m, 1H); MS (CI,
m/z): 279 [(M+H)+]. Anal. (C15H15O2SF) C, H, S, F.
thiabicyclo[3.2.1]-2-octene (1S-6f). ½aꢂ +51ꢁ (c 0.25,
D
MeOH). All other spectral data were identical to those
for racemic 6f. Anal. (C15H14O2SCl2) C, H, S, Cl.
8.11. 2-Carbomethoxy-3-(3,4-difluorophenyl)-8-thiabicy-
clo[3.2.1]-2-octene (6g)
8.7. 2-Carbomethoxy-3-(4-chlorophenyl)-8-thiabicyclo-
[3.2.1]-2-octene (6c)
Compound 6g was prepared from 5 with 3,4-dif-
luorophenylboronic acid as described for 6a. Compound
6g was obtained (89%) as an oil: Rf 0.19 (5% EtOAc/
hexanes). 1H NMR: d 7.09 (dt, J = 8.2 Hz, 10.2 Hz,
1 H), 6.90 (ddd, J = 2.1 Hz, 7.4 Hz, 11.0 Hz, 1H), 6.78
(m, 1H), 4.31 (d, J = 5.2 Hz, 1H), 3.89 (m, 1H), 3.51
(s, 3H), 2.89 (ddd, J = 1.9, 4.1, 19.2 Hz, 1H), 2.49?2.12
(m, 4H), 1.98 (m, 1H); MS (CI, m/z): 295 [M+]. Anal.
(C15H14O2SF2) C, H, S, F.
Compound 6c was prepared from 5 with 4-chloro-
phenylboronic acid as described for 6a. Compound 6c
was obtained (93%) as white solid: mp 47–48 ꢁC; Rf
0.25 (5% EtOAc/hexanes). 1H NMR: d 7.27 (d,
J = 8.2 Hz, 2H), 7.01 (d, 2H), 4.31 (d, J = 5.2 Hz, 1H),
3.89 (m, 1H), 3.48 (s, 3H), 2.91 (ddd, J = 1.9, 4.2,
19.0 Hz, 1H), 2.50 (m, 1H), 2.42 (dd, J = 2.2, 19.0,
1H), 2.34–2.17 (m, 2H), 2.01 (m, 1H); MS (CI, m/z):
295 [M+]. Anal. (C15H15O2SCl) C, H, S, Cl.
8.12. 2-Carbomethoxy-3-(2-naphthyl)-8-thiabicyclo-
[3.2.1]-2-octene (6h)
8.8. 2-Carbomethoxy-3-(4-bromophenyl)-8-thiabicyclo-
[3.2.1]-2-octene (6d)
Compound 6h was prepared from 5 with 2-naphthylbo-
ronic acid as described for 6a. A clear viscous oil was
obtained (93%): Rf 0.27 (10% EtOAc/hexanes).
Compound 6d was prepared from 5 with 4-bro-
mophenylboronic acid as described for 6a. Compound

1076
D.-P. Pham-Huu et al. / Bioorg. Med. Chem. 15 (2007) 1067–1082
1H NMR d 7.82–7.76 (m, 3H), 7.54 (d, J = 1.7, 1H),
7.48–7.42 (m, 2H), 7.20 (dd, J = 1.7, 8.4 Hz, 1H), 4.36
(d, J = 4.9 Hz, 1H), 3.94 (m, 1H), 3.40 (s, 3H), 3.03
(ddd, J = 1.9, 4.4, 19.3 Hz, 1H), 2.60–2.50 (m, 2H),
2.41–2.23 (m, 2H), 2.05 (m, 1H); MS (CI, m/z): 311
[(M+H)+]. Anal. (C19H18O2S) C, H, S.
8.16. General procedure for de-esterification
8.16.1.
2b-Carboxy-3a-phenyl-8-thiabicyclo[3.2.1]-oc-
tanes and 2b-carboxy-3b-phenyl-8-thiabicyclo[3.2.1]oc-
tane. To AlCl3 (798 mg, 6 mmol) powder was added
dropwise dimethyl sulfide (6 ml)41 at 0 ꢁC under an argon
atmosphere. The solution was stirred for 10 min and al-
lowed to warm to room temperature. A solution of com-
pounds 7a and 8a in CH2Cl2 (5 ml) was added slowly. The
reaction was monitored by TLC every hour (For TLC:
AlCl3 was quenched by methanol). When the reaction
was complete, the reaction mixture was poured into
water, to which 1 M HCl solution was added. The reac-
tion mixture was extracted with CH2Cl2 (2· 100 ml).
The combined organic phase was washedwith brine, dried
(Na2SO4), and filtered. The solvents were removed on a
rotary evaporator to give a solid. The crude products were
purified and separated by flash chromatography using 3%
MeOH in CHCl3 to give the carboxylic acid of 7a (307 mg,
62%) and the carboxylic acid of 8a (67 mg, 14%). These
8.13. 2-Carbomethoxy-3-(4-chloro-3-fluorophenyl)-8-thi-
abicyclo[3.2.1]-2-octene (6i)
Compound 6i was prepared from 5 with 4-chloro-3-flu-
orophenylboronic acid as described for 6a. Compound
6i was obtained (89%) as an oil; Rf 0.35 (10% EtOAc/
hexanes). 1H NMR: d 7.31 (t, J = 7.9 Hz, 1H), 6.87
(dd, J = 2.1 Hz, 9.9 Hz, 1H), 6.78 (dd, 1H), 4.31 (d,
J = 5.2 Hz, 1H), 3.89 (m, 1H), 3.53 (s, 3H), 2.91 (ddd,
J = 1.9, 4.1, 19.2 Hz, 1H), 2.49–2.14 (m, 4H), 2.02 (m,
1H); MS (CI, m/z): 313 [M+]. Anal. (C15H14O2SFCl)
C, H, S, F, Cl.
1
8.14. 2-Carbomethoxy-3-(3-chloro-4-fluorophenyl)-8-thi-
abicyclo[3.2.1]-2-octene (6j)
carboxylic acids were characterized by H NMR: and
converted to their methyl esters as described below.
Compound 6j was prepared from 5 with 3-chloro-4-flu-
orophenylboronic acid as described for 6a. Compound
6j was obtained (90%) as a white solid: mp 76–77 ꢁC;
Rf 0.33 (10% EtOAc/hexanes). 1H NMR d 7.11 (dd,
J = 2.2 Hz, 7.1 Hz, 1H), 7.05 (d, J = 8.5 Hz, 1H), 6.93
(ddd, 1H), 4.31 (d, J = 5.5 Hz, 1H), 3.90 (m, 1H), 3.51
(s, 3H), 2.91 (ddd, J = 1.9, 4.3, 19.2 Hz, 1H), 2.50–2.14
(m, 4H), 2.01 (m, 1H); MS (CI, m/z): 313 [M+]. Anal.
(C15H14O2SFCl) C, H, S, F, Cl.
8.16.2. 2b-Carboxy-3a-phenyl-8-thiabicyclo[3.2.1]octane.
Yield 62%. 1H NMR: d 7.32–7.15 (m, 5 H); 3.79 (d,
J = 6.3 Hz, 1H); 3.66 (dd, J = 5.3 Hz, 8.5 Hz, 1H); 3.26
(dt, J = 7.5 Hz, 11.5 Hz, 1H); 2.53 (d, J = 11.3 Hz,
1H); 2.45–1.89 (m, 5H), 1.34 (t, J = 13.4 Hz, 1H).
8.16.3. 2b-Carboxy-3b-phenyl-8-thiabicyclo[3.2.1]octane.
Yield 14%. 1H NMR: d 7.35–7.15 (m, 5H); 3.97 (t,
J = 4.8 Hz, 1H); 3.74 (t, J = 4.7 Hz, 1H); 3.21–3.12 (m,
2H); 2.70 (t, J = 12.9 Hz, 1H); 2.27–1.94 (m, 5H).
8.15. General procedure for synthesis of 3a-aryl- and 3b-
aryl bicyclo[3.2.1]octanes
8.16.4.
2b-Carboxy-3a-(4-fluorophenyl)-8-thiabicyclo-
[3.2.1]octane. Yield 57%. 1H NMR: d 7.15 (dd,
J = 5.4 Hz, J = 8.5 Hz, 2H); 6.95 (t, J = 8.5 Hz, 2H); 3.78
(d, J = 6.3 Hz, 1H); 3.66 (dd, J = 5.5 Hz, 9.1 Hz, 1H);
3.25 (dt, J = 7.2, 11.8 Hz, 1H); 2.46 (d, J = 11.3 Hz, 1H);
2.43–1.85(m, 5H), 1.29 (t, J = 13.2 Hz, 1H).
8.15.1. 2b-Carbomethoxy-3a-phenyl-8-thiabicyclo[3.2.1]-
octane (7a) and 2b-carbomethoxy-3b-phenyl-8-thiabicy-
clo[3.2.1]octane (8a). Compound 6a (520 mg, 2 mmol)
was dissolved in a mixture of THF (30 mL) and isopro-
pyl alcohol (10 mL). To the stirred solution at ꢀ60 ꢁC
under a nitrogen atmosphere, SmI2 (80 mL, 0.1M in
THF) was added dropwise. The mixture was stirred at
ꢀ60 ꢁC for 3 h. Water was added (10 mL) and the
reaction mixture was allowed to warm to room temper-
ature. A saturated solution of NaHCO3 (120 mL) was
added. The mixture was stirred for 1 h, then filtered
and washed with ether (2· 100 mL). The organic phase
was washed with brine (100 mL) and dried (Na2SO4).
The solvents were removed on a rotary evaporator
and the residue was purified by gravity column chroma-
tography (10% EtOAc/hexanes) providing a mixture of
460 mg of the two isomers 7a and 8a in a ratio 5:1 (1H
NMR), which was used in the next reaction without fur-
ther separation.
8.16.5.
2b-Carboxy-3b-(4-fluorophenyl)-8-thiabicyclo-
[3.2.1]octane. Yield 17%. 1H NMR: d 7.21 (dd,
J = 5.4 Hz, J = 8.6 Hz, 2H); 6.96 (t, J = 8.6 Hz, 2H);
3.97 (t, J = 4.7 Hz, 1H); 3.73 (m, 1H); 3.17–3.06 (m,
2H); 2.66 (t, J = 12.6 Hz, 1H); 2.32–1.91 (m, 5H).
8.16.6.
2b-Carboxy-3a-(4-chlorophenyl)-8-thiabicyclo-
[3.2.1]octane. Yield 56%. 1H NMR: d 7.21 (dd,
J = 5.2 Hz, J = 8.5 Hz, 2H); 7.13 (t, J = 8.5 Hz, 2H);
3.74 (d, J = 6.2 Hz, 1H); 3.69 (dd, J = 5.5 Hz, 9.0 Hz,
1H); 3.30 (dt, J = 7.1, 11.5 Hz, 1H); 2.45 (d,
J = 11.4 Hz, 1H); 2.42–1.89 (m, 5H), 1.31 (t,
J = 13.2 Hz, 1H).
8.16.7.
2b-Carboxy-3b-(4-chlorophenyl)-8-thiabicyclo-
Note: The two reduced isomers (3a-aryl and 3b-aryl)
could not be readily separated either by flash or by grav-
ity column chromatography. Therefore a two-step pro-
cedure was utilized to obtain configurationally pure
3a-aryl- and 3b-aryl compounds. The mixed esters 7/8
were de-esterified, separated, and re-esterified to obtain
pure 7 and 8, as detailed below.
[3.2.1]octane. Yield 15%. 1H NMR: d 7.28–7.12 (m,
4H); 3.99 (t, J = 4.9 Hz, 1H); 3.75 (m, 1H); 3.18–3.06
(m, 2H); 2.72 (t, J = 12.7 Hz, 1H); 2.32–1.91 (m, 5H).
8.16.8.
[3.2.1]octane. Yield 42%. 1H NMR:
J = 8.5 Hz, 2H); 7.06 (d, 2H); 3.79 (d, J = 6.3 Hz, 1H);
2b-Carboxy-3a-(4-bromophenyl)-8-thiabicyclo-
d
7.38 (d,

D.-P. Pham-Huu et al. / Bioorg. Med. Chem. 15 (2007) 1067–1082
1077
1
3.67 (dd, J = 5.5 Hz, 9.0 Hz, 1H); 3.27 (dt, J = 7.1,
11.5 Hz, 1H); 2.45 (d, J = 11.1 Hz, 1H); 2.40–1.85 (m,
5H), 1.28 (t, J = 13.2 Hz, 1H).
mp 49–50 ꢁC; Rf 0.26 (10% EtOAc/hexanes); H NMR:
d 7.32–7.15 (m, 5H); 3.73 (d, J = 6.3 Hz, 1H); 3.67 (dd,
J = 5.5 Hz, 9.1 Hz, 1H); 3.52 (s, 3H); 3.32 (dt,
J = 7.4 Hz, 11.5 Hz, 1H); 2.51 (d, J = 11.4 Hz, 1H);
2.45–1.89 (m, 5H), 1.37 (t, J = 12.7 Hz, 1H); MS (CI,
m/z): 263 [(M+H)+]. Anal. (C15H18O2S) C, H, S.
8.16.9.
2b-Carboxy-3b-(4-bromophenyl)-8-thiabicyclo-
7.32 (d,
[3.2.1]octane. Yield 22%. 1H NMR:
d
J = 8.5 Hz, 2H); 7.00 (d, 2H); 3.90 (t, J = 5.1 Hz, 1H);
3.64 (t, J = 4.4 Hz, 1H); 3.06 (t, J = 4.7 Hz, 1H); 2.96
(dt, J = 4.7 Hz, 12.9 Hz, 1H); 2.57 (t, J = 12.9 Hz, 1H);
2.32–1.84 (m, 5H).
8.16.16. 2b-Carbomethoxy-3a-(4-fluorophenyl)-8-thiabi-
cyclo[3.2.1]octane (7b). Compound 7b was prepared
from 2b-carboxy-3a-(4-fluorophenyl)-8-thiabicyclo[3.2.
1]octane as described for 8a. Compound 7b was ob-
tained (90%) as a syrup; Rf 0.26 (10% EtOAc/hexanes);
1H NMR: d 7.15 (dd, J = 5.4 Hz, J = 8.5 Hz, 2H); 6.95
(t, J = 8.5 Hz, 2H); 3.71 (d, J = 6.0 Hz, 1H); 3.67 (m,
1H); 3.53 (s, 3H); 3.31 (dt, J = 7.1, 11.6 Hz, 1H); 2.44
(d, J = 11.3 Hz, 1H); 2.40–1.87 (m, 5H), 1.31 (t,
J = 12.6 Hz, 1H); MS (CI, m/z): 281 [(M+H)+]. Anal.
(C19H17O2SF) C, H, S, F.
8.16.10.
2b-Carboxy-3a-(4-iodophenyl)-8-thiabicyclo-
7.58 (d,
[3.2.1]octane. Yield 37%. 1H NMR:
d
J = 8.5 Hz, 2H); 6.94 (d, 2H); 3.75 (d, J = 6.2 Hz, 1H);
3.68 (dd, J = 5.5 Hz, 9.1 Hz, 1H); 3.27 (dt, J = 7.1,
11.4 Hz, 1H); 2.45 (d, J = 11.4 Hz, 1H); 2.40–1.85 (m,
5H), 1.32 (t, J = 13.1 Hz, 1H).
8.16.11.
[3.2.1]octane. Yield 13%. 1H NMR:
J = 7.7 Hz, 2H); 6.95 (d, 2H); 3.95 (t, J = 4.7 Hz, 1H);
3.71 (m, 1H); 3.11 (t, J = 4.6 Hz, H); 3.01 (dt,
J = 4.7 Hz, 12.6 Hz, 1H); 2.62 (t, J = 12.9 Hz, 1H);
2.32–1.84 (m, 5H).
2b-Carboxy-3b-(4-iodophenyl)-8-thiabicyclo-
7.57 (d,
d
8.16.17. 2b-Carbomethoxy-3b-(4-fluorophenyl)-8-thiabi-
cyclo[3.2.1]octane (8b). Compound 8b was prepared
from 2b-carboxy-3b-(4-fluorophenyl)-8-thiabicyclo[3.2.
1]octane as described for 8a. Compound 8b was ob-
tained (90%) as white solid: mp 114–115 ꢁC; Rf 0.27
(10% EtOAc/hexanes); 1H NMR:
d
7.21 (dd,
J = 5.4 Hz, J = 8.6 Hz, 2H); 6.96 (t, J = 8.6 Hz, 2H);
3.96 (t, J = 4.8 Hz, 1H); 3.73 (m, 1H); 3.51 (s, 3H);
3.14 (t, J = 4.8 Hz, 1H); 3.06 (m, 1H); 2.72 (t,
J = 12.7 Hz, 1H); 2.32–1.91 (m, 5H); MS (CI, m/z):
281 [(M+H)+]. Anal. (C19H17O2SF) C, H, S, F.
8.16.12. 2b-Carboxy-3a-(2-naphthyl)-8-thiabicyclo[3.2.1]-
octane. Yield 54%. 1H NMR: d 7.79–7.72 (m, 3H),
7.61 (s, 1H), 7.47–7.38 (m, 2H), 7.31 (dd, J = 1.7 Hz,
8.5 Hz, 1H); 3.80 (d, J = 6.3 Hz, 1H), 3.69 (dd,
J = 5.2 Hz, 9.0 Hz, 1H), 3.44 (dt, J = 7.1 Hz, 11.5 Hz,
1H), 2.65 (d, J = 11.1 Hz, 1H); 2.47–1.91 (m, 5H), 1.43
(t, J = 12.9 Hz, 1H).
8.16.18. 2b-Carbomethoxy-3a-(4-chlorophenyl)-8-thiabi-
cyclo[3.2.1]octane (7c). Compound 7c was prepared
from 2b-carboxy-3a-(4-chlorophenyl)-8-thiabicyclo[3.2.
1]octane as described for 8a. Compound 7c was ob-
tained (89%) as white solid: mp 69–70ꢁC; Rf 0.26 (10%
EtOAc/hexanes); 1H NMR: d 7.22 (dd, J = 5.4 Hz,
J = 8.5 Hz, 2H); 7.12 (t, J = 8.5 Hz, 2H); 3.72 (d,
J = 6.3 Hz, 1H); 3.67 (dd, J = 5.5 Hz, 9.1 Hz, 1H); 3.54
(s, 3H); 3.31 (dt, J = 7.1, 11.6 Hz, 1H); 2.44 (d,
J = 11.3 Hz, 1H); 2.40–1.85 (m, 5H), 1.30 (t,
J = 13.1 Hz, 1H); MS (CI, m/z): 297 [(M+H)+]. Anal.
(C15H17O2SCl) C, H, S, Cl.
8.16.13. 2b-Carboxy-3b-(2-naphthyl)-8-thiabicyclo[3.2.1]-
1
octane. Yield 17%. H NMR: d 7.79–7.72 (m, 3H), 7.65
(s, 1H), 7.47–7.35 (m, 3H), 4.00 (m, 1H), 3.78 (m, 1H),
3.33–3.24 (m, 2H), 2.82 (t, J = 12.8 Hz, 1H); 2.36–2.01
(m, 5H).
8.16.14. General procedure for esterification of 2b-
carboxy-3-aryl-8-thiabicyclo[3.2.1]octane to provide 7
and 8. 2b-Carbomethoxy-3b-phenyl-8-thiabicyclo[3.2.1]-
octane (8a). 2b-Carboxy-3b-phenyl-8-thiabicyclo[3.2.1]-
octane (150 mg, 0.6 mmol) was dissolved in THF
(15 mL) and 0.5 M HCl in methanol (5 mL). To the stir-
red solution was added dropwise a 2 M solution of
TMSCHN2 (1.2 mL, 2.4 mmol) at 0 ꢁC. After the addi-
tion was complete, the mixture was stirred for 4 h at
room temperature, then concentrated. The residue was
purified by flash column chromatography (10%
EtOAc/hexanes) to provide compound 8a (124 mg,
80%) as white solid: mp 95–96 ꢁC; Rf 0.25 (10%
8.16.19. 2b-Carbomethoxy-3b-(4-chlorophenyl)-8-thiabi-
cyclo[3.2.1]octane (8c). Compound 8c was prepared
from 2b-carboxy-3b-(4-chlorophenyl)-8-thiabicyclo-
[3.2.1]octane as described for 8a. Compound 8c was ob-
tained (87%) as white solid: mp 100–101 ꢁC; Rf 0.25
1
(10% EtOAc/hexanes); H NMR: d 7.28–7.12 (m, 4H);
3.97 (t, J = 5.0 Hz, 1H); 3.73 (m, 1H); 3.51 (s, 3H);
3.15 (t, J = 4.7 Hz, 1H); 3.06 (m, 1H); 2.72 (t,
J = 12.7 Hz, 1H); 2.32–1.91 (m, 5H); MS (CI, m/z):
297 [(M+H)+]. Anal. (C15H17O2SCl) C, H, S, Cl.
1
EtOAc/hexanes). H NMR: d 7.32–7.15 (m, 5H); 3.97
(t, J = 4.8 Hz, 1H); 3.74 (t, J = 4.7 Hz, 1H); 3.50 (s,
3H); 3.20 (t, J = 4.7 Hz, 1H); 3.12 (m, 1H); 2.76 (t,
J = 12.6 Hz, 1H); 2.27–1.91 (m, 5H); MS (CI, m/z):
263 [(M+H)+]. Anal. (C15H18O2S) C, H, S.
8.16.20. 2b-Carbomethoxy-3a-(4-bromophenyl)-8-thiabi-
cyclo[3.2.1]octane (7d). Compound 7d was prepared
from 2b-carboxy-3a-(4-bromophenyl)-8-thiabicyclo[3.2.
1]octane as described for 8a. Compound 7d was ob-
tained (89%) as white solid: mp 106–107 ꢁC; Rf 0.32
8.16.15. 2b-Carbomethoxy-3a-phenyl-8-thiabicyclo[3.2.1]-
octane (7a). Compound 7a was prepared from 2b-car-
boxy-3a-phenyl-8-thiabicyclo[3.2.1]octane as described
for 8a. Compound 7a was obtained (77%) as white solid:
1
(10% EtOAc/hexanes); H NMR: d 7.38 (d, J = 8.5 Hz,
2H); 7.06 (d, 2H); 3.72 (d, J = 6.1 Hz, 1H); 3.67 (dd,

1078
D.-P. Pham-Huu et al. / Bioorg. Med. Chem. 15 (2007) 1067–1082
J = 5.6 Hz, 9.1 Hz, 1H); 3.54 (s, 3H); 3.30 (dt, J = 7.1,
11.6 Hz, 1H); 2.45 (d, J = 11.3 Hz, 1H); 2.40–1.85 (m,
5H), 1.30 (t, J = 13.2 Hz, 1H); MS (CI, m/z): 341, 343
[(M+H)+]. Anal. (C15H17O2SBr) C, H, S, Br.
8.17. General procedure for synthesis of octanes 7f, g, i, j,
and 8f, g, i, j
8.17.1. 2b-Carbomethoxy-3a-(3,4-dichlorophenyl)-8-thia-
bicyclo[3.2.1]octanes (7f) and 2b-Carbomethoxy-3b-(3,4-
dichlorophenyl)-8-thiabicyclo[3.2.1]octanes (8f). Com-
pound 6f (659 mg, 2 mmol) was dissolved in a mixture
of THF (30 mL) and isopropyl alcohol (10 mL). SmI2
(0.1 M, 80 mL) was added dropwise to the stirred solu-
tion at ꢀ60 ꢁC under a nitrogen atmosphere. The mix-
ture was stirred at ꢀ60 ꢁC for 3 h, after which water
was added (10 mL) and the reaction mixture was al-
lowed to warm to room temperature. A saturated solu-
tion of NaHCO3 (120 mL) was added. The mixture was
stirred for 1 h, then filtered and washed with ether (2·
100 mL). The organic phase was washed with brine
(100 mL) and dried (Na2SO4). The solvents were re-
moved on a rotary evaporator and the residue was puri-
fied by flash column chromatography (10% EtOAc/
hexanes) to give a mixture of 2b,3a and 2b,3b isomers
in a ratio 1:1 (554 mg). The mixture was repeatedly
recrystallized from heptane to provide pure 6f (82 mg).
The combined mother liquors were concentrated and
subjected to gravity chromatography (10% EtOAc in
hexanes). Fractions were collected and monitored by
TLC and GC. The first fraction was pure 2b,3a com-
pound 7f (97 mg). The second fraction (116 mg) was a
mixture of 2b,3a and 2b,3b isomers, which was enriched
with the 2b,3a isomer. The third fraction (242 mg) was a
mixture of 2b,3a and 2b,3b isomers, which was enriched
with 2b,3b isomer. The third fraction was concentrated
and recrystallized twice from heptane to give pure
2b,3b isomer 8f (120 mg). The mother liquors and the
second fraction were combined and purified by gravity
column chromatography (10% EtOAc/hexanes) fol-
lowed by recrystallization of the enriched mixture of
two isomers to give another portion of pure 7f
(108 mg) and 8f (32 mg). Compound 7f was obtained
(205 mg, 31%) as white solid: mp 99–100 ꢁC; Rf 0.28
8.16.21. 2b-Carbomethoxy-3b-(4-bromophenyl)-8-thiabi-
cyclo[3.2.1]octane (8d). Compound 8d was prepared
from 2b-carboxy-3b-(4-bromophenyl)-8-thiabicyclo-
[3.2.1]octane as described for 8a. Compound 8d was
obtained (84%) as white solid: mp 141–143 ꢁC; Rf 0.31
1
(10% EtOAc/hexanes); H NMR: d 7.39 (d, J = 8.5 Hz,
2H); 7.11 (d, 2H); 3.96 (t, J = 4.9 Hz, 1H); 3.73 (m,
1H); 3.51 (s, 3H); 3.15 (t, J = 4.7 Hz, 1H); 3.05 (dt,
J = 4.9 Hz, 12.9 Hz, 1H); 2.71 (t, J = 12.9 Hz, 1H);
2.32–1.91 (m, 5H); MS (CI, m/z): 341, 343 [(M+H)+].
Anal. (C15H17O2SBr) C, H, S, Br.
8.16.22. 2b-Carbomethoxy-3a-(4-iodophenyl)-8-thiabicy-
clo[3.2.1]octane (7e). Compound 7e was prepared from
2b-carboxy-3a-(4-iodophenyl)-8-thiabicyclo[3.2.1]octane
as described for 8a. Compound 7e was obtained (94%)
as white solid: mp 137–138 ꢁC; Rf 0.29 (10% EtOAc/hex-
1
anes); H NMRd 7.57 (d, J = 8.5 Hz, 2H); 6.94 (d, 2H);
3.72 (d, J = 6.3 Hz, 1H); 3.66 (dd, J = 5.6 Hz, 9.1 Hz,
1H); 3.54 (s, 3H); 3.28 (dt, J = 7.1, 11.6 Hz, 1H); 2.45
(d, J = 11.3 Hz, 1H); 2.40–1.85 (m, 5H), 1.29 (t, J =
13.2 Hz, 1H); MS (CI, m/z): 389 [(M+H)+]. Anal.
(C15H17O2SI) C, H, S, I.
8.16.23. 2b-Carbomethoxy-3b-(4-iodophenyl)-8-thiabicy-
clo[3.2.1]octane (8e). Compound 8e was prepared from
2b-carboxy-3b-(4-iodophenyl)-8-thiabicyclo[3.2.1]octane
as described for 8a. Compound 8e was obtained (93%)
as white solid: mp 167–168 ꢁC; Rf 0.28 (10% EtOAc/hex-
anes); 1H NMR: d 7.59 (d, J = 8.3 Hz, 2H); 7.00 (d, 2H);
3.96 (t, J = 4.8 Hz, 1H); 3.73 (m, 1H); 3.52 (s, 3H); 3.14
(t, J = 4.7 Hz, 1H); 3.04 (m, 1H); 2.70 (t, J = 13.0 Hz,
1H); 2.31–1.91 (m, 5H); MS (CI, m/z): 389 [(M+H)+].
Anal. (C15H17O2SI) C, H, S, I.
1
(10% EtOAc/hexanes); H NMR d 7.32 (d, J = 8.2 Hz,
1H); 7.27 (d, J = 2.1 Hz, 1H); 7.04 (dd, 1H); 3.73 (d,
J = 6.3 Hz, 1H); 3.66 (dd, J = 5.8 Hz, 8.8 Hz, 1H); 3.56
(s, 3H); 3.31 (dt, J = 7.3, 11.7 Hz, 1H); 2.43 (d,
J = 11.5 Hz, 1H); 2.40–1.88 (m, 5H), 1.29 (t,
J = 12.8 Hz, 1H); MS (CI, m/z): m/z 331, 333
[(M+H)+]. Anal. (C15H16O2SCl2) C, H, S, Cl. Com-
pound 8f was obtained (234 mg, 35%) as white solid:
mp 131–132 ꢁC; Rf 0.28 (10% EtOAc/hexanes; 1H
NMR: d 7.35–7.26 (m, 2H); 7.10 (dd, J = 1.9 Hz,
8.3 Hz, 1H); 3.98 (t, J = 4.9 Hz, 1H); 3.73 (m, 1H);
3.54 (s, 3H); 3.15 (t, J = 4.6 Hz, 1H); 3.05 (dt, J=
4.7 Hz, 11.3 Hz, 1H); 2.68 (t, J = 12.7 Hz, 1H); 2.28–
1.91 (m, 5H); MS (CI, m/z): 331, 333 [(M+H)+]. Anal.
(C15H16O2SCl2) C, H, S, Cl.
8.16.24. 2b-Carbomethoxy-3a-(2-naphthyl)-8-thiabicy-
clo[3.2.1]octane (7h). Compound 7h was prepared from
2b-carboxy-3a-(2-naphthyl)-8-thiabicyclo[3.2.1]octane
as described for 8a. Compound 7h was obtained (91%)
as white solid: mp 122–123 ꢁC; Rf 0.29 (10% EtOAc/hex-
anes); 1H NMR: d 7.82–7.74 (m, 3H), 7.64 (d, 1H), 7.47–
7.41 (m, 2H), 7.32 (dd, J = 1.7 Hz, 8.5 Hz, 1H); 3.76 (d,
J = 6.1 Hz, 1H), 3.70 (dd, J = 5.8 Hz, 9.1 Hz, 1H), 3.57–
3.46 (m, 4H), 2.65 (d, J = 11.3 Hz, 1H); 2.50–1.91 (m,
5H), 1.47 (t, J = 12.4 Hz, 1H); MS (CI, m/z): 313
[(M+H)+]. Anal. (C19H20O2S) C, H, S.
8.16.25.
2b-Carbomethoxy-3b-(2-naphthyl)-8-thiabicy-
clo[3.2.1]octane (8h). Compound 8h was prepared from
2b-carboxy-3b-(2-naphthyl)-8-thiabicyclo[3.2.1]octane
as described for 8a. Compound 8h was obtained (85%)
as white solid: mp 111–112 ꢁC; Rf 0.29 (10% EtOAc/hex-
anes); 1H NMR: d 7.79–7.74 (m, 3H), 7.68 (s, 1H), 7.48–
7.37 (m, 3H), 4.01 (m, 1H), 3.79 (m, 1H), 3.45 (s, 3H),
3.33–3.24 (m, 2H), 2.90 (t, J = 12.5 Hz, 1H); 2.33–2.04
(m, 5H); MS (CI, m/z): 313 [(M+H)+]. Anal.
(C19H20O2S) C, H, S.
8.17.2. (1R)-2b-Carbomethoxy-3a-(3,4-dichlorophenyl)-8-
thiabicyclo[3.2.1]octanes (1R-7f) and (1R)-2b-Carbome-
thoxy-3b-(3,4-dichlorophenyl)-8-thiabicyclo[3.2.1]octanes
21
(1R-8f). Compound (1R-7f): ½aꢂ
ꢀ101ꢁ (c 0.25,
D
MeOH). All other spectral data were identical to those
reported for racemic 7f. Anal. (C15H16O2SCl2) C, H, S,
Cl.

D.-P. Pham-Huu et al. / Bioorg. Med. Chem. 15 (2007) 1067–1082
1079
21
Compound (1R-8f): ½aꢂ ꢀ105ꢁ (c 0.25, MeOH). All
1
(10% EtOAc/hexanes); H NMR d 7.21 (dd, J = 2.2 Hz,
7.4 Hz, 1H); 7.04 (m, 2H); 3.72 (d, J = 6.3 Hz, 1H); 3.66
(dd, J = 5.5 Hz, 9.1 Hz, 1H); 3.56 (s, 3H); 3.30 (dt,
J = 7.1, 11.7 Hz, 1H); 2.42 (d, J = 11.6 Hz, 1H); 2.40–
1.88 (m, 5H), 1.28 (t, J = 13.2 Hz, 1H); MS (CI, m/z):
315 [(M+H)+]. Anal. (C15H16O2SFCl) C, H, S, F, Cl.
D
other spectral data were identical to those reported for
racemic 8f. Anal. (C15H16O2SCl2) C, H, S, Cl.
8.17.3. (1S)-2b-Carbomethoxy-3a-(3,4-dichlorophenyl)-8-
thiabicyclo[3.2.1]octanes (1S-7f) and (1S)-2b-Carbome-
thoxy-3b-(3,4-dichlorophenyl)-8-thiabicyclo[3.2.1]octanes
21
(1S-8f). Compound (1S-7f): ½aꢂ +95ꢁ (c 0.25, MeOH).
8.17.9. 2b-Carbomethoxy-3b-(3-chloro-4- fluorophenyl)-
8-thiabicyclo[3.2.1]octanes (8j). Compound 8j was pre-
pared from 6j as described for 8f. Compound 8j was ob-
tained (23%) as white solid: mp 130–131 ꢁC; Rf 0.28
(10% EtOAc/hexanes); 1H NMR: d 7.26 (m, 1H);
7.16–7.02 (m, 2H); 3.97 (t, J = 5.2 Hz, 1H); 3.72 (m,
1H); 3.54 (s, 3H); 3.13 (t, J = 4.6 Hz, 1H); 3.03 (dt,
J = 4.7 Hz, 11.3 Hz, 1H); 2.68 (t, J = 12.9 Hz, 1H);
2.28–1.91 (m, 5H); MS (CI, m/z): 315 [M+]. Anal.
(C15H16O2SFCl) C, H, S, F, Cl.
D
All other spectral data were identical to those reported
for racemic 7f. Anal. (C15H16O2SCl2) C, H, S, Cl.
21
(1S-8f): ½aꢂ +103ꢁ (c 0.25, MeOH). All other spectral
D
data were identical to those reported for racemic 8f.
Anal. (C15H16O2SCl2) C, H, S, Cl.
8.17.4. 2b-Carbomethoxy-3a-(3,4-difluorophenyl)-8-thia-
bicyclo[3.2.1]octanes (7g). Compound 7g was prepared
from 6g as described for 7f. Compound 7g was obtained
(43%) as white solid: mp 102–103 ꢁC; Rf 0.29 (10%
8.18. General procedure for the oxidation of 8-thiabicy-
clo[3.2.1]octan(ene)s to 8-oxo-8-thiabicyclo[3.2.1]-
octan(ene)s, 9a, 10a–f, 11a,b
1
EtOAc/hexanes); H NMR: d 7.11–6.92 (m, 3H); 3.72
(d, J = 6.3 Hz, 1H); 3.67 (dd, J = 5.6 Hz, 9.0 Hz, 1H);
3.56 (s, 3H); 3.30 (dt, J = 7.2, 11.5 Hz, 1H); 2.41 (d,
J = 11.3 Hz, 1H); 2.40–1.85 (m, 5H), 1.28 (t,
J = 13.2 Hz, 1H); MS (CI, m/z): 299 [(M+H)+]. Anal.
(C15H16O2SF2) C, H, S, F.
8.18.1.
2-Carbomethoxy-3-phenyl-8-oxo-8-thiabicyclo-
[3.2.1]oct-2-ene (9a). A mixture of compound 6a
(447 mg, 1.72 mmol), KO2 (244 mg, 3.43 mmol) in dry
acetonitrile (5 mL) was stirred at 0 ꢁC and a solution
of trimethylsilyl chloride (373 mg, 3.43 mmol) in aceto-
nitrile (15 mL) was added dropwise to the solution with
vigorous stirring under an argon atmosphere. After stir-
ring for 4 h at 0 ꢁC, the reaction was quenched by addi-
tion of 0.2 M HCl (30 mL) and then extracted with ethyl
acetate (2· 50 mL). The combined extracts were washed
with brine, dried (Na2SO4), and concentrated in vacuo.
The residue was purified by flash chromatography (2–
5% CH3OH in CHCl3) and recrystallized from hep-
tane/EtOAc (1:1) to give the product 9a as a solid
(268 mg, 56%); mp 151–152 ꢁC, Rf 0.20 (2% CH3OH
8.17.5. 2b-Carbomethoxy-3b-(3,4-difluorophenyl)-8-thia-
bicyclo[3.2.1]octanes (8g). Compound 8g was prepared
from 6g as described for 8f. Compound 8g was obtained
(19%) as white solid: mp 102–103 ꢁC; Rf 0.27 (10%
1
EtOAc/hexanes); H NMR: d 7.14–6.92 (m, 3H); 3.97
(t, J = 4.9 Hz, 1H); 3.72 (m, 1H); 3.53 (s, 3H); 3.14 (t,
J = 4.6 Hz, 1H); 3.02 (dt, J = 4.7 Hz, 11.2 Hz, 1H);
2.67 (t, J = 12.9 Hz, 1H); 2.29–1.92 (m, 5H); MS (CI,
m/z): 299 [(M+H)+]. Anal. (C15H16O2SF2) C, H, S, F.
8.17.6. 2b-Carbomethoxy-3a-(4-chloro-3- fluorophenyl)-
8-thiabicyclo[3.2.1]octanes (7i). Compound 7i was pre-
pared from 6i as described for 7f. Compound 7i was ob-
tained (38%) as white solid: mp 85–87 ꢁC; Rf 0.37 (10%
EtOAc/hexanes); 1H NMR d 7.27 (m, 1H); 6.96 (m, 2H);
3.73 (d, J = 6.0 Hz, 1H); 3.66 (dd, J = 5.4 Hz, 9.1 Hz,
1H); 3.57 (s, 3H); 3.31 (dt, J = 7.1, 11.6 Hz, 1H); 2.43
(d, J = 11.1 Hz, 1H); 2.40–1.87 (m, 5H), 1.28 (t,
J = 13.3 Hz, 1H); MS (CI, m/z): 315 [(M+H)+]. Anal.
(C15H16O2SFCl) C, H, S, F, Cl.
1
in CHCl3); H NMR: d 7.31 (m, 3H); 7.05 (m, 2H);
4.30 (d, J = 4 Hz, 1H); 3.659 (m, 1H); 3.45 (s, 3H);
3.10 (dd, 1H); 2.64–2.81 (m, 4H); 2.17 (m, 1H); MS
(CI, m/z): 277 [M+]. Anal. (C15H16O3S) C, H, S.
8.18.2.
2b-Carbomethoxy-3a-phenyl-8-oxo-8-thiabicy-
clo[3.2.1]octane (10a). Compound 10a was prepared
from 7a as described for 9a. Compound 10a was ob-
tained (59%) as white solid after flash chromatography
with CHCl3/MeOH (50:1): mp 140–142 ꢁC; Rf 0.20
(2% CH3OH in CHCl3); 1H NMR: d 7.14–7.29 (m,
5H); 3.71 (d, J = 6 Hz, 1H); 3.63 (m, 1H); 3.57 (s, 3H);
3.35 (m, 1H); 3.00 (d, J = 10.8 Hz, 1H); 2.79 (m, 2H);
2.61 (m, 1H); 2.05 (m, 2H); 1.93 (t, 1H); MS (CI, m/z):
279 [(M+H)+]. Anal. (C15H18O3S) C, H, S.
8.17.7. 2b-Carbomethoxy-3b-(4-chloro-3- fluorophenyl)-
8-thiabicyclo[3.2.1]octanes (8i). Compound 8i was pre-
pared from 6i as described for 8f. Compound 8i was ob-
tained (27%) as white solid: mp 97–98 ꢁC; Rf 0.37 (10%
EtOAc/hexanes); 1H NMR d 7.28 (dd, J = 8.2 Hz,
10.6 Hz, 1H); 7.03 (dd, J = 1.9 Hz, 10.6 Hz, 1H); 6.96
(dd, J = 1.9 Hz, 8.2 Hz, 1H); 3.98 (t, J = 4.9 Hz, 1H);
3.73 (m, 1H); 3.53 (s, 3H); 3.16 (t, J = 4.8 Hz, 1H);
3.04 (dt, J = 4.8 Hz, 12.9 Hz, 1H); 2.67 (t, J = 12.9 Hz,
1H); 2.28–1.94 (m, 5H); MS (CI, m/z): 315 [M+]. Anal.
(C15H16O2SFCl) C, H, S, F, Cl.
8.18.3. 2b-Carbomethoxy-3a-(4-bromophenyl)-8-oxo-8-
thiabicyclo[3.2.1]octane (10b). Compound 10b was pre-
pared from 7b as described for 9a. Compound 10b was
obtained (49%) as white solid: mp 122–123 ꢁC; Rf 0.23
(2% CH3OH in CHCl3); 1H NMR: d 7.41 (d, 2H);
7.02 (d, 2H); 3.69 (d, J = 6 Hz, 1H); 3.59 (m, 1H); 3.59
(s, 3H); 3.33 (m, 1H); 2.93 (d, J = 12 Hz, 1H); 2.81 (m,
2H); 2.60 (m, 1H); 2.09 (m, 2H); 1.85 (t, J = 13.5 Hz,
1H); MS (CI, m/z): 357 [M+], 359. Anal. (C15H17O3SBr)
C, H, S, F, Br.
8.17.8. 2b-Carbomethoxy-3a-(3-chloro-4- fluorophenyl)-
8-thiabicyclo[3.2.1]octanes (7j). Compound 7j was
prepared from 6j as described for 7f. Compound 7j was
obtained (34%) as white solid: mp 88–89 ꢁC; Rf 0.28

1080
D.-P. Pham-Huu et al. / Bioorg. Med. Chem. 15 (2007) 1067–1082
8.18.4. 2b-Carbomethoxy-3a-(3,4-dichlorophenyl)-8-oxo-
8-thiabicyclo[3.2.1]octane (10c). Compound 10c was pre-
pared from 7f as described for 9a. Compound 10c was
obtained as white solid (94%): mp 140–142 ꢁC; Rf 0.17
(2% CH3OH in CHCl3); 1H NMR: d 7.35 (d, 1H);
7.24 (d, 1H); 7.00 (dd, 1H); 3.70 (d, J = 6 Hz, 1H);
3.69 (m, 1H); 3.62 (s, 3H); 3.32 (m, 1H); 2.92 (d,
J = 9.6 Hz, 1H); 2.89 (m, 2H); 2.61 (m, 1H); 2.07 (m,
2H); 1.85 (t, 1H); MS (CI, m/z): 347 [(M+H)+], 349,
351. Anal. (C15H16O3SCl2) C, H, S, Cl.
2.60 (m, 1H); 2.07 (m, 2H); 1.83 (ddd, 1H); MS (CI,
m/z): 315 [(M+H)+]. Anal. (C15H16O3SF2) C, H, S, F.
8.18.10. Single-crystal X-ray analysis of 2b-carbome-
thoxy-3a-(3,4-difluorophenyl)-8-oxo-8-thiabicyclo[3.2.1]-
octane (10f). Monoclinic crystals of the purified 10f were
obtained from ethyl acetate/heptane. A representative
crystal was selected and a data set was collected at room
temperature. Pertinent crystal, data collection, and
refinement parameters: crystal size, 0.52 · 0.16 · 0.16
3
˚
mm ; cell dimensions, a = 6.4713(3) A, b = 30.4744(14)
˚
˚
A, c = 7.2817(3) A, a = 90ꢁ, b = 90.2200 (10)ꢁ, c = 90ꢁ;
formula, C15H16F2SO3; formula weight = 314.34; vol-
8.18.5. 2b-Carbomethoxy-3b-(3,4-dichlorophenyl)-8-oxo-
8-thiabicyclo[3.2.1]octane (11a). Compound 11a was
prepared from 8f as described for 9a. Compound 11a
was obtained as white solid (57%): mp 142–143 ꢁC;
3
˚
ume = 1436.01 (11) A ; calculated density = 1.454 g
cmꢀ3; space group = P2(1)/c; number of reflections =
11418 of which 3530 were considered independent
(Rint = 0.02717). Refinement method was full-matrix
least-squares on F2. The final R-indices were [I > 2r
(I)] R1 = 0.0533, wR2 = 0.1465.
1
Rf 0.14 (2% CH3OH in CHCl3); H NMR: d 7.34 (d,
1H); 7.30 (d, 1H), 7.06 (dd, 1H); 3.87 (m, 1H); 3.76
(t, 1H); 3.54 (s, 3H); 3.21 (m, 1H); 3.05 (m, 1H);
2.67–2.76 (m, 3H); 2.16 (m, 2H); 2.13 (m, 1H); MS
(CI, m/z): 347 [M+]. 349; Anal. (C15H16O3SCl2) C, H,
S, F, Cl.
8.18.11. Single-crystal X-ray analysis of (1R)-2-carbo-
methoxy-8-thiabicyclo[3.2.1]oct-2-ene-3-(10S)-campha-
nate, (1R,10S)-4a. Orthorhombic crystals of the purified
(1R,10S)-4a were obtained from methylene chloride/hex-
ane. A representative crystal was selected and a data set
was collected at room temperature. Pertinent crystal, data
collection, and refinement parameters: crystal size,
0.54 · 0.24 · 019 mm3; cell dimensions, a = 6.2331(13)
8.18.6. 2b-Carbomethoxy-3a-(3-chloro-4- fluorophenyl)-
8-oxo-8-thiabicyclo[3.2.1]octane (10d). Compound 10d
was prepared from 7j as described for 9a. Compound
10d was obtained as white solid (91%): mp 150–
1
152 ꢁC; Rf 0.27 (2% CH3OH in CHCl3); H NMR: d
7.18 (dd, 1H); 7.02 (m, 2H); 3.69 (d, J = 6 Hz, 1H);
3.63 (m, 1H); 3.59 (s, 3H); 3.33 (m, 1H); 2.91 (d,
J = 12 Hz, 1H); 2.87 (m, 2H); 2.60 (m, 1H); 2.08 (m,
2H); 1.84 (ddd, 1H); MS (CI, m/z): 331 [M+], 333. Anal.
(C15H16O3SClF) C, H, S, F, Br.
˚
˚
˚
A, b = 6.8802(14) A, c = 43.357(10) A, a = 90ꢁ, b = 90ꢁ,
c = 90ꢁ; formula, C19H24SO6; formula weight = 380.44;
3
˚
volume = 1859.4(7) A ; calculated density = 1.359
g cmꢀ3; space group = P21 21 21; number of reflec-
tions = 6936 of which 3198 were considered independent
(Rint = 0.0297). Refinement method was full-matrix
least-squares on F2. The final R-indices were [I > 2r (I)]
R1 = 0.0424, wR2 = 0.1041.
8.18.7. 2b-Carbomethoxy-3a-(4-chloro-3- fluorophenyl)-
8-oxo-8-thiabicyclo[3.2.1]octane (10e). Compound 10e
was prepared from 7i as described for 9a. Compound
10e was obtained (64%) as white solid: mp 151–152 ꢁC;
1
8.18.12. Dopamine transporter assay. The dopamine
transporter was labeled with [3H]WIN35,428
([3H]CFT, 2b-carbomethoxy-3b-(4-fluorophenyl)-N-
[3H]methyltropane, 81–84 Ci/mmol, DuPont-NEN).
The affinity of [3H]WIN35,428 for the dopamine trans-
porter was determined in experiments by incubating tis-
sue with a fixed concentration of [3H]WIN35,428 and a
range of concentrations of unlabeled WIN35,428. The
assay tubes received, in Tris–HCl buffer (50 mM, pH
7.4, at 0–4 ꢁC; NaCl 100 mM), the following constitu-
ents at a final assay concentration: WIN35,428, 0.2 mL
(1 pM–100 or 300 nM), [3H]WIN35,428 (0.3 nM); mem-
brane preparation 0.2 mL (4 mg original wet weight of
tissue/mL). The 2 h incubation (0–4 ꢁC) was initiated
by addition of membranes and terminated by rapid fil-
tration over Whatman GF/B glass fiber filters pre-
soaked in 0.1% bovine serum albumin (Sigma Chem.
Co.). The filters were washed twice with 5 mL Tris–
HCl buffer (50 mM), incubated overnight at 0–4 ꢁC in
scintillation fluor (Beckman Ready-Value, 5 mL), and
radioactivity was measured by liquid scintillation spec-
trometry (Beckman 1801). Cpm were converted to
dpm following determination of counting efficiency
(>45%) of each vial by external standardization. Total
binding was defined as [3H]WIN35,428 bound in the
Rf 0.16 (2% CH3OH in CHCl3); H NMR: d 7.30 (m,
1H); 6.91 (m, 2H); 3.69 (d, J = 6 Hz, 1H); 3.61 (m,
1H); 3.60 (s, 3H); 3.33 (m, 1H); 2.92 (d, J = 12 Hz,
1H); 2.81 (m, 2H); 2.61 (m, 1H); 2.06 (m, 2H); 1.84 (t,
J = 13.5 Hz, 1H); MS (CI, m/z): 331 [M+], 333. Anal.
(C15H16O3SClF) C, H, S, F, Cl.
8.18.8. 2b-Carbomethoxy-3b-(4-chloro-3-fluorophenyl)-8-
oxo-8-thiabicyclo[3.2.1]octane (11b). Compound 11b was
prepared from 8i as described for 9a. Compound 11b
was obtained (18%) as white solid: mp 121–122 ꢁC; Rf
0.13 (2% CH3OH in CHCl3); 1H NMR: d 7.25 (m,
1H); 7.06 (m, 2H); 3.86 (t, 1H); 3.75 (t, 1H); 3.53 (s,
3H); 3.19 (m, 1H); 3.08 (m, 1H); 2.65–2.75 (m, 3H);
2.16 (m, 2H); 2.03 (m, 1H); MS (CI, m/z): 331 [M+],
333. Anal. (C15H16O3SClF) C, H, S, F, Cl.
8.18.9. 2b-Carbomethoxy-3a-(3,4-difluorophenyl)-8-oxo-
8-thiabicyclo[3.2.1]octane (10f). Compound 10f was pre-
pared from 7g as described for 9a Compound 10f was
obtained (94%) as white solid: mp 134–136 ꢁC; Rf 0.39
(2% CH3OH in CHCl3); 1H NMR: d 6.87–7.09 (m,
3H); 3.69 (d, J = 6 Hz, 1H); 3.61 (m, 1H); 3.60 (s, 3H);
3.32 (m, 1H); 2.90 (d, J = 11.1 Hz, 1H); 2.86 (m, 2H);

D.-P. Pham-Huu et al. / Bioorg. Med. Chem. 15 (2007) 1067–1082
1081
presence of ineffective concentrations of unlabeled
References and notes
WIN35,428 (1 or 10 pM). Non-specific binding was de-
fined as [3H]WIN35,428 bound in the presence of an ex-
cess (30 lM) of (ꢀ)-cocaine. Specific binding was the
difference between the two values. Competition experi-
ments to determine the affinities of other drugs at
[3H]WIN 35,428 binding sites were conducted using pro-
cedures similar to those outlined above. Stock solutions
of water-soluble drugs were dissolved in water or buffer
and stock solutions of other drugs were made in a range
of ethanol/HCl solutions. Several of the drugs were son-
icated to promote solubility. The stock solutions were
diluted serially in the assay buffer and added (0.2 mL)
to the assay medium as described above.
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8.18.13. Serotonin transporter assay. The serotonin
transporter was assayed in caudate-putamen membranes
using conditions similar to those for the dopamine
transporter. The affinity of [3H]citalopram (spec. act.:
82 Ci/mmol, Perkin-Elmer, Boston) for the serotonin
transporter was determined in experiments by incubat-
ing tissue with a fixed concentration of [3H]citalopram
and a range of concentrations of unlabeled citalopram.
The assay tubes received, in Tris–HCl buffer (50 mM,
pH 7.4, at 0–4 ꢁC; NaCl 100 mM), the following constit-
uents at a final assay concentration: citalopram, 0.2 mL
(1 pM–100 or 300 nM), [3H]citalopram (1 nM); mem-
brane preparation 0.2 mL (4 mg original wet weight of
tissue/ml). The 2 h incubation (0–4 ꢁC) was initiated by
addition of membranes and terminated by rapid filtra-
tion over Whatman GF/B glass fiber filters pre-soaked
in 0.1% polyethyleneimine. The filters were washed twice
with 5 mL Tris–HCl buffer (50 mM), incubated over-
night at 0–4 ꢁC in scintillation fluor (Beckman Ready-
Value, 5 mL), and radioactivity was measured by liquid
scintillation spectrometry (Beckman 1801). Cpm were
converted to dpm following determination of counting
efficiency (>45%) of each vial by external standardiza-
tion. Total binding was defined as [3H]citalopram bound
in the presence of ineffective concentrations of unlabeled
citalopram (1 or 10 pM). Non-specific binding was de-
fined as [3H]citalopram bound in the presence of an ex-
cess (10 lM) of fluoxetine. Specific binding was the
difference between the two values. Competition experi-
ments to determine the affinities of other drugs at [3H]ci-
talopram binding sites were conducted using procedures
similar to those outlined above.
15. Carroll, F. I.; Lewin, A. H.; Kuhar, M. J. Med. Chem.
Res. 1998, 8, 59.
16. Meltzer, P. C.; Blundell, P.; Madras, B. K. Med. Chem.
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This work was supported by the National Institute on
Drug Abuse: NIDA 1-8825 (P.M.), NIDA 11542
(P.M.), NIDA 06303 (B.K.M.), and NIDA 09462
(B.K.M.).

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