Heteroaromatic analogs of 1-[2-(diphenylmethoxy)ethyl]- and 1-[2- [bis(4-fluorophenyl)methoxy]ethyl]-4-(3-phenylpropyl)piperazines (GBR 12935 and GBR 12909) as high-affinity dopamine reuptake inhibitors

Article abstract of DOI:10.1021/jm9606599

A new series of heteroaromatic GBR 12935 [1-[2-(diphenylmethoxy)ethyl]- 4-(3-phenylpropyl)-piperazine] (1) and GBR 12909 [1-[2-[bis(4- fluorophenyl)methoxy]ethyl]-4-(3-phenylpropyl)-piperazine] (2) analogs was synthesized and evaluated as dopamine transpo

Full text of DOI:10.1021/jm9606599

J . Med. Chem. 1997, 40, 705-716
705
Heter oa r om a tic An a logs of 1-[2-(Dip h en ylm eth oxy)eth yl]- a n d
1-[2-[Bis(4-flu or op h en yl)m eth oxy]eth yl]-4-(3-p h en ylp r op yl)p ip er a zin es (GBR
12935 a n d GBR 12909) a s High -Affin ity Dop a m in e Reu p ta k e In h ibitor s
Dorota Matecka, David Lewis, Richard B. Rothman,† Christina M. Dersch,† Francis H. E. Wojnicki,
J ohn R. Glowa, A. Courtney DeVries,‡ Agu Pert,‡ and Kenner C. Rice*
Laboratory of Medicinal Chemistry, Building 8, Room B1-23, National Institute of Diabetes and Digestive and Kidney
Diseases, National Institutes of Health, 9000 Rockville Pike, Bethesda, Maryland 20892, Clinical Psychopharmacology Section,
IRP, National Institute on Drug Abuse, National Institutes of Health, Baltimore, Maryland 21224, and Biological Psychiatry
Branch, National Institute of Mental Health, National Institutes of Health, 9000 Rockville Pike, Bethesda, Maryland 20892
Received September 20, 1996X
A new series of heteroaromatic GBR 12935 [1-[2-(diphenylmethoxy)ethyl]-4-(3-phenylpropyl)-
piperazine] (1) and GBR 12909 [1-[2-[bis(4-fluorophenyl)methoxy]ethyl]-4-(3-phenylpropyl)-
piperazine] (2) analogs was synthesized and evaluated as dopamine transporter (DAT) ligands.
Analogs 5-16, in which the benzene ring in the phenylpropyl side chain of the GBR molecule
had been replaced with a thiophene, furan, or pyridine ring, exhibited high affinity and
selectivity for the DAT vs serotonin transporter (SERT) and stimulated locomotor activity in
rats in a manner similar to the parent compound 2. In cocaine and food self-administration
studies in rhesus monkeys, both thiophene-containing (6 and 8) and pyridine-containing (14
and 16) derivatives displayed potency comparable to 2 in decreasing the cocaine-maintained
responding at the doses tested (0.3, 1.7, and 3 mg/kg). However, these compounds did not
produce the degree of separation between food- and cocaine-maintained responding that was
seen with 2. Among the bicyclic fused-ring congeners 17-38, the indole-containing analog of
2, 22, showed the greatest affinity for binding to the DAT, with IC50 ) 0.7 nM, whereas the
corresponding indole-containing derivative of 1, 21, displayed the highest selectivity (over 600-
fold) at this site vs the SERT site.
In tr od u ction
tutes one approach for the treatment of cocaine addic-
tion.10,12,13 The disubstituted piperazines14 including
GBR 12935 [1-[2-(diphenylmethoxy)ethyl]-4-(3-phenyl-
propyl)piperazine] (1) and GBR 12909 [1-[2-[bis(4-
fluorophenyl)methoxy]ethyl]-4-(3-phenylpropyl)pipera-
zine] (2) were among the first agents with high affinity
and selectivity at the DA reuptake site.15,16 Compound
2 exhibits a neurochemical and behavioral profile that
renders it a promising candidate as a cocaine abuse
therapeutic agent. It is a slowly dissociating DAT
ligand with slow onset, long duration of action and lower
in vivo efficacy as a motor stimulant in rats compared
to cocaine.17 Compound 2 was shown to attenuate
extracellular DA levels elevated by cocaine in rat
striatum and nucleus accumbens in microdialysis ex-
periments.18,19 Recent experiments in cocaine and food
self-administration studies revealed that 2 decreases the
cocaine-maintained responding without decreasing nor-
mal food-maintained responding in rhesus monkeys.20,21
It has also been shown that humans administered an
oral dose of 2 report a sedative rather than a stimulant
effect.22 Because of these properties, we selected 1, 2,
and their double-bond-containing derivatives GBR 12783
[1-[2-(diphenylmethoxy)ethyl]-4-(3-phenyl-2-propenyl)-
piperazine]23 (3) and GBR 13069 [1-[2-[bis(4-fluorophe-
n yl)m et h oxy]et h yl]-4-(3-ph en yl-2-pr open yl)piper a -
zine]24 (4), respectively, as templates to develop novel
ligands for the DAT as potential agents for the treat-
ment of cocaine abuse.
Cocaine is one of the most abused drugs known. Its
abuse continues to have a devastating effect on public
health worldwide and plays a major role in the rapid
spread of acquired immune deficiency syndrome and
drug-resistant tuberculosis,1 which results largely from
needle sharing, sex for drugs, a common practice of
cocaine base (crack) smoking, and related activities in
shooting galleries, crack houses, and similar establish-
ments.1,2 Consequently, the development of safe and
effective medications for the treatment of cocaine ad-
diction is of national and worldwide interest. A number
of multidisciplinary studies are currently attempting to
elucidate the cocaine mechanism of action in the brain
and its behavioral consequences.3-6 It has been hy-
pothesized that a primary modulator of the reinforcing
effects of cocaine is the mesolimbic dopamine system.4,7,8
The specific interaction of cocaine with its receptor
[dopamine (DA) transporter (DAT) proteins] results in
blocking reuptake of DA into dopaminergic neurons and
increasing dopaminergic neurotransmission.8 The el-
evated levels of dopamine in the synapse interact with
dopamine receptors on the postsynaptic neurons, which
results in a broad spectrum of reinforcing and stimulat-
ing effects.9 An obvious target for research aimed at
the treatment of cocaine abuse is the development of
agents which are potent and selective ligands for the
DAT and which may reduce the effects of cocaine.10,11
The development of high-affinity, slowly dissociating,
low-intrinsic activity cocaine receptor agonists consti-
In earlier studies it was shown that a significant
increase in affinity and selectivity at the DAT site could
be attained by modifying the central piperazine ring of
the GBR molecule.25-28 Additionally, the diamine-
modified ligands displayed an in vivo pharmacological
† National Institute on Drug Abuse.
‡ National Institute of Mental Health.
X Abstract published in Advance ACS Abstracts, J anuary 1, 1997.
S0022-2623(96)00659-0 This article not subject to U.S. Copyright. Published 1997 by the American Chemical Society

706 J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 5
Matecka et al.
Ch a r t 1
Portions of this work have been reported in preliminary
communications.33,34
Ch em istr y
The monosubstituted piperazines 1-[2-(diphenyl-
methoxy)ethyl]piperazine or 1-[2-[bis(4-fluorophenyl)-
methoxy]ethyl]piperazine were synthesized as previ-
ously described14 by a two-step sequence: reaction of
commercially available suitably substituted benzhydrol
with 2-chloroethanol in the presence of sulfuric acid and
subsequent reaction of the resulting alkyl chloride with
excess piperazine (Scheme 1). These monosubstituted
amines were then either coupled with the appropriate
heteroaromatic carboxylic acid using dicyclohexylcar-
bodiimide (DCC) (method A) or treated with a suitable
acid chloride under Schotten-Baumann conditions
(method E). The resulting intermediate amides were
subsequently reduced with aluminum hydride35 (method
B) to yield the target amines 4, 7, 8, 11, 12, 14-22, and
25-38. Hydrogenation of 7, 8, 11, and 12 using 10%
Pd/C in methanol (method C) afforded saturated GBR
analogs 5, 6, 9, and 10, respectively. Compound 13 was
synthesized by K2CO3-catalyzed coupling of 1-[2-(diphe-
nylmethoxy)ethyl]piperazine with 3-(3-chloropropyl)-
pyridine in DMF in the presence of KI (method D).
Compounds 23 and 24 were obtained from 2-(chlorom-
ethyl)benzimidazole and 1-[2-(diphenylmethoxy)ethyl]-
piperazine or 1-[2-[bis(4-fluorophenyl)methoxy]ethyl]-
piperazine, respectively, following the same procedure
(method D). Benzo[b]thiophene-2-carboxylic acid, which
was used for the synthesis of 17 and 18, was obtained
by deprotonation of benzo[b]thiophene with n-BuLi in
tetrahydrofuran followed by the addition of excess dry
ice (method F). All final amines were purified and
crystallized as salts with the indicated organic or
inorganic acids (Tables 1 and 2).
Resu lts a n d Discu ssion
The binding data indicate that replacement of the
phenylpropyl side chain in 1-4 with a variety of
heteroaromatic-containing moieties resulted in the cre-
ation of a series of potent inhibitors of dopamine
reuptake with high affinity and selectivity at the DAT
(Tables 3 and 4). Among the bioisosteric analogs 5-16
(Table 3), the furan-containing derivative of 4, pipera-
zine 12, exhibited the highest affinity for the DAT (IC50
) 1.8 nM), while the furan-containing analog of 3,
compound 11, was the most selective ligand (367- and
281-fold more potent for the binding to the DAT vs
SERT and inhibition of DA vs 5-HT reuptake, respec-
tively). While the pyridine-containing derivatives 13-
16 displayed slightly reduced potency for binding to the
DAT and inhibition of DA reuptake with respect to the
furan and thiophene analogs, they retained the selectiv-
ity at the DA vs 5-HT reuptake site. Generally, the bis-
(4-fluoro)-substituted compounds containing an unsat-
urated side chain (i.e., lead compound 4 and its
thiophene-, furan-, or pyridine-containing analogs 8, 12,
and 16, respectively) exhibited slightly higher affinity
at the DAT than their desfluoro and saturated analogs
in all four subgroups of ligands: 1-4, 5-8, 9-12, and
13-16, respectively. However, this relationship was not
the same with respect to their ability to inhibit DA
reuptake. Interestingly, compound 4, which exhibited
the highest affinity for binding to the DAT among all
profile different from that of 1 and 2.25,28 While it has
been previously established that the (diphenylmethoxy)-
ethyl moiety is a very important pharmacophore for
effective binding to the DAT and possibly to the [3H]-
cocaine-binding site, very few modifications to the
phenylpropyl portion of the GBR structure have been
reported.29,30 Replacement of a benzene ring with a
heteroaromatic isostere has been a very useful and well-
documented modification in medicinal chemistry. This
has been applied successfully in the context of nonopioid
analgesics, among other studies.31,32 We have employed
this bioisosteric concept to a new series of GBR-related
ligands, in which the benzene ring in the phenylpropyl
chain was replaced with either thiophene, furan, or
pyridine (Chart 1, compounds 5-16). Substitution of
the phenylpropyl chain of the GBR molecule with
aromatic and heteroaromatic, five- and six-membered
fused-ring systems afforded a series of structurally
restricted analogs (Chart 2, compounds 17-38). Herein,
we report the binding affinity of these ligands to the
DA and serotonin (5-HT) transporters (SERT) and their
ability to inhibit the reuptake of DA and 5-HT. Pre-
liminary locomotor activity studies in rats along with
cocaine and food self-administration studies in monkeys
were used to evaluate heteroaromatic analogs of 1 and
2 as potential agents for the treatment of cocaine abuse.

High-Affinity Dopamine Reuptake Inhibitors
J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 5 707
Ch a r t 2
Sch em e 1a
a
(A) Appropriate heteroaromatic carboxylic acid, DCC, CH2Cl2/THF; (B) aluminum hydride, THF; (C) H2, 10% Pd/C, MeOH; (D) 3-(3-
chloropropyl)pyridine or 2-(chloromethyl)benzimidazole, K2CO3, KI, DMF; (E) 1- or 2-naphthoyl chloride, aq NaHCO3, CHCl3.
the ligands in Table 3, also displayed a high ratio (12.2-
fold) of the IC50 for inhibition of dopamine reuptake
versus binding to the DAT. The thiophene and furan
derivatives 8 and 12, respectively, also exhibited an
improved ratio of 5.9 and 4, respectively (Table 3), in
comparison to the parent 2 with a ratio of 2. However,
the biological significance of relatively small differences
among the ratios of compounds is not clear.
It is interesting to note that in the second group of
fused-rings ligands, the ratio was always higher for the
bis(4-fluoro)-substituted compounds than for their des-
fluoro analogs (Table 4). This ratio was significantly
improved for several new analogs, i.e., the 2-indolyl,
1-naphthyl, or 2-benzo[b]thienyl derivative 22, 36, or
18, respectively. Our interest in the synthesis of
compound 18 was spurred by recent studies,36 in which
a series of piperazines with structural and biochemical
similarities to the GBR- and BTCP-type [N-[1-(2-benzo-
[b]thienyl)cyclohexyl]piperidine] of DAT ligands was
synthesized and tested at the DA transport site. Sur-
prisingly, 1-[1-(2-benzo[b]thienyl)cyclohexyl]-4-[1-[2-
(diphenylmethoxy)ethyl]piperazine, which is a hybrid
between BTCP and 3 (Chart 3), exhibited a relatively
low, micromolar affinity for the binding to the DAT
labeled with [3H]BTCP. We synthesized new GBR and
BTCP hybrids, compounds 17 and 18, which lack the
bulky spirocyclohexyl residue of BTCP. The preliminary
molecular modeling experiments performed with the
Quanta program provided a good structural fit of BTCP,
4, and 18 (data not shown). The results from in vitro
studies, using [125I]RTI-55 as an agent labeling the DAT,
confirmed this close fit, with 18, the benzothiophene
analog of 2, displaying 4.1 nM affinity at this site and

708 J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 5
Matecka et al.
Ta ble 1. Reaction Conditions of the Intermediate Amide Reduction (Method B) and Physical Properties of the Final Amines
excess reducing
agent (equiv)
reduction
temp (°C)
target amine
reduction time
salta
mp (°C)
crystn solvent
MeOH
MeOH
2-PrOH
yieldb (%)
7
8
2
2
10 min
10 min
rt
rt
2 maleate
2 maleate
2 HCl
179-180
188-189
204-205
dec
80
83
11
12
2
2
10 min
10 min
rt
rt
2 maleate
2 maleate
2 HCl
176-177
168-170
189-190
dec
MeOH
MeOH
2-PrOH
65
71
13c
14d
15
16
17
18
19
20
21
2 maleate
2 maleate
2 maleate
2 maleate
2 maleate
2 maleate
2 maleate
2 maleate
2 maleate
2 maleate
2.5 oxalate
2 maleate
2 maleate
148-149
149-150
157-158
179-180
199-200
193-194
192-193
186-188
192-194
191.5-192
178-179
170-171
183-184
dec
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
2-PrOH:MeOH (4:1)
MeOH
64
76
54
52
68
74
82
79
65
84
80
87
15e
2
2
1.3
5
3
5
3
5
2
10 min
10 min
1 h
30 min
5 min
30 min
10 min
30 min
10 min
rt
rt
0
rt
rt
rt
rt
rt
rt
22
23c
24c
25
1.5
15 min
-5-0
26
27
28
29
30
31
32
33
34
35
36
37
38
3
5
2
5
1.5
4
4
5
3
5
3
5
3
10 min
30 min
5 min
1 h
15 min
30 min
10 min
50 min
12 h
0
2 maleate
2 maleate
2 maleate
2 maleate
2 maleate
3 maleate
3 maleate
2 maleate
2 maleate
2 maleate
2 maleate
2 maleate
2 maleate
180-180.5
170-172
190.5-191
198-200
190-191
196-198
193-194
203-204
194-196
170-171
171-172
181-182
180-182
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
25e
18e
55
43
83
62
65
76
87
66
73
65
54
rt
rt
rt
rt
rt
rt
rt
rt
rt
rt
rt
rt
50 min
12 h
1 h
12 h
a
The CI mass spectra of all the final amines and precursor amides contained predicted (M + 1) peaks. All compounds gave CHN
analysis within (0.4 of calculated value. Total yield of two steps. c Synthesized according to method D. Compound 14 was synthesized
by DCC condensation of starting piperazine and hydrogenated 3-pyridineacrylic acid (Table 2) followed by the reduction of the resulting
amide. e Due to very low yield of amide reduction.
b
d
Ta ble 2. Hydrogenation Conditions (Method C) and Physical Properties of the Final Compounds
hydrogen
pressure
reaction
time
target compd
reactn solvent
salta
crystn solvent
MeOH
MeOH
MeOH:2-PrOH (1:3)
MeOH
MeOH
2-PrOH
MeOH
mp (°C)
yield (%)
5
6
MeOH
MeOH
50 psi
45 psi
12 h
36 h
2 maleate
2 maleate
2 HCl
2 maleate
2 maleate
2 HCl
178-180
183-185
94
96
214-215 dec
174-175
9
10
MeOH
MeOH
atm
atm
30 min
40 min
82
97
172-173
207-208 dec
147-150
3-(3-pyridyl)propionic acid
MeOH/THF
45 psi
24 h
97
a
All compounds gave CHN analysis within (0.4 of calculated value.
17, the derivative of 1, showing 184-fold selectivity at
the DAT vs 5-HT site.
potent and the desfluoro congeners more selective for
the DAT vs SERT, mainly because of their significantly
lower affinity at the 5-HT transport site. Furthermore,
the combination of fused rings with only one heteroatom
placed in the 2-position of the five-membered ring
(compounds 17-22) appeared to be more favorable in
terms of selectivity of the new ligands at the DA
transport site. The incorporation of an additional
nitrogen atom in the five-membered ring (benzimidazole
derivatives 23 and 24, respectively) resulted in the
decrease of both affinity and selectivity at the DA
transport site (compare 23 and 24 vs 21 and 22,
respectively). The increase of the number of atoms
between the piperazine nitrogen and heteroaromatic
ring (i.e., benzimidazopropyl analogs 31 and 32 vs their
benzimidazomethyl congeners 23 and 24, respectively)
further decreased the selectivity of these ligands at the
DA uptake site, again, mainly because of their improved
In general, compounds containing a five-membered
aromatic ring fused with the benzene ring (17-24) were
designed to make 1 and 2 more rigid and to retain the
favorable three-atom linkage between the nitrogen atom
of piperazine and the phenyl ring in the phenylpropyl
side chain of the typical GBR structure. Most of the
five-membered aromatic ring-containing compounds
exhibited the highest selectivity for both DAT (vs SERT)
binding and DA (vs 5-HT) reuptake inhibition among
all congeners belonging to the series of fused-ring GBR-
related ligands (Table 4). The indole derivative 22, an
analog of 2, was the most potent ligand for the binding
to the DAT with IC50 ) 0.7 nM, whereas 21, the indole
derivative of 1, displayed the highest DAT/SERT bind-
ing selectivity (over 600-fold) at this site. As seen in
previous GBR series, the bis(4-fluoro) analogs were more

High-Affinity Dopamine Reuptake Inhibitors
J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 5 709
Ta ble 3. Binding Affinities at the DA and 5-HT Transporters Labeled with [125I]RTI-55 and σ Sites Labeled with
[3H]-(+)-Pentazocine and Affinities for DA and 5-HT Reuptake Inhibition of Heteroaromatic GBR Analogs 5-16 (IC50 ( SD, nM)a
ratios
binding
reuptake
binding
SERT/DA
reuptake
5-HT/DA
reuptake/
binding (DA)
ligand
DAT
SERT
[3H]DA
[3H]-5-HT
σ binding
17 ( 2
1
3.7 ( 0.3
3.7 ( 0.4
623 ( 13
3.7 ( 0.4
7.3 ( 0.2
298 ( 29
168
34
78
10
1
2
(GBR 12935)
2
(GBR 12909)
126 ( 5
73 ( 2
43 ( 1
4
5
6
7
8
9
10
11
12
13
14
15
16
0.9 ( 0.1
5.2 ( 0.3
3.3 ( 0.1
6.4 ( 0.3
2.2 ( 0.1
6.5 ( 0.2
5.9 ( 0.3
5.0 ( 0.3
1.8 ( 0.3
78 ( 4
135 ( 7
842 ( 30
105 ( 2
11 ( 0.6
9.7 ( 0.2
6.1 ( 0.7
10 ( 0.7
13 ( 1.4
8.5 ( 0.5
7.9 ( 0.5
9.6 ( 0.3
7.2 ( 0.4
70 ( 6
576 ( 32
1990 ( 58
335 ( 17
51 ( 1
n/d
38 ( 1
n/d
41 ( 0.9
n/d
62 ( 2
n/d
43 ( 3
n/d
79 ( 2
n/d
158
162
32
184
40
234
35
367
62
51
205
55
200
29
300
52
281
61
12.2
1.9
1.8
1.6
5.9
1.3
1.3
1.9
4
0.9
1.3
1.5
1.1
1170 ( 31
88 ( 2
2020 ( 141
374 ( 17
1520 ( 47
204 ( 7
1840 ( 59
109 ( 4
2420 ( 65
2800 ( 139
2670 ( 66
334 ( 12
2550 ( 87
412 ( 9
2700 ( 136
442 ( 23
3700 ( 148
6520 ( 293
3620 ( 179
666 ( 21
31
175
61
53
321
57
16 ( 0.2
44 ( 3
20 ( 0.8
64 ( 2
13.6 ( 0.2
14.5 ( 1.9
59 ( 3
25
46
a
The IC50 values of the test agents were determined in the above assays as described in Biological Methods.
Ch a r t 3
affinity at the serotonin uptake site. Interestingly,
were the most selective compounds for both binding to
the DAT and inhibition of DA reuptake. In contrast,
their isomers, 35 and 36, with naphthalene substituted
in the 1-position lost selectivity at this site. In fact, they
were more potent in inhibition of 5-HT than DA re-
uptake. However, the addition of another carbon atom
between the piperazine nitrogen atom and the phenyl
ring of the 1-naphthalene moiety resulted in at least a
10-fold improvement in the affinity of 1-naphthalene
GBR analogs for the inhibition of DA reuptake (compare
35 and 36 vs 37 and 38, respectively). In this small
series of naphthalene analogs, compound 36 was espe-
cially interesting with its much higher affinity for the
binding to the DAT than for the inhibition of DA
reuptake (ratio of reuptake to binding ) 10.1, Table 4).
Generally, this series of conformationally restricted
GBR-type ligands may serve as excellent templates for
computer-assisted molecular modeling studies in the
GBR series, which we have already initiated.
compounds containing a quinoline ring, which was
attached to the rest of the molecule in different positions
such as 2, 3, and 6 (25-30), displayed a broad range of
affinities for binding to the DAT. It is intriguing that
whereas the 2-indole congener 22 was one of the most
selective ligands at the DA site, its 2-quinoline analog
26 exhibited a comparably high affinity at both DA and
5-HT sites. Since the only structural difference between
22 and 26 was the additional methine atom in the ring
of quinoline-containing analog 26, the difference in the
affinity at both sites of these two ligands may be
explained by either the different electronic character of
their nitrogen atoms or the presence of a hydrogen-
bonding donor in analog 22.
The ability for hydrogen bonding in the drug-receptor
interaction may also explain the difference in binding
properties of all the quinoline analogs (25-30), in which
the quinoline ring is bound in different positions i.e., 2,
3, or 6. In the series of naphthalene analogs 33-38,
the two 2-naphthalenemethyl derivatives 33 and 34
As noted above, the ratio of DA reuptake inhibition
to binding inhibition was moderately high for several

710 J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 5
Matecka et al.
Ta ble 4. Binding Affinities at the DA and 5-HT Transporters Labeled with [125I]RTI-55 and DA and 5-HT Reuptake Inhibition of
Fused-Ring GBR Analogs 17-38 (IC50 ( SD, nM)a
ratios
binding
reuptake
binding
5-HT/DA
reuptake
5-HT/DA
reuptake/
binding (DA)
ligand
DAT
SERT
[3H]DA
[3H]-5-HT
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
18 ( 1
4.1 ( 1.1
17 ( 0.5
6.4 ( 0.2
1.1 ( 0.1
0.7 ( 0.1
46 ( 1
15 ( 0.2
199 ( 5
56 ( 1
72 ( 2
16 ( 3
190 ( 6
62 ( 2
23 ( 0.5
2.5 ( 0.1
43 ( 2
8.0 ( 0.3
114 ( 5
31 ( 1
92 ( 13
7.8 ( 0.2
2420 ( 109
495 ( 18
1890 ( 48
286 ( 10
668 ( 39
119 ( 5
19 ( 1
34 ( 2
22 ( 0.7
18.6 ( 0.6
8.8 ( 0.7
13 ( 0.2
37 ( 2
20 ( 0.8
192 ( 8
106 ( 12
111 ( 3
74 ( 3
140 ( 4
73 ( 3
17 ( 0.7
8.1 ( 0.3
32 ( 0.6
30 ( 1
406 ( 11
312 ( 19
42 ( 0.9
25 ( 0.8
3520 ( 289
1230 ( 40
3040 ( 213
767 ( 27
2120 ( 166
506 ( 23
4076 ( 221
797 ( 43
4120 ( 212
339 ( 31
3040 ( 252
851 ( 36
1640 ( 58
1040 ( 46
627 ( 12
74 ( 4
131
121
110
45
619
163
41
17
10
<1
16
30
4
184
36
136
41
241
39
110
40
21
3
27
12
12
14
39
9
1.1
8.3
1.3
2.9
8
18.6
0.8
1.3
1
1.9
1.5
4.6
0.7
1.2
0.7
3.2
0.7
3.8
3.6
10.1
0.5
3.2
1884 ( 72
256 ( 7
1990 ( 5
51 ( 16
1160 ( 27
485 ( 16
845 ( 15
551 ( 21
309 ( 9
9
13
11
21
39
3
8
5
6
28 ( 2
903 ( 47
312 ( 15
336 ( 22
243 ( 6
926 ( 33
588 ( 39
83 ( 5
257 ( 12
578 ( 17
119 ( 4
30
20
<1
<1
14
5
462 ( 17
46 ( 1
a
The IC50 values of the test agents were determined in the above assays as described in Biological Methods.
Ta ble 5. IC50 Values of Selected Compounds for Inhibition of
[3H]DA Uptake and [125I]RTI-55 Binding in Nonstandard
Conditions (IC50 ( SD, nM)a
standard
nonstandard
[3H]DA
uptake
[
125I]RTI-55 ratio uptake/ ratio uptake/
binding
congener
bindingb
bindingc
2
4
19
20
21
22
1.75 ( 0.14 2.63 ( 0.14
1.82 ( 0.12 2.07 ( 0.12
2.0
12.2
1.3
2.9
8.0
0.66
0.88
0.71
0.69
1.19
0.63
31.0 ( 1.1
12.3 ( 0.3
43.6 ( 1.1
17.8 ( 0.4
2.62 ( 0.04 2.19 ( 0.21
1.86 ( 0.05 2.94 ( 0.27
18.6
a
Each value is the mean ( SD of three independent experi-
ments. b Standard binding conditions have been described.38 Briefly,
assays were conducted using brain membranes (not synaptosomes)
and 55.2 mM sodium phosphate buffer, pH 7.4, for 18-24 h at 4
°C. c Nonstandard binding conditions have been described,37 and
details are included in the Experimental Section.
congeners in this new series of GBR ligands. To
determine the influence of assay procedures on the
magnitude of this ratio, the IC50 values of selected
agents for inhibition of [3H]DA uptake and for inhibition
of [125I]RTI-55 were measured under identical conditions
at the same time. Thus, as described in an earlier
F igu r e 1. Effects of several heteroaromatic analogs of 2 on
horizontal locomotor activity in rats following ip injection (50
mg/kg). Repeated measure analysis of variance revealed a
significant drug-time interaction (F ) 2.2, p < 0.5). Post hoc
comparisons indicated that locomotor activity was increased
significantly relative to the vehicle only after treatment with
compounds 2, 6, and 14 (p < 0.5); n ) 6 in each group.
publication,37 125I]RTI-55 binding was conducted under
[
“uptake” conditions. The data (Table 5) showed that
conducting the binding assay under “uptake” conditions
eliminated the high uptake/binding ratios which were
apparent under “standard” assay38 conditions. These
data suggest that investigators who utilize the uptake/
binding ratio to detect a putative cocaine antagonist
should conduct both assays using exactly the same assay
conditions.
As a continuation of our previous interest28 in the
affinity of DA reuptake inhibitors for binding to σ
receptors, several new ligands, all analogs of 2 and 4
(i.e., 6, 8, 10, 12, 14, and 16), were tested at the σ-1 site
(Table 3). All of these compounds retained an affinity
for displacement of [3H]-(+)-pentazocine39 at this site
(IC50 ) 38-79 nM) comparable to the parent compounds
(IC50 ) 43 and 51 nM for 2 and 4, respectively). These
derivatives may constitute a novel group of heteroaro-
matic congeners in the piperazine class of σ ligands.
Preliminary experiments in vivo revealed that the
new analogs of 2 containing the simple heteroaromatic
rings thiophene, furan, and pyridine (i.e., 6, 8, 10, 12,
14, and 16, respectively) stimulated the locomotor
activity in rats following ip injection. This stimulating
effect of a dose of 50 mg/kg for each analog is shown in
Figures 1 and 2. However, the effect of the saturated
compounds 6, 10, and 14 seemed to be slightly attenu-
ated in comparison with 2 (Figure 1). Nonetheless,
these were the first modified GBR derivatives displaying
the behavioral profile similar to the parent compounds.
On the basis of these results, the thiophene and pyridine
derivatives 6, 8, 14, and 16 were further tested in
cocaine and food self-administration studies in rhesus

High-Affinity Dopamine Reuptake Inhibitors
J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 5 711
F igu r e 2. Effects of heteroaromatic unsaturated congeners,
analogs of 4, on horizontal locomotor activity in rats following
ip injection (50 mg/kg). Repeated measure analysis of variance
revealed a significant drug-time interaction (F ) 2.4, p < 0.5).
Post hoc comparisons indicated that locomotor activity was
increased significantly relative to the vehicle only after treat-
ment with compounds 4, 12, and 16 (p < 0.5); n ) 6 in each
group.
F igu r e 4. Effects of cumulative doses of 6 and 8 on rates of
responding (top panel) and number of food and cocaine
deliveries (bottom panel) maintained under a multiple FR food
(0), FR cocaine (O, 10 µg/kg/injection) schedule. Drug effects
are expressed as the mean (n ) 4 for each compound)
percentage of individual control as a function of the dose (mg/
kg), with variability expressed as the standard error of the
mean (SEM). Control variability is expressed as a coefficient
of variation ((SD, as a percentage of control).
differed for each. At 1.0 mg/kg 2 had no effect on food-
maintained responding but decreased cocaine-main-
tained responding to 16% of the control. At the highest
dose tested (3.0 mg/kg) 2 decreased food-maintained
responding to 57% of control, and cocaine-maintained
responding to 4% of control. The bottom panel of Figure
3 shows a similar effect of 2 on food and cocaine intake.
At 1.0 mg/kg 2 had no effect on food intake but
decreased cocaine intake to 47% of control. At the
highest dose (3.0 mg/kg) tested 2 decreased food intake
to 70% of control and cocaine intake to 12% of control.
The effects of 6 and 8 on the rates of responding are
shown in the top panel of Figure 4. In general, 6
decreased both food- and cocaine-maintained responding
in a dose-dependent manner, although the cocaine-
maintained responding was not affected by 1.0 mg/kg.
Compound 8 decreased both response rate measures in
a dose-dependent manner, although the lowest dose (0.3
mg/kg) increased the rates of food-maintained respond-
ing. The effects of 6 and 8 on the average number of
food and cocaine deliveries (Figure 4, bottom panel) were
similar to those seen in the response rate data; both
compounds decreased food and cocaine intake in a dose-
related manner.
F igu r e 3. Effects of single doses of 2 on rates of responding
(top panel)20,21 and number of food and cocaine deliveries
(bottom panel) maintained under a multiple fixed ratio (FR)
food (0), FR cocaine (O, 10 µg/kg/injection) schedule. Drug
effects are expressed as the mean (n ) 8) percentage of
individual control as a function of the dose (mg/kg) of GBR
12909, with variability expressed as the standard error of the
mean (SEM). Control variability is expressed as a coefficient
of variation ((SD, as a percentage of control).
monkeys and the results compared to the parent drug
2. Furan derivatives 10 and 12, however, were elimi-
nated from these studies due to the adverse side effects
they caused in monkeys.
The effects of 2 on the average rates of responding
are shown in the top panel of Figure 3. In general, 2
decreased both the food and cocaine response rates in a
dose-dependent manner, but the slopes of the curves
The effects 14 and 16 on the rates of responding are
shown in the top panel of Figure 5. Compound 14
slightly increased food-maintained responding at a dose
of 1 mg/kg and decreased both response rate measures
at higher doses in a dose-dependent manner. However,
cocaine-maintained responding was decreased to a
larger degree than food-maintained responding. Con-
gener 16 decreased both food and cocaine rates of

712 J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 5
Matecka et al.
pounds for binding to the DAT. Some of these ligands
were more selective than the lead compounds at this
site vs the 5-HT reuptake site. However, several
congeners from quinoline- and naphthalene-containing
series were more potent for binding to the SERT than
DAT or more potent at inhibiting 5-HT rather than DA
reuptake. The series of conformationally restricted ring-
fused analogs provides an interesting set of ligands for
molecular modeling studies in order to further establish
the electronic and sterical requirements for the high
affinity and selectivity of GBR-related congeners at the
DA reuptake site. Compounds substituted with simple
heteroaromatics such as thiophene, furan, or pyridine
stimulated locomotor activity in rats following ip injec-
tion. These compounds (thiophene and pyridine deriva-
tives) were also potent but less selective in decreasing
cocaine-maintained versus food-maintained responding
in monkeys. Overall, these results suggest that the
development of a partial agonist, or a series of partial
agonists, GBR-type of compounds with high affinity and
selectivity at the DAT may offer a suitable approach
toward the development of potential medications for the
treatment of cocaine abuse and addiction. Further in
vivo experiments are being conducted to study the
effects of novel ring-fused analogs of 1 and 2 on both
locomotor activity in rats and cocaine and food self-
administration in monkeys.
F igu r e 5. Effects of cumulative doses of 14 and 16 on rates
of responding (top panel) and number of food and cocaine
deliveries (bottom panel) maintained under a multiple FR food
(0), FR cocaine (O, 10 µg/kg/injection) schedule. Drug effects
are expressed as the mean (n ) 4) percentage of individual
control as a function of the dose (mg/kg), with variability
expressed as the standard error of the mean (SEM). Control
variability is expressed as a coefficient of variation ((SD, as
a percentage of control).
Exp er im en ta l Section
1. Ch em ica l Meth od s. Melting points were determined
on a Thomas-Hoover capillary apparatus and are uncorrected.
Elemental analyses were performed by Atlantic Microlabs,
Atlanta, GA. Chemical ionization mass spectra (CIMS) were
obtained using a Finnigan 1015 mass spectrometer. 1H NMR
spectra of the free bases were recorded in CDCl3 using a Varian
XL-300 spectrometer. Chemical shifts are expressed in parts
per million (ppm) on the δ scale relative to a TMS internal
standard. Thin layer chromatography (TLC) was performed
using 250 µm Analtech GHLF silica gel plates. The TLC
systems employed are as follows: CHCl3:MeOH ) 19:1, CHCl3:
MeOH ) 9:1, and CHCl3:MeOH:NH4OH ) 90:9:1. No attempt
was made to optimize the yields reported.
Met h od A: Gen er a l P r oced u r e of DCC-Ca t a lyzed
Con d en sa tion . To a stirred solution (or suspension) of the
appropriate heteroaromatic acid (2-2.5 equiv) in CH2Cl2 or
in a mixture of CH2Cl2 and THF was added a solution of DCC
(2-2.5 equiv) in CH2Cl2. After 30 min of stirring at room
temperature, a solution of 1-[2-(diphenylmethoxy)ethyl]pip-
erazine or 1-[2-[bis(4-fluorophenyl)methoxy]ethyl]piperazine (1
equiv) in CH2Cl2 was first added followed by pyridine (a few
drops), and the mixture was stirred until the reaction was
complete (TLC, typically 24 h). The mixture was filtered
through a pad of Celite, the solvent removed at reduced
pressure, and the reaction mixture worked up according to one
of the following procedures: (1) The crude product was
chromatographed (silica gel, flash column). Dicyclohexylurea,
a side product of the reaction, was eluted with ethyl acetate,
and then the eluent was switched to a mixture of CH2Cl2 and
MeOH (100:1) yielding the desired amide as an oily and
colorless material. (2). The crude product was dissolved in
chloroform, and this solution was treated (three times) with
10% aqueous citric acid. The layers were separated, and the
acidic phase was basified with 15% aqueous NaOH and the
resulting solution extracted with CH2Cl2 to afford the amide
which was then used in the next step without further purifica-
tion.
responding in a dose-dependent manner with a greater
effect on cocaine-maintained responding. The effects of
14 and 16 on the average number of food and cocaine
deliveries (Figure 5, bottom panel) are similar to those
seen in the response rate data; both compounds de-
creased cocaine intake more than food intake.
These results show that the thiophene- and pyridine-
containing GBR analogs decreased the rates of cocaine-
maintained responding and the number of cocaine
deliveries in a dose-dependent manner. However, all
of these agents also affected the food-maintained re-
sponding. In these studies, only 2 clearly decreased the
rates of cocaine-maintained responding and the number
of cocaine deliveries at the 1.0 and 1.7 mg/kg doses
without affecting the rates of food-maintained respond-
ing or the number of food deliveries. This selective
effect was still observed at the highest dose (3.0 mg/kg)
of 2. However, the rates of food-maintained responding
and the number of food deliveries were also slightly
decreased. All the new analogs tested, both the
thiophene (6 and 8) and pyridine (14 and 16) deriva-
tives, exhibited a comparable potency to the parent
compound in decreasing the cocaine self-administration
in monkeys at most doses tested. Both pyridine-
containing congeners 14 and 16 were more selective
than 6 and 8 in decreasing cocaine- vs food-maintained
responding. However, the degree of separation between
the food and cocaine curves was still smaller than that
seen with 2.
Meth od B: Am id e Red u ction sGen er a l P r oced u r e. A
1 M solution of aluminum hydride in THF35 was added
dropwise to a solution of an amide in THF and stirred under
nitrogen at the indicated temperature until the reduction was
completed by TLC analysis (Table 1). Excess aluminum
Con clu sion s
The heteroaromatic substitution in the GBR structure
resulted in retention of high affinity of the new com-

High-Affinity Dopamine Reuptake Inhibitors
J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 5 713
hydride was decomposed with cooled 15% NaOH, and the
reaction mixture was extracted with Et2O. The organic layer
was then dried over Na2SO4 and the solvent evaporated at
reduced pressure to yield the final amine as an oily product,
which was purified by flash chromatography (silica gel) and/
or converted to a salt of the indicated acid and recrystallized
from the appropriate solvent (Table 1).
Meth od C: Hyd r ogen a tion . A solution of the unsaturated
amine in methanol or in a mixture of methanol and THF (1:1)
was hydrogenated in the presence of 10% Pd/C at room
temperature until the reaction was completed (TLC; Table 2).
The reaction mixture was then filtered through a pad of Celite,
to remove the catalyst. The catalyst was washed with
methanol, and the solvents were evaporated to yield an oily
product which was transformed into a salt of the indicated
acid from the appropriate solvent (Table 2).
J ) 6.8, 15.6 Hz), 6.65 (d, 1H, J ) 15.6 Hz), 6.94-6.96 (m,
1H), 7.01 (t, 4H, J ) 8.8 Hz), 7.14 (d, 1H, J ) 4.9 Hz), 7.25-
7.30 (m, 5H).
9: δ 1.77-1.87 (m, 2H), 2.38 (t, 2H, J ) 7.5 Hz), 2.48 (m,
4H, -N-CH2-), 2.55 (m, 4H, -N-CH2-), 2.64 (t, 2H, J ) 7.5 Hz),
2.68 (t, 2H, J ) 6.0 Hz), 3.60 (t, 2H, J ) 6.0 Hz), 5.37 (s, 1H),
5.97 (m, 1H, furyl), 6.26 (m, 1H, furyl), 7.12-7.35 (m, 11H,
2Ph, 1 furyl).
10: δ 1.82 (quintet, J ) 7.5 Hz, 2H), 2.37 (t, 2H, J ) 7.6
Hz), 2.47-2.68 (m, 12H), 3.56 (t, 2H, J ) 6.1 Hz), 5.34 (s, 1H),
5.98 (d, 1H, J ) 3.0 Hz), 6.27 (d, 1H, J ) 2.5 Hz), 6.97-7.03
(m, 4H), 7.25-7.29 (m, 5H).
11: δ 2.54 (m, 8H, -N-CH2CH2-N-), 2.69 (t, 2H, J ) 6.0 Hz),
3.11 (d, 2H, J ) 6.8 Hz), 3.60 (t, 2H, J ) 6.1 Hz), 5.37 (s, 1H,
Ph2C-H), 6.15-6.23 (m, 1H), 6.32-6.38 (m, 2H), 7.20-7.35 (m,
12H).
Meth od D. Benzimidazo analogs 23 and 24 were synthe-
sized by stirring a mixture of 2-(chloromethyl)benzimidazole
(1 equiv), K2CO3 (2 equiv), KI (2 equiv), and 1-[2-(diphenyl-
methoxy)ethyl]piperazine or 1-[2-[bis(4-fluorophenyl)methoxy]-
ethyl]piperazine (1 equiv), respectively, in DMF at 60 °C
overnight. The reaction mixture was then cooled, poured into
ice-water, and extracted with ethyl acetate. The crude, oily
amine was chromatographed (silica gel column, CH2Cl2:MeOH
) 100:1) and transformed into the salt of the indicated acid
(Table 1). Analog 13 was synthesized following the same
procedure from 1-[2-(diphenylmethoxy)ethyl]piperazine and
3-(3-chloropropyl)pyridine (Table 1).
Met h od E : Sch ot t en -Ba u m a n n Con d en sa t ion . To a
vigorously stirred two-phase mixture of a saturated aqueous
solution of sodium bicarbonate and a chloroform solution of
1-[2-(diphenylmethoxy)ethyl]piperazine [or 1-[2-[bis(4-fluo-
rophenyl)methoxy]ethyl]piperazine] was added the appropriate
acid chloride (1.1 equiv). The reaction was monitored by TLC.
After the reaction was complete, the layers were separated
and the aqueous phase was discarded. The resulting organic
solution was dried over Na2SO4 and chloroform evaporated
under reduced pressure to yield the amide which was used in
the next step without further purification.
Meth od F : Ben zo[b]th iop h en e-2-ca r boxylic Acid . A 2.5
M solution of n-BuLi in hexanes (7.6 mL, 1.2 equiv) was added
to a solution of benzo[b]thiophene (16 mmol) in dry THF (15
mL) at -20 °C. The reaction mixture was stirred at this
temperature for 10 min. Dry ice was then added and reacted
spontaneously. The reaction mixture was allowed to warm
up to room temperature, stirred for 2 h, and poured into ice-
water. The layers were separated, and the organic phase was
washed with water (2×). The aqueous extracts were combined
and treated with concentrated HCl to pH 2-3. The pale yellow
solid precipitated out of solution was collected on a filter
affording benzo[b]thiophene-2-carboxylic acid (77% yield): mp
>220 °C dec.
12: δ 2.55 (br s, 8H), 2.68 (t, 2H, J ) 6.0 Hz), 3.12 (d, 2H,
J ) 6.7 Hz), 3.56 (t, 2H, J ) 6.0 Hz), 5.35 (s, 1H), 6.15-6.23
(m, 2H), 6.33-6.38 (m, 2H), 7.00 (t, J ) 8.6 Hz, 4H), 7.25-
7.33 (m, 5H).
13: δ 1.76-1.83 (m, 2H), 2.35 (t, 2H, J ) 7.4 Hz), 2.46 (m,
4H), 2.55 (m, 4H), 2.64 (t, 2H, J ) 7.6 Hz), 2.68 (t, 2H, J ) 6.0
Hz), 3.60 (t, 2H, J ) 6.0 Hz), 5.38 (s, 1H, Ph2
C-H), 7.19 (m,
1H, pyridyl), 7.22-7.35 (m, 10H, 2Ph), 7.48-7.51 (m, 1H,
pyridyl), 8.42-8.44 (m, 2H, pyridyl).
14: δ 1.81 (quintet, J ) 7.6 Hz, 2H), 2.35 (t, 2H, J ) 7.4
Hz), 2.45-2.53 (m, 8H), 2.61-2.68 (m, 4H), 3.56 (t, 2H, J )
6.0 Hz), 5.33 (s, 1H), 7.00 (t, 4H, J ) 8.7 Hz), 7.20 (dd, 1H, J
) 4.8, 7.8 Hz), 7.25-7.30 (m, 5H), 7.50 (d, 1H, J ) 7.8 Hz),
8.43-8.45 (m, 1H).
15: δ 2.57 (m, 8H, -N-CH2CH2-N-), 2.70 (t, 2H, J ) 6.0 Hz),
3.17 (d, 2H, J ) 6.3 Hz), 3.60 (t, 2H, J ) 5.9 Hz), 5.36 (s, 1H,
Ph2
C-H), 6.32-6.40 (m, 1H, vinyl), 6.49-6.55 (d, 1H, J ) 16.2
Hz, vinyl), 7.21-7.35 (m, 11H, 2Ph, 1 pyridyl), 7.70 (m, 1H,
pyridyl), 8.46 (m, 1H, pyridyl), 8.58 (m, 1H, pyridyl).
16: δ 2.56 (br s, 8H), 2.68 (t, 2H, J ) 6.1 Hz), 3.17 (d, 2H,
J ) 6.8 Hz), 3.56 (t, 2H, J ) 5.9 Hz), 5.33 (s, 1H), 6.34 (dt, 1H,
J ) 6.6, 15.9 Hz), 6.52 (d, 1H, J ) 15.9 Hz), 7.00 (t, J ) 8.6
Hz, 4H), 7.21-7.30 (m, 5H, 2Ph, 1 pyridyl), 7.67-7.70 (m, 1H),
8.45-8.47 (m, 1H), 8.58 (br s, 1H).
17: δ 2.57 (m, 8H, -N-CH2CH2-N-), 2.69 (t, 2H, J ) 6.0 Hz),
3.60 (t, 2H, J ) 6.0 Hz), 3.78 (s, 2H), 5.37 (s, 1H, Ph2C-H),
7.14 (s, 1H, Ar), 7.22-7.35 (m, 12H, 2Ph, 2Ar), 7.67 (m, 1H,
Ar), 7.78 (m, 1H, Ar).
18: δ 2.56 (br s, 8H), 2.67 (t, 2H, J ) 6.0 Hz), 3.56 (t, 2H,
J ) 6.0 Hz), 3.78 (s, 2H), 5.31 (s, 1H), 7.00 (t, 4H, J ) 8.7 Hz),
7.14 (s, 1H), 7.24-7.32 (m, 6H), 7.68 (d, 1H, J ) 6.8 Hz), 7.79
(d, 1H, J ) 8.7 Hz).
19: δ 2.60 (m, 8H, -N-CH2CH2-N-), 2.71 (t, 2H, J ) 5.7 Hz),
3.60 (t, 2H, J ) 5.9 Hz), 3.69 (s, 2H), 5.36 (s, 1H, Ph2C-H),
6.59 (s, 1H, Ar), 7.20-7.34 (m, 12H, 2Ph, 2Ar), 7.46-7.53 (m,
2H, Ar).
20: δ 2.58 (br s, 8H), 2.67 (t, 2H, J ) 6.0 Hz), 3.55 (t, 2H,
J ) 6.0 Hz), 3.69 (s, 2H), 5.32 (s, 1H), 6.59 (s, 1H), 6.99 (t, 4H,
J ) 8.6 Hz), 7.20-7.28 (m, 6H), 7.46-7.53 (m, 2H).
21: δ 2.52 (m, 8H, -N-CH2CH2-N-), 2.69 (t, 2H, J ) 6.0 Hz),
3.59 (t, 2H, J ) 6.0 Hz), 3.65 (s, 2H), 5.37 (s, 1H, Ph2C-H),
7.04-7.17 (m, 4H, indole), 7.21-7.34 (m, 10H, 2Ph), 7.54 (d,
1H, J ) 7.8 Hz, indole), 8.48 (br s, 1H, indole NH).
22: δ 2.52 (br s, 8H), 2.67 (t, 2H, J ) 6.0 Hz), 3.56 (t, 2H,
J ) 6.0 Hz), 3.65 (s, 2H), 5.33 (s, 1H), 6.35 (s, 1H), 7.00 (t, 4H,
J ) 8.7 Hz), 7.05-7.17 (m, 2H), 7.24-7.29 (m, 4H), 7.34 (d,
1H, J ) 7.9 Hz), 7.55 (d, 1H, J ) 7.7 Hz), 8.54 (br s, 1H, indole
NH).
1H NMR (CDCl3) data for compounds 4-38 are as follows:
4: δ 2.56 (br s, 8H), 2.68 (t, 2H, J ) 5.9 Hz), 3.15 (d, 2H, J
) 6.9 Hz), 3.56 (t, 2H, J ) 5.9 Hz), 5.33 (s, 1H), 6.27 (dt, 1H,
J ) 6.8, 15.6 Hz, vinyl), 6.52 (d, 1H, J ) 15.6 Hz, vinyl), 7.00
(t, 4H, J ) 8.8 Hz), 7.23-7.39 (m, 9H).
5: δ 1.81-1.89 (m, 2H), 2.38 (t, 2H, J ) 6.4 Hz), 2.47 (m,
4H, -N-CH2-CH2-N-), 2.54 (m, 4H, -N-CH2CH2-N-), 2.68 (t, 2H,
J ) 5.9 Hz), 2.85 (t, 2H, J ) 7.2 Hz), 3.60 (t, 2H, J ) 6.0 Hz),
5.37 (s, 1H, Ph2C-H), 6.77-6.78 (m, 1H, thienyl), 6.89-6.92
(m, 1H, thienyl), 7.09-7.11 (m, 1H, thienyl), 7.20-7.35 (m,
10H, 2Ph).
6: δ 1.82-1.92 (m, 2H), 2.39 (t, 2H, J ) 7.8 Hz), 2.44-2.58
(m, 4H), 2.67 (t, 2H, J ) 5.9 Hz), 2.86 (t, 2H, J ) 7.9 Hz),
3.54-3.58 (m, 2H), 5.34 (s, 1H, Ph2C-H), 6.77-6.78 (m, 1H,
thienyl), 6.79 (br s, 1H, thienyl), 6.91 (dd, 1H, J ) 2.9, 4.9 Hz,
thienyl), 7.01 (t, 4H, J ) 8.8 Hz), 7.11 (d, 2H, J ) 3.9 Hz),
7.25-7.30 (m, 4H).
7: δ 2.54 (m, 8H, -N-CH2CH2-N-), 2.69 (t, 2H, J ) 6.0 Hz),
3.11 (d, 2H, J ) 6.8 Hz), 3.60 (t, 2H, J ) 5.9 Hz), 5.37 (s, 1H),
6.04-6.14 (m, 1H), 6.61-6.67 (d, 1H, J ) 15.6 Hz, vinyl), 6.94
(m, 1H, thienyl), 7.12-7.14 (m, 1H, thienyl), 7.20-7.35 (m,
11H, 2Ph, 1 thienyl).
23: δ 2.57 (m, 8H, -N-CH2
CH2-N-), 2.68 (t, 2H, J ) 6.0 Hz),
3.59 (t, 2H, J ) 5.9 Hz), 3.80 (s, 2H), 5.36 (s, 1H, Ph2C-H),
7.20-7.34 (m, 12H, 2Ph, 2Ar), 7.41 (br s, 1H, Ar), 7.72 (br s,
1H, Ar), 9.86 (br s, 1H, N-H).
24: δ 2.62 (br s, 8H), 2.70 (t, 2H, J ) 5.9 Hz), 3.59 (t, 2H,
J ) 5.9 Hz), 3.85 (s, 2H), 5.35 (s, 1H), 6.99-7.04 (m, 4H), 7.23-
7.30 (m, 6H), 7.59 (br s, 2H), 9.81 (br s, 1H, N-H).
25: δ 2.58 (br s, 8H, -N-CH2CH2-N-), 2.69 (t, 2H, J ) 6.1
Hz), 3.60 (t, 2H, J ) 6.1 Hz), 3.84 (s, 2H), 5.37 (s, 1H, Ph2C-
H), 7.20-7.35 (m, 10H), 7.49-7.54 (m, 1H), 7.62-7.72 (m, 2H),
7.78-7.81 (m, 1H), 8.07 (d, 1H, J ) 8.5 Hz), 8.12 (d, 1H, J )
8.6 Hz).
8: δ 2.55 (br s, 8H), 2.68 (t, 2H, J ) 5.9 Hz), 3.11 (d, 2H, J
) 6.8 Hz), 3.56 (t, 2H, J ) 5.9 Hz), 5.34 (s, 1H), 6.10 (dt, 1H,

714 J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 5
Matecka et al.
26: δ 2.61 (br s, 8H), 2.70 (t, 2H, J ) 5.9 Hz), 3.59 (t, 2H,
J ) 5.9 Hz), 3.86 (s, 2H), 5.35 (s, 1H), 7.01 (t, 4H, J ) 8.7 Hz),
7.28-7.31 (m, 4H), 7.53 (t, 1H, J ) 7.3 Hz), 7.64 (d, 1H, J )
8.3 Hz), 7.71 (t, 1H, J ) 6.9 Hz), 7.82 (d, 1H, J ) 7.7 Hz), 8.09
(d, 1H, J ) 8.5 Hz), 8.14 (d, 1H, J ) 8.5 Hz).
27: δ 2.54 (m, 8H, -N-CH2CH2-N-), 2.70 (t, 2H, J ) 6.1 Hz),
3.60 (t, 2H, J ) 6.0 Hz), 3.69 (s, 2H), 5.36 (s, 1H, Ph2C-H),
7.12-7.34 (m, 10H, 2Ph), 7.54 (t, 1H, J ) 7.3 Hz, Ar), 7.69 (t,
1H, J ) 7.9 Hz, Ar), 7.80 (d, 1H, J ) 8.0 Hz, Ar), 8.05-8.11
(m, 2H, Ar), 8.89 (s, 1H, Ar).
28: δ 2.54 (br s, 8H), 2.67 (t, 2H, J ) 5.9 Hz), 3.56 (t, 2H,
J ) 6.1 Hz), 3.69 (s, 2H), 5.33 (s, 1H), 7.00 (t, 4H, J ) 8.7 Hz),
7.24-7.29 (m, 4H), 7.54 (t, 1H, J ) 7.2 Hz, Ar), 7.69 (m, 1H),
7.80 (d, 1H, J ) 7.5 Hz), 8.06-8.12 (m, 2H), 8.90 (d, 1H, J )
2.1 Hz).
29: δ 2.55 (m, 8H, -N-CH2CH2-N-), 2.70 (t, 2H, J ) 6.0 Hz),
3.60 (t, 2H, J ) 6.0 Hz), 3.68 (s, 2H), 5.37 (s, 1H, Ph2C-H),
7.22-7.41 (m, 10H, 2Ph), 7.73 (m, 3H, Ar), 8.04-8.14 (m, 2H,
Ar), 8.88 (m, 1H, Ar).
30: δ 2.54 (br s, 8H), 2.68 (t, 2H, J ) 6.0 Hz), 3.56 (t, 2H,
J ) 5.9 Hz), 3.68 (s, 2H), 5.33 (s, 1H), 6.99 (t, 4H, J ) 8.6 Hz),
7.24-7.29 (m, 4H), 7.39 (q, 1H, J ) 4.2 Hz), 7.73 (d, 3H, J )
7.1 Hz), 8.06 (d, 2H, J ) 9.2 Hz), 8.13 (d, 1H, J ) 8.6 Hz),
8.89 (d, 1H, J ) 5.9 Hz).
31: δ 1.96-1.99 (m, 2H), 2.58-2.68 (m, 8H, -N-CH2CH2-
N-), 2.77 (t, 2H, J ) 5.9 Hz), 2.88 (t, 2H, J ) 4.8 Hz), 3.10 (t,
2H, J ) 6.1 Hz), 3.65 (t, 2H, J ) 5.9 Hz), 5.37 (s, 1H, Ph2C-
H), 7.17-7.37 (m, 12H, 2Ph, 2 benzimidazole), 7.53-7.56 (m,
3H, benzimidazole).
32: δ 1.95-2.02 (m, 2H), 2.62 (t, 2H, J ) 5.2 Hz), 2.68 (br
s, 8H), 2.76 (t, 2H, J ) 5.9 Hz), 3.11 (t, 2H, J ) 6.1 Hz), 3.62
(t, 2H, J ) 5.9 Hz), 5.36 (s, 1H, Ph2C-H), 7.01 (t, 4H, J ) 8.7
Hz), 7.19 (q, 2H, J ) 3.0 Hz), 7.26-7.32 (m, 6H), 7.54 (br s,
1H).
33: δ 2.66 (m, 8H, -N-CH2CH2-N-), 2.73 (t, 2H, J ) 6.0 Hz),
3.27 (t, 2H, J ) 5.1 Hz), 3.29 (t, 2H, J ) 5.1 Hz), 3.63 (t, 2H,
J ) 6.0 Hz), 5.39 (s, 1H, Ph2C-H), 6.99 (1H, t, J ) 6.0 Hz, Ar),
7.22-7.40 (m, 12H, 2Ph, 2Ar), 7.49-7.54 (m, 2H, Ar), 7.72 (d,
1H, J ) 7.2 Hz, Ar), 7.85 (d, 1H, J ) 9.0 Hz, Ar), 8.05 (d, 1H,
J ) 7.8 Hz).
34: δ 2.52-2.76 (m, 12H), 3.26-3.31 (m, 2H), 3.59 (t, 2H,
J ) 5.9 Hz), 5.35 (1H, s), 6.98-7.06 (m, 4H), 7.25-7.32 (m,
5H), 7.35-7.38 (m, 1H), 7.41-7.55 (m, 2H), 7.73 (d, 1H, d, J
) 7.8 Hz), 7.86 (d, 1H, d, J ) 7.8 Hz), 8.06 (d, 1H, J ) 7.8 Hz).
35: δ 2.55 (m, 8H, -N-CH2CH2-N-), 2.70 (t, 2H, J ) 6.0 Hz),
3.60 (t, 2H, J ) 6.0 Hz), 3.66 (s, 2H), 5.36 (s, 1H, Ph2C-H),
7.22-7.34 (m, 10H, 2Ph), 7.44-7.50 (m, 3H, Ar), 7.73-7.81
(m, 4H, Ar).
36: δ 2.53 (br s, 8H), 2.67 (t, 2H, J ) 5.8 Hz), 3.56 (t, 2H,
J ) 6.0 Hz), 3.66 (s, 2H), 5.33 (s, 1H), 6.99 (t, 4H, J ) 8.8 Hz),
7.24-7.29 (m, 5H), 7.44-7.50 (m, 3H), 7.73 (br s, 1H), 7.79-
7.84 (m, 2H).
37: δ 2.53 (m, 8H, -N-CH2CH2-N-), 2.67 (t, 2H, J ) 6.0 Hz),
3.59 (t, 2H, J ) 6.0 Hz), 3.89 (s, 2H), 5.36 (s, 1H, Ph2C-H),
7.22-7.51 (m, 14H, 2Ph, 4 naphthyl), 7.75-7.77 (m, 1H, Ar),
7.82-7.85 (m, 1H, Ar), 8.28-8.30 (m, 1H, Ar).
38: δ 2.53 (m, 8H), 2.65 (t, 2H, J ) 6.0 Hz), 3.55 (t, 2H, J
) 6.1 Hz), 3.90 (s, 2H), 5.32 (s, 1H), 6.99 (t, 4H, J ) 8.7 Hz),
7.24-7.28 (m, 5H), 7.37-7.44 (m, 1H), 7.47-7.51 (m, 2H),
7.76-7.79 (m, 1H), 7.84-7.86 (m, 1H), 8.28-8.31 (m, 1H).
1H NMR (CDCl3) data for representative examples of
precursor amides are as follows.
Precursor for amine 11: δ 2.55 (m, 4H), 2.70 (t, 2H, J ) 5.7
Hz), 3.61 (t, 2H, J ) 5.9 Hz), 3.72 (m, 4H), 5.37 (s, 1H), 6.45
(m, 1H, vinyl), 6.54 (m, 1H, furyl), 6.79 (d, 1H, J ) 15.3 Hz,
vinyl), 7.24-7.33 (m, 10H, 2Ph), 7.42 (br s, 1H, furyl), 7.48
(br s, 1H, furyl).
Precursor for amine 29: δ 2.51 (m, 2H), 2.63 (m, 2H), 2.73
(t, 2H, J ) 5.6 Hz), 3.47 (m, 2H), 3.62 (t, 2H, J ) 5.4 Hz), 3.83
(m, 2H), 5.37 (s, 1H), 7.24-7.33 (m, 10H, 2Ph), 7.44-7.49 (m,
1H, quinoline), 7.70-7.73 (m, 1H, quinoline), 7.90 (br s, 1H,
quinoline), 8.13-8.21 (m, 2H, quinoline), 8.97-8.98 (m, 1H,
quinoline).
2H), 5.34 (s, 1H), 7.23-7.33 (m, 12H, Ar), 7.39 (m, 1H, Ar),
7.54 (m, 1H, Ar), 7.82 (m, 1H, Ar), 7.87 (m, 1H, Ar), 7.97 (m,
1H, Ar).
2. Biologica l Meth od s. A. Bin d in g a n d Reu p ta k e
In h ibition Assa ys. Binding assays for the DAT followed
published procedures and used 0.01 nM [125I]RTI-5538 (SA )
2200 Ci/mmol). Briefly, 12 × 75 mm polystyrene test tubes
were prefilled with 100 µL of drug, 100 µL of radioligand ([125I]-
RTI-55), and 50 µL of a “blocker” or buffer. Drugs and blockers
were made up in 55.2 mM sodium phosphate buffer, pH 7.4
(BB), containing 1 mg/mL bovine serum albumin (BB/BSA).
Radioligands were made up in a protease inhibitor cocktail
containing 1 mg/mL BSA [BB containing chymostatin (25 µg/
mL), leupeptin (25 µg/mL), EDTA (100 µM), and EGTA (100
µM)]. The samples were incubated in triplicate for 18-24 h
at 4 °C (equilibrium) in a final volume of 1 mL. Brandel cell
harvesters were used to filter the samples over Whatman GF/B
filters, which were presoaked in wash buffer (ice-cold 10 mM
Tris-HCl/150 mM NaCl, pH 7.4) containing 2% poly(ethylen-
imine).
The [3H]DA and [3H]-5-HT uptake assays also proceeded
according to published procedures.25 Briefly, synaptosomes
were prepared by homogenization of rat caudate (for [3H]DA
reuptake) or whole rat brain minus cerebellum (for [3H]-5-HT
reuptake) in ice-cold 10% sucrose, using a Potter-Elvehjem
homogenizer. After a 1000g centrifugation for 10 min at 4 °C,
the supernatants were retained on ice. The uptake assays
were initiated by the addition of 100 µL of synaptosomes to
12 × 75 mm polystyrene test tubes prefilled with 750 µL of
[3H]ligand (5 nM final concentration) in a Krebs-phosphate
buffer (pH 7.4), which contained ascorbic acid (1 mg/mL) and
pargyline (50 µM) (buffer), 100 µL of test drugs made up in
buffer, and 50 µL of buffer. The nonspecific uptake of each
[3H]ligand was measured by incubations in the presence of 1
µM GBR 12909 ([3H]DA) and 10 µM fluoxetine ([3H]-5-HT).
The incubations were terminated after a 15 min ([3H]DA) or
30 min ([3H]-5-HT) incubation at 25 °C by adding 4 mL of wash
buffer (10 mM Tris-HCl, pH 7.4, containing 0.9% NaCl at 25
°C) followed by rapid filtration over Whatman GF/B filters and
one additional wash cycle. The Krebs-phosphate buffer con-
tained 154.5 mM NaCl, 2.9 mM KCl, 1.1 mM CaCl2, 0.83 mM
MgCl2, and 5 mM glucose. The tritium retained on the filters
was counted, in a Taurus beta counter, after an overnight
extraction into ICN Cytoscint cocktail.
Nonstandard [125I]RTI-55 binding assay and [3H]DA uptake
assay were carried out with minor modifications of the method
described above, using the Krebs-phosphate buffer detailed
above.37 Assays were initiated by the addition of 100 µL of
synaptosomes to 12 × 75 mm polystyrene test tubes which
were prefilled with either Krebs-phosphate buffer plus 1 mg/
mL BSA or various concentrations of test drugs in Krebs-
phosphate buffer plus 1 mg/mL BSA. After a 60 min prein-
cubation at 25 °C, [3H]DA uptake or [125I]RTI-55 binding was
initiated by the addition of 750 µL of radioligand (5 nM [3H]-
DA or 10 pM [125I]RTI-55) in Krebs-phosphate buffer. The
incubations were terminated after a 20 min incubation at 25
°C by adding 4 mL of wash buffer (10 mM Tris-HCl, pH 7.4,
containing 0.9% NaCl at 25 °C) followed by rapid filtration
over Whatman GF/B filters [presoaked in 2% poly(ethylen-
imine)] and one additional wash cycle. Nonspecific binding
and uptake were defined using 1 µM GBR 12909. Control
studies indicated that specific [3H]DA uptake and [125I]RTI-
55 binding were linear with time up to 30 min and directly
proportional to the protein concentration range used here.37
For the [3H]-(+)-pentazocine (σ) binding assay large batches
of frozen membranes were prepared from frozen guinea pig
brains (Pel Freeze) as previously described.40 The [3H]-(+)-
pentazocine binding assay proceeded with minor modifications
of previously published procedures.41 Briefly, incubations
proceeded for 4-6 h at 25 °C (steady state) in 5 mM Tris-HCl,
pH 8.0, with a protease inhibitor cocktail [chymostatin (10 µg/
mL), leupeptin (10 µg/mL), EDTA (10 µM), EGTA (10 µM)].
The incubations were terminated by rapid filtration over
Whatman GF/B filters presoaked in 1% poly(ethylenimine)
followed by two 4 mL washes with ice-cold 5 mM Tris-HCl,
pH 8.0. The tritium on the filters was measured after an
Precursor for amine 37: δ 2.37 (t, 2H, J ) 4.9 Hz), 2.51 (t,
2H, J ) 5.1 Hz), 2.65 (t, 2H, J ) 5.7 Hz), 3.43 (t, 2H, J ) 5.0
Hz), 3.56 (t, 2H, J ) 5.8 Hz), 3.70 (t, 2H, J ) 5.0 Hz), 4.15 (s,

High-Affinity Dopamine Reuptake Inhibitors
J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 5 715
overnight extraction in 5 mL of ICN Cytoscint cocktail, using
standard liquid scintillation counting methods. Nonspecific
binding was determined by incubations in the presence of 10
µM DTG.
and completion of 30 lever presses in the presence of red
stimulus lamps was followed by a drug delivery in a volume
proportional to the weight of the monkey (0.75 cc of solution
over a 2.7 s period, per 10 kg of weight). Each FR-30
requirement was constrained by a 60 s limited hold (reinforce-
ment delivery was contingent upon the emission of 30 re-
sponses within 60 s from the last reinforcer delivery), and each
reinforcer delivery was followed by 3 s of darkness during
which there were no scheduled consequences for lever pressing.
Within each component a maximum of 10 reinforcers could
be delivered. Thus, a component consisted of either 10 FR-
30s, 10 limited holds, or any combination of both to total 10.
This sequence of events was repeated four times during all
sessions. At the beginning of each of the four 15 min TO
periods, increasing doses of the GBR analogs were delivered,
namely, 0.3, 0.7, 0.7, and 1.3 mg/kg, culminating in a cumula-
tive dose sequence of 0.3, 1.0, 1.7, and 3.0 mg/kg.
For the structure-activity study, initial experiments were
conducted to determine the appropriate concentration range
of each test agent at each binding site. After this, eight-point
inhibition curves, ranging from 90% to 10% of control, were
generated. The data of two separate experiments were pooled
and fit, using the nonlinear least-squares curve-fitting lan-
guage MLAB-PC42 (Civilized Software, Bethesda, MD), to the
two-parameter logistic equation41 for the best-fit estimates of
the IC50 and slope factor. The data are reported as IC50 values.
As reported elsewhere,25 the Km values for [3H]-5-HT and [3H]-
DA reuptake are 17.4 ( 0.8 and 38.3 ( 1.6 nM, respectively.
The Kd values for [3H]GBR 12935, [125I]RTI-55 binding, and
[3H]-(+)-pentazocine are 1.35 ( 0.14, 0.91 ( 0.04, and 4.9 (
0.1 nM, respectively.38,43,44 The sources of radioligands and
reagents are published.25,38,43,44
Ack n ow led gm en t. We would like to thank Noel
Whittaker and Wesley White of the Laboratory of
Analytical Chemistry for mass spectral data and ac-
knowledge the National Institute on Drug Abuse,
Medications Development Division, for partial financial
support of this work. We also thank Dr. Andrsej Wilk
for his help with molecular modeling experiments.
B. Locom otor Activity in Ra ts. Su bjects. Male Spra-
gue-Dawley rats weighting 250-300 g were group housed and
maintained on a 12 h light-dark cycle (lights on 0600-1800
h) with food and water available ad libitum in the home cage.
All the animals were adapted to the vivarium conditions for
at least 1 week before experimentation was begun. Behavioral
testing was always performed between 1000 and 1700 h.
Ap p a r a tu s. Locomotor activity was assessed in photocell
activity monitors (Omnitech Electronics, Columbus, OH) which
were constructed from clear Plexiglas (30.5 cm high × 42 cm
long). The activity monitors were enclosed in sound-attenuat-
ing compartments equipped with a 15 W fluorescent light, a
ventilating fan that also provides masking noise, and a one-
way mirror (21 × 21 cm) mounted in the door, to allow visual
observation of the animals during testing. A series of 16
equally spaced infrared photocell detectors were located along
two adjacent walls of the chamber 4 cm from the floor surface.
Interruptions of the infrared light source by the animals were
recorded and stored by an IBM AT computer.
Dr u gs. The drugs were dissolved in a solution comprised
of 25% propylene glycol and 75% sterile water in a concentra-
tion of 30 mg/mL. It was necessary to slightly heat some of
the drug solutions. Drugs were injected in a volume of 1 mL/
kg.
P r oced u r e. All rats were placed in the locomotor activity
chambers for 30 min. Data were collected in 10 min intervals.
The animals were then removed from the apparatus, injected
with the appropriate drugs or vehicle, and returned to the
activity monitors for an additional 60 min. Data were collected
again in 10 min intervals.
C. Self-Ad m in istr a tion Stu d ies in Mon k eys. Eight
adult, male rhesus monkeys (Macaca mulatta), maintained at
90% of their ad libitum weight, were used as subjects (4
animals/group). All monkeys were surgically implanted with
a subcutaneous vascular access port system, according to the
described method,45 and trained to press a lever for food pellets
and intravenous cocaine injections.20,21 After lever pressing
was established, responding was maintained under a multiple
fixed ratio 30-fixed ratio 30 schedule of reinforcement for food
and cocaine, respectively, in a manner described previously21
but with the following schedule modifications to allow for
cumulative dosing of the GBR analogs. A daily session
consisted of eight components (four food and four drug
components) with a 15 min time out (TO) period preceding
each food component and a 5 min TO period preceding each
drug component. These TO periods were signaled by turning
off all stimulus lamps. During TO periods 1-4 preceding the
food components, a GBR analog was infused via an iv line.
The sequence of doses during TO periods 1-4 was 0.3, 0.7,
0.7, and 1.3 mg/kg, respectively, allowing for a cumulative dose
of 3.0 mg/kg being delivered by the end of the fourth TO period.
The GBR analog was delivered in a volume proportional to
the weight of the monkey (3.0 cc of solution over a 3.0 s period,
per 10 kg of weight). During the TO periods preceding the
drug components, there were no scheduled consequences for
responding. Completion of 30 lever presses in the presence
of blue stimulus lamps was followed by a food pellet delivery,
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