Structure-activity relationships at the monoamine transporters and σ receptors for a novel series of 9-[3-(cis-3,5-dimethyl-1- piperazinyl)propyl]carbazole (rimcazole) analogues

Article abstract of DOI:10.1021/jm9902943

9-[3-(cis-3,5-Dimethyl-1-piperazinyl)propyl]carbazole (rimcazole) has been characterized as a receptor antagonist that binds to the dopamine transporter with moderate affinity (K(i) = 224 nM). Although the binding affinities at the dopamine transporter of rimcazole and cocaine are comparable, rimcazole only depressed locomotor activity in mice and antagonized the stimulant effects produced by cocaine. The neurochemical mechanisms underlying the attenuation of cocaine's effects are not understood, although interaction at a low affinity site/state of the dopamine transporter has been suggested. To explore further this class of compounds, a series of rimcazole analogues was designed and synthesized. Displacement of [³H]WIN 35,428 binding at the dopamine transporter in rat caudate-putamen revealed that aromatic substitutions on rimcazole were not well tolerated, generally, with significant reductions in affinity for the 3,6-dibromo (5; K(i) = 3890 nM), 1,3,6-tribromo (6; K(i) = 30300 nM), 3-amino (8; K(i) = 2400 nM), and 3,6-dinitro (9; K(i) = 174000 nM) analogues. The N-phenylpropyl group was the only terminal piperazine nitrogen substituent that retained moderate affinity at the dopamine transporter (11; K(i) = 263 nM). Analogues in which the carbazole ring was replaced with a freely rotating diphenylamine moiety were also prepared. Although the diphenylamino analogue in which the terminal piperazine nitrogen was unsubstituted, as in rimcazole, demonstrated relatively low binding affinity at the dopamine transporter (24; K(i) = 813 nM), the N-phenylpropyl analogue was found to have the highest affinity for the dopamine transporter within the series (25; K(i) = 61.0 nM). All of the analogues that had affinity for the dopamine transporter inhibited [³H]dopamine uptake in synaptosomes, and potencies for these two effects showed a positive correlation (r² = 0.7731, p = 0.0018). Several of the analogues displaced [³H]paroxetine from serotonin transporters with moderate to high affinity, with the N-phenylpropyl derivative (11) having the highest affinity (K(i) = 44.5 nM). In contrast, none of the analogues recognized the norepinephrine transporter with an affinity of < 1.3 μM. Binding affinities for σ₁ and σ₂ receptors were also determined, and several of the compounds were more potent than rimcazole with affinities ranging from 97 nM to >6 μM at σ₁ sites and 145 to 1990 nM at σ₂ sites. The compound with the highest affinity (25) at σ₁ sites was also the compound with highest affinity at the dopamine transporter. These novel rimcazole analogues may provide important tools with which to characterize the relationship between the low affinity site or state of the dopamine transporter, σ receptors, and their potential roles in modulating cocaine's psychostimulant actions.

Full text of DOI:10.1021/jm9902943

4446
J . Med. Chem. 1999, 42, 4446-4455
Str u ctu r e-Activity Rela tion sh ip s a t th e Mon oa m in e Tr a n sp or ter s a n d σ
Recep tor s for a Novel Ser ies of 9-[3-(cis-3,5-Dim eth yl-1-p ip er a zin yl)-
p r op yl]ca r ba zole (Rim ca zole) An a logu es
Stephen M. Husbands,† Sari Izenwasser,‡ Theresa Kopajtic,‡ Wayne D. Bowen,§ Bertold J . Vilner,§
J onathan L. Katz,‡ and Amy Hauck Newman*,†
Medicinal Chemistry and Psychobiology Sections, National Institute on Drug Abuse-Intramural Research Program,
Baltimore, Maryland 21224, and Laboratory of Medicinal Chemistry, NIDDK, National Institutes of Health,
Bethesda, Maryland 20892
Received J une 9, 1999
9-[3-(cis-3,5-Dimethyl-1-piperazinyl)propyl]carbazole (rimcazole) has been characterized as a
σ receptor antagonist that binds to the dopamine transporter with moderate affinity (Ki ) 224
nM). Although the binding affinities at the dopamine transporter of rimcazole and cocaine are
comparable, rimcazole only depressed locomotor activity in mice and antagonized the stimulant
effects produced by cocaine. The neurochemical mechanisms underlying the attenuation of
cocaine’s effects are not understood, although interaction at a low affinity site/state of the
dopamine transporter has been suggested. To explore further this class of compounds, a series
of rimcazole analogues was designed and synthesized. Displacement of [3H]WIN 35,428 binding
at the dopamine transporter in rat caudate-putamen revealed that aromatic substitutions on
rimcazole were not well tolerated, generally, with significant reductions in affinity for the 3,6-
dibromo (5; Ki ) 3890 nM), 1,3,6-tribromo (6; Ki ) 30300 nM), 3-amino (8; Ki ) 2400 nM), and
3,6-dinitro (9; Ki ) 174000 nM) analogues. The N-phenylpropyl group was the only terminal
piperazine nitrogen substituent that retained moderate affinity at the dopamine transporter
(11; Ki ) 263 nM). Analogues in which the carbazole ring was replaced with a freely rotating
diphenylamine moiety were also prepared. Although the diphenylamino analogue in which
the terminal piperazine nitrogen was unsubstituted, as in rimcazole, demonstrated relatively
low binding affinity at the dopamine transporter (24; Ki ) 813 nM), the N-phenylpropyl analogue
was found to have the highest affinity for the dopamine transporter within the series (25; Ki
) 61.0 nM). All of the analogues that had affinity for the dopamine transporter inhibited [3H]-
dopamine uptake in synaptosomes, and potencies for these two effects showed a positive
correlation (r2 ) 0.7731, p ) 0.0018). Several of the analogues displaced [3H]paroxetine from
serotonin transporters with moderate to high affinity, with the N-phenylpropyl derivative (11)
having the highest affinity (Ki ) 44.5 nM). In contrast, none of the analogues recognized the
norepinephrine transporter with an affinity of <1.3 µM. Binding affinities for σ1 and σ2 receptors
were also determined, and several of the compounds were more potent than rimcazole with
affinities ranging from 97 nM to >6 µM at σ1 sites and 145 to 1990 nM at σ2 sites. The compound
with the highest affinity (25) at σ1 sites was also the compound with highest affinity at the
dopamine transporter. These novel rimcazole analogues may provide important tools with which
to characterize the relationship between the low affinity site or state of the dopamine
transporter, σ receptors, and their potential roles in modulating cocaine’s psychostimulant
actions.
Rimcazole (9-[3-(cis 3,5-dimethyl-1-piperazinyl)prop-
yl]carbazole; 1) has been reported to decrease locomotor
activity in mice and, when administered in combination
with cocaine (2), to attenuate the cocaine-induced
stimulation of activity (Chart 1).1 Moreover, the sensi-
tization that develops to repeat exposures to cocaine can
be attenuated by rimcazole.2 Thus rimcazole has a
behavioral profile that sharply contrasts with that of
cocaine and may function to antagonize at least some
of the behavioral effects of cocaine. When these studies
were reported, rimcazole was primarily known as an
“atypical antipsychotic” and a moderately potent σ
receptor antagonist.3-5 The attenuation of cocaine-
induced behavior was then attributed to rimcazole’s σ
antagonist properties. Although the pharmacological
significance of σ receptors has not been determined,
there are a number of reports in the literature suggest-
ing a possible relationship between σ receptors and the
dopamine transporter. For example, cocaine has been
reported to bind with low affinity to σ receptors labeled
with [3H]haloperidol in rats.6 Moreover, the high affinity
binding of many of the aryl 1,4-dialkyl(en)yl piperazine
series of ligands (e.g., GBR 12909, 3)7 to both σ sites
and the dopamine transporter suggests an overlap in
structural requirements for binding to these sites.8-10
In addition, the photoaffinity label [125I]iodo-azidoco-
† Medicinal Chemistry Section, National Institute on Drug Abuse-
Intramural Research Program.
‡ Psychobiology Section, National Institute on Drug Abuse-Intra-
mural Research Program.
§ National Institutes of Health.
10.1021/jm9902943 This article not subject to U.S. Copyright. Published 1999 by the American Chemical Society
Published on Web 10/01/1999

SAR of a Novel Series of Rimcazole Analogues
J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 21 4447
Ch a r t 1. Chemical Structures of Dopamine Uptake
Inhibitors
ration and chemical modification. We were particularly
interested in determining if rimcazole and its analogues
would have structure-activity relationships resembling
any of the other well-known dopamine transporter
ligands. In particular, rimcazole shares structural simi-
larities with GBR 12909 (3) which has well-described
structure-activity relationships at both the dopamine
transporter and σ receptors.9,10 In addition, it was
anticipated that with a more extensive series of com-
pounds to evaluate, the potential mechanistic roles of
the dopamine transporter and/or σ sites in the behav-
ioral actions of these compounds might be elucidated.
Recently, we published a series of isothiocyanato
analogues of rimcazole of which one compound (4)
demonstrated high affinity, irreversible binding to the
dopamine transporter.17 This study suggested that the
rimcazole isothiocyanate analogue may be irreversibly
binding to a low affinity site or state of the dopamine
transporter.17 On the basis of rimcazole’s lack of cocaine-
like actions we have hypothesized that this class of
drugs may be binding to a low affinity site or state of
the dopamine transporter that is distinct from cocaine’s
high affinity binding site. In support of this concept,
recent studies have suggested that the locomotor stimu-
lant18 and subjective effects19 of cocaine and numerous
dopamine uptake inhibitors are positively related to
interactions at the high affinity binding site on the
dopamine transporter. Hence, the low affinity site may
not play a primary role in the actions of cocaine and
may provide a target for drugs with therapeutic poten-
tial in the treatment of cocaine abuse. Thus, in the
present investigation, a structure-activity relationship
study of the binding site on the dopamine transporter
at which rimcazole and structurally related dopamine
uptake inhibitors may interact was undertaken. In this
pursuit, we considered the carbazole ring and secondary
nitrogen of the piperazine ring to be amenable to
considerable structural modification. Carbazole ring
substituted analogues and analogues in which the
structurally rigid carbazole was replaced with the more
flexible, untethered diphenylamine moiety were pre-
pared. In addition, selected N-substituted analogues
with either the carbazole or diphenylamine moiety at
the opposite terminus were synthesized.
Evaluation of the rimcazole analogues at the dopam-
ine transporter and comparison of the structure-
activity relationships to those determined at the σ1 and
σ2 receptors were of primary interest. However, to assess
their selectivity, an evaluation of these ligands at the
other monoamine transporters (serotonin and norepi-
nephrine) was undertaken. Finally, it was our aim to
compare the rimcazole analogues with other existing
classes of dopamine uptake inhibitors that share struc-
tural features of rimcazole, such as the aryl 1,4-dialkyl-
(en)yl piperazine series of compounds. In this way
comparisons of the structural, binding, and behavioral
profiles of these different classes of compounds could
be undertaken, and conclusions regarding the neuro-
chemical bases of these drugs’ actions might be ascer-
tained.
caine was reported to recognize both high and low
affinity cocaine binding sites on the dopamine trans-
porter, but when photoactivated this ligand selectively
labeled a polypeptide with the pharmacology of a σ
receptor.11 Recently, σ ligands related to arylethylene-
diamines have been shown to attenuate the locomotor
and toxic effects of cocaine.12,13 The mechanism of these
effects appears to involve specific antagonism at σ
receptors. These studies, taken together, suggest a
structural and potentially functional relationship be-
tween σ sites and the cocaine binding site on the
dopamine transporter.
A variety of σ ligands have also been tested for their
ability to inhibit [3H]WIN 35,428 binding to the dopam-
ine transporter and also their potency in inhibiting
dopamine uptake.14 All of the σ ligands inhibited [3H]-
WIN 35,428 binding in a dose-dependent and monopha-
sic manner, in contrast to cocaine and many cocaine
analogues, which recognize both high and low affinity
binding sites.15,16 Of the σ ligands studied, rimcazole
demonstrated the highest affinity for the dopamine
transporter (Ki ) 103 nM).14 Further, rimcazole showed
a significantly lower potency for inhibiting dopamine
uptake (IC50 ) 4.22 µM), compared to its binding
affinity, than any of the other ligands evaluated or any
other dopamine transporter ligands reported to date.14
This ratio of dopamine uptake inhibition (IC50)/dopam-
ine transporter binding affinity (Ki) for rimcazole sug-
gested a 40-fold difference in potency for the inhibition
of dopamine uptake as compared to rimcazole’s binding
affinity for the dopamine transporter. The significance
of this ratio in terms of in vivo function and behavior
has not been established. Nevertheless, as rimcazole
does not produce cocaine-like psychomotor stimulant
effects and has been reported to attenuate the locomotor
stimulant effects of cocaine,1 a novel action at the
dopamine transporter was suggested.14 This novel neu-
rochemical and behavioral profile suggested that rim-
cazole would be a suitable candidate for further explo-
Ch em istr y
Initial synthetic effort was directed at preparing aryl
ring substituted analogues of rimcazole (1). Both the 3,6-

4448 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 21
Husbands et al.
Sch em e 1a
Sch em e 2a
a
Reagents and conditions: (i) CH2O, NaBH3CN; (ii) 3-phenyl-
propionylchloride; (iii) LAH.
a
Reagents and conditions: (i) Br2, HBr/HOAc; (ii) HNO3/HOAc;
Sch em e 3a
(iii) HNO3/H2SO4; (iv) H2, 10% Pd/C.
dibromo (5) and 1,3,6-tribromo (6) analogues could be
obtained by treating 1 with bromine in aqueous hydro-
gen bromide/acetic acid (Scheme 1). The dibromo ana-
logue (5) was formed in the greater amount (58%), but
column chromatography, followed by recrystallization,
resulted in the isolation of the tribromo analogue (6) in
26% yield.
To gain insight into the effects of highly polar
aromatic substitutions, we targeted the mononitro (7)
and dinitro (9) analogues and their reduced counter-
parts, monoamino (8) and the diamino analogues. Rim-
cazole (1) could be nitrated by modification of the
method used for the nitration of imipramine.20 We
previously described the monosubstituted 3-NO2 (7) and
3-NH2 (8) ligands17 but did not report the synthesis or
pharmacological evaluation of these compounds. Thus
1 was treated with 2.4 equiv of nitric acid in acetic acid,
to give a quantitative yield of 7 (Scheme 1). By using a
stronger acid, in this case sulfuric acid, the 3,6-dinitro
derivative (9) could be obtained, in 38% yield. Catalytic
hydrogenation (10% Pd/C) of 7 gave the amine 8 in
quantitative yield. However, reaction of the dinitro
intermediate 9 under identical conditions resulted in the
extremely polar diamino compound that could not be
purified sufficiently for testing by either chromatogra-
phy or recrystallization.
a
Reagents and conditions: (i) NaH, 15-crown-5; (ii) HOAc/H2O;
In a continuation of previous studies17 investigating
the effects of modification at the terminal piperazine
nitrogen of rimcazole (3) by addition of methyl, aryl, and
3-phenylpropyl moieties was undertaken. Compound 10
was previously described17 but was included in this
study for additional pharmacological testing. Compound
11 was designed based on the structurally similar
dopamine uptake inhibitor GBR 12909 (3). Acylation of
1 with 3-phenylpropionyl chloride to give the amide
intermediate was followed by reduction with LAH to
(iii) Ph3P, CBr4; (iv) K2CO3.
give 11, as depicted in Scheme 2. In Scheme 3, the 2,6-
dimethylpiperazine of 1 was replaced with aryl-pipera-
zines. 3-Bromopropanol was reacted with dihydropyran
to give the tetrahydropyran (THP)-protected alcohol 12
which was reacted with carbazole (13) under the basic
conditions of sodium hydride in the presence of 1,4,7,-
10,13-pentaoxacyclopentadecane (15-crown-5) to yield
compound 14. Deprotection under aqueous acid condi-

SAR of a Novel Series of Rimcazole Analogues
J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 21 4449
Sch em e 4a
inhibition of [3H]dopamine uptake were compared to
cocaine (2) and GBR 12909 (3, Table 1). In general,
chemical modification to the rimcazole structure re-
sulted in a decrease in binding affinity at the dopamine
transporter. The 3-NO2 analogue, 7, was slightly more
potent (Ki ) 109 nM) than rimcazole, 1, (Ki ) 224 nM),
but reduction to the 3-NH2 analogue, 8, significantly
decreased binding affinity (Ki ) 2400 nM). Addition of
a second nitro group (9) eliminated binding at the
dopamine transporter (Ki ) 174 µM) as did di- or
tribromination (5 and 6; Ki ) 3890 and 30300 nM,
respectively). N-Methylation (10) decreased binding
affinity by 2-fold, and replacement of the methyl group
with an aryl ring eliminated binding altogether (18 and
19, Ki ) 4.9 and 113 µM, respectively). It should be
noted that in the N-aryl substituted analogues, 18 and
19, the 2,6-dimethyl substituents on the piperazine ring
are eliminated, and this may have contributed to the
loss of binding affinity. However, for GBR 12909 (3; Ki
) 12.0 nM), these pendant methyl groups are not
present on the piperazine ring, suggesting that these
groups are unnecessary for high affinity binding at the
dopamine transporter. When the phenyl ring was
extended away from the piperazine terminal nitrogen
by a propyl chain, as seen for GBR 12909 (3), binding
affinity was somewhat restored (11, Ki ) 263 nM). This
trend was also observed with the isothiocyanate moiety
in the series of irreversible ligands based on rimcazole
(1), reported previously.17
When the carbazole ring was replaced with freely
rotating diphenylamine group, binding affinity was
reduced by 4-fold (24, Ki ) 813 nM). However, as in the
carbazole series, addition of a 3-phenylpropyl substitu-
ent at the terminal piperazine nitrogen increased bind-
ing affinity, resulting in the most potent compound in
this series, 25 (Ki ) 61.0 nM). The structure of this
compound most closely resembles that of GBR 12909
(3, Ki ) 12.0 nM), suggesting that the nitrogen in the
diphenylamine function of 25 may be serving as a spacer
between the aryl rings and the piperazine functionality
as has been reported for the nonterminal piperazine
nitrogen in the aryl 1,4-dialkyl(en)yl piperidine series
of compounds.21
a
Reagents and conditions: (i) 12, NaH, 15-crown-5; (ii) HOAc/
H2O; (iii) Ph3P, CBr4; (iv) 2,6-dimethylpiperazine, K2CO3; (v)
3-phenylpropionylchloride; (vi) LAH.
tions followed by treatment with carbon tetrabromide
and triphenylphosphine gave the alkylbromide 15.
Alkylation with the aryl piperazines 16 and 17 gave the
products 18 and 19, respectively.
Rimcazole (1) and most of the analogues that dem-
onstrated moderate to low binding affinities for the
dopamine transporter were evaluated for inhibition of
[3H]dopamine uptake in synaptosomes. Although we
had previously reported that rimcazole demonstrated
relatively poor potency for inhibition of dopamine
uptake in a chopped tissue preparation (IC50 ) 4.22
µM),14 in the synaptosome preparation its potency was
more comparable to its binding affinity at the dopamine
transporter (IC50 ) 140 nM). This experience in our own
laboratory further underscores the caution that must
be taken in comparing binding affinities and inhibition
of dopamine uptake potencies in assays that are con-
ducted under differing conditions, as we and others have
discussed previously.22-24 In this case, simply the dif-
ference of chopped tissue versus a synaptosome prepa-
ration yielded significantly different results (IC50 ) 4.22
µM vs 140 nM) which changed a ratio of dopamine
uptake inhibition to binding affinity at the dopamine
transporter from ∼40 to 1. Likewise, using the synap-
tosome preparation, each of the rimcazole analogues
Compound 24 was chosen as the target for studying
the nature of the aromatic moiety of rimcazole by
replacing the planar carbazole ring system with the
freely rotating diphenylamine function. Diphenylamine
(20) was alkylated with the THP-protected 1-bromopro-
panol (12) using sodium hydride in the presence of 15-
crown-5, as the base, to yield 21 (Scheme 4). As
described above, deprotection with aqueous acid to yield
the alcohol (22), followed by treatment with triph-
enylphosphine and carbon tetrabromide, gave the alkyl-
bromide (23) in good yield (97% over two steps). Alky-
lation of 21 with 2,6-dimethylpiperazine gave 24 in 41%
yield. Acylation of the amine (24) with 3-phenylprop-
ionyl chloride followed by reduction with LAH yielded
the N-3-phenylpropyl substituted analogue 25 in 70%
yield, over two steps (Scheme 4).
Str u ctu r e-Activity Rela tion sh ip s
The binding affinities of rimcazole (1) and its ana-
logues for all three monoamine transporters and for

4450 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 21
Husbands et al.
Ta ble 1. Binding Affinities of Rimcazole Analogues at the Dopamine, Serotonin, and Norepinephrine Transporters and Inhibition of
Dopamine Uptake
substituents group,
R1, R2, R3
[3H]WIN 35,428, DAT [3H]DA uptake inhibition [3H]paroxetine, 5HTT [3H]nisoxetine, NET
compound
25
Ki, nM ( SEMa
IC50, nM ( SEM
Ki, nM ( SEMa
Ki, nM ( SEMa
B, -, -, phenylpropyl
A, 3-NO2, H, H
A, H, H, H
A, H, H, phenylpropyl
A, H, H, CH3
61.0 ( 6.1
109 ( 7
36.6 ( 4.9
111 ( 22
140 ( 5
219 ( 32
1170 ( 100
825 ( 111
44.5 ( 6.6
373 ( 14
13100 ( 1410
2100 ( 280
1130 ( 147
cIA
1850 ( 290
1610 ( 250
cIA
172 ( 15
24.1 ( 2.3
3640 ( 440
4580 ( 1200
2160 ( 300
2490 ( 310
9370 ( 1840
6810 ( 600
13900 ( 4400
1300 ( 150
4120 ( 920
3660 ( 470
8540 ( 2910
cIA
7
1; rimcazole
11
10
24
8
5
18
9
224 ( 16d
263 ( 34
639 ( 70.3
472 ( 44
1060 ( 297
bnd
436 ( 44
B, -, -, H
813 ( 22
A, 3-NH2, H, H
A, 3-Br, 6-Br, H
C, -, -, phenyl
A, 3-NO2, 6-NO2, H
A, 1,3-diBr, 6-Br, H
C, -, -, 2-Cl-phenyl
2400 ( 144
3890 ( 506
4930 ( 444
174000 ( 24400
30300 ( 2420
112700 ( 1130
187 ( 19
bnd
1820 ( 239
3670 ( 145
bnd
2770 ( 403
205 ( 13
2.30 ( 0.14
6
19
2; cocaine
3; GBR 12909
3300 ( 170
1270 ( 190
12.0 ( 1.9
a
b
Each Ki value represents data from at least three independent experiments, each performed in triplicate. nd ) not determined. c IA
) inactive. Ki value obtained in the present study was 2-fold higher than the previously reported value.14
d
Ta ble 2. Binding Affinities of Rimcazole Analogues at σ1 and
inhibited dopamine uptake with a potency essentially
equal to its binding affinity at the dopamine transporter.
σ2 Receptors
[3H]pentazocine,
[3H]DTG,
There was a direct relation between potency for dopam-
ine uptake inhibition and affinity in displacement of
[3H]WIN 35,428 with a significant correlation between
log transforms of Ki and IC50 values (r2 ) 0.7731, p )
0.0018).
compound
25
11
24
10
7
1; rimcazole
5
8
6
σ1 Ki, nM ( SEMa
σ2 Ki, nM ( SEMa
97.2 ( 14.0
104.1 ( 0.4
138 ( 2
183 ( 8
145 ( 18
351 ( 44
230 ( 20
193 ( 33
302 ( 37
675 ( 58
1660 ( 200
1990 ( 44
116 ( 13
552 ( 110
596 ( 66
908 ( 99
4420 ( 27
5720 ( 440
>6000
At the serotonin transporter, most of these rimcazole
analogues demonstrated moderate affinities, with rim-
cazole binding with a Ki of 825 nM. In general, chemical
modifications to the rimcazole structure were better
tolerated than at the dopamine transporter. Some
differences were dramatic. For example, 3,6-dinitro
substitution in compound 9 virtually eliminated binding
at the dopamine transporter (Ki ) 174 µM), whereas
only a 2-fold decrease in affinity was observed at the
serotonin transporter (Ki ) 1850 nM) as compared to
the parent drug, 1. Also di- and tribromination in
compounds 5 and 6 showed a similar effect, where the
serotonin transporter was far more tolerant of these
aromatic substitutions (Ki ) 1130 and 1610 nM, respec-
tively) than the dopamine transporter. Interestingly the
N-3-phenylpropyl analogue, 11, demonstrated relatively
high affinity for the serotonin transporter (Ki ) 44.5
nM); it was slightly less potent than GBR 12909 (Ki )
24.1 nM), whereas a 4-fold decrease in affinity was
observed when the carbazole ring was replaced by the
diphenylamine function (25, Ki ) 219 nM). These
structure-activity relationships are in contrast to those
seen at the dopamine transporter and provide clues to
separability within this class of compounds. Underscor-
ing the different structure-activity relationships for
binding to the dopamine and serotonin transporters is
that there was not a significant correlation among log
Ki values in these two effects (r2 ) 0.3187; p ) 0.06).
None of the analogues demonstrated appreciable affinity
at the norepinephrine transporter (all Ki values were
3; GBR 12909
318 ( 18
a
Ki values are the averages of 2-3 experiments, (SEM. Each
experiment was carried out in duplicate.
>1.3 µM). As demonstrated with the serotonin trans-
porter, no significant correlation among log Ki values
for binding to the dopamine and norepinephrine trans-
porters was apparent (r2 ) 0.2006; p ) 0.14).
Since rimcazole was first described as a σ ligand and
often as a σ antagonist,3-5 binding affinities at σ1 and
σ2 receptors were obtained for the analogues and
compared to the parent drug as well as GBR 12909 (3,
Table 2). At σ1 receptors, rimcazole (1) demonstrated a
Ki of 908 nM. Binding affinities were improved slightly
(∼2-fold) for compounds 7 and 10. A significant im-
provement in binding affinity was only achieved either
by replacing the carbazole with the diphenylamine
moiety (24 and 25, Ki ) 138 and 97 nM, respectively)
or by adding the 3-phenylpropyl group at the terminal
piperazine nitrogen (11 and 25, Ki ) 104 and 97 nM,
respectively). In comparison, GBR 12909 demonstrated
a binding affinity of 318 nM at σ1 sites. The other
rimcazole analogues that were evaluated were es-
sentially inactive at σ1 sites.
At σ2 receptors, rimcazole demonstrated a Ki of 302
nM. The range of Ki values from most potent (11, Ki )

SAR of a Novel Series of Rimcazole Analogues
J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 21 4451
145 nM) to least potent (6, Ki ) 1990 nM) was only ∼11-
fold. In essence, most of the analogues, regardless of
chemical modification, had very similar binding affini-
ties as compared to the parent drug. GBR 12909 (3) was
slightly more potent at σ2 sites (Ki ) 116 nM) than any
of the rimcazole analogues. Interestingly, affinities at
σ1 (r2 ) 0.5991; p ) 0.0144) and at σ2 (r2 ) 0.8023; p )
0.0011) were, in fact, significantly related to affinities
at the dopamine transporter, adding to the linkages
between σ receptors and the dopamine transporter that
have been described above.
transporter are responsible for the lack of cocaine-like
behavioral profiles for these compounds is underway.
Exp er im en ta l Section
All melting points were determined on a Thomas-Hoover
1
melting point apparatus and are uncorrected. The H and 13C
NMR data were recorded on a Bruker (Billerica, Mass) AC-
300 instrument. Samples were dissolved in an appropriate
deuterated solvent. Proton chemical shifts are reported as
parts per million (δ) relative to tetramethylsilane (Me4Si; 0.00
ppm) which was used as an internal standard. Carbon chemi-
cal shift values (δ) are reported in parts per million (ppm)
relative to deuterated chloroform (CDCl3; 77.0 ppm). Mass
spectra were recorded on a Hewlett-Packard (Palo Alto, CA)
5971A mass selective ion detector in the electron-impact mode
with sample introduction via a HP-5890 series II gas chro-
matograph fitted with an HP-1 (cross-linked methyl silicone
gum) 25 m × 0.2 mm i.d., 50 µm film thickness. Ultrapure
grade helium was used as the carrier gas at a flow rate of 1.2
mL/min. The injection port and transfer line temperatures
were 250 and 280 °C, respectively. The initial oven tempera-
ture was 100 °C, held for 3.0 min, programmed to 295 °C at
15.0 °C/min, and maintained at 295 °C for 10.0 min. Infrared
spectra were recorded on a Perkin-Elmer 1600 Series FTIR.
Microanalyses were performed by Atlantic Microlab, Inc.
(Norcross, GA) and agree within 0.4% of calculated values. All
column chromatography was performed in flash-grade silica
gel (230-400 mesh, 60 Å). All chemicals and reagents were
purchased from Aldrich Chemical Co. or Lancaster Synthesis,
Inc.
Su m m a r y
In summary, a series of rimcazole analogues have
been prepared where the effects of chemical modification
to the carbazole ring system and the terminal piperazine
nitrogen substituent were determined. The compounds
were evaluated for binding affinities at dopamine,
serotonin, and norepinephrine transporters as well as
at σ1 and σ2 receptors. In addition, compounds were
evaluated for inhibition of [3H]dopamine uptake, and
these data were positively correlated to their binding
affinities at the dopamine transporter. Structure-
activity relationships demonstrated that most aromatic
substitutions in the carbazole ring system decreased
binding affinity at the dopamine transporter. When the
carbazole ring system was replaced with the freely
rotating diphenylamine function, binding affinity was
slightly decreased. However, when this compound was
further modified with a phenylpropyl group at the
terminal piperazine nitrogen, the most potent compound
(25) in the series resulted. Structure-activity relation-
ships at the serotonin transporter were significantly
different from those observed at the dopamine trans-
porter in that modifications of the carbazole ring system
were better tolerated. In addition, the carbazole ring
was favored over the diphenylamine system in the
N-phenylpropyl substituted analogues, with the most
potent analogue being compound 11. None of the
compounds recognized the norepinephrine transporter
with affinities of <1.3 µM.
3,6-Dib r om o-9-[3-(cis-3,5-d im e t h yl-1-p ip e r a zin yl)-
p r op yl]ca r ba zole Hyd r och lor id e (5) a n d 1,3,6-Tr ibr om o-
9-[3-(cis-3,5-dim eth yl-1-piper azin yl)pr opyl]car bazole Hy-
d r och lor id e (6). To a solution of rimcazole (1) in glacial AcOH
(8 mL/mmol) were added H2O (7 mL/mmol), Br2 (14 drops/
mmol), and aqueous HBr (4 drops of 48%/mmol). The solution
was stirred for 72 h at room temperature, before being made
basic with NaHCO3 and extracting the organics into CHCl3.
Drying (Na2SO4) and evaporation gave the crude product.
Column chromatography (5% CHCl3/MeOH/NH4OH) gave both
compounds 5 (58%) at Rf 0.58 (10% CHCl3/MeOH/NH4OH) and
6 (26%) at Rf 0.62 (10% CHCl3/MeOH/NH4OH). The HCl salts
were formed by dissolving the respective free bases in metha-
nolic HCl. Recrystallization of the salts in MeOH gave the
products as white crystals. Compound 5: mp >250 °C; IR
1
(CHCl3) 732, 799 (Ph) cm-1; H NMR δ 1.02 (6H, d, J ) 6.5
Hz, 2 × CH3), 2.63 (2H, dd, J ) 11.1 and 1.9 Hz, 2 × CH),
2.94 (2H, m, 2 × CH), 4.36 (2H, t, J ) 6.5 Hz, CH2N), 7.35
(2H, d, J ) 8.8 Hz, H-1 aryl), 7.49 (2H, dd, J ) 8.8 and 2.1
Hz, H-2 aryl), 8.13 (2H, d, J ) 2.0 Hz, H-4 of aryl); 13C NMR
δ 20.0, 26.1, 41.0, 50.5, 55.0, 61.5, 110.2, 112.4, 124.8, 125.0,
128.2, 139.9; CI M+1 480. Anal. (C21H25N3Br2‚2HCl), C, H, N.
Although a clear structure-activity relationship pro-
file between the dopamine transporter and σ1 and σ2
receptors is not apparent, the positive correlations in
binding affinities, as well as previously reported over-
laps in actions of a variety of compounds at these sites,
are intriguing. Further examination of the relationship
between the dopamine transporter and σ sites and their
roles in modulating the behavioral actions of this class
of compounds is thus being pursued.
1
Compound 6: mp >250 °C; IR (CHCl3) 754 cm-1; H NMR δ
1.04 (6H, d, J ) 6.4 Hz, 2 × CH3), 2.69 (2H, d, J ) 9.1 Hz, 2
× CH), 2.89 (2H, m, 2 × CH), 4.73 (2H, t, J ) 7.2 Hz, CH2N),
7.41 (1H, d, J ) 8.8 Hz, o-H on mono-Br ring), 7.56 (1H, d, J
) 8.8 and 1.8 Hz, m-H on mono-Br ring), 7.73 (1H, d, J ) 1.8
Hz, m-H on mono-Br ring), 8.07 (1H, d, J ) 1.9 Hz, m-H on
di-Br ring), 8.09 (1H, d, J ) 1.9 Hz, m-H on di-Br ring); 13C
NMR δ 19.7, 28.1, 42.5, 50.5, 55.5, 60.5, 103.3, 111.8, 112.1,
113.3, 122.4, 123.53 126.8, 129.5, 133.6, 140.1. Anal. (C21H24N3-
Br3.2HCl‚0.5H2O), C, H, N.
In addition, behavioral evaluation of the most pro-
vocative analogues, 11 and 25, is currently being
conducted. We are interested in determining whether
these rimcazole analogues demonstrate a cocaine-like
profile, as does GBR 12909, or are different, as is the
parent compound rimcazole. Preliminary results in
behavioral studies suggest that rimcazole (1) and its
analogues 11 and 25 do not demonstrate cocaine-like
behavioral effects. These differences in actions, in
comparison to cocaine, may suggest alternative interac-
tions at the dopamine transporter, on a molecular
level.25,26 Further investigation into the possibility that
interactions at a low affinity site/state of the dopamine
3-Nitr o-9-[3-(cis-3,5-dim eth yl-1-piper azin yl)pr opyl]car -
ba zole Hyd r och lor id e (7). Rimcazole (1, 1.7 g, 5.3 mmol)
was dissolved in glacial AcOH (39 mL), and 70% HNO3 was
added dropwise (0.8 mL).20 A yellow precipitate started to form
immediately, and the solution was stirred overnight. The
mixture was then diluted with H2O (75 mL), and then 37%
HCl was added (2.8 mL). The aqueous layer was washed with
ether (2 × 30 mL) and then basified with NH4OH. The product
was extracted into CHCl3 (3 × 30 mL), dried (Na2SO4), and
evaporated to yield a red oil. The product was purified by
column chromatography (7% CHCl3/MeOH/NH4OH) to give
1.59 g (82%) as a yellow solid. Formation of the HCl salt and

4452 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 21
Husbands et al.
recrystallization from 2-PrOH yielded yellow crystals (55%):
mp >250 °C; Rf 0.43 (10% CHCl3/MeOH/NH4OH); H NMR δ
1.08 (6H, d, 2 × CH3), 2.70 (2H, d), 2.93 (2H, m), 4.44 (2H, t,
CH2N), 7.34 (1H, m), 7.53 (3H, m), 8.18 (1H, d, H m to NO2),
8.37 (1H, m, H o to NO2), 9.00 (1H, s, H o to NO2); FAB 367
(M++1). Anal. (C21H26N4O2‚HCl). C, H, N.
followed by addition of NaH (1.45 g: 60 mmol) and 15-crown-5
(1 mL, 5 mmol). After the mixture was stirred for 20 min at
room temperature, compound 12 (5.45 g, 25 mmol) was added,
and the mixture was warmed to reflux for 4 days. The reaction
was then cooled to room temperature and quenched with H2O.
The organics were extracted with CHCl3 (2 × 150 mL), dried
(Na2SO4), and evaporated to yield the crude product as a red
oil. Column chromatography (7% EtOAc in petroleum ether
35-60) gave 6.3 g (85%) of the product as a clear oil: 1H NMR
δ 1.52-1.89 (6H, m), 2.12 (2H, m), 3.26 (1H, m), 3.42 (1H, m),
3.81 (2H, t, J ) 7.3 Hz), 4.48 (3H, m), 7.22 (2H, m), 7.42 (4H,
m), 8.08 (2H, d, J ) 7.5 Hz); EI 309 (M+), 180 (M+, CH2CH2-
OTHP).
9-(1-Br om o-3-p r op yl)ca r ba zole (15). Deprotection of 14
was effected by dissolving 14 (6.3 g, 20 mmol) in an AcOH:
THF:H2O (75 mL:30 mL:15 mL) mixture and warming to 80
°C for 3 h. After this time, the solution was allowed to cool
and then was basified with NH4OH, and the organics were
extracted into CHCl3 (2 × 30 mL). The organic solution was
dried (Na2SO4) and evaporated to leave an orange oil that was
homogeneous by TLC and was used in the next step without
further purification. The deprotected alcohol (5.5 g, 24 mmol)
was dissolved in acetonitrile (70 mL), and triphenylphosphine
(9.7 g, 37 mmol) was added to the solution, followed by carbon
tetrabromide (12.4 g, 37 mmol). The solution was stirred at
room temperature for 2 h before basifying with 15% NaOH
(100 mL) and extracting the organics into ether (3 × 50 mL).
The combined organic fractions were washed with brine (1 ×
100 mL), dried (Na2SO4), and evaporated to give the crude
product as a red semisolid. The product was dissolved in ether,
and residual triphenylphosphine oxide was removed by filtra-
tion to give 11.3 g of crude product. Column chromatography
(10% EtOAc in hexane) yielded 7.1 g (99%) of a light green
oil: 1H NMR δ 2.38 (2H, M, CH2), 3.37 (2H, t, J ) 7.0 Hz,
NCH2), 4.49 (2H, t, J ) 7.2 Hz, BrCH2), 7.27 (2H, m), 7.47
(4H), m), 8.07 (2H, d, J ) 7.6 Hz); EI 287, 289 (M+, M+2),
180 (M+-CH2CH2Br).
9-[(4-P h en yl-1-p ip er a zin yl)p r op yl]ca r b a zole H yd r o-
br om id e (18). Compound 15 (1.4 g, 4.9 mmol) was dissolved
in a mixture of DMF (40 mL) and H2O (2 mL) and then
1-phenylpiperazine hydrochloride (16; 0.75 mL, 4.9 mmol) was
added, along with potassium carbonate (2.7 g, 20 mmol). The
solution was then warmed to 80 °C for 2h, by which time no
15 remained, by TLC. The mixture was diluted with H2O (100
mL), and the organics were extracted into ether/ethyl acetate
(2:1, 3 × 100 mL). The combined organic fraction was washed
with H2O (5 × 50 mL) and brine (1 × 50 mL), dried (Na2SO4),
and evaporated under reduced pressure to yield 1.34 g (74%)
as an oil. Column chromatography (5% CHCl3/MeOH/NH4OH)
gave the solid free base (540 mg) which was converted to the
HBr salt by adding saturated HBr in MeOH to a methanolic
solution of the free base, to pH 2. Recrystallization from
MeOH/ether gave the HBr salt as fine needles: mp >250 °C;
Rf 0.05 (10% EtOAc:petroleum ether); 1H NMR δ 2.08 (2H, m),
2.32 (2H, t, J ) 7.3 Hz), 2.56 (2H, m), 3.22 (2H, m), 4.40 (2H,
t, J ) 6.7 Hz), 6.90 (3H, m), 7.25 (4H, m), 8.10 (2H, d, J ) 7.6
Hz); 13C NMR δ 25.8, 40.4, 49.1, 53.0, 54.8, 108.7, 115.9, 118.7,
119.6, 120.2, 122.7, 125.4, 129.0, 140.4, 151.2; EI 369 (M+).
Anal. (C25H27N3 HBr) C, H, N.
9-[(4-[1-Ch lor op h e n yl]-1-p ip e r a zin yl)p r op yl]ca r b a -
zole Hyd r obr om id e (19). Compound 19 was prepared as
described for compound 18, using 3-chlorophenyl-1-piperazine
hydrochloride (17) to give 1.5 g (76%) crude product. Column
chromatography (5% CHCl3/MeOH/NH4OH) gave the free base
as an orange oil (820 mg) which was converted to the HBr
salt as described for compound 18; mp 230 °C; Rf 0.1 (10%
EtOAc:petroleum ether); 1H NMR δ 2.08 (2H, m), 2.37 (2H, t,
J ) 7.3 Hz), 2.55 (4H, m), 4.41 (2H, t, J ) 6.6 Hz), 6.08 (1H,
m), 7.05 (1H, m), 7.22 (3H, m), 7.34-7.50 (4H, m), 8.10 (2H,
d, J ) 7.6 Hz). Anal. (C25H26N3ClHBr) C, H, N.
1
3-Am in o-9-[3-(cis-3,5-d im eth yl-1-p ip er a zin yl)p r op yl]-
ca r ba zole Hyd r och lor id e (8). Compound 7 (900 mg, 2.46
mmol) was dissolved in MeOH (60 mL) and reduced under a
H2 atmosphere (35 psi) with a 10% Pd/C (150 mg) catalyst for
45 min. The mixture was filtered through Celite and evapo-
rated to yield the product as a brown foam. Purification by
column chromatography (5-10% CHCl3/MeOH/NH4OH) gave
550 mg (67%) as a cream colored solid: Rf 0.25 (10% CHCl3/
MeOH/NH4OH). The HCl salt was formed by dissolving 8 in
methanolic HCl and then recrystallized from MeOH/ether: mp
1
>250 °C; IR (CHCl3) 3424, 3354, 3213 (NH) cm-1; H NMR δ
1.04 (6H, d, J ) 6.4 Hz, 2 × CH3), 2.72 (2H, d, J ) 9.1 Hz, 2
× CH), 2.95 (2H, m, 2 × CH), 4.32 (2H, t, J ) 6.7 Hz, CH2N),
6.90 (1H, dd, J ) 6.6 and 2.1 Hz, aryl-H), 7.15 (1H, m, aryl-
H), 7.28 (1H, d, J ) 8.9 Hz, aryl-H), 7.40 (2H, m, aryl-Hs),
7.43 (1H, d, J ) 2.1 Hz, aryl-H), 7.98 (1H, d, J ) 7.7 Hz, aryl-
H); 13C NMR δ 19.9, 26.0, 40.0, 50.6, 55.2, 60.6, 106.2, 108.8,
109.4, 115.5, 118.1, 120.3, 125.4. Anal. (C21H28N4‚2HCl), C, H,
N.
3,6-Din itr o-9-[3-(cis-3,5-d im eth yl-1-p ip er a zin yl)p r op yl]-
ca r ba zole Hyd r och lor id e (9). Rimcazole (1; 0.31 g, 0.97
mmol) was dissolved in sulfuric acid (5 mL) and H2O (4 mL)
and cooled in an ice bath.20 Nitric acid (0.31 mL) was then
added slowly at which point the solution turned black. The
reaction mixture was allowed to warm to room temperature
and stirring was continued for 45 min. The solution was then
carefully basified using 10% NH4OH and the product extracted
into 5% MeOH in CHCl3 (2 × 30 mL). The organic layers were
then washed with brine (1 × 30 mL), dried (Na2SO4), and
evaporated to leave a dark gold foam (0.4 g). Column chro-
matography (6% CHCl3/MeOH/NH4OH) yielded the purified
product as a yellow solid. The HCl salt was formed by
dissolving the free base in MeOH and adding methanolic HCl
to pH 2. Recrystallization was carried out in H2O/2-PrOH (180
1
mg, 38%); Rf 0.33; mp >250 °C; H NMR δ 1.06 (6H, d, J )
6.4 Hz, 2 × CH3), 4.54 (2H, t, J ) 6.7 Hz, NCH2), 7.66 (2H, d,
J ) 9.2, 2 × m-H), 8.47 (2H, dd, J ) 9.2, 2.2 Hz, 2 × o-H),
9.09 (2H, d, J ) 2.2 Hz, 2 × o-H); 13C NMR δ 19.3, 25.3, 41.3,
50.4, 54.0, 50.0, 109.9, 117.5, 122.4, 122.5, 141.7, 144.8; EI 412
(M++1). Anal. (C21H25N5O4‚2HCl‚0.5H2O) C, H, N.
9-[3-(cis-3,5-Dim eth yl-4-[3-ph en ylpr opyl]-1-piper azin yl)-
p r op yl]ca r ba zole Hyd r obr om id e (11). Rimcazole (3) was
treated in the same manner as is described for compound 24
to give the intermediate amide (81%); Rf 0.95 (10% CHCl3/
MeOH/NH4OH); IR (CDCl3) 1725 cm-1; NMR (CDCl3) δ 1.41
(d, 6H), 1.97 (m, 4H), 2.28 (t, 2H), 2.68 (m, 4H), 2.97 (m, 2H),
4.42 (t, 2H), 7.25 (m, 7H), 7.43 (d, 4H), 8.14 (d, 2H). Reduction
of the amide with lithium aluminum hydride was conducted
in a manner identical to that described for compound 25 to
yield, after chromatography, 81% of the product. The HBr salt
was prepared by dissolving the free base in methanolic HBr
and recrystallizing from THF/ether: mp 179-181 °C; Rf 0.23;
IR (CHCl3) 749, 724, 699 (Ph) cm-1; 1H NMR δ 0.98 (6H, d, J
) 6.2 Hz, 2 × CH3), 4.37(2H, t, J ) 6.6 Hz, CH2N), 7.17-7.32
(9H, m, aryl-Hs), 7.45 (2H, m, aryl-Hs), 8.09 (2H, d, J ) 7.7
Hz, aryl-Hs); 13C NMR δ 18.0, 24.4, 25.9, 33.8, 40.6, 47.5, 53.6,
54.8, 61.3, 108.8, 118.7, 120.3, 122.8, 125.5, 125.8, 128.3, 128.3,
140.5, 142.0. Anal. (C30H37N3‚HBr), C, H, N.
1-Br om o-3-p r op yltetr a h yd r op yr a n ol (12). To a solution
of 3-bromo-1-propanol (9.08 g, 65 mmol) in CHCl3 (150 mL)
were added 3,4-dihydro-2H-pyran (5.45 g, 65 mmol) and a
catalytic amount of toluenesulfonic acid (100 mg) and the
mixture was allowed to stir at room temperature for 2 h. The
reaction mixture was washed with H2O (2 × 100 mL) and brine
(2 × 50 mL) and evaporated under reduced pressure to give
13.7 g (94%) of the product as a clear oil.
1-Tetr a h yd r op yr a n ol-3-p r op yld ip h en yla m in e (21). Di-
phenylamine (20; 2.70 g, 16 mmol) was dissolved in toluene
(100 mL) before adding NaH (0.8 g, 33 mmol) and 15-crown-5
(3.2 mL, 16 mmol). After 20 min at room temperature,
9-(1-Tetr a h yd r op yr a n ol-3-p r op yl)ca r ba zole (14). Car-
bazole (4.85 g, 30 mmol) was dissolved in toluene (150 mL)

SAR of a Novel Series of Rimcazole Analogues
J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 21 4453
compound 12 (3.0 g, 13 mmol) was added and the mixture
warmed to 90 °C for 4 h. The reaction was then cooled to room
temperature and then quenched with H2O. The organics were
extracted with CHCl3 (2 × 100 mL), dried (Na2SO4), and
evaporated to yield a red oil. Column chromatography (3%
EtOAc in petroleum ether 35-60) gave 2.0 g (48%) of the
product as an oil: Rf 0.8 (5% EtOAc in petroleum ether 35-
cooled (0 °C) mixture of lithium aluminum hydride (0.14 g,
3.69 mmol) in THF (5 mL). The mixture was then stirred at
room temperature overnight before quenching with solid
Rochelle salt. After being stirred for a further 15 min, the
mixture was diluted with H2O (15 mL) and the organics were
extracted into ethyl acetate (3 × 15 mL). This solution was
dried (Na2SO4) and evaporated to yield an orange oil. Column
chromatography (5% CHCl3/MeOH/NH4OH) gave 0.67 g (86%)
as a light yellow oil. The HCl salt was formed by dissolving
the free base in methanolic HCl and then recrystallized from
methanol/ether: mp 195 °C; Rf 0.15 (4% CHCl3/MeOH/NH4-
1
60); H NMR δ 1.5-1.9 (10H, m), 3.43 (2H, m), 3.82 (4H, m),
4.48 (1H, t, J ) 4.9 Hz), 6.91 (2H, t, J ) 7.5 Hz), 7.04 (4H, d,
J ) 7.6 Hz), 7.28 (4H, t, J ) 7.5 Hz); EI 311 (M+), 182 (M+-
CH2CH2OTHP).
1
OH); IR (CHCl3) 44, 697 (Ph) cm-1; H NMR δ 0.98 (6H, d, J
1-Dip h en yla m in o-3-p r op a n ol (22). Compound 21 (2.0 g:
6.4 mmol) was dissolved in a AcOH:THF:H2O (25 mL:13 mL:7
mL) mixture and warmed to 85 °C for 2.5 h. After this time,
the solution was allowed to cool and then basified with NH4-
OH and the organics were extracted into CHCl3 (2 × 30 mL).
The organic solution was dried (Na2SO4) and evaporated to
leave an orange oil, 1.4 g (100%), that was homogeneous by
TLC and was used in the next step without further purifica-
tion: Rf 0.15 (5% EtOAc in petroleum ether 35-60); IR (CHCl3)
3398 (OH) cm-1; 1H NMR δ 1.85 (2H, m), 3.72 (2H, t, J ) 7.1
Hz), 3.81 (2H, t, 7.1 Hz), 6.93 (2H, t, 7.4 Hz), 6.99 (4H, d, J )
7.5 Hz), 7.26 (2H, t, 7.4 Hz); EI 227 (M+), 182 (M+-CH2CH2-
OH).
) 6.2 Hz, 2 × CH3), 3.73 (2H, t, J ) 7.3 Hz, CH2N), 6.93 (2H,
t, J ) 7.3 Hz, 2 × H-4), 7.02 (4H, d, J ) 7.6 Hz, 2 × H-2 and
2 × H-6), 7.16-7.31 (9H, m, aryl-Hs); 13C NMR δ 17.8, 24.1,
25.0, 33.9, 47.3, 49.9, 53.4, 55.1, 61.3, 120.8, 121.0, 125.7, 128.2,
129.1, 142.1, 148.3. Anal. (C30H39N3‚2HCl‚0.5H2O) C, H, N.
P h a r m a cology. 1. Ch em ica ls. Chemicals and reagents
were obtained from the following sources: [3H]WIN 35,428 (2-
â-carbomethoxy-3-â-(4-flurophenyl)tropane 1,5-naphthalene
disulfonate; specific activity 84.5 Ci/mmol) from New England
Nuclear (NEN, Boston, MA); cocaine hydrochloride from Sigma
Chemical Co. (St. Louis, MO); [3H]paroxetine (specific activity
17 Ci/mmol, NEN); [3H]nisoxetine (specific activity 86 Ci/mmol,
NEN); [3H]dopamine (specific activity 50 Ci/mmol, Amersham);
[3H](+)-pentazocine (specific activity 51.7 Ci/mmol) was syn-
thesized as described previously;27 [3H]DTG (specific activity
35.2 Ci/mmol, NEN).
2. Dop a m in e Tr a n sp or ter Bin d in g Assa y. Male Spra-
gue-Dawley rats (200-250 g, Taconic, Germantown, NY) were
decapitated, and their brains were removed to an ice-cooled
dish for dissection of the caudate-putamen. The tissue was
homogenized in 30 volumes of ice-cold modified Krebs-HEPES
buffer (15 mM HEPES, 127 mM NaCl, 5 mM KCl, 1.2 mM
MgSO4, 2.5 mM CaCl2, 1.3 mM NaH2PO4, 10 mM glucose, pH
adjusted to 7.4) using a Teflon/glass homogenizer and centri-
fuged at 20000g for 10 min at 4 °C. The resulting pellet was
then washed two more times by resuspension in ice-cold buffer
and centrifugation at 20000g for 10 min at 4 °C. Fresh
homogenates were used in all experiments.
Binding assays were conducted in modified Krebs-HEPES
buffer on ice, essentially as previously described.16 The total
volume in each tube was 0.5 mL, and the final concentration
of membrane after all additions was approximately 0.3%
(w/v) corresponding to 150-300 µg of protein/sample. Increas-
ing concentrations of the drug being tested were added to
triplicate samples of membrane suspension. Five minutes
later, [3H]WIN 35,428 (final concentration 1.5 nM) was added,
and the incubation was continued for 1 h on ice. The incubation
was terminated by the addition of 3 mL of ice-cold buffer and
rapid filtration through Whatman GF/B glass fiber filter paper
(presoaked in 0.1% BSA in water to reduce nonspecific binding)
using a Brandel Cell Harvester (Gaithersburg, MD). After
filtration, the filters were washed with three additional 3 mL
washes and transferred to scintillation vials. Absolute ethanol
(0.5 mL) and Beckman Ready Value scintillation cocktail (2.75
mL) were added to the vials which were counted the next day
at an efficiency of about 36%. Under these assay conditions,
an average experiment yielded approximately 6000 dpm total
binding per sample and approximately 250 dpm nonspecific
binding. Nonspecific binding was defined as binding in the
presence of 100 µM cocaine. Ki values were derived from 14
point competition assays using increasing concentrations of
unlabeled compounds (0.05 nM to 100 µM) against 1.5 nM [3H]-
WIN 35,428. Displacement data were analyzed by the use of
the nonlinear least squares curve-fitting computer program
LIGAND.28
1-Br om o-3-p r op yld ip h en yla m in e (23). The deprotected
alcohol 22 (2.0 g, 8.8 mmol) was dissolved in acetonitrile (30
mL), and triphenylphosphine (3.5 g, 13.3 mmol) was added to
the solution, followed by carbon tetrabromide (4.4 g, 13.3
mmol). The solution was stirred at room temperature for 1 h
before basifying with 15% NaOH (30 mL) and extracting the
organics into ether (3 × 30 mL). The solution was dried (Na2-
SO4) and evaporated to give the crude product as a red oil.
Column chromatography (10% EtOAc in hexane) yielded 2.5
g (97%) of a light green oil: Rf 0.95 (10% EtOAc in hexane);
1
IR (CHCl3) 1249 (C-Br) cm-1; H NMR δ 2.24 (2H, m), 3.43
2H, t, J ) 7.0 Hz), 3.89 (2H, t, J ) 7.0 Hz), 7.08 (6H, m), 7.28
(4H, t, J ) 7.5 Hz); EI 290 (M+), 182 (M+-CH2CH2Br).
[3-(cis-3,5-Dim et h yl-1-p ip er a zin yl)p r op yl]d ip h en yl-
a m in e Oxa la te (24). Compound 23 (0.35 g: 1.21 mmol) was
dissolved in a mixture of DMF (10 mL) and H2O (0.5 mL) and
then 2,6-dimethylpiperazine (0.14 g, 1.21 mmol) was added,
along with K2CO3 (0.67 g, 4.84 mmol). The solution was then
warmed to 80 °C for 2h, at which time no 23 remained, by
TLC. The mixture was diluted with H2O (30 mL), and the
organics were extracted into CH2Cl2 (3 × 30 mL). Drying (Na2-
SO4), followed by evaporation, yielded an oil that contained
large amounts of DMF. Column chromatography (5% CHCl3/
MeOH/NH4OH) yielded 190 mg (41%) of 24 as an oily solid:
Rf 0.5 (10% CHCl3/MeOH/NH4OH). The oxalate salt of 24 was
formed by warming a solution of the free base with 2 equiv of
oxalic acid in EtOH. The salt was then recrystallized from
2-PrOH: mp 157-159 °C; IR (CHCl3) 3401 (NH), 748, 695 (Ph)
1
cm-1; H NMR δ 1.03(6H, d, J ) 6.3 Hz, 2 × CH3), 2.74 (2H,
d, J ) 9.5 Hz, 2 × CH of piperazine), 2.92 (2H, m, 2 × CH of
piperazine), 3.79 (2H, t, J ) 7.2 Hz, CH2N), 6.95 (2H, dd, J )
7.3 Hz, 2 × p-H), 7.02 (4H, d, J ) 7.6 Hz, 4 × o-H), 7.27 (4H,
t, J ) 7.5 Hz, 4 × m-H); 13C NMR δ 19.5, 24.6, 50.0, 50.7,
55.4, 60.3, 120.8, 121.0, 129.1, 147.9; EI 323 (M+). Anal.
(C21H29N3‚1.5oxalate) C, H, N.
[3-(cis-3,5-Dim eth yl-4-[3-p h en ylp r op yl]-1-p ip er a zin yl)-
p r op yl]d ip h en yla m in e Hyd r och lor id e (25). Hydrocinnam-
ic acid (0.52 g, 3.5 mmol) was dissolved in thionyl chloride (9
mL, 123 mmol) and the solution warmed to 50 °C for 90 min.
The excess thionyl chloride was then removed in vacuo, and
the residue (3-phenylpropionyl chloride) was taken up in
toluene (10 mL) and added to a solution of 24 (0.70 g, 2.12
mmol) in toluene (10 mL). The solution was heated to reflux
overnight, then washed with a 20% Na2CO3 solution (1 × 15
mL) and then brine (1 × 15 mL), and finally dried (Na2SO4).
Evaporation of the solvent yielded the crude amide as a dark
oil that was purified by column chromatography (5% CHCl3/
MeOH/NH4OH) to give 0.8 g (81%) of the amide as a light red
oil: IR (CHCl3) 1725 (CO) cm-1. The intermediate amide (0.80
g, 1.75 mmol) was dissolved in THF (5 mL) and added to a
3. Ser oton in Tr a n sp or ter Bin d in g Assa y. Brains from
male Sprague-Dawley rats weighing 200-225 g (Taconic
Labs) were removed, and the midbrain was dissected and
rapidly frozen. Membranes were prepared by homogenizing
tissues in 20 volumes (w/v) of 50 mM Tris containing 120 mM
NaCl and 5 mM KCl (pH 7.4 at 25 °C), using a Brinkman
Polytron (setting 6 for 20 s) and centrifuged at 50000g for 10

4454 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 21
Husbands et al.
min at 4 °C. The resulting pellet was resuspended in buffer,
recentrifuged, and resuspended in buffer to a concentration
of 15 mg/mL. Ligand binding experiments were conducted in
assay tubes containing 4.0 mL of buffer for 90 min at room
temperature. Each tube contained 0.2 nM [3H]paroxetine and
1.5 mg of midbrain tissue (original wet weight). Nonspecific
binding was determined using 1 µM citalopram. Incubations
were terminated by rapid filtration through Whatman GF/B
filters, presoaked in 0.05% polyethylenimine, using a Brandel
R48 filtering manifold (Brandel Instruments Gaithersburg,
Maryland). The filters were washed twice with 5 mL of cold
buffer and transferred to scintillation vials. Beckman Ready
Safe (3.0 mL) was added, and the vials were counted the next
day using a Beckman 6000 liquid scintillation counter (Beck-
man Coulter Instruments, Fullerton, CA). Data were analyzed
by using GraphPad Prism software (San Diego, CA).
4. Nor ep in ep h r in e Tr a n sp or ter Bin d in g Assa y. Brains
from male Sprague-Dawley rats weighing 200-225 g (Taconic
Labs) were removed, and the frontal cortex was dissected and
rapidly frozen. Membranes were prepared by homogenizing
tissues in 20 volumes (w/v) of 50 mM Tris containing 120 mM
NaCl and 5 mM KCl (pH 7.4 at 25 °C), using a Brinkman
Polytron (setting 6 for 20 s), and were centrifuged at 50000g
for 10 min at 4 °C. The resulting pellet was resuspended in
buffer, recentrifuged, and resuspended in buffer to a concen-
tration of 80 mg/mL. Ligand binding experiments were con-
ducted in assay tubes containing 0.5 mL of buffer for 60 min
at 0-4 °C. Each tube contained 0.5 nM [3H]Nisoxetine and 8
mg of frontal cortex tissue (original wet weight). Nonspecific
binding was determined using 1 µM desipramine. Incubations
were terminated by rapid filtration through Whatman GF/B
filters, presoaked in 0.05% polyethylenimine, using a Brandel
R48 filtering manifold (Brandel Instruments, Gaithersburg,
MD). The filters were washed twice with 5 mL of cold buffer
and transferred to scintillation vials. Beckman Ready Safe (3.0
mL) was added, and the vials were counted using a Beckman
6000 liquid scintillation counter (Beckman Coulter Instru-
ments, Fullerton, CA). Data were analyzed by using GraphPad
Prism software (San Diego, CA).
5. σ Recep tor Bin d in g Assa ys. σ1 Receptors were labeled
as described previously, using the σ1-selective probe [3H](+)-
pentazocine and guinea pig brain membranes.27 Guinea pig
brain membranes (350-500 µg of membrane protein) were
incubated with 3 nM [3H]-(+)-pentazocine in a total volume
of 0.5 mL of 50 mM Tris-HCl, pH 8.0. Incubations were carried
out for 120 min at 25 °C. Nonspecific binding was determined
in the presence of 10 µM unlabeled haloperidol. Assays were
terminated by dilution with 5 mL of ice-cold 10 mM Tris-HCl,
pH 8.0, and vacuum filtration through glass fiber filters using
a Brandel cell harvester (Gaithersburg, MD). Filters were then
washed twice with 5 mL of ice-cold 10 mM Tris-HCl, pH 8.0.
Filters were soaked in 0.5% polyethyleneimine for at least 30
min at 25 °C prior to use. Filters were counted in CytoScint
cocktail (ICN, Costa Mesa, CA) after an overnight extraction
of counts. Membranes were prepared from frozen guinea pig
brains (minus cerebella) as previously described.27 IC50 values
were determined using the iterative curve-fitting program
GraphPAD InPlot (San Diego, CA). IC50 values were then
converted to apparent Ki values using the Cheng-Prusoff
equation, and radioligand Kd values were determined previ-
ously.27,29
decapitation and their brains removed to an ice-cooled dish
for dissection of the caudate-putamen. [3H]Dopamine uptake
was measured in a synaptosomal preparation as described
previously.30 Briefly, the tissue was homogenized in ice-cold
buffer (320 mM sucrose, 5 mM HEPES salt, pH 7.4) followed
by centrifugation at 1000g for 10 min at 4 °C. The supernatant
was saved and spun in a centrifuge at 10000g for 20 min at 4
°C. The supernatant was discarded, and the pellet was
resuspended in cold modified Krebs-HEPES buffer (see above
for binding).
The synaptosomal tissue preparation was incubated in
buffer in glass test tubes at 37 °C to which either the drug
being tested or no drug was added, as appropriate. After a 5
min incubation period in the presence of drug, [3H]dopamine
(final concentration 15 nM) was added to each tube. After 5
min, the incubation was terminated by the addition of 2 mL
of ice-cold buffer to each tube and rapid filtration through
Whatman GF/B glass fiber filter paper (presoaked in 0.1%
polyethylenimine in water) using a Brandel cell harvester
(Gaithersburg, MD). After filtration, the filters were washed
with three additional 2 mL washes and transferred to scintil-
lation vials. Methanol (1 mL) and 0.2 M HCl (2 mL) were
added, and the vials were then heated at 70 °C for 2 h to
extract the accumulated [3H]dopamine. After cooling, 10 mL
of Ready Value scintillation cocktail were added, and radio-
activity was determined by liquid scintillation spectrometry
at an efficiency of approximately 30%. The reported values
represent specific uptake from which nonspecific uptake was
subtracted (defined as uptake in the presence of 100 µM
cocaine). Data were analyzed using the nonlinear regression
analysis of GraphPad Prism software (San Diego, CA).
Ack n ow led gm en t. We thank Dr. Gordon Hodgson
for providing insight on the structural analogues of
rimcazole that were synthesized at The Wellcome
Research Laboratories but remain unpublished. S.M.H.
was supported by a National Institutes of Health
visiting fellowship. Animals were cared for according
to the PHS guidelines and the NIH guide for the care
and use of laboratory animals.
Refer en ces
(1) Menkel, M.; Terry, P.; Pontecorvo, M.; Katz, J . L.; Witkin, J . M.
Selective σ ligands Block Stimulant Effects of Cocaine. Eur. J .
Pharmacol. 1991, 201, 251-252
(2) Ujike, H.; Kuroda, S.; Otsuki, S. σ Receptor Antagonists Block
the Development of Sensitization to Cocaine. Eur. J . Pharmacol.
1996, 296, 123-128.
(3) Ferris, R. M.; Harfenist, M.; McKenzie, G. M.; Cooper, B.; Soroko,
F. E.; Maxwell, R. A. BW 234U, (cis-9-[3-(3,5-dimethyl-1-
piperazinyl)propyl]carbazole dihydrochloride): a Novel Anti-
psychotic Agent. J . Pharm. Pharmacol. 1982, 34, 388-390.
(4) Ferris, R. M.; White, H. L.; Tang, F. L. M.; Russell, A.; Harfenist,
M. Rimcazole (BW 234U) Novel Antipsychotic Agent Whose
Mechanism of Action Cannot Be Explained by a Direct Blockade
of Postsynaptic Dopaminergic Receptors in Brain. Drug Dev. Res.
1986, 9, 171-188.
(5) Ferris, R. M.; Tang, F. L. M.; Chang, K.-J .; Russell, A. Evidence
that the Potential Antipsychotic Agent Rimcazole (BW 234U) is
a Specific, Competitive Antagonist of Sigma Sites in Brain. Life
Sci. 1986, 38, 2329-2337.
(6) Sharkey, J .; Glen, K. A.; Wolfe, S.; Kuhar, M. J . Cocaine Binding
to σ-Receptors. Eur. J . Pharmacol. 1988, 149, 171-174.
(7) van der Zee, P.; Koger, H. S.; Gootjes, J .; Hespe, W. Aryl 1,4-
dialk(en)ylpiperazines as Selective and Very Potent Inhibitors
of Dopamine Uptake. Eur. J . Med. Chem. 1980, 15, 363-370.
(8) Contreras, P. C.; Bremer, M. E.; Rao, T. S. GBR-12909 and
Fluspirilene Potently Inhibited Binding of [3H](+)3-PPP to
Sigma Receptors in Rat Brain. Life Sci. 1990, 47, PL-133-PL-
137.
(9) Matecka, D.; Rothman, R. B.; Radesca, L.; de Costa, B. R.;
Dersch, C. M.; Partilla, J . S.; Pert, A.; Glowa, J . R.; Wojnicki, F.
H. E.; Rice, K. C. Development of Novel, Potent and Selective
Dopamine Reuptake Inhibitors through Alteration of the Pip-
erazine Ring of 1-[2-(Diphenylmethoxy)ethyl]- and 1-[2-[Bis(4-
flurophenyl)methoxy]ethyl-4-(3-phenylpropyl)piperazines (GBR
12935 and GBR 12909). J . Med. Chem. 1996, 39, 4704-4716.
σ2 Receptors were labeled as previously described using rat
liver membranes, a rich source of σ2 sites, and [3H]1,3-di-o-
tolylguanidine ([3H]DTG) in the presence of 1 µM dextrallor-
phan to mask σ1 receptors.29 Assays were performed in 50 mM
Tris-HCl, pH 8.0, for 120 min at 25 °C in a volume of 0.5 mL
with 160 µg of membrane protein and 5 nM radioligand.
Assays included 1 µM dextrallorphan to mask σ1 binding.
Nonspecific binding was determined in the presence of 10 µM
haloperidol. All other manipulations were as described above
for the σ1 receptor assay. Rat liver membranes were prepared
from the livers of male Sprague-Dawley rats as previously
described.29
6. [3H]Dop a m in e Up ta k e Assa y. Rats were sacrificed by

SAR of a Novel Series of Rimcazole Analogues
J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 21 4455
(10) Matecka, D.; Lewis, D.; Rothman, R. B.; Dersch, C. M.; Wojnicki,
F. H. E.; Glowa, J . R.; DeVries, A. C.; Pert, A.; Rice, K. C.
Heteroaromatic Analogues of 1-[2-(Diphenylmethoxy)ethyl]- and
1-[2-[Bis(4-flurophenyl)methoxy]ethyl-4-(3-phenylpropyl)pipera-
zines (GBR 12935 and GBR 12909) as High Affinity Dopamine
Reuptake Inhibitors. J . Med. Chem. 1997, 40, 705-716.
(11) Kahoun, J . R.; Ruocho, A. E. [125I]Iodoazidococaine, a Photoaf-
finity Label for the Haloperidol-Sensitive Sigma Receptor. Proc.
Natl. Acad. Sci. U.S.A. 1992, 89, 1393-397.
(21) Madras, B. K.; Reith, M. E. A.; Meltzer, P. C.; Dutta, A. K. O-526,
a Piperidine Analogue of GBR 12909, Retains High Affinity for
the Dopamine Transporter in Monkey Caudate-Putamen. Eur.
J . Pharmacol. 1994, 267, 167-173.
(22) Rothman, R. B.; Becketts, K. M.; Radesca, L. R.; de Costa, B.
R.; Rice, K. C.; Carroll, F. I.; Dersch, C. M. Studies of the
Biogenic Amine Transporters. II. A Brief Study on the Use of
[3H]DA-Uptake-inhibition to Transporter-binding-inhibition Ra-
tios for the in vitro Evaluation of Putative Cocaine Antagonists.
Life Sci. 1993, 53, PL 267-272.
(23) Newman, A. H.; Allen, A. C.; Izenwasser, S.; Katz, J . L. Novel
3R-Diphenylmethoxytropane Analogues are Potent Dopamine
Uptake Inhibitors without Cocaine-like Behavioral Profiles. J .
Med. Chem. 1994, 37, 2258-2261.
(24) Katz, J . K.; Izenwasser, S., Kline, R. H., Allen, A. C.; Newman,
A. H. Novel 3R-Diphenylmethoxytropane Analogues: Selective
Dopamine Uptake Inhibitors with Behavioral Effects Distinct
from those of Cocaine. J . Pharmacol. Exp. Ther. 1999, 288, 302-
315.
(25) Katz, J . L.; Izenwasser, S.; Newman, A. H. Relations Between
Heterogeneity of Dopamine Transporter Binding and Function
and the Behavioral Pharmacology of Cocaine. Pharmacol. Bio-
chem. Behav. 1997, 57, 505-512.
(26) Vaughan, R. A.; Agoston, G. E.; Lever, J . R.; Newman, A. H.
Differential Binding Sites of Tropane-Based Photoaffinity Ligands
on the Dopamine Transporter. J . Neurosci. 1999, 19, 630-636.
(27) Bowen, W. D.; de Costa, B. R.; Hellewell, S. B.; Walker, J . M.;
Rice, K. C. [3H](+)-Pentazocine: A potent and highly selective
benzomorphan-based probe for sigma-1 receptors. Mol. Neurop-
harmacol. 1993, 3, 117-126.
(28) Munson, P. J .; Rodbard, D. Ligand: A Versatile Approach for
Characterization of Ligand-binding Systems. Anal. Biochem.
1980, 107, 220-239.
(12) McCracken, K. A.; Bowen, W. D.; Matsumoto, R. R. Novel sigma
receptor ligands attenuate the locomotor and stimulatory effects
of cocaine. Eur. J . Pharmacol. 1999, 365, 35-38.
(13) McCracken, K. A.; Bowen, W.; D.; de Costa, B. R.; Matsumoto,
R. R. Two novel sigma receptor ligands, BD1047 and LR172,
attenuate cocaine-induced toxicity and locomotor activity. Eur.
J . Pharmacol. 1999, 370, 225-232.
(14) Izenwasser, S.; Newman, A. H.; Katz, J . L. Cocaine and Sigma
Ligands Inhibit Dopamine Uptake via a Common Low Affinity
Site in the Rat Caudate-putamen. Eur. J . Pharmacol. 1993, 243,
201-205.
(15) Madras, B. K.; Spealman, R. D.; Fahey, M. A.; Neumeyer, J . L.
Saha, J . K.; Milius, R. A. Cocaine Receptors Labeled by [3H]2â-
Carbomethoxy-3â-(4-fluorophenyl)tropane. Mol. Pharmacol. 1989,
36, 518-524.
(16) Izenwasser, S.; Rosenberger, J . G.; Cox, B. M. The Cocaine
Analogue WIN 35,428 Binds to Two Sites in Fresh Rat Caudate-
putamen: Significance of Assay Procedures. Life Sci./ Pharma-
col. Lett. 1993, 52, PL 141-145.
(17) Husbands, S. M.; Izenwasser, S.; Loeloff, R. J .; Katz, J . L.;
Bowen, W. D.; Vilner, B. J .; Newman, A. H. Irreversible
Analogues of Rimcazole: Novel Probes for the Dopamine Trans-
porter. J . Med. Chem. 1997, 40, 4340-4346.
(18) Izenwasser, S.; Terry, P.; Heller, B.; Witkin, J . M.; Katz, J . L.
Differential relationships among dopamine transporter affinities
and stimulant potencies of various uptake inhibitors. Eur. J .
Pharmacol. 1994, 263, 277-283.
(19) Katz, J . L.; Izenwasser, S.; Terry, P. Relationships among
dopamine transporter affinities and cocaine-like discriminative
stimulus effects. Psychopharmacology 1999, in press.
(20) Rehavi, M.; Ittah, Y.; Skolnick, P.; Rice, K. C.; Paul, S. M.
Nitroimipramines - Synthesis and Pharmacological Effects of
Potent Long-Acting Inhibitors of [3H]Serotonin Uptake and [3H]-
Imipramine Binding. Naunyn-Schmiedeberg’s Arch. Pharmacol.
1982, 320, 45-49.
(29) Hellewell, S. B.; Bruce, A.; Feinstein, G.; Orringer, J .; Williams,
W.; Bowen, W. D. Rat liver and kidney contain high densities of
sigma-1 and sigma-2 receptors: Characterization by ligand
binding and photoaffinity labeling. Eur. J . Pharmacol. - Mol.
Pharmacol. Sect. 1994, 268, 9-18.
(30) Izenwasser, S.; Rosenberger, J . G.; Cox, B. M. Inhibition of [3H]-
Dopamine and [3H]Serotonin Uptake by Cocaine: Comparison
Between Chopped Tissue Slices and Synaptosomes. Life Sci.
1992, 50, 541-547.
J M9902943