Expansion of structure-activity studies of piperidine analogues of 1-[2-(diphenylmethoxy)ethyl]-4-(3-phenylpropyl)piperazine (GBR 12935) compounds by altering substitutions in the N-benzyl moiety and behavioral pharmacology of selected molecules

Article abstract of DOI:10.1021/jm010316x

A series of substituted N-benzyl analogues of the dopamine transporter (DAT) specific compound, 4-[2-(diphenylmethoxy)ethyl]-1-benzylpiperidine were synthesized and biologically characterized. Different 4′-alkyl, 4′-alkenyl, and 4′-alkynyl substituents were introduced in the phenyl ring of the benzyl moiety along with the replacement of the same phenyl ring by the isomeric α- and β-naphthyl groups. Different polar substitutions at the 3′- and 4′-position were also introduced. Novel compounds were tested for their binding affinity at the dopamine, serotonin, and norepinephrine transporter systems in the brain by competing for [³H]WIN 35 428, [³H]citalopram, and [³H]nisoxetine, respectively. Selected compounds were also evaluated for their activity in inhibiting the uptake of [³H]dopamine. Binding results demonstrated that alkenyl and alkynyl substitutions at the 4′-position produced potent compounds in which compound 6 with a vinyl substitution was the most potent. In vivo evaluation of three selected compounds indicated that despite their high potency at the DAT, these compounds stimulated locomotor activity (LMA) less than cocaine when tested across similar dose ranges. In a drug discrimination study procedure, none of these three compounds generalized from cocaine in mice trained to discriminate 10 mg/kg cocaine from vehicle. In a 4 h time course LMA experiment, one of our previous lead piperidine derivatives (1a) showed considerable prolonged action. Thus, in this report, we describe a structure-activity relationship study of novel piperidine analogues assessed by both in vitro transporter assays and in vivo behavioral activity measurements.

Full text of DOI:10.1021/jm010316x

654
J . Med. Chem. 2002, 45, 654-662
Exp a n sion of Str u ctu r e-Activity Stu d ies of P ip er id in e An a logu es of
1-[2-(Dip h en ylm eth oxy)eth yl]-4-(3-p h en ylp r op yl)p ip er a zin e (GBR 12935)
Com p ou n d s by Alter in g Su bstitu tion s in th e N-Ben zyl Moiety a n d Beh a vior a l
P h a r m a cology of Selected Molecu les
Aloke K. Dutta,*,† Matthew C. Davis,†,‡ Xiang-Shu Fei,† Patrick M. Beardsley,§ Charles D. Cook,§ and
Maarten. E. A. Reith|
Department of Pharmaceutical Sciences, Wayne State University, Detroit, Michigan 48202, Virginia Commonwealth University,
Richmond, Virginia, and Department of Biomedical and Therapeutic Sciences, College of Medicine, University of Illinois,
Peoria, Illinois 61605
Received J uly 10, 2001
A series of substituted N-benzyl analogues of the dopamine transporter (DAT) specific
compound, 4-[2-(diphenylmethoxy)ethyl]-1-benzylpiperidine were synthesized and biologically
characterized. Different 4′-alkyl, 4′-alkenyl, and 4′-alkynyl substituents were introduced in
the phenyl ring of the benzyl moiety along with the replacement of the same phenyl ring by
the isomeric R- and â-naphthyl groups. Different polar substitutions at the 3′- and 4′-position
were also introduced. Novel compounds were tested for their binding affinity at the dopamine,
serotonin, and norepinephrine transporter systems in the brain by competing for [3H]WIN 35
428, [3H]citalopram, and [3H]nisoxetine, respectively. Selected compounds were also evaluated
for their activity in inhibiting the uptake of [3H]dopamine. Binding results demonstrated that
alkenyl and alkynyl substitutions at the 4′-position produced potent compounds in which
compound 6 with a vinyl substitution was the most potent. In vivo evaluation of three selected
compounds indicated that despite their high potency at the DAT, these compounds stimulated
locomotor activity (LMA) less than cocaine when tested across similar dose ranges. In a drug
discrimination study procedure, none of these three compounds generalized from cocaine in
mice trained to discriminate 10 mg/kg cocaine from vehicle. In a 4 h time course LMA
experiment, one of our previous lead piperidine derivatives (1a ) showed considerable prolonged
action. Thus, in this report, we describe a structure-activity relationship study of novel
piperidine analogues assessed by both in vitro transporter assays and in vivo behavioral activity
measurements.
In tr od u ction
relates to its reinforcing effects.11 In another recent
study, the DA hypothesis for cocaine’s reinforcing effects
was further strengthened by the demonstration that in
DAT KO mice cocaine and amphetamine increase ex-
tracellular DA in the nucleus accumbens but not in the
caudate putamen.12 This observation perhaps explains
the results of a recent experiment showing self-
administration of cocaine by DAT KO mice13 as cocaine
will still block norepinephrine transporter (NET), which
is known to accumulate DA efficiently,14 in DAT KO
mice in nucleus accumbens and, thus, will increase the
extracellular concentration of DA.15 These results sup-
port a drug development approach targeting the dopa-
minergic system as a viable avenue to develop medica-
tions for cocaine addiction.16
Cocaine is a naturally occurring molecule that is well-
known for its strong reinforcing and abuse potential.1,2
The development of treatments for cocaine abuse is
urgently required. A number of approaches have been
taken to develop medications for cocaine addiction.3,4
Cocaine binds to all three monoamine neurotransporter
systems in the brain.5 It is now well-established that
binding of cocaine to the dopamine (DA) transporter
(DAT), resulting in decreased clearance of neuronally
released DA, is responsible for its strong reinforcing
effects.6,7 The DA hypothesis of cocaine addiction was
further supported by a series of in vivo experiments and
also from molecular biology studies involving a DAT
knockout (KO) mice model.8-10 Thus, binding potencies
of DA receptor agonist and DAT specific compounds
correlated very well with their relative reinforcing
effects in animal experiments.7,9 In a microdialysis
experiment, it was demonstrated that cocaine increases
DA preferentially in the nucleus accumbens and this
Different classes of molecules have been developed for
the DAT with an aim to modulate the action of cocaine.
These molecules represent a wide variety of structurally
diverse ligands with selective affinity for the DAT.17,18
Our ongoing structure-activity relationship (SAR) stud-
ies with piperidine derivatives of modified GBR 12909
(1-[2-[bis(4-fluorophenyl)methoxy]ethyl]-4-(3-phenylpro-
pyl)piperazine, 2b) developed many potent and selective
compounds for the DAT.19-23 Many of these molecules
are more selective than GBR 12909 (2b) and 12935 (1-
[2-(diphenylmethoxy)ethyl]-4-(3-phenylpropyl)pipera-
* To whom correspondence should be addressed. Tel: 1-313-577-
1064. Fax: 1-313-577-2033. E-mail: adutta@wizard.pharm.wayne.edu.
† Wayne State University.
‡ Current address: Naval Air Warfare Center, Code 4T4200D, China
Lake, CA 93555.
§ Virginia Commonwealth University.
| University of Illinois.
10.1021/jm010316x CCC: $22.00 © 2002 American Chemical Society
Published on Web 12/21/2001

Structure-Activity Studies of Piperidine Analogues
J ournal of Medicinal Chemistry, 2002, Vol. 45, No. 3 655
Ch a r t 1
validity of this approach was successfully tested in the
treatment of heroin addiction by longer-acting metha-
done.39 DAT selective GBR derivatives demonstrated a
longer duration of action, and recently, a longer-acting
decanoate ester of 2b was shown to decrease cocaine
self-administration in a sustained manner without
affecting food intake.40,41 In our own study, some of our
previous lead compounds showed considerable prolong
duration of action and were much longer than cocaine
in this respect. A detailed study on one of our com-
pounds is included here.
In our previous SAR studies, we have shown that the
presence of electronegative and electron-withdrawing
groups in the aromatic ring of the N-benzyl moiety had
a significant influence on binding to the DAT. This
indicated an important effect of the nature of N-benzyl
moiety substitution in activity and selectivity. In our
current study, we wanted to explore the effect of
different alkyl, alkene, and alkyne substitutions on the
phenyl ring of the N-benzyl group and also the replace-
ment of the phenyl moiety by isomeric naphthyl groups.
In addition, polar hydroxy groups and lipophilic iodine
substitutions were also introduced. Such structural
transformations resulted in the production of com-
pounds with varied lipophilicity, electronic characters,
and steric environments. Our objectives were to char-
acterize the effect of these physicochemical parameters
on binding activity with selected compounds on in vivo
activity.
Ch em istr y. The starting amine (3) intermediate was
converted into iodo compound 4 (see Scheme 1) by
reacting with benzyl iodide in the presence of a base.
Similarly, compounds 3a -d were produced in 80-95%
yield by an N-alkylation reaction involving compound
3 with appropriate halides in the presence of a base.
This synthetic avenue provided an easy access to our
final targets.
Next, compound 4 was used as a starting precursor
for the preparation of compounds 5-8 by reacting with
appropriate organometallic reagents in the presence of
a palladium catalyst as carried out by Blough et al.42
Thus, Stille-coupling of 4 with tributyl(ethynyl)tin or
tributyl(vinyl)tin in the presence of palladium(0) cata-
lyst in refluxing toluene yielded 5 or 6 in 80-90%
yield.43 The in situ prepared (isopropenyl)zinc chloride
was reacted with 4 in the presence of dichlorobis-
(triphenylphosphine) palladium(II) to provide 7 in 40%
yield. Last, compound 8 (see Scheme 2) was synthesized
zine, 2a ) (Chart 1).24 Most importantly, the selectivity
of these compounds was exhibited in a pharmacophoric
requirement that is different from the conventional GBR
molecules.25 This led us to speculate the involvement
of different binding modes for these novel piperidine
analogues as compared to the conventional GBR com-
pounds. This notion was further supported by our recent
experiment with a novel photoaffinity ligand that was
developed based on our piperidine analogue.26,27 This
novel DAT specific photoaffinity ligand was shown to
incorporate equally well into the two different domains
of the 12-transmembrane domain (Tms) DAT primary
sequence, an N-terminal site containing Tms 1-2 and
a second site containing Tms 4-6.27 This result is in
sharp contrast to the binding profiles of the other known
photoaffinity ligands belonging to either the tropane or
the GBR class of compounds, which showed specific
labeling preferentially to one of those above two sites.28,29
The dual hybrid binding profile of the piperidine-based
photoaffinity ligand with the DAT indicates the pres-
ence of an unique binding profile that is different from
the conventional GBR compound.
Our current photoaffinity ligand binding results are
also supportive of the ongoing contention that different
structural classes of DAT blockers possess nonidentical
overlapping binding domains.30,31 These nonidentical
binding interactions are also reflected in their dif-
ferential in vivo activity as overlapping or different
binding domains may lead to changes in transporter
function.32,33 This is evident in the case of some tropane
analogues and GBR derivatives that share somewhat
identical binding potencies but quite different in vivo
activity.34a-b Furthermore, cocaine and DA binding sites
were shown to involve different amino acid residues on
the DAT molecule as demonstrated in mutant DAT
molecular experiments.35,36 This raises the possibility
of developing agents selectively targeting the cocaine
binding site but sparing the DA reuptake site, which
can potentially give rise to a possible cocaine antagonist.
In another scenario, compounds that interact with both
cocaine and DA binding sites on the DAT, either par-
tially or completely, may potentially give rise to dif-
ferent degrees of indirect partial agonist or full agonist
properties.
Sch em e 1
Another important aspect considered in medications
development is the duration and onset of action of
potential agonists or partial agonists. It is expected that
a medicating agent with a long duration of action and
slower onset will have less abuse liability as compared
to a powerful reinforcer like cocaine, which has a much
faster onset and shorter duration of action.37,38 The

656 J ournal of Medicinal Chemistry, 2002, Vol. 45, No. 3
Dutta et al.
Sch em e 2
Sch em e 3
iodo derivative for the DAT (IC50, DAT ) 0.96 nM,
serotonin (SERT)/DAT ) 3041). In fact, compound 4
turned out to be among the few known compounds with
a high potency (IC50 of <1 nM) that is also highly
selective for the DAT (SERT/DAT > 2000).18 The activ-
ity of this compound is interesting considering the fact
that the activities of the other corresponding halides
from our previous studies, with the exception of a fluoro
derivative, were less active. This might be due to the
fact that the introduction of a large iodo atom can
potentially induce larger changes in steric and lipophilic
environments as compared to other halide analogues
resulting in favorable interaction.
by coupling 4 and 1-(trimethylsilyl)-1-propyne mediated
by fluoride ion and palladium catalyst. This was similar
to a previous method, although palladium(0) was used.44
Reductive amination of the intermediate 3 with the
appropriate hydroxy-benzaldehyde produced compounds
9 and 10 in good yield (see Scheme 3).
In our next series of compounds, various 4′-alkyl-, 4′-
alkenyl-, and 4′-alkynyl-substituted phenyl derivatives
were synthesized. In these derivatives, we wanted to
explore the effects of steric, lipophilic, and electronic
environments arising from these substituents on activ-
ity. In this regard, similar studies were evaluated with
the tropane class of compounds, which yielded 3â-phenyl
derivatives where some of them exhibited high potencies
for both DAT and SERT.42 We wanted to compare the
activities of our derivatives with those of tropane
analogues. Our SAR studies demonstrated that moder-
ately bulky isopropyl substitution as in compound 3d
was tolerated well and was quite active. The introduc-
tion of unsaturated substituents in the forms of alkenyes
and alkynyes derivatives maintained a strong potency
and selectivity for the DAT in most part. Compounds 5
and 6 with acetylinic and vinylic groups were the most
active for the DAT (IC50 4.10 and 2.96 nM, respectively)
whereas isopropenyl analogue 7 was slightly less active
as compared to 6 (IC50 11.6 vs 2.96 nM). The activity
profile of these derivatives is somewhat different from
the corresponding tropane derivatives as some of the
tropane derivatives exhibited equipotencies for the DAT
and the SERT. In contrast, all of the present substituted
Resu lts a n d Discu ssion
In our current SAR studies, we focused on structural
changes on the N-substituted benzyl moiety part of our
piperidine analogues. In this respect, we concentrated
on introducing different alkyl, alkenyl, and alkynyl
substitutions at the 4′-position of the phenyl ring along
with the introduction of polar substitutions such as
methoxy and hydroxy groups thereby altering lipophilic,
steric, and electronic environments in these novel
analogues. In addition, we also introduced in our series
of compounds isomeric naphthyl substitutions by re-
placing the phenyl ring of the benzyl moiety, which also
resulted in considerable changes of steric and lipophilic
environments.
The novel iodo analogue 4, which was used as a
precursor for the synthesis of alkene and alkyne deriva-
tives, was tested for its activity. The results demon-
strated very high potency and extreme selectivity of this

Structure-Activity Studies of Piperidine Analogues
J ournal of Medicinal Chemistry, 2002, Vol. 45, No. 3 657
Ta ble 1. Affinity of Drugs at the DAT, SERT, and NET in Rat Striatum and in Inhibition of DA Reuptake
DAT, IC50, nM,
SERT, IC50, nM,
[3H]citaloprama
NET, IC50, nM,
[3H]nisoxetinea
[3H]DA uptake
compd
cocaine
[3H]WIN 35, 428a
inhibition,IC50, nMa
266 ( 37
737 ( 160
132 ( 0
3,530 ( 554
496 ( 22
GBR 12909 (2b)
10.6 ( 1.9
4.50 ( 0.64b
8.23 ( 5.49
113 ( 5
6.63 ( 0.43
20.6 ( 2.5
1.94 ( 0.31
1a
3a
3b
3c
3d
3e
4
5
6
7
8
1560 ( 210
924 ( 100
4160 ( 900
856 ( 210
1540 ( 240
1080 ( 260
2920 ( 430
1040 ( 160
1470 ( 350
1030 ( 90
2410 ( 510
4330 ( 750
984 ( 94
2620 ( 170
1490 ( 60
393 ( 66
1060 ( 240
472 ( 94
26.9 ( 3.0
63.1 ( 11.2
19.6 ( 2.6
0.96 ( 0.16
4.10 ( 1.30
2.96 ( 0.61
11.6 ( 1.8
65.1 ( 15.0
240 ( 15
6.68 ( 1.14
2.01 ( 0.64
4.81 ( 1.16
1.08 ( 0.28
3.10 ( 1.12
1150 ( 120
760 ( 212
715 ( 37
832 ( 28
1170 ( 120
3340 ( 760
678 ( 37
9
10
14.3 ( 3.7
10.4 ( 2.2
a
The DAT was labeled with [3H]WIN 35, 428, the SERT with [3H]citalopram, and the NET with [3H]nisoxetine. Results are the average
b
( SEM of three independent experiments assayed in triplicates. See ref 23.
Ta ble 2. Selectivity of Various Ligands for Their Activity at
identical in the uptake and binding measurements.
Monoamine Transporters
SERT
Compounds 5, 7, and 10 were chosen for further
evaluation in in vivo studies. As a part of our goal to
develop long-acting molecules for the treatment of
cocaine addiction, we additionally evaluated one of our
previous lead compounds, 1a , in extended 4 h locomotor
tests and compared it to cocaine.23
NET
[3H]DA
binding/DAT binding/DAT uptake/DAT
compd
binding
binding
47
binding
GBR 12909 (2b)
12
110
37
32
24
0.62
0.23
3a
3b
3c
3d
3e
4
5
6
7
13
15
17
As shown in Figure 1, cocaine and GBR 12909 (2b)
produced dose-dependent increases in total distance
travelled with significant increases relative to the
vehicle control obtained at doses of 10 and 30 mg/kg.23
These data are presented for comparison purposes and
were taken from a previous study.23 Across the dose
range tested, compound 10 failed to alter locomotor
55
24
0.34
2.1
1.2
0.36
0.26
3040
250
500
88
1200
180
240
72
8
37
18
9
18
14
activity (LMA) relative to the vehicle controls (F3,28
)
10
69
47
0.72
1.50, P > 0.05). The overall analysis of variance
(ANOVA) for compound 5 was significant (F4,35 ) 3.92,
P < 0.05); however, Dunnett’s post-hoc tests indicated
that doses of this compound were not significantly
different from the vehicle control. The overall ANOVA
for compound 7 was significant (F3,28 ) 4.00, P < 0.05),
with doses of 10 and 30 mg/kg significantly increasing
total distance traveled relative to the vehicle control.
The maximal increase in activity produced by compound
7 was approximately 170% of the vehicle control,
whereas cocaine (30 mg/kg) produced maximal increases
of approximately 450% of the vehicle control.
analogues maintained high selectivity for the DAT.
Interestingly, it was observed that the terminal H-atom
in the acetylinic group of 5 is necessary for potent
activity as the replacement of it by a methyl group led
to a weaker congener (8, IC50 65 vs 4.10 nM). The
apparent loss of high potency may be due to the
presence of a methyl group imposing steric bulk in the
interaction or absence of a relatively acidic acetylinic
H-atom. In general, unsaturated alkenyl and alkynyl
substitutions were more potent than a simple alkyl
substitution.
Figure 2 shows the 4 h time course LMA experiment.
A repeated measures ANOVA indicated a main effect
for dose (F2,20 ) 8.56, P < 0.05) and a dose by time
interaction (F46,460 ) 19.23, P < 0.05). Examination of
the effect of dose within each 10 min interval indicated
that cocaine produced stimulant effects greater than the
vehicle during intervals 1-7 (P < 0.05). Compound 1a
also produced stimulant effects greater than the vehicle
during intervals 6 and 7 (P < 0.05). Stimulant effects
(relative to vehicle) were observed with compound 1a
during intervals 9-24 (P < 0.05), whereas cocaine
produced effects similar to the vehicle (P > 0.05). In our
earlier report, this compound was described as exhibit-
ing a locomotor depressant effect when studied within
a 1 h time period.23 The depressant effect was more
pronounced at a higher dose (100 mg/kg). Because a
longer duration LMA effect for this compound was not
evaluated previously, we now wanted to observe this
effect at a single dose.
We observed differential activities in the isomeric (R
and â) naphthalene derivatives (3b and c), which might
reflect an important contribution of electrostatic inter-
action differently contributed by these two isomeric
compounds. â-Naphthalene substitution was found to
be more active for the DAT as compared to R-naphtha-
lene (IC50 26.9 vs 113 nM). In our final molecular design,
the introduction of polar groups as in compounds 3e, 9,
and 10 produced a mixture of activities in these mol-
ecules. Compound 3e and its demethylated analogue 10
were active, but interestingly, the 4-hydroxy analogue
9 was not active.
Potent selected compounds were next tested for their
activity in inhibiting the DA reuptake process. Overall
uptake and binding correlated quite well, with uptake
and binding values being less than 4-fold different. The
general tendency for higher uptake than binding activity
could be a reflection of assay conditions that were not

658 J ournal of Medicinal Chemistry, 2002, Vol. 45, No. 3
Dutta et al.
F igu r e 1. Effects of cocaine, GBR 12909 (2b), and compounds
10 (n ) 8), 5 (n ) 8), and 7 (n ) 8) on total distance traveled
(cm) in mice during a 60 min test session expressed as a
percentage of each individual drug’s vehicle control. Brackets
indicate SEM; where not indicated, the SEM fell within the
data point. * ) P e 0.05 relative to saline control. LMA data
for cocaine were taken from Dutta et al. (2001) and are
presented for comparison.
F igu r e 3. Top frames: effects of cocaine (n ) 12) and com-
pounds 10 (n ) 6), 5 (n ) 6), and 7 (n ) 7) on the percentage
of lever presses emitted upon the cocaine-associated lever and
rate of responding in mice trained to discriminate 10 mg/kg
cocaine from saline. Brackets indicate SEM; where not indi-
cated, the SEM fell within the data point. Bottom frames:
response rate expressed as mean lever presses per second.
Each symbol represents the mean number of lever presses
emitted during the 15 min test session. Brackets indicate SEM.
F igu r e 2. Locomotor time-course effects for vehicle, 30 mg/
kg cocaine, and 30 mg/kg compound 1a over the 240 min (4 h)
test session.
Test compounds were administered prior to the start
of the discrimination test sessions coinciding with times
of obvious activity indicated during LMA tests. Ad-
ditionally, we tested all compounds with doses in which
at least one dose decreased response rates suggesting
that the tested dose ranges included behaviorally active
doses. As shown in Figure 3, cocaine produced dose-
dependent increases in cocaine lever responding. The
rate of responding was decreased by approximately 50%
relative to saline control levels at the highest dose of
cocaine tested (30 mg/kg). Both compounds 10 and 5
maximally produced 30% cocaine lever responding. At
a dose of 75 mg/kg of compound 10, two mice responded
40 and 56% on the cocaine lever, whereas in one mouse
87% cocaine lever responding was obtained. In the
remaining three mice, cocaine lever responding was less
than 3%. At a dose of 100 mg/kg of compound 5, two
mice responded greater than 90% on the cocaine lever,
whereas the remaining four mice responded less than
2% on the cocaine lever. Across the doses tested, 7
produced mainly saline lever responding. With com-
pounds 10, 5, and 7, the rate of responding was slightly
depressed at the highest dose tested. Thus, our in vivo
results indicated that the relatively nonpolar alkenyl-
and alkynyl-substituted compounds 5 and 7 were more
active in locomotor stimulation than the relatively polar
hydroxy-substituted compound 10. In this regard, previ-
ous studies indicated that certain structurally related
benztropine analogues exhibited much less locomotor
stimulant properties and did not generalize in a drug
discrimination paradigm while exhibiting high potency
for the DAT.45 However, 2a and 2b were reported to
reproduce a discriminative stimulus effect of cocaine.46
Con clu sion
In our current study, we have demonstrated that
alkyl, alkenyl, and alkynyl substitutions at the 4-posi-
tion in the phenyl ring of the benzyl group were
tolerated well. Among those derivatives, compounds 5
and 6 were the most potent for the DAT. The iodo
analogue 4 turned out to be among the few compounds
known to date that combine very high potency and
selectivity for the DAT, and it will therefore be impor-
tant to behaviorally characterize it in future experi-
ments. In in vivo studies, compound 7 exhibited more
stimulant effects than the other two compounds but was
much less stimulating than cocaine at identical doses.
In drug discrimination tests, compound 7 did not
generalize with the cocaine discriminative stimulus. In
an extended 4 h time course LMA study, compound 1a
showed a prolonged stimulant action that was signifi-
cantly different from cocaine.
Exp er im en ta l Section
Analytical silica gel-coated thin-layer chromatography (TLC)
plates (Si 250F) were purchased from Baker, Inc. and were
visualized with UV light or by treatment with phosphomolyb-
dic acid. Flash chromatography was carried out on Baker Silica
Gel 40 mM. 1H nuclear magnetic resonance (NMR) spectra
were routinely obtained at GE-300 MHz Fourier transform
NMR. The NMR solvent used was CDCl3 as indicated. Tet-
ramethylsilane was used as an internal standard. Elemental
analyses were performed by Atlantic Microlab, Inc. and were
within (0.4% of the theoretical value.
[3H]WIN 35 428 (86.0 Ci/mmol), [3H]nisoxetine (80.0 Ci/
mmol), and [3H]dopamine ([3H]DA, 48.2 Ci/mmol) were ob-
tained from Dupont-New England Nuclear (Boston, MA).
[3H]citalopram (85.0 Ci/mmol) was from Amersham Pharmacia

Structure-Activity Studies of Piperidine Analogues
J ournal of Medicinal Chemistry, 2002, Vol. 45, No. 3 659
Biotech Inc. (Piscataway, NJ ). Cocaine hydrochloride was
purchased from Mallinckrodt Chemical Corp. (St. Louis, MO).
WIN 35 428 naphthalene sulfonate was purchased from
Research Biochemicals, Inc. (Natick, MA). (-)-Cocaine HCl
was obtained from the National Institute on Drug Abuse. GBR
12909 dihydrochloride (1-[2-[bis(4-fluorophenyl)methoxy]ethyl]-
4-[3-phenylpropyl]piperazine) was purchased from SIGMA-
Aldrich (#D-052; St. Louis, MO).
converted into its oxalate salt; mp ) 163-165 °C; Anal. C28H33-
NO2, (COOH)2.
Syn t h esis of 4-[2-(Dip h en ylm et h oxy)et h yl]-1-[(4-io-
d op h en yl)m eth yl]p ip er id in e (4). 4-[(2-Diphenylmethoxy)-
ethyl]piperidine (0.23 g, 0.77 mmol) was reacted with 4-iodo
benzyl bromide (0.76 g, 2.5 mmol) and K2CO3 (1.00 g, 7 mmol)
in EtOH (10 mL) to give a thick oil, 0.17 g (46%). 1H NMR
(300 MHz, CDCl3): δ 1.21-1.63 (7H, m), 1.87-1.93 (t, J ) 11
Hz, 2H, N(CH2)-), 2.79-2.83 (bd, J ) 12 Hz, 2H, N(CH2)-),
3.41-3.49 (4H, m), 5.31 (s, 1H, Ph2CHO-), 7.05-7.63 (14H,
m, ArH). Free base was converted into its oxalate salt; mp )
160-161 °C; Anal. C27H30INO, (COOH)2.
Syn th esis of 4-[2-(Dip h en ylm eth oxy)eth yl]-1-[(4-eth y-
n ylp h en yl)m eth yl]p ip er id in e (5). To a solution of 4-[2-
(diphenylmethoxy)ethyl]-1-[(4-iodophenyl)methyl]piperidine
(0.23 g, 0.496 mmol) in toluene (10 mL) under an N2 atmo-
sphere were added tetrakis(triphenylphosphine)palladium(0)
(30 mg, 0.026 mmol) and tributyl(ethynyl)tin (0.17 g, 0.546
mmol, 1.1 equiv), and the mixture was refluxed. After 3 h, the
color was very dark, and the reaction was completed by TLC
(4:1; hex:acetone). The solvent was evaporated, and the residue
was chromatographed to yield 0.162 g (90%) of the free base
as a yellow oil. 1H NMR (CDCl3, 400 MHz): δ 1.2-1.3 (2H,
m), 1.4-1.65 (5H, m), 1.9-2.0 (2H, m), 2.84 (2H, bd, J ) 11.2
Hz), 3.06 (1H, s), 3.4-3.5 (4H, m), 5.32 (1H, s), 7.2-7.35 (12H,
m), 7.44 (2H, d, J ) 8 Hz). The free base was converted into
its oxalate salt; mp 166-170 °C; Anal. C31H33NO5‚H2O.
P r oced u r e A. Syn th esis of 4-[2-(Dip h en ylm eth oxy)-
e t h yl]-1-[(4-m e t h oxyca r b on ylp h e n yl)-m e t h yl]p ip e r i-
d in e (3a ). A mixture of 4-[2-(diphenylmethoxy)ethyl]piperi-
dine(0.23g,0.76mmol),175mgofmethyl4-(bromomethyl)benzoate
(0.17 g, 0.76 mmol), and powdered K2CO3 (0.15 g, 1.1 mmol,
1.5 equiv) in 3 mL of EtOH was refluxed for 1 h. The solvent
was evaporated, and the residue was chromatographed (SiO2;
CH2Cl2/MeOH) to yield the free base (0.23 g, 80%) as an oil
1
that slowly crystallized (mp 91-3 °C; hexane/Et2O). H NMR
(300 MHz, CDCl3): δ 1.2-2.0 (9H, m), 2.83 (2H, bd, J ) 11.1
Hz), 3.4-3.6 (4H, m), 3.91 (3H, s), 5.31 (1H, s), 7.07 (2H, d, J
) 7.8 Hz), 7.2-7.39 (10H, m), 7.39 (2H, d, J ) 7.8 Hz), 7.97
(2H, d, J ) 7.8 Hz). The free base was converted into its oxalate
salt; mp 129-133 °C; Anal. C31H35NO7.
4-[(2-Dip h en ylm eth oxy)eth yl]-1-(1-n a p h th ylm eth yl)p i-
p er id in e (3b). 4-[(2-Diphenylmethoxy)ethyl]piperidine (0.18
g, 0.61 mmol) was reacted with 2-bromo methylnaphthalene
(0.21 g, 0.95 mmol) and K2CO3 (0.85 g, 0.61 mmol) in EtOH
(10 mL) to give a thick oil, 0.25 g (96%), procedure A. 1H NMR
(300 MHz, CDCl3): δ 1.22-1.33 (2H, m), 1.48-1.53 (1H, m),
1.58-1.66 (4H, m), 1.66-2.02 (2H, dt, J ) 1.6, 11.2 Hz,
N(CH)2), 2.89-2.92 (2H, bd, J ) 11.2 Hz, N(CH)2), 3.47-3.50
(2H, t, J ) 6.4 Hz, OCH2), 3.65 (2H, s, NCH2Ar), 5.32 (1H, s,
Ph2CHO), 7.22-7.35 (10H, m, ArH), 7.43-7.51 (3H, m, ArH),
7.74 (1H, s, ArH), 7.81 (2H, m, ArH). Free base was converted
into its oxalate salt; mp ) 194-195 °C; Anal. C31H33NO,
(COOH)2.
4-[(2-Dip h en ylm eth oxy)eth yl]-1-(2-n a p h th ylm eth yl)p i-
p er id in e (3c). 4-[(2-Diphenylmethoxy)ethyl]piperidine (0.11
g, 0.37 mmol) was reacted with 1-chloro methylnaphthalene
(0.12 g, 0.68 mmol) and K2CO3 (0.52 g, 3.77 mmol) in EtOH
(10 mL) to give a thick oil, 0.14 g (86%), procedure A. 1H NMR
(300 MHz, CDCl3): δ 1.20-1.29 (2H, m), 1.51-1.54 (1H, m),
1.55-1.63 (4H, m), 2.01-2.07 (2H, t, J ) 12 Hz, N(CH)2),
2.91-2.95 (2H, bd, J ) 12 Hz, (NCH)2), 3.88 (2H, s, NCH2Ar),
5.33 (1H, s, Ph2CHO), 7.23-7.55 (13H, m, ArH), 7.76-7.78
(1H, d, J ) 8.0 Hz, ArH), 7.84-7.87 (1H, d, J ) 9.6 Hz, ArH),
8.31-8.33 (1H, d, J ) 8.0 Hz, ArH). Free base was converted
into its oxalate salt; mp ) 158-160 °C; Anal. C31H33NO,
(COOH)2.
4-[(2-Dip h en ylm eth oxy)eth yl]-1-[((4-isop r op yl)p h en yl-
)m eth yl]piper idin e (3d). A mixture of 4-[(2-diphenylmethoxy)-
ethyl]piperidine (0.18 g, 0.61 mmol), 4-isopropylbenzyl chloride
(0.19 g, 1.13 mmol), and K2CO3 (0.85 g, 6.16 mmol) in EtOH
(10 mL) was stirred at 50 °C for 6 h. The mixture was filtered,
and the organic phase was evaporated to give the crude
product, which was purified by flash chromatography (EtOAc/
Hexane ) 1/5) to give a thick oil, 0.21 g (80%), procedure A.
1H NMR (300 MHz, CDCl3): δ 1.21-1.28 (2H, m), 1.23-1.25
(6H, d, J ) 6.4 Hz, (CH3)2CH), 1.42-1.50 (1H, m), 1.56-1.61
(4H, m), 1.87-1.93 (2H, t, J ) 11.2 Hz, N(CH)2), 2.83-2.90
(3H, m, N(CH)2, PhCH(CH3)2), 3.44 (2H, s, NCH2Ar), 3.45-
3.48 (2H, t, J ) 6.4 Hz, -OCH2 ), 5.31 (1H, s, Ph2CHO), 7.15-
7.34 (14H, m, ArH). Free base was converted into its oxalate
salt; mp ) 118-120 °C; Anal. C30H37NO, (COOH)2‚0.2H2O.
4-[(2-Diph en ylm eth oxy)eth yl]-1-[((3-m eth oxyl)ph en yl)-
m eth yl]p ip er id in e(3e). 4-[(2-Diphenylmethoxy)ethyl]piperi-
dine (0.15 g, 0.50 mmol) was reacted with 3-methoxy benzyl
bromide (0.13 g, 0.65 mol) and K2CO3 (0.52 g, 3.77 mmol) in
EtOH (10 mL) to give a thick oil, 0.18 g (86%), procedure A.
1H NMR (300 MHz, CDCl3): δ 1.20-1.30 (2H, m), 1.46-1.50
(1H, m), 1.51-1.64 (4H, m), 1.87-1.93 (2H, t, J ) 12 Hz,
N(CH)2), 2.84-2.87 (2H, bd, J ) 12 Hz, N(CH)2), 3.46-3.50
(4H, m, OCH2, NCH2Ph), 3.81 (3H, s, OCH3), 5.33 (1H, s, Ph2-
CHO), 6.79-6.81 (1H, d, J ) 8.0 Hz, ArH), 6.90-6.92 (1H, d,
J ) 8.0 Hz, ArH), 7.21-7.36 (12H, m, ArH). Free base was
Syn t h esis of 4-[2-(Dip h en ylm et h oxy)et h yl]-1-[(4-vi-
n ylp h en yl)m eth yl]p ip er id in e (6). To a solution of 4-[2-
(diphenylmethoxy)ethyl]-1-[(4-iodophenyl)methyl]piperidine (0.2
g, 0.384 mmol) in toluene (10 mL) under a nitrogen atmosphere
were added tetrakis(triphenylphosphine)palladium(0) (30 mg,
0.026 mmol) and tributyl(vinyl)tin (0.12 g, 0.38 mmol, 1 equiv),
and the mixture was refluxed. After 4 h, the color was very
dark, and the reaction was completed by TLC (4:1; hexane:
acetone). The mixture was filtered through Celite, then the
solvent was evaporated, and the residue was chromatographed
1
to yield 0.14 g (86%) of the free base as a pale yellow oil. H
NMR (CDCl3, 400 MHz): δ 1.2-2.1 (9H, m), 2.93 (2H, bs), 3.46
(2H, t, J ) 6.4 Hz), 3.59 (2H, bs), 5.23 (1H, d, J ) 11.6 Hz),
5.29 (1H, s), 5.74 (1H, d, J ) 17.6 Hz), 6.7 (1H, dd, J ) 11.2
and 16 Hz), 7.19-7.4 (14H, m). The free base was converted
into its oxalate salt; mp 136-141 °C; Anal. C31H35NO5‚3/4H2O.
Syn t h esis of 4-[2-(Dip h en ylm et h oxy)et h yl]-1-[(4-(2-
p r op en yl)p h en yl)m eth yl]p ip er id in e (7). To a stirred solu-
tion of 2-bromopropene (0.69 g, 5.76 mmol, 3 equiv) in 4 mL
of tetrahydrofuran (THF) at -78 °C was added dropwise 2.88
mL of 2 M n-BuLi in pentane (17.28 mmol, 3 equiv). After the
solution was stirred for 15 min, 3.84 mL of 0.5 M ZnCl in THF
(17.28 mmol, 3 equiv) was added and the solution remained
stirring at -78 °C for a further 30 min. Then, 4-[2-(diphenyl-
methoxy)ethyl]-1-[(4-iodophenyl)methyl]piperidine (1 g, 1.92
mmol) dissolved in 2 mL of THF was added dropwise to the
solution followed by dichlorobis(triphenylphosphine) palla-
dium(II) (100 mg, 0.14 mmol). The mixture was stirred at -78
°C for 2 h, and then, the cooling bath was removed and allowed
to warm and stir at room temperature for 12 h. The solvent
was evaporated, and the residue was chromatographed (SiO2;
hexane:acetone) to furnish the free base (0.33 g, 40%) as a pale
yellow oil. 1H NMR (CDCl3, 400 MHz): δ 1.2-2.0 (9H, m), 2.8-
2.9 (2H, bs), 3.46 (2H, t, J ) 6.8 Hz), 3.55 (2H, bs), 5.07 (1H,
s), 5.30 (1H, s), 5.36 (1H, s), 7.2-7.35 (13H, m), 7.42 (1H, d, J
) 8.4 Hz). The free base was converted into oxalate salt; mp
128-132 °C; Anal. C32H35NO5‚1.5 H2O.
Syn th esis of 4-[2-(Dip h en ylm eth oxy)eth yl]-1-[(4-p r o-
p yn ylp h en yl)m eth yl]p ip er id in e (8). A mixture of 4-[2-
(diphenylmethoxy)ethyl]-1-[(4-iodophenyl)methyl]piperidine (0.5
g, 0.96 mmol), 1-(trimethylsilyl)-1-propyne (0.12 g, 1.15 mmol,
1.2 equiv), tetrakis(triphenylphosphine)palladium(0) (110 mg,
10 mol %), tetrabutylammonium fluoride (0.25 g, 1.2 equiv),
and 52 mg of ethanol (1.2 equiv) in 10 mL of THF was heated
to 50 °C for 2 h. Saturated K2CO3 was added, and the mixture
was extracted thrice with CH2Cl2. These were collected, dried
(MgSO4), and evaporated to a brown oil. The oil was chro-

660 J ournal of Medicinal Chemistry, 2002, Vol. 45, No. 3
Dutta et al.
matographed (SiO2) eluting with CH2Cl2 to remove a dark-
colored material and changing (hexane/EtOAc/MeOH) to elute
the title compound (140 mg, 41%) as a light brown oil. 1H NMR
(CDCl3, 400 MHz): δ 1.2-1.3 (2H, m, H-3ax), 1.4-1.5 (1H,
m, H-4), 1.56-1.65 (4H, m, CH2CH2O, H-3eq), 1.92 (2H, t, J
) 9.6 Hz, H-2ax), 2.05 (3H, s, CH3), 2.82 (2H, d, J ) 11.2 Hz,
H-2eq), 3.4-3.5 (4H, m, CH2O, NCH2Ar), 5.32 (1H, s,
CH(C6H5)2), 7.2-7.35 (14H, m, ArH). The compound was
precipitated with oxalic acid dihydrate; mp 80-120 °C; Anal.
12 h light-dark cycle, and all testing occurred during the light
component.
Ap p a r a tu s a n d P r oced u r e. The LMA chambers and
procedure have been described in detail elsewhere.23 Briefly,
four automated activity monitoring chambers were used that
permitted the simultaneous recording of two mice. Mice were
injected with the vehicle or test compound and placed im-
mediately into the test chambers where their activity was
recorded for 60 or 240 min. The total distance traveled (cm)
during the experiment session was recorded for each mouse.
The raw data at each test dose were converted to a percentage
of the vehicle control total distance traveled (60 min session
only). A one-factor (dose) ANOVA was conducted on each drug,
and its respective vehicle was followed by Dunnett’s post-hoc
tests when the overall ANOVA was significant (60 min
session). A repeated measures ANOVA was conducted on a
drug dose (between subjects factor) and 10 min interval (within
subjects factor) followed by Dunnett’s post-hoc tests when the
overall ANOVA was significant (240 min session). Next, simple
effects analyses were conducted at each 10 min interval to
examine the effect of drug dose. The R-level for all comparisons
was set at 0.05.
Dr u gs. Cocaine (National Institute of Drug Abuse) was
dissolved in 0.05% sterile saline. Compounds 5, 7, and 10 were
dissolved in Alkamuls EL-620:ethanol:water in a 1:1:18 ratio.
All drugs were administered by the intraperitoneal (ip) route
in a volume of 10 mL/kg.
Dr u g Discr im in a tion . Su bjects. Adult male Swiss Web-
ster mice (Harlan Sprague Dawley, Inc., Indianapolis, IN) were
used. Mice were individually housed, maintained on a 12 h
light-dark cycle, and provided with continuous access to
water. Training and testing occurred during the light compo-
nent. Mice were maintained at 35 ( 5 g by supplemental
postsession feedings.
C
32H35NO5‚1.75 H2O.
4-[(2-Dip h en ylm eth oxy)eth yl]-1-[((4-h yd r oxy)p h en yl)-
m eth yl]p ip er id in e (9). A mixture of 4-[(2-diphenylmethoxy)-
ethyl]piperidine (0.22 g, 0.74 mmol), 4-hydroxybenzaldehyde
(0.10 g, 0.82 mmol), and sodium triacetoxyborohydride (0.31
g, 1.47 mmol) in ClCH2CH2Cl (10 mL) was stirred at room
temperature overnight. After the solvent was removed, the
residue was diluted with EtOAc (100 mL) and washed with
saturated NaHCO3 and brine. The solution was dried over
Na2SO4 and evaporated under vacuo to give the crude product,
which was purified with flash chromatography (EtOAc/MeOH
) 1/1) to give a solid, 0.26 g (86%). 1H NMR (300 MHz,
CDCl3): δ 1.20-1.28 (m, 2H), 1.43-1.66 (m, 5H), 1.93-2.00
(t, J ) 11 Hz, 2H, N(CH)2), 2.90-2.94 (d, J ) 11 Hz, 2H,
N(CH)2), 3.41 (s, 2H, NCH2Ph), 3.44-3.48 (t, J ) 6.6 Hz, 2H,
OCH2), 5.30 (s, 1H, Ph2CHO), 6.63-6.65 (d, J ) 7.8 Hz, 2H,
Ar-H), 7.08-7.11 (d, J ) 7.8 Hz, 2H, Ar-H), 7.23-7.34 (m,
10H, Ar-H). Free base was converted into its oxalate salt; mp
220-222 °C; Anal. [C27H31NO2‚0.5(CO2H)2‚0.31H2O].
4-[(2-Dip h en ylm eth oxy)eth yl]-1-[((3-h yd r oxy)p h en yl)-
m eth yl]p ip er id in e (10). 4-[(2-Diphenylmethoxy)ethyl]pip-
eridine was reacted with 3-hydroxybenzaldehyde and sodium-
triacetoxyborohydride in ClCH2CH2Cl to give 0.18 g (83%). 1H
NMR (300 MHz, CDCl3): δ 1.22-1.28 (m, 2H), 1.43-1.65 (m,
5H), 1.99-2.11 (t, J ) 11 Hz, 2H, N(CH)2), 2.95-2.98 (d, J )
11 Hz, N(CH)2), 3.42-3.46 (t, J ) 5.7 Hz, 2H, OCH2), 3.48 (s,
2H, NCH2Ph), 5.29 (s, 1H, Ph2CHO), 6.68-6.76 (m, 2H,
Ar-H), 7.07-7.12 (d, J ) 7.5 Hz, 1H, AR-H), 7.22-7.31 (m,
10H, ArH). Free base was converted into its oxalate salt; mp
161-161 °C; Anal.C27H31NO2‚(CO2H)2.
Tr a n sp or ter Bin d in g Assa ys. The affinity of test com-
pounds for the rat DAT, SERT, and NET was assessed by the
inhibition of binding of [3H]WIN 35 428, [3H]citalopram, and
[3H]nisoxetine, respectively, exactly as described by us previ-
ously.23 Briefly, rat striatum was the source for DAT, and
cerebral cortex was the source for SERT and NET (see Table
1). The final [Na+] was 30 mM for DAT and SERT assays and
was 225 mM for NET assays. All binding assays were
conducted at 0-4 °C, for a period of 2 h for [3H]WIN 35 428
and [3H]citalopram binding and 3 h for [3H]nisoxetine binding.
Nonspecific binding of [3H]WIN 35 428 and [3H]citalopram
binding was defined with 100 µM cocaine and that of [3H]-
nisoxetine binding with 1 µM desipramine. Test compounds
were dissolved in dimethyl sulfoxide (DMSO) and diluted out
in 10% (v/v) DMSO. Additions from the latter stocks resulted
in a final concentration of DMSO of 0.5%, which by itself did
not interfere with radioligand binding. At least five triplicate
concentrations of each test compound were studied, spaced
evenly around the IC50 value.
DAT Up ta k e Assa ys. Uptake of [3H]DA into rat striatal
synaptosomes was measured exactly as described by us
previously.23 Briefly, rat striatal P2 membrane fractions were
incubated with the test drug for 8 min in uptake buffer (for
composition see ref 47) followed by the additional presence of
[3H]DA for 4 min at 25 °C. Nonspecific uptake was defined
with 100 µM cocaine. Construction of inhibition curves and
dissolvement of test compounds were as described above.
Ap p a r a tu s a n d P r oced u r e. The drug discrimination
chambers and procedure have been described in detail else-
where.23 Briefly, experimental sessions were conducted in
light- and sound-attenuated chambers equipped with two
response levers separated by a trough into which a 0.01 mL
dipper cup could be presented. Each chamber was equipped
with a house light.
Mice were initially trained to press one of the two levers
under a fixed ratio 1 FR1 schedule of sweetened condensed
milk. The response requirement was gradually increased to
FR20. Subsequently, the mice were reinforced for pressing the
opposite lever until reliable responding was obtained under
FR20 conditions. Discrimination training occurred daily (Mon-
day-Friday) in 15 min experimental sessions. Mice were
injected with cocaine (10 mg/kg) or saline ip 10 min prior to
the start of the session. The cocaine- and saline-associated
levers were counterbalanced across the mice. Responses on the
injection appropriate lever resulted in delivery of the sweet-
ened milk solution. Responses on the injection inappropriate
lever resulted in resetting the response requirement on the
correct lever. A pseudo-random schedule was used to deter-
mine which injection was administered, with the restriction
that the same injection was not given on more than two
consecutive sessions and over 30 training sessions the number
of saline and cocaine injections were approximately equal.
Testing commenced when (i) a mouse completed the first
fixed ratio (FFR) on the correct lever on at least 8 or 10
consecutive days and (ii) at least 80% of the total responses
were made on the correct lever during those eight sessions.
Tests were conducted on Tuesdays and Fridays, provided that
the mouse completed the FFR on the correct lever during the
most recent cocaine and saline training sessions; otherwise, a
training session was administered. During test days, respond-
ing on either lever was reinforced with milk.
LMA. Su bjects. Adult male Swiss Webster mice (Harlan
Sprague Dawley, Inc., Indianapolis, IN) weighing 30-35 g
were used. Mice were housed five per cage, had continuous
access to food and water, and were allowed to acclimate to the
vivarium environment 1 week prior to the start of any ex-
periment. The mice were housed in an AALAC-accredited
animal facility with a controlled temperature (22-24 °C) on a
An a lyses. The percentage of responses on the cocaine lever
was calculated for each mouse during training and test
sessions by dividing the number of lever presses emitted upon
the cocaine lever by the total number of lever presses emitted
on both levers, and then, this quotient was multiplied by 100.
Additionally, the rate of responding was calculated for each

Structure-Activity Studies of Piperidine Analogues
J ournal of Medicinal Chemistry, 2002, Vol. 45, No. 3 661
(18) Singh, S. Chemistry, design, and structure-activity relationship
of cocaine antagonists. Chem. Rev. 2000, 100, 925-1024.
(19) Dutta, A. K.; Xu, C.; Reith, M. E. A. Structure-Activity
Relationship Studies of Novel 4-[2-[Bis(4-fluorophenyl)methoxy]-
ethyl]-1-(3-phenylpropyl)piperidine Analogues: Synthesis and
Biological Evaluation at the Dopamine and Serotonin Trans-
porter Sites. J . Med. Chem. 1996, 39, 749-756.
(20) Dutta, A. K.; Coffey, L. L.; Reith, M. E. A. Highly selective, novel
analogues of 4-[2-(diphenylmethoxy)ethyl]-1-benzylpiperidine for
the dopamine transporter: Effect of different aromatic substitu-
tions on their affinity and selectivity. J . Med. Chem. 1997, 40,
35-43.
(21) Dutta, A. K.; Coffey, L. L.; Reith, M. E. A. Potent and selective
ligands for the dopamine transporter (DAT): Structure-activity
relationship studies of novel 4-[2-(diphenylmethoxy)ethyl]-1-(3-
phenylpropyl)piperidine analogues. J . Med. Chem. 1998, 41,
699-705.
(22) Dutta, A. K.; Xu, C.; Reith, M. E. A. Tolerance in the Replace-
ment of the benzhydrylic O-atom in 4-[2-(Diphenyl-methoxy)-
ethyl]-1-benzylpiperidine derivatives by an N-atom: Develop-
ment of new-generation potent and selective N-analogue molecules
for the dopamine transporter. J . Med. Chem. 1998, 41, 3293-
3297.
mouse by dividing the total number of responses emitted on
both levers by 900 s. Individual cocaine lever responding
percentages and responses per second were then averaged ((
the standard error of the mean (SEM)). If a mouse failed to
complete a FFR, then its data was excluded from calculations
of mean cocaine lever responding but were included for mean
response rate calculations.
Dr u gs. Cocaine HCl (National Institute of Drug Abuse) was
dissolved in 0.05% sterile saline. Compounds 5, 7, and 10 were
dissolved in Alkamuls EL-620:ethanol:water in a 1:1:18 ratio.
All drugs were administered by the ip route in a volume of 10
mL/kg at a time prior to the start of the test sessions coinciding
with a time of obvious activity indicated during LMA tests.
Both 5 and 7 were administered 20 min prior to the session
start, and 10 was administered 30 min prior to the session
start.
Ack n ow led gm en t. This work was supported by the
National Institute on Drug Abuse, Grant No. DA 12449
(A.K.D.).
(23) Dutta, A. K.; Fei, X.-S.; Beardsley, P.; Newman, J .; Reith, M. E.
A. Structure-Activity Relationship Studies of 4-[2-(Diphenyl-
methoxy)-ethyl]-1-benzylpiperidine Derivatives and their N-
analogues: Evaluation of Behavioral Activity of O- and N-An-
alogues and their Binding to Monoamine transporters. J . Med.
Chem. 2001, 44, 937-948.
(24) Andersen, P. H. Biochemical and Pharmacological Characteriza-
tion of [3H] GBR 12935 Binding in Vitro to Rat Striatal
Membranes: Labeling of the Dopamine Uptake Complex. J .
Neurochem. 1987, 48, 1887-1896.
(25) 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.
(26) Dutta, A. K.; Fei, X.-S.; Vaughan, R. A.; Gaffaney, J . D.; Wang,
N.; Lever, J . R.; Reith, M. E. A. Design, Synthesis, and
Characterization of a Novel, 4-[2-(Diphenylmethoxy)ethyl]-1-
Benzyl Piperidine-Based, Dopamine Transporter Photoaffinity
Label. Life Sci. 2001, 68 (16), 1839-1849.
(27) Vaughan, R. A.; Gaffaney, J . D.; Lever, J . R.; Reith, M. E. A.;
Dutta, A. K. Dual Incorporation of Photoaffinity Ligands on
Dopamine Transporters Implicates Proximity of Labeled Do-
mains. Mol. Pharmacol. 2001, 59, 1157-1164.
(28) Vaughan, R. A.; Kuhar, M. J . Dopamine Transporter Ligand
Binding Domains: Structural and Functional Properties Re-
vealed by Limited Proteolysis. J . Biol. Chem. 1996, 271, 21672-
21680.
(29) Vaughan, R. A.; Agoston, G. E.; Lever, J . R.; Newman, A. H.
Differential binding of tropane-based photoaffinity ligands on
the dopamine transporter. J . Neurosci. 1999, 19, 630-636.
(30) Berger, P.; Elsworth, J . D.; Reith, M. E. A.; Tanen, D.; Roth, R.
H. Complex interaction of cocaine with the dopamine uptake
carrier. Eur. J . Pharmacol. 1990, 176, 251-252.
(31) Saadouni, S.; Lyamani-Refahi, F.; Costentin, J .; Bonnet, J .-J .
Cocaine and GBR 12783 recognize nonidentical, overlapping
binding domains on the dopamine neuronal carrier. Eur. J .
Pharmacol. 1994, 268, 187-197.
Refer en ces
(1) Substance Abuse and Mental Health Services Administration
National Household Survey on Drug Abuse: Main Findings
1997; Department of Health and Human Services: Washington,
D.C., 1998.
(2) J ohanson, C. E.; Schuster, R. S. Cocaine. In Psychopharmacol-
ogy: the Fourth Generation of Progress; Bloom, F. E., Kupfer, D.
J ., Eds.; Raven Press: New York, 1995; pp 1685-1697.
(3) McCance, E. F. Overview of potential treatment medications for
cocaine dependence. NIDA Res. Monogr. 1997, 175, 36-72.
(4) Carroll, F. I.; Howell, L. L.; Kuhar, M. J . Pharmacotherapies
for Treatment of Cocaine Abuse: Preclinical Aspects. J . Med.
Chem. 1999, 42, 2721-2736.
(5) Ritz, M. C.; Cone, E. J .; Kuhar, M. J . Cocaine inhibition of ligand
binding at dopamine, norpinephrine and serotonin transport-
ers: A structure-activity study. Life Sci. 1990, 46, 635-645.
(6) Ritz, M. C.; Lamb, R. J .; Goldberg, R.; Kuhar, M. J . Cocaine
receptors on dopamine transporters are related to self-admin-
stration of cocaine. Science 1987, 237, 1219-1223.
(7) Spealman, R. D.; Madras, B. K.; Bergman, J . Effects of Cocaine
and Related Drugs in Nonhuman Primates. II. Stimulant Effects
on Schedule-Controlled Behavior. J . Pharmacol. Exp. Ther. 1989,
251, 142-149.
(8) (a) Kuhar, M. J .; Ritz, M. C.; Boja, J . W. The dopamine
hypothesis of the reinforcing properties of cocaine. Trends
Neurosci. 1991, 14, 299-302. (b) Koob, G. F.; Bloom, F. E.
Cellular and molecular mechanisms of drug dependence. Science
1988, 242, 715-723.
(9) Witkins, J . M.; Nichols, D. E.; Terry, P.; Katz, J . L. Behavioral
effects of selective dopaminergic compounds in rats discriminat-
ing cocaine injections. J . Pharmacol. Exp. Ther. 1991, 257, 706-
713.
(10) Giros, B.; J aber, M.; J ones, S. R.; Wightman, R. M.; Caron, M.
G. Hyperlocomotion and indifference to cocaine and amphet-
amine in mice lacking the dopamine transporter. Nature 1996,
379, 606-612.
(32) Rothman, R. B.; Grieg, N.; Kim, A.; de Costa, B. R.; Rice, K. C.;
Carroll, F. I.; Pert, A. Cocaine and GBR 12909 produce equiva-
lent motoric reponses at different occupancy of the dopamine
transporter. Pharmacol. Biochem. Behav. 1992, 43, 1135-1142.
(33) Tella, S. R.; Ladenheim, B.; Andrews, A. M.; Goldberg, S. R.;
Cadet, J . L. Differential reinforcing effects of cocaine and GBR
12909: Biochemical evidence for divergent neuroadaptive changes
in the mesolimbic dopaminergic system. J . Neurosci. 1996, 16,
7416-7427.
(34) (a) Izenwasser, S.; Terry, P.; Heller, B.; Witkin, J . M.; Katz, J .
L. Differential relationships among dopamine transporter af-
finities and stimulant potencies of various uptake inhibitors.
Eur. J . Pharmacol. 1994, 263, 277-283. (b) Katz, J . L.; Izen-
wasser, S.; Kline, R. H.; Allen, A. C.; Newman, A. H. Novel 3a-
diphenylmethoxytropane analogues: selective dopamine uptake
inhibitors with behavioral effects distinct from those of cocaine.
J . Pharmacol. Exp. Ther. 1999, 288, 302-315.
(35) Kitayama, S.; Shimada, S.; Xu, H.; Markham, L.; Donovan, D.;
Uhl, G. Dopamine transporter site-directed mutations differen-
tially alter substrate transport and cocaine binding. Proc. Natl.
Acad. Sci. U.S.A. 1992, 89, 7782-7785.
(36) Giros, B.; Wang, Y.-M.; Suter, S.; McLeskey, S. B.; Pifl, C.; Caron,
M. G. Delineation of discrete domains for substrate, cocaine and
tricyclic antidepressant interactions using chimeric dopamine-
norepinephrine transporters. J . Biol. Chem. 1994, 269, 15985-
15988.
(11) Di Chiara, G.; Imperato, A. Drugs abused by humans preferen-
tially increase synaptic dopamine concentrations in the me-
solimbic system of freely moving rats. Proc. Natl. Acad. Sci.
U.S.A. 1988, 85, 5274-5278.
(12) Carboni, E.; Spielewoy, C.; Vacca, C.; Nosten-Bertrand, M.;
Giros, B.; Di Chiara, G. Cocaine and Amphetamine Increase
Extracellular Dopamine in the Nucleus Accumbens of Mice
Lacking the Dopamine Transporter Gene. J . Neurosci. 2001, 21,
RC141.
(13) Rocha, B. A.; Fumagalli, F.; Gainetdinov, R. R.; J ones, S.; Ator,
R.; Giros, B.; Miller G. W.; Caron, M. Cocaine self-administration
in dopamine transporter knockout mice. Nat. Neurosci. 1998,
1, 132-137.
(14) Yamamoto, B. K.; Novotney, S. Regulation of Extracellular
Dopamine by the Norepinephrine Transporter. J . Neurochem.
1998, 71, 274-280.
(15) Eshleman, A. J .; Carmolli, M.; Cumbay, M.; Martens, C. R.;
Neve, K. A.; J anowsky, A. Characteristics of drug interactions
with recombinant biogenic amine transporters expressed in the
same cell type. J . Pharmacol. Exp. Ther. 1999, 289, 877-885.
(16) Smith, M. P.; Hoepping, A.; J ohnson, K. M.; Trzcinska, M.;
Kozikowski, A. P. Dopaminergic agents for the treatment of
cocaine abuse. Drug Discovery Today 1999, 4, 322-332.
(17) Carrol, F. I.; Lewin, A. H.; Kuhar, M. J . Dopamine transporter
uptake blockers: Structure activity relationships. In Neu-
rotransmitter Transporters: Structure and Function; Reith, M.
E. A., Eds.; Human Press: Totowa, NJ , 1997; pp 263-295.

662 J ournal of Medicinal Chemistry, 2002, Vol. 45, No. 3
Dutta et al.
(37) Negus, S. S.; Brandt, M. R.; Mello, N. K. Effects of the long-
acting monoamine reuptake inhibitor indatraline on cocaine self-
administration in rhesus monkeys. J . Pharmacol. Exp. Ther.
1999, 291, 60-69.
(38) Gorelick, D. A.; The rate hypothesis and agonist substitution
approaches to cocaine abuse treatment. Adv. Pharmacol. 1998,
42, 995-997.
2â-carboxylic acid methyl esters: Serotonin transporter selective
analogues. J . Med. Chem. 1996, 39, 4027-4035.
(43) McKean, D. R.; Parrinello, G.; Renaldo, A. F.; Stille, J . K.
Synthesis of functional styrenes via palladium-catalyzed cou-
pling of aryl bromides with vinyl tin reagents. J . Org. Chem.
1987, 52, 422-424.
(44) Krause, M.; Ligneau, X.; Stark, H.; Garbarg, M.; Schwartz, J .-
C.; Schunack, W. 4-Alkynylphenyl imidazoylpropyl as selective
histamine H3-receptor antagonists with high oral central nervous
system activity. J . Med. Chem. 1998, 41, 4171-4176.
(45) Agoston, G. E.; Wu, J . H.; Izenwasser, S.; George, C.; Katz, J .;
Kline, R. H.; Newman, A. H. Novel N-substituted 3R-[bis(4′-
fluorophenyl)methoxy]tropane analogues: selective ligands for
the dopamine transporter. J . Med. Chem. 1997, 40, 4329-4339.
(46) Melia, K. F.; Spealman, R. D. Pharmacological characterization
of the discriminative-stimulus effects of GBR 12909. J . Phar-
macol. Exp. Ther. 1991, 258, 626-632.
(47) Xu, C.; Coffey, L. L.; Reith, M. E. A. Translocation of dopamine
and binding of 2â-carbomethoxy-3â-(4-fluorophenyl)tropane (WIN
35, 428) measured under identical conditions in rat striatal
synaptosomal preparations. Inhibition by various blockers.
Biochem. Pharmacol. 1995, 49, 339-350.
(39) Ball, J . C., Ross, A., Eds. The Effectiveness of Methadone
Maintenance Treatment; Springer-Verlag: New York, 1991.
(40) Rothman, R. B.; Glowa, J . R.
A review of the effects of
dopaminergic agents on humans, animals, and drug-seeking
behavior, and its implications for medication development. Focus
on GBR 12909. Mol. Neurobiol. 1995, 11, 1-19.
(41) Glowa, J . R.; Fantegrossi, W. E.; Lewis, D. B.; Matecka, D.; Rice,
K. C.; Rothman, R. B. Sustained decrease in cocaine-maintained
responding in rhesus monkeys with 1-[2-[bis(4-fluorophenyl)-
methoxy]ethyl]4-(3-hydroxy-3-phenylpropyl)piperazinyl decanoate,
a long-acting ester derivative of GBR 12909. J . Med. Chem. 1996,
39, 4689-4691.
(42) Blough, B. E.; Abraham, P.; Lewin, A. H.; Kuhar, M. J .; Boja, J .
W.; Carroll, F. I. Synthesis and transporter binding properties
of 3â-(4′-Alkyl-, 4′-alkenyl-, and 4′-alkynylphenyl)nortropane-
J M010316X