Development of novel, potent, and selective dopamine reuptake inhibitors through alteration of the piperazine ring of 1-[2-(diphenylmethoxy)ethyl]- and 1-[2-[bis(4-fluorophenyl)methoxy]ethyl]-4-(3-phenylpropyl)piperazines (GBR 12935 and GBR 12909)

Article abstract of DOI:10.1021/jm960305h

The design, synthesis, and biological evaluation of compounds related to the dopamine (DA) uptake inhibitors: 1-[2-(diphenylmethoxy)ethyl]-4-(3-phenylpropyl)piperazine (1) and 1-[2-[bis-(4-fluorophenyl)methoxy]ethyl]-4-(3-phenylpropyl)piperazine (2) (GBR

Full text of DOI:10.1021/jm960305h

4704
J . Med. Chem. 1996, 39, 4704-4716
Develop m en t of Novel, P oten t, a n d Selective Dop a m in e Reu p ta k e In h ibitor s
th r ou gh Alter a tion of th e P ip er a zin e Rin g of 1-[2-(Dip h en ylm eth oxy)eth yl]- a n d
1-[2-[Bis(4-flu or op h en yl)m eth oxy]eth yl]-4-(3-p h en ylp r op yl)p ip er a zin es (GBR
12935 a n d GBR 12909)
Dorota Matecka, Richard B. Rothman,† Lilian Radesca, Brian R. de Costa, Christina M. Dersch,†
J ohn S. Partilla,† Agu Pert,‡ J ohn R. Glowa, Francis H. E. Wojnicki, and Kenner C. Rice*
Laboratory of Medicinal Chemistry, Building 8, Room B1-23, National Institute of Diabetes and Digestive and
Kidney Diseases, and Biological Psychiatry Branch, National Institute of Mental Health, National Institutes of Health,
9000 Rockville Pike, Bethesda, Maryland 20892, and Clinical Psychopharmacology Section, IRP,
National Institute on Drug Abuse, National Institutes of Health, Baltimore, Maryland 21224
Received April 24, 1996X
The design, synthesis, and biological evaluation of compounds related to the dopamine (DA)
uptake inhibitors: 1-[2-(diphenylmethoxy)ethyl]-4-(3-phenylpropyl)piperazine (1) and 1-[2-[bis-
(4-fluorophenyl)methoxy]ethyl]-4-(3-phenylpropyl)piperazine (2) (GBR 12395 and GBR 12909,
respectively), directed toward the development and identification of new ligands interacting
with high potency and selectivity at the dopamine transporter (DAT) is reported. The
substitution of the piperazine ring in the GBR structure with other diamine moieties resulted
in the retention of the high affinity of new ligands for the DAT. Some of the modified GBR
analogs (e.g. 8, 10, (-)-49, or (-)-50) displayed substantially higher selectivity (4736- to 693-
fold) for the dopamine (DA) versus the serotonin (5HT) reuptake site than the parent
compounds. The bis(p-fluoro) substitution in the (diphenylmethoxy)ethyl fragment slightly
increased the affinity of the ligands at the DA reuptake site but reduced their selectivity at
this site (e.g. 9 and 8, 11 and 10, or 17 and 16, respectively). Congeners, such as the series of
monosubstituted and symmetrically disubstituted piperazines and trans-2,5-dimethylpipera-
zines, which lack the (diphenylmethoxy)ethyl substituent lost the affinity for the DAT yet
exhibited very high potency for binding to the σ receptors (e.g. 28). The chiral pyrrolidine
derivatives of 1, (-)-49, and (+)-49, exhibited an enantioselectivity ratio of 181 and 146 for
the inhibition of DA reuptake and binding to the DAT, respectively.
In tr od u ction
opioid antagonist naloxone) is known, the dopamine
hypothesis leaves open the possibility that such a drug
may ultimately be identified.
The current epidemic of cocaine abuse is a major
international problem which continues to be exacer-
bated by the appearance of cocaine base (“crack”)
smoking, an extremely reinforcing route of self-
administration.1-6 The heightened health and social
problems in many United States areas related to cocaine
have encouraged new efforts toward the development
of pharmacotherapies for the treatment and prevention
of cocaine abuse. Such efforts, including the National
Institute on Drug Abuse Medications Development
Program, have benefited from intensive studies of the
mechanism of action of this drug. Although cocaine
potently inhibits the reuptake of both norepinephrine
(NE) and serotonin (5HT), many lines of evidence
indicate that its ability to increase dopaminergic
transmission by inhibiting the reuptake of dopamine
(DA) into dopaminergic neurons is the prevailing neu-
rochemical pathway responsible for its reinforcing
effects.7-13 Cocaine exerts this effect via specific inter-
action with DA transporter (DAT) proteins (cocaine
receptor) located on DA nerve terminals. This increase
of dopaminergic transmission in the reward mediating
brain mesolimbic system is the essence of the dopamine
hypothesis of reinforcement advanced by Wise10 and his
associates and elaborated for cocaine by Kuhar.8 Al-
though no pure cocaine antagonist (analogous to the
A number of drugs from a variety of pharmacological
classes have been tested in both clinical and preclinical
studies as potential medications for the treatment of
cocaine abuse.1,14-19 These include opioid receptor
agonists15,20 and antagonists,18,20 antidepressants,1,14
dopamine antagonists21,22 and agonists.23 dopamine
reuptake inhibitors,12,24 and many others. Since the
dopamine transporter seems to play an essential role
in the mechanism of cocaine action in the brain, a
variety of structurally diverse DAT ligands have been
subjected to a number of pharmacological studies.7,25-29
Disubstituted piperazines 1 and 2 (Chart 1) proved to
be among the most potent and selective DA reuptake
inhibitors.30-32 It has been hypothesized that the
development of a high-affinity, low intrinsic activity
partial cocaine agonist, which noncompetitively inhibits
the DA reuptake but does not produces euphoria (the
DA reuptake blocker type 233,34), might be a suitable
approach to treat cocaine addiction in humans. In
microdialysis experiments, the slowly dissociating DAT
ligand, 1-[2-[bis(4-fluorophenyl)methoxy]ethyl]-4-(3-phe-
nylpropyl)piperazine (2, GBR 12909), was shown to
attenuate the extracellular DA (ECDA) levels enhanced
by cocaine in rat striatum35 and nucleus accumbens.36
Glowa et al. recently showed that 2 decreases the
cocaine-maintained responding without decreasing the
food-maintained responding in cocaine and food self-
administration studies in rhesus monkeys.37,38 These
† National Institute on Drug Abuse.
‡ National Institute of Mental Health.
X Abstract published in Advance ACS Abstracts, October 15, 1996.
S0022-2623(96)00305-6
This article not subject to U.S. Copyright. Published 1996 by the American Chemical Society

Novel Dopamine Reuptake Inhibitors
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 24 4705
1278348). Subsequently, since one of the intermediates
in the trans-2,5-dimethylpiperazine series, 13 (Scheme
1), exhibited a relatively high affinity and selectivity at
the DA reuptake site, and 19 (Table 4) was practically
inactive at this site, we decided to expand this series of
ligands. We synthesized monosubstituted and sym-
metrically disubstituted trans-2,5-dimethylpiperazines
and piperazines 20-28 (Table 5) in order to confirm the
hypothesis that the (diphenylmethoxy)ethyl fragment
attached to a diamine moiety is an essential or even
sufficient pharmacophore to retain the high affinity of
these ligands at the dopaminergic site.
Ch a r t 1
results and other characteristics of 2 including its slow
onset, long duration of action, lower in vivo efficacy as
a motoric stimulant in rats as compared to cocaine39 and
nonstimulant profile of action in normal human volun-
teers following oral administration40 suggest that GBR-
type of agents may be useful for the treatment of cocaine
abuse.12,24
In order to study the effect of chirality in this series
we obtained earlier, as mentioned above, (-)- and (+)-
13 by optical resolution of (()-13 and converted these
enantiomers to (+)- and (-)-15, respectively.47 Further
alteration of the piperazine ring in the GBR structure
provided chiral pyrrolidines: (-)- and (+)-49 (Scheme
4). Although the attempt to further improve the potency
of the more active enantiomer (-)-49 by preparing its
bis(p-fluoro) or hydroxy derivatives, (-)-50 and (-)-52,
respectively, was not successful, this series of chiral
congeners may be a very useful research tool for the
study of the DA transporter since the potential problems
of biological study of racemates is well-known.49
The novel GBR analogs were evaluated in vitro at the
DA transporter of rat striatum labeled with [3H]GBR
12935 or [125I]RTI 55. Their inhibitory effect on [3H]-
DA reuptake into striatal synaptosomes and [3H]5HT
reuptake into whole brain synaptosomes was also
evaluated. Furthermore, in vitro binding affinity of new
GBR derivatives for the σ receptors was assessed. As
a result of these studies it was possible to distinguish
the main structural elements responsible for the binding
to the dopaminergic versus σ sites.
Our studies have been focused on the development
and identification of novel compounds in the GBR series,
which interact with high affinity and selectivity at dopa-
minergic sites. It had been shown earlier that it was
possible to retain the high affinity of new ligands at the
DAT by several modifications in (diphenylmethoxy)ethyl
and phenylpropyl moieties of the GBR molecule.32,41,42
Other researchers showed that one nitrogen atom
attached to the phenylpropyl chain of 2 is sufficient for
the retention of high affinity for the binding to the
DAT43 and recently synthesized a series of piperidine-
based, GBR related, compounds.44 Our primary experi-
ments involved the expansion of the piperazine ring of
1, which dramatically improved the selectivity of a new
GBR analog, homopiperazine 8 (LR-1111),45,46 at the DA
reuptake site. As a continuation of these studies, we
reported also the synthesis and evaluation in vitro of
chiral trans-2,5-dimethylpiperazines, which displayed
a 35-fold enantioselectivity ratio for the binding to the
DAT.47 In this paper we describe the design, synthesis,
and biological evaluation of “GBR related” congeners
with further modifications in the piperazine moiety as
high-affinity and selectivity DAT ligands.
Ch em istr y
New analogs of 1 and 2 were prepared by standard
chemical routes illustrated in Schemes 1-4. Initially,
we used the general method of Van der Zee et al.32
Reaction of benzhydrol or 4,4′-difluorobenzhydrol with
2-chloroethanol in toluene in the presence of sulfuric
acid afforded 2-chloroethyl diphenylmethyl ether 5a or
its bis(4-fluoro) derivative 5b, respectively, in 95% yield.
The monoalkylation of commercially available homopip-
erazine (method A; Table 1) or trans-2,5-dimethylpip-
erazine followed by coupling with the appropriate acid
chloride and reduction of the resulting amides (method
B; Table 2) yielded the target GBR analogs 9-11 or 14-
17, respectively (Scheme 1). The same synthetic route
afforded opened-ring analogs of 1: 30, 32, and 35
(Scheme 2). The diamine monoalkylation yielded mono-
substituted piperazines: 6, 7, 29, 31, and 34 (method
A; Table 1) or 12, 13, 23, and 24 (method C), whereas
symmetrically disubstituted 20 and 21 or 26 and 27
(Table 5) were obtained as products of dialkylation of
trans-2,5-dimethylpiperazine and piperazine, respec-
tively (method C). Similarly, 19 and 25 or 22 and 28
(Table 5) were synthesized by mono- or diacylation of
trans-2,5-dimethylpiperazine and piperazine (method
D), respectively, followed by the lithium aluminum
hydride or aluminum hydride reduction of the mono-
or diamide precursors. Amides obtained in the coupling
reaction of a diamine with the acid chloride were
generally used in the following step without further
purification. The synthesis of 3,3-dimethylhomopipera-
Design Ra tion a le
Our initial synthetic plan was to modify the pipera-
zine moiety of 1 without significantly changing the rest
of the molecule. These modifications included (a) al-
teration of the steric bulk of the piperazine moiety (i.e.
seven-45 and eight-membered-ring analogs 8 and 36 or
trans-2,5-dimethylpiperazine 14 and dimethylhomopip-
erazine 33; Schemes 1 and 2), (b) opening the piperazine
ring (e.g. congener 30; Scheme 2), and (c) changes in
the dihedral angle between the C-N bonds (e.g. ho-
mopiperidines 40 and 43; Scheme 3). Initially, we tried
to preserve the ethylenediamine moiety of piperazine
ring as a basic and important pharmacophore for
effective binding. Eventually, we also tested precursors
such as 32 and 35 (Scheme 2), which represent further
examples of ring-opened analogs of 1 with three and four
carbon atoms between two nitrogen atoms, respectively.
The homopiperazine and trans-2,5-dimethylpiperazine
series (Scheme 1) include analogs with the bis(4-fluoro)
substitution in the (diphenylmethoxy)ethyl fragment
(e.g. compounds 9 and 15, analogs of 2) and/or the
double bond in the phenylpropyl chain (e.g. compounds
10 and 16, analogs of 1-[2-[bis(4-fluorophenyl)methoxy]-
ethyl]-4-(3-phenyl-2-propenyl)piperazine
(3,
GBR

4706 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 24
Matecka et al.
Sch em e 1a
a
(a) HOCH2CH2Cl, H2SO4, PhCH3; (b) homopiperazine, K2CO3, PhCH3; (c) PhCH2CH2COCl, CHCl3; (d) LAH, THF; (e) PhCHdCHCOCl,
CHCl3; (f) AlH3, THF; (g) trans-2,5-dimethylpiperazine, K2CO3, PhCH3; (h) optical resolution with (-)- and (+)-dibenzoyltartaric acids,
2-PrOH.
zine 33 or 1,4-diazaoctane 36 (Scheme 2), was achieved
by refluxing of their precursors 32 or 35, respectively,
with the excess 1,2-dibromoethane and K2CO3 in xy-
lenes (method E). R-Amino-ꢀ-caprolactam was trans-
formed into 40 or 43 by a sequence of several standard
steps depicted in Scheme 3.
ethylamino)propyl]-3-ethylcarbodiimide as a coupling
agent to yield (+)-54, which was followed by its N-Boc
deprotection with trifluoroacetic acid, then alkylation
of (+)-55 with 5a , and finally the reduction of the
resulting amide (+)-56.
Resu lts a n d Discu ssion
The synthesis of optically pure enantiomeric trans-
2,5-dimethylpiperazines (-)- and (+)-13 or (+)- and (-)-
15 (Scheme 1) has been described in detail elsewhere.47
Commercially available L-(-)-prolinamide and N-Boc-
D-(+)-proline were used as starting materials in the
synthesis of the chiral pyrrolidines (-)- and (+)-49, (-)-
50 and (-)-52 (Scheme 4). Substituted amines (-)-46
and (-)-48 were prepared by treatment of L-(-)-proli-
namide with 5a or 5b, respectively (method A; Table 1)
followed by reduction of the amide function. Coupling
of (-)-46 and (-)-48 with hydrocinnamoyl chlorides
followed by amide reduction afforded (-)-49 and (-)-
50, respectively. 2-(Aminomethyl)pyrrolidine (-)-46
was then reacted with m-(benzyloxy)cinnamic acid
(prepared by O-benzylation of commercially available
m-hydroxycinnamic acid with benzyl bromide in DMF)
in the presence of 1,3-dicyclohexylcarbodiimide (DCC)
to yield (-)-51. The double bond in (-)-51 was reduced
and the protecting benzyl group was removed by hy-
drogenation in the presence of 10% Pd/C. The reduction
of the carbonyl group with AlH3 afforded the target
amine (-)-52. The synthesis of (+)-49 involved the
condensation of N-Boc-D-(+)-proline with 3-phenylpro-
pylamine in the presence of water soluble 1-[3-(dim-
This series of GBR-related compounds was synthe-
sized and evaluated in vitro to determine the SAR
requirements for high affinity binding to the DAT and
inhibition of [3H]DA reuptake. The data in Tables 3 and
4 indicate that replacement of the piperazine ring in 1
and 2 with another diamine moiety can result in the
retention of high affinity of the new ligands for binding
to the DAT and essential improvement of their selectiv-
ity at this site versus 5HT site. The expansion of the
piperazine ring of 1 to the seven-membered ring in the
structure of 8 did not significantly change the affinity
for inhibition of [3H]DA, but greatly improved its
selectivity at this site (>4700-fold).45 However, further
increase of the bulk of the piperazine moiety by incor-
poration of another methylene group in the homopip-
erazine ring in eight-membered-ring analog 36 or
addition of two methyl groups to this ring in case of
congener 33, attenuated both affinity and selectivity of
these ligands at the DAT site in comparison to 1 and 8.
The ring-opened ethylenediamine analog 30 retained
high affinity for binding to the DAT (IC50 ) 18 nM) and
inhibition of [3H]DA reuptake (Table 3: IC50 ) 27 nM).
It also exhibited a 2-fold improvement in selectivity over

Novel Dopamine Reuptake Inhibitors
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 24 4707
Sch em e 2a
a
(a) MeNHCH2CH2NHMe, K2CO3, PhCH3; (b) Ph(CH2)2COCl, CHCl3; (c) LAH, THF; (d) H2N(CH2)4NH2, K2CO3, PhCH3; (e) Ph(CH2)3Cl,
K2CO3, PhCH3; (f) BrCH2CH2Br, K2CO3, Ph(CH3)2; (g) H2NCH2C(Me)2CH2NH2, K2CO3, PhCH3; (h) AlH3, THF.
Sch em e 3a
compounds. However, the ethylene moiety seems to be
the optimal linkage between two nitrogen atoms in the
GBR structure. Interestingly, both ring-opened analogs
32 and 35 as well as other intermediates such as 29,
31, and 34, which were practically inactive for binding
to the DAT (Table 3: IC50 > 800 nM for all three),
contain in their structures at least one primary or
secondary amine function, in contrast to tertiary di-
amine 30 (Scheme 2), which retains high affinity at this
site. The semirigid GBR derivatives, homopiperidines
40 and 43 (Scheme 3), represent a very interesting pair
of regioisomers that exhibit a 6-fold difference in affinity
for the inhibition of [3H]DA reuptake as well as a 3-fold
difference in selectivity at this site in favor of 43 (Table
3).
In the homopiperazine and trans-2,5-dimethylpipera-
zine series of GBR derivatives (Table 4), bis(4-fluoro)-
substituted congeners were slightly more potent than
their desfluoro analogs for binding to the DAT labeled
with [3H]GBR 12935, except for one pair (14 and 15).
However, the desfluoro analogs displayed greatly im-
proved selectivity in inhibiting [3H]DA reuptake (versus
[3H]5HT reuptake), mainly due to their significantly
lower affinity at the 5HT sites (compare 8 and 9, 10
and 11, 14 and 15, or 16 and 17). Addition of a double
bond increased affinity for inhibition of [3H]DA reuptake
13 times (e.g. compare 8 and 10). However, this
correlation was not the same for other, similarly sub-
stituted pairs of homologs in this series (Table 4). In
contrast to our previous observation with the other
partial structures (29, 31, or 34, Table 3), both mono-
a
(a) 5a , K2CO3, PhCH3; (b) AlH3, THF; (c) Ph(CH2)2COCl,
CHCl3; (d) LAH, THF.
1 at the DA versus 5HT site. These results suggest that
high-affinity binding to the DAT of GBR-type ligands
does not require a conformationally restricted piperazine
ring and that some degree of structural flexibility is
allowed at this site. However, other ring-opened con-
geners such as 32 and 35 were less potent and much
less selective than 30 at the DAT site (compare 23-, 11-,
and 136-fold ratio of IC50 for inhibition of [3H]DA versus
[3H]5HT reuptake for 32, 35, and 30, respectively). It
is difficult to make any further conclusions at this point
because of other structural differences among these

4708 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 24
Matecka et al.
Sch em e 4a
a
(a) 5a or 5b, K2CO3, PhCH3; (b) LAH, THF; (c) Ph(CH2)2COCl, CHCl3; (d) m-(benzyloxy)cinnamic acid, DCC, CH2Cl2; (e) H2, 10%
Pd-C, MeOH; (f) AlH3, THF; (g) Ph(CH2)3NH2, 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide, CH2Cl2; (h) CF3COOH, CH2Cl2.
Ta ble 1. Method A: Reaction Conditions
ratio
reaction
time (h)
mp (salt)a
(°C)
crystallization
solvent
yield
(%)
compd
starting amine
homopiperazine
(chloride:amine:K2CO3)
6
1:7:2
1:5:2
1:7:2
1:5:2
24
12
18
8
12
45
48
24
24
48
134-134.5
128.5-129.5
128-129.5
144.5-146
168-170
MeOH
MeOH
MeOH
2-PrOH:MeOH
2-PrOH:MeOH
Et2O
2-PrOH:MeOH
2-PrOH:MeOH
MeOH
71
61
79
82
51
83
74
36
32
60
7
homopiperazine
29
31
34
38
N,N′-dimethyl-ethylenediamine
2,2-dimethyl-1,3-propanediamine
1,4-diaminobutane
R-amino-ꢀ-caprolactam
42
1:5:3
1:1.2:2
1:1.2:2
1:1.2:2
1:1.2:2
1:1:5
115-117b
43
110-112
187.5-188.5
230-231 dec
(-)-45
(-)-47
(+)-56
L-(-)-prolinamide
L-(-)-prolinamide
(+)-55
a
b
Salt form of the base indicated in the Experimental Section. Free base.
substituted homopiperazine and trans-2,5-dimethylpip-
erazine 7 and 13 exhibited high potency for the inhibi-
tion of [3H]DA reuptake. Furthermore, in contrast to
fully substituted diamines in the homopiperazine and
trans-2,5-dimethylpiperazine series, both partial fluoro
derivatives 7 and 13 were not only more potent binding
ligands and [3H]DA reuptake inhibitors but also more
selective than their desfluoro homologs 6 and 12,
respectively. On the other hand, two diamines mono-
substituted with the phenylpropyl moiety of the GBR
molecule 18 and 19 were inactive at the DAT site (Table
4). These observations prompted us to synthesize a
series of monosubstituted and symmetrically disubsti-
tuted trans-2,5-dimethylpiperazines and piperazines
(Table 5). The SAR studies in this group of congeners
provided interesting relations between dopaminergic
and σ binding properties of GBR related ligands.
Compounds with at least one (diphenylmethoxy)ethyl
substituent retain good affinity for the inhibition of [3H]-
DA reuptake from high (26, IC50 ) 12 nM) to modest
(12, IC50 ) 138 nM) degrees, and for binding to the DAT,
whereas mono- or disubstituted piperazines with phe-
nylpropyl chain 19, 22, 25, and 28, practically lost all
affinity at this site. On the other hand, these four
ligands displayed very high affinity for binding to the σ
receptors (Table 5). σ binding was tested because 1 and
250 as well as some of their new analogs (Table 3)
displayed relatively high affinity at this site. The
significance of affinity for binding to the σ receptors of
these and other DA reuptake inhibitors (e.g. BTCP, 1-[1-
(2-benzo[b]thienyl)cyclohexyl]piperidine51) is still un-
clear. It has been known, however, that cocaine binds
to the σ receptors with a weak affinity.52 Other studies
have shown that several σ ligands antagonized some of

Novel Dopamine Reuptake Inhibitors
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 24 4709
Ta ble 2. Method B: Reaction Conditions
acid
chloride
reducing
agent
reduction
time (h)
reduction
temp ( °C)
mp (salt)a
( °C)
crystallization
solvent
yieldb
(%)
product
8
9
10
11
14
15
16
17
18
30
32
35
40
Hc
H
Cf
C
H
H
C
Ld
Ae
A
A
A
A
A
A
A
L
A
A
A
L
L
L
24
24
24
0.25
1
2
1
3
0.5
24
48
8
1
2
rt
rt
rt
rt
rt
rt
0-5
0-5
0-5
rt
rt
reflux
rt
reflux
reflux
reflux
143.5-144.5
137.5-138
141-142.5
146-147
149-151
154-157
171-173
179-180
155-158
137-138
159-160
170-172
159-162
145-146
155-156
138-140
MeOH
2-PrOH
2-PrOH
2-PrOH
2-PrOH:MeOH
2-PrOH:MeOH
2-PrOH
MeOH
MeOH
MeOH
2-PrOH:MeOH
2-PrOH
2-PrOH:MeOH
2-PrOH
2-PrOH
71
62
56
77
70
58
63
49
74
45
48
23
28
43
57
63
C
C
H
H
H
H
H
H
H
42
(-)-49
(-)-50
4
3
2-PrOH:EtOAc
a
b
d
Salt form of the base indicated in the Experimental Section. Total yield for two steps. c H ) hydrocinnamoyl chloride. L ) lithium
aluminum hydride. e A ) aluminum hydride. f C ) cinnamoyl chloride.
Ta ble 3. DA and 5HT Reuptake Inhibition and Binding Affinities at the DAT and σ Receptors: GBR 12935 Analogs with Modified
Diamine Moiety
IC50 ( SD (nM)a
ratio
[3H]DA
reuptake
[3H]GBR 12935
binding (DAT)
[3H]5HT
reuptake
[3H]-(+)-pentaz
binding (σ)
([3H]5HT/[3H]
DA reuptake)
compound
1 (GBR 12935)
8
14
29
30
31
32
33
34
35
36
40
43
cocaine
3.7 ( 0.4
7.2 ( 0.5
9.6 ( 1.5
545 ( 38
18 ( 1
4.1 ( 0.6
7.9 ( 1.7
21 ( 1.0
834 ( 31
27 ( 4
289 ( 29
17 ( 2
26 ( 2
8.6 ( 0.1
231 ( 13
34 ( 2
n/d
78
4736
180
34100 ( 3590
1730 ( 70
>10000
2450 ( 57
>10000
1890 ( 268
3150 ( 491
6830 ( 1502
376 ( 19
1590 ( 60
2860 ( 45
1480 ( 69
304 ( 10
136
453 ( 20
83 ( 7
1460 ( 90
169 ( 5
n/d
n/d
23
36
13
11
17
50
159
0.6
87 ( 5
286 ( 8
510 ( 19
35 ( 2
9780 ( 4090
80 ( 6
>10000
1050 ( 35
180 ( 9
78 ( 13
83 ( 11
n/d
93 ( 6
864 ( 91
74 ( 5
57 ( 10
9.3 ( 1.8
478 ( 25
20 ( 0.7
660 ( 30b
a
b
The IC50 values of the test agents were determined in the above assays as described in Methods; n/d, not done. Published data; Ki
value (nM).60
Ta ble 4. DA and 5HT Reuptake Inhibition and Binding Affinities at the DAT Labeled by [3H]GBR 12935: Homopiperazine and
trans-2,5-Dimethylpiperazine Series
IC50 ( SD (nM)a
[3H]DA
reuptake
[3H]GBR 12935
binding (DAT)
[3H]5HT
reuptake
ratio
compound
([3H]5HT/[3H]DA reuptake)
1 (GBR 12935)
2 (GBR 12909)
6
7
8 (LR-1111)
9
10
11
12
13
14
15
16
17
18b
19c
3.7 ( 0.4
4.3 ( 0.3
651 ( 82
17 ( 1.6
7.2 ( 0.5
3.4 ( 0.4
0.6 ( 0.1
3.4 ( 0.4
138 ( 43
30 ( 5
4.1 ( 0.6
5.5 ( 0.4
1360 ( 316
143 ( 17
7.9 ( 1.7
4.4 ( 0.4
8.6 ( 1.1
2.6 ( 0.4
1000 ( 65
106 ( 9
289 ( 29
78
17
22
73 ( 1.5
14300 ( 90
2080 ( 96
34100 ( 3590
112 ( 24
503 ( 103
234 ( 10
25300 ( 1180
8940 ( 317
1720 ( 70
459 ( 26
122
4736
33
838
69
183
298
180
31
134
42
9.6 ( 1.5
15 ( 2
21 ( 1.0
40 ( 1
20 ( 4
28 ( 5
252 ( 16
>30000
103 ( 13
23 ( 3
1730 ( 141
>30000
2680 ( 122
1180 ( 404
20 ( 0.9
0.08
12200 ( 429
a
b
The IC50 values of the test agents were determined in the above assays as described in Methods. 18 [1-(3-phenyl-2-propenyl)ho-
mopiperazine]. c 19 [trans-2,5-dimethyl-1-(3-phenylpropyl)piperazine].
the behaviors induced by cocaine in animals,53,54 sug-
gesting their potential therapeutic usage for the treat-
ment of cocaine abuse.55 In the series of congeners
shown in Table 5, compound 28 exhibited the highest
(IC50 ) 0.5 nM) affinity for displacement of σ1 selective
[3H]-(+)-pentazocine.56 It should be pointed out that 28
highly resembles the structures of some of the com-
pounds belonging to the piperazine class of σ ligands.57
It is also noteworthy that piperazines which are sym-
metrically disubstituted only with the (diphenylmethoxy)-
ethyl moiety (20, 21, 26, and 27) displayed dramatically
lower, micromolar affinity at σ site.

4710 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 24
Matecka et al.
Ta ble 5. DA and 5HT Reuptake Inhibition and Binding Affinities at the DAT and σ Receptors: Monosubstituted and Symmetrically
Disubstituted Piperazines
IC50 ( SD (nM)a
ratio ([3H]DA
reuptake/ DAT
binding)
[3H]DA
reuptake
[3H]GBR 12935
binding (DAT)
[
125I]RTI 55
[3H]5HT
reuptake
[3H]-(+)-pentaz
binding (σ)
ligand
R1
R2
R3
binding (DAT)
GBR 12935
3.7 ( 0.4
4.1 ( 0.6
3.7 ( 0.3
289 ( 29
17 ( 2
0.9
1b
0.4
0.3
0.7b
12
13
Ac
Bc
H
H
Me
Me
138 ( 43
30 ( 5
1000 ( 65
106 ( 9
n/d
44 ( 1
>25000
8940 ( 317
67 ( 9
65 ( 16
19
20
21
22
23
24
25
26
Cc
A
B
C
A
B
C
A
H
A
B
C
H
H
H
A
Me
Me
Me
Me
H
H
H
H
>30000
35 ( 9
>30000
33 ( 16
36 ( 5
9940 ( 666
110 ( 7
104 ( 13
>30000
9.3 ( 1.7
n/d
n/d
n/d
n/d
n/d
n/d
n/d
1.6 ( 0.04
12200 ( 429
6220 ( 465
4240 ( 313
2530 ( 116
9570 ( 1111
1400 ( 58
8.5 ( 0.1
4001 ( 338
3640 ( 541
8.5 ( 0.6
1.1
2.4
0.1
1.1
0.7
86 ( 31
1330 ( 418
124 ( 25
71 ( 12
>30000
12 ( 0.4
1480 ( 119
965 ( 114
109 ( 20
361 ( 12
1710 ( 234
>10000
1.3
7.5b
5.5
27
B
C
B
C
H
H
40 ( 2
7.3 ( 1
1.1 ( 0.02
278 ( 32
>10000
36.4b
0.2
28
cocaine
1640 ( 433
478 ( 25
7760 ( 654
660 ( 30
n/d
341 ( 25d
1340 ( 81
304 ( 10
0.5 ( 0.1
n/d
a
b
The IC50 values of the test agents were determined in the above assays as described in Methods. Ratio of IC50 for [3H]DA reuptake
over IC50 for the displacement of [125I]RTI 55 at the DAT. c Substituents: A, 2-(diphenylmethoxy)ethyl; B, 2-[bis(p-fluorophenyl)methoxy-
]ethyl; C, 3-phenylpropyl; n/d, not done. Published data; Ki value (nM).61
d
Ta ble 6. DA and 5HT Reuptake Inhibition and Binding
It is interesting to note the improved ratios of IC50
Affinities at the DAT: Chiral Pyrrolidines
for [3H]DA reuptake inhibition to IC50 for [3H]GBR
12935 displacement for the series of GBR derivatives
IC50 ( SD (nM)a
ratio
reported in Table 5. All the piperazines symmetrically
[3H]GBR
([3H]5HT/
[3H]DA 12935 binding
[3H]5HT
reuptake
3H]DA
reuptake)
disubstituted with the diphenylmethoxyethyl moiety,
i.e. 20, 21, 26, and 27, exhibited a ratio between 1 and
5.5 in contrast to 1 with a ratio of 0.9. The ratio for 27
increases to 36 when the calculation involves the IC50
value for the binding to the DAT labeled with [125I]RTI
55 instead of [3H]GBR 12935 (Table 5). Some investiga-
tors suggest that this ratio may offer a strategy for the
identification of a potential cocaine antagonist.42 How-
ever, since the ratio may vary with the conditions of the
assay,58 and since this hypothesis has not been validated
with bioassays, the results produced for the present
series of GBR analogs should be viewed cautiously.
We have previously reported the first example of
enantioselective binding in the GBR series of DA
reuptake ligands.47 The optical resolution of racemic
trans-2,5-dimethylpiperazine 13 was performed with
(-)- and (+)-dibenzoyltartaric acids and enantiomers of
13 were then used to obtain (+)- and (-)-15. These two
pairs of enantiomers, (-)- and (+)-13 and (-)- and (+)-
15 exhibited a 7-fold and a 35-fold enantioselectivity
ratio of IC50 for the inhibition of [3H]DA reuptake,
respectively, in favor of the 2S,5R absolute configuration
in both cases,47 which suggested some degree of struc-
tural homology at this site. As shown in Scheme 4, the
enantiospecific synthesis of the second type of chiral
GBR derivatives (+)-49, (-)-49, (-)-50, and (-)-52
avoided frequently cumbersome optical resolution by
utilization of chiral starting materials (-)-44 and (+)-
53. Two pyrrolidine derivatives (-)-49 and (+)-49
displayed a 181- and a 146-fold enantioselectivity for
the inhibition of [3H]DA reuptake and binding to the
DA transporter labeled with [3H]GBR 12935, respec-
compound
reuptake
(DAT)
1 (GBR 12935) 3.7 ( 0.4
2 (GBR 12909) 4.3 ( 0.3
4.1 ( 0.6
5.5 ( 0.6
5.1 ( 0.4
747 ( 163
104 ( 8
289 ( 29
78
17
1409
25
693
28
73 ( 1.5
(-)-49
(+)-49
(-)-50
(-)-52
0.7 ( 0.05
127 ( 10
29 ( 2
986 ( 34
3210 ( 450
20100 ( 2400
857 ( 17
31 ( 0.1
222 ( 13
a
The IC50 values of the test agents were determined in the
above assays as described in Methods.
tively (Table 6). There was also a striking difference
in the ratio of IC50 for the inhibition of [3H]5HT versus
[3H]DA reuptake inhibition for these two isomers (1409-
versus 25-fold). However, the aromatic bis(4-fluoro) or
m-hydroxy substitution did not improve the affinity of
the more potent enantiomer for the inhibition of [3H]-
DA reuptake or binding to the DAT site. In fact, the
phenolic derivative (-)-52 proved to be dramatically less
selective at the DA versus the 5HT reuptake site than
its precursor (-)-49 (28- versus 1409-fold, respectively).
These compounds represent a new generation of opti-
cally active GBR-type ligands which may be very useful
in the studies of structure and function of DAT.
The preliminary in vivo studies have shown that
several new, modified GBR derivatives were inactive in
rats at doses up to 30 mg/kg injected ip (Figure 1; graphs
show the effect of only one dose 30 mg/kg of each GBR
analog; ip injection), in contrast to 1 and 2 which
produced strong stimulation of motoric behavior follow-
ing the same route of administration. For example, 8
failed to stimulate locomotor activity in rats at doses of
up to 40 mg/kg following ip injection45 and also failed

Novel Dopamine Reuptake Inhibitors
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 24 4711
mass measurements (HRMS) were obtained using a V. G.
Micro Mass 7070F mass spectrometer. 1H NMR spectra were
recorded on the free bases in CDCl3 or CDCl3 plus D2O using
a Varian XL-300 spectrometer. Chemical shifts are expressed
in parts per million (ppm) on the δ scale relative to a TMS
internal standard. Thin layer chromatography (TLC) was
performed on 250 µm Analtech GHLF silica gel plates. The
following TLC systems were employed: A, CHCl3:MeOH ) 19:
1; B, CHCl3:MeOH ) 9:1; C, CHCl3:MeOH:NH4OH ) 90:9:1;
D, CHCl3:MeOH:NH4OH ) 80:18:2. No attempt was made to
optimize the yields reported.
Meth od A. General procedure (yields and reaction condi-
tions are reported in Table 1). 2-(Diphenylmethoxy)ethyl or
2-[bis(4-fluorophenyl)methoxy]ethyl chloride (5a ) or (5b), re-
spectively, was added dropwise to a refluxing solution of a
diamine in toluene. Anhydrous K2CO3 was then added, and
the mixture was refluxed for the indicated number of hours
(Table 1). The reaction mixture was cooled to room temper-
ature and washed with water (3×), and then toluene was
removed in vacuum. The resulting substituted diamine,
isolated as an oil, was either transformed directly into a salt
or chromatographed on silica gel using the specified eluent
and then converted into a salt with the indicated acid.
Meth od B. General procedure (yields and reaction condi-
tions are reported in Table 2). The acid chloride (1.2 equiv)
was added dropwise to the vigorously stirred solution of
monosubstituted diamine (1 equiv) in chloroform at room
temperature. After the reaction was complete (typically 24
h; monitored by TLC; solvent system A, B, C, or D), the organic
layer was washed with saturated NaHCO3 solution (3×) and
water (1×) and dried (anhydrous Na2SO4) and solvent removed
in vacuum to afford an amide. This crude product was usually
employed without further purification. A solution of an amide
in THF was added dropwise to a 1 M solution of LAH or AlH3
(2-5 equiv excess) in THF, and the mixture was stirred at
room temperature or refluxed for the indicated number of
hours (Table 2) until completion (TLC). Workup: (1) (LAH
reduction) water, 10% NaOH and again water was carefully
added; the reaction mixture was filtered, the filter cake was
washed with Et2O and organic solvents removed in vacuum;
(2) (AlH3 reduction) the reaction mixture was treated with 10%
NaOH and extracted with Et2O (3×). Organic extracts were
combined, dried (Na2SO4), and evaporated to give an oily
product. The final diamine was purified (silica gel chroma-
tography using the specified eluent), if required, and (or)
directly transformed into a salt.
1-[2-(Dip h en ylm eth oxy)eth yl]h om op ip er a zin e (6) was
synthesized following method A (Table 1). 1H NMR (CDCl3
plus D2O) δ 1.70-1.78 (m, 2H), 2.71-2.78 (m, 10H), 3.58 (t, J
) 6.1 Hz, 2H), 5.35 (s, 1H), 7.21-7.37 (m, 10H); MS (CI-NH3)
m/ z 311 (MH+). Anal. 6‚2maleate (C20H26N2O‚2C4H4O4) C,
H, N.
1 -[2 -[B i s (4 -fl u o r o p h e n y l )m e t h o x y ]e t h y l ]h o m o -
p ip er a zin e (7) was synthesized following method A (Table
1): 1H NMR (CDCl3 plus D2O) δ 2.65-2.69 (m, 2H), 2.69-
2.93 (m, 10H), 3.52 (t, J ) 5.8 Hz, 2H), 5.32 (s, 1H), 6.95-
7.05 (m, 4H), 7.20-7.34 (m, 4H); MS (CI-NH3) m/ z 347 (MH+).
Anal. 7‚2maleate (C20H24F2N2O‚2C4H4O4) C, H, N.
1-[2-(Dip h en ylm et h oxy)et h yl]-4-(3-p h en ylp r op yl)h o-
m op ip er a zin e (8) was synthesized from 6 following method
B (Table 2). 1H NMR (CDCl3) δ 1.72-1.84 (m, 4H), 2.48 (t, J
) 6.9 Hz, 2H), 2.59-2.78 (m, 10H), 2.82 (t, J ) 6.3 Hz, 2H),
3.57 (t, J ) 6.2 Hz, 2H), 5.35 (s, 1H), 7.17-7.37 (m, 15H); MS
(CI-NH3) m/ z 429 (MH+). Anal. 8‚2maleate (C29H36N2O‚-
2C4H4O4‚0.5H2O) C, H, N.
1-[2-[Bis(4-flu or op h en yl)m et h oxy]et h yl]-4-(3-p h en yl-
p r op yl)h om op ip er a zin e (9) was synthesized from 7 follow-
ing method B (Table 2): 1H NMR (CDCl3) δ 1.70-1.85 (m, 4H),
2.48 (t, J ) 7.3 Hz, 2H), 2.58-2.76 (m, 10H), 2.80 (t, J ) 6.2
Hz, 2H), 3.52 (t, J ) 6.1 Hz, 2H), 5.32 (s, 1H), 6.96-7.03 (m,
3H), 7.16-7.19 (m, 2H), 7.24-7.30 (m, 8H); MS (CI-NH3) m/ z
465 (MH+). Anal. 9‚2maleate (C29H34F2N2O‚2C4H4O4) C, H,
N.
F igu r e 1. Effects of several GBR analogs on horizontal
locomotor activity in rats following ip injection (30 mg/kg).
Repeated measures analyses of variance revealed a significant
postdrug treatment effect only between the vehicle group and
the group injected with GBR 12935.
to decrease either food intake or cocaine self-adminis-
tration (5.6-10 µg/kg per injection) in rhesus monkeys
at doses of up to 5.6 mg/kg, iv (data not shown).
However, 8 caused long-lasting stimulation of locomotor
activity in rats when administered intravenously.45
These results suggest that GBR analogs with the
modified diamine moiety may exhibit a poor blood-brain
barrier permeability and/or be subjected to degradative
metabolic processes in the liver. Additional experiments
are required to explain the differences in pharmacologi-
cal profile of the new GBR analogs from cocaine and
the parent compounds.
Con clu sion s
New GBR derivatives were synthesized and evaluated
at the DA reuptake site. These studies have shown that
significant structural variations are permitted in the
GBR series of compounds and that the conformationally
restricted piperazine ring may be substituted by other,
more flexible or more bulky, diamine moieties and still
retain the high affinity for both binding to the DAT and
inhibition of [3H]DA reuptake. At least one (diphenyl-
methoxy)ethyl substituent in the GBR structure is
required for high-affinity binding to the DAT. Several
new, modified analogs reported here are among the
ligands of the highest selectivity at the DA versus 5HT
reuptake site known to date within the class of GBR
compounds as well as the other structurally different
DA reuptake inhibitors. Further in vivo studies of
novel, potent, and selective DAT ligands are being
conducted and will be reported in due course. These
compounds as well as the enantiomeric GBR analogs
provide novel probes and leads for the development of
research tools to study the structure and functions of
the DA transporter. They may be also useful in the
identification of successful therapeutics for the treat-
ment and prevention of cocaine abuse.
Exp er im en ta l Section
Ch em ica l Meth od s. Melting points were determined on
a Thomas-Hoover capillary apparatus and are uncorrected.
Determination of specific rotation at the sodium-D line were
obtained in a 1 dm cell using a Perkin-Elmer 241-MC pola-
rimeter. Elemental analyses were performed by Atlantic
Microlabs, Atlanta, GA, and were within (0.4% for the
elements indicated. Chemical ionization mass spectra (CIMS)
were obtained using a Finnigan 1015 mass spectrometer.
Electron ionization mass spectra (EIMS) and high-resolution
1-[2-(Dip h en ylm eth oxy)eth yl]-4-(3-p h en yl-2-p r op en yl-
)h om op ip er a zin e (10) was synthesized from 6 following
method B (Table 2). 1H NMR (CDCl3) δ 1.76-1.84 (m, 2H),
2.68-2.87 (m, 10H), 3.27 (dd, J ) 0.7, 6.8 Hz, 2H), 3.58 (t, J

4712 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 24
Matecka et al.
) 5.9 Hz, 2H), 5.36 (s, 1H), 6.29 (dt, J ) 6.8, 15.8 Hz, 1H),
6.49 (d, J ) 15.8 Hz, 1H), 7.18-7.40 (m, 15H); MS (CI-NH3)
m/ z 427 (MH+). Anal. 10‚2maleate (C29H34N2O‚2C4H4O4) C,
H, N.
(m, 10H), 2.97-3.02 (m, 1H), 3.52-3.55 (m, 2H), 5.32 (s, 1H),
6.97-7.03 (m, 3H), 7.15-7.19 (m, 2H), 7.22-7.30 (m, 8H); MS
(CI-NH3) m/ z 479 (MH+). Anal. 15‚2fumarate (C30H36N2F2O‚-
2C4H4O4) C, H, N.
1-[2-[Bis(4-flu or op h en yl)m et h oxy]et h yl]-4-(3-p h en yl-
2-p r op en yl)h om op ip er a zin e (11) was synthesized from 7
following method B (Table 2): 1H NMR (CDCl3) δ 1.75-1.86
(m, 2H), 2.62-2.85 (m, 10H), 3.25-3.35 (m, 2H), 3.45-3.60
(t, J ) 6.4 Hz, 2H), 5.34 (s, 1H), 6.25-6.45 (m, 1H), 6.50 (d, J
) 15.0 Hz, 1H), 6.95-7.05 (m, 4H), 7.15-7.45 (m, 9H); MS
(CI-NH3) m/ z 463 (MH+). Anal. 11‚2maleate (C29H32F2N2O‚-
2C4H4O4) C, H, N.
Meth od C. tr a n s-2,5-Dim eth yl-1-[2-(diph en ylm eth oxy)-
eth yl]p ip er a zin e (12) a n d tr a n s-2,5-Dim eth yl-1,4-bis[2-
(d ip h en ylm eth oxy)eth yl]p ip er a zin e (20). trans-2,5-Dim-
ethylpiperazine (20.0 g, 175 mmol) was refluxed in toluene (70
mL), and a solution of 5a (14.4 g, 58 mmol) in toluene (30 mL)
was added dropwise. Anhydrous K2CO3 (16.2 g, 116 mmol)
was added, and the reaction mixture was refluxed for 36 h.
The organic phase was washed with water to remove the
unreacted trans-2,5-dimethylpiperazine and then extracted
with 10% citric acid to separate the mono- from the disubsti-
tuted product.
tr a n s-2,5-Dim eth yl-1-[2-(d ip h en ylm eth oxy)eth yl]-4-(3-
p h en yl-2-p r op en yl)p ip er a zin e (16) was synthesized from
12 following method B (Table 2): 1H NMR (CDCl3) δ 1.04 (d,
J ) 6.1 Hz, 3H), 1.09 (d, J ) 6.1 Hz, 3H), 2.05-2.09 (m, 1H),
2.26-2.29 (m, 1H), 2.43-2.55 (m, 2H), 2.61-2.69 (m, 1H), 2.83
(d, J ) 10.4 Hz, 2H), 2.96-3.07 (m, 2H), 3.54-3.67 (m, 3H),
5.36 (s, 1H), 6.26-6.34 (m, 1H), 6.57 (d, J ) 15.8 Hz, 1H),
7.21-7.38 (m, 15H); MS (CI-NH3) m/ z 441 (MH+). Anal. 16‚-
2fumarate (C30H36N2O‚2C4H4O4) C, H, N.
tr a n s-2,5-Dim eth yl-1-[2-[bis(4-flu or op h en yl)m eth oxy]-
et h yl]-4-(3-p h en yl-2-p r op en yl)p ip er a zin e (17) was ob-
tained from 13 as described in procedure B (Table 2). 1H NMR
(CDCl3) δ 1.01-1.09 (m, 6H), 1.21-1.30 (m, 2H), 2.00-3.03
(m, 8H), 3.49-3.68 (m, 3H), 5.32 (s, 1H), 6.51 (d, J ) 15.9 Hz,
1H), 6.97-7.03 (m, 2H), 6.20-7.38 (m, 11H); MS (CI-NH3) m/ z
477 (MH+). Anal. 17‚2fumarate (C30H34N2F2O‚2C4H4O4) C,
H, N.
1-(3-P h en yl-2-p r op en yl)h om op ip er a zin e (18) was ob-
tained from homopiperazine as described in procedure B (Table
2). 1H NMR (CDCl3 plus D2O) δ 1.72-1.81 (m, 2H), 2.65-
2.73 (m, 4H), 2.88-2.95 (m, 4H), 3.35 (d, J ) 7.2 Hz, 2H), 6.26
(dt, J ) 7.1, 16.5 Hz, 1H), 6.47 (d, J ) 16.5 Hz, 1H), 7.15-
7.37 (m, 5H); MS (CI-NH3) m/ z 217 (MH+). Anal. 18‚
2fumarate (C14H20N2‚2C4H4O4‚0.25H2O) C, H, N.
Meth od D. tr a n s-2,5-Dim eth yl-1-(3-p h en ylp r op yl)p ip -
er a zin e (19) a n d tr a n s-2,5-Dim eth yl-1,4-bis(3-p h en ylp r o-
p yl)p ip er a zin e (22). trans-2,5-Dimethylpiperazine (5.0 g, 44
mmol) and hydrocinnamoyl chloride (7.4 g, 44 mmol) were
stirred in chloroform at room temperature overnight. The
reaction mixture was then washed with saturated NaHCO3
and water and extracted with 10% citric acid. The organic
layer yielded diamide I (4.5 g) as an oily residue which
solidified after treatment with ethyl ether. The acidic layer
was basified with 15% NaOH and extracted with CH2Cl2. The
combined organic extracts yielded monosubstituted amide II
(0.6 g).
1. The toluene was removed from the organic phase under
vacuum to yield the disubstituted piperazine 20 (1.2 g), which
had higher Rf value (TLC, system C). The product was
crystallized as the oxalate salt from MeOH: mp 178.5-180
1
°C; H NMR (CDCl3) δ 0.99 (s, 3H), 1.01 (s, 3H), 2.12 (t, J )
10.5 Hz, 2H), 2.39-2.41 (m, 2H), 2.56-2.64 (m, 2H), 2.76 (dd,
J ) 2.5, 11.2 Hz, 2H), 2.95-3.04 (m, 2H), 3.51-3.59 (m, 4H),
5.36 (s, 2H), 7.20-7.35 (m, 20H); MS (CI-NH3) m/ z 535 (MH+).
Anal. 20‚2oxalate (C36H42N2O2‚2C2H2O4) C, H, N.
2. The citric acid layer was neutralized with 15% NaOH
and extracted with CH2Cl2. The organic phase was dried
(anhydrous Na2SO4), and the solvent was evaporated under
vacuum to give 12 (17.8 g) as an oily residue. This compound
was purified as the fumarate salt from 2-PrOH; mp 185-187
°C dec; 1H NMR (CDCl3 plus D2O) δ 1.01 (d, J ) 6.2 Hz, 3H),
1.03 (d, J ) 6.3 Hz, 3H), 1.97 (t, J ) 11.2 Hz, 1H), 2.29-2.31
(m, 1H), 2.49-2.57 (m, 1H), 2.63-2.70 (m, 1H), 2.80-2.88 (m,
3H), 2.99-3.04 (m, 1H), 3.55-3.60 (m, 2H), 5.36 (s, 1H), 7.21-
7.33 (m, 10H); MS (CI-NH3) m/ z 325 (MH+). Anal. 12‚0.5fu-
marate (C21H28N2O‚0.5C4H4O4) C, H, N.
tr a n s-2,5-Dim eth yl-1-[2-[bis(4-flu or op h en yl)m eth oxy]-
eth yl]p ip er a zin e (13) a n d tr a n s-2,5-d im eth yl-1,4-bis[2-
[bis(4-flu or op h en yl)m eth oxy]eth yl]p ip er a zin e (21) were
prepared from trans-2,5-dimethylpiperazine (9.2 g, 81 mmol)
and 5b (7.6 g, 27 mmol) and purified following method C.
1. The monosubstituted amine 13 (7.5 g) was converted into
the fumarate salt (2-PrOH:MeOH ) 3:1): mp 121-123 °C; 1H
NMR (CDCl3 plus D2O) δ 0.99 (d, J ) 6.2 Hz, 3H), 1.02 (d, J
) 6.3 Hz, 3H), 1.94 (t, J ) 10.7 Hz, 1H), 2.18-2.26 (m, 1H),
2.49-2.65 (m, 2H), 2.78-2.89 (m, 3H), 2.98-3.03 (m, 1H),
3.51-3.57 (m, 2H), 5.33 (s, 1H), 6.98-7.03 (m, 3H), 7.25-7.31
(m, 5H); MS (CI-NH3) m/ z 361 (MH+). Anal. 13‚2fumarate
(C21H26N2F2O‚2C4H4O4‚0.5H2O) C, H, N.
2. Compound 21 (2.2 g) was purified as the fumarate salt
by crystallization from MeOH:2-PrOH ) 2:1; mp 164-167 °C;
1H NMR (CDCl3) δ 1.01 (s, 3H), 1.02 (s, 3H), 2.12-3.02 (m,
10H), 3.52 (s, broad, 4H), 5.32 (s, 2H), 6.96-7.04 (m, 6H),
7.23-7.29 (m, 10H); MS (CI-NH3) m/ z 607 (MH+). Anal. 21‚-
2fumarate (C36H38N2F4O2‚2C4H4O4‚H2O) C, H, N.
tr a n s-2,5-Dim eth yl-1-[2-(d ip h en ylm eth oxy)eth yl]-4-(3-
p h en ylp r op yl)p ip er a zin e (14) was synthesized from 12
following method B (Table 2). The crude product was chro-
matographed on a silica gel column (CH2Cl2:MeOH ) 100:2):
1H NMR (CDCl3) δ 0.98 (d, J ) 5.9 Hz, 3H), 1.04 (d, J ) 6.1
Hz, 3H), 1.78-1.83 (m, 2H), 1.96-2.05 (m, 1H), 2.18-2.84 (m,
10H), 2.96-3.04 (m, 1H), 3.54-3.60 (m, 2H), 5.38 (s, 1H),
7.15-7.35 (m, 15H); MS (CI-NH3) m/ z 443 (MH+). Anal. 14‚-
2fumarate (C30H38N2O‚2C4H4O4) C, H, N.
1. Diamide I (1.9 g, 5 mmol) was then reduced with AlH3
(workup according to method B) to afford 22 (1.5 g, 88% yield)
which was transformed into the fumarate salt from MeOH:2-
PrOH ) 1:3: mp 195-196 °C; 1H NMR (CDCl3) δ 0.99 (d, J )
6.2 Hz, 6H), 1.77-1.81 (m, 4H), 1.95-2.05 (m, 2H), 2.22-2.38
(m, 4H), 2.55-2.64 (m, 4H), 2.74-2.80 (m, 4H), 7.15-7.19 (m,
4H), 7.25-7.30 (m, 6H); MS (CI-NH3) m/ z 351 (MH+). Anal.
22‚2fumarate (C24H34N2‚2C4H4O4) C, H, N.
2. Monoamide II (0.6 g, 2.3 mmol) was reduced with LAH
(workup according to method B) to yield the monoamine 19
(0.45 g, 85%) which was converted to the 2fumarate salt from
1
MeOH:2-PrOH ) 1:2: mp 154-156 °C; H NMR (CDCl3 plus
D2O) δ 0.99 (d, J ) 6.2 Hz, 3H), 1.05 (d, J ) 6.3 Hz, 3H), 1.76-
1.89 (m, 3H), 2.24-2.33 (m, 2H), 2.54-2.64 (m, 4H), 2.74-
2.92 (m, 4H), 7.18-7.31 (m, 5H); MS (CI-NH3) m/ z 233 (MH+).
Anal. 19‚2fumarate (C15H24N2‚2C4H4O4‚0.5H2O) C, H, N.
1-[2-(Dip h en ylm eth oxy)eth yl]p ip er a zin e (23)32 was pre-
pared according to method C.
1-[2-[Bis(4-flu or op h e n yl)m e t h oxy]e t h yl]p ip e r a zin e
(24)32 was prepared according to method C.
1,4-Bis[2-(d ip h en ylm eth oxy)eth yl]p ip er a zin e (26) was
obtained from piperazine (0.43 g, 5 mmol), 5a (2.5 g, 10 mmol),
and K2CO3 (1.4 g, 10 mmol) as described in method C
(compound with a higher Rf; TLC system B) as an oily residue
(0.6 g, 24%) which formed the maleate salt from MeOH: mp
194-195 °C; 1H NMR (CDCl3) δ 2.53 (s, broad, 8H), 2.66 (t, J
) 6.1 Hz, 4H), 3.59 (t, J ) 6.1 Hz, 4H), 5.37 (s, 2H), 7.24-
7.36 (m, 20H); MS (CI-NH3) m/ z 507 (MH+). Anal. 26‚-
2maleate (C34H38N2O2‚2C4H4O4) C, H, N.
1,4-Bis[2-[b is(4-flu or op h e n yl)m e t h oxy]e t h yl]p ip e r -
a zin e (27) was obtained from piperazine (0.26 g, 3 mmol), 5b
(1.7 g, 6 mmol), and K2CO3 (0.84 g, 6 mmol) as described in
method C (compound with a higher Rf; TLC system B) as an
oily residue (1.26 g, 73%) which formed the 2maleate from
MeOH: mp 199-200 °C; 1H NMR (CDCl3) δ 2.52 (s, broad,
8H), 2.65 (t, J ) 6.1 Hz, 4H), 3.55 (t, J ) 6.1 Hz, 4H), 5.33 (s,
tr a n s-2,5-Dim eth yl-1-[2-[bis(4-flu or op h en yl)m eth oxy]-
eth yl]-4-(3-p h en ylp r op yl)p ip er a zin e (15) was synthesized
from 13 following method B (Table 2). The crude product was
chromatographed on a silica gel column (CH2Cl2:MeOH ) 100:
5): 1H NMR (CDCl3) δ 0.97 (d, J ) 6.1 Hz, 3H), 1.02 (d, J )
6.2 Hz, 3H), 1.75-1.81 (m, 2H), 1.93-2.02 (m, 1H), 2.11-2.79

Novel Dopamine Reuptake Inhibitors
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 24 4713
2H), 6.97-7.03 (m, 6H), 7.25-7.29 (m, 10H); MS (CI-NH3) m/ z
579 (MH+). Anal. 27‚2maleate (C34H34N2F4O2‚2C4H4O4) C, H,
N.
gel column, CHCl3:MeOH ) 9:1) to give pure and oily 36 (28%
yield), which was isolated as a powder by lyophilization of the
hydrochloride salt from water. 1H NMR (CDCl3) δ 1.60-1.79
(m, 6H), 2.46 (t, J ) 7.1 Hz, 2H), 2.54-2.57 (m, 2H), 2.61-
2.79 (m, 6H), 2.79-2.83 (m, 4H), 3.53 (t, J ) 6.2 Hz, 2H), 5.37
(s, 1H), 7.15-7.36 (m, 15H); MS (CI-NH3) m/ z 443 (MH+);
HRMS: MH+ (calcd for C30H38N2O) ) 443.3060; MH+ (found)
) 443.3062.
r-[N-[2-(Dip h en ylm et h oxy)et h yl]a m in o]-E-ca p r ola c-
ta m (38) was synthesized following method A (Table 1). 1H
NMR (CDCl3 plus D2O) δ 1.38-1.99 (m, 6H), 2.76-2.82 (m,
1H), 2.91-2.99 (m, 1H), 3.13-3.18 (m, 2H), 3.35-3.39 (m, 1H),
3.57-3.61 (m, 2H), 5.39 (s, 1H), 5.85 (s, broad, 1H), 7.20-7.37
(m, 10H); MS (CI-NH3) m/ z 339 (MH+). Anal. 38 base
(C21H26N2O2) C, H, N.
1-(3-P h en ylp r op yl)p ip er a zin e (25) a n d 1,4-bis(3-p h e-
n ylp r op yl)p ip er a zin e (28) were synthesized according to the
procedure and separation technique described in method D.
The monosubstituted amine 25 was purified as the maleate
salt from MeOH: mp 154-156 °C; 1H NMR (CDCl3 plus D2O)
δ 1.83 (quintet, J ) 7.7 Hz, 2H), 2.28-2.41 (m, complex, 6H),
2.63 (t, J ) 7.8 Hz, 2H), 2.88 (t, J ) 4.9 Hz, 4H), 7.18-7.31
(m, 5H); MS (CI-NH3) m/ z 205 (MH+). Anal. 25‚2maleate
(C13H20N2‚2C4H4O4‚0.5H2O) C, H, N. The disubstituted amine
28 was transformed into the hydrochloride salt (2-PrOH); mp
>245 °C dec; 1H NMR (CDCl3) δ 1.21 (t, J ) 6.9 Hz, 2H), 1.82
(quintet, J ) 7.7 Hz, 4H), 2.35-2.48 (m, complex, 8H), 2.63
(t, J ) 7.8 Hz, 4H), 3.48 (q, J ) 6.9 Hz, 2H), 7.15-7.30 (m,
10H); MS (CI-NH3) m/ z 323 (MH+). Anal. 28‚2hydrochloride
(C22H30N2‚2HCl) C, H, N.
N,N′-Dim eth yl-N-[2-(d ip h en ylm eth oxy)eth yl]eth ylen e-
d ia m in e (29) was synthesized following method A (Table 1).
1H NMR (CDCl3 plus D2O) δ 2.28 (s, 3H), 2.36 (s, 3H), 2.50-
2.70 (m, 6H), 3.55 (t, J ) 6.0 Hz, 2H), 5.38 (s, 1H), 7.18-7.42
(m, 10H); MS (CI-NH3) m/ z 299 (MH+). Anal. 29‚2maleate
(C19H26N2O‚2C4H4O4) C, H, N.
N,N′-Dim eth yl-N-[2-(diph en ylm eth oxy)eth yl]-N′-(3-ph e-
n ylp r op yl)eth ylen ed ia m in e (30) was synthesized from 29
according to method B (Table 2): 1H NMR (CDCl3) δ 1.78 (m,
2H), 2.22 (s, 3H), 2.29 (s, 3H), 2.38 (dd, J ) 7.2, 8.6 Hz, 2H),
2.44-2.65 (m, 6H), 2.70 (t, J ) 6.2 Hz, 2H), 3.58 (t, J ) 6.2
Hz, 2H), 5.38 (s, 1H), 7.12-7.40 (m, 15H); MS (CI-NH3) m/ z
417 (MH+). Anal. 30‚2maleate (C28H36N2O‚2C4H4O4) C, H,
N.
2,2-Dim et h yl-N-[2-(d ip h en ylm et h oxy)et h yl]-1,3-p r o-
p a n ed ia m in e (31) was synthesized following method A (Table
1): 1H NMR (CDCl3 plus D2O) δ 0.87 (s, 6H), 2.41 (s, 2H), 2.50
(s, 2H), 2.82 (t, J ) 5.3 Hz, 2H), 3.58 (t, J ) 5.3 Hz, 2H), 5.37
(s, 1H), 7.22-7.35 (m, 10H); MS (CI-NH3) m/ z 313 (MH+).
Anal. 31‚2fumarate (C20H28N2O‚2C4H4O4‚C3H8O) C, H, N.
2,2-Dim eth yl-N-[2-(d ip h en ylm eth oxy)eth yl]-N′-(3-p h e-
n ylp r op yl)-1,3-p r op a n ed ia m in e (32) was obtained from 31
following procedure B (Table 2): 1H NMR (CDCl3 plus D2O) δ
0.91 (s, 6H), 1.75-1.80 (m, 2H), 2.42-2.44 (m, 4H), 2.55-2.63
(m, 4H), 2.83 (t, J ) 5.2 Hz, 2H), 3.57 (t, J ) 5.2 Hz, 2H), 5.36
(s, 1H), 7.14-7.34 (m, 15H); MS (CI-NH3) m/ z 431 (MH+).
Anal. 32‚2maleate (C29H38N2O‚2C4H4O4) C, H, N.
Meth od E. 3,3-Dim eth yl-1-[2-(diph en ylm eth oxy)eth yl]-
5-(3-p h en ylp r op yl)h om op ip er a zin e (33). The free base 32
(0.2 g, 0.47 mmol), 1,2-dibromoethane (0.176 g, 0.94 mmol),
and K2CO3 (0.26 g, 1.88 mmol) were stirred and refluxed in
xylenes (10 mL) for 72 h. The reaction mixture was then
cooled down and washed with water (3×). The organic solvent
was removed under vacuum, and the residue was chromato-
graphed (silica gel column; CH2Cl2:MeOH ) 40:1) to afford the
pure diamine 33 (0.1 g, 47%) as an oil, which was isolated as
a powder by lyophilization of the HCl salt from water: 1H
NMR (CDCl3) δ 0.81 (s, 6H), 1.73-1.77 (m, 2H), 2.27 (s, broad,
2H), 2.42 (s, broad, 4H), 2.55-2.65 (m, 6H), 2.77-2.79 (m, 2H),
3.54 (t, J ) 6.1 Hz, 2H), 5.36 (s, 1H), 7.17-7.36 (m, 15H); MS
(CI-NH3) m/ z 457 (MH+); HRMS MH+ (calcd for C31H40N2O)
) 457.3219; MH+ (found) ) 457.3234.
N-[2-(Dip h en ylm eth oxy)eth yl]-1,4-d ia m in ebu ta n e (34)
was synthesized following method A (Table 1); 1H NMR (CDCl3
plus D2O) δ 1.46-1.53 (m, 4H), 2.60 (t, J ) 6.8 Hz, 2H), 2.68
(t, J ) 6.6 Hz, 2H), 2.82 (t, J ) 5.2 Hz, 2H), 3.59 (t, J ) 5.2
Hz, 2H), 5.37 (s, 1H), 7.24-7.34 (m, 10H); MS (CI-NH3) m/ z
299 (MH+). Anal. 34‚2maleate (C19H26N2O‚2C4H4O4‚0.5H2O)
C, H, N.
N-[2-(Dip h en ylm et h oxy)et h yl]-N′-(3-p h en ylp r op yl)-
1,4-bu ta n ed ia m in e (35) was obtained from 34 following
procedure B (Table 2). 1H NMR (CDCl3 plus D2O) δ 1.43-
1.49 (m, 4H), 1.81 (quintet, J ) 7.5 Hz, 2H), 2.58-2.67 (m,
complex, 8H), 2.82 (t, J ) 5.1 Hz, 2H), 3.58 (t, J ) 5.2 Hz,
2H), 5.36 (s, 1H), 7.18-7.33 (m, 15H); MS (CI-NH3) m/ z 417
(MH+). Anal. 35‚2maleate (C28H36N2O‚2C4H4O4) C, H, N.
1-[2-(Dip h en ylm eth oxy)eth yl]-4-(3-p h en ylp r op yl)-1,4-
d ia za octa n e (36) was prepared using the conditions described
in method E. The crude product was chromatographed (silica
3-[N-[2-(Dip h en ylm et h oxy)et h yl]a m in o]h om op ip er -
id in e (39) was obtained by AlH3 reduction of 38 in THF in
79% yield (workup according to method B). The final amine
was converted into the maleate salt and crystallized from
1
MeOH: mp 152-54 °C; H NMR (CDCl3 plus D2O) δ 1.65-
1.93 (m, 6H), 2.73-2.93 (m, complex, 7H), 3.58 (t, J ) 5.2 Hz,
2H), 5.37 (s, 1H), 7.23-7.33 (m, 10H); MS (CI-NH3) m/ z 325
(MH+). Anal. 39‚2maleate (C21H28N2O‚2C4H4O4) C, H, N.
3-[N-[2-(Dip h en ylm et h oxy)et h yl]a m in o]-1-(3-p h en yl-
p r op yl)h om op ip er id in e (40) was obtained from 39 following
method B (Table 2): 1H NMR (CDCl3 plus D2O) δ 1.63-1.80
(m, complex, 10H), 2.52-2.92 (m, complex, 7H), 3.30-3.48 (m,
2H), 3.60-3.89 (m, 2H), 5.30 (s, 1H), 7.11-7.31 (m, 15H); MS
(CI-NH3) m/ z 443 (MH+). Anal. 40‚2fumarate (C30H38N2O‚-
2C4H4O4‚0.5H2O) C, H, N.
3-[N-(3-P h en ylp r op yl)a m in o]h om op ip er id in e (42) was
synthesized from 37 according to method B (Table 2): 1H NMR
(CDCl3 plus D2O) δ 1.23 (t, J ) 6.9 Hz, 2H), 1.44-1.49 (m,
2H), 1.52-1.71 (m, 2H), 1.80 (quintet, J ) 7.5 Hz, 2H), 2.58-
2.76 (m, complex, 4H), 2.76-2.91 (m, 3H), 3.48 (q, J ) 7.1 Hz,
2H), 7.16-7.31 (m, 5H); MS (CI-NH3) m/ z 233 (MH+). Anal.
42‚2maleate (C15H24N2‚2C4H4O4) C, H, N.
1-[2-(Dip h en ylm eth oxy)eth yl]-3-[N-(3-p h en ylp r op yl)-
a m in o]h om op ip er id in e (43) was synthesized according to
method A (Table 1): 1H NMR (CDCl3 plus D2O) δ 1.63-1.79
(m, 10H), 2.49-2.79 (m, complex, 7H), 2.83 (t, J ) 5.8 Hz, 2H),
3.55 (t, J ) 5.8 Hz, 2H), 5.30 (s, 1H), 7.12-7.37 (m, 15H); MS
(CI-NH3) m/ z 443 (MH+). Anal. 43‚2oxalate (C30H38N2O‚-
2C2H2O4) C, H, N.
(S)-(-)-N-[2-(Diph en ylm eth oxy)eth yl]pr olin am ide [(-)-
45] was prepared from (S)-(-)-prolinamide [(-)-44] following
the procedure described in method A (Table 1): [R]23D ) -11.8°
1
(hydrobromide, MeOH, c ) 1.14); H NMR (CDCl3 plus D2O)
δ 1.71-1.82 (m, complex, 2H), 1.88-1.98 (m, 1H), 2.11-2.25
(m, 1H), 2.30-2.39 (m, 1H), 2.70 (dt, J ) 3.8, 13.3 Hz, 1H),
2.96-3.04 (m, complex, 1H), 3.09-3.28 (m, 2H), 3.46-3.61 (m,
2H), 5.36 (s, 1H), 7.21-7.36 (m, 10H); MS (CI-NH3) m/ z 325
(MH+). Anal. (-)-45‚hydrobromide (C20H24N2O2‚HBr) C, H,
N.
(S)-(-)-2-(Am in om eth yl)-N-[2-(d ip h en ylm eth oxy)eth -
yl]p yr r olid in e [(-)-46] was obtained as a product of LAH
reduction of (-)-45 in THF in 93% yield (workup according to
method B). The final amine was purified as the oxalate salt
and crystallized from MeOH: mp 130-130.5 °C; [R]23D ) -8.4°
(2oxalate, MeOH, c ) 1.05); 1H NMR (CDCl3 plus D2O) δ 1.52-
1.65 (m, 1H), 1.65-1.78 (m, 2H), 1.78-1.90 (m, 1H), 2.26 (q,
J ) 8.2 Hz, 1H), 2.40-2.60 (m, 2H), 2.66 (d, J ) 4.9 Hz, 2H),
2.98-3.09 (m, 1H), 3.09-3.17 (m, 1H), 3.58 (t, J ) 5.9 Hz, 2H),
5.38 (s, 1H), 7.20-7.40 (m, 10H); MS (CI-NH3) m/ z 311 (MH+).
Anal. (-)-46‚2oxalate (C20H26N2O‚2C2H2O4‚H2O) C, H, N.
(S)-(-)-N-[2-[Bis(4-flu or op h en yl)m eth oxy]eth yl]p r oli-
n a m id e [(-)-47] was prepared from L-(-)-prolinamide [(-)-
44] following the procedure described in method A (Table 1):
[R]23 ) -13.9° (hydrobromide, MeOH, c ) 0.51); 1H NMR
D
(CDCl3 plus D2O) δ 1.22 (t, J ) 6.9 Hz, 2H), 1.76-1.84 (m,
1H), 1.89-1.99 (m, complex, 1H), 2.14-2.24 (m, 1H), 2.33-
2.42 (m, 1H), 2.73 (dt, J ) 4.1, 13.3 Hz, 1H), 2.96-3.04 (m,
complex, 1H), 3.12-3.21 (m, 1H), 3.45-3.59 (m, 2H), 5.33 (s,
1H), 7.03-7.07 (m, 4H), 7.25-7.32 (m, 4H); MS (CI-NH3) m/ z
361 (MH+). Anal. (-)-47‚hydrobromide (C20H22N2F2O2‚HBr)
C, H, N.

4714 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 24
Matecka et al.
(S )-(-)-2-(Am in om e t h yl)-N -[2-[b is(4-flu or op h e n yl)-
m eth oxy]eth yl]p yr r olid in e [(-)-48] was obtained as a
product of LAH reduction of (-)-47 in THF in 93% yield
(workup according to method B). The final amine was purified
on a silica gel column (CH2Cl2:MeOH ) 100:15) and used as
in ethyl acetate. The organic solution was extracted with 10%
citric acid (3×), and the acidic extracts were discarded. The
organic phase was washed with saturated solution of sodium
bicarbonate and water, dried (Na2SO4), and evaporated to
dryness to afford pure (+)-54 as a colorless oil: [R]21D ) +69.2°
1
an oil in the next step: [R]23 ) -25.8° (free base, CHCl3, c )
(free base, CH2Cl2, c ) 0.57); H NMR (CDCl3) δ 1.46 (s, 9H),
D
0.43); 1H NMR (CDCl3 plus D2O) δ 1.57-1.69 (m, complex, 1H),
1.71-1.78 (m, complex, 2H), 1.82-1.91 (m, complex, 1H), 2.28
(q, J ) 8.5 Hz, 1H), 2.48-2.58 (m, 2H), 2.68 (d, J ) 4.5 Hz,
2H), 3.05 (quintet, J ) 6.4 Hz, 1H), 3.11-3.17 (m, 1H), 3.55
(t, J ) 5.9 Hz, 2H), 5.36 (s, 1H), 7.03 (t, J ) 8.6 Hz, 4H), 7.28-
7.34 (m, 4H); MS (CI-NH3) m/ z 347 (MH+); HRMS: MH+
(calcd for C20H24N2F2O) ) 347.1935; MH+ (found) ) 347.1922.
(S)-(-)-1-[2-(Dip h en ylm eth oxy)eth yl]-2-[[N-(3-p h en yl-
p r op yl)a m in o]m eth yl]p yr r olid in e [(-)-49] was synthe-
1.78-1.88 (m, 6H), 2.65 (t, J ) 7.5 Hz, 2H), 3.24-3.39 (m, 5H),
4.23 (s, broad, 1H), 7.16-7.19 (m, 3H), 7.21-7.31 (m, 2H); MS
(CI-NH3) m/ z 333 (MH+).
2. (+)-55. A solution of (+)-54 (0.84 g, 2.53 mmol) in CH2-
Cl2 (10 mL) and trifluoroacetic acid (5 mL) were stirred at room
temperature until the reaction was complete (2 h, TLC system
A). The reaction mixture was then quenched with a saturated
solution of potassium carbonate, stirred for 0.5 h, and extracted
with CH2Cl2. The organic extracts were combined and dried
(Na2SO4) and the solvent removed under vacuum to afford 0.58
sized from (-)-46 according to method B (Table 2): [R]22
)
D
-5.7° (2oxalate, MeOH, c ) 0.67); 1H NMR (CDCl3 plus D2O)
δ 1.54-1.78 (m, 6H), 1.81-1.91 (m, 1H), 2.22-2.32 (m, 2H),
2.51-2.64 (m, 6H), 3.02-3.16 (m, 2H), 3.55 (t, J ) 5.8 Hz, 2H),
5.41 (s, 1H), 7.09-7.38 (m, 15H); MS (CI-NH3) m/ z 429 (MH+).
Anal. (-)-49‚2oxalate (C29H36N2O‚2C2H2O4) C, H, N.
g (97% yield) of pure (+)-55 (TLC system A): [R]21 ) +43.9°
D
(free base, CH2Cl2, c ) 0.31); 1H NMR (CDCl3) δ 1.66-1.75
(m, 2H), 1.76-1.96 (m, 3H), 2.08-2.20 (m, 1H), 2.65 (t, J )
7.7 Hz, 2H), 2.89 (dt, J ) 6.3, 10.2 Hz, 1H), 3.01 (dt, J ) 6.8,
10.2 Hz, 1H), 3.27 (dd, J ) 7.0, 13.3 Hz, 2H), 3.74 (dd, J )
5.3, 9.2 Hz, 1H), 7.16-7.19 (m, 3H), 7.21-7.31 (m, 2H), 7.63
(s, broad, 1H); MS (CI-NH3) m/ z 233 (MH+).
(S)-(-)-1-[2-[Bis(4-flu or op h en yl)m eth oxy]eth yl]-2-[[N-
(3-p h en ylp r op yl)a m in o]m eth yl]p yr r olid in e [(-)-50] was
synthesized from (-)-48 according to method B (Table 2):
[R]23D ) -2.3° [2(L-tartate), MeOH, c ) 0.49]; 1H NMR (CDCl3
plus D2O) δ 1.19-1.25 (m, 1H), 1.58-1.62 (m, complex, 1H),
1.64-1.79 (m, complex, 4H), 1.82-1.91 (m, complex, 1H), 2.23
(q, J ) 8.7 Hz, 1H), 2.47-2.65 (m, 7H), 2.99-3.12 (m, 2H),
3.47-3.53 (m, 2H), 5.33 (s, 1H), 6.95-7.01 (m, 4H), 7.14-7.30
(m, 9H); MS (CI-NH3) m/ z 465 (MH+). Anal. (-)-50‚2(L-
tartate) (C29H34N2F2O‚2C4H6O6‚0.5H2O) C, H, N.
(S)-(-)-1-[2-(Dip h en ylm et h oxy)et h yl]-2-[[N-[3-(m -h y-
d r oxyp h en yl)p r op yl]a m in o]m eth yl]p yr r olid in e [(-)-52].
1. (-)-51. To a solution of m-(benzyloxy)cinnamic acid (2.54
g, 10 mmol) stirred under nitrogen in CH2Cl2 (50 mL) was
added a solution of dicyclohexylcarbodiimide (DCC) (2.06 g,
10 mmol) in CH2Cl2 (20 mL). After 40 min of stirring, a
solution of (-)-46 (1.55 g, 5 mmol) in CH2Cl2 (20 mL) and
pyridine (0.15 mL) were added. This mixture was stirred for
5 h until the reaction was complete (TLC, system A). The
precipitated solid material was filtered off, and the solvent was
evaporated. The crude product was chromatographed (silica
gel, short column, CH2Cl2) to yield (-)-51 (2.3 g, 82% yield)
as an oil, which was used without further purification in the
next step; [R]21D ) -31.8° (free base, MeOH, c ) 0.32); 1H NMR
(CDCl3) δ 1.58-1.95 (m, 3H), 2.35-2.82 (m, 3H), 3.15-3.42
(m, 5H), 3.60 (s, broad, 2H), 5.02 (s, 2H), 5.40 (s, 1H), 6.85-
6.95 (m, 2H), 7.12-7.40 (m, complex, 19H); MS (CI-NH3) m/ z
547 (MH+).
3. (+)-56. The N-[2-(diphenylmethoxy)ethyl]-substituted
pyrrolidine (+)-56 was obtained from pyrrolidine (+)-55
according to method A (Table 1). The pure oily (+)-56 was
used in the next step without further purification: [R]21
)
D
1
+26.8° (free base, CH2Cl2, c ) 0.23); H NMR (CDCl3) δ 1.57
(quintet, J ) 7.5 Hz, 2H), 1.69-1.79 (m, 2H), 1.83-1.92 (m,
1H), 2.14-2.21 (m, 1H), 2.29-2.38 (m, 1H), 2.45 (t, J ) 7.9
Hz, 2H), 2.66 (dt, J ) 3.9, 13.2 Hz, 1H), 2.90-3.03 (m, 2H),
3.10-3.22 (m, 3H), 3.47-3.56 (m, 2H), 5.36 (s, 1H), 7.08 (d, J
) 7.1 Hz, 1H), 7.17-7.35 (m, 14H), 7.80 (s, broad, 1H); MS
(CI-NH3) m/ z 443 (MH+).
4. (+)-49. A 1 M solution of AlH3 in THF (10 mL) was
added to the solution of (+)-56 (0.6 g, 1.35 mmol) in THF (10
mL) and refluxed with stirring for 5 h. After usual workup
(see method B), the pure oily amine (+)-57 (0.49 g, 84% yield)
was converted into the oxalate salt from 2-PrOH: mp 162-
1
164 °C; [R]23 ) +8.5° (2oxalate, MeOH, c ) 0.44); H NMR
D
(CDCl3 plus D2O) δ 1.58-1.79 (m, 6H), 1.81-1.96 (m, 1H),
2.31-2.45 (m, 2H), 2.45-2.56 (m, 2H), 2.58-2.68 (m, 4H),
3.04-3.17 (m, 2H), 3.53-3.63 (m, 2H), 5.45 (s, 1H), 7.08 (d, J
) 6.9 Hz, 1H), 7.17-7.37 (m, 14H); MS (CI-NH3) m/ z 429
(MH+). Anal. (+)-49‚2oxalate (C29H36N2O‚2C2H2O4) C, H, N.
Biologica l Meth od s. 1. Bin d in g a n d Reu p ta k e In h ibi-
tion Assa ys. Binding assays for the DAT followed published
procedures and used 2 nM [3H]GBR 1293560 (SA ) 42.5 Ci/
mmol) and 0.01 nM [125I]RTI 5561 (SA ) 2200 Ci/mmol).
Briefly, 12 × 75 mm polystyrene test tubes were prefilled with
100 µL of drug, 100 µL of radioligand ([3H]GBR 12935 or [125I]-
RTI 55), and 50 µL of a “blocker” or buffer. Drugs and blockers
were made up in 55.2 mM sodium phosphate buffer, pH 7.4
(BB) containing 1 mg/mL bovine serum albumin (BB/BSA).
Radioligands were made up in a protease inhibitor cocktail
containing 1 mg/mL BSA {BB containing chymostatin (25 µg/
mL), leupeptin (25 µg/mL), EDTA (100 µM), and EGTA (100
µM)}. The samples were incubated in triplicate for 18-24 h
at 4 °C (equilibrium) in a final volume of 1 mL. Brandel cell
harvesters were used to filter the samples over Whatman GF/B
filters, which were presoaked in wash buffer (ice-cold 10 mM
TRIS-HCl/150 mM NaCl), pH 7.4) containing 2% polyethyl-
enimine.
2. (-)-52. The amide (-)-51 (2.0 g, 3.66 mmol) was
hydrogenated (H2, atmospheric pressure) with 5% Pd-C in
MeOH (30 mL) at room temperature for 24 h until the reaction
was complete (TLC, system B). The reaction mixture was then
filtered through a pad of Celite and the solvent evaporated to
give an oily product (1.56 g, 93%), MS (CI-NH3) m/ z 459
(MH+). This amide was then directly reduced with AlH3 to
afford the final phenolic amine (-)-52 which was chromato-
graphed (silica gel column, CH2Cl2:MeOH:NH4OH ) 100:10:
1) (0.85 g, 58%), and converted to the amorphous dihydrochlo-
ride by lyophilization from water; [R]23 ) -21.9° (free base,
D
1
CHCl3, c ) 0.75); H NMR (CDCl3 plus D2O) δ 1.20-1.26 (m,
1H), 1.57-1.88 (m, 6H), 2.25-2.36 (m, 2H), 2.48-2.65 (m, 6H),
3.04-3.13 (m, 2H), 3.56 (t, J ) 5.9 Hz, 2H), 5.38 (s, 1H), 6.60-
6.67 (m, 2H), 7.08-7.36 (m, 12H); MS (CI-NH3) m/ z 445
(MH+). Anal. (-)-52‚2hydrochloride (C29H36N2O2‚2HCl) C, H,
N.
The [3H]DA and [3H]5HT uptake assays also proceeded
according to published procedures.45 Briefly, synaptosomes
were prepared by homogenization of rat caudate (for [3H]DA
reuptake) or whole rat brain minus cerebellum (for [3H]5HT
reuptake) in ice-cold 10% sucrose, using a Potter-Elvehjem
homogenizer. After a 1000g centrifugation for 10 min at 4 °C,
the supernatants were retained on ice. The uptake assays
were initiated by the addition of 100 µL of synaptosomes to
12 × 75 mm polystyrene test tubes, which were prefilled with
750 µL of [3H]ligand (5 nM and 2 nM final concentration
for [3H]DA and [3H]5HT, respectively) in a Krebs-phosphate
buffer (pH 7.4), which contained ascorbic acid (1 mg/mL)
and pargyline (50 µM) (buffer), 100 µL of test drugs made
up in buffer, and 50 µL of buffer. The nonspecific uptake
(R)-(+)-1-[2-(Dip h en ylm eth oxy)eth yl]-2-[[N-(3-p h en yl-
p r op yl)a m in o]m eth yl]p yr r olid in e [(+)-49]. 1. (+)-54. To
a solution of N-Boc-D-proline [(+)-53] (0.65 g, 3 mmol) in CH2-
CL2 (10 mL), a solution of 1-[3-(dimethylamino)propyl]-3-
ethylcarbodiimide (0.77 g, 3.6 mmol, 1.2 equiv) in CH2Cl2 (10
mL) followed by 1-hydroxybenzotriazole59 (0.49 g, 3.6 mmol,
1.2 equiv) was added and stirred for 40 min. A solution of
3-phenyl-1-propylamine (0.6 g, 4.5 mmol, 1.5 equiv) in CH2-
Cl2 (5 mL) was then added dropwise, and the reaction mixture
was stirred at room temperature overnight. The solvent was
then removed under vacuum, and the residue was dissolved

Novel Dopamine Reuptake Inhibitors
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 24 4715
of each [3H]ligand was measured by incubations in the
presence of 1 µM GBR 12909 ([3H]DA) and 10 µM fluoxetine
([3H]5HT). The incubations were terminated after a 15 min
([3H]DA) or 30 min ([3H]5HT) incubation at 25 °C by adding 4
mL of wash buffer (10 mM Tris-HCl, pH 7.4 containing 0.9%
NaCl at 25 °C), followed by rapid filtration over Whatman
GF/B filters and one additional wash cycle. The Krebs-
phosphate buffer contained 154.5 mM NaCl, 2.9 mM KCl, 1.1
mM CaCl2, 0.83 mM MgCl2, and 5 mM glucose. The tritium
retained on the filters was counted, in a Taurus beta counter,
after an overnight extraction into ICN Cytoscint cocktail.
For the [3H]-(+)-pentazocine (σ) binding assay large batches
of frozen membranes were prepared from frozen guinea pig
brains (Pel Freeze) as previously described.62 The [3H]-(+)-
pentazocine binding assay proceeded with minor modifications
of previously published procedures.63 Briefly, incubations
proceeded for 3-4 h at 25 °C (steady state) in 5 mM Tris-HCl,
pH 8.2, with a protease inhibitor cocktail (chymostatin [10 µg/
mL], leupeptin [10 µg/mL], EDTA [10 µM], EGTA [10 µM]).
The incubations were terminated by rapid filtration over
Whatman GF/B filters presoaked in 1% polyethylenimine,
followed by two 4 mL washes with ice-cold 5 mM Tris-HCl,
pH 8.0. The tritium on the filters was measured after an
overnight extraction in 5 mL of ICN Cytoscint coctail, using
standard liquid scintillation counting methods. Nonspecific
binding was determined by incubations in the presence of 10
µM DTG.
Ack n ow led gm en t. We would like to thank Noel
Whittaker and Wesley White of the Laboratory of
Analytical Chemistry for mass spectral data and ac-
knowledge the National Institute on Drug Abuse,
Medications Development Division for partial financial
support of this work.
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