Dual DAT/σ1 receptor ligands based on 3-(4-(3-(bis(4-fluorophenyl)amino)propyl)piperazin-1-yl)-1-phenylpropan-1-ol

Article abstract of DOI:10.1016/j.bmcl.2008.08.065

Ester analogs of (±)3-(4-(3-(bis(4-fluorophenyl)amino)propyl)piperazin-1-yl)-1-phenylpropan-1-ol were synthesized and evaluated for binding at DAT, SERT, NET, and σ1 receptors, and compared to GBR 12909 and several known σ1 receptor ligands. Most of these compounds demonstrated high affinity (K_i = 4.3-51 nM) and selectivity for the DAT among the monoamine transporters. S- and R-1-(4-(3-(bis(4-fluorophenyl)amino)propyl)piperazin-1-yl)-3-phenylpropan-2-ol were also prepared wherein modest enantioselectivity was demonstrated at the DAT. However, no enantioselectivity at σ1 receptors was observed and most of the ester analogs of the more active S-enantiomer showed comparable binding affinities at both DAT and σ1 receptors with a maximal 16-fold DAT/σ1 selectivity.

Full text of DOI:10.1016/j.bmcl.2008.08.065

Bioorganic & Medicinal Chemistry Letters 18 (2008) 5238–5241
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Dual DAT/r1 receptor ligands based on 3-(4-(3-(bis(4-fluorophenyl)amino)
propyl)piperazin-1-yl)-1-phenylpropan-1-ol
Jianjing Cao a, Theresa Kopajtic b, Jonathan L. Katz b, Amy Hauck Newman a,
*
a Medicinal Chemistry Section, National Institute on Drug Abuse––Intramural Research Program, National Institutes of Health, 333 Cassell Drive, Baltimore, MD 21224, USA
b Psychobiology Section, National Institute on Drug Abuse––Intramural Research Program, National Institutes of Health, 251 Bayview Boulevard, Baltimore, MD 21224, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Ester analogs of ( )3-(4-(3-(bis(4-fluorophenyl)amino)propyl)piperazin-1-yl)-1-phenylpropan-1-ol were
Received 30 July 2008
Revised 14 August 2008
Accepted 19 August 2008
Available online 22 August 2008
synthesized and evaluated for binding at DAT, SERT, NET, and
r1 receptors, and compared to GBR 12909
and several known receptor ligands. Most of these compounds demonstrated high affinity
r1
(Ki = 4.3–51 nM) and selectivity for the DAT among the monoamine transporters. S- and R-1-(4-(3-
(bis(4-fluorophenyl)amino)propyl)piperazin-1-yl)-3-phenylpropan-2-ol were also prepared wherein
modest enantioselectivity was demonstrated at the DAT. However, no enantioselectivity at
was observed and most of the ester analogs of the more active S-enantiomer showed comparable binding
r1 receptors
Keywords:
Dopamine transport inhibitors
affinities at both DAT and
r
1 receptors with a maximal 16-fold DAT/
r
1 selectivity.
Published by Elsevier Ltd.
r
Receptors
Cocaine
Rimcazole
GBR 12909
Several lines of evidence have linked
r
1 receptors to the atten-
1-recep-
F
F
uation of the behavioral effects of cocaine.1 Rimcazole, a
r
tor antagonist,2 also binds with moderate affinity to the dopamine
transporter (DAT),3,4 but exhibits neither cocaine-like psychomotor
stimulant nor cocaine discriminative stimulus effects in rodents.5,6
Further, rimcazole attenuates cocaine-induced stimulation of loco-
motor activity,6 convulsions,7 and place conditioning;8 actions that
N
N
N
N
N
NH
have been suggested to be mediated via blockade of
However, as rimcazole and its analogs have similar
r
1 receptors.
OH
r
1- and DAT-
JJC 2-010, 1
rimcazole
binding affinities, a role of the DAT in these behavioral effects
remains to be established. We have recently demonstrated that
rimcazole and selected analogs bind the DAT in a conformation
that differs from that for cocaine, which may be related to their
unique in vivo effects.9
F
F
F
F
N
N
In earlier studies of rimcazole analogs, we identified com-
pounds with varying affinities and selectivities for
r1 receptors
N
N
RO
and the DAT as potential in vivo probes.4,10–12 The hydroxylated
linking chain analogue, JJC 2-010 (1, ( )3-(4-(3-(bis(4-fluoro-
phenyl) amino)propyl)piperazin-1-yl)-1-phenylpropan-1-ol) dem-
onstrated high affinity and selectivity for the DAT over serotonin
(SERT) and norepinephrine transporters (NET) and provided the
template for the next generation of compounds (Fig. 1).
N
N
OR
compounds 7a-e
compounds 2a-g
Figure 1. Dual DAT/r1 receptor ligands.
in this paradigm, suggesting that either this compound is an atyp-
ical dopamine uptake inhibitor13,14 and/or its
1 receptor antago-
JJC 2-010 (1) did not generalize in rats trained to discriminate
10 mg/kg cocaine from saline (Fig. 2). Moreover, JJC 2-010 (1), at
10 and 24 mg/kg, had no effect on the cocaine dose–effect curve
r
nist actions affect the discriminative stimulus effects of cocaine. In
order to further develop structure–activity relationships (SAR) in
this series of compounds, and provide in vivo tools with which to
characterize the roles of
r1 receptors and the DAT in the interac-
* Corresponding author. Tel.: +1 443 740 2887; fax: +1 443 740 2111.
tions of rimcazole analogs and cocaine, additional analogs were
E-mail address: anewman@intra.nida.nih.gov (A.H. Newman).
0960-894X/$ - see front matter Published by Elsevier Ltd.
doi:10.1016/j.bmcl.2008.08.065

J. Cao et al. / Bioorg. Med. Chem. Lett. 18 (2008) 5238–5241
5239
4b were synthesized via a regioselective epoxide ring opening
using the Grignard reagent prepared from bromobenzene (3) as de-
scribed previously.15 These chiral synthons (4a and 4b) were then
alkylated with the previously reported 4-fluoro-N-(4-fluoro-
phenyl)-N-(3-(piperazin-1-yl)propyl)aniline11 to give the S and R
(6a and 6b, respectively) enantiomers. These enantiomers were
tested for binding at the DAT and it was discovered that the S-
enantiomer had slightly higher affinity for the DAT, and thus ester
analogs (7a–e) were prepared (Scheme 2) of the more active enan-
tiomer (6a) only. Of note, similarly modest enantioselectivity was
also observed in the GBR 12909 series15 and did not inspire us to
pursue the enantiomers of ( )1.
Binding affinities at
r1 receptors, as well as the DAT, SERT, and
NET for 2a–g, 6a, 6b, and 7a–e were determined and compared to
those of rimcazole and JJC 2-010 (1), as well as GBR 12909 and sev-
eral known
r1 receptor agonists. Note, binding affinities at DAT
and 1 for 1, rimcazole, and GBR 12909 are slightly higher than
r
what was previously reported, due to slightly modified binding
methods employed.18 All the ester analogs of 1 demonstrated
high-affinity binding at the DAT, although the additional steric
bulk of esters 2f and 2g reduced binding affinity ꢀ10-fold. All com-
pounds were uniformly less active at the SERT and NET, but had
similar affinities to 1 at
r1 receptors, again with a slight decrease
in affinity for the sterically bulky analogs. As mentioned above, the
S-enantiomer 6a showed slightly higher affinity (Ki = 1.72 nM) for
DAT than its R-enantiomer 6b (Ki = 5.36 nM) and was the highest
affinity compound in this series. Esterification of 6a yielded esters
7a–e that showed similar binding profiles to 2a–g (Table 1).
Selectivity profiles based on Ki ratios are displayed in Table 2.
All of the new analogs were selective for DAT over SERT and NET,
with compound 6a showing the highest DAT selectivity ratios.
Analogs of rimcazole are of particular interest because they
bind to the DAT but do not produce behavioral effects similar to
Figure 2. Discriminative stimulus effects of JJC 2-010 alone and with cocaine in rats
trained to discriminate 10 mg/kg cocaine from saline (ip).
those of cocaine.6,11 Because
r receptor antagonists have been re-
ported to block several actions of cocaine, it has been proposed
that these drugs block actions of cocaine mediated by sigma recep-
designed (Fig. 1). Using simple esterification of the linking chain
OH group, steric tolerance could be explored.
In the present series, analogs with an esterification of the –OH
group in JJC 2-010 (1) were synthesized and tested for binding at
tors, or that
r-receptor-mediated effects modulate the actions of
cocaine. In addition, our previous results suggest that rimcazole
analogs, including JJC 2-010, in contrast to cocaine analogs, bind
the DAT in a manner that promotes its inward facing conforma-
tion.9 Among the present compounds are several that have differ-
r
1 receptors and the DAT, as well as the SERT and NET (2a–g). Fur-
ther, additional SAR studies conducted on the GBR 12909 template
have been reported recently15,16 that led us to prepare the homol-
ogous 1-(4-(3-(bis(4-fluorophenyl)amino) propyl)piperazin-1-yl)-
3-phenylpropan-2-ol series to investigate enantioselectivity and
then make ester analogs (7a–e) of the more active enantiomer (6a).
Compound 1 was prepared as previously described11 and ester-
ified (Scheme 1)17 to give 2a–g. In Scheme 2,17 compounds 4a and
ent degrees of selectivity for the DAT over
r1-receptors.
Behavioral evaluation of selected ligands will prove useful in disen-
tangling these molecular contributions to behavioral outcomes.
Thus this set of compounds will provide additional tools with
which to explore the potential of compounds with dual actions
at the DAT and
discovery.
r
1 receptors as leads for cocaine abuse medication
F
F
F
F
N
N
a
N
N
N
N
OH
OR
1
2a; R=COCH3
2b; R=COCH2CH3
2c; R=COCH(CH3)2
2d; R=COCH=CH2
2e; R=COCH2Ph
2f; R=CO(CH2)2Ph
2g; R=CO(CH2)3Ph
Scheme 1. Reagents: (a) RCOCl, TEA, CH2Cl2.

5240
J. Cao et al. / Bioorg. Med. Chem. Lett. 18 (2008) 5238–5241
c
a, b
OH
Cl
Br
4a; S (shown)
4b; R
3
F
F
F
F
d
N
N
N
OH
N
OR
N
N
6a; S (shown)
6b; R
7a; R=COCH3
7b; R=COCH2CH3
7c; R=CO(CH2)2CH3
7d; R=COCH=CH2
7e; R=COCH2Ph
Scheme 2. Reagents: (a) Mg, I2, THF; (b) R or S-epichlorohydrin, CuI, THF; (c) 5 (4-fluoro-N-(4-fluorophenyl)-N-(3-(piperazin-1-yl)propyl)aniline,11 K2CO3, MeOH; (d) RCOCl,
TEA, CH2Cl2.
Table 1
Binding data for DAT/
r
1 compoundsa
DAT Ki SEM (nM)
Compound
SERT Ki SEM (nM)
NET Ki SEM (nM)
r1 Ki SEM (nM)
1
2a
2b
2c
2d
2e
2f
2g
6a
6b
7a
7b
7c
7d
7e
NE-100
3.45 0.410/8.5 0.8b
4.28 0.552
5.57 0.608
9.36 1.16
6.71 0.622
14.9 1.74
36.6 4.00
51.3 4.75
1.72 0.126
5.36 0.397
21.7 2.84
15.1 1.27
33.5 3.04
3.26 0.289
6.92 0.884
3620 389
NT
803 99.1b
204 15.2
273 40.7
543 35.3
318 20.1
1230 50.8
1300 84.0
2190 292
779 85.2
521 48.5
835 110
1040 103
1680 10.4
660 79.0
1950 88.9
>10,000
1250 178/532 38b
990 48.1
1500 128
1520 141
1950 194
2740 250
5350 584
>10,000
766 112
2110 266
1050 121
1360 154
3460 509
810 78.0
1680 190
ND
45.0 6.51/372 21b
56.6 2.89
76.0 4.86
88.3 6.49
87.3 9.47
135 20.1
235 28.8
246 23.1
28.1 1.3
33.4 4.77
75.0 9.26
81.8 9.35
292 38.1
45.5 5.01
87.4 7.42
2.38 0.265
5.60 0.31
(+) Pentazocine
(À) Pentazocine
Rimcazole
GBR 12909
NT
NT
NT
NT
NT
497 17.0
NT
97.7 12
1.77 0.181
83.4 11.1
1711 71.5
104 11.4
893 91.4/908 99b
50.8 6.68/318 18c
a
DAT binding was performed with [3H]WIN 35,428 in 0.32 M sucrose, 10 mM phosphate buffer using previously frozen rat striatum for 120 min on ice. SERT binding was
performed with [3H]Citalopram in buffer containing 50 mM Tris, 5 mM KCl and 120 mM NaCl using previously frozen rat brain stem for 60 min at 25 °C. NET binding was
performed with [3H]Nisoxetine in buffer containing 50 mM Tris, 5 mM KCl, and 120 mM NaCl using previously frozen rat frontal cortex for 180 min on ice.
r1 binding was
performed with [3H](+)-pentazocine in 50 mM Tris buffer using previously frozen guinea pig brain minus cerebellum for 120 min at 25 °C.
b
Ref. 11.
Ref. 4.
c
Table 2
Acknowledgment
Selectivity profiles based on Ki ratios
Compound
SERT /DAT
NET /DAT
r1/DAT
The research reported herein was supported by funds from the
NIDA Intramural Research Program.
1
2a
2b
2c
2d
2e
2f
2g
6a
6b
7a
7b
7c
7d
7e
233
48
49
58
47
83
36
43
453
97
38
69
50
202
282
18
362
231
269
162
291
184
146
248
445
393
48
13
13
14
9
13
9
6
5
16
6
3
5
9
14
13
9
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmcl.2008.08.065.
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