Conversion of a highly selective sigma-1 receptor-ligand to sigma-2 receptor preferring ligands with anticocaine activity

Article abstract of DOI:10.1021/jm701357m

Cocaine's toxicity can be mitigated by blocking its interaction with sigma-1 receptors. The involvement of sigma-2 receptors remains unclear. To investigate their potential role, we have designed compounds through a convergent synthesis utilizing a highly selective sigma-1 ligand and elements of a selective sigma-2 ligand. Among the synthesized compounds was produced a subnanomolar sigma-2 ligand with an 11-fold preference over sigma-1 receptors. These compounds may be useful in developing effective pharmacotherapies for cocaine toxicity.

Full text of DOI:10.1021/jm701357m

1482
J. Med. Chem. 2008, 51, 1482–1486
Conversion of a Highly Selective Sigma-1 Receptor–Ligand to Sigma-2 Receptor Preferring
Ligands with Anticocaine Activity
Christophe Mésangeau,† Sanju Narayanan,† Andrea M. Green,† Jamaluddin Shaikh,‡ Nidhi Kaushal,‡ Eddy Viard,‡
Yan-Tong Xu,‡ James A. Fishback,‡ Jacques H. Poupaert,§ Rae R. Matsumoto,‡ and Christopher R. McCurdy*,†,‡
Department of Medicinal Chemistry, Department of Pharmacology, School of Pharmacy, The UniVersity of Mississippi, UniVersity,
Mississippi 38677, and School of Pharmacy, UniVersité Catholique de LouVain, AVenue Emmanuel Mounier 74, B-1200 Brussels, Belgium
ReceiVed October 30, 2007
Cocaine’s toxicity can be mitigated by blocking its interaction with sigma-1 receptors. The involvement of
sigma-2 receptors remains unclear. To investigate their potential role, we have designed compounds through
a convergent synthesis utilizing a highly selective sigma-1 ligand and elements of a selective sigma-2 ligand.
Among the synthesized compounds was produced a subnanomolar sigma-2 ligand with an 11-fold preference
over sigma-1 receptors. These compounds may be useful in developing effective pharmacotherapies for
cocaine toxicity.
Chart 1. Structures of Lead Compounds
Introduction
Cocaine abuse is widespread and responsible for more serious
intoxications and deaths than any other illicit drug.1 Currently,
there are no approved medications to treat cocaine abuse or
addiction. For years, treatment approaches for cocaine abuse
and addiction have targeted the dopaminergic system with
limited success. Moreover, it is apparent that this strategy may
only provide molecules that substitute for cocaine.2 This has
led researchers to shift the focus of medications development
toward the involvement of other protein systems. Indeed, cocaine
interacts with many proteins, and it is now well-established that
cocaine interacts with sigma receptors at physiologically relevant
concentrations.3 Earlier studies have indicated that reducing
brain sigma-1 receptor levels with antisense oligonucleotides
attenuates the convulsive and locomotor stimulant actions of
cocaine.4 Synthetic small molecule antagonists for sigma
receptors have also been shown to mitigate the actions of cocaine
in animal models.3,4 From prior work, the role of the sigma-1
subtype has been clearly linked to the actions of cocaine.
Although there has recently been literature indicating that the
sigma-2 receptor may be involved in the actions of cocaine,5
its role has been less clear due to the lack of truly selective
ligands for this subtype. To add to the complexity, the sigma-2
receptor has yet to be cloned. Furthermore, it is unclear if a
compound with mixed affinity for both sigma-1 and sigma-2
receptors, with minimal to no affinity for other proteins, would
be of benefit or utility in the treatment of cocaine toxicity or
abuse.
cyclohexylpiperazine moiety could be acting as a selectivity
element for the sigma-2 receptor preference. With this in mind,
we have designed and synthesized a series of compounds
replacing the azepane ring in compound 1 with the putative
selectivity element (N-cyclohexylpiperazine) for the sigma-2
receptor, exemplified by compound 2, to obtain mixed affinity
ligands or sigma-2 selective ligands. In addition to the cyclo-
hexylpiperazine moiety affording sigma-2 affinity, it has been
suggested that a four methylene spacer between the piperazine
and the heterocyclic system is optimal for sigma-2 affinity over
sigma-1.7 Therefore, it was warranted to examine the spacer
length between the two portions by varying it from two to six
carbons. We also wanted to investigate the effects of changing
the 2-oxo position of the heterocycles to a sulfur to modulate
the potential for hydrogen bonding interactions and determine
their possible importance in receptor affinity and selectivity.
Chemistry. Our synthesis of the initial series of compounds
was very straightforward as outlined in Scheme 1. Commercially
available 2(3H)-benzoxazolone (3a) or 2(3H)-benzothiazolone
(3b) were alkylated with various dibromoalkanes to give
compounds with the desired spacer lengths (4a-4j). These were
then coupled with the commercially available cyclohexylpip-
erazine to afford compounds 5a-5j. Finally, hydrochloride salts
were formed for biological testing. To investigate the effect of
sulfur in the 2-position, compound 3a was thionated with
Lawesson’s reagent to give 7 (Scheme 2). Initially, alkylation
of the heterocycle with 1,4-dibromobutane was directed to the
more reactive 2-thiocarbonyl. Subsequently, compound 7 (Scheme
2) was utilized to alkylate the cyclohexylpiperazine, resulting
Compound 1 (Chart 1) was previously reported6 to have high
affinity and selectivity for sigma-1 receptors with respect to
several other proteins and it was hypothesized that the 2(3H)-
benzothiazolone moiety could be a useful template to improve
the selectivity toward sigma receptors over other proteins. The
recent report7 of compound 2 (Chart 1) provided a lead
compound with high sigma-2 selectivity (40-fold over sigma-1
receptors), and along this line, we hypothesized that the
* To whom correspondence should be addressed. Address: Department
of Medicinal Chemistry, 419 Faser Hall, The University of Mississippi,
University, MS 38677. Tel.: 662-915-5882. Fax: 662-915-5638. E-mail:
cmccurdy@olemiss.edu.
†
Department of Medicinal Chemistry, The University of Mississippi.
Department of Pharmacology, The University of Mississippi.
Université Catholique de Louvain.
‡
§
10.1021/jm701357m CCC: $40.75
2008 American Chemical Society
Published on Web 02/16/2008

Brief Articles
Journal of Medicinal Chemistry, 2008, Vol. 51, No. 5 1483
Scheme 1. Synthesis of Various Substituted 2(3H)-Benzoxazolones and 2(3H)-Benzothiazolonesa
a Reagents and conditions: (a) dibromoalkane, K2CO3, DMF, 60° C, 2 h; (b) cyclohexylpiperazine, K2CO3, DMF, 60° C, 3 h.
Scheme 2. Synthesis of Compound 8a
a Reagents and conditions: (a) Lawesson’s reagent, toluene, reflux, 4 h; (b) 1,4-dibromobutane, K2CO3, DMF, 60° C, 2 h; (c) cyclohexylpiperazine,
K2CO3, DMF, 60° C, 3 h.
Scheme 3. Synthesis of 13a and 13ba
a Reagents and conditions: (a) benzoic acid, K2CO3, 60° C, 1 h; (b) Lawesson’s reagent, toluene, reflux, 24 h; (c) NaOH, H2O, CH3OH, reflux, 1 h; (d)
CH3SO2Cl, Et3N, -10° C, 1 h; (e) cyclohexylpiperazine, K2CO3, DMF, 60° C, 3 h.
in compound 8. We felt it would be worthwhile to explore the
attachment position of the heterocycle, and Scheme 3 outlines
the synthesis of the desired N-alkylated compounds containing
sulfur in the 2-position of the heterocycles. Compounds 4e and
4f were reacted with potassium benzoate to form the respective
esters, 9a and 9b. These compounds were then treated with
Lawesson’s reagent to thionate the 2-oxo position, yielding 10a
and 10b, respectively. Hydrolysis of the benzoate afforded the
alcohols 11a and 11b, which were mesylated (12a and 12b)
and reacted with N-cyclohexylpiperazine to afford compounds
13a and 13b in high yields.
brain homogenates using routine assay conditions.8 In addition,
compound 13b was subjected to selected nonsigma receptor
binding assays in rat brain homogenates to determine the
selectivity of this template over other proteins usually associated
with sigma receptor–ligands. Because seizure is a common result
of cocaine overdose and earlier sigma receptor antagonists
attenuated the convulsive effects of cocaine in mice,4 we tested
whether pretreatment with representative sigma receptor–ligands
produced similar anticocaine actions.
Results and Discussion
Biology. All final compounds were subjected to in vitro
binding studies against sigma-1 and sigma-2 receptors in rat
As can be seen from Table 1, all compounds demonstrated
high affinity for sigma-1 and sigma-2 receptors. Compounds

1484 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 5
Brief Articles
Table 3. Nonsigma Protein Binding Affinities of Compound 13ba
radioligand nonspecific binding Ki (nM)
Table 1. Sigma Receptor Binding Affinities and Selectivity Ratios of
5a–5j, 8, 13a, and 13ba
cmpd
σ-1 (Ki, nM)
σ-2 (Ki, nM)
σ-1/σ-2
Monoamine Transporters
dopamineb
serotoninc
0.5 nM [3H]WIN 35,428 50 µM cocaine
1175 ( 10
5a
5b
5c
5d
5e
5f
5g
5h
5i
5j
8
13a
13b
6.90 ( 0.37
4.66 ( 0.74
5.22 ( 1.11
5.61 ( 0.74
11.26 ( 1.25
4.17 ( 0.62
10.55 ( 2.52
4.98 ( 0.42
4.60 ( 1.08
6.55 ( 0.25
3.37 ( 0.28
4.90 ( 1.70
1.28 ( 0.38
5.43 ( 0.78
2.25 ( 0.37
8.74 ( 2.30
3.05 ( 0.41
1.83 ( 0.17
0.39 ( 0.06
5.89 ( 1.31
2.44 ( 0.26
3.06 ( 0.45
1.49 ( 0.18
3.77 ( 0.35
0.77 ( 0.06
0.55 ( 0.08
1.27
2.07
0.60
1.84
6.15
10.69
1.79
2.04
1.50
4.40
0.89
6.36
2.33
0.2 nM [3H]paroxetine
1.5 µM imipramine 1402 ( 152
norepinephrined 0.5 nM [3H]nisoxetine
4 µM desipramine >10000
Other Receptorse
0.5 nM [3H]bremazocine 10 µM levallorphan >10000
5 nM [3H]TCP
5 nM [3H](-)-sulpiride 1 µM haloperidol
2 nM [3H]ketanserin
1 µM mianserin
opioid
NMDA
dopamine D2
5-HT2
10 µM cyclazocine >10000
1041 ( 9
1326 ( 159
a Affinities of 13b for nonsigma binding sites were determined in rat
brain homogenates. The values in this table represent the mean ( SEM
from replicate assays. Values of >10000 nM signify that there was less
than 30% displacement of the radioligand at that concentration. b Rat brain
homogenates, striatum. c Rat brain homogenates, brainstem. d Rat brain
homogenates, cortex. e Rat brain homogenates, whole brain.
a Affinities (Ki in nM) were determined in rat brain homogenates using
standard assays conditions. Sigma-1 receptors were labeled with [3H](+)-
pentazocine. Sigma-2 receptors were labeled with [3H]DTG in the presence
of (+)-pentazocine to block sigma-1 receptors. Nonspecific binding was
determined in the presence of haloperidol. The values in this table represent
the mean ( SEM from replicate assays.
Table 2. Sigma Receptor Binding Affinities and Selectivity Ratios of
Lead Compounds 1, 2, and Haloperidola
cmpd
σ-1 (Ki, nM)
σ-2 (Ki, nM)
σ-1/σ-2
1
2
0.12 ( 0.0096
1.48 ( 0.40
3.35 ( 0.80
830.95 ( 72.35
1.11 ( 0.031
80.60 ( 14.10
0.00014
1.33
0.042
haloperidol
a Affinities (Ki in nM) were determined in rat brain homogenates using
standard assays conditions. Sigma-1 receptors were labeled with [3H](+)-
pentazocine. Sigma-2 receptors were labeled with [3H]DTG in the presence
of (+)-pentazocine to block sigma-1 receptors. Nonspecific binding was
determined in the presence of haloperidol. The values in this table represent
the mean ( SEM from replicate assays.
with a spacer length of four carbons (5e, 5f, and 13a) seemed
to have the most preference for sigma-2 receptors. Furthermore,
it can be noted that subnanomolar affinity for sigma-2 receptors
resulted from at least one sulfur atom being present in the
heterocycle. Because the binding mode of these analogs or the
structure of the proteins is unknown, this data may indicate a
presence of a hydrogen bonding element in the sigma-1 site
that may either be absent or cause an unfavorable steric
interaction in the sigma-2 site. In general, the 2(3H)-benzothia-
zoles had higher affinities for sigma-2 receptors than their
respective 2(3H)-benzoxazole counterparts. Moreover, com-
pounds 13a and 13b, where the 2-oxo was replaced with a
sulfur, also resulted in compounds with subnanomolar affinity
for sigma-2 receptors. It is interesting to note that compound
13b where two sulfur atoms are present (in the 1 and 2 positions)
resulted in high affinity, but no selectivity, for both the sigma-1
and sigma-2 receptors. Compound 8, where the heterocycle is
connected to the linker via the 2-thio position, was nonselective
and showed equivalent affinity for both sigma-1 and sigma-2
receptors. This may indicate that the attachment position of the
heterocycle may not be important for high affinity but potentially
for selectivity.
The most selective compound for sigma-2 receptors, 5f, was
11-fold selective over sigma-1. This was a surprising result as
we envisioned these compounds having a similar selectivity
profile to lead compound 2. This result prompted us to evaluate
compounds 1, 2, and haloperidol (as a control) under our
receptor binding assay conditions, which differ slightly from
those previously reported for each of them. This data is presented
in Table 2. Haloperidol, a known sigma ligand, demonstrated
binding affinities similar to those reported in the literature.9
Compound 1 retained high affinity and selectivity for sigma-1
receptors in our assays. Interestingly, compound 2 in our assay
Figure 1. Attenuation of cocaine-induced convulsions in Swiss
Webster mice by select sigma ligands. *P < 0.05, ***P < 0.001.
Asterisks separated by commas indicate significance for three different
ligands at that datapoint.
exhibited high affinity for sigma-2 receptors but also had equally
high affinity for sigma-1 receptors, revealing that it is not
selective under our assay conditions.
The most interesting finding from this work is that our design
indeed provided compounds with high mixed-affinity for
sigma-1 and sigma-2 receptors, as well as compounds with a
preference for sigma-2 receptors. Compound 13b has the highest
affinity values so far reported for both subtypes. We therefore
examined 13b in several nonsigma binding assays as shown in
Table 3. Compound 13b had essentially no affinity for other
proteins of interest, indicating the validity of our design.
To determine the compound’s abilities to attenuate the effects
of cocaine-induced convulsions, we examined those compounds
with high sigma-2 affinities (2, 5e, 5f, 8, 13a, and 13b) in vivo
along with compound 1 as a control. Indeed, as shown in Figure
1, compound 1 acts as a sigma-1 receptor antagonist and at least
one dose of each of the compounds with sigma-2 affinity
significantly attenuated cocaine-induced convulsions. Because
attenuation of sigma-1 receptors alone is sufficient to mitigate
cocaine-induced convulsions,4 it is difficult to distinguish the
contribution of sigma-2 receptors in the mixed affinity ligands.
Nevertheless, it is worth noting that other sigma-2 preferring
compounds have been reported to attenuate cocaine-induced
convulsions.5 However, until the development and testing of
truly selective sigma-2 ligands, the role of sigma-2 receptors
in cocaine-induced convulsions will remain suggestive, but
unclear. The most efficacious compound was 13b, which also

Brief Articles
Journal of Medicinal Chemistry, 2008, Vol. 51, No. 5 1485
1.21–1.10 (m, 5H). HRMS calcd for C21H32N3O2 [M + H]+,
358.2495; found, 358.2498. Anal. (C21H31N3O2 ·1/4H2O) C, H, N.
Benzo[d]oxazole-2(3H)-thione (6). Lawesson’s reagent (2.99 g,
7.4 mmol) was added, under stirring, to a solution of benzo[d]ox-
azol-2(3H)-one (1.5 g, 11.1 mmol) in anhydrous toluene (80 mL).
The reaction mixture was heated under reflux for 4 h, cooled to
room temperature, and purified by flash column chromatography
(SiO2) using petroleum ether/ethyl ether (8:2) as the eluent. The
solid was then recrystallized from toluene/hexanes to give 1.2 g (72%)
of 7 as a white solid. 1H NMR (DMSO-d6): δ 13.82 (s, 1H), 7.49–7.47
(m, 1H), 7.28–7.22 (m, 3H). MS m/z 150 (M+ - 1).
4-(2-Oxobenzo[d]oxazol-3(2H)-yl)butyl Benzoate (9a). K2CO3
(2.35 g, 17 mmol) and benzoic acid (1.04 g, 8.51 mmol) were added,
under stirring, to a solution of 4e (1.77 g, 6.55 mmol) in anhydrous
DMF (10 mL). The reaction mixture was heated at 60 °C for 2 h.
After cooling, the mixture was poured into 100 mL of water,
extracted with ethyl acetate (3 × 70 mL), and the combined organic
layers were washed with a 0.5 N solution of KOH and with
saturated aqueous NaCl. The solvent was dried over magnesium
sulfate and removed in vacuo to give 2 g (98%) of 9a as a white
solid. 1H NMR (DMSO-d6): δ 7.92 (d, J ) 7.2 Hz, 2H), 7.62 (t, J
) 7.2 Hz, 1H), 7.49 (t, J ) 7.6 Hz, 2H), 7.31 (d, J ) 7.6 Hz, 2H),
7.19 (t, J ) 7.6 Hz, 1H), 7.11 (d, J ) 7.6 Hz, 1H), 4.30 (t, J ) 6.4
Hz, 2H), 3.88 (t, J ) 6.4 Hz, 2H), 1.97–1.72 (m, 4H). MS m/z 334
(M+ + 23).
had the highest affinities for sigma receptors. These results are
encouraging toward the development of new medications to treat
cocaine toxicities, and further studies are underway to determine
their ability to attenuate cocaine abuse.
Conclusion
We successfully converted a highly selective sigma-1 an-
tagonist (1) into a series of compounds that have high, mixed-
affinity for sigma-1 and sigma-2 receptors. We also have an
interesting lead molecule (5f) for the development of highly
selective sigma-2 compounds. Although the role of sigma-2
receptors in cocaine toxicity could not be clarified in this study,
there may be a benefit to a high affinity, mixed sigma-1/sigma-2
ligand in the treatment of cocaine abuse. These data, taken
together, suggest that further studies are warranted to evaluate
their potential to treat cocaine abuse. Additionally, because many
psychostimulants (e.g., methamphetamine and methylene-
dioxymethamphetamine) bind to sigma receptors, mixed affinity
sigma-1/sigma-2 receptor–ligands represent a potential new class
of drugs to treat psychostimulant abuse. Presently, we are
investigating the utility of compound 13b as a treatment of
cocaine abuse in further in vivo assays to be reported in due
time.
4-(2-Oxobenzo[d]thiazol-3(2H)-yl)butyl Benzoate (9b). K2CO3
(11.18 g, 81 mmol) and benzoic acid (4.94 g, 40.5 mmol) were
added, under stirring, to a solution of 4f (8.91 g, 31.1 mmol) in
anhydrous DMF (30 mL). The reaction mixture was heated at 60
°C for 1 h. After cooling, the mixture was poured into 100 mL of
water, extracted with ethyl acetate (3 × 70 mL), and the combined
organic layers were washed with a 0.5 N solution of KOH and
with saturated aqueous NaCl. The solvent was dried over magne-
sium sulfate and removed in vacuo to give 10 g (98%) of 9b as a
Experimental Section
Chemistry. Reagents and starting materials were obtained from
commercial suppliers and were used without purification. Precoated
silica gel GF Uniplates from Analtech were used for thin-layer
chromatography (TLC). Column chromatography was performed
on silica gel 60 (Sorbent Technologies). 1H and 13C NMR spectra
were obtained on a Bruker APX400 at 400 and 100 MHz,
respectively. The high resolution mass spectra (HRMS) were
recorded on a Waters Micromass Q-Tof Micro mass spectrometer
with a lock spray source. The mass spectra (MS) were recorded on
a Waters Acquity Ultra Performance LC with ZQ detector in ESI
mode. Elemental analyses (C, H, N) were recorded on an elemental
analyzer, Perkin-Elmer CHN/SO Series II Analyzer. Chemical
names were generated using ChemDraw Ultra (CambridgeSoft,
version 10.0).
General Procedure A. Synthesis of (bromoalkyl)benzo[d]ox-
azol-2(3H)-one and Derivatives. 3-(4-Bromobutyl)benzo[d]ox-
azol-2(3H)-one (4e). K2CO3 (9.2 g, 66.6 mmol) and 1,4-
dibromobutane (21.0 mL, 177.6 mmol) were added, under stirring,
to a solution of benzo[d]oxazol-2(3H)-one (3.0 g, 22.2 mmol) in
anhydrous DMF (30 mL). The reaction mixture was heated at 60
°C for 3 h. After cooling, the mixture was poured into 100 mL of
water and extracted with ethyl acetate (3 × 70 mL). The combined
organic layers were washed with saturated aqueous NaCl and dried
over magnesium sulfate. The solvent was removed in vacuo, and
the residue was purified by flash column chromatography (SiO2)
using petroleum ether/ethyl acetate (8:2) as the eluent to give 3.8 g
1
white solid. H NMR (CDCl3): δ 8.01–7.99 (m, 2H), 7.54 (t, J )
7.2 Hz, 1H), 7.43–7.39 (m, 3H), 7.29 (t, J ) 8.0 Hz, 1H), 7.14 (t,
J ) 7.2 Hz, 1H), 7.04 (d, J ) 8.0 Hz, 1H), 4.36 (t, J ) 6.0 Hz,
2H), 4.02 (t, J ) 6.8 Hz, 2H), 1.91–1.86 (m, 4H). MS m/z 350
(M+ + 23).
4-(2-Thioxobenzo[d]oxazol-3(2H)-yl)butyl Benzoate (10a).
Lawesson’s reagent (1.9 g, 4.69 mmol) was added, under stirring,
to a solution of 9a (1.95 g, 6.26 mmol) in anhydrous toluene (80
mL). The reaction mixture was heated under reflux for 20 h. The
solvent was removed in vacuo, and the residue was purified by
flash column chromatography (SiO2) using petroleum ether/ethyl
acetate (8:2) as the eluent to give 1.56 g (76%) of 10a as a white
1
solid. H NMR (DMSO-d6): δ 7.92–7.90 (m, 2H), 7.64–7.28 (m,
7H), 4.32–4.26 (m, 4H), 1.97–1.76 (m, 4H). MS m/z 350 (M+
23).
+
4-(2-Thioxobenzo[d]thiazol-3(2H)-yl)butyl Benzoate (10b).
Lawesson’s reagent (1 g, 3 mmol) was added, under stirring, to a
solution of 9b (0.93 g, 2.3 mmol) in anhydrous toluene (50 mL).
The reaction mixture was heated under reflux for 15 h. The solvent
was removed in vacuo, and the residue was purified by flash column
chromatography (SiO2) using petroleum ether/ethyl ether (8:2) as
the eluent to give 0.66 g (63%) of 10b as a colorless oil. 1H NMR
(CDCl3): δ 8.03–8.00 (m, 2H), 7.57–7.02 (m, 7H), 4.51 (t, J ) 6.8
Hz, 2H), 4.40 (t, J ) 6 Hz, 2H), 2.03–1.90 (m, 4H). MS m/z
344(M+ + 1).
1
(64%) of 4e as a white solid. H NMR (CDCl3): δ 7.19–7.08 (m,
3H), 6.99–6.97 (m, 1H), 3.85 (t, J ) 6.4 Hz, 2H), 3.44 (t, J ) 6.0
Hz, 2H), 1.95–1.93 (m, 4H). MS m/z 272 (M+ + 2), 270 (M+).
General Procedure B. Synthesis of the Cyclohexylpipera-
zine Derivatives. 3-(4-(4-Cyclohexylpiperazin-1-yl)butyl)benzo-
[d]oxazol-2(3H)-one (5e). K2CO3 (0.46 g, 3.33 mmol) and 1-cy-
clohexylpiperazine (0.18 g, 1.11 mmol) were added, under stirring,
to a solution of 4e (0.3 g, 1.11 mmol) in anhydrous DMF (4 mL).
The reaction mixture was heated at 60 °C for 3 h. After cooling,
the mixture was poured into 20 mL of water and extracted with
ethyl acetate (3 × 30 mL). The combined organic layers were
washed with saturated aqueous NaCl and dried over magnesium
sulfate. The solvent was removed in vacuo, and the residue was
purified by flash column chromatography (SiO2) using dichlo-
romethane/methanol (9.5:0.5) as the eluent to give 0.27 g (69%)
3-(4-Hydroxybutyl)benzo[d]oxazole-2(3H)-thione (11a). To a
solution of 10a (1.44 g, 4.39 mmol) in methanol (20 mL) was added
a solution of sodium hydroxide (0.44 g, 10.98 mmol) in water (20
mL). The mixture was heated at 100 °C for 1 h, concentrated in
vacuo, poured into 1 N HCl (20 mL), and extracted with ethyl
acetate (3 × 20 mL). The combined organic layers were washed
with a 10% solution of K2CO3 and brine and dried over magnesium
sulfate. The solvent was removed in vacuo, and the residue was
purified by flash column chromatography (SiO2) using petroleum
ether/ethyl acetate (5:5) as the eluent to give 0.42 g (43%) of 11a
1
of 5e as a white solid. H NMR (CDCl3): δ 7.21–6.98 (m, 4H),
1
3.84 (t, J ) 6.7 Hz, 2H), 2.59–2.22 (m, 11H), 1.89–1.57 (m, 9H),
as a white solid. H NMR (CDCl3): δ 7.31–7.12 (m, 4H), 4.20 (t,

1486 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 5
Brief Articles
J ) 7.2 Hz, 2H), 3.67 (t, J ) 6.4 Hz, 2H), 2.28 (s, 1H), 1.94–1.89
(m, 2H), 1.66–1.60 (m, 2H). MS m/z 246 (M+ + 23).
Acknowledgment. This project was supported by NIDA
(DA013978, DA011979, DA023205) and NCRR (P20 RR021929).
We appreciate the initial work from Prof. Daniel Lesieur’s group
that led to the discovery of compound 1, and the technical
assistance of Caroline Croom and Babuk Shariat-Madar in
conducting some of the behavioral studies. This investigation
was conducted in a facility constructed with support from a
research facilities improvement program grant from NCRR (C06
RR14503).
3-(4-Hydroxybutyl)benzo[d]thiazole-2(3H)-thione (11b). To a
solution of 10b (0.61 g, 1.77 mmol) in methanol (20 mL) was added
a solution of sodium hydroxide (0.18 g, 4.44 mmol) in water (20
mL). The mixture was heated at 60 °C for 1 h, concentrated in
vacuo, poured into 1 N HCl (20 mL), and extracted with ethyl
acetate (3 × 20 mL). The combined organic layers were washed
with saturated aqueous NaCl, dried over magnesium sulfate, and
removed under reduced pressure. The residue was purified by flash
column chromatography (SiO2) using petroleum ether/ethyl ether
(8:2) as the eluent to give 0.30 g (71%) of 11b as a white solid. 1H
NMR (CDCl3): δ 7.46–7.23 (m, 4H), 4.44 (t, J ) 7.6 Hz, 2H),
3.70 (t, J ) 6 Hz, 2H), 2.41 (m, 1H), 1.71–1.66 (m, 2H), 1.91–1.86
(m, 2H). MS m/z 262 (M+ + 23).
Supporting Information Available: Detailed experimental data
for all compounds. This material is available free of charge via the
Internet at http://pubs.acs.org.
References
4-(2-Thioxobenzo[d]oxazol-3(2H)-yl)butyl Methanesulfonate
(12a). A solution of methanesulfonyl chloride (0.16 mL, 2.01 mmol)
in methylene chloride (5 mL) was slowly added to a solution of
11a (0.3 g, 1.34 mmol) and triethylamine (0.56 mL, 4.03 mmol)
in dichloromethane (20 mL) at 0 °C. The mixture was stirred for
1 h at 0 °C and the solvent was evaporated. The residue was purified
by flash column chromatography (SiO2) using petroleum ether/ethyl
acetate (6:4) as the eluent to give 7.4 g (97%) of 12a as a white
(1) (a) Substance Abuse and Mental Health Services Administration, Office
of Applied Studies. Drug Abuse Warning Network, 2005: National
Estimates of Drug-Related Emergency Department Visits. DAWN
Series D-29, DHHS Publication No. (SMA) 07-4256, Rockville, MD,
2007. (b) Substance Abuse and Mental Health Services Administration,
Office of Applied Studies. Drug Abuse Warning Network, 2003: Area
Profiles of Drug-Related Mortality. DAWN Series D-27, DHHS
Publication No. (SMA) 05-4023, Rockville, MD, March, 2005.
(2) (a) Grabowski, J.; Shearer, J.; Merrill, J.; Negus, S. S. Agonist-like,
replacement pharmacology for stimulant abuse and dependence. Addict.
BehaV. 2004, 29, 1439–1464. (b) Carroll, F. I.; Howell, L. L.; Kuhar,
M. J. Pharmacotherapies for treatment of cocaine abuse: preclinical
aspects. J. Med. Chem. 1999, 42, 2721–2736.
1
solid. H NMR (DMSO-d6): δ 7.56–7.53 (m, 2H), 7.39–7.29 (m,
2H), 4.26–4.23 (m, 4H), 3.15 (s, 3H), 1.91–1.73 (m, 4H). MS m/z
324 (M+ + 23).
4-(2-Thioxobenzo[d]thiazol-3(2H)-yl)butyl Methanesulfonate
(12b). A solution of methanesulfonyl chloride (2.75 mL, 35.4 mmol)
in methylene chloride (20 mL) was slowly added to a solution of
11b (5.65 g, 23.6 mmol) and triethylamine (8.3 mL, 59.1 mmol)
in dichloromethane (120 mL) at 0 °C. The mixture was stirred for
1 h at 0 °C and poured into water. The two layers were separated
and the organic layer was washed with water and dried over
magnesium sulfate. The solvent was removed in vacuo, and the
residue was purified by flash column chromatography (SiO2) using
petroleum ether/ethyl acetate (6:4) as the eluent to give 7.4 g (98%)
of 12b as a white solid. 1H NMR (CDCl3): δ 7.49 (d, J ) 7.8 Hz,
1H), 7.42 (t, J ) 7.5 Hz, 1H), 7.30 (t, J ) 7.6 Hz, 1H), 7.24 (d, J
) 8.2 Hz, 1H), 4.48 (t, J ) 6.9 Hz, 2H), 4.31 (t, J ) 6.0 Hz, 2H),
3.02 (s, 3H), 2.00–1.90 (m, 4H). MS m/z 318 (M+ + 1).
Radioligand Binding Assays. The assays were performed in
rat brain homogenates using procedures previously published in
detail.9 Sigma-1 receptors were labeled with 5 nM [3H](+)-
pentazocine. Sigma-2 receptors were labeled with 3 nM [3H]DTGa
in the presence of 300 nM (+)-pentazocine to block sigma-1
receptors. Nonspecific binding was determined in the presence of
10µMhaloperidol.Ki valueswerecalculatedusingtheCheng-Prusoff
equation.10
(3) Matsumoto, R. R.; Liu, Y.; Lerner, M.; Howard, E. W.; Brackett, D. J.
Sigma receptors: Potential medications development target for anti-
cocaine agents. Eur. J. Pharmacol. 2003, 469, 1–12.
(4) (a) Matsumoto, R. R.; McCracken, K. A.; Friedman, M. J.; Pouw, B.;
De Costa, B. R.; Bowen, W. D. Conformationally restricted analogs
of BD1008 and an antisense oligodexoynucleotides targeting sigma-1
receptors produce anti-cocaine effects in mice. Eur. J. Pharmacol.
2001, 419, 163–174. (b) Matsumoto, R. R.; McCracken, K. A.; Pouw,
B.; Zhang, Y.; Bowen, W. D. Involvement of sigma receptors in the
behavioral effects of cocaine: evidence from novel ligands and
antisense oligodeoxynucleotides. Neuropharmacology 2002, 42, 1043–
1055.
(5) Matsumoto, R. R.; Pouw, B.; Mack, A. L.; Daniels, A.; Coop, A.
Effects of UMB24 and (+/-)-SM21, putative sigma2-preferring
antagonists, on behavioral toxic and stimulant effects of cocaine in
mice. Pharmacol. Biochem. BehaV. 2007, 86, 86–91.
(6) Yous, S.; Wallez, V.; Belloir, M.; Caignard, D. H.; McCurdy, C. R.;
Poupaert, J. H. Novel 2(3H)-Benzothiazolones as highly potent and
selective sigma-1 receptor ligands. Med. Chem. Res. 2005, 14, 158–
168.
(7) Berardi, F.; Ferorelli, S.; Abate, C.; Colabufo, N. A.; Contino, M.;
Perrone, R.; Tortorella, V. 4-(Tetralin-1-yl)- and 4-(naphthalen-1-
yl)alkyl derivatives of 1-cyclohexylpiperazine as sigma receptor ligands
with agonist sigma-2 activity. J. Med. Chem. 2004, 47, 2308–2317.
(8) Nguyen, E. C.; McCracken, K. A.; Liu, Y.; Pouw, B.; Matsumoto,
R. R. Involvement of sigma receptors in the acute actions of
methamphetamine: Receptor binding and behavioral studies. Neurop-
harmacology 2005, 49, 638–645.
Cocaine-Induced Convulsions. Male, Swiss Webster mice were
pretreated (i.p.) with saline or test compound, then challenged 15
min later with a convulsive dose of cocaine (70 mg/kg, i.p.). Mice
were observed for the next 30 min for convulsions, which were
defined as a loss of righting reflexes for at least 5 s, combined
with the presence of clonic limb movements or popcorn jumping.
The data were analyzed using Fisher’s exact tests.
(9) (a) McCann, D. J.; Weissman, A. D.; Su, T. P. Sigma-1 and sigma-2
sites in rat brain: Comparison of regional, ontogenetic, and subcellular
patterns. Synapse 1994, 17, 182–189. (b) Matsumoto, R. R.; Pouw,
B. Correlation between neuroleptic binding to sigma-1 and sigma-2
receptors and acute dystonic reactions. Eur. J. Pharmacol. 2000, 401,
155–160.
(10) Cheng, Y.; Prusoff, W. H. Relationship between the inhibition constant
(Ki) and the concentration of inhibitor which causes 50% inhibition
(I50) of an enzymatic reaction. Biochem. Pharmacol. 1973, 22,
3099–3108.
a Abbreviations: DTG, 1,3-di-o-tolylguanidine; i.p., intraperitioneal;
NMDA, N-methyl D-aspartate; TCP, N-(1-[thienyl]cyclohexyl)piperidine;
WIN 35,428, (-)2-beta-carbomethoxy-3-beta-(4-fluorophenyl)tropane 1,5-
napthalenedisulfonate.
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