Identification of a novel partial inhibitor of dopamine transporter among 4-substituted 2-phenylquinazolines

Article abstract of DOI:10.1016/S0960-894X(02)00348-7

In an attempt to identify novel ligands for the dopamine transporter, a series of 4-substituted-2-phenylquinazolines were synthesized and evaluated. Among the compounds studied, 4-[(diphenylmethyl)amino]-2-phenylquinazoline (4g) was identified as a novel partial inhibitor of [¹²⁵I]RTI-55 binding to the dopamine transporter and a partial inhibitor of [³H]dopamine uptake.

Full text of DOI:10.1016/S0960-894X(02)00348-7

Bioorganic & Medicinal Chemistry Letters 12 (2002) 2225–2228
Identification of a Novel Partial Inhibitor of Dopamine
Transporter Among 4-Substituted 2-Phenylquinazolines
a,
a
a
a
Subramaniam Ananthan, * Surendra K. Saini, Rashmi Khare, Sarah D. Clayton,
b
b
Christina M. Dersch and Richard B. Rothman
aOrganic Chemistry Department, Southern Research Institute, Birmingham, AL 35255, USA
bClinical Psychopharmacology Section, IRP, National Institute on Drug Abuse, Baltimore, MD 21224, USA
Received 10 December 2001;accepted 16 April 2002
Abstract—In an attempt to identify novel ligands for the dopamine transporter, a series of 4-substituted-2-phenylquinazolines were
synthesized and evaluated. Among the compounds studied, 4-[(diphenylmethyl)amino]-2-phenylquinazoline (4g) was identified as a
1
25
3
novel partial inhibitor of [ I]RTI-55 binding to the dopamine transporter and a partial inhibitor of [ H]dopamine uptake. # 2002
Elsevier Science Ltd. All rights reserved.
Cocaine (1) is a powerful stimulant of the central ner-
vous system with severe addiction liability. The reinfor-
cing and stimulant properties of cocaine are thought to
be mediated through its binding and inhibition of
monoamine transport systems, in particular the dopa-
mine (DA) transporter (DAT).1 Other neuro-
DAT-binding ligands raising the possibility of develop-
ment of a small molecule cocaine antagonist which
would specifically inhibit cocaine binding at DAT while
1
2,13
permitting the normal transport of dopamine.
Despite this theoretical possibility, however, the dis-
covery and development of such a ligand remains to be
2
3
14
transmitters such as norepinephrine and serotonin
achieved. Recent evidence suggests that certain classes
of dopamine uptake inhibitors that are structurally dis-
tinct from cocaine exhibit a non-cocaine like pharma-
likely contribute to the addictive effects of cocaine in
humans. The binding of cocaine at the DAT blocks the
translocation of dopamine from the synaptic cleft into
the presynaptic neurons leading to potentiation of the
actions of dopamine at the postsynaptic receptors.
Although numerous cocaine analogues and a variety of
other structural classes of compounds with exceptional
binding potency for DAT have been reported, many of
these compounds have been found to display a cocaine-
1
5,16
cological profile.
Hence, in the search for novel
therapeutics for cocaine abuse there is a renewed inter-
est in compounds that are structurally divergent from
those that have been tested todate, as novel pharmaco-
phoric elements may engender novel modes of interac-
tion at the DAT and provide ligands with the desired
pharmacological profile.
4
like behavioral profile in animal models of drug abuse.
Major classes of DAT ligands that have been identified
thus far include 3-aryltropanes, 8-oxa-3-aryltropanes,
7
In an effort to identify novel ligands structurally distinct
from hitherto investigated classes, we focused our
attention on a small group of readily accessible quina-
zoline derivatives. Recently, Meltzer and coworkers
reported their finding that simple aromatic compounds
such as 2 and 3 display surprisingly potent binding to
the DAT with affinities (2, IC =0.548 mM; 3,
5
6
benztropines, piperazines and pipieridines related to
8
9
the GBR-series of compounds, mazindol and methyl-
1
0
phenidate analogues. Accumulating evidence indicates
that these disparate DAT inhibitors do not all interact
1
1,12
with the DAT in the same manner.
Moreover,
5
0
several lines of evidence indicate the presence of
distinct binding sites at DAT for dopamine and other
IC =0.145 mM) in the same range as that of cocaine
5
0
17
(IC =0.09 mM). Molecular overlays indicated that a
5
0
template such as the 2-phenylquinazoline could mimic
the aromatic systems present in 2 and 3. On this basis
we used the 2-phenylquinazoline nucleus to append
substituent groups at the easily derivatized 4-position to
generate and examine a small group of compounds
*
2
Corresponding author. Tel.: +1-205-581-2822;fax: +1-205-581-
726;e-mail: ananthan@sri.org
0
960-894X/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(02)00348-7

2226
S. Ananthan et al. / Bioorg. Med. Chem. Lett. 12 (2002) 2225–2228
Scheme 1. Synthesis of 4-alkoxy- and 4-alkylaminoquinazolines.
The affinities of the compounds for the dopamine
transporter (DAT) and serotonin transporter (SERT) in
rat caudate membranes were determined by displace-
1
25
ment assays using [ I]RTI-55 as the radioligand. As
described elsewhere, when assaying DAT either 100 nM
paroxetine or 100 nM citalopram was used to block
SERT binding and when assaying SERT, 100 nM
2
4
GBR12935 was used to block DAT binding. The
binding affinity data are presented in Table 1. The
alkoxy and alkylthio compounds 4a–d possessing a
pendant basic nitrogen displayed DAT binding affinities
in the 5–10 mM range with the tropanyloxy derivative 4a
showing the highest affinity within this group. Among
the diphenylmethyl compounds, while the diphe-
nylmethylthio compound 4f was devoid of any sig-
nificant binding affinity to DAT, the binding profile of
the diphenylmethylamino compound 4g turned out to
be of particular interest. In the binding studies with
represented by the generic structure 4 as DAT ligands.
We chose to derivatize the 4-position of the 2-phe-
nylquinazoline nucleus with substituents carrying a
pendant dialkylamino or diphenylmethyl group as these
structural motifs occur as pharmacophoric functions in
benztropine (5) dibucaine (6), chloroquine (7) and
piperazine-GBR series of DAT ligands (8). Although
the quinolines 6 and 7 reportedly bind to DAT with
relatively low affinities (K for 6=10.8 mM; K for 7=24
1
25
DAT, 4g inhibited [ I]RTI-55 binding in a biphasic
manner with the inhibition curve reaching a plateau at
about 20% of control. Characterization of the binding
2
5
of 4g to DAT using binding surface analysis showed
that a two site model fit the data better than one site
model. According to the two site model of DAT binding
in rat caudate the compound discriminates the two sites
i
i
mM), among a group of compounds that were examined
for DAT binding and DA uptake inhibition under
identical assay conditions, these two compounds dis-
played significant differential in the binding and DA
uptake inhibition (K uptake/K binding=9.04 and 10.21
binding with a K value of 530 nM at one site and with
i
2
6
negligible affinity at the other site. In the dopamine
3
uptake experiment using [ H]dopamine, the compound
again displayed partial inhibition of dopamine uptake
with an apparent plateau at about 50% of control. The
i
i
1
8
for 6 and 7, respectively).
3
estimated IC50 value for the inhibition of [ H] dopamine
2
6
As shown in Scheme 1, all of the 4-alkoxy- and 4-alky-
uptake was 6.38 mM. Although some studies have
reported high and low affinity binding sites associated
with DAT, we have consistently observed a single
1
9
lamino-2-phenylquinazolines including 4j were pre-
pared by nucleophilic displacement reaction of 4-
chloro-2-phenylquinazoline (10) with the appropriate
sodium alkoxide generated from the aminoalcohol and
sodium hydride in THF or DMSO or with an excess of
appropriate amine in refluxing dioxane. The thioether
1
25
[
I]RTI-55 binding site as well as one component of
3
24,27
[ H]dopamine uptake in rat caudate membranes.
The binding and uptake inhibition profile of 4g therefore
appears to be unique among DAT ligands.
2
0
derivatives 4d and 4f were obtained through the
alkylation of 4-mercapto-2-phenylquinazoline with the
In an effort to investigate the importance of the diphe-
nylmethylamino moiety for DAT binding, we synthesized
2
1ꢀ23
appropriate alkyl halide in the presence of a base.

S. Ananthan et al. / Bioorg. Med. Chem. Lett. 12 (2002) 2225–2228
Table 1. Binding affinities at the dopamine and serotonin transpor-
ters
2227
Compd
XR
DAT binding
a
SERT binding
a
K
i
, mM
i
K , mM
4a
5
.1 (ꢁ0.4)
5.1 (ꢁ0.3)
4
4
4
b
9.1 (ꢁ0.3)
9.9 (ꢁ0.3)
6.1 (ꢁ0.2)
>10
c
>10
db
9.6 (ꢁ0.4)
Figure 1. Inhibition of [125I]RTI-55 binding to DAT by 4g, 4i and
cocaine.
4
e
f
>10
>10
>10
played by 4g, 4i and cocaine are shown in Figure 1.
Compound 4j lacking one of the phenyl groups of the
diphenylmethyl moiety displays only weak affinity for
4
>10
DAT (K =7.9 mM). Interestingly, while introduction of
i
a methyl group in the R configuration on the prochiral
methylene carbon of 4j did not produce any significant
c
4
g
h
0.53 (ꢁ0.1)
>10
>10
change in the binding affinity (4h, K =6.1 mM), the
i
introduction of the methyl group in the S configuration
(
4i, K =1.8 mM) led to a 4-fold enhancement in binding
i
affinity. These results indicate sterically defined lipo-
philic interactions with two aryl groups or an aryl and
an alkyl group are involved in the binding of these
ligands at the ligand binding site in the DAT. Moreover,
the phenyl group at the 2-position of the quinazoline
ring also seems to be essential for binding at the DAT
since compound 9, an analogue of 4g lacking this fea-
4
6.1 (ꢁ0.3)
4
4
4
i
1.8 (ꢁ0.07)
7.9 (ꢁ0.4)
5.4 (ꢁ0.1)
>10
>10
>10
jd
k
ture did not display appreciable binding affinity (K >10
i
mM). With the exception of 4a and 4d, all of the quin-
azolines were devoid of any significant binding affinity
to the serotonin transporter.
In summary, we have examined a series of 4-substituted-
2-phenylquinazolines as ligands for dopamine transpor-
4
1
l
>10
>10
ter and have identified 4g as a novel ligand that func-
tions as a partial inhibitor of dopamine transporter
binding and dopamine uptake. Further molecular
manipulations should lead to the identification of newer
DAT ligands with novel binding and activity profiles.
Moreover studies with 4g and related compounds might
lead to the discovery of ligands with unique pharmaco-
logical and behavioral profiles that are desired in a
pharmacotherapeutic agent for the treatment of cocaine
addiction.
Cocaine
0.46 (ꢁ0.03)
0.13 (ꢁ0.01)
aValues are means of three experiments, standard deviation is given in
parentheses.
b
Ref 20.
See Table 4 in ref 26.
c
d
Ref 19.
and evaluated a few other analogues in which the
diphenylmethyl goup was replaced with a 1-phenylethyl
or benzyl group (4h–j) and in which the diphenylmethyl
group was incorporated as a pendant group on an ami-
noalkyl chain (4k and 4l). Unlike 4g all of these com-
pounds displayed DAT binding profile similar to that of
cocaine. The partial and full inhibition profiles dis-
Acknowledgements
The authors would like to thank Dr. J. M. Riordan for
NMR data and Mr. M. D. Richardson for mass spectral
data.

2228
S. Ananthan et al. / Bioorg. Med. Chem. Lett. 12 (2002) 2225–2228
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3
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6
3
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1
1
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1
1
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f
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3
–
1
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2
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1
1
1
1
1
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