Discovery and synthesis of novel 3-phenylcoumarin derivatives as antidepressant agents

Article abstract of DOI:10.1016/j.bmcl.2011.02.040

A series of 3-phenylcoumarins were synthesized and screened for potential antidepressant activity by tail suspension test (TST) in mice. Three compounds (6, 7 and 13) exhibited impressive antidepressant activity, measured in terms of percentage decrease i

Full text of DOI:10.1016/j.bmcl.2011.02.040

Bioorganic & Medicinal Chemistry Letters 21 (2011) 1937–1941
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Discovery and synthesis of novel 3-phenylcoumarin derivatives
as antidepressant agents q
Koneni V. Sashidhara a, , Abdhesh Kumar a, Manavi Chatterjee b, K. Bhaskara Rao a, Seema Singh b,
⇑
Anil Kumar Verma b, Gautam Palit b
a Medicinal and Process Chemistry Division, Central Drug Research Institute, CSIR, Lucknow 226 001, India
b Pharmacology Division, Central Drug Research Institute, CSIR, Lucknow 226 001, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of 3-phenylcoumarins were synthesized and screened for potential antidepressant activity by tail
suspension test (TST) in mice. Three compounds (6, 7 and 13) exhibited impressive antidepressant activ-
ity, measured in terms of percentage decrease in immobility duration (% DID). In addition, the active anti-
depressant compounds were subsequently studied at their most effective dose and activity of these
compounds were confirmed in forced swimming test (FST) animal model, in which the compounds at
a low dose of 0.5 mg/kg significantly decreased the immobility time and exhibited greater efficacy than
the reference standards fluoxetine and imipramine. The potent compounds did not show any neurotox-
icity in the rotarod test and the preliminary results are promising enough to warrant further studies
around this scaffold.
Received 16 December 2010
Revised 9 February 2011
Accepted 11 February 2011
Available online 15 February 2011
Keywords:
Synthesis
Coumarin
Antidepressant activity
Forced swim test
Tail suspension test
Ó 2011 Elsevier Ltd. All rights reserved.
Depression is a serious and burdensome psychiatric illness
associated with high rates of chronicity, relapse and that is charac-
terized generally, by pervasive low mood, anxiety, cognitive
impairment, loss of interest or pleasure in normally enjoyable
activities and suicidal behaviours.1,2 According to WHO estimation,
121 million people worldwide suffer from mental depression. The
high prevalence of suicide in depressed patients (up to 15%) cou-
pled with complications arising from stress and its effect on the
cardiovascular system have suggested, that it will become the sec-
ond leading cause of premature death or disability worldwide by
the year 2020.3 Despite a broad range of antidepressants available
today, a significant proportion of these patients will not respond to
treatment, or will show only partial response.4 Clinical limitations
and adverse effects of currently used antidepressants necessitate
continuous development of novel, efficient and safe drugs for treat-
ment of depression.
Natural as well as synthetic coumarins have recently drawn
much attention due to its diverse pharmacological activities. Many
coumarins and their derivatives underwent extensive investiga-
tions aimed to assess their potential beneficial effects on human
health.5,6 In addition many coumarin derivatives have antidepres-
sant properties.7–10 The recognition of key structural features with-
in coumarin family is crucial for the design and development of
new analogues with improved activity and for the characterization
of their mechanism of action and potential side effects. The differ-
ent substituents in the coumarin nucleus strongly influence the
biological activity of the resulting derivatives.
Figure 1 shows the chemical structures of some potent antide-
pressant molecules that contains a coumarin in its molecular
makeup and form the basis of our designed prototype. Capra et al.
revealed that the scopoletin (Fig. 1) isolated from Polygala sabulosa
produces a specific antidepressant-like effect in the tail suspension
test, an animal model predictive of antidepressant activity and was
also able to reverse a depressant-like behaviour induced by acute
immobility stress.11 Also, coumarins such as Psoralidin12 (Fur-
ocoumarins) and Esuprone13 belong to the new generation of
monoamine oxidase (MAO) inhibitors and demonstrated to possess
potent antidepressant properties. Many synthetic efforts based on
this coumarin scaffold are also currently under investigation for
antidepressant activity as exemplified by the compounds LU
534399 (Fig. 1) and other coumarin derivatives.14–17
In continuation of our interest, in this class of compounds,18 we
embarked on the synthesis of novel coumarin derivatives as
potential antidepressant agents. Herein, we wish to describe the
synthesis and biological evaluation of novel 3-phenylcoumarin
derivatives as potential antidepressant agents.
The synthesis of the substituted 3-phenylcoumarins is illus-
trated in Scheme 1. Commercially available 2-substituted phenols
(1 and 2) underwent the Duff formylation reaction in presence
of hexamethylene tetramine (HMTA) and TFA at 120 °C to fur-
nish substituted salicylaldehydes (3 and 4). Subsequent Perkin
q
Part VIII in the series, ‘‘Advances in drug design and discovery’’.
Corresponding author. Tel.: +91 991 9317940; fax: +91 522 2623405.
E-mail addresses: sashidhar123@gmail.com, kv_sashidhara@cdri.res.in (K.V.
⇑
Sashidhara).
0960-894X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2011.02.040

1938
K. V. Sashidhara et al. / Bioorg. Med. Chem. Lett. 21 (2011) 1937–1941
Figure 1. Chemical structure of some coumarin based potent antidepressant agents and general structure of our synthesized compounds.
Scheme 1. Synthesis of novel 3-phenylcoumarin derivatives (5–11 and 12–15). Reagents and conditions: (a) (1) HMTA/TFA, 120 °C, 3 h; (2) 10% H2SO4, 90–100 °C, 2 h; (b)
DCC, DMSO, 110 °C, 24 h.
condensation19 reaction of these substituted salicylaldehydes and
the appropriately substituted phenylacetic acids, was carried out
with N,N-dicyclohexylcarbodiimide (DCC) as dehydrating agent,
in DMSO, at 110 °C reflux, for 24 h, resulted in the formation of
coumarinic compounds (5–11). Similarly, the other substituted
salicylaldehyde compound 12 underwent the Perkin reaction with
the appropriately substituted phenylacetic acids to furnish another
set of coumarinic compounds in good yields (13–15).20 Structures
of the compounds were substantiated by 1H NMR, 13C NMR, 2D
NMR, Mass spectrometry and IR spectroscopy. The purity of these
compounds was ascertained by TLC and spectral analysis (Supple-
mentary data).
at d 2.61, 3.82, 7.33, & 7.83 for methyl protons, methoxy protons,
proton at C-5 and proton C-4, respectively. Remaining multiplets
at d 6.99–8.62 affirmed the presence of eight aromatic protons.
13C NMR of 13 indicated presence of methyl carbon with peak at
d 19.2, methoxy carbon gave a peak at d 55.4 and while the car-
bonyl carbon resonated at d 161.0. Peaks for eighteen carbons in
the aromatic region from d 114.0 to 160.1, underlined the presence
of required aromatic skeleton. Mass spectra (ESI-MS) of 13 showed
a molecular ion peak at m/z 317 (M+H)+.21
For the purpose of biological evaluation of synthesized com-
pounds, adult male Swiss Albino mice (20–25 g) were used. Mice
were housed in six per cage and maintained in humidity and
temperature controlled rooms with day–night cycle. They were
allowed to acclimatize with the environment for one week before
commencement of the experiments. Free access to food and water
was permitted. All synthesized compounds 5–11 and 13–15 were
In the IR spectrum of the prototype compound 13 exhibited
absorption band of lactone carbonyl at 1705 cmꢀ1. Presence of aro-
matic skeleton is confirmed by peak at 3067 cmꢀ1 corresponding
to aromatic C–H stretching. The 1H NMR of 13 displayed singlets

K. V. Sashidhara et al. / Bioorg. Med. Chem. Lett. 21 (2011) 1937–1941
1939
assayed for antidepressant activities at dose of 0.5 mg/kg (ip), in
tail suspension test (TST)22,23 model in mice and the results are
shown in Figure 2. Among 10 compounds tested, three compounds
(6, 7 and 13) showed potent antidepressant activity. In TST, after
initial escape-oriented movements, mice develop an immobile
posture when placed in an inescapable stressful situation. This
stressful situation involved haemodynamic stress of being hung
in an uncontrollable fashion by their tail. Duration of immobility
was recorded by a fire-wire camera for a 6 min period and
analyzed using ANY-maze video tracking system (Stoelting CO,
v.4.72). In this established behavioural model, the ability of a com-
pound to decrease immobility duration is taken as a measure of its
antidepressant activity. The solutions of standard drugs (fluoxe-
tine, and imipramine) were prepared in water. The solutions of
the synthesized compounds were prepared by dissolving these
compounds in DMSO and diluted with water till the concentration
became 1.0 mg/mL and administered intraperitoneally (ip) to mice.
To control group, 1% DMSO was injected (ip) at a constant volume
of 0.1 mL/10 g. The acute treatment of synthesized compounds
(0.5 mg/kg, ip) was administered 30 min prior to experiments.
Similarly, fluoxetine (20 mg/kg, ip) and imipramine (30 mg/kg,
ip), conventional antidepressants were used as a positive control.
Test was performed 30 min after the administration of last dose
repetition. Percentage decrease in immobility duration (% DID)
300
200
100
**
***
***
***
***
0
Figure 2. Effect of treatment of mice with novel 3-phenylcoumarin derivatives (at
dose of 0.5 mg/kg), fluoxetine (20 mg/kg) and imipramine (30 mg/kg) given
intraperitoneally (ip) on the immobility time in the tail suspension test. Results
are represented as mean S.E.M. with n = 12 in each group. Values are significant at
⁄P <0.05, ⁄⁄P <0.01, ⁄⁄⁄P <0.001 when compared with control group.
Table 1
Evaluation of novel 3-phenylcoumarin derivatives at a dose of 0.5 mg/kg, ip in tail suspension test model in mice
Compound
Structure
Duration of immobility (s) (mean SEM)
% Decrease in immobility duration (% DID)
5
234.4 11.19
78.1
6
7
117.5 27.36
142.0 15.77
39.1
47.3
8
9
ND
214.2 13.43
71.4
10
217.6 18.77
72.5
(continued on next page)

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K. V. Sashidhara et al. / Bioorg. Med. Chem. Lett. 21 (2011) 1937–1941
Table 1 (continued)
Compound
Structure
Duration of immobility (s) (mean SEM)
% Decrease in immobility duration (% DID)
11
212.0 21.50
70.6
13
14
149.8 19.21
49.9
ND
15
191.0 22.50
63.6
Control
Fluoxetine (20 mg/kg)
Imipramine (30 mg/kg)
239.8 4.47
135.3 38.86
62.00 7.13
79.9
45.1
20.6
ND = not done due to solubility problem.
for test and standard drugs was calculated using following
formula:
250
200
150
100
50
%DID ¼ ½ðA ꢀ BÞ=Aꢁ ꢂ 100
Where A is the duration of immobility (s) in control group and B is
the duration of immobility (s) in test group.
***
***
***
**
Majority of the synthesized compounds exhibited considerable
antidepressant potential as evident from their duration of immo-
bility values and high % DID values (Table 1). Compounds (6, 7
and 13) that were found most potent in the tail suspension test
(Fig. 2), were further evaluated in forced swim test (FST)24 for con-
firmation of their antidepressant activity. Forced swimming test in
mice, is a behavioural despair test. This experimental model is
based on the observation that mice, when forced to swim in an
inescapable condition, after an initial period of agitation/flurry,
adopt an immobility behavior. Thus, mice were individually forced
to swim in an open cylindrical container (diameter 10 cm, height
25 cm), containing approximately 20 cm of water at 25 1 °C.
The immobility time, defined as the absence of escape-oriented
behaviors, such as swimming, was recorded using a fire-wire cam-
era for duration of 6 min and analyzed ANY-maze video tracking
system (Stoelting CO, v.4.72). Each mouse was judged immobile
when it ceased struggling and remained floating motionless in
the water, making only those movements necessary to keep its
head above water. Conventional antidepressants decrease the
immobility time in this test. All three compounds (6, 7 and 13),
have shown good activity profile at very low dose 0.5 mg/kg com-
pare to standard drug imipramine at the dose of 30 mg/kg ip and
the results are shown in Figure 3.
0
Figure 3. Effect of treatment of mice with novel 3-phenylcoumarin derivatives (at
dose of 0.5 mg/kg) and imipramine (30 mg/kg) given intraperitoneally (ip) given on
the immobility time in the forced swim test. Results are represented as mean
-
S.E.M. with n = 12 in each group. Values are significant at ⁄P <0.05, ⁄⁄P <0.01, ⁄⁄⁄P
<0.001 when compared with control group.
(M/s Columbus Instruments, USA). Rotarod consisted of a rod which
was coated with polypropylene foam to provide friction and to pre-
vent animals from slipping off the rod. The distance between rod and
floor was kept 15 cm to avoid intentional jumping of mice. The rod
was driven by a motor and the rotational speed was maintained at
8 rpm. Animals were trained on the rotarod for 2 min per trail, with
3 day per trial for two day. On the third day, mice were given trial
before and after treatment of coumarin derivatives. The compounds
After confirmed antidepressant activities of the compounds (6, 7
and 13), these potent compounds were next tested for their neuro-
logical toxicity by rotarod toxicity test as described by Dunham
and Miya (1957)25 and were studied in the Rotamex 4/8 apparatus

K. V. Sashidhara et al. / Bioorg. Med. Chem. Lett. 21 (2011) 1937–1941
1941
250
200
150
100
50
**
***
***
***
***
***
***
**
***
0
Comp 6
Comp 7
Comp 13
Figure 4. Effect of treatment of mice with compounds 6, 7, and 13 given intraperitoneally (ip) at graded doses on the immobility time in the forced swim test. Results are
represented as mean S.E.M. with n = 12 in each group. Values are significant at ⁄P <0.05, ⁄⁄P <0.01, ⁄⁄⁄P <0.001 when compared with control group.
were used at highest dose of 1 mg/kg (ip), to evaluate any defect in
motor coordination. All the three compounds did not show any
defects in neuro-muscular coordination.
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´
´
´
~
´
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compound 6 did not show any neurotoxicity in the rotarod test and
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21. 3-(4-Methoxyphenyl)-6-methyl-2H-benzo[h]chromen-2-one (13). Purified by
chromatography using 98:2 hexane/ethyl acetate as eluent. Light yellow solid,
Authors acknowledge the SAIF Division for providing the
spectroscopic and analytical data. We are also thankful to Dr. T.K.
Chakraborty (Director, CDRI) for his constant support and encour-
agement. A.K., M.C. and K.B.R. are thankful to CSIR, New Delhi,
India for financial support. This is CDRI publication number 8026.
yield: 68%; mp 135–137 °C; IR (KBr): 3067, 1705, 1641, 1026 cmꢀ1 1H NMR
;
(CDCl3, 300 MHz) d: 8.62–8.58 (m, 1H), 8.01–7.98 (m, 1H), 7.83 (s, 1H), 7.70 (d,
J = 8.8 Hz, 2H), 7.68–7.64 (m, 2H), 7.33 (s, 1H), 6.96 (d, J = 8.8 Hz, 2H), 3.87 (s,
3H), 2.70 (s, 3H); 13C NMR (CDCl3, 75 MHz) d: 161.0, 160.1, 149.1, 139.0, 133.7,
130.8, 129.8, 128.3, 127.4, 127.1, 126.8, 124.4, 123.6, 122.9, 122.7, 114.9, 114.0,
55.4, 19.2; DEPT (CDCl3, 75 MHz) d: 139.0, 129.8, 128.3, 126.8, 124.4, 123.6,
122.7, 114.0, ESI-MS: m/z: 317 (M+H)+.
Supplementary data
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Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmcl.2011.02.040.