Design and synthesis of some novel 3-[5-(4-substituted) phenyl- 1,3,4-oxadiazole-2yl]-2-phenylquinazoline-4(3H)-ones as possible anticonvulsant agent

Article abstract of DOI:10.1007/s00044-010-9475-2

A novel series 7(a-f) 3-[5-(4-substituted) phenyl- 1,3,4-oxadiazole-2yl]-2 phenylquinazoline-4(3H)-ones have been synthesized and screened for its anticonvulsant and neurotoxic activity. After i.p. injection to mice at doses of 30, 100, and 300 mg/kg body weight 2,3-disubstitutedquinazolin- 4(3H)-ones were examined in the maximal electroshock induced seizures (MES) and subcutaneous pentylenetetrazole (scPTZ) induced seizure models in mice. Spectroscopic data were consistent with the structure of newly synthesized compounds. The neurotoxicity was assessed using the rotorod method. In the prepared series, 7a was found to be active in the MES screen at 0.5 h, whereas 7f showed anticonvulsant activity at both 0.5 and 4 h. Springer Science+Business Media, LLC 2010.

Full text of DOI:10.1007/s00044-010-9475-2

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res (2011) 20:1638–1642
DOI 10.1007/s00044-010-9475-2
ORIGINAL RESEARCH
Design and synthesis of some novel 3-[5-(4-substituted) phenyl-
1,3,4-oxadiazole-2yl]-2-phenylquinazoline-4(3H)-ones as possible
anticonvulsant agent
•
Anjali Gupta Sushil K. Kashaw Neha Jain
•
•
•
Harish Rajak Abhishek Soni J. P. Stables
•
Received: 5 March 2010 / Accepted: 14 October 2010 / Published online: 4 November 2010
Ó Springer Science+Business Media, LLC 2010
Abstract A novel series 7(a–f) 3-[5-(4-substituted) phe-
nyl-1,3,4-oxadiazole-2yl]-2 phenylquinazoline-4(3H)-ones
have been synthesized and screened for its anticonvulsant
and neurotoxic activity. After i.p. injection to mice at doses
of 30, 100, and 300 mg/kg body weight 2,3-disubstituted-
quinazolin-4(3H)-ones were examined in the maximal
electroshock induced seizures (MES) and subcutaneous
pentylenetetrazole (scPTZ) induced seizure models in mice.
Spectroscopic data were consistent with the structure of
newly synthesized compounds. The neurotoxicity was
assessed using the rotorod method. In the prepared series, 7a
was found to be active in the MES screen at 0.5 h, whereas 7f
showed anticonvulsant activity at both 0.5 and 4 h.
for improved agents for the treatment of seizures, since
currently available drugs are effective only in 60–80% of
epileptic patients. Polytherapy with antiepileptic drugs
(AEDs) is necessary in clinical practice because of the
limited efficacy of monotherapy. In recent years, many new
chemical entities (NCE) have been designed that were
structurally dissimilar from many common anticonvulsant
containing dicarboximide function (CONRCO), which
contributes toxic side effects. 4(3H)-Quinazolinones and
related quinazolines are classes of fused heterocyclic that
are of considerable interest. Quinazoline and quinazolinone
derivatives have diverse pharmacological activities like
anti-tumor, anti-inflammatory, CNS depressant, stimulant,
anthelmentic, muscle relaxant, antifertility, hypoglycemic,
and anti-microbial activities (Raffa et al., 2004a, b; Ala-
garsamy et al., 2003; Mukerji et al., 1980; Gupta et al.,
2008; Shukla and Saxena, 1979; Hussain and Gupta, 1982;
Abdel-Aleem and Abdel-ghaffer, 1980). Literature survey
revealed that presence of substituted aromatic ring at
position 3 and methyl group at position 2 are necessary
requirement for the central nervous system (CNS) depres-
sant and anticonvulsant activities. Modification of methyl
group by some other chemical moiety yielded structural
analogues with anticonvulsant activity. The reported work
is based on 4(3H)-quinazolinone nucleus containing well
known sedative-hypnotic and anticonvulsant methaqualone
(2-methyl-3-o-tolyl-4(3H)-quinazolinone) and already
reported compounds by us in search of potential anticon-
vulsant compounds (Jatav et al., 2008a, b; Kashaw et al.,
2008, 2009). The structural requirement as presented in the
Fig. 1 prompted us to undertake the present work.
Keywords 1,3,4-Oxadiazole Á Semicarbazone Á
Anticonvulsant
Introduction
Epilepsy is a chronic brain disease of diverse etiology,
characterized by recurrent paroxysmal episodes of uncon-
trolled excitation of brain neurons. There is currently a need
A. Gupta Á S. K. Kashaw (&) Á N. Jain Á A. Soni
Pharmaceutical Chemistry Division, Department of
Pharmaceutical Sciences, Dr. H. S. Gour University,
Sagar 470003, MP, India
e-mail: sushilkashaw@gmail.com
H. Rajak
Institute of Pharmaceutical Sciences,
Guru Ghasidas University, Bilaspur, CG 495 009, India
It was also expected to get synergistic response of 4(3H)-
quinazolinone nucleus itself, placement of substituted 1,3,4-
oxadiazole at third position and chemically modifying
secondpositionof4(3H)-quinazolinone(substituting–C6H5).
J. P. Stables
Preclinical Pharmacology Section, Epilepsy Branch,
National Institutes of Health, Bethesda, MD 20892-9020, USA
123

Med Chem Res (2011) 20:1638–1642
1639
B
were prepared by cyclization of semicarbazones of the
corresponding aromatic aldehydes in the presence of bro-
mine in glacial acetic acid (Rajak et al., 2007). N-benzoyl
anthranilic acid (5) was prepared by reaction of anthranilic
acid with benzoyl chloride. The reaction is followed by
dehydrative cyclization of N-benzoyl anthranilic acid to
form 2-phenyl benzoxazinone (6) (Raffa et al., 2004a, b).
Title compounds 7(a–f) were synthesized by refluxing
2-phenyl benzoxazinone (6) with 2-amino-5-aryl-1,3,
4-oxadiazole (3) in glacial acetic acid. All the synthesized
compounds were characterized by spectral analysis (IR,
H1-NMR). Thin layer chromatography (TLC) was run
throughout the reaction to optimize the reaction for purity
and completion.
B
CH3
O
O
H
H
N
N
N
N
O
N
N
CH
N
3 A
N
CH3/C6H5
A
(ii)
(i)
O
N
R1
O
N
B
N
N
R1
O
B
N
S
N
R2
A
A
R2
(iv)
(iii)
Fig. 1 Comparative pictorial representation of the proposed hypoth-
esis (iv), methaqualone (ii) and previously reported compounds (ii)
and (iii)
Chemistry
Pharmacology
The synthetic route is outlined in Fig. 2. Substituted aryl
semicarbazones (2) were prepared according to the method
reported in the literature using semicarbazide hydro-
chloride and substituted aldehydes in alcohol (Furniss
et al., 2005a, b). 2-Amino-5-aryl-1,3,4-oxadiazoles (3)
Initial anticonvulsant evaluation of the target compounds
were undertaken by anticonvulsant drug development
(ADD) program, NIH protocol. The profile of anticonvul-
sant activity was established after i.p. injections by one
electrical and one chemical test. The electrical test
N
N
H
N
Br2,CH3CO2H
CH3CO2Na
CH3CO2Na
R
R
NH2
CHO
+ NH2NHCONH2
Semicarbazide
O
R
HN
O
(1a-1f)
Substituted aldehydes
(2a-2f)
(3a-3f)
H2N
Substituted semicarbazones
Substituted oxadiazole amines
O
N
CO2H
COOH
O
C6H5COCl
NaOH
(CH3)2CO
Reflux 2 h
NH2
NHCOC6H5
(4)
(5)
N-benzoyl anthranilic acid
(6)
Anthranilic acid
2-Phenyl benzoxazinone
O
N
N
O
O
N
N
N
N
O
NH2
+
O
R
R
N
(3a-3f)
(6)
(7a-7f)
2-Phenyl benzoxazinone
Substituted oxadiazole amines
Fig. 2 Scheme for synthesis of target compounds
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Med Chem Res (2011) 20:1638–1642
employed was the MES pattern test. The chemical test
employed was the subcutaneous metrazole seizure thresh-
old test. Minimal motor impairment was measured by the
rotorod (neurotoxocity, NT) test.
pellets, H1-NMR spectra were recorded on Bruker Avance
Spectrometer at 400 MHz using CDCl3 as the solvent.
Chemical shifts were reported in parts per million (ppm)
using trimethylsilane (TMS) as an internal standard. The
purity of the compounds was confirmed by thin layer
chromatography using silica gel glass plates and a solvent
system of chloroform:methanol (8:2). The spots were
developed in iodine chamber and visualized under ultra
violet lamp.
Results and discussion
Structure of the prepared compounds was confirmed with
the help of spectral analysis. Initial anticonvulsant activity
and neurotoxicity data for the quinazolinone analogs are
reported in Table 2. In the prepared series, 7a and 7f were
found to be active at 300 mg/kg in the MES screen at 0.5 h,
whereas 7f showed anticonvulsant activity at 4 h. Out of
six compounds only two compounds namely 7a and 7f
exhibited activity at 300 mg/kg body weight. Three com-
pounds out of six exhibited neurotoxicity at a maximum
dose level of 300 mg/kg. None of the compounds showed
neurotoxicity at a dose of 100 mg/kg. Compounds 7c, 7d,
and 7e showed extended level of neurotoxicity up to 4 h. It
was observed that, as the electronegativity of substituted
group increases, their anticonvulsant activity and duration
of action also increases. In compound 7a, R is –H which is
less electronegative as compared to –F. Compound 7f
showed rapid onset of action. Compound 7a which was
active at 300 mg/kg in anticonvulsant screening showed no
neurotoxicity, which suggested its selectivity.
Synthesis of 4-substitutedbenzaldehyde semicarbazone
(2a–2f)
A solution of aromatic aldehyde (0.2 mol) in warm alcohol
(250 ml) and a solution of semicarbazide (0.2 mol) and
sodium acetate (0.4 mol) in 50–60 ml of warm water were
mixed slowly with continuous stirring. The product sepa-
rated immediately on cooling.
Synthesis of 2-amino-5-aryl-1,3,4-oxadiazoles (3a–3f)
Substituted semicarbazone (0.1 mol) and sodium acetate
(0.2 mol) was dissolved in 300–350 ml of warm glacial
acetic acid with continuous stirring. Bromine (7 ml in
50 ml of glacial acetic acid) was added slowly to it.
Solution was stirred for an hour and then poured onto
crushed ice. The separated solid was dried and recrystal-
lized from 95% hot ethanol.
Conclusion
Synthesis of N-benzoyl anthranilic acid (5a–5f)
Out of six synthesized compounds, 7a and 7f showed
anticonvulsant activity while three compounds (7c–7f)
exhibited the neurotoxicity (at 300 mg/kg body weight).
Almost all the neurotoxic compounds also exhibited
extended level of activity up to 4 h. Compound 7f was
active at 300 mg/kg body weight during 0.5 and 4 h time
duration but unfortunately it was also toxic at the same
dose. Compound with halogen substitution at position R
was active but with neurotoxicity. Based on the experi-
mental results, it may be concluded that the synthesized
compounds showed more neurotoxic as compared to
anticonvulsant.
Anthranilic acid (4) (0.1 mol) was added in 360 ml of (5%)
sodium hydroxide solution in a well-corked conical flask.
Benzoyl chloride (36 ml) was added slowly with constant
shaking until the odor of benzoyl chloride disappeared. The
resulting solid was separated, dried and recrystallised from
95% ethanol.
Synthesis of 2-phenyl benzoxazinone (6a–6f)
The mixture of N-benzoyl anthranilic acid (5) (0.01mol)
and acetic anhydride (0.1 mol) was refluxed under anhy-
drous condition for 2 h. The excess acetic anhydride was
distilled off under reduced pressure. The product so
obtained as a solid mass was used up immediately for next
step. Physico-chemical data and m.p. of the 5 and 6 was in
agreement with the data reported in the literature.
Experimental
Chemistry
Synthesis of title compounds (7a–7f)
Melting points were determined in one end open capillary
tubes on a Buchi 530 melting point apparatus and are
uncorrected. Infrared (IR) spectra were recorded for the
compounds on Perkin Elmer Spectrophotometer in KBr
To the mixture of 2-phenyl benzoxazinone (0.1 mol),
2-amino-5-aryl-1,3,4-oxadiazole (0.1 mol) in 100 ml of
glacial acetic acid was added and refluxed under anhydrous
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Med Chem Res (2011) 20:1638–1642
1641
Pharmacology
condition for 4 h. After cooling, it was poured into crushed
ice. The solid was filtered out, dried and recrystallized from
hot ethanol (95%). The yields and melting point of syn-
thesized compound are recorded in Table 1.
The new derivatives obtained from the reaction sequence
were injected intraperitoneally into mice and evaluated in
the maximal electroshock (MES), subcutaneous metrazole
(ScMET), and neurotoxicity screens, using doses of 30,
100, and 300 mg/kg at two different time intervals. These
data are presented in Table 2.
7a IR (cm-1) 1683.1 (C=O str. in quinazolinone ring), 1608.7 (C=N
str.), 1159.3 (C–O–C str. in oxadiazole ring), 849.3 (Ar-CH out
of plane bending vibration), 1HNMR (400 MHz, d) 7.22–7.9 (m,
14H, 3Ar-H)
Anticonvulsant screening
7b IR (cm-1) 1684.3 (C=O str. in quinazolinone ring), 1608.9 (C=N
str.), 1180.6 (C–O–C str. in oxadiazole ring), 849.3 (Ar-CH out
of plane bending vibration) 1HNMR (400 MHz, d) 7.29–7.9 (m,
13H, 3Ar-H)
7c IR (cm-1) 1684.4 (C=O str. in quinazolinone ring), 1609.4 (C=N
str.), 1180.5 (C–O–C str. in oxadiazole ring), 1231.5 (Asym.
C–O–C str. of aryl alkyl ether), 1025.0 (sym. C–O–C str. of aryl
alkyl ether), 2983.4 (Alkane C–H str.) 848.3 (Ar-CH out of
plane bending vibration) 1HNMR (400 MHz, d) 6.83–7.9 (m, 13
H, 3Ar-H), 3.73 (s, 3H, OCH3)
7d IR (cm-1) 1660.9 (C=O str. in quinazolinone ring), 1583.8 (C=N
str.), 1181.8 (C–O–C str. in oxadiazole ring), 2853.6 (Alkane
C–H str.), 829.1 (Ar-CH out of plane bending vibration)
1HNMR (400 MHz, d) 7.12–7.9 (m, 13H, 3Ar-H), 2.35 (s, 3H,
CH3)
Albino mice were used for this experiment. Food was
withdrawn 12–15 h before the commencement of the
experiments, while water was withdrawn immediately
before the experiment. Maximum seizures were induced by
applications of electrical current across the brain via cor-
neal electrodes primed with normal saline (0.9% NaCl).
The stimulus parameters were 50 mA AC in a pulse of
60 Hz for 0.2 s. After applying shock mice were observed
for the type of convulsion produced and the hind limb
extensor response was taken as the end point. Animals
showing positive hind limb extensor response were used
for testing drug substance. For ScMET test the test com-
pounds were administrated i.p. to all animals in a group.
Pentylenetetrazole (85 mg/kg) was injected subcutane-
ously, 30 min and 4 h after the administration of the
compounds. The absence or presence of an episode of
clonic convulsion was taken as the end point. Initially, all
the compounds were administered i.p. in a volume of
0.01 ml/g body weight for mice and 0.004 ml/g body
weight for rats at doses of 30, 100, and 300 mg/kg to one to
7e IR (cm-1) 1685.0 (C=O str. in quinazolinone ring), 1643.4 (C=N
str.), 1158.3 (C–O–C str. in oxadiazole ring), 1538.5 (Asym.
NO2 str.), 1314.9 (Asym. NO2 str.) 849.6 (Ar-CH out of plane
1
bending vibration) HNMR (400 MHz, d) 7.29–8.25 (m, 13H,
3Ar-H)
7f IR (cm-1) 1684.8 (C=O str. in quinazolinone ring), 1645.6 (C=N
str), 1157.9 (C–O–C str. in oxadiazole ring), 1039.2 (Aromatic
C–F str.) 843.1(Ar-CH out of plane bending vibration) 1HNMR
(400 MHz, d), 7.03–7.9 (m, 13H, 3Ar-H)
Table 2 Anticonvulsant activity and minimal motor impairment of
3-[5-(4-substituted) phenyl-1,3,4-oxadiazole-2yl]-2-phenylquinazo-
line-4(3H)-ones
Table 1 Physical data of 3-[5-(4-substituted)phenyl-1,3,4-oxadiaz-
ole-2yl]-2-phenylquinazoline-4(3H)-ones
Code no.
Intraperitoneal injection in micea
O
MES screen scPTZ screen Neurotoxicity screen
N
N
0.5 h 4 h 0.5 h 4 h
0.5 h
4 h
N
O
7a
300
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
R
7b
–
300
300
300
–
N
7c
–
–
300
–
(7a-7f)
7d
–
–
7e
–
–
300
300
100
7f
300
300
30
S. no. Code Molecular formula –R
M.P. (°c) % Yield
Phenytoinb
Carbamazepineb 30
30
100
300
1
2
3
4
5
6
7a
7b
7c
7d
7e
7f
C22H14N4O2
–H
123–125 37.20
113–116 42.56
100 100
300 100
C
C
C
C
C
22H13ClN4O2
23H16N4O3
23H16N4O2
22H13N5O4
22H13FN4O2
–Cl
a
Doses of 30, 100, and 300 mg/kg were administered. The figures in
the table indicates the minimum dose whereby bioactivity was dem-
onstrated in half or more of the mice. The animals were examined 0.5
and 4 h after injections. (–) indicates an absence of activity at max-
imum dose administered (300 mg/kg)
–OCH3 132–135 29.32
–CH3
–NO2
–F
162–165 46.82
155–158 25.80
149–152 26.89
b
Reference drug
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Neurotoxicity screen
The test is used to evaluate whether any drug is interfering
with established anticonvulsant activity. Minimal motor
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by the rotorod test. The mice were trained to stay on an
accelerating rotorod that rotated at six revolutions per
minute. Only those animals showing ability to remain on
the revolving rod for at least 1 min were selected for the
test. These trained mice were divided into group of four
animals each and were given test compounds intraperito-
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diameter was 3.2 cm. Neurotoxicity was indicated by the
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Acknowledgments The authors deeply appreciate the assistance of
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screening the compounds for anticonvulsant activity.
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