Synthesis and in vivo anticonvulsant screening of coumarin incorporated Schiff bases of 1,3,4-oxadiazoles

Article abstract of DOI:10.1002/jccs.200800199

A series of coumarin incorporated Schiff bases of 1,3,4-oxadiazoles (1-18) was synthesized. The structures of the synthesized compounds were confirmed on the basis of spectral data and elemental analysis. The anticonvulsant and neurotoxicity was studied by maximal electroshock seizure (MES) and rotorod method, respectively. A majority of the compounds were active in MES test. All the compounds were less neurotoxic than the standard drug phenytoin.

Full text of DOI:10.1002/jccs.200800199

1326
Journal of the Chinese Chemical Society, 2008, 55, 1326-1331
Synthesis and In Vivo Anticonvulsant Screening of Coumarin
Incorporated Schiff Bases of 1,3,4-Oxadiazoles
Nadeem Siddiqui,* Mashooq A. Bhat, Suroor A. Khan, Waquar Ahsan and M. Shamsher Alam
Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Jamia Hamdard (Hamdard University),
Hamdard Nagar, New Delhi-110062, India
A series of coumarin incorporated Schiff bases of 1,3,4-oxadiazoles (1-18) was synthesized. The
structures of the synthesized compounds were confirmed on the basis of spectral data and elemental analy-
sis. The anticonvulsant and neurotoxicity was studied by maximal electroshock seizure (MES) and
rotorod method, respectively. A majority of the compounds were active in MES test. All the compounds
were less neurotoxic than the standard drug phenytoin.
Keywords: Coumarin; MES test; 1,3,4-Oxadiazoles; Schiff bases.
INTRODUCTION
Epilepsy, one of the most frequent neurological disor-
carbazones coumarin etc.3-6 In the present investigation we
have synthesized coumarin incorporated Schiff bases of
1,3,4-oxadizoles (Scheme I). The compounds were evalu-
ated in vivo for anticonvulsant activity by MES test and
neurotoxicity by rota-rod method.
ders, is a major public health issue, affecting about 4% of
individuals over their lifetime. Despite the increasing un-
derstanding of the pathogenesis of seizures and epilepsy,
the cellular basis of human epilepsy remains a mystery. In
the absence of specific etiological understanding, ap-
proaches to drug therapy for epilepsy must necessarily be
directed towards the control of symptoms, that is the sup-
pression of seizures by chronic administration of Anti-
epileptic Drugs (AEDs). However, seizures remain uncon-
trolled in at least 30% of all epilepsies, even when an ade-
quate AED therapy is administered. During recent years, a
large number of new AEDs have been marketed world-
wide, but the proportion of patients failing to respond to
drug treatment has not been changed in a significant extent.
This disease affects a large number of populations of
different age groups and sex. The classical antiepileptic
drugs comprise phenobarbital, available since 1911; phen-
ytoin, marketed in 1939; carbamazepine, used for epilepsy
in Europe from the mid 1960s; and valproic acid,1 available
in several European countries as of the late 1960s. All cur-
rently approved antiepileptic drugs have dose-related
toxicity and idiosyncratic side effects.2 In response to the
premise that major medical breakthroughs in non-pharma-
cologic therapies for the treatment of epilepsy in the near
future seem remote, the search for new antiepileptic drugs
with lower toxicities and fewer side effects continues.
In our previous researches on anticonvulsants, differ-
ent moieties were selected for the synthesis of anticon-
vulsant agent e.g., sulphonamides, benzothiazoles, semi-
Scheme I
O
O
O
O
O
N
O
N
CNBr
NHNH2
(Z)
(Z)
NH2
R
CH3COOH
OHC
N
N
O
O
(E)
N
R
O
(Z)
(1-18)
1: R = 3-NO2; 2: R = 3,4-(OCH3)2; 3: R = 4-OH; 4: R = 2-OH; 5:
R = 2-NO2; 6: R = 3-OH; 7: R = 4-N(CH3)2; 8: R = 4-F; 9: R =
4-OCH3; 10: R = 2-Cl; 11: R = 3-Cl; 12: R = 4-Cl; 13: R = H; 14:
R = 4-NO2; 15: R = 3-F; 16: R = 2-F; 17: R = 2-OCH3; 18: R =
3-OCH3.
EXPERIMENTAL SECTION
Compounds 3-(5-{[(1E)-(substituted phenyl)methyl-
ene]amino}-1,3,4-oxadiazol-2-yl)-2H-chromen-2-ones
were synthesized by reacting coumarin hydrazide with cy-
anogen bromide to form 3-(5-amino-1,3,4-oxadiazol-2-
yl)-2H-chromen-2-one (Step II). In IR spectrum bands at

Newer 1,3,4-Oxadiazoles as Anticonvulsants
J. Chin. Chem. Soc., Vol. 55, No. 6, 2008 1327
3000 cm-1, 1622 cm-1, 1600 cm-1, 1275 cm-1 confirmed the
presence of C-H, C=O (coumarin), C=C and C-O groups,
respectively. The 1H-NMR spectra showed multiplet at d
6.99-8.71 for five aromatic protons. A singlet appears at d
11.38 for two NH protons. The compound 3-(5-amino-1,3,4-
oxadiazol-2-yl)-2H-chromen-2-one was reacted with 3-
nitrobenzaldehyde in presence of acetic acid to form Schiff
base. In IR spectrum bands at 3000 cm-1, 2700 cm-1, 1699
cm-1, 1348 cm-1, 1268 cm-1 confirm the presence of C-H,
N=CH, C=O (coumarin), C-N and C-O groups, respec-
violet lamp. The IR spectra were recorded in KBr pellets on
(BIO-RAD FTS 135) WIN-IR spectrophotometer. 1H-NMR
spectra were recorded on a Bruker model DPX 300 FT-
NMR spectrometer in (CDCl3) using tetramethylsilane
(Me4Si) TMS as an internal standard. The chemical shifts
are reported in d ppm scale.
Synthesis of 3-(5-{[(1E)-(substituted phenyl)methyl-
ene]amino}-1,3,4-oxadiazol-2-yl)-2H-chromen-2-ones
Step I: 2-Oxo-2H-chromene-3-carbohydrazide
1
tively. The H NMR spectra showed the multiplet at d
Ethyl-2-oxo-2H-chromene-3-carboxylate (0.01 mol)
and hydrazine hydrate 99% (0.01 mol) were dissolved in
ethanol (50 mL) to give clear solution and refluxed for 10
h. The contents were concentrated to half volume and al-
lowed to cool. The solid mass which separated out on cool-
ing was retained by filtering and washed with small amount
of ice-cooled ethanol (90%). (m.p. = 136-138 °C).
6.96-8.3 with J = 10 Hz for nine aromatic protons. Asinglet
appears at 11.33 for one N=CH proton. The synthesized
compounds were characterized by elemental analysis, FT-
1
IR and H-NMR. The IR spectra revealed the following
bands for N=CH, C=O (coumarin), C-N, C-O groups at
2700 cm-1, 1721-1619 cm-1, 1662-1348 cm-1, 1304-1268
cm-1, respectively. The 1H-NMR spectra confirm the pres-
ence of aromatic protons at d 6.9-8.5. The singlet for
N=CH-Ar appears at d 11.0-11.4.
Step II: 3-(5-amino-1,3,4-oxadiazol-2-yl)-2H-chromen-
2-one
To an ethanolic solution of 2-oxo-2H-chromene-3-
carbohydrazide (0.01 mol), cyanogen bromide (0.01 mol)
was added. The reaction mixture was warmed at 55-60 °C
for 90 min. The resulting solution was cooled and neutral-
ized by sodium bicarbonate (NaHCO3) solution. The solid
was filtered out. (m.p. = 200 °C).
MATERIALS AND METHODS
Animals
Male albino mice (Swiss, 18-25 g) were used as ex-
perimental animals. The test compounds were suspended in
polyethylene glycol (PEG). The animals were maintained
on an adequate diet and allowed free access to food and wa-
ter except during the short time they were removed from
cages for testing. The animals were maintained at room
temperature (25-30 °C). All the experimental protocols
were carried out with the permission from Institutional An-
imal Ethics Committee (IAEC), form no. 304. Animals
were obtained from Central Animal House Facility, Ham-
dard University, New Delhi-110062, India. Registration
number and date of registration of Animal House Facility:
(173/CPCSEA, 28, JAN-2000).
Step III: 3-(5-{[(1E)-(3-nitrophenyl)methylene]amino}-
1,3,4-oxadiazol-2-yl)-2H-chromen-2-one (1)
3-(5-Amino-1,3,4-oxadiazol-2-yl)-2H-chromen-2-
one (0.01 mol), 3-nitrobenzaldehyde (0.01 mol) and glacial
acetic acid (2 mL) were refluxed in 1,4-dioxan (40 mL) for
8 h. The solvent was distilled off at reduced pressure. The
product was obtained by pouring the reaction mixture in
ice-cold water. It was recrystallized from ethanol. (m.p. =
105 °C). Similarly other compounds (2-18) of the series
were synthesized.
The physico-chemical characteristics of the com-
pounds are presented in (Table 1). The data of elemental
analysis agree with the results of analytical calculations ac-
cording to molecular formulas.
Chemistry
All the solvents were of LR grade and were obtained
from Merck, CDH and s. d. fine chemicals. Melting points
were determined in open capillary tubes and are uncor-
rected. All the compounds were subjected to elemental
analysis (CHN) and the measured values agreed within
0.4% with the calculated ones. Thin layer chromatogra-
phy was performed on Silica gel G (Merck). The spots were
developed in iodine chamber and visualized with an ultra-
Anticonvulsant screening
Electroshock-induced seizures (MES test)
Albino mice (20-25 g) were used in this test. Animals
were divided in groups of six and were stimulated through
corneal electrodes to 50 mA current at a pulse of 60 Hz al-

1328 J. Chin. Chem. Soc., Vol. 55, No. 6, 2008
Siddiqui et al.
Table 1. Physical and spectral properties of the tested compounds (1-18)
M.p
Compd
Molecular formula*
C18H10N4O5
Spectral Data
(°C)
1
105
IR (n, cm-1): (C-H) str. 3000; (N=C-H) str. 2700; (C=O, coumarin) str.
1669; (C-N) str. 1348; (C=C) str. 1527, (C-O) str. 1268; 1H-NMR
(CDCl3) d ppm: 7.2-7.6 (m, 8H, Ar-H), 8.7 (s, 1H, Ar-H, C-4), 11.3 (s,
1H, N=CH-Ar); 13C-NMR (CDCl3) d ppm: 116.4, 119.2, 120.5, 120.9,
122.3, 123.8, 125.2, 125.9, 126.4, 128.3, 130.5, 134.3, 142.1, 145.2,
155.0, 156.4, 163.7, 168.5.
2
3
4
5
6
7
8
9
180
182
C20H12N3O5
C18H11N3O4
C18H11N3O4
C18H10N4O5
C18H11N3O4
C20H17N4O3
C18H10N3O3F
C19H13N3O4
IR (n, cm-1): (C-H) str. 3000; (N=C-H) str. 2700; (C=O, coumarin) str.
1658; (C-O) str. 1304; (C-N) str. 1492; (=C-H) out of plane 789, 824;
1H-NMR (CDCl3) d ppm: 3.4 (s, 6H, 2 ´ OCH3), 7.3-8.7 (m, 8H, J = 10
Hz, Ar-H), 11.3 (s, 1H, N=CH-Ar); 13C-NMR (CDCl3) d ppm: 56.0,
112.3, 112.6, 116.1, 117.3, 119.2, 120.2, 122.4, 123.8, 124.3, 125.4,
134.6, 140.2, 142.4, 143.6, 155.2, 156.2, 163.5, 168.4.
IR (n, cm-1): (-OH) str. 3650; (C-H) str. 3000; (N=C-H) str. 2700;
(C=O, coumarin) str. 1620, 1574; (C-N) str. 1484; (C-O) str. 1271; 1H-
NMR (CDCl3) d ppm: 6.9-7.7 (m, 8H, J = 10 Hz, Ar-H), 8.5 (s, 1H, Ar-
H, H-4), 8.7 (s, 1H, Ar-OH), 11.3 (s, 1H, -N=CH-Ar); 13C-NMR
(CDCl3) d ppm: 112.4, 116.2, 119.4, 120.4, 122.5, 123.6, 124.1, 125.4,
126.6, 134.4, 143.9, 154.2, 155.3, 156.3, 163.5, 168.5.
IR (n, cm-1): (-OH) str. 3600; (C-H) str. 3046; (N=C-H) str. 2700;
(C=O, coumarin) str. 1619; (C=C) str. 1573; (C-N) str. 1485; (C-O) str.
1271; 1H-NMR (CDCl3) d ppm: 6.9-7.7 (m, 8H, J = 10 Hz), 8.5 (s, 1H,
Ar-H, H-4), 8.7 (s, 1H, Ar-OH), 11.3 (s, 1H, -N=CH-Ar); 13C-NMR
(CDCl3) d ppm: 111.2, 113.5, 115.4, 115.7, 120.1, 123.5, 124.6, 125.4,
126.5, 127.3, 129.3, 134.3, 144.1, 152.4, 155.2, 156.2, 163.6, 168.4.
IR (n, cm-1): (C-H) str. 3246; (N=C-H) str. 2700, (C=O, coumarin) str.
1619; (C=C) str. 1500; (C-N) str. 1457; (C-O) str. 1270; (=C-H) out of
plane; 1H-NMR (CDCl3) d ppm: 750; 7.2-7.6 (m, 8H, Ar-H), 8.7 (s, 1H,
Ar-H, C-4), 11.3 (s, 1H, N=CH-Ar); 13C-NMR (CDCl3) d ppm: 115.5,
119.8, 121.2, 122.3, 122.6, 123.8, 124.3, 125.5, 126.0, 128.1, 130.4,
134.4, 144.3, 155.1, 156.4, 163.2, 167.9.
IR (n, cm-1): (C-H) str. 3000; (N=C-H) str. 2700, (C=O, coumarin) str.
1622; (C=C) str. 1486, 1573, (C-N) str. 1382; (C-O) str. 1271; 1H-NMR
(CDCl3) d ppm: 7.0-7.3 (m, 8H, Ar-H), 8.7 (s, 1H, Ar-H, C-4), 8.7 (s,
1H, Ar-OH), 11.4 (s, 1H, N=CH-Ar); 13C-NMR (CDCl3) d ppm: 112.4,
115.0, 119.3, 119.6, 123.2, 124.3, 125.2, 127.4, 126.9, 125.3, 129.3,
134.6, 144.8, 155.4, 156.1, 160.7, 163.4, 168.4.
IR (n, cm-1): (C-H) str. 2900; (N=C-H) str. 2700; (C=O, coumarin) str.
1619; (C=C) str. 1523, 1486, (C-N) str. 1366; (C-O) str. 1270; 1H-NMR
(CDCl3) d ppm: 1.5 (s, 6H, 2 ´ NCH3), 7.0-7.3 (m, 8H, Ar-H), 8.7 (s,
1H, Ar-H, C-4), 11.3 (s, 1H, N=CH-Ar); 13C-NMR (CDCl3) d ppm:
45.4, 109.2, 116.7, 118.3, 122.2, 122.6, 123.8, 125.1, 126.6, 127.4,
134.7, 142.9, 144.8, 157.0, 161.4, 164.1, 168.8.
IR (n, cm-1): (C-H) str. 3000; (N=C-H) str. 2700; (C=O, coumarin) str.
1619; (C=C) str. 1550, 1486, (C-N) str. 1400; (C-O) str. 1270; 1H-NMR
(CDCl3) d ppm: 7.0-7.6 (m, 8H, J = 10 Hz, Ar-H), 8.7 (s, 1H, Ar-H, C-
4), 11.2 (s, 1H, N=CH-Ar); 13C-NMR (CDCl3) d ppm: 111.3, 116.4,
121.3, 122.6, 123.7, 124.8, 125.1, 126.3, 128.6, 133.3, 144.7, 156.3,
159.7, 160.8, 164.4, 168.6.
IR (n, cm-1): (C-H) str. 3000; (N=C-H) str. 2700, (C=O, coumarin) str.
1622; (C=C) str. 1486, 1573, (C-N) str. 1382; (C-O) str. 1271; 1H-NMR
(CDCl3) d ppm: 3.2 (s, 3H, OCH3), 7.2-7.7 (m, 8H, J = 10 Hz, Ar-H),
8.5 (s, 1H, Ar-H, H-4), 11.3 (s, 1H, -N=CH-Ar); 13C-NMR (CDCl3) d
ppm: 55.1, 110.1, 116.4, 119.4, 121.3, 122.6, 123.6, 124.1, 125.3,
127.1, 134.6, 144.8, 158.1, 159.7, 162.2, 164.6, 168.5.
190
360 (d°)
160
315 (d°)
100
140

Newer 1,3,4-Oxadiazoles as Anticonvulsants
J. Chin. Chem. Soc., Vol. 55, No. 6, 2008 1329
IR (n, cm-1): (C-H) str. 2900; (N=C-H) str. 2700; (C=O, coumarin) str.
10
11
12
13
14
15
16
17
18
160
140
130
165
120
125
90
C18H10N3O3Cl
C18H10N3O3Cl
C18H10N3O3Cl
C18H11N3O3
C18H10N4O5
C18H10N3O3F
C18H10N3O3F
C19H13N3O4
C19H13N3O4
1619; (C=C) str. 1572, 1484; (C-N) str. 1374; (C-O) str. 1270; (=C-H)
out of plane 731; 1H-NMR (CDCl3) d ppm: 7.0-7.3 (m, 8H, Ar-H), 8.7
(s, 1H, Ar-H, C-4), 11.3 (s, 1H, N=CH-Ar); 13C-NMR (CDCl3) d ppm:
116.1, 121.2, 122.3, 123.7, 125.6, 126.1, 127.0, 127.4, 128.3, 129.4,
130.2, 131.3, 134.4, 144.8, 157.0, 160.6, 164.1, 168.5.
IR (n, cm-1): (C-H) str. 3000; (N=C-H) str. 2700; (C=O, coumarin) str.
1721; (C-N) str. 1662; (C=C) str. 1572; (C-O) str. 1272; (=C-H) out of
plane 680, 750; 1H-NMR (CDCl3) d ppm: 6.9-7.3 (m, 8H, Ar-H), 8.7 (s,
1H, Ar-H, C-4), 11.3 (s, 1H, N=CH-Ar); 13C-NMR (CDCl3) d ppm:
116.3, 121.2, 122.4, 123.5, 124.1, 125.7, 126.1, 127.5, 127.9, 128.4,
129.2, 130.6, 131.9, 136.5, 144.6, 160.4, 164.4, 168.6.
IR (n, cm-1): (C=O, coumarin) str. 1622; (C-O) str. 1269; (C-N) str.
1486; (C=C) str. 1572; (N=C-H) str. 2700; (C-H) str. 3000; 1H-NMR
(CDCl3) d ppm: 6.9-7.8 (m, 8H, J = 10 Hz, Ar-H), 8.7 (s, 1H, Ar-H, C-
4), 11.3 (s, 1H, N=CH-Ar); 13C-NMR (CDCl3) d ppm: 116.4, 121.1,
122.6, 123.8, 124.2, 125.0, 125.5, 126.3, 127.4, 132.1, 136.6, 144.8,
157.4, 160.7, 164.6, 168.8.
IR (n, cm-1): (C-H) str. 3000; (N=C-H) str. 2700; (C=O, coumarin) str.
1619; (C=C) str. 1573; (C-N) str. 1480; (C-O) str. 1270 (=C-H) out of
plane 731, 748; 7.0-7.4 (m, 9H, Ar-H), 8.7 (s, 1H, Ar-H, C-4), 11.3 (s,
1H, N=CH-Ar); 13C-NMR (CDCl3) d ppm: 116.3, 121.2, 123.5, 124.7,
125.1, 125.8, 127.3, 127.8, 128.7, 129.1, 136.5, 144.8, 159.8, 160.7,
164.6, 168.7.
IR (n, cm-1): (C-H) str. 3246; (N=C-H) str. 2700, (C=O, coumarin) str.
1619; (C=C) str. 1500; (C-N) str. 1457; (C-O) str. 1270; (=C-H) out of
plane 750; 1H-NMR (CDCl3) d ppm: 7.2-7.6 (m, 8H, Ar-H), 8.7 (s, 1H,
Ar-H, C-4), 11.3 (s, 1H, N=CH-Ar); 13C-NMR (CDCl3) d ppm: 116.2,
121.1, 123.2, 124.6, 125.7, 127.1, 127.6, 128.4, 129.5, 136.6, 144.7,
146.8, 159.0, 160.5, 164.1, 168.5.
IR (n, cm-1): (C-H) str. 3000; (N=C-H) str. 2700; (C=O, coumarin) str.
1619; (C=C) str. 1550, 1486, (C-N) str. 1400; (C-O) str. 1270; (=C-H)
out of plane 750, 740; 1H-NMR (CDCl3) d ppm: 7.2-7.9 (m, 8H, Ar-H),
8.7 (s, 1H, Ar-H, C-4), 11.2 (s, 1H, N=CH-); 13C-NMR (CDCl3) d ppm:
112.1, 113.8, 116.5, 121.5, 122.3, 123.6, 124.7, 125.4, 126.3, 127.3,
128.5, 137.6, 146.8, 157.0, 159.2, 160.7, 163.9, 167.8.
IR (n, cm-1): (C-H) str. 3000; (N=C-H) str. 2700; (C=O, coumarin) str.
1619; (C=C) str. 1550, 1486, (C-N) str. 1400; (C-O) str. 1270; (=C-H)
out of plane 750, 740; 1H-NMR (CDCl3) d ppm: 7.2-7.6 (m, 8H, Ar-H),
8.5 (s, 1H, Ar-H, C-4), 11.0 (s, 1H, N=CH-); 13C-NMR (CDCl3) d ppm:
111.5, 113.2, 116.1, 121.3, 122.6, 124.5, 125.3, 126.1, 127.4, 128.1,
129.4, 136.4, 144.7, 157.3, 158.6, 163.9, 164.8, 168.9.
IR (n, cm-1): (C-H) str. 3000; (N=C-H) str. 2700, (C=O, coumarin) str.
1622; (C=C) str. 1486, 1573, (C-N) str. 1382; (C-O) str. 1271; 1H-NMR
(CDCl3) d ppm: 3.1 (s, 3H, OCH3), 7.1-7.4 (m, 8H, J = 10 Hz, Ar-H),
8.5 (s, 1H, Ar-H, H-4), 11.3 (s, 1H, -N=CH-Ar); 13C-NMR (CDCl3) d
ppm: 54.6, 110.1, 112.4, 116.9, 117.3, 121.2, 122.5, 123.5, 124.1,
125.9, 127.1, 128.8, 136.5, 144.7, 157.1, 159.5, 160.7, 163.9, 168.0.
IR (n, cm-1): (C-H) str. 3000; (N=C-H) str. 2700, (C=O, coumarin) str.
1622; (C=C) str. 1486, 1573, (C-N) str. 1382; (C-O) str. 1271; 1H-NMR
(CDCl3) d ppm: 3.0 (s, 3H, OCH3), 7.2-7.6 (m, 8H, J = 10 Hz, Ar-H),
8.5 (s, 1H, Ar-H, H-4), 11.3 (s, 1H, -N=CH-Ar); 13C-NMR (CDCl3) d
ppm: 54.9, 110.5, 112.6, 116.6, 121.2, 122.4, 123.6, 124.3, 125.1,
126.5, 127.7, 136.6, 144.6, 158.1, 159.7, 160.5, 164.6, 168.3.
150
55
* The values established by elemental analysis were within ± 0.4% in comparison to calculated values.

1330 J. Chin. Chem. Soc., Vol. 55, No. 6, 2008
Siddiqui et al.
ternating current applied for 0.25 s. The mice were previ-
ously administered i.p. with the test drug solution in poly-
ethylene glycol at three dose levels (30, 100 and 300 mg/
kg), the anticonvulsant activity was assessed after 30 min.
and 4 h intervals of administration. The abolition of hind
limb tonic extensor spasm was recorded as a measure of
anticonvulsant activity.7
Table 2. Anticonvulsant profile and rota-rod toxicity of the
examined compounds (1-18) in mice
Intraperitonial injection in micea
MES screen Toxicity screen
Compd.
0.5 h
4 h
0.5 h
4 h
1
030
100
100
100
030
100
300
100
030
030
030
030
300
030
100
100
030
030
030
030
100
100
300
300
300
100
300
300
300
100
100
100
100
300
100
300
300
100
100
030
100
030
300
300
300
300
300
300
300
300
300
300
300
300
300
300
300
300
300
300
100
100
100
-
2
-
3
-
Neurotoxic effects
4
300
-
5
Rota-rod test
6
300
300
300
100
100
300
300
300
300
300
300
100
100
100
300
300
Minimal motor impairment was measured in mice by
the rotorod test.8 The mice were trained to stay on an accel-
erating rotorod that rotates at 10 revolutions/min. The rod
diameter was 3.2 cm. Trained animals were given i.p. injec-
tion of the test compounds 30, 100 and 300 mg/kg. Neuro-
toxicity was indicated by the inability of the animal to main-
tain equilibrium on the rod for at least 1 min. in each of the
trials.
7
8
9
10
11
12
13
14
15
16
Histopathological studies
17
18
The selected compounds were evaluated for their his-
topathological study. The Luna’s technique9 was used to
access the livers of mice, which were administered with
test compounds at the dose level of 30 mg/kg body weight
for 15 days; comparison was done with the control group.
Microphotographs of section of liver were taken at the
magnification of 100X and 400X.
Phenytoinb
Carbamazepineb
Phenobarbitalb
a Doses of 30, 100 and 300 mg/kg were administered. The figure
in the table indicates the minimum dose whereby bioactivity
was demonstrated in half or more of the animals (n = 6). The
animals were examined 0.5 and 4 h after administration. The (-)
indicates an absence of activity at maximum dose administered
(300 mg/kg).
RESULTS AND DISCUSSION
b Data from references10-12
The pharmacological evaluation of the compounds
(1-18) was initially carried out according to the protocols
of antiepileptic drug development programme (ADD), Epi-
lepsy Branch, NIH. The methods employed have been pre-
viously described.7 The compounds were initially screened
in the mouse MES test. Minimal motor impairment was
measured by rotorod test. Data is represented in (Table 2).
All the coumarin incorporated Schiff bases of oxadiazoles
were active in MES test at a dose of 300 mg/kg indicative
of their ability to protect the seizure spread. At a dose of 30
mg/kg, compounds that showed protection in half or more
tested mice were (1, 5, 9, 10, 11, 12, 14, 17 and 18) after 0.5
h time interval. These compounds also showed protection
after 4 h but at a higher dose of 100 mg/kg. The compounds
(2, 3, 4, 6, 8, 15 and 16) showed protection at a dose 100
mg/kg after 0.5 h. These compounds also showed protec-
tion after 4 h but at a higher dose of 300 mg/kg. Compounds
(7 and 13) showed protection in MES test at 300 mg/kg
both after 0.5 h and 4 h duration.
In neurotoxicity screening, the compounds (1, 2, 3
and 5) were neurotoxic at a maximal dose of 300 mg/kg af-
ter 0.5 h. Compounds (9, 10, 17 and 18) showed neuro-
toxicity at a dose of 100 mg/kg after 4 h. All the compounds
showed neurotoxicity at a higher dose of 300 mg/kg after
0.5 h time interval. However all the compounds were less
neurotoxic than phenytoin.
In hepatotoxicity studies samples from group 1 (com-
pounds showing protection at 30 mg/kg at 0.5 h) showed
normal hepatic parenchyma and were similar to control
group (Fig. 1).
CONCLUSIONS
Substitutions of NO2, Cl and OCH3 at distal phenyl
ring showed potent activity against MES test. The Presence

Newer 1,3,4-Oxadiazoles as Anticonvulsants
J. Chin. Chem. Soc., Vol. 55, No. 6, 2008 1331
Commission (UGC, Government of India) for providing fi-
nancial assistance. The authors are thankful to IIT Delhi for
1H NMR and to Dr. Ashok Mukherjee, MD (consultant pa-
thologist) AIIMS, New Delhi, India for histopathological
studies.
Received June 11, 2008.
REFERENCES
1. Hess, R. In Antiepileptic Drugs; Frey, H. H.; Janz, D., Eds.;
Springer-Verlag: Berlin, 1985; p 35.
2. Brodie, M. J. Lancet 1990, 336, 350.
3. Pandeya, S. N.; Kohli, S.; Siddiqui, N. Polish J. Pharmacol.
2003, 55, 565.
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Arshad, M. F. J. Pharm. Res. 2006, 5, 87.
Fig. 1. Low power (HE ´ 100x) and high power (HE ´
400x) photomicrographs of liver from group 1
showing a normal PT = portal triad, BD = Bile
Duct as compared to control.
7. Krall, R. L.; Penry, J. K.; White, B. G.; Kupferberg, H. J.;
Swinyard, E. A. Epilepsia 1978, 19, 409.
8. Meza-Toledo, S. E.; Zenteno-Garcia, M. T.; Juarez-Carvajal,
E.; Martinez-Munoz, D.; Carvajal-Sandoval, G. Arzneim-
Forsch. Drug. Res. 1990, 40, 1289.
of OH, F and 3,4-(OCH3)2 at distal phenyl ring showed
moderate activity against MES test. Substitution with
N(CH3)2 showed protection against MES test at higher dose
of 300 mg/kg. Introduction of double bond in the structures
provides additional feature of rigidity. In conclusion, the
majority of the compounds of coumarin incorporated
Schiff bases of 1,3,4-oxadiazoles were active in MES test
and all the compounds were less neurotoxic than pheny-
toin.
9. Manual of Histological Staining Methods of the Armed
Forces Institute of Pathology, 3rd ed.; Luna, L. G.; Eds.; Mc-
Graw-Hill: New York, 1968; p 567.
10. Dimmock, J. R.; Puthucode, R. N.; Smith, J. M.; Hethering-
ton, J. W.; Pugazhenthi, U.; Lechler, T.; Stables, J. P. J. Med.
Chem. 1996, 39, 3984.
11. Flaherty, P. T.; Greenwood, T. D.; Manheim, A. L.; Wolfe, J.
F. J. Med. Chem. 1996, 39, 1509.
12. Porter, R. J.; Cereghino, J. J.; Gladding, G. D.; Hessie, B. J.;
Kupferberg, H. J.; Scoville, B.; White, B. G. Cleveland.
Clin. Q. 1984, 51, 293.
ACKNOWLEDGMENT
One of the authors is thankful to University Grants