Novel semicarbazones based 2,5-disubstituted-1,3,4-oxadiazoles: One more step towards establishing four binding site pharmacophoric model hypothesis for anticonvulsant activity

Article abstract of DOI:10.1016/j.bmcl.2010.05.059

A series of novel N¹-{5-[(naphthalene-2-yloxy)methyl]-1,3,4-oxadiazol-2-yl}-N⁴-(4-substitutedbenzaldehyde)-semicarbazone, N¹-{5-[(naphthalene-2-yloxy)methyl]-1,3,4-oxadiazol-2-yl}-N⁴-[1-(4-substitutedphenyl)etha

Full text of DOI:10.1016/j.bmcl.2010.05.059

Bioorganic & Medicinal Chemistry Letters 20 (2010) 4168–4172
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Novel semicarbazones based 2,5-disubstituted-1,3,4-oxadiazoles: One more
step towards establishing four binding site pharmacophoric model
hypothesis for anticonvulsant activity
a
b
c
d
Harish Rajak a, , Ravitas Deshmukh , Ravichandran Veerasamy , Ajay Kumar Sharma , Pradeep Mishra ,
*
Murli Dhar Kharya e
a Medicinal Chemistry Research Laboratory, SLT Institute of Pharmaceutical Sciences, Guru Ghasidas University, Bilaspur 495 009, CG, India
b Faculty of Pharmacy, AIMST University, Semeling, 08100 Bedong, Kedah Darul Aman, Malaysia
c Pharmacology Research Laboratory, Department of Pharmacy, G.S.V.M., Medical College, Kanpur 208 002, UP, India
d GLA Institute of Pharmaceutical Sciences and Research, Mathura 281 406, UP, India
e Department of Pharmaceutical Sciences, Dr. H. S. Gour University, Sagar 470 003, MP, India
a r t i c l e i n f o
a b s t r a c t
A series of novel N1-{5-[(naphthalene-2-yloxy)methyl]-1,3,4-oxadiazol-2-yl}-N4-(4-substitutedbenzalde-
hyde)-semicarbazone, N1-{5-[(naphthalene-2-yloxy)methyl]-1,3,4-oxadiazol-2-yl}-N4-[1-(4-substituted-
phenyl)ethanone]-semicarbazone and N1-{5-[(naphthalene-2-yloxy)methyl]-1,3,4-oxadiazol-2-yl}-N4-
[1-(4-substitutedphenyl) (phenyl) methanone]-semicarbazone were designed and synthesized on the
basis of semicarbazone based pharmacophoric model to meet the structural requirements necessary
for anticonvulsant activity. The anticonvulsant activities of the compounds were investigated using max-
imal electroshock seizure (MES), subcutaneous pentylenetrtrazole (scPTZ) and subcutaneous strychnine
(scSTY) models. Some of the selected active compounds were subjected to GABA assay to confirm their
mode of action. The efforts were also made to establish structure activity relationships among synthe-
sized compounds. The results of the present studying validated that the pharmacophoric model with four
binding sites is essential for anticonvulsant activity.
Article history:
Received 8 February 2010
Revised 13 May 2010
Accepted 14 May 2010
Available online 20 May 2010
Keywords:
1,3,4-Oxadiazoles
Semicarbazones
Anticonvulsant activity
Neurotoxicity
Ó 2010 Elsevier Ltd. All rights reserved.
Epilepsy is a ubiquitous neurological disorder, characterized by
paroxysmal cerebral dysrhythmia, manifested as brief episodes (sei-
zures) of loss or disturbance of consciousness, often followed by
convulsions. About 50 million people worldwide have epilepsy, with
almost 90% of these people being in developing countries.1 Epilepsy
also affects about 4% of individuals over their lifetime. The incidence
of epilepsy is highest among children below 7 years-of-age and in
individuals of above 55 years. Epilepsy is the third most widely
spread neurological disorder found in the elderly after cerebrovas-
cular disease and dementia. Despite the development of several
new anticonvulsants, over 30% of people with epilepsy do not have
seizure control and others do so only at the expense of significant
dose-related toxicity and peculiar adverse effects that range in
harshness from minimal brain impairment and megaloblastic ane-
mia to death from aplastic anemia or hepatic failure.2,3 These limita-
tions with conventional antiepileptic drugs demand the need for the
development of a more effective and safer antiepileptic drug.
Several investigations have recognized aryl semicarbazones as a
structurally novel class of compounds with noteworthy anticon-
vulsant activity.4–6 On the other hand, several investigations have
also revealed the anticonvulsant potential of 1,3,4-oxadiazole ana-
logues.7–9
A pharmacophoric model has been put forward for antiepileptic
activity owing to conformational investigations on prevailing anti-
convulsant drugs such as phenytoin, carbamazepine, rufinamide,
lamotrigine and phenobarbitone.10,11 This semicarbazones based
pharmacophoric model comprises of following four essential bind-
ing sites: (i) An aryl hydrophobic binding site (A) with halo substi-
tuent preferably at para position; (ii) A hydrogen bonding domain
(HBD); (iii) An electron donor group (D) and (iv) Another hydro-
phobic-hydrophilic site regulating the pharmacokinetic properties
of the anticonvulsant (C) (Fig. 1). In earlier studies on this pharma-
cophoric model, our research group has established that the pres-
ence of halogen substituted aryl group near the semicarbazone
moiety is one of the crucial parameters for anticonvulsant
activity.12,13
The title compounds were prepared using the synthetic strat-
egy described in Scheme 1. The ethyl (naphthalene-2-yloxy) ace-
tate II was synthesized by esterification of 2-naphthol I with
ethylbromoacetate in the presence of anhydrous potassium car-
bonate using anhydrous acetone as solvent. Compound II, on
* Corresponding author. Tel.: +91 9827911824; fax: +91 7752 417720.
E-mail address: harishdops@yahoo.co.in (H. Rajak).
0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2010.05.059

H. Rajak et al. / Bioorg. Med. Chem. Lett. 20 (2010) 4168–4172
4169
N
N
D
R1
O
NH
NH
N
C
O
O
HBD
R2
A
1-18
C
Figure 1. Semicarbazone based pharmacophoric model and its vital structural features present in title compounds: (A) hydrophobic aryl ring system, (HBD) hydrogen
binding domain, (D) electron donor moiety and (C) distal aryl ring.
reaction with hydrazine hydrate in absolute ethanol, resulted in the
formation of 2-(naphthalene-2-yloxy) acetohydrazide III.14 The 2-
amino-5-(2-naphthyloxymethyl)-1,3,4-oxadiazole IV was synthe-
sized by the reaction of hydrazide III with cyanogen bromide in
the presence of Na2CO3. The compound IV on reaction with phenyl
formate in the presence of chloroform resulted in the formation of
phenyl{5-[(naphthalen-2-yloxy)methyl]-1,3,4-oxadiazol-2-yl}car-
bamate V. N-{5-[(Naphthalen-2-yloxy)methyl]-1,3,4-oxadiazol-2-
yl}hydrazin-ecarboxamide VI was prepared by condensation of
carbamate V with hydrazine hydrate in the presence of methylene
dichloride. The title compounds 1–18 were synthesized by reaction
of hydrazinecarboxamide VI with appropriate aldehyde and
ketone.15
4-Aminobutyric acid (GABA) is the major inhibitory neurotrans-
mitter in the central nervous system (CNS) and is largely concerned
with epilepsy.20,21 It has been observed that inhibition of GABAergic
neurotransmission or administration of GABA antagonists has been
shown to advance and accelerate seizures,22 while enhancement of
GABAergic neurotransmission has proved effective as anticonvul-
sants in a variety of experimental models of epilepsy and in epileptic
patients.23 The aryl semicarbazones have been found to possess
anticonvulsant activity through GABA mediation.24,25 Most active
compounds found after initial anticonvulsant screening were sub-
jected to neurochemical estimation of GABA level in adult Wistar
rat brain. The determination of GABA in brain extract is based on
the use of an enzyme system found in the bacterium Pseudamonas
fluorescens grown on pyrrolidine which converts GABA to succinate
via transamination and oxidation coupled to triphosphopyrindine
nucleotide reduction. The animals were sacrificed after 2 h of drug
administration by decapitation and the brain regions that is,
midbrain, medulla oblongata and cerebellum were dropped into
separate vessel containing 6–8 ml of ice-cold 80% ethanol and pro-
cessed further as per reported procedure.26,27 Some of these com-
pounds were found to increase the GABA level many times as
compared to the control which confirmed that the presently studied
aryl semicarbazones containing 1,3,4-oxadiazole moiety exhibit
anticonvulsant activity via GABA mediation (Table 3).
We have designed and synthesized the title compounds while
remembering the fact that a number of clinically active anticonvul-
sants possess a nitrogen hetero atomic system with one or two
phenyl rings and at least one carbonyl group in their structure.
The structure of the title compounds 1–18 satisfied all the pharma-
cophoric structural requirements that is, presence of 5-[(naphtha-
lene-2-yloxy)methyl]-1,3,4-oxadiazol-2-yl moiety as hydrophobic
portion, N as electron donor system, and another hydrophobic distal
aryl ring responsible for controlling the pharmacokinetic properties
of the anticonvulsant. Thus, these findings confirmed the long-
established four binding site hypothesis for semicarbazones. In the
present study N1-{5-[(naphthalene-2-yloxy)methyl]-1,3,4-oxa-
diazol-2-yl}-N4-[1-(4-nitrophenyl) (phenyl) methanone]-semicar-
bazone 17 emerged out as the most active compound with a wide
spectrum of anticonvulsant activity without any neurotoxicity.
In conclusion, a series of novel N1-{5-[(naphthalene-2-yloxy)-
methyl]-1,3,4-oxadiazol-2-yl}-N4-(4-substitutedbenzaldehyde)-semi-
carbazone 1–9, N1-{5-[(naphthalene-2-yloxy)methyl]-1,3,4-oxa-
diazol-2-yl}-N4-[1-(4-substitutedphenyl)ethanone]-semicarbazone
10–14, and N1-{5-[(naphthalene-2-yloxy)methyl]-1,3,4-oxadiazol-
2-yl}-N4-[1-(4-substitutedphenyl) (phenyl) methanone]-semicar-
bazone 15–18 were synthesized to meet structural requirements
necessary for anticonvulsant activity. The result of the GABA assay
implies that the test compounds have inhibited or attenuated
seizures by facilitating GABAergic neurotransmission. Our results
validated that the pharmacophoric model with four binding sites
The anticonvulsant screening16–18 was accomplished using
male albino mice (swiss, 18–25 g) and rat (Wistar 100–150 g).
The anticonvulsant potential of the test compounds was assessed
by three models namely, maximal electroshock seizure (MES), sub-
cutaneous pentylenetrtrazole (scPTZ), and subcutaneous strychnine
(scSTY) models. Acute neurological toxicity in mice was evaluated by
rotorod test.19 All the synthesized oxadizole analogues were
screened for their anticonvulsant potential through MES and scPTZ
models in doses of 30, 100, 300 mg/kg by intraperitoneal (ip) injec-
tion. The majority of the compounds that is, 1, 4–7, 9–11 and 13 to 18
exhibited activity in either of the MES, scPTZ or scSTY models after
4 h, indicating that the test compounds are slow acting anticonvul-
sants. The data indicates that 72% of the compounds that is, 1, 3, 4, 6,
7, 9, 11, 13–18 were active in the MES screening, 44% of the com-
pounds that is, 5, 7, 10, 11, 12, 14, 16 and 17 were active in the scPTZ
test and 39% of the compounds that is, 3, 6, 8, 11, 14, 16 and 17 were
active in scSTY test. These results show that compounds possess
some MES selectivity (Tables 1 and 2). The subcutaneous strychnine
(scSTY) test provides some hints about possible interaction of test
compounds with glycine receptors. The activity of compounds that
is, 3, 6, 8, 11, 14, 16 and 17 in scSTY test indicates that their anticon-
vulsant activity may be through inhibitory glycine receptors.
On correlating the structures of the synthesized compounds with
their biological activity, it has been observed that compounds bear-
ing the groupslike nitro, hydroxyon distantphenylring possess high
potency in MES, scPTZ, and scSTY tests. On the other hand, replace-
ment of these groups with methoxy or methyl groups on the distant
phenyl ring has resulted in compounds with lesser anticonvulsant
activity. Replacement of the proton on the carbimino carbon atom
by methyl group that is, 10–14 or phenyl ring that is, 15–18 has
exhibited alteration in biological activity due to increase in the
dimension of the group at this position of the molecule. Compounds
with phenyl ring exhibited considerable anticonvulsant activity in
comparison to methyl group. The increase in anticonvulsant activity
of test compounds 15–18 may be attributed to the existence of phe-
nyl substitution which might be accountable for additional van der
Waals bonding to the binding site.

4170
H. Rajak et al. / Bioorg. Med. Chem. Lett. 20 (2010) 4168–4172
O
O
OH
a
O
II
I
b
O
N
N
NH2
O
O
NH
NH2
c
O
IV
+
III
O
Cl
O
d
O
O
N
N
NH
O
O
V
e
O
NH2
N
N
NH
NH
O
O
VI
R1
f
O
3
N
4
N
1''
2''
4''
N
NH
2
R2
8'
5'
10'
5
NH
O
9'
3''
6''
O
7'
6'
1'
2'
1
5''
1-18
4'
3'
Compound R1 R2
Code
Compound R1
Code
R2
Compound R1
Code
R2
1
2
3
4
5
6
H
H
H
H
H
H
H
4-Cl
4-NO2
4-CH3
4-OCH3 11
4-OH 12
7
8
9
10
H
H
H
3-OH
3-OCH3 4-OH 14
4-N(CH3)2
13
CH3
CH3
C6H5
C6H5 4-OH
C6H5 4-NO2
C6H5 4-OCH3
4-OH
4-NH2
H
15
16
17
18
CH3 4-Cl
CH3 4-NO2
CH3 4-CH3
Scheme 1. Synthesis of 2,5-disubstituted-1,3,4-oxadiazole analogues 1–18. Reaction conditions: (a) anhydrous K2CO3, anhydrous acetone, reflux for 16 h, 60%; (b) NH2NH2ꢀH2O,
absolute ethanol, reflux for 6 h, 64%; (c) BrCN, NaHCO3, ethanol, 55–60 °C, 1.5 h, 62%; (d) CHCl3, N(C2H5), 56%; (e) NH2NH2ꢀH2O, CH2Cl2, 59%; (f) aldehyde or ketone, glacial acetic
acid, ethanol, 53–69%.

H. Rajak et al. / Bioorg. Med. Chem. Lett. 20 (2010) 4168–4172
4171
Table 1
Anticonvulsant and neurotoxicity screening of 2,5-disubstituted 1,3,4-oxadiazoles
Compounda
MES screeningb
4.0 h
scPTZ screeningb
4.0 h
scSTY screeningc
4.0 h
NT screeningb
4.0 h
0.5 h
0.5 h
0.5 h
0.5 h
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
—
—
300
—
—
100
—
—
100
—
100
—
100
—
—
100
100
—
30
30
300
—
300
—
—
300
—
300
300
—
300
—
300
—
300
300
300
300
300
300
30
—
—
—
—
—
—
—
—
—
—
—
300
—
—
—
—
100
—
—
—
—
—
300
—
300
—
—
—
—
—
—
100
—
—
—
—
—
—
—
—
—
—
—
—
—
300
—
—
300
—
300
—
—
300
—
—
300
—
300
300
—
100
—
—
300
—
—
—
100
—
300
—
—
—
300
—
—
300
—
—
300
—
300
—
—
100
300
—
300
—
—
—
300
—
—
—
—
300
100
300
—
—
300
300
—
—
300
—
300
300
—
—
300
—
17
18
—
—
—
300
300
—
Phenytoin
Carbamazepine
Na valproate
Ethosuximide
—
100
100
—
100
—
—
100
300
100
—
—
300
—
—
Abbreviations: MES = maximal electroshock seizure; scPTZ = subcutaneous pentylenetetrazole; scSTY = subcutaneous strychnine; NT = neurotoxicity.
a
30, 100 and 300 mg/kg of doses were administered ip in the animals. The data in the table indicates the minimal dose whereby biological activity was demonstrated in
half or more of the animals. The activity was measured after 0.5 and 4.0 h of dose administration of test compounds. The sign — (mdash) represents an absence of activity at
maximum dose administered (300 mg/kg).
b
Mice were employed in this biological evaluation.
Rats were employed in this biological evaluation.
c
Table 2
assistance. The help rendered by SAIF, CDRI Lucknow for elemental
and spectral analysis is gratefully acknowledged. We are highly
thankful to Dr. Chhabra, Dean, Chhattisgarh Institute of Medical
Sciences (CIMS), Bilaspur for their helpful discussion regarding
in vivo studies.
Anticonvulsant evaluation of compounds after oral administration in rats
Compound
Oral administration in ratsa
MES screening NT screening
0.25 h 0.5 h 1 h 2 h 4 h 0.25 h 0.5 h 1 h 2 h 4 h
6
11
16
17
0
0
0
0
0
1
0
0
1
0
0
0
0
0
1
0
1
1
1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
1
0
1
0
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmcl.2010.05.059.
a
The compounds were administered in a dose of 30 mg/kg. The data in the table
indicates the number of protected rats out of four.
References and notes
Table 3
1. Fisher, R.; Boas, W. V. E.; Blume, W.; Elger, C.; Genton, P.; Lee, P.; Engel, J.
Epilepsia 2005, 46, 470.
GABA assay for compounds found active in anticonvulsant screening
2. Brown, T. R.; Holmes, G. L. N. Eng. J. Med. 2001, 344, 1145.
3. Kramer, G. Epilepsia 2001, 42, 55.
4. Thirumurugan, R.; Sriram, D.; Saxena, A.; Stables, J.; Yogeeswari, P. Bioorg. Med.
Chem. 2006, 14, 3106.
5. Dimmock, J. R.; Puthucode, R. N.; Smith, J. M.; Hetherington, M.; Quail, J. W.;
Pugazhenthi, U.; Lechler, T. J. Med. Chem. 1996, 39, 3984.
6. Siddiqui, N.; Rana, A.; Khan, S. A.; Bhat, M. A.; Haque, S. E. Bioorg. Med. Chem.
Lett. 2007, 17, 4178.
7. Omar, A. M. M. E.; Aboulwafa, O. M. J. Heterocycl. Chem. 1984, 21, 1415.
8. Zarghi, A.; Faizi, M.; Shafaghi, B.; Ahadian, A.; Khojastehpoor, H. R.; Zangaheh,
V.; Tabatabai, S. A.; Shafiee, A. Bioorg. Med. Chem. Lett. 2005, 15, 3126.
9. Almasirad, A.; Tabatabai, S. A.; Faizi, M.; Kebriaeizadeh, A.; Mehrabai, N.;
Dalvandi, A.; Shafiee, A. Bioorg. Med. Chem. Lett. 2004, 14, 6057.
10. Pandeya, S. N.; Ponnilavarasan, I.; Pandey, A.; Lakhan, R.; Stables, J. P. Pharmazie
1999, 54, 923.
S. No.
Compound
GABA concentration in l
g/100 mga
Midbrain
Medulla oblangata
Cerebellum
1
2
3
4
5
6
6b
53.77 2.95
45.50 3.79
62.25 2.38
67.72 1.84
69.51 3.76
35.87 2.65
35.48 1.62
40.42 2.29
37.74 2.73
46.62 3.04
47.53 1.96
31.66 4.27
28.53 2.66
27.56 1.69
31.41 2.15
29.75 1.63
35.44 2.39
24.68 2.18
11b
16b
17b
Clobazamc
Control
a
Each value represents the mean SEM of six rats significantly different from the
control at P <0.001.
b
The compounds were tested at a dose of 100 mg/kg (ip).
The standard drug was tested at dose of 30 mg/kg (ip).
c
11. Wong, M. G.; Dejina, J. A.; Andrews, P. R. J. Med. Chem. 1986, 29, 562.
12. Aggarwal, N.; Mishra, P. J. Pharm. Sci. 2004, 7, 260.
13. Rajak, H.; Deshmukh, R.; Aggarwal, N.; Kashaw, S.; Kharya, M. D.; Mishra, P.
Arch. Pharm. 2009, 342, 453.
14. Gulay, S.; Palaska, E.; Ekizoglu, M.; Ozalp, M. Il Farmaco 2002, 57, 539.
15. Compound 11: MP (°C) 235–237; yield 62%; IR (cmꢁ1) (KBr) 3046.2 (aromatic
C–H str), 1604.5 and 1502.7 (aromatic C–C str), 1088.3 (C–O of 1,3,4-
oxadiazole nucleus), 1670.5 (C@N of 1,3,4-oxadiazole nucleus), 1034.1 (Ar–
O–C str), 1671.6 (C@O str of amide), 3435.2 (N–H str of amide), 1626.4 (C@N
group), 1522.6 and 1363.8 (N@O str of Ar–NO2 group); 13C NMR (75 MHz,
DMSO-d6, TMS, d ppm): 157.7 (C-10), 118.6 (C-20), 129.6 (C-30), 129.2 (C-40),
127.7 (C-50), 123.8 (C-60), 126.6 (C-70), 126.9 (C-80), 134.7 (C-90), 105.9 (C-100),
is vital for anticonvulsant activity. These new facts might be expe-
dient in the future research and development of semicarbazones as
novel anticonvulsants.
Acknowledgments
One of the authors, Ravitas Deshmukh, is thankful to AICTE New
Delhi, India for awarding Junior Research Fellowship and financial

4172
H. Rajak et al. / Bioorg. Med. Chem. Lett. 20 (2010) 4168–4172
72.5 (OCH2), 172.5 (C-2), 169.7 (C-5), 157.3 (NHCONHNC), 154.8 (NHCONHNC),
127.8 (C-50), 123.6 (C-60), 126.5 (C-70), 126.9 (C-80), 134.8 (C-90), 105.9 (C-100),
72.2 (OCH2), 172.6 (C-2), 169.4 (C-5), 157.3 (NHCONHNC), 155.7 (NHCONHNC),
137.4 (C-100), 131.1 (C-200 and C-600), 123.8 (C-300 and C-500), 150.9 (C-400), 131.3
(C-1000), 128.8 (C-2000 and C-6000), 128.5 (C-3000 and C-5000), 130.7 (C-4000); 1H NMR
(300 MHz, DMSO-d6, TMS, d ppm): 7.0–8.2 (m, 16H, ArH), 5.3 (s, 2H, OCH2), 6.3
(s, 1H, NHCONH), 9.6 (s, 1H, NHCONH); ESI-MS (methanol) m/z 509.5 ([M+H]+).
16. Krall, R. L.; Penry, J. K.; White, B. G.; Kupferberg, H. J.; Swinyard, E. A. Epilepsia
1978, 19, 409.
17.6 (NHCONHNCCH3), 137.5 (C-100), 129.9 (C-200 and C-600), 123.9 (C-300 and C-
500), 150.8 (C-400); 1H NMR (300 MHz, DMSO-d6, TMS, d ppm): 6.9–8.2 (m, 11H,
ArH), 5.3 (s, 2H, OCH2), 6.3 (s, 1H, NHCONH), 9.4 (s, 1H, NHCONH), 1.1 (s, 3H,
Carbimino CH3); ESI-MS (methanol) m/z 447.5 ([M+H]+).
Compound 16: Mp (°C) 262–263; yield 64%; IR (cmꢁ1) (KBr) 3041.5 (aromatic
C–H str), 1601.8 and 1501.6 (aromatic C–C str), 1093.0 (C–O of 1,3,4-
oxadiazole nucleus), 1667.1 (C@N of 1,3,4-oxadiazole nucleus), 1024.8 (Ar–
O–C str), 1695.2 (C@O str of amide), 3439.4 (N–H str of amide), 1615.5 (C@N
group), 3456.5 (O–H str of alcoholic group), 1174.7 (C–O str of alcoholic
17. Porter, R. J.; Hessie, B. J.; Cereghino, J. J.; Gladding, G. D.; Kupferberg, H. J.;
Scoville, B.; White, B. G. Fed. Proc. 1985, 44, 2645.
18. Loscher, W.; Schmidt, D. Epilepsy Res. 1994, 17, 95.
13
group); C NMR (75 MHz, DMSO-d6, TMS, d ppm): 157.7 (C-10), 118.7 (C-20),
129.8 (C-30), 129.3 (C-40), 127.8 (C-50), 123.5 (C-60), 126.4 (C-70), 126.9 (C-80),
134.7 (C-90), 105.8 (C-100), 72.3 (OCH2), 172.7 (C-2), 169.3 (C-5), 157.4
(NHCONHNC), 155.8 (NHCONHNC), 123.8 (C-100), 130.5 (C-200 and C-600),
115.7 (C-300 and C-500), 159.8 (C-400), 131.4 (C-1000), 129.2 (C-2000 and C-6000),
128.7 (C-3000 and C-5000), 130.9 (C-4000); 1H NMR (300 MHz, DMSO-d6, TMS, d
ppm): 6.8–7.7 (m, 16H, ArH), 5.2 (s, 2H, OCH2), 6.4 (s, 1H, NHCONH), 9.6 (s, 1H,
NHCONH), 5.3 (s, 1H, ArOH); ESI-MS (methanol) m/z 480.6 ([M+H]+).
19. Vogel, H. G. Drug Discovery and Evaluation—Pharmacological Assays; Springer:
Germany, 2002. pp 487–493.
20. Okada, R.; Negishi, H. Brain Res. 1989, 480, 383.
21. Olsen, R. W. J. J. Neurochem. 1981, 27, 1.
22. Gale, K. Epilepsia 1992, 33, S3.
23. Suzdak, P. D.; Jansen, J. A. Epilepsia 1995, 36, 612.
24. Yogeeswari, P.; Sriram, D.; Veena, V.; Kavya, R.; Rakhra, K.; Mehta, S.;
Thirumurugan, R.; Stables, J. P. Biomed. Pharmacother. 2005, 59, 51.
25. Yogeeswari, P.; Sriram, D.; Thirumurugan, R.; Ragavendran, J. V.; Sudhan, K.;
Kumar, R.; Stables, J. P. J. Med. Chem. 2005, 48, 6202.
26. Baxter, C. F.; Roberts, E. J. Biol. Chem. 1961, 236, 3287.
27. Roberts, E.. In Methods in Enzymology; Academic: New York, 1963; Vol. 6, p
610.
Compound 17: MP (°C) 275–276; yield 61%; IR (cmꢁ1) (KBr) 3040.2 (aromatic
C–H str), 1603.5 and 1501.6 (aromatic C–C str), 1086.2 (C–O of 1,3,4-
oxadiazole nucleus), 1665.8 (C@N of 1,3,4-oxadiazole nucleus), 1026.8 (Ar–
O–C str), 1693.6 (C@O str of amide), 3439.4 (N–H str of amide), 1619.8 (C@N
group), 1532.5 and 1359.8 (N@O str of Ar–NO2 group); 13C NMR (75 MHz,
DMSO-d6, TMS, d ppm): 157.9 (C-10), 118.7 (C-20), 129.6 (C-30), 129.2 (C-40),