Synthesis and evaluation on anticonvulsant activities of pyrazolyl semicarbazones

Article abstract of DOI:10.14233/ajchem.2014.18218

In this paper, a series of 2-[(5-phenoxy-3-methyl-1-phenyl-1H-pyrazol-4-yl)-methylene]hydrazine carboxamides were synthesized and evaluated for their anticonvulsant activities using the maximal electroshock method. Their neurotoxicities were determined ap

Full text of DOI:10.14233/ajchem.2014.18218

Asian Journal of Chemistry; Vol. 26, No. 23 (2014), 8234-8238
ASIAN JOURNAL OF CHEMISTRY
http://dx.doi.org/10.14233/ajchem.2014.18218
Synthesis and Evaluation on Anticonvulsant Activities of Pyrazolyl Semicarbazones
*
XIAN-QING DENG , MING-XIA SONG and HAI-HONG YU
Medical College, Jinggangshan University, No 28, Xueyuan Road, Ji'an 343009, Jiangxi, P.R. China
*Corresponding author: Tel/Fax: +86 796 8117893; E-mail: dengxianqing1121@126.com
Received: 30 May 2014;
Accepted: 5 August 2014;
Published online: 15 November 2014;
AJC-16332
In this paper, a series of 2-[(5-phenoxy-3-methyl-1-phenyl-1H-pyrazol-4-yl)-methylene]hydrazine carboxamides were synthesized and
evaluated for their anticonvulsant activities using the maximal electroshock method. Their neurotoxicities were determined applying the
rotarod test. Interestingly, all compounds showed anticonvulsant activity with long duration of protection effects in the maximal electroshock
test. Among which, compound 5m was found to have promising anticonvulsant activity, which gave an ED50 of 42.4 mg/kg and a
protective index value of 3.7, possessing better anticonvulsant activity and higher safety than marketed drugs valproate, but weaker than
phenobarbital. Furthermore, the antagonistic activity against seizures induced by pentylenetetrazole of the compound 5m was also
established, which suggested that compound 5m may exert anticonvulsant activity through γ-aminobutyric acid (GABA)-mediated
mechanisms.
Keywords: Anticonvulsant, Pyrazole, Semicarbazone, Maximal electroshock.
important pharmacological activities. Therefore they are useful
materials in drug research and they are of interest as potential
INTRODUCTION
anticonvulsant agents15-18
.
Epilepsy, one of the most frequent neurological afflictions
in men characterized by recurrent unprovoked seizures, inflicts
more than 60 million people worldwide1,2. The conventional
antiepileptic drugs (AEDs) like phenytoin, carbamazepine,
valproic acid and barbiturates, though widely prescribed,
exhibited unfavorable side effects such as drowsiness, ataxia
and hepatotoxicity3-6. Recently, several new antiepileptic drugs
such as lamotrigine, oxcarbazepine, felbamate and rufinamide
have been approved with an improved efficacy and lower
toxicity. However, it is roughly estimated that up to 28-30 %
of patients with epilepsy have inadequate control of seizures
with the currently available antiepileptic drugs. Therefore, it
is essential to search for newer chemical entities with better
efficacy and lower toxicity for the treatment of epilepsy.
Semicarbazide has been recognized earlier as a promising
pharmacophore and a number of semicarbazide derivatives
have been synthesized and tested for their anticonvulsant
activity7-11. Different aryl and heteroaryl moieties have been
clubbed to the semicarbazide pharmacophore as hydrophobic
domain which led to the increase in the activity significantly.
Recently, several semicarbazones have emerged as structurally
novel anticonvulsants and were found to act by blocking the
Based on the above facts, herein we planned to attach the
semicarbazide to substituted pyrazoles moiety expecting to
obtain some hybrid compounds having a synergistic effect in
dealing with epilepsy. A series of 2-[(5-phenoxy-3-methyl-1-
phenyl-1H-pyrazol-4-yl)methylene]hydrazine carboxamide
derivatives were synthesized and evaluated for anticonvulsant
activity. Their structures were confirmed by infrared spectra
(IR), nuclear magnetic resonance (NMR) and HRMS (High
resolution mass spectra). Their anticonvulsant activities and
neurotoxicities were evaluated using the maximal electroshock
(MES)-induced seizure model and the rotarod assay in mice,
respectively. The anticonvulsant activity of some of the target
compounds possessing better activity were quantified and the
compound 5m was tested in subcutaneous pentylenetetrazole
(sc-PTZ) induced seizure test.
EXPERIMENTAL
Melting points were determined in open capillary tubes
and were uncorrected. IR spectra were recorded (in KBr) on IR
Prestige-21 (Shimadzu, Japan). 1H NMR spectra were measured
on an AV-300 (Bruker, Switzerland) and all chemical shifts
were given in ppm relative to tetramethysilane. High resolution
mass spectra were measured on an MALDI-TOF/TOF mass
spectrometer (Bruker Daltonik, Germany). The major chemicals
voltage-gated Na+ channels12-14
.
Pyrazoles are important five-membered heterocyclic
compounds with double nitrogen, whose derivatives possess

Vol. 26, No. 23 (2014)
Synthesis and Evaluation on Anticonvulsant Activities of Pyrazolyl Semicarbazones 8235
were purchased fromAldrich Chemical Corporation (St Louis,
USA).
2-[{5-(2,6-Dichlorophenoxy)-3-methyl-1-phenyl-1H-
pyrazol-4-yl}methylene]hydrazine carboxamide (5g): m.p.:
120-121 ºC, yield: 78 %. 1H NMR (DMSO-d6, 300 MHz), δ
2.34 (s, 3H, CH3), 6.07 (br.s, 2H, NH2), 7.07-7.70 (m, 9H, Ar-
H, CH=N), 10.03 (s, 1H, NH). IR (KBr, νmax, cm-1): 3492 3374
3283 (N-H), 1685 (C=O). ESI-HRMS calcd for C18H16Cl2N5O2+
([M + H]+): 404.0676; found: 404.0675.
Procedures for synthesis of compounds 2, 3 and 4:
Compound 2, 3 and 4 was previously reported19.
Procedures for preparation of compounds 5a-5m: To
a solution of compound 4 (0.01 mol) in 50 % ethanol solution
was added an equimolar quantity of hydrazine carboxamide
hydrochloride (SEM HCl) and the mixture was refluxed for
0.5-3 h until the completion of the reaction. The solid formed
was collected by filtration to give crude product, which was
re-crystallized from ethanol to afford the products in 71-87 %
yield.
2-[{5-(4-Bromophenoxy)-3-methyl-1-phenyl-1H-
pyrazol-4-yl}methylene]hydrazine carboxamide (5h): m.p.:
214-215 ºC, yield: 81 %. 1H NMR (DMSO-d6, 300 MHz), δ
2.42 (s, 3H, CH3), 6.09 (br.s, 2H, NH2), 6.95-7.58 (m, 9H, Ar-
H), 7.62 (s, 1H, CH=N), 10.03 (s, 1H, NH). IR (KBr, νmax, cm-1):
3484 3269 3190 (N-H), 1690 (C=O). ESI-HRMS calcd for
C18H17BrN5O2+ ([M + H]+): 414.0560; found: 414.0559.
2-[{5-(2-Methylphenoxy)-3-methyl-1-phenyl-1H-
pyrazol-4-yl}methylene]hydrazine carboxamide (5i): m.p.:
190-192 ºC, yield: 77 %. 1H NMR (DMSO-d6, 300 MHz), δ
2.33 (s, 3H, CH3), 2.43 (s, 3H, CH3), 5.92 (br.s, 2H, NH2),
6.54-7.60 (m, 10H, Ar-H, CH=N), 9.99 (s, 1H, NH). IR (KBr,
Characterization for the target compounds (5a-5m)
2-[(5-Phenoxy-3-methyl-1-phenyl-1H-pyrazol-4-yl)-
methylene]hydrazine carboxamide (5a): m.p.: 226-228 ºC,
yield: 78 %. 1H NMR (DMSO-d6, 300 MHz), δ 2.43 (s, 3H,
CH3), 5.83 (br.s, 2H, NH2), 6.95-7.64 (m, 11H,Ar-H, CH=N),
10.01 (s, 1H, NH). IR (KBr, νmax, cm-1): 3434 3182 3296 (N-H),
1686 (C=O). ESI-HRMS calcd for C18H18N5O2+ ([M + H]+):
336.1455; found: 336.1445.
ν
max, cm-1): 3475 3271 3196 (N-H), 1687 (C=O). ESI-HRMS
calcd for C19H20N5O2+ ([M + H]+): 350.1612; found: 350.1621.
2-[{5-(4-Methylphenoxy)-3-methyl-1-phenyl-1H-
pyrazol-4-yl}methylene]hydrazine carboxamide (5j): m.p.:
204-206 ºC, yield: 81 %. 1H NMR (DMSO-d6, 300 MHz), δ
2.22 (s, 3H, CH3), 2.42 (s, 3H, CH3), 5.88 (br.s, 2H, NH2),
6.84 (d, 2H, J = 8.6 Hz, Ar-H), 7.13 (d, 2H, J = 8.6 Hz, Ar-H),
7.28-7.62 (m, 6H, Ar-H, CH=N), 9.99 (s, 1H, NH). IR (KBr,
2-[{5-(4-Fluorophenoxy)-3-methyl-1-phenyl-1H-
pyrazol-4-yl}methylene]hydrazine carboxamide (5b): m.p.:
202-204 ºC, yield: 69 %. 1H NMR (DMSO-d6, 300 MHz), δ
2.42 (s, 3H, CH3), 5.88 (br.s, 2H, NH2), 7.00-7.62 (m, 10H,
Ar-H, CH=N), 10.01 (s, 1H, NH). IR (KBr, νmax, cm-1): 3486
3244 3267 (N-H), 1689 (C=O). ESI-HRMS calcd for
C18H17FN5O2+ ([M + H]+): 354.1361; found: 354.1352.
2-[{5-(2-Chlorophenoxy)-3-methyl-1-phenyl-1H-
pyrazol-4-yl}methylene]hydrazine carboxamide (5c): m.p.:
ν
max, cm-1): 3471 3268 3198 (N-H), 1688 (C=O). ESI-HRMS
calcd for C19H20N5O2+ ([M + H]+): 350.1612; found: 350.1614.
2-[{5-(2,4-Dimethylphenoxy)-3-methyl-1-phenyl-1H-
pyrazol-4-yl}methylene]hydrazine carboxamide (5k): m.p.:
173-174 ºC, yield: 74 %. 1H NMR (DMSO-d6, 300 MHz), δ
2.18 (s, 3H, CH3), 2.28 (s, 3H, CH3), 2.42 (s, 3H, CH3), 5.94
(br.s, 2H, NH2), 6.43-7.59 (m, 9H, Ar-H, CH=N), 9.99 (s, 1H,
NH). IR (KBr, νmax, cm-1): 3457 3266 3189 (N-H), 1685 (C=O).
1
195-197 ºC, yield: 79 %. H NMR (DMSO-d6, 300 MHz), δ
2.42 (s, 3H, CH3), 5.72 (br.s, 1H, NH2), 6.18 (br.s, 1H, NH2),
7.09-7.62 (m, 10H, Ar-H, CH=N), 10.03 (s, 1H, NH). IR (KBr,
ν
max, cm-1): 3499 3279 3175 (N-H), 1691 (C=O). ESI-HRMS
calcd for C18H17ClN5O2+ ([M + H]+): 370.1065; found: 370.1060.
2-[{5-(3-Chlorophenoxy)-3-methyl-1-phenyl-1H-
pyrazol-4-yl}methylene]hydrazine carboxamide (5d): m.p.
170-172 ºC, yield: 87 %. 1H NMR (DMSO-d6, 300 MHz), δ
2.42 (s, 3H, CH3), 5.77 (br.s, 1H, NH2), 6.20 (br.s, 1H, NH2),
6.91-7.59 (m, 9H, Ar-H), 67.64 (s, 1H, CH=N), 10.03 (s, 1H,
NH). IR (KBr, νmax, cm-1): 3490 3281 3178 (N-H), 1690 (C=O).
ESI-HRMS calcd for C18H17ClN5O2+ ([M + H]+): 370.1065;
found: 370.1070.
+
ESI-HRMS calcd for C20H22N5O2 ([M + H]+): 364.1768;
found: 364.1763.
2-[{5-(2-Methoxyphenoxy)-3-methyl-1-phenyl-1H-
pyrazol-4-yl}methylene]hydrazine carboxamide (5l): m.p.:
1
202-204 ºC, yield 75 %. H NMR (DMSO-d6, 300 MHz), δ
2.40 (s, 3H, CH3), 3.83 (s, 3H, OCH3), 5.95 (br.s, 2H, NH2),
6.70-7.62 (m, 10H, Ar-H, CH=N), 9.99 (s, 1H, NH). IR (KBr,
ν
max, cm-1): 3479 3247 3164 (N-H), 1692 (C=O). ESI-HRMS
calcd for C19H20N5O3+ ([M + H]+): 366.1561; found: 366.1556.
2-[{5-(4-Methoxyphenoxy)-3-methyl-1-phenyl-1H-
pyrazol-4-yl}methylene]hydrazine carboxamide (5m): m.p.:
195-196 ºC, yield: 71 %. 1H NMR (DMSO-d6, 300 MHz), δ
2.42 (s, 3H, CH3), 3.69 (s, 3H, OCH3), 5.94 (br.s, 2H, NH2),
6.86-7.61 (m, 10H,Ar-H, CH=N), 10.01 (s, 1H, NH). IR (KBr,
2-[{5-(4-Chlorophenoxy)-3-methyl-1-phenyl-1H-
pyrazol-4-yl}methylene]hydrazine carboxamide (5e): m.p.
214-215 ºC, yield: 85 %. 1H NMR (DMSO-d6, 300 MHz), δ
2.42 (s, 3H, CH3), 5.89 (br.s, 2H, NH2), 7.02 (d, 2H, J = 7.7
Hz, Ar-H), 7.30-7.47 (m, 5H, Ar-H), 7.57 (d, 2H, J = 7.7 Hz,
Ar-H), 7.63 (s, 1H, CH=N), 10.02 (s, 1H, NH). IR (KBr, νmax
,
cm-1): 3490 3292 3188 (N-H), 1690 (C=O). ESI-HRMS calcd
for C18H17ClN5O2+ ([M + H]+): 370.1065; found: 370.1059.
2-[{5-(2,4-Dichlorophenoxy)-3-methyl-1-phenyl-1H-
pyrazol-4-yl}methylene]hydrazine carboxamide (5f): m.p.
ν
max, cm-1): 3477 3250 3168 (N-H), 1694 (C=O). ESI-HRMS
calcd for C19H20N5O3+ ([M + H]+): 366.1561; found: 366.1559.
Pharmacology: Male KunMing mice (supplied from the
Laboratory of Animal Research, Yanbian University, China)
weighting 18-22 g were used for pharmacological study.Animals
were allowed free access to food and water except during the
experiment and housed at controlled room temperature with
12 h light/dark schedule. All compounds were dissolved in
DMSO with the injection volume of 0.05 mL per 20 g, which
had no effect on the test system.
1
195-196 ºC, yield 73 %. H NMR (DMSO-d6, 300 MHz), δ
2.42 (s, 3H, CH3), 5.75 (br.s, 1H, NH2), 6.21 (br.s, 1H, NH2),
6.87-7.75 (m, 9H, Ar-H, CH=N), 10.05 (s, 1H, NH). IR (KBr,
max, cm-1): 3504 3389 3276 (N-H), 1686 (C=O). ESI-HRMS
ν
+
calcd for C18H16Cl2N5O2 ([M + H]+): 404.0676; found:
404.0678.

8236 Deng et al.
Asian J. Chem.
H
O
Anticonvulsant activity of the synthesized compounds was
O
Cl
H
determined through the evaluation of the ability of the comp-
ounds to protect mice against maximal electroshock-induced
seizures. The maximal electroshock test was carried out follo-
wing procedures proposed by the NIH anticonvulsant drug
development (ADD) program20,21. Seizures were elicited with
a 60 Hz alternating current of 50 mA intensity in mice. The
current was applied via clip electrodes for 0.2 s. Protection
against the spread of maximal electroshock-induced seizures
was defined as the abolition of tonic maximal extension of the
hind leg. In preliminarily screening, each compound was
administered at the dose levels of 30, 100 and 300 mg/kg for
evaluating preliminarily the anticonvulsant activity and
neurotoxicity at 0.5 and 4 h interval after intraperitoneal
administration (i.p.). For determination of the median effective
dose (ED50) and the median toxic dose (TD50), the next phase
screening was carried out. Groups of 10 mice were given a
range of i.p. doses of the tested compound until at least three
points were established in the range of 10-90 % seizure
protection or neurotoxicity. From the plot of this data, the
respective ED50, TD50 values and 95 % confidence intervals
were calculated by probit analysis.
N
EAA
DMF
NH2
N
N
N
N
POCl3
2
1
3
NH2
O
HN
N
O
N
H
O
O
R
R
Phenols
SEM HCl
EtOH/H2O
N
K2CO3/DMF
N
N
4
5a-5m
EAA: ethyl acetoacetate; DMF: dimethyl formamide; SEM: hydrazinecarboxamide
Fig. 1. Synthesis route of the target compounds (5a-5m)
programs. Of these, the maximal electroshock and pentylene-
tetrazole seizure models represent the two animal seizure
models most widely used in the search for new antiepileptic
drugs22,23. The maximal electroshock test is thought to predict
drugs effective against generalized seizures of the tonic-clonic
(grand mal) type, whereas the pentylenetetrazole test is used
to find drugs effective against the generalized seizures of the
petit mal (absence) type. In this study, the maximal electroshock
model was used for screening the anticonvulsant activity of
target compounds. In the preliminary evaluation of anticon-
vulsant activity, doses of 30, 100 and 300 mg/kg were used
and the results were presented in Table-1.
In the pentylenetetrazole (PTZ)-induced seizures, animals
were divided into 3 groups (10 mice in one group), which were
administrated compound 5m, carbamazepine and vehicle DMSO,
respectively.At 2.5 h after the administration, 85 mg/kg penty-
lenetetrazole dissolved in saline was administered subcutane-
ously (s.c.) for each group. Then the animals were placed in
individual cages and observed for 0.5 h. The numbers of clonic
and tonic seizures as well as the number of deaths were
All the tested compounds showed anti-maximal electro-
shock activity indicative of their ability to prevent seizure spread.
At the dose of 100 mg/kg, all the compounds showed protection
against the maximal electroshock model at 0.5 h period and
5b-5m kept the protection to 4 h, which indicated that these
compounds are potent having a rapid onset of action and long
duration of action. Compounds showed protection against the
maximal electroshock model at 30 mg/kg including 5c, 5d,
5i, 5j, 5m.Among them, compounds 5j and 5m showed activity
at 0.5 h and 4 h periods, while compounds 5c, 5d and 5i showed
activity only at 4 h. In the acute neurotoxicity test, compounds
5a, 5b, 5e-5h, 5k, 5l did not show neurotoxicity at the dose of
100 mg/kg, while the others showed neurotoxicity in different
degree at the same dose. None is found to be neurotoxic at the
dose of 30 mg/kg.
noted20,21
.
The neurotoxicity of the compounds was measured in
mice by the rotarod test20,21. The mice were trained to stay on
a rotarod of diameter 3.2 cm which rotates at 10 rpm. Trained
animals were given i.p. injection of the test compounds.
Neurotoxicity was tested at 0.5 h (or 2.5 h for the quantification
test) after the administration and indicated by the inability of
the animal to maintain equilibrium on the rod for at least 1 min
in each of the trials.
RESULTS AND DISCUSSION
From the data in Table-1, it can be seen that each comp-
ound has almost equal activity at the end of 0.5 h and 4 h. This
fact indicated that the time to peak effect (TPE) of drugs are
likely to present in the time range of 0.5 to 4 h. To obtain the
TPE of compounds 5a-5m, we conducted a time-course test
for the selected 5m, in which compound 5m reached the TPE
at 2.5 h after i.p. (Fig. 2). Therefore, the 2.5 h time interval
was chosen as the assessment time for the test compounds in
the next quantitative tests.
The target compounds (5a-5m) were synthesized accor-
ding to the route as shown in Fig. 1. Briefly, phenylhydrazine
was reacted with ethyl acetoacetate (EAA) to afford 3-methyl-
1-phenyl-2-pyrazolin-5-one (2). Compound 2 was subjected
to a Vilsmeier Haack reaction to provide 5-chloro-3-methyl-
1-phenyl-1H-pyrazole-4-carboxaldehyde (3), which was
subsequently reacted with different substituted-phenols to
obtain the intermediates 4. Finally, the target compounds were
synthesized by refluxing 4 with hydrazine carboxamide
hydrochloride (SEM HCl) in 50 % ethanol. The structures of
On the basis of the results recorded in the preliminary
screening, compounds 5c, 5d, 5i, 5j, 5k and 5m were subjected
to the next phase of trials concerning quantification of their
anticonvulsant activity (indicated by ED50) and neurotoxicity
(indicated by TD50) in mice. Results of the quantitative tests
for the selected compounds, together with the corresponding
data for the currently marketed antiepileptic drugs, including
phenobarbital and valproate, are shown in Table-2.
1
the target compounds were confirmed by IR, H NMR and
mass spectral.
A very important step in antiepileptic drug discovery is
the choice of an appropriate animal model for the initial scree-
ning. At present, there are three models in vivo - the maximal
electroshock, the pentylenetetrazole and the kindling model -
which are routinely used by most antiepileptic drugs discovery

Vol. 26, No. 23 (2014)
Synthesis and Evaluation on Anticonvulsant Activities of Pyrazolyl Semicarbazones 8237
TABLE-1
PRELIMINARY ANTICONVULSANT ACTIVITY AND NEUROTOXOCITY OF
COMPOUNDS 5a-5m ADMINISTERED INTRAPERITONEALLY (i.p.) TO MICE
NH2
HN
O
N
O
N
N
R
MESa (mg/kg)
Toxicityb (mg/kg)
Compds.
R
0.5 h
100
1/3
2/3
3/3
3/3
2/3
1/3
1/3
1/3
3/3
3/3
3/3
1/3
3/3
4 h
100
0/3
2/3
3/3
3/3
2/3
2/3
2/3
1/3
3/3
3/3
2/3
1/3
3/3
0.5 h
100
0/3
0/3
0/3
2/3
0/3
0/3
0/3
0/3
2/3
0/3
0/3
0/3
0/3
4 h
100
0/3
0/3
1/3
3/3
0/3
0/3
0/3
0/3
2/3
1/3
0/3
0/3
1/3
30
300
3/3
3/3
3/3
3/3
3/3
3/3
3/3
3/3
3/3
3/3
3/3
3/3
3/3
30
300
3/3
3/3
3/3
3/3
3/3
3/3
3/3
3/3
3/3
3/3
3/3
3/3
3/3
30
c
300
2/3
3/3
3/3
3/3
3/3
3/3
3/3
1//33
3/3
3/3
3/3
1/3
3/3
30
-
300
3/3
3/3
3/3
3/3
3/3
3/3
3/3
2/3
3/3
3/3
3/3
2/3
3/3
H
4-F
0/3
0/3
0/3
0/3
0/3
0/3
0/3
0/3
0/3
1/3
0/3
0/3
1/3
0/3
0/3
1/3
1/3
0/3
0/3
0/3
0/3
1/3
1/3
0/3
0/3
1/3
-
5a
5b
5c
5d
5e
5f
-
-
2-Cl
-
0/3
0/3
-
3-Cl
0/3
4-Cl
-
-
2,4-2Cl
2,6-2Cl
4-Br
-
-
-
5g
5h
5i
-
-
2-CH3
3-CH3
2,4-2CH3
2-OCH3
4-OCH3
0/3
-
0/3
0/3
-
5j
-
5k
5l
-
-
-
0/3
5m
All positive reaction numbers are in bold italic; aMaximal electroshock test (number of animals protected/number of animals tested), the number of
mice is three; bAcute neurotoxicity (number of animals toxic/number of animals tested), the number of mice is three; cNot tested
TABLE-2
QUANTITATIVE ANTICONVULSANT EVALUATION IN MICE AFTER INTRAPERITONEAL ADMINISTRATION (i.p.)
Compounds
R
2-Cl
ED50a (mg/kg) (MES)
52.8 (45.8-60.9)d
63.4 (55.0-73.1)
58.9 (51.5-67.3)
76.0 (65.9-87.7)
56.8 (49.2-65.5)
42.4 (37.1-48.5)
21.8 (21.8-25.5)
272 (247-338)
TD50b (mg/kg) (NT)
152.1 (131.8-175.5)
81.8 (71.6-93.5)
PIc
2.9
1.3
1.6
1.6
3.1
3.7
3.2
1.6
5c
3-Cl
5d
2-CH3
3-CH3
2,4-2CH3
4-OCH3
-
94.7 (82.1-109.3)
118.3 (102.5-136.5)
176.0 (152.6-203.0)
157.8 (136.8-182.0)
69.1 (62.8–72.9)
426 (369-450)
5i
5j
5k
5m
Phenobarbital
Valproate
-
aED50: Median effective dose; bTD50: Median toxic dose; cPI = Protective index (TD50/ ED50); dThe 95 % confidence limits
100
methyl-1-phenyl-1H-pyrazol-4-yl}methylene]hydrazine
carboxamide (5m) possessed nice anti-maximal electroshock
activity with an ED50 of 42.4 mg/kg and a protective index of
3.7, which was superior to phenobarbital and valproate in the
aspect of safety.
80
60
40
For further exploring the anticonvulsant activity of these
compounds, pentylenetetrazole-induced seizure model was
made to 5m. As shown in Table-3, 80 % protection against
pentylenetetrazole induced tonic seizures and death was
observed when pretreated by 5m (50 mg/kg), which suggested
compound 5m could work against the seizure spread induced
by pentylenetetrazole. Pentylenetetrazole has been reported
to produce seizures by inhibiting γ-aminobutyric acid neuro-
transmission24,25. γ-Aminobutyric acid (GABA) is the main
inhibitory neurotransmitter in the brain and is widely impli-
cated in epilepsy. Inhibition of GABAergic neurotransmission
or activity has been shown to promote and facilitate seizures,
while enhancement of GABAergic neurotransmission is known
20
0
0.5
1
2
2.5
3
4
5
Time (h)
Fig. 2. Time-course of compound 5m (50 mg/kg) in the maximal
electroshock seizure test (i.p)
As shown in Table-2, all the test compounds showed
weaker anticonvulsant activity than phenobarbital, but better
than valproate. Interestingly, 2-[{5-(4-Methoxyphenoxy)-3-

8238 Deng et al.
Asian J. Chem.
TABLE-3
EFFECTS OF COMPOUND 5M ON PENTYLENETETRAZOL-INDUCED SEIZURES IN MICE (i.p.)
Chemical substances
Compound
DMSO
Doses (mg/kg) Test time (h) Clonic seizures (%)
Tonic seizures (%)
Lethality (%)
-
0.5
0.5
2.5
100
100
80
100
0
100
10
Pentylenetetrazol
Carbamazepine
5m
50
50
20
20
to inhibit or attenuate seizures26. Based on these, it is speculated
that the mechanism of action of the compound 5m may be
involved in the GABAergic neurotransmission.
4. D.M. Taylor, C. Young and C. Paton, J. Clin. Psychiatry, 64, 30 (2003).
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Conclusion
A series of 2-[(5-phenoxy-3-methyl-1-phenyl-1H-pyrazol-
4-yl)methylene]-hydrazine carboxamide derivatives (5a-5m)
were synthesized and studied for their anticonvulsant activity.
The results of this study demonstrated that pyrazolyl semicar-
bazones have potent anticonvulsant activity. Among the com-
pounds synthesized, compound 5m was found to have promising
anticonvulsant activity, which gave an ED50 of 42.4 mg/kg
and a TD50 of 157.8 mg/kg, resulting in a PI value of 3.7. In
addition, compound 5m demonstrated antagonistic activity
against seizures induced by pentylenetetrazole, which suggested
that compound 5m may exert anticonvulsant activity through
γ-aminobutyric acid-mediated mechanisms. This study provide
a new nuclear/structure for further design of new anticonvulsant
agents.
8. J.R. Dimmock, K.K. Sidhu, R.S. Thayer, P. Mack, M.J. Duffy, R.S.
Reid, J.W. Quail, U. Pugazhenthi, A. Ong and J.A. Bikker, J. Med.
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Dimmock, Eur. J. Med. Chem., 33, 595 (1998).
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Heterocycl. Chem., 43, 1287 (2006).
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42B, 2657 (2003).
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and W. Ahsan, Eur. J. Med. Chem., 45, 2467 (2010).
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ACKNOWLEDGEMENTS
18. P. Aragade, S. Kolhe, H. Kamble, D. Baheti and V. Maddi, Int. J. Drug
Design Discovery, 3, 688 (2012).
This work was supported by Educational Commission of
Jiangxi Province, China (Grant No. GJJ14570) and Natural
Science Foundation of Jiangxi Province, China (Grant No.
20142BAB215022).
19. M.X. Song, C.J. Zheng, X.Q. Deng, L.P. Sun, Y. Wu, L. Hong, Y.J. Li,
Y. Liu, Z.Y. Wei, M.J. Jin and H.R. Piao, Eur. J. Med. Chem., 60, 376
(2013).
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Epilepsia, 19, 409 (1978).
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