Heteroaryl-substuted semicarbazones: Synthesis and anticonvulsant activity of N-(3-methylpyridin-2-yl)-substituted semicarbazones

Article abstract of DOI:10.1002/jhet.5570430522

A series of substituted N-(3-methylpyridin-2-yl) semicarbazones was designed and synthesized to meet the structural requirements essential for anticonvulsant activity. The structures of all the synthesized compounds were confirmed by means of spectral and elemental analysis. All the compounds were evaluated for their anticonvulsant activity by maximal electroshock seizures (MES) test, subcutaneous pentylenetetrazole (scPTZ) screen, subcutaneous strychnine (scSTY) pattern test and subcutaneous picrotoxin (scPIC) seizure threshold test along with the behavioral, and neurotoxicity evaluation. A number of N-(3-methylpyridin-2-yl) semicarbazone derivatives exhibited significant protection after intraperitoneal administration at the dose of 100 and 300 mg/kg. Compound N¹-(3-methylpyridin-2-yl)-N⁴-(isatin) semicarbazone (19) emerged as the most active analogue of the series, being more effective in most of the test models than ethosuximide and sodium valporate.

Full text of DOI:10.1002/jhet.5570430522

Sep-Oct 2006
1287
Heteroaryl-substuted Semicarbazones: Synthesis and Anticonvulsant
Activity of N-(3-Methylpyridin-2-yl)-substituted Semicarbazones
Shalini Mehta [a], Roheeth Kumar Pavana [a], Perumal Yogeeswari [a]*,
Dharmarajan Sriram [a], and James Stables [b]
[a] Medicinal Chemistry Research Laboratory, Pharmacy Group,
Birla Institute of Technology & Science, Pilani-333031, India
[b] Preclinical Pharmacology Section, Epilepsy Branch,
National Institute of Health, Bethesda, USA
Received December 20, 2005
R
CH3
CH3
H
R
H
N
OR
R1
N
HN
N
N
HN
N
N
O
O
O
19-20
1-18
A series of substituted N-(3-methylpyridin-2-yl) semicarbazones was designed and synthesized to meet
the structural requirements essential for anticonvulsant activity. The structures of all the synthesized
compounds were confirmed by means of spectral and elemental analysis. All the compounds were
evaluated for their anticonvulsant activity by maximal electroshock seizures (MES) test, subcutaneous
pentylenetetrazole (scPTZ) screen, subcutaneous strychnine (scSTY) pattern test and subcutaneous
picrotoxin (scPIC) seizure threshold test along with the behavioral, and neurotoxicity evaluation. A number
of N-(3-methylpyridin-2-yl) semicarbazone derivatives exhibited significant protection after intraperitoneal
administration at the dose of 100 and 300 mg/kg. Compound N1-(3-methylpyridin-2-yl)-N4-(isatin)
semicarbazone (19) emerged as the most active analogue of the series, being more effective in most of the
test models than ethosuximide and sodium valporate.
J. Heterocyclic Chem., 43, 1287 (2006).
In recent years, the field of AED development is quite
dynamic, affording many promising research opportunities.
The chemical diversity and various mechanisms of action
of anticonvulsants, make it difficult to identify the
common pharmacophore. Unverferth et al. [6], suggested
a pharmacophoric model by the conformational analysis
of the older generation clinically active anticonvulsants
drugs such as hydantoin, succinimides, glutarimides,
oxazolidine-2,4-diones, pyrimidine-2,6-diones and barbi-
turic acids, comprising aromatic rings or their equivalent
in a favored orientation, electron donor moiety and a third
region usually, a cyclic ureide, containing a number of
hydrogen bond forming functional groups. Recently
Dimmock [7-10], Pandeya [11-13], Yogeeswari [13-18]
and coworkers have evaluated various aryl semicar-
bazones as candidate anticonvulsants. Our interest in
developing semicarbazones rests upon the structural
dissimilarity to existing antiepileptic drugs, so it was
hoped that such novel compounds would lack the side
effects seen with many of the currently available
medications [7]. For the aryl semicarbazones the aryl ring
and the semicarbazono group (H2NCONHN=) were
considered to interact at both an aryl binding site and a
hydrogen bonding area, respectively [9-10], and an
additional hydrophobic binding area has also been
proposed. The analysis of the distance relationship
Introduction.
About 2 million people in the United States are affected
by epilepsy [1]; the term “epilepsy” encompasses a
number of different syndromes whose cardinal feature is a
predisposition to recurrent unprovoked seizures. It has
afflicted many historical figures, and an enormous
collection of research has been performed in an effort to
understand the many facets of the disease. More than half
of a century has elapsed since the anticonvulsant
properties of phenytoin [2] was first evidenced in the
laboratory animal models with the successful therapeutic
administration in epileptic patients [3]. Today in addition
to phenytoin; several AEDs (antiepileptic drugs) are
widely utilized in the treatment of various forms of
epilepsy [4]. Some of the other conventional drugs
include carbamazepine, phenobarbital, ethosuximide,
valproic acid and various benzodiazepines, in addition
several new agents are in human clinical experimentation.
Unfortunately, current medications are ineffective for
more than one third of the patients with epilepsy [1].
Many continue to have seizures, while others experience
disturbing side effects (e.g., drowsiness, dizziness,
nausea, liver damage) [5]. Current therapies have failed to
adequately control this disorder, documenting the need for
new agents with different mechanisms of action.

1288
S. Mehta, R. K. Pavana, P. Yogeeswari , D. Sriram , and J. Stables
Vol 43
showed that aryl semicarbazones fulfill the essential
demands of the pharmacophore when compared with
conventional antiepileptic drugs [16,17].
Pharmacology.
The synthesized compounds (1-20) were evaluated at
dose levels of 30, 100 and 300 mg/kg intraperitoneally in
mice for anticonvulsant activity by following the standard
anticonvulsant drug development (ADD) program
protocols [24-26]. Table 1 lists the results obtained from
the initial anticonvulsant evaluation of the synthesized
compounds compared to the clinically proven anti-
epileptics such as phenytoin, ethosuximide and sodium
valporate. The tests included one electrical and three
chemoshock tests i.e. maximal electroshock seizure test
(MES), subcutaneous pentylenetetrazole (scPTZ) seizure
threshold test, subcutaneous strychnine (scSTY) pattern
test and subcutaneous picrotoxin (scPIC) seizure
threshold test. The acute neurological toxicity was
determined by the rotorod test. Nine compounds showed
activity in the preliminary MES screen, indicative of their
ability to prevent seizure spread. Compounds 7, 16, and
19 showed protection at 100 mg/kg (0.5h) and other active
compounds showed protection at 300 mg/kg dose.
Compounds 2, 12, 15, and 16 exhibited shorter duration
of action (i.e. activity at 0.5 h interval only) whereas
compound 1 showed late onset of action. Other
compounds showed activity at both 0.5 h and 4 h
intervals. In the subcutaneous pentylenetetrazole (scPTZ)
screen, a test used to identify compounds that elevates
seizures threshold, nine compounds (1, 2, 4, 7, 10-12, 15,
and 16) showed protection. The compounds 1, 10, and 16
showed protection at 100mg/kg up to 0.5 h time period.
ELECTRON DONOR
ARYL UNIT
HYDROGEN BOND ACCEPTOR-DONOR UNIT
Figure 1. Pharmacophore model for anticonvulsants.
Previous studies revealed that substitution with the
methyl group on the aryl binding ring of semicarbazones
led to an increase in the anticonvulsant activity when the
compounds were administered by the intraperitoneal route
to mice [19-22]. Earlier, various methyl substituted
pyridyl derivatives were found to possess antiepileptic
properties [23]. With this as background, the present work
focuses on the synthesis and anticonvulsant evaluation
of N-(3-methylpyridin-2-yl) semicarbazones, towards
exploring the effect of replacement of the aryl ring with
heteroaryl ring i.e. pyridyl ring, in combination with
methyl substituent on anticonvulsant activity of
semicarbazones.
Scheme 1
Results and Discussion.
Chemistry.
O
O
H2N
NH
H2SO4
In the present investigation,
a
series of N-(3-
HNO3
+
+
H2N
NH2
Urea
NO2
methylpyridin-2-yl) semicarbazones was synthesized and
evaluated for their anticonvulsant activity. The
preparation of the pyridyl semicarbazones was achieved
as depicted in Scheme. Substituted pyridyl amine i.e. 2-
amino-3-methyl pyridine, was treated with nitrourea,
which led to the synthesis of 1-(3-methylpyrin-2-yl)urea.
The urea derivatives on condensation with hydrazine
hydrate in ethanol gave substituted semicarbazides, which
further on reaction with appropriate aldehydes and
ketones gave the semicarbazone derivatives i.e., N-(3-
methylpyridin-2-yl)semicarbazones (1-20). All the
synthesized compounds were characterized by physical,
analytical and spectral data. In general the IR spectra
showed the C=N peak at 1620-1590 cm-1 and the NH
stretching vibrations at 3450 cm-1, amide bond at 3300-
Nitro urea
CH3
N
NH2
CH3
CH3
NH2NH2. H2O
. HCl
H
N
N
HN
con. HCl
N
NH2
HN
NH2
O
O
Aldehydes or
Ketones
CH3COONa
R
CH3
CH3
HN
3200 cm-1 and 1710-1680 cm-1. The H-NMR spectrum
revealed that the hydrazino proton (=N-NH) showed a
singlet at ꢀ 9.56-10.28 and the aryl NH at 8.28-9.26 both
of which were D2O exchangeable.
1
H
R
H
N
OR
R1
N
HN
N
N
HN
N
N
O
O
O
19-20
1-18

Sep-Oct 2006
Heteroaryl-substuted Semicarbazones
1289
Some selected compounds (1, 2, 10-12, 15-17, and 19)
were examined in the scSTY and scPIC animal models.
All the tested compounds except 1 and 11 showed
protection in the subcutaneous strychnine-induced seizure
model. Compound 19 showed activity at 100 mg/kg and
other compounds showed activity at 300mg/kg. Only
compounds 10, 16, and 19 exhibited a longer duration
(0.5 h and 4 h) of action. The results are presented in
Table 1.
In the acute neurological toxicity screen, the
compounds 1, 10 and 11, showed activity but no
neurotoxicity at the maximum dose administered (300
mg/kg), and compounds 3, 5, 6, 8, 9, 13, 14, 18, and 20
did not exhibit anticonvulsant activity as well as
neurotoxicity. Compound 19 showed no neurotoxicity at
the anticonvulsive dose and compound 2, 7, 15-17
exhibited neurotoxicity at the anticonvulsive dose.
Compound 4 was found to be more neurotoxic at the
anticonvulsive dose.
locomotor activity i.e. possessed behavioural despair side
effect. The compound with 4-chloro benzylidene
substituents (7) showed no motor impairment with the
maximum actophotometer score of 308.00±8.00 (0.5 h)
and 272.50±5.06 (1 h). The semicarbazones derivatives
were also studied for CNS depressant effect by porsolt’s
forced swim pool test and compared with carbamazepine.
Compounds except 1-6, 8-10 and 20, did not show
significant increase in immobility time as compared to the
control, indicating significant CNS depressant than the
conventional drugs (table 3).
In terms of interaction at the binding site, as proposed
previously [6,9,10], the pharmacophoric descriptors were
thought to be a lipophilic aryl ring and hydrogen bonding
semicarbazone moiety. The distal aryl ring at the
carbimino terminal (benzylidene ring) may be essential
for the pharmacokinetic properties of the compounds
since variation in the substituents at the distal aryl ring
was found to affect the biological activity. Among the
benzylidene derivatives, 4-methyl (7) and 2-chloro (10)
substituents were found to be most favourable.
In the behavioral despair test, compounds except 7, 13,
and 16, showed significant decrease in motor activity as
indicated by the actophotometer scores. The standard drug
phenytoin also showed significant decrease in the
Replacement of the proton on the carbimino carbon atom
by the methyl (13-16) or the phenyl (17-18) or the
Table 1
Anticonvulsant and Minimal Motor Impairment of 4-Methyl-substituted-pyridy semicarbazones
Intraperitoneal injection in micea
MES screen
scPTZ screen
scSTY screen
scPIC screen
Neurotoxicity
screen
Comp.
0.5h
4h
0.5h
4h
0.5h
4h
0.5h
4h
0.5h
4h
1
2
3
4
-
300
-
300
-
-
100
300
-
300
-
-
-
-
-
300
x
-
-
x
300
300
x
300
-
x
-
300
-
100
-
-
-
-
-
-
x
x
x
x
5
-
-
-
-
x
x
x
x
-
-
6
7
8
9
10
11
12
13
14
15
16
17
18
-
100
-
-
300
-
-
300
-
-
-
-
-
-
300
-
300
-
30
-
300
-
-
-
-
-
300
x
x
x
x
300
-
300
x
x
x
x
x
300
-
-
x
x
x
x
x
x
300
300
300
x
x
x
x
x
300
-
-
x
x
100
300
-
x
300
x
x
-
-
-
100
-
-
-
-
-
-
-
300
-
-
-
-
300
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
300
-
300
-
100
300
300
-
-
-
x
x
-
300
100
300
-
100
-
30
-
-
300
100
-
-
-
300
300
300
x
100
x
-
100
300
300
x
300
x
x
-
-
300
100
300
-
300
-
100
-
-
300
-
x
100
x
-
-
-
-
-
19
20
-
-
-
100
-
Phenytoin
Ethsuximide
Sod. valporate
-
300
100
300
100
-
-
-
aDoses of 30, 100 and 300mg/kg were administered. The figures in the table indicate the minimum dose whereby
bioactivity was demonstrated in half or more of the mice. The dash (-) indicates an absence of activity at
maximum dose administered (300mg/kg). The cross (x) indicates the compounds not tested in the animals.

1290
S. Mehta, R. K. Pavana, P. Yogeeswari , D. Sriram , and J. Stables
Vol 43
Table 2
Physical data of 3-Methyl-substituted-pyridyl-semicarbazones
#
R
R1
Yield
(%)
M.P.
(°C)
Molecular
Formulab
Mol.
Weight
Rfc
CLog Pd
1
2
3
4
5
6
7
8
9
H
H
H
H
H
H
H
H
H
H
H
H
H
2-NO2
3-NO2
4-NO2
2-OH
2-CH3
4-CH3
4-OCH3
4-N(CH3)2
2-Cl
57
38
49
58
62
67
48
64
58
56
65
44
150
60
145
95
185
90
220
185
125
210
135
250
C14H14N4O
C14H13N5O3
C14H13N5O3
C14H13N5O3
C14H14N4O2
C15H16N4O
C15H16N4O
C15H16N4O2
C16H19N5O
C14H13N4OCl
C14H13N4OCl
C15H16N4O3
254
299
299
299
270
268
268
284
297
288
288
300
0.75
0.64
0.76
0.62
0.54
0.66
0.63
0.64
0.52
0.66
0.78
0.70
2.39
1.60
1.29
1.55
0.78
2.36
2.58
2.45
1.96
2.60
3.08
1.71
10
11
12
4-Cl
4-OH
3-OCH3
H
4-OH
4-NH2
4-CH3
H
4-Br
-
-
13
14
15
16
17
18
19
20
CH3
CH3
CH3
CH3
C6H5
C6H5
H
72
40
54
73
72
61
48
78
115
130
72
184
85
65
180
135
C15H16N4O
C15H16N4O2
C15H17N5O
C16H18N4O
C20H18N4O
C20H17N4OBr
C15H13N5O2
C15H12N5O2.F
268
284
283
282
330
409
295
313
0.50
0.67
0.70
0.84
0.59
0.73
0.62
0.66
2.08
1.51
0.91
2.34
3.19
3.69
1.04
2.97
F
aMelting points of the compounds at their decomposition. bElemental analyses for C, H, N were with in ± 0.4 % of the
theoretical values. cMobile phase CHCl3 : CH3OH ( 9:1). dLog P was generated using Alkemey 2000 and SciLog P softwares
Table 3
CNS Study of 3-Methyl-substituted-pyridyl-semicarbazones
Actophotometer
(Locomotor activity score)b
Immobility Time
(Sec) c
Compd
Noa
0.5h
1h
Control
Test
(After 1 h)
Control
318.00±13.68
184.67±3.13
182.00±4.16
159.01±4.88
198.50±3.35
201.56±4.02
231.50±5.98
308.00±8.00 NS
209.50±6.34
188.50±5.54
272.00±5.06 *
200.00±7.42
216.00±5.34
286.53±12.64 NS
188.17±4.93
184.00±12.43
295.00±6.78 NS
281.33±11.42NS
207.33±4.35
272.50±4.84 *
217.00±8.16
104.11±14.56
-
288.50±11.31
142.50±5.18
145.00±4.14
160.50±5.11
196.00±7.04
150.00±6.18
192.00±4.72
272.50±5.06 NS
188.33±4.42
156.00±3.84
170.50±4.86
179.00±6.18
150.00±3.92
271.00±12.00 NS
205.50±6.90
167.00±8.64
268.00±8.48 NS
194.20±8.55
200.50±7.49
212.00±4.59
187.00±5.11
106.23±12.44
-
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
102.00±4.13
158.00±4.04
158.00±5.56
162.00±5.26
148.00±.4.49
154.00±5.03
192.00±8.58
120.00±7.93
160.00±3.48
184.00±6.47
161.50±8.03
194.00±15.98
198.00±11.73
179.00±4.12
100.50±18.12
179.00±4.12
205.00±5.13
128.50±16.21
100.50±18.12
139.00±14.36
-
144.50±5.65
196.00±7.14
182.00±8.12 **
195.00±5.16 *
168.50±2.78 *
166.00±2.73 **
206.50±7.64 NS
165.00±9.34 *
193.00±7.69 *
206.00±6.42 **
171.00±10.15NS
232.00±6.94 NS
207.50±6.58 NS
179.50±3.94 NS
141.50±9.49 NS
179.50±3.94 NS
212.50±4.16 NS
131.00±15.29 NS
111.50±9.58 NS
186.83±5.16 *
-
Phenytoind
Carbamazepined
131.50±9.32
207.33±08.49
a
b
The compounds were tested at the dose level of 100mg/kg. Each value represents the mean ± SEM of six mice significantly
c
different from the control at p < 0.0005 and * p< 0.05. Each value represents the mean ± SEM of six mice significantly different
from the control at p < 0.0005, *p < 0.005 and **p < 0.05 Student t’ test). d The compounds were tested at the dose level of 30mg/kg.

Sep-Oct 2006
Compound
Heteroaryl-substuted Semicarbazones
1291
Table 4
Elemental Analysis of 3-Methyl-substituted-pyridyl-semicarbazones
Analytical (%)
H
Experimental (%)
Molecular Formula
Mol.wt
C
N
C
N
H
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
C14H14N4O
C14H13N5O3
C14H13N5O3
C14H13N5O3
C14H14N4O2
C15H16N4O
C15H16N4O
C15H16N4O2
C16H19N5O
C14H13N4OCl
C14H13N4OCl
C15H16N4O3
C15H16N4O
C15H16N4O2
C15H17N5O
C16H18N4O
C20H18N4O
C20H17N4OBr
C15H13N5O2
C15H12N5O2.F
254
299
299
299
270
268
268
284
297
288
288
300
268
284
283
282
330
409
295
313
66.13
56.18
56.18
56.18
62.21
67.15
67.15
63.37
64.63
58.24
58.24
59.99
67.15
63.37
63.59
68.06
72.71
58.69
61.01
57.51
5.55
4.38
4.38
4.38
5.22
6.01
6.01
5.67
6.44
4.54
4.54
5.37
6.01
5.67
6.05
6.43
5.49
4.19
4.44
3.86
22.03
23.40
23.40
23.40
20.73
20.88
20.88
19.71
23.55
19.40
19.40
18.66
20.88
19.71
24.72
19.84
16.96
13.69
23.72
22.35
66.23
57.03
56.96
56.67
62.21
67.46
67.78
63.65
64.42
58.78
59.04
59.69
67.31
63.64
63.17
68.28
72.03
58.31
61.27
57.02
5.43
22.26
23.14
22.98
23.85
20.73
21.46
21.32
19.98
23.85
19.49
19.32
18.09
21.32
19.89
24.01
20.24
16.45
14.01
23.32
21.97
4.58
4.56
4.88
5.22
6.89
6.34
5.87
6.93
4.84
5.02
5.68
6.42
5.87
6.17
6.14
5.23
4.38
4.26
3.62
isatinimino ring (19-20) leading to increase in the size of the
distal aryl binding groups has shown variation in activity, due
to additional Vander Waals bonding or alternatively steric
impedance to alignment at the binding site. Among the
acetophenone derivatives, amino and methyl groups when
substituted at the 4-position (15, 16), exhibited anticonvulsant
activity in all four animal models. Subsequently the bulkier
phenyl ring with bromo substitution (18) led to complete loss
of activity whereas the unsubstituted compound (17) retained
activity in three animal models of seizure. Similarly the
unsubstituted isatinimino derivative (19) was found to show
better activity profile than the fluoro substituted compound
(20) and emerged as the most effective when compared to the
benzylidene and acetophenone derivatives.
lipophilic heteroaryl ring i.e. pyridine ring, which led to a
series of compounds with broad spectrum of activity in
the anticonvulsants screens with lesser neurotoxicity. In
accordance with our previous work, methyl substitution
has been found to be favorable for the anticonvulsant
activity. Compound with isatinimino substitution (19)
emerged as the most effective compound with broad
spectrum of activity and lesser neurotoxicity.
EXPERIMENTAL
Chemistry.
Melting points were determined in one end open capillary tubes
using Buchi 530 melting point apparatus and are uncorrected. The
homogeneity of the compounds was monitored by TLC, on silica
gel G (Merck) coated aluminium plates, using chloroform:
methanol (9:1) as solvent system. Elemental analyses (C, H, and N)
were undertaken with Perkin-Elmer model 240C analyzer. Infrared
(IR) and proton nuclear magnetic resonance (1H-NMR) spectra
were recorded for the compounds on Jasco IR report 100 (KBr) and
Brucker Avance (300 MHz) instruments respectively. Chemical
shifts are reported in parts per million (ppm) using tetra-
methylsilane as internal standard. All exchangeable protons were
confirmed by the addition of D2O. Log P values were calculated
using Alkemy-2000 and Scilog P software (Tripos Co.).
The MES and scPTZ have become the most widely
employed seizures models for the early identification and
high-throughput screening of investigational antiepileptic
drugs and only a very few standard anticonvulsants
exhibit a broad spectrum of activity in all the threshold
models. In this respect, it is clear that N-(3-methylpyridin-
2-yl) semicarbazones have the potential to treat a wide
range of seizure types by their multiple mechanism of
action as indicated by their activity in four animal models
of seizures, viz. MES, scPTZ, scSTY, and scPIC tests.
Five compounds had shown activity in all the four
screens, exhibiting a broad spectrum of anticonvulsant
activity. The compounds were found to be equipotent or
more potent as compared to some of the conventional
AED i.e phenytoin, ethosuximde, sodium valporate, in
one or other anticonvulsant screens.
Preparation of 1-(3-Methylpyrin-2-yl)urea.
1-(3-Methylpyrin-2-yl)urea was prepared by following the
nitro urea method [9]. Addition of a saturated aqueous solution
of nitrourea to equimolar quantity of 2-amino-3methyl-pyridine
in room temperature, gave an immediate white precipitate which
was washed and dried at room temperature; IR (Potassium
bromide): 3400 (Ar C-H def), 3340 (Secondary -NH), 1700
1
In conclusion, the present work indicates that the aryl
ring of the semicarbazones can be replaced by other
(O=C), 1320 (Ar-NH), 750 (subs. Ar), H NMR (DMSO-d6,
ppm, 300 MHz ): ꢀ 2.08 (s, 3H, Pyridyl-CH3), 7.21-7.58 (m, 3H,

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S. Mehta, R. K. Pavana, P. Yogeeswari , D. Sriram , and J. Stables
Vol 43
Pyridyl-H), 8.12 (s, 1H, Pyridyl-NH, D2O exchangeable), 10.08
(s, 2H, CONH, D2O exchangeable).
imine H), 8.64 (s, 1H, Pyridyl-NH, D2O exchangeable), 9.14 (s,
1H, CONH, D2O exchangeable).
Anal. Calcd. for C7H9N3O: C, 55.62: H, 16.00: N, 27.80: O,
10.58. Found: C, 54.92: H, 16.08 N, 33.98: O, 9.58.
4-Hydroxy-3-methoxybenzaldehyde N-(3-methylpyridin-2-yl)-
semicarbazone (12).
Synthesis of N-(3-Methylpyridin-2-yl) semicarbazide.
1H NMR (DMSO-d6): ꢀ 2.12 (s, 3H, Pyridyl-CH3), 3.64 (s,
3H, OCH3), 7.14-7.78 (m, 6H, Pyridyl & Ar-H), 8.24 (s, 1H,
imine H), 8.42(s, 1H, Pyridyl-NH, D2O exchangeable), 8.64 (s,
1H, CONH, D2O exchangeable) 10.28 (s, 1H, ArOH, D2O
exchangeable).
1-(3-Methylpyrin-2-yl)urea (0.05 mol) and excess of
hydrazine hydrate (0.1 mol) in ethanol were refluxed for 24 hrs.
The two third volume of alcohol was distilled by vacuum
distillation unit and poured into ice. The resultant precipitate
was collected by filtration, washed with water and dried. The
solid was recrystallised with 90% alcohol; IR (Potassium
bromide): 3400 (Ar C-H def), 3280 (Sec. O=C-NH), 1640
(O=C), 760 (subs. Ar); 1H NMR (DMSO-d6,, ppm, 300 MHz ): ꢀ
2.18 (s, 3H, Pyridyl-CH3), 7.14-7.60 (m, 3H, Pyridyl-H), 5.68 (s,
2H, NH2, D2O exchangeable), 8.04 (s, 1H, Pyridyl-NH, D2O
exchangeable), 9.94 (s, 1H, CONH, D2O exchangeable).
1-(4-Hydroxyphenyl)ethan-1-one N-(3-methylpyridin-2-yl)semi-
carbazone (14).
1H NMR (DMSO-d6): ꢀ 2.02 (s, 3H, CH3), 2.14 (s, 3H,
Pyridyl-CH3), 7.04-7.86 (m, 7H, Pyridyl & Ar-H), 8.60 (s, 1H,
Pyridyl-NH, D2O exchangeable) 9.26(s, 1H, CONH, D2O
exchangeable), 9.84 (s, 1H, ArOH, D2O exchangeable).
Anal. Calcd for C7H10N4O: C, 50.59: H, 16.07: N, 33.17: O,
9.63. Found: C, 49.87: H, 15.66: N, 34.08: O, 8.40.
1-(4-Aminophenyl) ethan-1-one N-(3-methylpyridin-2-yl)semi-
carbazone (15).
Synthesis of N-(3-Methylpyridin-2-yl) semicarbazones.
1H NMR (DMSO-d6): ꢀ 1.98 (s, 3H, CH3), 2.27 (s, 3H,
Pyridyl-CH3), 5.34 (s, 2H, Ar-NH2, D2O exchangeable), 7.18-
7.56 (m, 7H, Pyridyl & Ar-H), 8.68 (s, 1H, Pyridyl-NH, D2O
exchangeable), 10.04 (s, 1H, CONH, D2O exchangeable).
The N-(3-methylpyridin-2-yl) semicarbazones was synthesized
from the corresponding semicarbazide hydrochloride salt i.e. by
the addition of conc. hydrochloric acid to the solution of
semicarbazide in ethanol, according to a reported procedure [15].
To the solution of N-(3-methylpyridin-2-yl) semicarbazide
hydrochloride salt (0.001 mol, 600-800 mg) in 25 ml of methanol
was added sodium acetate solution in water (0.06 g in 2 ml of
water). This mixture was added to appropriate aldehyde or ketone
in alcohol, with stirring. The reaction was carried out for 5-10-
mins. The solid product was collected by filtration, dried and
recrystallized from hot alcohol. The compounds were mixtures of
E/Z isomers. The IR spectra of the semicarbazone derivatives
(Table 2) were identical in the following aspects; IR (Potassium
bromide): 3380 (Sec. N-H), 3310 (amide-NH), 3090 (Ar-C-H),
1-(4-Methylphenyl) ethan-1-one N-(3-methylpyridin-2-yl)semi-
carbazone (16).
1H NMR, (DMSO-d6): ꢀ 1.92 (s, 3H, CH3), 2.24 (s, 6H,
Pyridyl- & ArCH3), 7.28- 8.02 (m, 7H, Pyridyl & Ar-H), 8.28
(s, 1H, ArNH, D2O exchangeable), 10.20 (s, 1H, CONH, D2O
exchangeable).
Diphenylmethanone N-(3-methylpyridin-2-yl)semicarbazone
(17).
1H NMR, (DMSO-d6): ꢀ 2.22 (s, 3H, ArCH3), 7.18-8.16 (m,
13H, ArH), 8.54 (s, 1H, ArNH, D2O exchangeable), 10.20 (s,
1H, CONH, D2O exchangeable).
1
1680 (O=C), 1580-1540 (C=N), 740 (Sub. Ar). H NMR (300
MHz,) spectra of some representative compounds are as follows:
Benzaldehyde N-(3-methylpyridin-2-yl)semicarbazone (1).
Pharmacology.
1H NMR (DMSO-d6): ꢀ 2.28 (s, 3H, Pyridyl-CH3), 7.20-7.81
(m, 8H, Pyridyl & Ar-H), 8.60 (s, 1H, imine H), 9.24 (s, 1H,
Pyridyl-NH, D2O exchangeable), 9.98 (s, 1H, CONH, D2O
exchangeable).
Male albino mice (CF-1 Strain, 18-25g) and male albino rats
(Sprague-Dawely, 100-150 g) were used as experimental
animals. All the test compounds were suspended in 30 % PEG.
The animals were kept at 24 °C, in the groups of 5 per cage
receiving chow pellets and water. The light dark cycle was
12h:12h. Efforts were made in order to avoid any unnecessary
distress to the animals. All the animal tests have been performed
in accordance with the animal ethics approval of the institute.
2-Hydroxybenzaldehyde N-(3-methylpyridin-2-yl)semi-
carbazone (5).
1H NMR (DMSO-d6): ꢀ 2.10 (s, 3H, Pyridyl-CH3), 6.94-7.86
(m, 7H, Pyridyl & Ar-H), 8.48 (s, 1H, imine H), 9.05(s, 1H,
Pyridyl-NH, D2O exchangeable), 9.56 (s, 1H, CONH, D2O
exchangeable), 10.58 (s, 1H, ArOH, D2O exchangeable).
Anticonvulsant Screening.
The preliminary anticonvulsant evaluation was done using
reported procedures [24-26]. All the test compounds were
administered intraperitoneally in a volume of 0.01 ml/g body
weights for mice and 0.004 ml/g body weights for rats at doses
of 30, 100, and 300 mg/kg to one to four mice. Anticonvulsant
activity was assessed after 30 min. and 4 hr after administration.
Activity was established using MES, scPTZ, scSTY and scPIC
tests and data are presented in the tables 2 & 3.
4-Methylbenzaldehyde N-(3-methylpyridin-2-yl)semicarbazone (7).
1H NMR (DMSO-d6): ꢀ 2.14 (s, 3H, Pyridyl-CH3), 2.24 (s,
3H, ArCH3), 6.74-7.96 (m, 7H, Pyridyl & Ar-H), 8.52 (s, 1H,
imine H), 8.75 (s, 1H, Pyridyl-NH, D2O exchangeable), 9.56 (s,
1H, CONH, D2O exchangeable).
4-Methoxybenzaldehyde N-(3-methylpyridin-2-yl)semi-
carbazone (8).
Neurotoxicity Screen.
1H NMR (DMSO-d6): ꢀ 2.20 (s, 3H, Pyridyl-CH3), 3.68 (s,
3H, OCH3), 7.16-8.10 (m, 7H, Pyridyl & Ar-H), 8.24 (s, 1H,
Minimal motor impairment was measured in mice by the rotorod
test. The mice were trained to stay on an accelerating rotorod that

Sep-Oct 2006
Heteroaryl-substuted Semicarbazones
1293
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rotates at 6 revolutions per minute. The rod diameter was 3.2 cm.
Neurotoxicity was indicated by the inability of the animal to
maintain equilibrium on the rod for at least 1 min in each of the
three trials. The dose at which the animal was unable to grasp the
rotarod, was determined, and presented in Table 1.
Behavioral Test.
The titled compounds (30 mg/kg) were screened for their
behavioral effects using actophotometer [27] at 30 min and 1 h
after injection. The behavior of animals inside the photocell was
recorded as a digital score. Increased scores suggest good
behavioral activity. The control animal was administered PEG.
The observations are tabulated as Table 3.
CNS – Depressant Study.
The forced swim pool method described earlier was followed
[28], Wistar rats were placed in a chamber (diameter: 45 cm,
height: 20 cm) containing water up to a height of 15 cm at 25 ±
2°C. Two swim sessions were conducted, an initial 15 min pre-
test, followed by a 5 min test session 24 h later. The animals
were administered an i.p. injection (30 mg/kg) of the test
compounds 30 min before the test session. The period of
immobility (passive floating without struggling, making only
those movements which are necessary to keep its head above the
surface of water) during the 5 min test period were measured.
The results are presented in Table 3.
Acknowledgement.
The authors wish to thank the Department of Science and
Technology, New Delhi (India) for funding the project under
SERC Fast track scheme for young scientist (SR/FT/L-84/2003).
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