Synthesis of novel 1-[5-(4-methoxy-phenyl)-[1,3,4]oxadiazol-2-yl]- piperazine derivatives and evaluation of their in vivo anticonvulsant activity

Article abstract of DOI:10.1016/j.ejmech.2013.04.054

A series of novel 1-[5-(4-methoxy-phenyl)-[1,3,4]oxadiazol-2-yl]-piperazine derivatives 8(a-o) were synthesized and characterized by elemental analyses, ¹H NMR, ¹³C NMR and mass spectral studies. The newly synthesized compounds were screened for their anticonvulsant activity against maximal electroshock seizure (MES) model in male wistar rats and compared with the standard drug phenytoin. The neurotoxic effects were determined by rotorod test by using mice. Compounds 8d, 8e, 8f and 8h were found to be most potent of this series. The same compounds showed no neurotoxicity at the maximum dose administered (100 mg/kg). The efforts were also made to establish the structure activity relationships among synthesized compounds. The pharmacophore model was used to validate the anticonvulsant activity of the synthesized molecules.

Full text of DOI:10.1016/j.ejmech.2013.04.054

European Journal of Medicinal Chemistry 65 (2013) 276e283
Contents lists available at SciVerse ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Synthesis of novel 1-[5-(4-methoxy-phenyl)-[1,3,4]oxadiazol-2-yl]-
piperazine derivatives and evaluation of their in vivo anticonvulsant
activity
,
b
Kikkeri P. Harish a, Kikkeri N. Mohana a , Lingappa Mallesha ,
*
Basavapatna N. Prasanna kumar a
a Department of Studies in Chemistry, University of Mysore, Manasagangotri, Mysore 570 006, Karnataka, India
b PG Department of Studies in Chemistry, JSS College of Arts, Commerce and Science, Ooty Road, Mysore 25, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of novel 1-[5-(4-methoxy-phenyl)-[1,3,4]oxadiazol-2-yl]-piperazine derivatives 8(aeo) were
synthesized and characterized by elemental analyses, 1H NMR, 13C NMR and mass spectral studies.
The newly synthesized compounds were screened for their anticonvulsant activity against maximal
electroshock seizure (MES) model in male wistar rats and compared with the standard drug phenytoin.
The neurotoxic effects were determined by rotorod test by using mice. Compounds 8d, 8e, 8f and 8h
were found to be most potent of this series. The same compounds showed no neurotoxicity at the
maximum dose administered (100 mg/kg). The efforts were also made to establish the structure activity
relationships among synthesized compounds. The pharmacophore model was used to validate the
anticonvulsant activity of the synthesized molecules.
Received 14 January 2013
Received in revised form
24 April 2013
Accepted 26 April 2013
Available online 11 May 2013
Keywords:
2,5-Disubstituted-1,3,4-oxadiazole
Sulfonyl Chloride
MES
Ó 2013 Elsevier Masson SAS. All rights reserved.
Anticonvulsant
1. Introduction
children at school [1]. Anticonvulsants are also called as antiepi-
leptic (AEDs) and antiseizure drugs. The new AEDs and anticon-
Epilepsy is a major neurological disorder affecting a large sec-
tion of people both male and female throughout the world.
Currently available drugs for the treatment of epilepsy are symp-
tomatically effective in only 60e70% of patients. Epilepsy also poses
a considerable economic burden on society. The direct costs of
epilepsy vary significantly depending on the severity of the disease
and the response to treatment. The anticonvulsants are a diverse
group of pharmaceuticals used in the treatment of epileptic sei-
zures. Anticonvulsants are also increasingly being used in the
treatment of bipolar disorder, since many seem to act as mood
stabilizers. The goal of anticonvulsants is to suppress the rapid
and excessive firing of neurons that start a seizure. An effective
anticonvulsant would prevent the spread of the seizure within
the brain and offer protection against possible excitotoxic effects
that may result in brain damage. Some studies suggest that anti-
convulsants themselves are linked to decreased performance of
vulsant agents have been reviewed during last few years [2]. The
chemical diversity and various mechanisms of action of anticon-
vulsants make it difficult to find a common way of identifying new
drugs. Novel anticonvulsant agents are discovered through con-
ventional screening and/or structure modification rather than a
mechanism driven design. Therefore, drug identification is usually
conducted via in vivo screening tests on the basis of seizure type
rather than etiology.
Five membered heterocyclic compounds show various types of
biological activities. Among them, 1,3,4-oxadiazoles are important
class of heterocyclic compounds with broad spectrum anticonvul-
sant activity [3,4]. The therapeutic importance of these compounds
prompted us to develop selective molecules in which a substituent
could be arranged in a pharmacophore pattern to display higher
pharmacological activities. 2,5-Disubstituted-1,3,4-oxadiazole de-
rivatives are known for anticonvulsant activity [5,6]. The choice of
1,3,4-oxadiazoles is due to its multi-applicability in the field of
medicine. In the present study, some new 1-[5-(4-methoxy-
phenyl)-[1,3,4]oxadiazol-2-yl]-piperazine derivatives 8(aeo) have
been synthesized and their anticonvulsant effects have been
determined through maximal electroshock seizure (MES) test.
* Corresponding author. Tel.: þ91 821 2419654, þ91 94496 27573 (mobile).
E-mail address: drknmohana@gmail.com (K.N. Mohana).
0223-5234/$ e see front matter Ó 2013 Elsevier Masson SAS. All rights reserved.
http://dx.doi.org/10.1016/j.ejmech.2013.04.054

K.P. Harish et al. / European Journal of Medicinal Chemistry 65 (2013) 276e283
277
2. Results and discussion
by MES induced seizure in rats at the dose of 100 mg/kg and the
results are summarized in Table 2. Compounds 8d, 8e, 8f and 8h
demonstrated significant protective effect on MES induced seizure,
and the effect was similar to that of standard (phenytoin). Similarly,
compounds 8a, 8c, 8j, 8k, 8n and 8o showed moderate protective
effect and a significant difference in protectiveness were observed
when compared to standard group. Compounds 8g, 8b, 8i, 8m and
8l have relatively lower anticonvulsant potencies. All the com-
pounds were examined for their neurotoxicity on mice using
rotorod method given in the dose of 100 mg/kg. Except compounds
8g, 8l and 8m, none of the compounds showed neurotoxicity. These
compounds showed 25% toxicity compared to standard once at 2 h
of oral administration (Table 3).
2.1. Chemistry
We herein report a versatile method for the synthesis of
new 1-[5-(4-methoxy-phenyl)-[1,3,4]oxadiazol-2-yl]-piperazine
derivatives 8(aeo) (Scheme 1). This synthetic approach represents
the most efficient route to a diverse array of 2,5-disubstituted
heterocyclics reported in the literature [7e12]. The synthesis
employs readily available starting materials and simple procedures
making this method very attractive and convenient for the syn-
thesis of various oxadiazoles. The formation of products was
confirmed by recording their elemental analyses, 1H NMR, 13C
NMR and mass spectra. The 1H NMR spectra of 8d and 8e
The initial structure activity relationship (SAR) can be drawn for
the compounds 8(aeo). As proposed by Pandeya and Raja [14], the
active compound of the series meets all the requirements vital for
anticonvulsant activity. On correlating the structures of the syn-
thesized compounds with their anticonvulsant activity, it was
observed that compounds bearing groups like nitro, phenoxy and
halogens on phenyl ring possess high potency in MES. The SAR
study of these compounds indicate that the introduction of a
piperazine group at position 5 of 1,3,4-oxadiazole ring-; tri-
fluoromethyl and nitro substituents at the para and ortho positions
of the benzenesulfonyl moiety showed the best anticonvulsant
activity in 8d. Compound 8f possessing a dichloro thiophene group
in the sulfonyl group had good anticonvulsant activity in the MES
model. Both compounds did not exhibit neurotoxicity at the highest
administered dose. The 4-phenoxy benzene ring in 8e resulted in
increased anticonvulsant activity. The presence of constituents like
OC6H5 at phenyl ring especially at para position showed higher
potent activity. A similar study [15] showed good anticonvulsant
property. The presence of isoxazole group in 8h shows good anti-
convulsant activity.
showed multiplet (piperazine ring) in the region of d, 3.41e3.60 and
3.06e3.63, respectively. The 13C NMR spectra present the correct
number of carbon atoms at the appropriate chemical shift values.
The mass spectra of 8d showed molecular ion peak at m/z 514.4
which is in agreement with the molecular formula, C20H18F3N5O6S.
The elemental analyses data showed good agreement between the
experimentally determined values and the theoretically calculated
values within ꢀ0.4%. The chemical structures and physical data of
all the synthesized compounds are tabulated in Table 1.
2.2. Anticonvulsant activity
All the synthesized oxadiazole analogues were screened for
their anticonvulsant potential through MES model using male
wistar rats in the dose of 100 mg/kg. Antiepileptic drug research
has for several decades focused on identifying new potential drugs
based on their anticonvulsant activity against a single acute seizure
induced by various stimulators, usually in mice and rats. All
established antiepileptic drugs have anticonvulsant activity in at
least MES model [13]. In the present study, the anticonvulsant ac-
tivity of the fifteen newly synthesized 1-[5-(4-methoxy-phenyl)-
[1,3,4]oxadiazol-2-yl]-piperazine derivatives 8(aeo) was evaluated
The presence of nitro group in 8j and halogen groups in 8k, 8a,
8n and 8o showed moderate anticonvulsant activity. The presence
of cyano group in 8c at aryl ring has moderate activity, and
NH2
HN
O
O
triethyl
N
N
SOCl2
EtOH
orthoformate
O
O
OH
O
NH2NH2.H2O
EtOH
O
O
O
O
4
1
3
2
N
N
BuLi Br2
O
O
N
N
N
N
mono BOC piperizine
O
O
O
Br
O
6
5
4N
HC
l in
diox
ane
N
O
N
N
N
N
O
O
O
RSO2Cl
N
O
S
N
NH
.2HCl
R
7
8(a-o)
O
Scheme 1. Synthetic route of 1-[5-(4-methoxy-phenyl)-[1,3,4]oxadiazol-2-yl]-piperazine derivatives.

278
K.P. Harish et al. / European Journal of Medicinal Chemistry 65 (2013) 276e283
Table 1
Chemical structure and melting range of 1-[5-(4-methoxy-phenyl)-[1,3,4]oxadiazol-2-yl]-piperazine derivatives 8(aeo).
N
N
O
O
N
O
N
S
R
O
Compound
R
Structure
N
O
N
O
N
8a
O
Br
N
S
Br
O
N
O
N
O
N
8b
O
N
S
O
N
O
N
O
N
8c
CN
O
S
N
CN
O
N
O
N
O
F
N
F
O
S
8d
F
F
N
F
F
O2N
O
O2N
N
N
O
O
N
O
O
8e
N
S
O
O
N
N
O
Cl
O
Cl
N
S
8f
O
N
S
S
Cl
O
Cl

K.P. Harish et al. / European Journal of Medicinal Chemistry 65 (2013) 276e283
279
Table 1 (continued )
Compound
R
Structure
N
N
O
O
N
8g
O
N
S
O
N
N
O
O
N
N
8h
O
N
O
N
O
S
O
N
N
O
O
N
8i
O
N
S
O
N
N
O
O2N
O
N
O2N
O
8j
N
S
O
N
N
F
F
O
O
F
F
F
O
N
F
8k
O
N
N
S
O
N
O
N
N
8l
CH3
O
S
CH3
O
N
O
N
O
N
8m
O
S
N
O
(continued on next page)

280
K.P. Harish et al. / European Journal of Medicinal Chemistry 65 (2013) 276e283
Table 1 (continued )
Compound
R
Structure
N
N
O
O
N
8n
Br
O
S
N
Br
O
N
N
O
O
N
8o
I
O
S
N
I
O
naphthalene group in 8g, biphenyl in 8b and tert-butyl in 8i were
weakly active in the MES test. Anticonvulsant activity has increased
considerably when methyl group in 8l was replaced by tolyl vari-
ation 8m. The presence of electron releasing methyl group in
benzene ring in 8m has more anticonvulsant activity as compared
to methyl group alone in 8l. The presence of sulfonyl linker is
important for MES activity, and it is common in all derivatives.
These compounds contribute to the 25% neurotoxicity at 2 h.
Among the synthesized compounds 8(aeo), all the compounds
showed activity in the range of 10.6e77.6% in comparison to
phenytoin which completely inhibited the convulsions produced by
electro-convulsometer, but compound 8d having electron with-
drawing groups showed excellent anticonvulsant activity. It has
already been established that there are at least a few parameters for
anticonvulsant drugs such as lipophilic domain (L), hydrophobic
unit (R) and electron donor (D) system [15]. Thus the proposed
pharmacophore model for 8d includes all the above factors
important for bioactivity (Fig. 1).
3. Conclusion
In conclusion, a series of novel 1-[5-(4-methoxy-phenyl)-[1,3,4]
oxadiazol-2-yl]-piperazine derivatives 8(aeo) were synthesized in
good yield, characterized by different spectral studies and their
anticonvulsant activity have been evaluated. Various substituted
sulfonamides showed potent anticonvulsant activity. Compounds
with electron withdrawing groups and hetero aryl derivatives like
8d, 8e, 8f and 8h showed excellent anticonvulsant activity on MES
model. Therefore, the nature of groups in sulfonyl moiety is very
important for anticonvulsant activity in MES model.
4. Experimental
4.1. Chemistry
All solvents and reagents were purchased from Sigma Aldrich
Chemicals Pvt Ltd. Melting range was determined by Veego Melting
Point VMP III apparatus. Elemental analyses were recorded
on VarioMICRO superuser V1.3.2 Elementar. 1H NMR and 13C NMR
Table 2
Effect of the tested compounds in the maximal electroshock seizure test.
Table 3
Treatment
E/F
% Protection
Neurotoxicity screening of the compounds 8(aeo).
8a
8b
8c
8d
8e
8f
8g
8h
8i
8j
8k
8l
8m
8n
8o
6.29
7.11
6.34
1.91
1.96
2.11
6.96
2.34
7.64
5.49
6.11
8.15
7.68
6.51
6.57
1.98
8.21
52.42
23.34
42.40
77.64
74.31
73.47
31.54
71.25
17.32
59.64
53.01
10.63
17.03
50.79
50.43
75.88
e
Compound
Neurotoxicity screen
0.5 h
1 h
2 h
4 h
8a
8b
8c
8e
8f
8g
8h
8i
8j
8k
8l
8m
8n
8o
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
1/4
0/4
0/4
0/4
0/4
1/4
1/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
1/4
0/4
0/4
0/4
0/4
1/4
1/4
0/4
0/4
0/4
Standard
Control (Vehicle)
Values are expressed as mean, n ¼ 6 animals in each group.
Standard
E/F ¼ Extension/Flexion [Decrease in ratio of extension phase (in seconds)/flexion
phase (in seconds)].
The data in the table represent ratio between the numbers of the animals that
exhibited neurotoxicity against the number of tested animals.
% Protection ¼ (control-Test)/(Control)*100.

K.P. Harish et al. / European Journal of Medicinal Chemistry 65 (2013) 276e283
281
reaction mass by maintaining the reaction temperature ꢂ65
to ꢂ70 ꢁC. Further stirred the reaction mass for 1.0 h. Reaction
completion was monitored by TLC. Reaction mass was warmed to
around ꢂ10 ꢁC and quenched with 1.0 N HCl solution (100 mL).
Reaction mass was warmed to room temperature and the com-
pound was extracted with ethyl acetate (2 ꢃ 100 mL). Combined
organic layer was washed with water (1 ꢃ 100 mL) followed by
brine (100 mL), dried over anhydrous sodium sulphate and
concentrated to one volume stage. Compound was crystallized
using petroleum ether to yield the title compound as white solid.
D
N
N
L
O
R
O
N
O
S
F
F
N
F
O
O2N
(Yield: 22.64 g, 93%). 1H NMR (400 MHz, DMSO- d6):
d 3.72 (s, 3H,
Fig. 1. The pharmacophore model of 8d for anticonvulsant activity.
OeCH3), 7.12 (dd, J ¼ 2.11, 6.91 Hz, 2H, AreH), 7.78 (dd, J ¼ 2.12,
6.93 Hz, 2H, AreH). MS (ESI) m/z: 256.0.
spectra were recorded on Bruker DRX -500 spectrometer at
400 MHz using DMSO-d6/chloroform as solvent and TMS as an
internal standard. Mass spectral data were obtained by LC/MSD
Trap XCT. Silica gel column chromatography was performed using
Merck 7734 silica gel (60e120 mesh) and Merck-made TLC plates.
4.1.5. Preparation of tert-butyl-4-[5-(4-methoxyphenyl)-1,3,4-
oxadiazol-2-yl]piperazine-1-carboxylate (6)
To a stirred solution of 5 (20.0 g, 0.078 mol), potassium car-
bonate (32.511 g, 0.2352 mol) in dimethyl formamide (240 mL),
mano boc piperazine (17.52 g, 0.0940 mol) were added and stirred
4.1.1. Preparation of ethyl 4-methoxybenzoate (2)
the reaction mass for 10 h at room temperature. Reaction
To a stirred solution of 4-methoxy benzoic acid (25.0 g,
0.1643 mol) in ethanol (250 mL) at 0e5 ꢁC, thionyl chloride
(0.197 mol) was added. Reaction mass was heated to reflux for 5 h.
Reaction completion was monitored by TLC. It was concentrated to
syrup and diluted with ethyl acetate (250 mL). Ethyl acetate layer
was washed with saturated sodium bicarbonate solution followed
by water and brine. Combined organic layer was dried over sodium
sulphate and concentrated to get the title compound as pale yellow
completion was monitored by TLC. Reaction mass was quenched
into ice water (2.0 L), stirred at room temperature for 1 h. The solid
formed was filtered and dried to yield the above compound as
white solid (Yield: 23.73 g, 84%). 1H NMR (400 MHz, DMSO-d6):
d
1.44 (s, 9H, t-butyl-H), 3.49 (s, 8H, 2(eCH2eNeCH2e)), 3.72 (s, 3H,
OeCH3), 7.10 (dd, J ¼ 2.10, 6.82 Hz, 2H, AreH), 7.78 (dd, J ¼ 2.12,
6.83 Hz, 2H, AreH). MS (ESI) m/z: 361.4.
liquid. (Yield: 26.7 g, 90%). 1H NMR (400 MHz, DMSO-d6):
d
1.14 (t,
4.1.6. Preparation of 1-[5-(4-methoxyphenyl)-1,3,4-oxadiazol-2-yl]
piperazine hydrochloride (7)
J ¼ 7.22 Hz, 3H, CeCH3), 3.72 (s, 3H, OeCH3), 4.33 (q, J ¼ 7.9 Hz, 2H,
OeCH3), 7.08 (dd, J ¼ 2.08, 6.88 Hz, 2H, AreH), 7.80 (dd, J ¼ 2.12,
6.84 Hz, 2H, AreH). MS (ESI) m/z: 181.0.
Toastirredsolutionof6(23g, 0.088mol)in1,4dioxaneat0e50ꢁC,
4 N HCl in dioxane (40.0 mL) was added. Reaction was stirred at room
temperature for 10 h, filtered the solid and it was washed with diethyl
ether, then dried under nitrogen atmosphere and packed in air tight
container. The title compound was obtained as white hygroscopic
4.1.2. Preparation of 4-methoxybenzohydrazide (3)
Toamixtureof2(25.0g,0.1387mol)inethanol(200mL)at0e5ꢁC,
hydrazine hydrate (13.87 mL, 0.2774 mol) was added. The reaction
mass was heated to reflux for 2.0 h. The reaction completion was
monitored by TLC. The reaction mixture was cooled to 0e5 ꢁC stirred
for 60 min. The solid formed was filtered and dried to get compound 3
as white solid (Yield: 18.4 g, 80%). 1H NMR (400 MHz, DMSO- d6):
solid (Yield: 24.75 g, 90%). 1H NMR (400 MHz, DMSO- d6):
d 3.25
(s, 4H, eCH2eNeCH2e), 3.70 (s, 3H, OeCH3), 3.80 (t, J ¼ 4.00 Hz,
4H, eCH2eNeCH2e), 7.13 (dd, J ¼ 2.13, 6.92 Hz, 2H, AreH), 7.79
(dd, J ¼ 2.2, 6.89Hz, 2H, AreH), 9.42(s, br,1H, NH), 9.81(s, br, 2H, HCl).
MS (ESI) m/z: 261.3.
d
3.72 (s, 3H, OeCH3), 4.54 (s, br, 2H, NH2), 7.10 (dd, J ¼ 2.18, 6.89 Hz,
2H, AreH), 7.80 (dd, J ¼ 2.22, 6.94 Hz, 2H, AreH), 9.82 (s, br, 1H, NH).
MS (ESI) m/z: 167.1.
4.1.7. General procedure for the synthesis of 1-[5-(4-methoxy-
phenyl)-[1,3,4]oxadiazol-2-yl]-piperazine derivatives 8(aeo)
To a mixture of 7 (1.0 eq) and triethyl amine (3.5 eq) in
dichloromethane (10 volume), substituted sulphonyl chloride
(1.2 eq) was added at 5e10 ꢁC and stirred overnight at room tem-
perature. The completion of the reaction was confirmed by TLC. The
reaction mixture was poured into separating funnel washed with
water followed by brine solution, dried over anhydrous sodium
sulphate and concentrated to syrup. Crude syrup was purified by
crystallization using dichloromethane and petroleum ether to yield
the oxadiazole substituted sulfonamide as white to white solid.
4.1.3. Preparation of 2-(4-methoxyphenyl)-1,3,4-oxadiazole (4)
To a mixture of 3 (18.0 g, 0.1083 mol) and triethyl orthoformate
(80.3 g, 0.541 mol) was heated to 100e110 ꢁC and maintained for
12 h. The reaction completion was monitored by TLC. The reaction
mixture was cooled to room temperature and concentrated to syrup.
Traces triethyl orthoformate was removed by azeotropic distillation
with toluene. The residue was purified by column chromatography
on silica gel using eluent 0e5% ethyl acetate in petroleum ether. The
title compound was yielded as pale yellow liquid (Yield: 17.55 g,
92%). 1H NMR (400 MHz, DMSO-d6):
d
3.74 (s, 3H, OeCH3), 7.09
4.1.7.1. 1-(4-Bromo-3-methyl-benzenesulfonyl)-4-[5-(4-methoxy-
(dd, J ¼ 2.10, 6.90 Hz, 2H, AreH), 7.82 (dd, J ¼ 2.12, 6.92 Hz, 2H,
phenyl)-[1,3,4]oxadiazol-2-yl]-piperazine (8a). Yield: 82% (White
AreH), 9.83 (s, 1H, HeteCH). MS (ESI) m/z: 177.2.
solid); m.p.: 185 ꢁC; 1H NMR (400 MHz, DMSO-d6):
d 2.43 (s, 3H,
AreCH3),
d
3.10 (t, J ¼ 4.32 Hz, 4H, eCH2eNeCH2e), 3.63
4.1.4. Preparation of 2-bromo-5-(4-methoxyphenyl)-1,3,4-
oxadiazole (5)
(t, J ¼ 4.20 Hz, 4H, eCH2eNeCH2e),3.82 (s, 3H, OeCH3), 7.10
(dd, J ¼ 2.14, 6.90 Hz, 2H, AreH), 7.69 (dd, J ¼ 2.18, 6.79 Hz, 2H,
AreH),7.82e7.87 (m, 3H, AreH). 13C NMR (400 MHz, DMSO-d6):
To a 500 mL four necked flask was charged tetra hydro furan
(170 mL) and 4 (17.0 g, 0.096 mol). The reaction mass was cooled
to ꢂ65 to ꢂ70 ꢁC under nitrogen atmosphere with stirring and
added n-butyl lithium (50.3 mL, 2.3 M in n-hexane, 0.1157 mol) over
a period of 1 h, further reaction mass was stirred at same tem-
perature for 1.0 h. Bromine (9.2 g, 0.1157 mol) was added slowly to
d
22.4 (AreC), 44.9, 45.1 (eCH2eNeCH2e), 55.4 (OeCH3), 123.7,
125.4, 126.8, 129.3, 129.5, 130.1, 130.8, 133.3, 134.4 (AreC), 153.4
(heteC), 158.6 (AreC), 163.6 (heteC). MS (ESI) m/z: 494.04. Anal.
Calcd. for C20H21BrN4O4S: C, 48.69; H, 4.29; N, 11.36; Found: C,
48.71; H, 4.32; N, 11.45%.

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K.P. Harish et al. / European Journal of Medicinal Chemistry 65 (2013) 276e283
4.1.7.2. 1-[Biphenyl-sulfonyl]-4-(5-(4-methoxyphenyl)-1,3,4-
7.08 (dd, J ¼ 2.08, 6.88 Hz, 2H, AreH), 7.60 (dd, J ¼ 2.12, 6.84 Hz, 2H,
AreH), 7.77 (dd, J ¼ 1.72, 8.70 Hz,1H, AreH), 7.86 (dd, J ¼ 1.40, 5.26 Hz,
2H, AreH), 7.94e7.96 (m, 1H, AreH), 8.00e8.02(m, 2H, AreH), 8.38 (s,
oxadiazol-2-yl)piperazine (8b). Yield: 80% (White solid); m.p.:
171 ꢁC; 1H NMR (300 MHz, DMSO-d6):
d
3.08 (t, J ¼ 4.14 Hz, 4H, e
CH2eNeCH2e), 3.60 (t, J ¼ 5.01 Hz, 4H, eCH2eNeCH2e), 3.79
(s, 3H, OeCH3), 7.04 (dd, J ¼ 2.10, 6.91 Hz, 2H, AreH), 7.40e7.52 (m,
3H,AreH), 7.64e7.87 (m, 6H,AreH), 7.93 (d, J ¼ 8.55 Hz, 2H, AreH).
1H, AreH). 13C NMR (400 MHz, CDCl3):
d 45.1, 45.8 (eCH2eNeCH2e),
55.6(OeCH3),122.6,124.1,125.8,128.0,128.8,129.1,129.2,129.6,130.7,
132.4 (AreC),155.0(heteC),161.7(AreC),163.4(heteC). MS(ESI)m/z:
451.5. Anal. Calcd. for C23H22N4O4S: C, 61.32; H, 4.92; N,12.44; Found:
C, 61.22; H, 4.83; N, 12.52%.
13C NMR (400 MHz, DMSO-d6):
d 44.8, 45.6 (eCH2eNeCH2e), 55.3
(OeCH3), 114.6, 116.3, 125.9, 127.1, 127.6, 128.6, 129.4, 132.6, 133.6,
138.2, 144.8 (AreC), 158.5 (heteC), 161.1 (AreC), 163.0 (heteC). MS
(ESI) m/z: 476.5. Anal. Calcd. for C25H24N4O4S: C, 63.01; H, 5.08; N,
11.76; Found: C, 63.21; H, 5.12; N, 11.70%.
4.1.7.8. 1-(3,5-Dimethyl-isoxazole-4-sulfonyl)-4-[5-(4-methoxy-
phenyl)-[1,3,4]oxadiazol-2-yl]-piperazine (8h). Yield: 79% (White
solid); m.p.: 152 ꢁC; 1H NMR (400 MHz, DMSO-d6):
d 2.35 (s, 3H,
4.1.7.3. 4-{4-[5-(4-Methoxy-phenyl)-[1,3,4]oxadiazol-2-yl]-pipera-
heteCH3), 2.63 (s, 3H, heteCH3), 3.22 (t, J ¼ 4.96 Hz, 4H, eCH2eNe
CH2e), 3.63 (t, J ¼ 5.28 Hz, 4H, eCH2eNeCH2e), 3.82 (s, 3H, OeCH3),
7.08 (dd, J ¼ 2.08, 6.88 Hz, 2H, AreH), 7.80 (dd, J ¼ 2.12, 6.84 Hz, 2H,
zine-1-sulfonyl}-benzonitrile (8c). Yield: 80% (White solid); m.p.:
225 ꢁC; 1H NMR (400 MHz, DMSO-d6):
d 3.12 (s, br, 4H, eCH2eNe
CH2e), 3.58 (s, br, 4H, CH2eNeCH2e), 3.79 (s, 3H, OeCH3), 7.04
(d, J ¼ 8.55 Hz, 2H, AreH), 7.75 (d, J ¼ 8.58 Hz, 2H, AreH), 7.93
(d, J ¼ 8.16 Hz, 2H, AreH), 8.12 (d, J ¼ 8.13 Hz, 2H, AreH).
AreH). 13C NMR (400 MHz, CDCl3):
d 11.4, 13.1 (heteCH3) 44.6, 46.1
(eCH2eNeCH2e), 55.8 (OeCH3), 112.7, 115.1, 116.9, 127.6 (AreC),
158.0, 159.0, 161.6 (heteC),163.5 (AreC), 174.7 (heteC). MS (ESI) m/z:
420.4. Anal. Calcd. for C18H21N5O5S: C, 51.54; H, 5.05; N, 16.70;
Found: C, 51.64; H, 5.12; N, 16.63%.
13C NMR (400 MHz, DMSO-d6):
d 45.1, 45.6 (eCH2eNeCH2e),
55.8 (OeCH3), 115.0 (eCN), 116.2, 116.8, 118.0, 127.6, 128.6, 134.1,
139.8 (AreC), 159.0 (heteC), 161.5 (AreC), 163.5 (heteC). MS (ESI)
m/z: 426.4. Anal. Calcd. for C20H19N5O4S: C, 56.46; H, 4.50; N, 16.46;
Found: C, 56.53; H, 4.43; N, 16.65%.
4.1.7.9. 1-(4-Tert-butyl-benzenesulfonyl)-4-[5-(4-methoxy-phenyl)-
[1,3,4]oxadiazol-2-yl]-piperazine (8i). Yield: 79% (White solid);
m.p.: 187 ꢁC; 1H NMR (400 MHz, DMSO-d6):
d 1.14 (s, 9H, t-butyl H),
4.1.7.4. 1-[5-(4-Methoxy-phenyl)-[1,3,4]oxadiazol-2-yl]-4-(2-nitro-
3.13 (s, br, 4H, eCH2eNeCH2e), 3.58 (s, br, 4H, eCH2eNeCH2e),
3.79 (s, 3H, OeCH3), 7.04 (d, J ¼ 8.55 Hz, 2H, AreH), 7.75 (d,
J ¼ 8.58 Hz, 2H, AreH), 7.93 (d, J ¼ 8.16 Hz, 2H, AreH), 8.12 (d,
4-trifluoromethyl-benzene sulfonyl)-piperazine (8d). Yield: 79%
(White solid); m.p.: 193 ꢁC; 1H NMR (400 MHz, DMSO-d6):
d 3.41 (t,
J ¼ 4.95 Hz, 4H, eCH2eNeCH2e), 3.60 (t, J ¼ 5.22 Hz, 4H, eCH2eNe
CH2e), 3.80 (s, 3H, OeCH3), 7.06 (d, J ¼ 8.91 Hz, 2H, AreH), 7.79 (d,
J ¼ 8.88 Hz, 2H, AreH), 8.25 (d, J ¼ 8.82 Hz, 2H, AreH), 8.65 (s, 1H,
J ¼ 8.13 Hz, 2H, AreH). 13C NMR (400 MHz, DMSO-d6):
d 31.2, 41.3
(t-butyl C), 45.1, 45.6 (eCH2eNeCH2e), 55.8(OeCH3), 115.0, 116.2,
118.0, 127.6, 128.6, 134.1, 139.8 (AreC), 158.0 (heteC), 161.5 (AreC),
163.5 (heteC). MS (ESI) m/z: 457.5. Anal. Calcd. for C23H28N4O4S: C,
60.51; H, 6.18; N, 12.27; Found: C, 60.44; H, 6.24; N, 12.31%.
AreH). 13C NMR (400 MHz, DMSO-d6):
d 45.0, 45.9 (eCH2eNeCH2e
), 55.8 (OeCH3),115.0,116.8,122.4 (AreC),124.5 (CeF3),127.6,129.8,
132.4, 134.3, 134.8, 148.4 (AreC), 159.1 (heteC), 161.6 (AreC), 163.5
(heteC). MS (ESI) m/z: 514.4. Anal. Calcd. for C20H18F3N5O6S: C,
46.78; H, 3.53; N, 13.64; Found: C, 46.84; H, 3.63; N, 13.73%.
4.1.7.10. 1-[5-(4-Methoxy-phenyl)-[1,3,4]oxadiazol-2-yl]-4-(2-nitro-
benzenesulfonyl)-piperazine (8j). Yield: 78% (Off white solid); m.p.:
175 ꢁC; 1H NMR (400 MHz, DMSO-d6):
d
3.37 (t, J ¼ 4.72 Hz, 4H, e
4.1.7.5. 1-[5-(4-Methoxy-phenyl)-[1,3,4]oxadiazol-2-yl]-4-(4-
phenoxy-benzenesulfonyl) piperazine (8e). Yield: 83% (White solid);
CH2eNeCH2e), 3.61 (t, J ¼ 5.20 Hz, 4H, eCH2eNeCH2e), 3.81 (s,
3H, OeCH3), 7.07 (dd, J ¼ 1.84, 8.42 Hz, 2H, AreH), 7.80 (dd, J ¼ 2.00,
8.34 Hz, 2H, AreH), 7.85e7.94 (m, 2H, AreH), 8.00e8.05 (m, 2H,
m.p.: 151 ꢁC; 1H NMR (400 MHz, DMSO- d6):
d
3.06 (t, J ¼ 4.84 Hz,
4H, eCH2eNeCH2e), 3.63 (t, J ¼ 5.24 Hz, 4H, eCH2eNeCH2e), 3.71
(s, 3H, OeCH3), 7.16 (dd, J ¼ 1.92, 6.80 Hz, 4H, AreH), 7.25e7.29 (m,
1H, AreH), 7.44e7.49 (m, 2H, AreH), 7.51e7.56 (m, 2H, AreH), 7.76
(dd, J ¼ 2.04, 6.86 Hz, 2H, AreH), 7.84e7.89 (m, 2H, AreH). 13C NMR
AreH). 13C NMR (400 MHz, DMSO-d6):
d 45.1, 45.9 (eCH2eNeCH2e
), 55.8 (OeCH3), 115.0, 116.8, 124.7, 127.6, 129.5, 130.8, 132.9, 135.4,
148.3 (AreC), 159.1 (heteC), 161.6 (AreC), 163.6 (heteC). MS (ESI)
m/z: 446.4. Anal. Calcd. for C19H19N5O6S: C, 51.23; H, 4.30; N, 15.72;
Found: C, 51.34; H, 4.23; N, 15.83%.
(400 MHz, DMSO-d6): d 45.3, 45.5 (eCH2eNeCH2e), 55.3 (OeCH3),
118.1, 120.7, 124.4, 125.5, 125.8, 129.0, 129.6, 130.6, 130.9, 131.2
(AreC), 155.0, 159.0 (heteC), 161.7 (AreC), 163.8 (heteC). MS (ESI)
m/z: 493.1. Anal. Calcd. for C25H24N4O5S: C, 60.96; H, 4.91; N, 11.37;
Found: C, 60.85; H, 4.78; N, 11.46%.
4.1.7.11. 1-[5-(4-Methoxy-phenyl)-[1,3,4]oxadiazol-2-yl]-4-(3-
trifluoromethyl-benzenesulfonyl)-piperazine (8k). Yield: 79% (Off
white solid); m.p.: 185 ꢁC; 1H NMR (400 MHz, DMSO-d6):
d 3.15 (t,
J ¼ 4.40 Hz, 4H, eCH2eNeCH2e), 3.60 (t, J ¼ 5.20 Hz, 4H, eCH2eNe
CH2e), 3.81 (s, 3H, OeCH3), 7.07 (dd, J ¼ 1.84, 8.42 Hz, 2H, AreH),
7.76 (dd, J ¼ 2.00, 8.34 Hz, 2H, AreH), 7.90e7.94 (m, 1H, AreH), 8.00
(s, 1H, AreH), 8.09e8.14 (m, 2H, AreH). 13C NMR (400 MHz, DMSO-
4.1.7.6. 1-(2,5-Dichloro-thiophene-3-sulfonyl)-4-[5-(4-methoxy-
phenyl)-[1,3,4]oxadiazol-2-yl]-piperazine (8f). Yield: 80% (White
solid); m.p.: 187 ꢁC; 1H NMR (300 MHz, DMSO-d6):
d 3.30 (t,
J ¼ 3.42 Hz, 4H, eCH2eNeCH2e), 3.59 (t, J ¼ 4.50 Hz, 4H, eCH2eNe
CH2e), 3.80 (s, 3H, eOeCH3), 7.06 (d, J ¼ 8.46 Hz, 2H, AreH), 7.39
(s, 1H, heteH), 7.78 (d, J ¼ 8.49 Hz, 2H, AreH). 13C NMR (400 MHz,
d6): d 45.2, 46.0 (eCH2eNeCH2e), 55.8 (OeCH3), 115.0, 116.8, 124.2
(AreC),124.3 (AreCF3),127.6,130.6,130.8,131.7,132.0,137.0 (AreC),
159.0 (heteC), 161.6 (AreC), 163.5 (heteC). MS (ESI) m/z: 469.4.
Anal. Calcd. for C20H19F3N4O4S: C, 51.28; H, 4.09; N, 11.96; Found: C,
51.11; H, 4.15; N, 11.84%.
DMSO-d6): d 45.1, 45.6 (eCH2eNeCH2e), 55.8 (OeCH3), 115.1, 116.9
(AreH), 127.3, 127.5, 127.6 (heteC), 131.0 (AreC), 132.8, 159.0 (hete
C), 161.6(AreC), 163.5 (heteC). MS (ESI) m/z: 476.3. Anal. Calcd. for
C
17H16Cl2N4O4S2: C, 42.95; H, 3.39; N, 11.79; Found: C, 42.86; H,
4.1.7.12. 1-Methanesulfonyl-4-[5-(4-methoxy-phenyl)-[1,3,4]oxadia-
3.43; N, 11.83%.
zol-2-yl]-piperazine (8l). Yield: 80% (Off white solid); m.p.: 169 ꢁC;
1H NMR (400 MHz, DMSO-d6):
d 2.84 (s, 3H, SeCH3), 3.10 (t,
4.1.7.7. 1-[5-(4-Methoxy-phenyl)-[1,3,4]oxadiazol-2-yl]-4-(naphtha-
J ¼ 4.32 Hz, 4H, eCH2eNeCH2e), 3.40 (t, J ¼ 5.10 Hz, 4H, eCH2eNe
CH2e), 3.71 (s, 3H, OeCH3), 7.10 (dd, J ¼ 1.92, 8.42 Hz, 2H, AreH),
7.86 (dd, J ¼ 2.00, 8.34 Hz, 2H, AreH). 13C NMR (400 MHz, DMSO-
lene-1-sulfonyl)-piperazine (8g). Yield: 78% (White solid); m.p.:
167 ꢁC;1HNMR(400 MHz, CDCl3):
CH2-), 3.74 (t, J ¼ 5.32 Hz, 4H, eCH2eNeCH2e),3.90 (s, 3H, OeCH3),
d
3.26(t, J ¼ 5.00 Hz,4H, eCH2eNe
d6): d 39.6 (s-CH3), 45.4, 46.1 (eCH2eNeCH2e), 55.7 (OeCH3), 117.0,

K.P. Harish et al. / European Journal of Medicinal Chemistry 65 (2013) 276e283
283
124.2, 128.1 (AreC), 157.0 (heteC), 159.8 (AreC), 163.5 (heteC). MS
(ESI) m/z: 339.4. Anal. Calcd. for C14H18N4O4S: C, 49.69; H, 5.36; N,
16.56; Found: C, 49.83; H, 5.26; N, 16.72%.
Seizures were induced in rats by delivering electroshock of 150 mA
for 0.2 s by means of a convulsiometer through a pair of ear clip
electrodes. The test compounds (100 mg/kg) were administered by
oral route in the form of solution (The compounds were dissolved
in 1% sodium carboxymethyl cellulose), 30 min before the maximal
electroshock seizure test. The animals were observed closely for
2 min. The percentage of inhibition of seizure relative to control
was recorded and calculated [16]. Phenytoin (100 mg/kg) was used
as a standard drug.
Neurotoxicity screening: The minimal motor impairment was
measured in mice by the rotorod test. Acute neurological toxicity in
mice was evaluated by rotorod test [16]. The mice were trained to
stay on the accelerating rotorod that rotates at 10 revolutions per
minute. The rod diameter was 3.2 cm. Trained animals were
administered with the test compounds at dose of 100 mg/kg.
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 trails. Phenytoin was used as a standard drug.
4.1.7.13. 1-[5-(4-Methoxy-phenyl)-[1,3,4]oxadiazol-2-yl]-4-(toluene-
4-sulfonyl)-piperazine (8m). Yield: 80% (Off white solid); m.p.:
161 ꢁC; 1H NMR (400 MHz, DMSO-d6):
d 2.2 (s, 3H, AreCH3) 3.13
(s, br, 4H, eCH2eNeCH2e), 3.60 (s, br, 4H, eCH2eNeCH2e), 3.79
(s, 3H, OeCH3), 7.04 (d, J ¼ 8.55 Hz, 2H, AreH), 7.75 (d, J ¼ 8.58 Hz,
2H, AreH), 7.93 (d, J ¼ 8.16 Hz, 2H, AreH), 8.12 (d, J ¼ 8.13 Hz, 2H,
AreH). 13C NMR (400 MHz, DMSO-d6):
d 28.3 (AreCH3), 45.1, 45.6
(eCH2eNeCH2e), 55.8, 115.0, 116.2, 118.0, 127.6, 128.6, 134.1, 139.8
(AreC), 159.0 (heteC), 161.5 (AreC), 163.5 (heteC). MS (ESI) m/z:
415.5. Anal. Calcd. for C20H22N4O4S: C, 57.96; H, 5.35; N, 13.52;
Found: C, 58.02; H, 5.57; N, 13.42%.
4.1.7.14. 1-(4-Bromo-benzenesulfonyl)-4-[5-(4-methoxy-phenyl)-
[1,3,4]oxadiazol-2-yl]-piperazine (8n). Yield: 80% (Off white solid);
m.p.: 211 ꢁC; 1H NMR(400 MHz, DMSO-d6):
d
3.06 (t, J ¼ 3.30 Hz,
Statistical analysis: In the present study, data were analyzed by
one way analysis of variance (ANOVA) followed by dunnet test to
compare difference between the groups.
4H, eCH2eNeCH2e), 3.45 (t, J ¼ 3.90 Hz, 4H, eCH2eNeCH2e), 3.80
(s, 3H, OeCH3), 7.05 (d, J ¼ 8.85 Hz, 2H, AreH), 7.68 (d, J ¼ 8.58 Hz,
2H, AreH), 7.76 (d, J ¼ 8.79 Hz, 2H, AreH), 7.86 (d, J ¼ 8.55 Hz, 2H,
AreH). 13C NMR (400 MHz, DMSO-d6):
d 45.2, 45.6 (eCH2eNeCH2e
Acknowledgements
), 55.8 (OeCH3), 115.1, 116.8, 127.6, 127.9, 129.9, 133.1, 134.8 (AreC),
159.0 (heteC), 161.6 (AreC), 163.5 (heteC). MS (ESI) m/z: 480.3.
Anal. Calcd. for C19H19BrN4O4S: C, 47.61; H, 4.00; N, 11.69; Found: C,
47.79; H, 4.34; N, 11.82%.
Authors thank Dr. B. Veeresh, B. Madhava Reddy and Nagula
Naresh Kumar, Department of Pharmacology and Toxicology, G
Pulla Reddy College of Pharmacy, Hyderabad, India to carryout
Anticonvulsant activity.
4.1.7.15. 1-(4-Iodo-benzenesulfonyl)-4-[5-(4-methoxy-phenyl)-
[1,3,4]oxadiazol-2-yl]-piperazine (8o). Yield: 80% (Off white solid);
m.p.: 208 ꢁC; 1H NMR (400 MHz, DMSO-d6):
d
3.10 (t, J ¼ 3.34 Hz,
References
4H, eCH2eNeCH2e), 3.46 (t, J ¼ 3.92 Hz, 4H, eCH2eNeCH2e), 3.80
(s, 3H, OeCH3), 7.15 (d, J ¼ 8.83 Hz, 2H, AreH), 7.69 (d, J ¼ 8.57 Hz,
2H, AreH), 7.78 (d, J ¼ 8.75 Hz, 2H, AreH), 7.85 (d, J ¼ 8.56 Hz, 2H,
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d 45.1, 45.5 (eCH2eNeCH2e
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158.9 (heteC), 161.6 (AreC), 163.4 (heteC). MS (ESI) m/z: 527.0.
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with Committee for the Purpose of Control and Supervision of
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reviewed and approved by the Institutional Animal Ethics Com-
mittee, G Pulla Reddy College of Pharmacy, Hyderabad, India.
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