Synthesis and anticonvulsant activity of sulfonamide derivatives-hydrophobic domain

Article abstract of DOI:10.1016/j.bmcl.2006.09.053

A series of sulphonamide derivatives (1-11) were synthesized in good yield and evaluated for their possible anticonvulsant activity and neurotoxic study. The structures of the synthesized compounds were confirmed on the basis of their spectral data and elemental analysis. Majority of the compounds were active in MES and scPTZ tests. All the compounds were less toxic than the standard drug phenytoin.

Full text of DOI:10.1016/j.bmcl.2006.09.053

Bioorganic & Medicinal Chemistry Letters 17 (2007) 255–259
Synthesis and anticonvulsant activity of sulfonamide
derivatives-hydrophobic domain
Nadeem Siddiqui,a,* Surendra N. Pandeya,b Suroor A. Khan,a James Stables,c
Arpana Rana,a Mahfuz Alam,a Md. Faiz Arshada and Mashooq A. Bhata
aDepartment of Pharmaceutical Chemistry, Faculty of Pharmacy, Jamia Hamdard, Hamdard Nagar, New Delhi-110 062, India
bDr. K. N. Modi Institutes of Pharmaceutical Education and Research, Modinagar, 201 201 UP, India
cAntiepileptic Drug Development (ADD) Programme, Epilepsy Branch, National Institute of Health, Rockville, MD, USA
Received 10 April 2006; revised 5 September 2006; accepted 19 September 2006
Available online 13 October 2006
Abstract—A series of sulphonamide derivatives (1–11) were synthesized in good yield and evaluated for their possible anticonvulsant
activity and neurotoxic study. The structures of the synthesized compounds were confirmed on the basis of their spectral data and
elemental analysis. Majority of the compounds were active in MES and scPTZ tests. All the compounds were less toxic than the
standard drug phenytoin.
Ó 2006 Elsevier Ltd. All rights reserved.
Epilepsy has been recognized as a neurological disorder,
affecting a large section of people both male and female
across the world. Every year approximately 2,50,000
new cases are added to this figure. Many patients have
seizures that are resistant to the available medical ther-
apies. Newer drugs such as flupirtine,1 topiramate,2 zon-
isamide,3 and vigabatrin4 have emerged as promising
anticonvulsants. Despite introduction of these new
drugs women of child bearing age and chronic patients
face specific problems of neurotoxicity, symptoms of
depression, and CNS related ailments. Therefore, it is
essential to search for newer chemical entities for the
treatment of epilepsy.
fonamide derivative, which is indicated as an adjunct
for partial seizures in patients over 12 years where sei-
zures are not controlled by first line drugs. During the
study of semicarbazones as potential anticonvulsant
agents, Pandeya7 has proposed the identifiable features
for anticonvulsant activity like (i) hydrophobic aryl ring,
(ii) a hydrogen bonding domain, (iii) an electron-donor
group, and (iv) another distal hydrophobic site. To test
this hypothesis the size of the hydrophobic aryl ring has
been varied to include indole nucleus with active
compounds.
In the present study, we describe the synthesis of phenyl
and benzothiazoles as potential hydrophobic aryl rings
and inclusion of sulfamido functionality resembling
the structure of zonisamide. The thioureido moiety
was introduced in the structures to increase the lipophil-
icity of the molecules.
Quite recently, semicarbazones are an emerging new
class of potent anticonvulsants.5,6 More than 300 com-
pounds have been prepared and tested in animal models.
Representative semicarbazones, like 4-bromobenzalde-
hyde semicarbazone, have been shown to have activity
comparable with or exceeding that of phenytoin (Dilan-
tin) in the maximal electroshock (MES)-induced seizure
test in mice. The MES test is a model, for example, gen-
eralized tonic–clonic seizures and identifies compounds
that prevent seizure spread and phenytoin is considered
as the prototypical in this model. Zonisamide is a sul-
Synthesis of N-(6-substituted-1,3-benzothiazol-2-yl)-4-
{[(substituted amino) carbonothioyl] amino} benzene
sulfonamides (1–6) involves condensation of the 2-ami-
no-6-substituted benzothiazoles with p-acetamidoben-
zenesulfonyl chloride to get condensed product N-(4-
{[(6-fluoro-1,3-benzothiazol-2-yl) amino] sulfonyl}
phenyl) acetamide. 2-Amino-6-substituted benzothiaz-
oles were synthesized according to the known protocol.8
The acetamido group was hydrolyzed with acetic acid to
give free amino group. Further the free amino group
was condensed with different isothiocyanates to get the
Keywords: Sulfonamide; Benzothiazole; Anticonvulsant.
*
Corresponding author.
nadeems_03@yahoo.co.in
Tel.:
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doi:10.1016/j.bmcl.2006.09.053

256
N. Siddiqui et al. / Bioorg. Med. Chem. Lett. 17 (2007) 255–259
desired compounds9 (1–6) (Scheme 1). Similarly N-(3-
substituted phenyl)-4-{[‘substituted’ amino carbono-
thionyl] amino} benzene sulfonamides10 (7–11) were
prepared from p-substituted anilines according to
Scheme 2. All the synthesized compounds were well
characterized by elemental analysis and spectroscopic
data. The physical data of all the synthesized com-
pounds are given in (Table 1).
O
S
O
R1
NH2
+
Cl
N
CH3
H
O
a
O
O
R1
N
H
N
H
S
The anticonvulsant evaluation was undertaken using
reported procedures.11,12 Male albino mice (CF-1 strain
or Swiss, 18-258) and rats (Spraque–Dawley or Wistar,
100–150 g) were used as experimental animals. The test-
ed compounds were suspended in 0.5% methyl cellulose–
water mixture or in polyethylene glycol (PEG).
CH3
O
b
O
MES—maximal electroshock seizure test: maximal elec-
troshock seizures were elicited with a 60 cycle altering
current of 50 mA intensity (5–7 times that necessary to
elicit minimal electroshock seizures) delivered for
R1
N
S
NH2
H
O
c
S
O
O
O
S
N
S
R1
N
H
N
H
S
NH
R2
+
NH2
Cl
a
N
CH3
H
R1
O
O
R1
R2
CH 3
7
8
9
Cl
Cl
Br
O
O
S
N
S
CH3
N
H
N
H
CH3
CH 3
R1
O
CH3
CH3
10 Br
b
11 CH3
Scheme 2. Reagents and conditions: (a) pyridine/Ac2O; (b)
CH3COOH (80%) boiling 6 h; (c) R2 NCS, EtOH/reflux, 2 h.
O
N
N
H
S
NH2
S
R1
O
0.25 s via corneal electrodes. A drop of 0.9% saline
was instilled in the eye prior to application of the elec-
trodes in order to prevent the death of the animal. Abo-
lition of the hind limb tonic extensor component of the
seizure is defined as protection, and results are expressed
as number of animal protected/number of animals
tested.
c
S
O
S
N
N
N
NH
R2
H
H
S
R1
O
R2
R1
NT—neurotoxicity: the rotorod test was used to evalu-
ate neurotoxicity. The animal was placed on a 3.2 cm
diameter Knurled rod rotating at 6 rpm. Normal mice
can remain on a rod rotating at this speed indefinitely.
Neurological toxicity is defined as the failure of the ani-
mal to remain on the rod for 1 min. and is expressed as
number of animals exhibiting toxicity/number of ani-
mals tested.
1
2
3
4
5
6
F
F
CH3
C2H5
CH3
C2H5
Cl
Cl
OCH3 CH3
OCH3 C2H5
The sulfonamido benzothiazoles were initially
screened at 30, 100, and 300 mg/kg intraperitoneally
in mice for anticonvulsant activity (Table 2). All
Scheme 1. Reagents and conditions: (a) pyridine/Ac2O; (b)
CH3COOH (80%) boiling 6 h; (c) R2 NCS, EtOH/reflux, 2 h.

N. Siddiqui et al. / Bioorg. Med. Chem. Lett. 17 (2007) 255–259
Table 1. Physical data of compounds (1–11)
257
Compound
R1
R2
Molecular formula
Found (Cal.) %
H
Yield%
Mp °C
Rfa
C
N
1
2
3
4
5
6
7
F
CH3
C2H5
CH3
C2H5
CH3
C2H5
CH3
C15H13 FN4O2S3
C16H15FN4O2S3
C15H13ClN4O2S3
C16H15ClN4O2S3
C16H16N4O3S3
45.41 (45.44)
46.43 (46.83)
44.04 (43.64)
45.42 (45.02)
46.66 (47.06)
48.04 (48.34)
49.07 (49.49)
3.36 (3.30)
3.25 (3.65)
3.54 (3.14)
3.11 (3.51)
3.51 (3.91)
4.46 (4.26)
4.50 (4.12)
14.20 (14.13)
14.04 (13.64)
13.16 (13.56)
13.42 (13.12)
13.41 (13.71)
13.35 (13.25)
12.76 (12.37)
50
70
58
54
55
52
68
220
226
232
230
235
215
150
0.92
0.90
0.86
0.90
0.79
0.94
0.70
F
Cl
Cl
OCH3
OCH3
Cl
C17H18N4O3S3
C14H14ClN3O2S2
8
Cl
C20H18ClN3O2S2
57.35 (57.76)
4.74 (4.33)
10.52 (10.10)
70
160
0.75
CH3
9
Br
Br
CH3
C14H14BrN3O2S3
C20H18BrN3O2S2
44.19 (43.76)
52.57 (52.18)
3.26 (3.64)
3.54 (3.91)
10.51 (10.94)
9.57 (9.13)
60
65
140
130
0.80
0.87
10
CH3
CH3
11
CH3
C21H21N3O2S2
63.37 (63.79)
5.73 (5.31)
10.22 (10.63)
60
119
0.80
a Solvent system: toluene/ethylacetoacetate/formic acid (5:4:1).
Table 2. Anticonvulsant activity and minimal motor impairment of sulfonamido derivatives
Compound
Intraperitoneal injection in micea
Neurotoxicity screen
MES
scPTZ
0.5 h
4.0 h
0.5 h
4.0 h
1
300
300
—
—
—
—
—
—
—
—
—
—
2
300
—
3
100
30
300
300
—
—
—
300
300
—
4
—
—
—
5
300
—
—
—
—
—
6
—
—
b
—
7
300
100
300
100
300
30
300
300
300
300
300
300
300
—
300
300
300
300
300
100
—
300
300
—
c
8
d
9
10
—
—
—
—
—
—
—
300
300
30
300
—
11
Phenytoin
Ethosuximide
Carbamazepine
Valporic acid
100
—
—
—
—
300
100
300
30
100
—
300
—
—
—
a Doses of 30, 100, and 300 mg/kg were administered, the figures in the table indicate the minimum dose whereby bioactivity was demonstrated in half
or more of the mice. The animals were examined 0.5 and 4.0 h after injection was made. The dash (—) indicates an absence of activity at maximum
dose administered (300 mg kg).
b Exhibited activity (2/5 after 4.25 and 5.0 h).
c Exhibited activity (2/5 and 1/5 after 4.25 and 5.0 h, respectively).
d Exhibited activity (1/3) after 4.25 and 5.0 h.
the compounds, except 6, exhibit anticonvulsant
activity. Majority of the compounds, except 1 and
5, were active in both MES and scPTZ tests making
them useful for broad spectrum of seizure types. In
the MES test compounds 8 and 10 with chloro-
and bromo substituents showed activity at 100 mg/kg
after 0.5 h. On the other hand, compounds 1, 2, 5,
7, 9, and 11 showed protection in mice at the dose
level of 300 mg/kg after 0.5 h. Some compounds like
7, 8, 10 and 11 were also active after 4.0 h extended
period of activity. Compounds 3 and 4 with chloro
substitution in the benzothiazole molecules were ac-
tive at lower doses of 100 and 30 mg/kg, respectively,
after 4.0 h. Thus, compound 4 showing activity at a
lower dose of 30 mg/kg seems to be very potent in
anticonvulsant MES screening. scPTZ screen is useful
for petitmal seizures. Majority of the compounds also
showed activity in scPTZ screen. Compounds 2, 7, 8,
9, 10, and 11 showed activity at 300 mg/kg after
0.5 h. However, compounds 3 and 4 showed activity
at 300 mg/kg after 4 h. Compounds showing activity
in scPTZ test were comparable to standard drug eth-
osuximide (300 mg/kg). Some of the selected com-
pounds 3 and 4 were further tested in oral MES
screen using rats at 30 mg/kg (Table 3) in which com-
pound 3 exhibited bioactivity throughout the time
period up to 4.0 h similar to phenytoin. Compound
4 also showed some activity after 4.0 h.

258
N. Siddiqui et al. / Bioorg. Med. Chem. Lett. 17 (2007) 255–259
Table 3. Evaluation of some components in the MES test after oral
administration (30 mg/kg) to rats
at a dose level of 300 mg/kg. The fluoro- and meth-
oxy-containing compounds were inactive. Compound
8 has shown activity in MES test at 100 mg/kg imme-
diately after 0.5 h. Compound 8 also exhibited activity
at 100 mg/kg in scPTZ test. The rapid onset of action
is believed to be due to the substitution of more lipo-
philic tolyl group in the distal thioureido moiety. Evi-
dently, this distal hydrophobic centre alters the
bioavailability of the compounds. These findings con-
firm to our hypothesis of action of anticonvulsant
compounds.
Compound
Time (h) Oral administration to ratsa
0.25
0.5
1.0
2.0
4.0
3
1
0
1
1
0
4
1
0
3
2
1
3
3
1
3
4
Phenytoin
a The figures indicate the number of rats out of four which were pro-
tected. Both compounds 3 and 4 exhibited no toxicity at dose of
30 mg/kg up to 4.0 h.
In conclusion from this study, it is quite apparent that
there are at least four parameters for the activity of
anticonvulsant drugs, that is, (i) a lipophilic domain,
(ii) a distal hydrophobic center whose size affects the
pharmacokinetic property, (iii) SO2NH-group acts as
a hydrogen donor, and (iv) a two-electron donor
(–C@N–) system is also present. Hydrophobic size ap-
pears to govern the MES or scPTZ activity. If there is
larger hydrophobic moiety as in chloro versus bromo,
then MES activity is favored. Compound 9 with a
bromo group shows anticonvulsant activity in MES
test after 4.25 and 5.0 h as compared with compound
7 with chloro substituents. These results further con-
firm our observation and proposals5 for a pharmaco-
phore model and modifying the size of the
hydrophobic domain (A) (Fig. 1). The structure of
benzothiazole derivatives can be superimposed on the
structure of zonisamide, a potent clinically effective
drug to see the geometrical requirements of pharmaco-
phore molecules for anticonvulsant drugs hitherto un-
known (Fig. 2).
In the rotorod neurotoxicity screening compounds 1, 2,
5, and 6 did not show any toxicity at the dose 300 mg/kg.
Compounds 7, 8, and 10 were toxic at 0.5 and 4.0 h.
Whereas compounds 9 and 10 showed toxicity only after
0.5 h and did not show toxicity after 4.0 h. Two com-
pounds 3 and 4 showed delayed toxicity that is toxicity
only after 4.0 h, which is comparable with that of car-
bamazepine (300 mg/kg). However, all the compounds
were less toxic than phenytoin (100 mg/kg).
The bioactivity in MES test exhibited by chloro-
substituted derivative 8 demonstrated that of the
hydrophobic center could be expanded to greater size
than the phenyl ring. The compound 3 has shown
good oral activity for a longer duration of action. It
has also shown activity in the scPTZ screen. Thus,
it has shown broad-spectrum of activity. On the other
hand, compound 4 had shown activity at a lower
dose of 30 mg/kg in the MES test again with longer
duration of activity. The only difference being the
substitution in the thioureido moiety, while 3 has
methyl group, 4 has more lipophilic ethyl group.
Again the compound 4 has also exhibited activity in
the scPTZ test. Both these compounds were not toxic
The synthesized compounds confirmed the pharmaco-
phore model requirements for activity such as A, hydro-
phobic domain; C, distal hydrophobic domain in some
compounds like 8, 10, and 11 of the series 6–11, and
D, electron donor moiety (NH) in all the synthesized
compounds.
Acknowledgments
Authors are thankful to Antiepileptic drug development
(ADD) Programme, Epilepsy Branch, National Institute
of Health, Rockville, Maryland, USA, for anticonvul-
sant evaluation and University Grants Commission
(UGC, Government of India) for providing financial
assitance.
Figure 1. Suggested pharmacophore model for anticonvulsant activity.
(A) Hydrophobic domain, (B) hydrogen bonding site, (C) distal
hydrophobic domain, and (D) electron donor moiety.
Figure 2. Superimposed structures of zonisamide on benzothiazole derivatives.

N. Siddiqui et al. / Bioorg. Med. Chem. Lett. 17 (2007) 255–259
259
product N-(6-fluoro-1,3-benzothiazol-2-yl)-4-{[(substitut-
ed amino) carbonothioyl] amino} benzene sulfonamide 2
so obtained was filtered and recrystallized from chloro-
form and DMSO. Yield: 70%; mp °C: 220; FT-IR (KBr)
cmÀ1: 3300–3250 (NH); 1300(SO2NH2); 1200(C@S); 1H
NMR (DMSO-d6) d ppm: 2.19 (q, 2H, CH2): 3.44(t, 3H,
CH3): 7.20–7.84 (m, 7H, Ar–H); 12.31 (s, 3H, NH).
References and notes
1. van Bebenburg, W.; Steinmetz, G.; Thielek, K. Chem. Ztg.
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3. Kubota, M.; Nishi-Nagase, M.; Sakakihora, Y. Brain Dev.
2000, 22, 230.
4. French, J. A. Epilepsia 1999, 40, 11.
10. Typical procedure: p-chloroaniline (1.27 g, 0.01 mol) was
taken in
a mixture of pyridine (4 ml) and acetic
anhydride (20 ml). To this mixture p-acetamidobenzene
sulfonyl chloride (2.33 g, 0.01 mol) was added and the
mixture was heated for 2 h on a water bath. The
reaction mixture was filtered and crystallized from
ethanol (80%). Prepared N-(4-{[(3-chlorophenyl)ami-
no]sulfonyl}phenyl)acetamide was hydrolyzed by boiling
it in (50 ml) of 80% acetic acid for 6 h to obtain the
product. The final product N-(3-chlorophenyl)-4-
{[(methylamino) carbonothionyl] amino} benzene sul-
5. Micale, N.; Zappala, M.; Zuccala, G.; Menniti, F. S.;
Ferreri, G.; De Sarro, G.; Grasso, S. Farmaco 2005, 60,
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vendran, J. V.; Sudhan, K.; Pavana, R. K.; Stables, J.
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8. Nadkarni, A. B.; Kamath, R. V.; Khadse, G. B. Ind. J.
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fonamide
7 was obtained by refluxing hydrolyzed
product 4-amino-N-(3-chlorophenyl) benzene sulfon-
amide (1.69 g, 0.006 mol) in ethanol (25 ml) with methyl
isothiocynate (0.438 g, 0.006 mol) for 2 h. The solid
product was filtered and recrystallized from ethanol.
Yield: 68%; mp °C: 150; FT-IR (KBr) cmÀ1: 3313–3204
(NH); 1172 (C@S), 1310 (NHSO2); 1H NMR (DMSO-
d6) d ppm: 7.58–7.61 (d, 4H, J = 14 Hz, Ar–H); 7.32–
7.35 (d, 4H, J = 14 Hz, Ar–H); 2.04 (s, 3H, CH3);
10.07(s, 3H, NH, NHC@S).
9. Typical procedure: the respective benzothiazole (1.7 g,
0.01 mol) was taken in a mixture of pyridine (4 ml) and
acetic anhydride (20 ml). To this mixture p-acetamidoben-
zenesulphonyl chloride (2.5 g, 0.01) was added and the
mixture was heated for 2 h on a water bath. The reaction
mixture was poured onto 30 ml of water; the solid product
obtained was filtered and crystallized from ethanol (80%).
Prepared N-(4-{[(6-fluoro-1,3-benzothiazol-2-yl) amino]
sulfonyl} phenyl) acetamide was hydrolyzed by boiling it
in (50 ml) of 80% acetic acid for 6 h to obtain the product.
Further 4-amino-N-(6-fluoro-1,3-benzothiazol-2-yl)ben-
zene sulfonamide hydrolyzed product was refluxed in
ethanol (25 ml) with ethyl isothiocyanate for 2 h. The final
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