Benzothiazole incorporated barbituric acid derivatives: Synthesis and anticonvulsant screening

Article abstract of DOI:10.1002/ardp.200900002

A series of 1-(6-substituted-1,3-benzothiazol-2-yl)-3-(substituted phenyl)hexahydro-2,4,6-pyrimidinetriones 4a-t were synthesized starting from substituted anilines. These compounds contained two active anticonvulsant pharmacophores, benzothiazole and bar

Full text of DOI:10.1002/ardp.200900002

462
Arch. Pharm. Chem. Life Sci. 2009, 342, 462–468
Full Paper
Benzothiazole Incorporated Barbituric Acid Derivatives:
Synthesis and Anticonvulsant Screening
Nadeem Siddiqui and Waquar Ahsan
Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Hamdard University, Hamdard Nagar, New
Delhi, India
A series of 1-(6-substituted-1,3-benzothiazol-2-yl)-3-(substituted phenyl)hexahydro-2,4,6-pyrimidi-
netriones 4a–t were synthesized starting from substituted anilines. These compounds contained
two active anticonvulsant pharmacophores, benzothiazole and barbituric acid. Structures of the
compounds were confirmed on the basis of different spectroscopic techniques. All the com-
pounds were evaluated for their anticonvulsant activity. Three compounds 4c, 4d, and 4s
showed promising anticonvulsant activities in Maximal Electroshock Seizure test (MES) and sub-
cutaneous pentylenetetrazole test (scPTZ). They also displayed a wide safety profile when tested
for the minimal motor impairment test.
Keywords: Anticonvulsants / Barbituric acid / Benzothiazole / Pyrimidinetriones /
Received: January 7, 2009; accepted: March 19, 2009
DOI 10.1002/ardp.200900002
and mephobarbital (Fig. 1) has been exploited previously
[3, 4] to get newer anticonvulsant agents that are better
anticonvulsants in terms of efficacy and safety.
Introduction
Epilepsy is one of the more common neurological disor-
ders affecting a large number of people. About 20 to 30%
of patients have seizures that are resistant to available
medical therapies [1]. All currently approved antiepilep-
tic drugs have a dose-related toxicity and idiosyncratic
side effects [2]. In response to the premise that major
medical breakthroughs in non-pharmacologic therapies
for the treatment of epilepsy in the near future seem
remote, the search for new antiepileptic drugs with
lower toxicities and fewer side effects continues. The real-
ization of such a possibility will necessitate a change in
our current antiepileptic drug discovery approach.
Drugs clinically active against epilepsy include deriv-
atives with common structural characteristics such as a
nitrogen-heterocyclic system with a carbonyl group and
an aromatic or heteroaromatic nucleus linked to the het-
erocyclic system. Barbituric acid being an essential com-
ponent of the current antiepileptic drugs phenobarbital
In recent years, benzothiazole derivatives have
acquired conspicuous significance due to their wide spec-
trum of biological activities. Although they have been
known from long ago to be biologically active [5–7], their
varied biological features are nowadays still of great sci-
entific interest. In search of new anticonvulsant agents,
we have already reported different substituted benzo-
thiazole derivatives that possess significant anticonvul-
sant activities [8–11].
The present series has been synthesized in the light of
the features discussed above; effort has been made to pro-
duce more potent and safer anticonvulsant agents by
adding two heterocyclic nuclei that are known to possess
anticonvulsant activity, namely benzothiazole and barbi-
turic acid.
Results and discussion
Correspondence: Nadeem Siddiqui, Department of Pharmaceutical
Chemistry, Faculty of Pharmacy, Hamdard University, Hamdard Nagar,
New Delhi 110062, India.
E-mail: nadeems_03@yahoo.co.in / nadeems_03@rediffmail.com
Fax: +91 11 2605-9688 / -5307
Chemistry
The synthesis of the target compounds 4a–t was accom-
plished as presented in Scheme 1. Appropriate substi-
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Arch. Pharm. Chem. Life Sci. 2009, 342, 462–468
Benzothiazole Barbiturates as Anticonvulsants
463
Figure 1. Barbituric acid derivatives as anticonvulsants.
Table 1. Physicochemical parameters of the titled compounds
4a–t.
Compound R
R9
Mol. Formulaa)
CLog Pb)
Rfc)
value
4a
4b
4c
4d
4e
4f
4g
4h
4i
Cl
Cl
Cl
Cl
2-CH3
4-CH3
2-OCH3
4-OCH3
H
2-CH3
4-CH3
2-OCH3
4-OCH3
H
2-CH3
4-CH3
2-OCH3
4-OCH3
H
2-CH3
4-CH3
2-OCH3
4-OCH3
H
C18H12ClN3O3S
C18H12ClN3O3S
C18H12ClN3O4S
C18H12ClN3O4S
C17H10ClN3O3S
C18H12BrN3O3S
C18H12BrN3O3S
C18H12BrN3O4S
C18H12BrN3O4S
C17H10BrN3O3S
C18H12FN3O3S
C18H12FN3O3S
C18H12FN3O4S
C18H12FN3O4S
C17H10FN3O3S
C18H12N4O5S
3.17 l 0.74 0.65
3.17 l 0.74 0.74
2.01 l 0.76 0.57
1.80 l 0.76 0.62
2.71 l 0.74 0.70
3.34 l 0.78 0.77
3.34 l 0.78 0.82
2.18 l 0.80 0.69
1.97 l 0.80 0.71
2.88 l 0.78 0.74
2.62 l 0.78 0.54
2.62 l 0.78 0.63
1.46 l 0.80 0.68
1.25 l 0.80 0.72
2.16 l 0.78 0.66
2.30 l 1.02 0.48
2.30 l 1.02 0.52
1.14 l 1.03 0.55
0.93 l 1.03 0.61
1.84 l 1.02 0.56
Cl
Br
Br
Br
Br
Br
F
F
F
F
F
NO2
NO2
NO2
NO2
NO2
4j
4k
4l
4m
4n
4o
4p
4q
4r
4s
4t
C18H12N4O5S
C18H12N4O6S
C18H12N4O6S
C17H10N4O5S
a)
Solvent of crystallization: ethanol.
CLog P was calculated using software ACD Labs 8.0 version.
Solvent system: toluene / ethyl acetate / formic acid (5 : 4 : 1).
b)
c)
t. Finally, the phenylurea derivatives were condensed
with malonic acid in the presence of acetyl chloride to
yield the title compounds 4a–t. The physico-chemical
parameters of the synthesized compounds are presented
in Table 1. The structures and purity of the final com-
pounds were confirmed on the basis of spectral and ele-
mental analyses and the data were within l 0.4% of the
theoretical values.
Reagents and conditions: (i) Br2, AcOH; (ii) ClCOOEt, triethylamine, reflux; (iii)
R'PhNH2, reflux; (iv) CH2(CO2H)2, CH3COCl, 408C, 4 h.
Scheme 1. Synthesis of the titled compounds 4a–t.
Pharmacology
Anticonvulsant activity
tuted anilines were treated with potassium thiocyanate
and bromine in acetic acid to yield substituted 2-amino
benzothiazole derivatives 1a–d. On refluxing with ethyl-
chloroformate and triethylamine, these derivatives
afforded the carbamate derivatives of benzothiazoles
2a–d. These carbamates when condensed with different
substituted anilines gave the phenylurea derivatives 3a–
The pharmacological testing of all the final compounds
was carried out according to the protocol of the Antiepi-
leptic Drug Development (ADD) program, Epilepsy
Branch, National Institute of Health (NIH), Rockville, MD,
USA.
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464
N. Siddiqui and W. Ahsan
Arch. Pharm. Chem. Life Sci. 2009, 342, 462–468
Table 2. Anticonvulsant activity and minimal motor impairment
of the synthesized compounds 4a–t.
pounds to prevent the seizure spread. Compounds that
showed protection from seizures in the MES model at the
30 mg/kg dose include 4c, 4d, and 4s which were active at
0.5 h of the administration. Interestingly, 4d continued
to protect from the seizures at the same dose after 4.0 h
also. It indicates that compound 4d had a rapid onset of
action as well as long duration at the lower dose. Com-
pounds 4c and 4s were also active at 4.0 h but at the
higher dose 100 mg/kg.
Compounds that were active at 100 mg/kg after 0.5 h
in MES tests include 4b, 4f, 4g, 4i, 4k, 4l, 4m, 4n, 4r, and
4t indicative of their good ability to protect from seizure
spread. Among these compounds, 4g, 4l, 4n, and 4r were
also active at the same dose after 4.0 h. This showed that
these have quick onset and long duration of action at rel-
atively higher dose. Compounds 4b, 4f, 4i, 4k, and 4t
were active after 4.0 h at 300 mg/kg. Compounds 4a, 4h,
and 4p were active after 0.5 h only at 300 mg/kg which
showed the rapid onset and shorter duration of action of
these compounds. Compounds 4e and 4o showed protec-
tion from seizures after 4.0 h at 300 mg/kg.
In the scPTZ screening, compounds that showed pro-
tection after 0.5 h were 4c, 4d, 4f, 4g, 4i, 4k, 4l, 4m, 4n,
4q, 4r, and 4s. Among these compounds, 4d, 4g, 4k, 4l,
4n, and 4s were active at a dose of 100 mg/kg which
showed the promising nature of the compounds against
the model. Interestingly, compounds 4g, 4l, 4n, and 4s
were also active after 4.0 h at 300 mg/kg indicative of the
long duration of action of these compounds.
In the neurotoxicity screen, compounds that did not
exhibit any neurotoxicity at the highest dose include 4c,
4d, 4e, 4l, and 4n. These compounds did not cause any
motor impairment at the three doses after the two time
periods. Rest of the compounds showed neurotoxicity
but at higher doses. Majority of the compounds were
found to be less neurotoxic than phenytoin.
Compound
Intraperitoneal injection in micea)
MES screen
scPTZ screen
Neurotoxicity
screen
0.5 h
4.0 h
0.5 h
4.0 h
0.5 h
4.0 h
b)
4a
4b
4c
4d
4e
4f
4g
4h
4i
4j
4k
4l
4m
4n
4o
4p
300
100
30
30
–
100
100
300
100
–
100
100
100
100
–
300
–
100
30
100
30
–
–
–
–
–
300
–
–
–
300
300
–
–
–
–
300
–
300
–
–
300
–
–
–
–
300
–
–
–
300
–
–
–
300
100
300
–
300
–
–
300
–
300
300
100
300
–
–
100
–
300
100
30
300
300
100
–
300
–
300
100
–
100
300
–
100
100
100
300
30
300
100
–
300
100
–
300
–
–
300
300
–
–
–
300
300
100
–
100
100
300
100
–
–
4q
4r
4s
4t
300
300
100
–
–
100
–
–
–
300
300
–
300
–
–
300
100
–
Phenytoinc)
Ethosuximided)
Phenobarbitale)
–
100
30
100
300
a)
Number of animals used: 6; solvent used: polyethylene glycol.
Dose of 30, 100, and 300 mg/kg were administered i.p. The
figures in the table indicate the minimum dose whereby bio-
activity was demonstrated in half or more of the mice. The
animals were examined at 0.5 h and 4 h after injections were
administered.
The dash (–) indicates an absence of activity at maximum
dose administered (300 mg/kg).
Data from reference [2].
b)
c)
d)
e)
Data from reference [12].
Data from reference [13].
Compounds were designed in such a way that the ben-
zothiazole moiety was substituted with different elec-
tron-withdrawing groups and the phenyl ring attached
to the pyrimidine ring was substituted with electron-
releasing groups at different positions. If we study the
structure-activity relationship of these compounds it was
found that the methoxy derivatives were more active
than the methyl and the unsubstituted derivatives. Com-
pounds with a methoxy group at the fourth position
were more active than those that bear the methoxy
group at the second position. On the other hand, the
chloro substituents were more potent and less neuro-
toxic than the bromo, fluoro, and nitro derivatives. Intro-
duction of nitro and bromo groups resulted in com-
pounds possessing more neurotoxicity than the chloro-
and fluoro-derived compounds.
The anticonvulsant activity was assessed by using the
electroshock (MES) and chemically-induced seizures
(scPTZ) methods. Maximal electroshock seizure (MES) test
is the standard model for tonic clonic type of seizures
and the subcutaneous pentylenetetrazole(scPTZ) test is
the standard model for the absence seizures. All the syn-
thesized compounds were administered intraperito-
neally (i.p.) into mice using doses of 30, 100 and 300 mg/
kg and the observations were taken at two different time
intervals (0.5 h and 4.0 h). Neurological impairment was
evaluated by the rotorod method. The data are presented
in Table 2.
In the preliminary (Phase I), screening all the com-
pounds except 4e, 4j, 4o, and 4q showed protection
against MES test which indicates the ability of these com-
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Arch. Pharm. Chem. Life Sci. 2009, 342, 462–468
Benzothiazole Barbiturates as Anticonvulsants
465
Table 3. Phase II quantitative anticonvulsant evaluation in mice.
PIc)
a)
b)
Compound
ED50
TD50
MES
22.8 (19.4 – 24.1)d)
13.9 (12.2 – 15.4)
25.4 (22.8 – 27.3)
9.5 (8.1 – 10.4)
8.8 (5.5 – 14.1)
21.8 (21.8 – 25.5)
272 (247 – 338)
scPTZ
MES
scPTZ
4c
4d
4s
204.6 (171.6 – 240.4) 432.3 (391.8 – 480.4)
65.2 (56.3 – 73.6)
74.8 (52.4 – 93.7)
>300
>100
13.2 (5.8 – 15.9)
149 (123 – 177)
18.9
38.8
3.4
6.9
8.1
2.1
8.2
1.1
a0.22
a0.22
5.2
540.4 (453.8 – 621.1)
88.6 (64.5 – 101.3)
65.5 (52.5 – 72.9)
71.6 (45.9 – 135)
69 (62.8 – 72.9)
Phenytoine)
Carbamazepinee)
Phenobarbitale)
Valproatee)
3.2
1.6
426 (369 – 450)
2.9
Number of animals used: 10; solvent used: polyethylene glycol (0.1 mL, i.p.).
a)
Dose in milligrams per kilogram body mass.
Minimal toxicity which was determined by rotorod test 30 min after the test drug was administered.
PI = Protective index (TD50/ED50).
Data in parentheses are the 95% confidence limits.
Data from references [14].
b)
c)
d)
e)
In the Phase-II anticonvulsant screening, the three Research Fellowship (SRF) as financial assistance. We are also
most active compounds 4c, 4d, and 4s were quantita- thankful to Shrenik Pharma Ltd., Mumbai for providing penty-
tively evaluated for their anticonvulsant activity (ED50) lenetetrazole as gift sample.
and neurotoxicity (TD50). The results are shown in
Table 3. All three compounds displayed encouraging The authors have declared no conflict of interest.
activities, which are comparable to some standard drugs.
Compounds 4c and 4d showed a higher protective index
than all the standard drugs.
Lipophilicity determination
The calculated LogP (ClogP) values were generated by
Experimental
Chemistry
using the software ACD Labs 8.0 version. It was found
that almost all the compounds have the ClogP value near
2.0, which is considered to be the optimum lipophilicity
for the congeners that act on the central nervous system
[15]. This may be the reason behind the rapid onset and
long duration of action of most of the compounds.
The melting points were determined in open capillary tubes in a
Hicon melting point apparatus (Hicon, India) and are uncor-
rected. The homogen elemental analyses (C, H, N) of all com-
pounds were performed on the Vario EL III CHNS Elementar
(Analysensysteme GmbH, Hanau, Germany). All the Fourier
transform infrared (FTIR) spectra were recorded in KBr pellets on
a Jasco FT/IR 410 spectrometer (Jasco, Tokyo, Japan). The 1H-NMR
spectra were taken on a Bruker 400 Ultra shieldTM NMR spec-
trometer (400 MHz; Bruker Bioscience, USA). Chemical shifts (d)
are expressed in ppm relative to tetramethylsilane (TMS) as an
internal standard. The homogeneity of the compounds was
checked by thin layer chromatography (TLC) on silica gel G-
coated plates (Merck, Germany) by using toluene / ethyl acetate /
formic acid (5 : 4 : 1) as solvent system. Iodine chamber and UV
lamp were used for the visualization of TLC spots.
Conclusion
The present series were designed by combining two
active pharmacophores showing anticonvulsant activity.
Interestingly, all the synthesized compounds showed
some degree of protection against the seizures induced
by both electroshock and chemically induced seizure
methods. Three compounds were found to be very prom-
ising as far as efficacy and safety is concerned. They also
showed optimum lipophilicity and lesser neurotoxicity
than some standard drugs. They may act as lead mole-
cules for future investigations.
General procedure for the synthesis of 6-substituted-1,3-
benzothiazol-2-amines 1a–d
A mixture of substituted aniline (0.01 mol) and potassium thio-
cyanate (0.01 mol) in glacial acetic acid was cooled and stirred.
To this solution bromine (0.01 mol) was added dropwise at such
a rate to keep the reaction temperature below 108C throughout
the addition. Stirring was continued for additional 3 h and the
separated hydrochloride salt was filtered, washed with acetic
acid, and dried. It was dissolved in hot water and neutralized
with aqueous ammonia solution (25%). The precipitate obtained
One of the authors (W. A.) is thankful to Council of Scientific
and Industrial Research (CSIR), New Delhi, India for the Senior
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466
N. Siddiqui and W. Ahsan
Arch. Pharm. Chem. Life Sci. 2009, 342, 462–468
was filtered, washed with water, dried, and recrystallized to
afford the 6-substituted-1,3-benzothiazol-2-amine 1a–d.
1-(6-Chloro-1,3-benzothiazol-2-yl)-3-phenylhexahydro-
2,4,6-pyrimidinetrione 4e
Yield: 83%; m.p.: 1558C; IR (KBr) mmax [cm– 1]: 3056 (CH-Ar), 1702
1
(C=O), 1524 (C=N), 1165 (C=S), 803 (C-Cl); H-NMR (CDCl3) d: 3.73
General procedure for the synthesis of ethyl (6-
(s, 2H, CH2), 6.84–8.12 (m, 3H, Benzoth.), 7.10–7.67 (m, 5H, ArH).
substituted-1,3-benzothiazol-2-yl)carbamates 2a–d
To the substituted bezothiazol-2-amines (1a–d, 0.01 mol) in ben-
zene were added ethylchloroformate (0.011 mol) and triethyl-
amine (2.5 mL), and the reaction mixture was refluxed for 3 h.
After cooling, the reaction mixture was poured into cold dil. HCl
(50%) and the carbamate thus formed was recrystallized from
benzene.
1-(6-Bromo-1,3-benzothiazol-2-yl)-3-(2-
methylphenyl)hexahydro-2,4,6-pyrimidinetrione 4f
Yield: 71%; m.p.: 1798C; IR (KBr) mmax [cm-1]: 3072 (CH-Ar), 1679
(C=O), 1478 (C=N), 1126 (C=S), 563 (C-Br); 1H-NMR (CDCl3) d: 2.41
(s, 3H, CH3), 3.78 (s, 2H, CH2), 7.12–8.16 (m, 3H, Benzoth.), 7.21–
7.59 (m, 4H, ArH).
General procedure for the synthesis of 1-(6-substituted-
1,3-benzothiazol-2-yl)-3-(substituted phenyl)ureas 3a–t
An equimolar mixture of carbamates 2a–d and substituted ani-
lines in ethanol was refluxed for 18–20 h. After the completion,
ethanol was removed and residue obtained was washed with
water, dried, and recrystallized from methanol.
4.1.4.7 1-(6-Bromo-1,3-benzothiazol-2-yl)-3-(4-
methylphenyl)hexahydro-2,4,6-pyrimidinetrione 4g
Yield: 84%; m.p.: 1968C; IR (KBr) mmax [cm– 1]: 3056 (CH-Ar), 1684
(C=O), 1474 (C=N), 1118 (C=S), 574 (C-Br); 1H-NMR (CDCl3) d: 1.76
(s, 3H, CH3), 3.97 (s, 2H, CH2), 7.08–8.06 (m, 3H, Benzoth.), 7.16–
7.43 (m, 4H, ArH).
General procedure for the synthesis of 1-(6-substituted-
1,3-benzothiazol-2-yl)-3-(substituted phenyl)hexahydro-
2,4,6-pyrimidinetriones 4a–t
1-(6-Bromo-1,3-benzothiazol-2-yl)-3-(2-
An equimolar mixture of phenyl ureas 3a–t and malonic acid
was refluxed in acetyl chloride (10 mL) for 4 h at 408C. The con-
tents were cooled, poured over crushed ice, and neutralized
with dilute sodium bicarbonate solution. The solid thus
obtained was filtered, washed with water, dried, and recrystal-
lized from ethanol to get the title compounds 4a–t.
methoxyphenyl)hexahydro-2,4,6-pyrimidinetrione 4h
Yield: 61%; m.p.: 1448C; IR (KBr) mmax [cm– 1]: 3066 (CH-Ar), 1686
1
(C=O), 1512 (C=N), 1448 (OCH3), 1074 (C=S), 612 (C-Br); H-NMR
(CDCl3) d: 3.51 (s, 3H, OCH3), 3.89 (s, 2H, CH2), 6.87–8.13 (m, 3H,
Benzoth.), 7.21–7.69 (m, 4H, ArH).
1-(6-Bromo-1,3-benzothiazol-2-yl)-3-(4-
1-(6-Chloro-1,3-benzothiazol-2-yl)-3-(2-
methoxyphenyl)hexahydro-2,4,6-pyrimidinetrione 4i
methylphenyl)hexahydro-2,4,6-pyrimidinetrione 4a
Yield: 73%; m.p.: 1868C; IR (KBr) mmax [cm– 1]: 3046 (CH-Ar), 1654
Yield: 70%; m.p.: 1658C; IR (KBr) mmax [cm–1]: 3071 (CH-Ar), 1681
1
1
(C=O), 1504 (C=N), 1467 (OCH3), 1026 (C=S), 603 (C-Br); H-NMR
(CDCl3) d: 3.71 (s, 3H, OCH3), 3.91 (s, 2H, CH2), 6.93–8.24 (m, 3H,
Benzoth.), 7.11–7.58 (m, 4H, ArH).
(C=O), 1520 (C=N), 1104 (C=S), 815 (C-Cl); H-NMR (CDCl3) d: 2.31
(s, 3H, CH3), 3.83 (s, 2H, CH2), 7.05–8.61 (m, 3H, Benzoth.), 7.34–
7.81 (m, 4H, ArH).
1-(6-Chloro-1,3-benzothiazol-2-yl)-3-(4-
1-(6-Bromo-1,3-benzothiazol-2-yl)-3-phenylhexahydro-
methylphenyl)hexahydro-2,4,6-pyrimidinetrione 4b
2,4,6-pyrimidinetrione 4j
Yield: 65%; m.p.: 1788C; IR (KBr) mmax [cm– 1]: 3111 (CH-Ar), 1632
Yield: 61%; m.p.: 1558C; IR (KBr) mmax [cm– 1]: 3116 (CH-Ar), 1712
(C=O), 1504 (C=N), 1161 (C=S), 631 (C-Br); 1H-NMR (CDCl3) d: 3.94
(s, 2H, CH2), 6.92–7.96 (m, 3H, Benzoth.), 7.21–7.57 (m, 5H, ArH).
1
(C=O), 1507 (C=N), 1135 (C=S), 807 (C-Cl); H-NMR (CDCl3) d: 1.91
(s, 3H, CH3), 3.55 (s, 2H, CH2), 6.95–8.25 (m, 3H, Benzoth.), 7.14–
7.61 (m, 4H, ArH).
1-(6-Fluoro-1,3-benzothiazol-2-yl)-3-(2-
1-(6-Chloro-1,3-benzothiazol-2-yl)-3-(2-
methylphenyl)hexahydro-2,4,6-pyrimidinetrione 4k
Yield: 56%; m.p.: 1788C; IR (KBr) mmax [cm– 1]: 3024 (CH-Ar), 1667
(C=O), 1472 (C=N), 1323 (C-F), 1153 (C=S); 1H-NMR (CDCl3) d: 2.34
(s, 3H, CH3), 3.67 (s, 2H, CH2), 7.01–8.34 (m, 3H, Benzoth.), 7.34–
7.68 (m, 4H, ArH).
methoxyphenyl)hexahydro-2,4,6-pyrimidinetrione 4c
Yield: 74%; m.p.: 1348C; IR (KBr) mmax [cm– 1]: 3072 (CH-Ar), 1671
1
(C=O), 1504 (C=N), 1460 (OCH3), 1141 (C=S), 809 (C-Cl); H-NMR
(CDCl3) d: 3.42 (s, 3H, OCH3), 3.93 (s, 2H, CH2), 6.91–8.21 (m, 3H,
Benzoth.), 7.23–7.68 (m, 4H, ArH).
1-(6-Chloro-1,3-benzothiazol-2-yl)-3-(4-
1-(6-Fluoro-1,3-benzothiazol-2-yl)-3-(4-
methoxyphenyl)hexahydro-2,4,6-pyrimidinetrione 4d
methylphenyl)hexahydro-2,4,6-pyrimidinetrione 4l
Yield: 69%; m.p.: 1938C; IR (KBr) mmax [cm– 1]: 3056 (CH-Ar), 1673
(C=O), 1452 (C=N), 1334 (C-F), 1201 (C=S); 1H-NMR (CDCl3) d: 2.59
(s, 3H, CH3), 3.77 (s, 2H, CH2), 6.87–8.14 (m, 3H, Benzoth.), 7.23–
7.56 (m, 4H, ArH).
Yield: 66%; m.p.: 1568C; IR (KBr) mmax [cm– 1]: 3112 (CH-Ar), 1692
1
(C=O), 1515 (C=N), 1475 (OCH3), 1171 (C=S), 824 (C-Cl); H-NMR
(CDCl3) d: 3.61 (s, 3H, OCH3), 3.87 (s, 2H, CH2), 6.99–8.37 (m, 3H,
Benzoth.), 7.11–7.53 (m, 4H, ArH).
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Arch. Pharm. Chem. Life Sci. 2009, 342, 462–468
Benzothiazole Barbiturates as Anticonvulsants
467
branch of the National Institute of Neurological Disorders and
Stroke (NINDS) following the protocol adopted by the Antiepilep-
tic Drug Development (ADD) program [16].
1-(6-Fluoro-1,3-benzothiazol-2-yl)-3-(2-
methoxyphenyl)hexahydro-2,4,6-pyrimidinetrione 4m
Yield: 86%; m.p.: 1938C; IR (KBr) mmax [cm– 1]: 3019 (CH-Ar), 1679
(C=O), 1508 (C=N), 1467 (OCH3), 1356 (C-F), 1034 (C=S); 1H-NMR
(CDCl3) d: 3.54 (s, 3H, OCH3), 3.87 (s, 2H, CH2), 6.84–8.10 (m, 3H,
Benzoth.), 7.23–7.64 (m, 4H, ArH).
The investigations were conducted with albino mice of either
sex (25 to 30 g; Animals were obtained from Central Animal
House Facility., Hamdard University, New Delhi-62. Registration
no. and date of registration is 173/CPCSEA, 28 Jan., 2000.). The
albino mice were kept under standard conditions at an ambient
temperature of 25 l 28C and allowed free access to food and
water except at the time they were brought out of the cage. All
the experimental protocols were carried out with permission
from Institutional Animal Ethics committee (IAEC), form no.
416.
1-(6-Fluoro-1,3-benzothiazol-2-yl)-3-(4-
methoxyphenyl)hexahydro-2,4,6-pyrimidinetrione 4n
Yield: 79%; m.p.: 2128C; IR (KBr) mmax [cm– 1]: 3051 (CH-Ar), 1693
(C=O), 1526 (C=N), 1434 (OCH3), 1361 (C-F), 1027 (C=S); 1H-NMR
(CDCl3) d: 3.61 (s, 3H, OCH3), 3.91 (s, 2H, CH2), 6.89–8.24 (m, 3H,
Benzoth.), 7.21–7.67 (m, 4H, ArH).
Anticonvulsant activity
1-(6-Fluoro-1,3-benzothiazol-2-yl)-3-phenylhexahydro-
Maximal electroshock test (MES)
2,4,6-pyrimidinetrione 4o
Yield: 74%; m.p.: 1368C; IR (KBr) mmax [cm– 1]: 3116 (CH-Ar), 1698
(C=O), 1523 (C=N), 1349 (C-F), 1154 (C=S); 1H-NMR (CDCl3) d: 3.84
(s, 2H, CH2), 6.97–8.16 (m, 3H, Benzoth.), 7.31–7.66 (m, 5H, ArH).
The maximal electroshock seizure test was carried out according
to the standard protocol [17]. Albino mice were stimulated
through corneal electrodes to 50 mA current at a pulse of 60 Hz
applied for 0.25 s. Animals were previously administered with
the test drug i.p. Abolition of hind-limb tonic extension spasm
was recorded as the anticonvulsant activity. The test compounds
were suspended in 0.5% methyl cellulose-water mixture or in
polyethylene glycol (PEG). In the preliminary screening, each
compound was administered as an i.p. injection at three dose
levels (30, 100, and 300 mg/kg body mass) and the anticonvul-
sant activity assessed after 0.5 h and 4.0 h intervals of adminis-
tration.
1-(2-Methylphenyl)-3-(6-nitro-1,3-benzothiazol-2-
yl)hexahydro-2,4,6-pyrimidinetrione 4p
Yield: 82%; m.p.: 1848C; IR (KBr) mmax [cm– 1]: 3023 (CH-Ar), 1676
(C=O), 1454 (C=N), 1339 (NO2), 1189 (C=S); 1H-NMR (CDCl3) d: 2.54
(s, 3H, CH3), 3.71 (s, 2H, CH2), 7.13–8.21 (m, 3H, Benzoth.), 7.31–
7.64 (m, 4H, ArH).
1-(4-Methylphenyl)-3-(6-nitro-1,3-benzothiazol-2-
yl)hexahydro-2,4,6-pyrimidinetrione 4q
Subcutaneous pentylenetetrazole-induced seizure test
(scPTZ)
Yield: 78%; m.p.: 2168C; IR (KBr) mmax [cm– 1]: 3056 (CH-Ar), 1664
(C=O), 1459 (C=N), 1345 (NO2), 1176 (C=S); 1H-NMR (CDCl3) d: 2.64
(s, 3H, CH3), 3.76 (s, 2H, CH2), 7.10–8.24 (m, 3H, Benzoth.), 7.21–
7.56 (m, 4H, ArH).
The subcutaneous pentylenetetrazole test was performed
according to the known protocol [18]. This method utilizes pen-
tylenetetrazole (75 mg/kg) that produces seizures in >95% of ani-
mals as a 0.5% solution subcutaneously in the posterior midline.
The animal was observed for 30 min., failure to observe even a
threshold seizure (a single episode of clonic spasms of at least 5 s
duration) was defined as protection.
The pharmacological parameters estimated in phase-I screen-
ing were quantified in phase-II screening (Table 3). Anticonvul-
sant activity was expressed in terms of the median effective dose
(ED50), and neurotoxicity was expressed as the median toxic dose
(TD50). For the determination of ED50 and TD50 values, groups of
ten mice were given a range of intraperitoneal doses of the test
drug until at least three points were established in the range of
10 to 90% seizure protection or minimal observed neurotoxicity.
From the plot of these data, the respective ED50 and TD50 values,
95% confidence intervals, slope of the regression line, and the
standard error of the slope were calculated by means of the com-
puter program by Litchfield and Wilcoxon's method [19].
1-(2-Methoxyphenyl)-3-(6-nitro-1,3-benzothiazol-2-
yl)hexahydro-2,4,6-pyrimidinetrione 4r
Yield: 71%; m.p.: 1718C; IR (KBr) mmax [cm-1]: 3034 (CH-Ar), 1665
(C=O), 1531 (C=N), 1447 (OCH3), 1356 (NO2), 1064 (C=S); 1H-NMR
(CDCl3) d: 3.34 (s, 3H, OCH3), 3.67 (s, 2H, CH2), 6.94–8.11 (m, 3H,
Benzoth.), 7.24–7.71 (m, 4H, ArH).
1-(4-Methoxyphenyl)-3-(6-nitro-1,3-benzothiazol-2-
yl)hexahydro-2,4,6-pyrimidinetrione 4s
Yield: 56%; m.p.: 1988C; IR (KBr) mmax [cm– 1]: 3059 (CH-Ar), 1651
(C=O), 1550 (C=N), 1489 (OCH3), 1368 (NO2), 1021 (C=S); 1H-NMR
(CDCl3) d: 3.41 (s, 3H, OCH3), 3.87 (s, 2H, CH2), 7.14–8.21 (m, 3H,
Benzoth.), 7.29–7.64 (m, 4H, ArH).
1-(6-Nitro-1,3-benzothiazol-2-yl)-3-phenylhexahydro-
2,4,6-pyrimidinetrione 4t
Neurotoxicity screening (NT)
Yield: 61%; m.p.: 1168C; IR (KBr) mmax [cm– 1]: 3112 (CH-Ar), 1667
(C=O), 1513 (C=N), 1343 (NO2), 1135 (C=S); 1H-NMR (CDCl3) d: 3.81
(s, 2H, CH2), 6.98–8.19 (m, 3H, Benzoth.), 7.21–7.55 (m, 5H, ArH).
The minimal motor impairment was measured in mice by the
rotorod test. The mice were trained to stay on an accelerating
rotorod (diameter 3.2 cm) that rotates at 10 rpm. Trained ani-
mals were injected intraperitoneally the test compounds at a
dose of 25 mg/kg. Neurotoxicity was indicated by the inability of
the animal to maintain equilibration on the rod for at least
1 min in each of the three trials [20].
Pharmacology
The pharmacological testing of all the final compounds was per-
formed according to the standard protocol given by the epilepsy
i 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.archpharm.com

468
N. Siddiqui and W. Ahsan
Arch. Pharm. Chem. Life Sci. 2009, 342, 462–468
[11] A. Rana, N. Siddiqui, S. A .Khan, S. E. Haque, M. A. Bhat,
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www.archpharm.com