New Benzo[d]thiazol-2-yl-aminoacetamides as Potential Anticonvulsants: Synthesis, Activity and Prediction of Molecular Properties

Article abstract of DOI:10.1002/ardp.201400466

A series of N-(substituted-2-oxo-4-phenylazetidin-1-yl)-2-((6-substitutedbenzo[d]thiazol-2-yl)amino)-acetamide derivatives were synthesized using pharmacophoric features with aromatic hydrophobic aryl ring (A), NH-C=O as hydrogen bonding domain, the nitrogen atom as electron donor (D), and phenyl as distal aryl ring (C). The synthesized molecules were initially screened for anticonvulsant activity using the maximal electroshock seizure (MES) test and the subcutaneous pentylenetetrazole test in albino mice. An acute neurotoxicity study on the synthesized molecules was also carried out using the rotarod test. The results of these tests revealed that two compounds, 5b and 5q, showed promising activity with ED₅₀ values of 15.4 and 18.6 mg/kg and protective indices of 20.7 and 34.9 in the MES test, respectively, which are found to be approximately fourfold higher than those of the standard drugs phenytoin (6.9) and carbamazepine (8.1). These molecules may act as lead of the designed scheme. The pharmacokinetic profiles of all the synthesized compounds were estimated using Molinspiration software. None of the compounds violated Lipinski's "rule of five". The possible structure-activity relationship was discussed. In conclusion, this manuscript shows that the developed model has a highly prognostic power for the further investigation of better benzothiazole derivatives for future discovery and development.

Full text of DOI:10.1002/ardp.201400466

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Arch. Pharm. Chem. Life Sci. 2015, 348, 254–265
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Full Paper
New Benzo[d]thiazol-2-yl-aminoacetamides as Potential
Anticonvulsants: Synthesis, Activity and Prediction of
Molecular Properties
Ruhi Ali and Nadeem Siddiqui
Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Hamdard University,
Hamdard Nagar, New Delhi, India
A series of N-(substituted-2-oxo-4-phenylazetidin-1-yl)-2-((6-substitutedbenzo[d]thiazol-2-yl)amino)-
acetamide derivatives were synthesized using pharmacophoric features with aromatic hydrophobic aryl
ring (A), NH–C–O as hydrogen bonding domain, the nitrogen atom as electron donor (D), and phenyl as
distal aryl ring (C). The synthesized molecules were initially screened for anticonvulsant activity using the
maximal electroshock seizure (MES) test and the subcutaneous pentylenetetrazole test in albino mice. An
acute neurotoxicity study on the synthesized molecules was also carried out using the rotarod test. The
results of these tests revealed that two compounds, 5b and 5q, showed promising activity with ED50 values
of 15.4 and 18.6 mg/kg and protective indices of 20.7 and 34.9 in the MES test, respectively, which are
found to be approximately fourfold higher than those of the standard drugs phenytoin (6.9) and
carbamazepine (8.1). These molecules may act as lead of the designed scheme. The pharmacokinetic
profiles of all the synthesized compounds were estimated using Molinspiration software. None of the
compounds violated Lipinski's “rule of five”. The possible structure–activity relationship was discussed. In
conclusion, this manuscript shows that the developed model has a highly prognostic power for the further
investigation of better benzothiazole derivatives for future discovery and development.
Keywords: Anticonvulsant / Benzothiazole / Hepatotoxicity / In vivo / In silico / Neurotoxicity
Received: December 23, 2014; Revised: February 17, 2015; Accepted: February 19, 2015
DOI 10.1002/ardp.201400466
Additional supporting information may be found in the online version of this article at the publisher's web-site.
:
Introduction
available for epilepsy, almost about 28–30% of patients are
estimated to be poorly treated [5, 6]. Considering this poor
treatment, efforts in the recent years have led to the
development of several newer and promising drugs like
stiripentol, zonisamide, tiagabine, levetiracetam, topira-
mate, etc. with better seizure controlling efficacy. However,
these newer drugs also carry serious and adverse side effects
such as hepatotoxicity, anorexia, gastrointestinal disturban-
ces, and hirsutism [7–11]. Therefore, research is envisaged for
development of anticonvulsant agents with better benefit/
risk ratio.
Epilepsy is a “common neurological disorder characterized
by seizures that are unpredictable in frequency” [1, 2]. It
affects people of all age groups with commencement often
in childhood and older adulthood. Globally, it influences
more than 50 million people worldwide [3], with about 2.4
million new cases added every year to this figure. It is also
reported that at some point in lifetime 1 in 26 individuals
develop epilepsy [4]. In spite of current treatment options
Benzothiazole is a bicyclic ring system with electron-rich
sulfur and nitrogen atom. Pharmacologically, benzothiazole
derivatives are known for wide range of biological proper-
ties like antimicrobial, antitubercular, anticonvulsant, anti-
tumor, antihyperglycemic, and HIV-1 integrase inhibition
[12, 13]. On the other hand, 2-aminobenzothiazoles have
Correspondence: Prof. Nadeem Siddiqui, Department of Phar-
maceutical Chemistry, Faculty of Pharmacy, Jamia Hamdard
University, Hamdard Nagar, New Delhi 110062, India.
E-mail: nadeems_03@rediffmail.com
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Arch. Pharm. Chem. Life Sci. 2015, 348, 254–265
New Benzo[d]thiazol-2-yl-acetamides as Anticonvulsants
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come out as new class of anticonvulsant agents and one
of its derivatives, riluzole, is a clinically offered anti-
convulsant [14].
Results and discussion
Chemistry
A pharmacophore-based model is an efficient tool for
designing and explaining interactions of prototypic mole-
cules [15]. Most optimal anticonvulsant pharmacophoric
element, that is amide group as hydrogen bonding domain,
is present in the title compounds. The other features include
benzothiazolyl ring as hydrophobic domain (A), sulphur and
nitrogen atoms as electron donor systems (D) with substituted
phenyl moiety as distal aryl ring (C), which influences the
blood–brain barrier diffusion and pharmacokinetic properties
of the anticonvulsants [16].
In our present work, we proposed to synthesize a series of
N-(substituted-2-oxo-4-phenylazetidin-1-yl)-2-((6-substituted-
benzo[d]thiazol-2-yl)amino)acetamide derivatives to explore
their behavior as anticonvulsant agents. None of the currently
available antiepileptic drug is ideal and most of them have
serious and acute adverse effects; therefore, the present study
also focused on the toxicity studies of the synthesized
compounds.
The present study describes the synthesis and anticonvulsant
screening of N-(substituted-2-oxo-4-phenylazetidin-1-yl)-2-((6-
substitutedbenzo[d]thiazol-2-yl)amino)acetamide derivatives.
A series of 20 new derivatives were synthesized in satisfactory
yields as per Scheme 1. The physicochemical parameters of the
synthesized compounds are given in Table 1.
The chemical structures of the synthesized compounds were
characterized by spectral analysis. The synthesized derivatives
showed N–H, C –– O, and C –– N stretching bands in the region of
ꢀ
1
3500–3310, 1780–1640, and 1660–1562 cm , respectively, in
1
their IR spectra. While in their H NMR, compounds exhibited
multiplets for Ar-H in the regions of 6.80–9.05 ppm, a singlet in
the region of 6.28–7.98 ppm (N–H) and a singlet for (CONH) in
1
3
the region of 9.80–11.0 ppm. C NMR spectra of a prototype
compound 5d revealed one upfield peak at 20.9 due to a one
methyl carbon, while carbonyl carbons of amide (CONH)
appeared downfield at 174.50. The other peaks of carbon
were observed at 170.3, 163.5, 150.2, 143.2, 134.6, 130.7, 128.1,
Scheme 1. Synthetic procedure for preparation of the target compounds 5a–t.
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Table 1. Physicochemical parameters of the synthesized compounds 5a–t.
0
a)
b)
c)
d)
Compounds
R
R
Molecular formula
Log P
Clog P
MP (°C)
R
f
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
p
q
r
Cl
F
NO
CH
OCH
Cl
F
NO
CH
OCH
Cl
F
NO
CH
OCH
Cl
F
NO
H
H
H
H
H
C
C
C
C
C
18
18
18
H
14Cl
2
N
4
O
4 2
2
S
3.70
3.40
3.92
3.71
3.12
4.20
3.80
3.29
4.26
3.62
3.90
3.68
2.94
3.50
2.86
4.40
3.88
3.65
4.35
3.54
4.65
3.98
3.80
4.43
4.23
5.10
4.53
4.25
4.88
4.35
4.57
4.00
3.72
4.35
4.15
5.37
4.80
4.51
5.14
4.95
209–212
247–251
210–212
225–227
231–233
202–204
216–220
206–209
228–231
256–259
236–238
197–199
262–264
213–215
189–192
277–279
220–222
246–248
214–216
272–274
0.78
0.56
0.63
0.87
0.50
0.58
0.72
0.89
0.67
0.75
0.59
0.91
0.80
0.77
0.62
0.64
0.78
0.93
0.82
0.66
H14ClFN O S
2
H
14ClN
17ClN
17ClN
5
O
O
O
4
2
3
S
S
S
3
19
H
19
H
4
3
3
3
3
4
2-CH
2-CH
2-CH
2-CH
2-CH
4-OCH
4-OCH
4-OCH
4-OCH
4-OCH
2-Cl
3
3
3
3
3
C
C
C
19
19
19
H
16Cl
2 4 2
N O S
H16ClFN O S
4 2
2
H
16ClN
19ClN
19ClN
5 4
O S
4
3
C
C
20
H
20
H
O
O
2
S
S
4
3
3
3
3
3
3
C
C
C
19
19
19
H
16Cl
2 4 3
N O S
H16ClFN O S
4 3
2
H
16ClN
19ClN
19ClN
5 5
O S
4
3
C
C
C
20
H
20
H
O
O
3
S
S
4
4
18
H13Cl
3 4 2
N O S
2
2-Cl
2-Cl
2-Cl
2-Cl
C
18
H
13Cl
FN
4
O
2
S
2
C
C
C
18
H
19
H
19
H
13Cl
16Cl
16Cl
2
N
N
N
5
O
O
O
4
2
3
S
S
S
s
t
CH
OCH
3
2
2
4
4
Solvent of crystallization: ethanol.
a)
Log P was calculated using octanol–phosphate buffer.
CLog P was calculated using software Chem. Draw Ultra 8.
b)
c)
Melting point of the compounds at their decomposition.
d)
Solvent system: toluene/ethyl acetate/formic acid (5:4:1), benzene/acetone (8:2).
1
26.9, 126.3, 121.3, 117.1, 67.4, 64.1, 57.3, confirming the
observations were taken at two different time intervals (0.5
and 4.0 h). Preliminary screening of all the newly synthesized
compounds exhibited some degree of anti-MES activity. The
protection offered by these compounds was an indication of
their pharmacological ability against seizure spread at a
certain dose level. The result of anticonvulsant activity of the
compounds 5a–t against MES- and scPTZ-induced seizures is
summarized in Table 2. The MES model is used for preclinical
evaluation of drugs meant for treatment of generalized
tonic–clonic seizures. The method has high reproducibility
and consistent endpoints. The electrographic and behavioral
changes produced in this model are similar to human seizure
condition. All the synthesized compounds successfully provid-
ed protection against MES-induced seizures. The protective
effect was observed 30 min post-treatment, indicating a quick
onset of action. At this duration, compounds 5b and 5q
showed activity at the lowest dose of 30 mg/kg which was
comparable to the standard drugs used in the study, viz.
phenytoin and carbamazepine. The effect at 30 mg/kg also
indicated relatively high potency of compounds 5b and 5q.
Upon evaluation of compounds 4 h post-treatment, it was
observed that compounds 5a, 5b, 5c, 5k, 5l, 5m, 5p, and 5r
showed antiseizure effect at 100 mg/kg whereas compounds
5f, 5g, 5j, 5o, and 5t exhibited this effect at the dose of
300 mg/kg. Compound 5q exclusively prevented seizures 4 h
postadministration of 30 mg/kg dose, exhibiting long dura-
tion of action along with high potency.
presence of 19 carbons in the compound. To access the stereo-
electronic effect on the anticonvulsant activity, benzothiazole
nucleus was substituted with different functional groups, that
is, electron-withdrawing groups and electron-donating groups
of varied sizes and electronic characteristics.
The general structure activity relationship of these com-
pounds showed that electron-withdrawing groups at benzo-
thiazole nucleus increases the activity and unsubstitution and
lipophillic electron-withdrawing groups on distal aryl ring
result in higher activity in comparison with substitution with
electron-releasing groups.
Pharmacological evaluation
The synthesized compounds were evaluated for preliminary
anticonvulsant activity and neurotoxicity following the
standard procedures proposed by the NIH anticonvulsant
drug development program [17]. Phase I studies involved
three tests: maximal electroshock seizure (MES), subcutane-
ous pentylenetetrazole (scPTZ), and rotarod test for neuro-
logical toxicity. The MES test is an established method of
generalized tonic–clonic seizures and categorizes those
clinical candidates that stop seizure spread, whereas scPTZ
test specifies its efficacy against absence seizures and is used
to categorize compounds that raise the seizure threshold.
The compounds 5a–t were administrated intraperitoneally
into the mice using dose of 30, 100, and 300 mg/kg and the
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Arch. Pharm. Chem. Life Sci. 2015, 348, 254–265
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Table 2. Phase I anticonvulsant activity and minimal motor impairment data of the synthesized compounds (5a–t).
Intraperitoneal injection in mice
MES
scPTZ
Neurotoxicity screen
Compounds
0.5 h
4 h
0.5 h
4 h
0.5 h
4 h
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
p
q
r
100
30
100
100
100
–
100
100
100
300
300
100
100
100
–
300
100
100
–
–
–
100
–
100
300
300
100
100
100
300
300
100
100
100
300
300
100
30
–
–
–
–
–
300
–
–
–
300
300
–
–
–
–
100
300
–
100
–
300
–
–
–
300
100
100
100
–
–
–
–
–
300
100
100
–
300
100
300
–
–
–
–
300
–
300
300
–
–
300
100
30
100
–
–
300
–
–
–
100
–
100
–
30
100
100
–
100
300
300
30
100
300
300
–
–
–
s
t
–
–
300
30
100
–
–
–
PHY
CBZ
–
100
100
100
300
30
100
300
Number of animals in each group (n) ¼ 4; solvent used: polyethylene glycol; doses of 30, 100, and 300 mg/kg were administered
intraperitoneally. The figures indicate the minimum dose, whereby bioactivity was demonstrated in half or more mice. The (–)
indicates an absence of activity at the maximum dose administered (300 mg/kg).
Pentylenetetrazole-induced seizure model is used for
screening of compounds which can raise seizure threshold.
PTZ produces seizures which are clonic in nature but not
typical absence type. These seizures are potentiated by GABA
agonist. In the present study, compounds 5a, 5b, 5c, 5f, 5g,
Most of the tested compounds did not produce neurotox-
icity in the tested animals. Few compounds which produced
neurotoxicity at 100 mg/kg include 5g and 5p at 0.5 h and 5a,
5g, and 5p at 4 h. At 300 mg/kg dose, compounds 5h, 5m, and
5n exhibited neurotoxicity at 0.5 h interval whereas only
compound 5l produced neurotoxicity at 4 h. It is important to
note that both standard drugs also produced neurotoxicity at
0.5 and 4 h intervals.
Based on the results of phase I evaluation of pharmaco-
logical activity and neurotoxicity, compounds 5b and 5q
were selected for phase II quantitative evaluation (Table 3).
Median effective doses (ED50) of compounds 5b and 5q were
found to be 15.4 and 18.6 mg/kg, respectively, in MES model,
exhibiting high potency. Whereas in scPTZ model, the
compounds 5b and 5q showed high ED50 values; although
these values were comparable to ED50 values of phenytoin.
Phase II evaluation also revealed that the median toxic doses
(TD50) of compounds 5b and 5q were 319.4 and 649.5
respectively, which were >5 folds higher than those of
phenytoin and carbamazepine. Further, low ED50 and high
TD50 values indicate high potency and a wider therapeutic
window of compounds 5b and 5q. Protective index of tested
compounds was also higher than that of the standards in
both MES and scPTZ models. Therefore, it can be concluded
5
h, 5l, 5m, and 5r produced antiseizure effect against scPTZ at
the dose of 100 mg/kg. Compounds 5d, 5e, 5k, 5s, and 5t
produced antiseizure effect at a higher dose of 300 mg/kg in
this model. Similar to MES model, 5q was found to be the most
potent among synthesized compounds. Results showed that
phenytoin was ineffective against PTZ-induced seizures.
However, carbamazepine blocked PTZ seizures at the
1
00 mg/kg dose level. Long-lasting blockade of scPTZ induced
after 4 h treatments was observed with compounds 5b, 5c, 5l,
q, and 5r at 100 mg/kg. Compounds 5a, 5e, 5h, and 5k also
5
showed long duration of action but at higher dose of 300 mg/
kg. However, this dose was also comparable to the standard
carbamazepine.
On correlating the activity of the compounds with their
structures, it may be concluded that compounds substituted
with electron-withdrawing groups (Cl, F, NO ) on hydropho-
2
bic aryl ring as well as on distal aryl ring were found to be
more active than compounds with electron-donating sub-
3 3
stituents, that is, CH , OCH .
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Table 3. Phase II quantitative evaluation of selected active compounds (5b and 5q).
a)
c)
ED50 (mg/kg)
PI
b)
Compounds
MES
ScPTZ
TD50 (mg/kg)
MES
scPTZ
d)
5
5
PHY
CBZ
b
q
15.4 (13.8–17.1)
18.6 (16.4–19.5)
9.5 (8.1–10.4)
8.8 (5.5–14.1)
367.6 (343.2–394.2)
245.6 (223.4–286.3)
>300
319.4 (316.2–328.3)
649.5 (631.8–667.6)
65.5 (52.5–72.9)
20.7
34.9
6.9
0.8
2.6
<0.2
<0.2
>100
71.6 (45.9–135)
8.1
Number of animals used ¼ 6; solvent used: polyethylene glycol (0.1 mL, intraperitoneally).
a)
ED50: median effective dose eliciting anticonvulsant protection in 50% of animals.
TD50: median toxic dose eliciting minimal neurological toxicity in 50% of animals.
b)
c)
PI ¼ protective index (TD50/ED50).
d)
Data in parentheses are the 95%confidence limits.
that phase II evaluation indicates high potency along with
good margin of safety of selected compounds.
molecular descriptors, viz. polar surface area (PSA), correlates
with human intestinal absorption. It is very useful in prediction
of drug transport properties. Calculation of total polar surface
area (TPSA) in the present study was based on summation of
the tabulated surfacecontributionsof polar fragments toward
their physicochemical environment [18, 19]. The percentage of
absorption (%ABS) was calculated using TPSA. Obtained data
showed that none of the synthesized compounds violated
Lipinski's “rule of five” (Table 5).
Liver toxicity is a major drawback for the clinical use of
anticonvulsant agents. Therefore, we screened the two novel
compounds for possible hepatic toxicity. The results of liver
enzyme estimation are shown in Table 4. None of the two
molecules shows any signs of hepatic toxicity as evident from
insignificant difference (p > 0.05) in liver enzymes level (i.e.,
serum glutamate oxaloacetate transaminase [SGOT], serum
glutamate pyruvate transaminase [SGPT], alkaline phospha-
tase [ALP], albumin, and total bilirubin) between compounds
5
b, 5q, and control (i.e., normal saline) group (Fig.1). Further,
Conclusion
the histopathological evaluation of liver tissue of groups
treated with compounds 5b and 5q was also carried out using
hematoxylin and eosin staining technique. Both compounds
A number of strategic derivatives of N-(substituted-2-oxo-
4-phenylazetidin-1-yl)-2-((6-substitutedbenzo[d]thiazol-2-yl)-
amino)acetamide derivatives were synthesized and evaluated
for anticonvulsant activity using MES and scPTZ screens. A
number of compounds showed good in vivo seizure control
and were free from neurotoxicity.
5
b and 5q showed normal histological features (Fig. 2).
Pharmacokinetic parameters
Druglikeness is an important method to preliminary assess the
balance among the molecular properties of a molecule which
affect the pharmacokinetic and pharmacodynamic aspects.
This helps in optimizing their absorption, distribution,
metabolism, and excretion (ADME) profile. This methodallows
estimating oral absorption as well as permeability for the
molecules which follow Lipinski's “rule of five”. However, the
predictability for the molecule which follows four or less
parameters carries high failure risk. For example, one of the
Experimental
Chemistry
TheentirechemicalsusedinthesynthesiswereprocuredfromE.
Merck and SD Fine-Chem Limited. Thin layer chromatography
(TLC) was performed with Silica gel 60 F254 TLC aluminum
Table 4. Enzyme estimation of selected compounds in serum level.
a)
b)
Compounds
SGOT
SGPT
Alkaline phosphatase
Albumin
Bilirubin
c)
Control
85.1 ꢁ 2.18
87.21 ꢁ 2.04
86.34 ꢁ 3.33
86.3 ꢁ 4.12
25.91 ꢁ 1.13
28.33 ꢁ 1.27
27.61 ꢁ 1.34
26.91 ꢁ 2.2
15.59 ꢁ 0.48
16.27 ꢁ 0.47
17.31 ꢁ 0.39
15.98 ꢁ 0.72
1.34 ꢁ 0.03
1.4 ꢁ 0.02
1.33 ꢁ 0.03
1.52 ꢁ 0.02
1.56 ꢁ 0.03
1.5 ꢁ 0.02
1.51 ꢁ 0.03
1.57 ꢁ 0.02
5
5
b
q
PHY
Number of animals tested (n ¼ 6).
a)
Serum glutamate oxaloacetate transaminase.
Serum glutamate pyruvate transaminase.
b)
c)
Non-significant (p > 0.05 vs. control). The mean levels were calculated using ANOVA followed by Dunnett's test.
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New Benzo[d]thiazol-2-yl-acetamides as Anticonvulsants
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Figure 1. Hepatic enzymes estimations after treatment with different test compounds. Number of animals tested (n ¼ 6). The mean
levels were calculated using ANOVA followed by Dunnett's test.
sheets (Merck) using toluene/ethyl acetate/formic acid (5:4:1)
and benzene/acetone (9:1) as eluents. Spots were visualized
under UV light (254 nm) and in iodine chamber. Ashless
Whatman No. 1 filter paper was used for vacuum filtration.
Melting points were determined using open capillary tubes in a
Hicon melting point apparatus (Hicon, India) and are uncor-
rected. The purity of the compounds was confirmed through
elemental analysis. The elemental analyses (C, H, N, and S) of all
compounds were performed on the CHNS Elementar (Analy-
sensystemeGmbH,Germany)VarioELIIIandresultswerewithin
benzothiazole scaffold. All these compounds were synthe-
sized from anilines as a starting material. The target
compounds were synthesized according to Scheme 1. Substi-
tuted anilines cyclized to 6-substituted benzo[d]thiazol-2-
amines (1a–e) on treatment with potassium thiocyanates and
bromine in glacial acetic acid, which was acetylated by
ethylchloroacetate to afford ethyl 2-((6-substituted benzo[d]-
thiazol-2-yl)amino)acetates (2a–e). This on further treatment
withhydrazine hydrateconvertedinto2-((6-substitutedbenzo-
[d]thiazol-2-yl)amino)acetohydrazides (3a–e), which were con-
densed with different aldehydes to yield corresponding N-(4-
substitutedbenzylidene)-2-((6-substitutedbenzo[d]thiazol-2-yl)-
amino)acetohydrazides (4a–t). The titled compounds N-(3-
chloro-2-(substitutedphenyl)-4-oxoazetidin-1-yl)-2-((6-substituted-
benzo[d]thiazol-2-yl)amino)acetamides (5a–t) were obtained
on treatment with chloroacetylchloride in presence of
triethylamine.
ꢁ
0.4% of the theoretical values. Fourier transform infrared
spectra were recorded in KBr pellets on a Shimadzu FTIR
1
13
6 3
spectrometer. H NMR and C NMR spectra in DMSO-d /CDCl
solutions were, respectively, recorded at 400 and 100MHz with
Bruker 400 Ultra shield TM NMR spectrometer using TMS
[
(CH
as follows: s, singlet; bs, broad singlet; d, doublet; t, triplet;
andm,multiplet. TheNHprotonswereD Oexchangedfortheir
3 4
) Si]asinternalstandard. Splittingpatternsarenominated
2
spectralcharacterization.Themassspectrawererecordedusing
Waters Micromass ZQ 2000 spectrophotometer (Jamia Ham-
dard, New Delhi, India). For pharmacokinetic parameters,
Molinspiration software was used.
Preparation of 6-substituted-1,3-benzo[d]thiazol-2-
amines (1a–e)
To substitute aniline (0.01 mol), potassium thiocyanate
(0.01 mol) in glacial acetic acid (10%) was added at 10°C
and stirred. Bromine (0.01 mol) was added dropwise to this
mixture at such a rate so as to keep the temperature below
10°C throughout the addition. Stirring was continued for an
The data set in this study consists of N-(substituted-2-oxo-
4
-phenylazetidin-1-yl)-2-((6-substitutedbenzo[d]thiazol-2-yl)-
amino)acetamide derivatives with different substitution on
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259

Arch. Pharm. Chem. Life Sci. 2015, 348, 254–265
R. Ali and N. Siddiqui
ARC HH PHARM
Archiv der Pharmazie
Figure 2. High power photomicrograph of portal triad area of liver tissue from animals treated with (a) control and (b) compound 5b
and (c) compound 5q showing a normal histological appearance (HE ꢂ 400). PT, portal triad; CV, central vein.
additional 3 h and the separated hydrochloride salt was
filtered, washed with acetic acid, and dried [17]. It was
dissolved in hot water and neutralized with aqueous
ammonia solution (25%). Resulting product was filtered,
washed with water, and dried, recrystallized with benzene to
obtain 6-substituted-1,3-benzothiazol-2-amines (1a–e).
6-Methyl-1,3-benzo[d]thiazol-2-amine (1d)
ꢀ
1
Yield 80%; IR: nmax (cm ) 3350 (NH), 1566 (C–N), 695 (C–S–C);
1
H NMR (DMSO-d
6
): (d, ppm) 2.34 (s, 3H, CH
3
), 6.99–7.35
(m, 3H, Ar-H), 7.27 (s, 2H, NH
2
, D O exchangeable).
2
6-Methoxy-1,3-benzo[d]thiazol-2-amine (1e)
ꢀ1
Yield 78%; IR : nmax (cm ) 3346 (NH), 1520 (C–N), 682 (C–S–C);
1
6
-Chloro-1,3-benzo[d]thiazol-2-amine (1a)
H NMR (DMSO-d
6
): (d, ppm) 3.84 (s, 3H, OCH
3
), 6.95–7.47
ꢀ
1
Yield 74%; IR: nmax (cm ) 3460 (NH), 1585 (C–N), 628 (C–S–C);
(m, 3H, Ar-H), 7.97 (s, 2H, NH
, D O exchangeable).
2
2
1
6 2 2
H NMR (DMSO-d ): (d, ppm) 6.10 (s, 2H, NH , D O exchange-
able), 6.70–7.20 (m, 3H, Ar-H).
Preparation of ethyl-2-((6-substitutedbenzo[d]thiazol-2-
yl)amino)acetates 2a–e
6
-Fluoro-1,3-benzo[d]thiazol-2-amine (1b)
Equimolarquantitiesof6-substituted-1,3-benzothiazol-2-amines
(1a–e) (0.1 mol), and ethyl chloroacetate (0.1 mol) were refluxed
in dry acetone (50 mL) on water bath for 24 h in the presence of
anhydrous potassium carbonate (19.5 g, 0.15 mol). The reaction
mixture was cooled and filtered. Dried acetone was removed
from the filtrate by distillation and the remaining filtrate was
poured into ice-cold water. The organic layer separated was
extracted with diethyl ether. The ether layer was washed with 5%
HCl and then removed by evaporation on a water bath. The
ꢀ
1
Yield 81%; IR: nmax (cm ) 3320 (NH), 1598 (C–N), 725 (C–S–C);
1
6 2 2
H NMR (DMSO-d ): (d, ppm) 6.50 (s, 2H, NH , D O exchange-
able), 6.75–7.30 (m, 3H, Ar-H).
6
-Nitro-1,3-benzo[d]thiazol-2-amine (1c)
ꢀ
1
Yield 72%; IR: nmax (cm ) 3255 (NH), 1610 (C–N), 670 (C–S–C);
1
6 2 2
H NMR (DMSO-d ): (d, ppm) 6.61 (s, 2H, NH , D O exchange-
able), 6.70–7.89 (m, 3H, Ar-H).
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Arch. Pharm. Chem. Life Sci. 2015, 348, 254–265
New Benzo[d]thiazol-2-yl-acetamides as Anticonvulsants
ARC HH PHARM
Archiv der Pharmazie
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Arch. Pharm. Chem. Life Sci. 2015, 348, 254–265
R. Ali and N. Siddiqui
ARC HH PHARM
Archiv der Pharmazie
remaining liquid was vacuum distilled to yield pure ethyl 2-(6-
CH-Ar), 5.52 (s, 1H, CHCl), 7.01 (br s, 1H, NH), 7.05–8.29 (m, 8H,
1
3
substitutedbenzo[d]thiazole-2-ylamino)acetates (2a–e). Yield
Ar-H, and benzothiazole-H), 10.02 (s, 1H, CONH); C NMR
(CDCl ) d ppm: 173.7, 170.0, 163.5, 150.5, 145.0, 132.6, 129.0,
128.8, 125.8, 118.0, 67.5, 64.2, 55.7; MS (m/z): 465.97 (Mþ1).
Anal. Found for C18 14ClFN S: C 46.42, H 3.05, N 12.03,
ꢀ
1
1
7
2%; IR: (cm ) 3355 (NH), 1780 (C –– O), 1580 (C –– N); H NMR
): (d, ppm) 1.25 (t, 3H, CH ), 4.09 (s, 2H, CH
C –– O), 4.50 (q,
), 6.98 (br s, 1H, NH), 7.33–7.89 (m, 3H, Ar-H).
3
(DMSO-d
6
3
2
2H, CH
2
H
4 2
O
S 6.68%. Calcd.: C 46.40, H 3.00, N 12.05, S 6.70%.
Preparation of 2-((6-substitutedbenzo[d]thiazol-2-yl)-
amino)acetohydrazides 3a–e
N-(3-Chloro-2-oxo-4-phenylazetidin-1-yl)-2-((6-
To the warm hydrazine hydrate (0.07 mol), solution of
respective acetates (2a–e) (0.05 mol) in ethanol, conc. NaOH
nitrobenzo[d]thiazol-2-yl)amino)acetamide (5c)
ꢀ
1
Yield: 82%; IR (KBr) n (cm ): 3446 (NH), 1690 (C–O), 1615
1
(
0.05 g) was added and refluxed for 6 h. The reaction mixture
(C–N); H NMR (DMSO-d
6
) d ppm: 3.92 (s, 2H, CH
2
), 5.01 (s, 1H,
was poured into crushed ice. The solid obtained was filtered
CH-Ar), 5.55 (s, 1H, CHCl), 6.56 (br s, 1H, NH), 6.95–9.05 (m, 8H,
1
3
off and dried to yield needle-like crystals of desired product
Ar-H, and benzothiazole-H), 10.12 (s, 1H, CONH); C NMR
(CDCl ) d ppm: 173.2, 170.4, 163.4, 150.9, 145.2, 130.6, 129.1,
128.0, 125.3, 117.0, 67.5, 64.2, 55.5; MS (m/z): 431.09 (Mþ1).
Anal. calcd. for C18 14ClN S: C 50.06, H 3.27, N 16.22, S
.42%. Found: C 50.01, H 3.20, N 16.20, S 7.40%.
ꢀ
1
(
(
(
3a–e). Yield 82%; IR (cm ) 3350 (NH), 1750 (C–O), 1613
3
1
C–N), H NMR (DMSO-d
): (d, ppm) 4.09 (s, 2H, CH
), 6.99–7.56 (m, 3H, Ar-H), 9.27 (s, 1H, CONH).
C–O), 6.85
6
2
s, 2H, NH
2
H
5 4
O
7
Preparation of N-(substitutedbenzylidene)-2-((6-
substitutedbenzo[d]thiazol-2-yl)amino)acetohydrazides
N-(3-Chloro-2-oxo-4-phenylazetidin-1-yl)-2-((6-
4
a–t
methylbenzo[d]thiazol-2-yl)amino)acetamide (5d)
ꢀ
1
To the solution of 3a–e (0.01 mol) in ethanol, appropriate
aromatic aldehydes (0.01 mol) were added together with few
drops of glacial acetic acid (0.01 mol). The reaction mixture
was refluxed on a water bath for 5 h. The precipitate formed
Yield: 77%; IR (KBr) n (cm ): 3446 (NH), 1697 (C–O), 3305
1
(NH), 1644 (C–N); H NMR (DMSO-d
6
) d ppm: 2.40 (s, 3H, CH
3
),
2
3.92 (s, 2H, CH ), 5.01 (s, 1H, CH-Ar), 5.49 (s, 1H, CHCl), 7.56
(br s, 1H, NH), 7.10–9.00 (m, 8H, Ar-H, and benzothiazole-H),
1
3
(
4a–t) was filtered, washed with ice-cold water, and recrystal-
3
9.89 (s, 1H, CONH); C NMR (CDCl ) d ppm: 174.5, 170.3, 163.5,
ꢀ
1
lized from methanol. Yield 82%; IR (cm ) 3350 (NH), 1750
150.2, 143.2, 134.6, 130.7, 128.1, 126.9, 126.3, 121.3,
1
(
C–O), 1600 (C–N). H NMR (DMSO-d
CH ), 6.03 (t, 1H, Ar-NH), 7.52–7.89 (m, 5H, Ar-H), 7.56–8.13 (m,
H, benzo-H), 8.20 (s, 1H, CONH).
6
): (d, ppm) 3.12 (s, 2H,
117.1,67.4, 64.1, 57.3, 20.9; MS (m/z): 400.09 (Mþ1). Anal.
2
4 2
calcd. for C19H17ClN O S: C 56.93, H 4.27, N 13.98, S 8.00%.
3
Found: C 56.90, H 4.25, N 13.96, S 7.95%.
Preparation of N-(3-chloro-2-(substitutedphenyl)-4-
oxoazetidin-1-yl)-2-((6-substitutedbenzo[d]thiazol-2-yl)-
amino)acetamides 5a–t
A solution of 4a–t (0.01 mol) in dioxane (25 mL) was added to a
well-stirred mixture of chloroacetyl chloride (0.01 mol) and
triethylamine (0.01 mol) in dioxane (15 mL) at 5–10°C. The
resulting mixture was stirred for 10 h and left at room
temperature for 48 h. The content was treated with cold
water and solid obtained was filtered, dried, and recrystal-
lized from methanol to obtain the final product (5a–t).
N-(3-Chloro-2-oxo-4-phenylazetidin-1-yl)-2-((6-
methoxybenzo[d]thiazol-2-yl)amino)acetamide (5e)
ꢀ
1
Yield:80%;IR(KBr)n (cm ):3320 (NH), 1640(C –– O), 1617(C –– N);
1
6 2 3
H NMR (DMSO-d ) d ppm: 3.75 (s, 2H, CH ), 3.90 (s, 3H, OCH ),
5.01 (s, 1H, CH-Ar), 5.42 (s, 1H, CHCl), 7.10 (brs, 1H, NH), 7.01–
8.12 (m, 8H, Ar-H, and benzothiazole-H), 10.11 (s, 1H, CONH);
1
3
C NMR (CDCl
131.7, 128.5, 118.1, 114.9, 67.4, 64.1, 57.3, 55.8;MS(m/z):416.07
17ClN S: C 54.74, H 4.11 N 13.44, S
3
) d ppm: 174.5, 170.7, 163.9, 156.2, 145.5, 143.5,
(Mþ1). Anal. calcd. for C19
H
4 3
O
7.69%. Found: C 54.72, H 4.09, N 13.50, S 7.65%.
N-(3-Chloro-2-oxo-4-phenylazetidin-1-yl)-2-((6-
N-(3-Chloro-2-oxo-4-(o-tolyl)azetidin-1-yl)-2-((6-
chlorobenzo[d]thiazol-2-yl)amino)acetamide (5a)
chlorobenzo[d]thiazol-2-yl)amino)acetamide (5f)
ꢀ
1
ꢀ1
Yield: 72%; IR (KBr) n (cm ): 3350 (NH), 1695 (C–O), 1562
Yield:80%;IR(KBr)n (cm ):3360 (NH), 1685(C –– O), 1635(C –– N);
1
1
(
C–N); H NMR (DMSO-d
6
) d ppm: 3.79 (s, 2H, CH
2
), 5.02 (s, 1H,
6 3 2
H NMR(DMSO-d )dppm:2.34(s, 3H,CH ),3.72(s, 2H, CH ),5.10
CH-Ar), 5.50 (s, 1H, CHCl), 6.95 (br s, 1H, NH), 7.08–8.10 (m, 8H,
(s, 1H, CH-Ar), 5.76(s, 1H,CHCl), 7.60(brs, 1H,NH), 6.94–8.13(m,
7H, Ar-H, and benzothiazole-H), 10.56 (s, 1H, CONH); C NMR
13
13
Ar-H, and benzothiazole-H), 9.82 (s, 1H, CONH); C NMR
CDCl ) d ppm: 173.9, 170.1, 163.5, 151.5, 145.9, 133.8, 129.2,
28.5, 126.9, 125.8, 117.0, 67.5, 64.2, 55.6. MS (m/z): 420.02
Mþ1). Anal. for C18 S: Found: C 51.32, H 3.35, N
3.30, S 7.61%. Calcd.: C 51.02, H 3.39, N 13.28, S 7.59%.
(
3
(CDCl
129.8, 126.6, 125.9, 114.9, 64.9, 57.3, 19.1; MS (m/z): 435.33
S: C 52.42, H 3.70, N 12.87,
3
) d ppm: 174.5, 170.2, 163.5, 151.2, 141.8, 134.7, 130.7,
1
(
H
2
14Cl N
4
O
2
(Mþ1). Anal. calcd. for C19
2 4 2
H16Cl N O
1
S 7.77%. Found: C 52.49, H 3.77, N 12.97, S 7.67%.
N-(3-Chloro-2-oxo-4-phenylazetidin-1-yl)-2-((6-
N-(3-Chloro-2-oxo-4-(o-tolyl)azetidin-1-yl)-2-((6-
fluorobenzo[d]thiazol-2-yl)amino)acetamide (5b)
fluorobenzo[d]thiazol-2-yl)amino)acetamide (5g)
ꢀ
1
ꢀ1
Yield: 80%; IR (KBr) n (cm ): 3431 (NH), 1705 (C–O), 1640
Yield:86%;IR(KBr)n (cm ):3450 (NH), 1710(C –– O), 1599(C –– N);
1
1
(
C–N); H NMR (DMSO-d
6
) d ppm: 3.92 (s, 2H, CH
2
), 5.09 (s, 1H,
6 3
H NMR(DMSO-d )dppm:2.38(s, 3H,CH ),3.79(s, 2H, CH
2
),5.06
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Arch. Pharm. Chem. Life Sci. 2015, 348, 254–265
New Benzo[d]thiazol-2-yl-acetamides as Anticonvulsants
ARC HH PHARM
Archiv der Pharmazie
(
7
s, 1H, CH-Ar), 5.52(s, 1H,CHCl), 6.80(brs, 1H,NH), 6.90–8.75(m,
6.94–8.72 (m, 7H, Ar-H, and benzothiazole-H), 10.03 (s, 1H,
CONH); C NMR (CDCl ) d ppm: 173.8, 170.0, 163.2, 158.2,
3
1
3
13
H, Ar-H, and benzothiazole-H), 10.11 (s, 1H, CONH); C NMR
) d ppm: 174.3, 170.5, 163.7, 151.5, 144.8, 134.7, 130.5,
29.9, 126.9, 125.0, 114.8, 64.9, 57.3, 19.1; MS (m/z): 479.98
16ClFN S: C 47.56, H 3.36, N 11.68,
(
CDCl
3
151.9, 142.0, 133.1, 130.8, 129.9, 125.0, 114.9, 64.7, 57.9, 55.3;
16ClFN S:
1
MS (m/z): 495.95 (Mþ1). Anal. calcd. for C19
H
4 3
O
(
Mþ1). Anal. calcd. for C19
H
O
4 2
C 46.03, H 3.25, N 11.30, S 6.47%. Found: C 46.09, H 3.28,
N 11.39, S 6.50%.
S 6.68%. Found: C 47.60, H 3.40, N 11.70, S 6.70%.
N-(3-Chloro-2-oxo-4-(o-tolyl)azetidin-1-yl)-2-((6-
N-(3-Chloro-2-(4-methoxyphenyl)-4-oxoazetidin-1-yl)-2-
nitrobenzo[d]thiazol-2-yl)amino)acetamide (5h)
((6-nitrobenzo[d]thiazol-2-yl)amino)acetamide (5m)
ꢀ
1
ꢀ1
Yield:86%;IR(KBr)n (cm ):3360 (NH), 1690(C –– O), 1609(C –– N);
Yield:86%;IR(KBr)n (cm ):3450 (NH), 1699(C –– O), 1600(C –– N);
1
1
6 3
H NMR(DMSO-d )dppm:2.40(s, 3H,CH ),3.69(s, 2H, CH
2
),5.04
6 2 3
H NMR (DMSO-d ) d ppm: 3.80 (s, 2H, CH ), 3.84 (s, 3H, OCH ),
(
7
(
1
s, 1H, CH-Ar), 5.46(s, 1H,CHCl), 7.78(brs, 1H,NH), 6.89–8.70(m,
5.04 (s, 1H, CH-Ar), 5.51 (s, 1H, CHCl), 6.49 (brs, 1H, NH), 6.95–
1
3
H, Ar-H, and benzothiazole-H), 9.90 (s, 1H, CONH); C NMR
) d ppm: 174.0, 170.1, 163.2, 150.9, 144.6, 134.3, 131.5,
29.8, 125.7, 125.2, 114.9, 64.7, 57.3, 20.1; MS (m/z): 445.06
16ClN S:C51.71, H 3.62, N15.86,S
.19%. Found: C 51.90, H 3.70, N 15.90, S 7.20%.
8.75 (m, 7H, Ar-H, and benzothiazole-H), 9.80 (s, 1H, CONH);
1
3
CDCl
3
C NMR (CDCl
133.7, 131.6, 129.1, 125.9, 114.7, 64.9, 57.9, 55.8; MS (m/z):
16ClN S: C 49.41, H 3.49, N
3
) d ppm: 173.5, 170.8, 163.5, 159.2, 152.5, 142.8,
(
7
Mþ1). Anal. calcd. forC19
H
O
5 4
461.82 (Mþ1). Anal. calcd. for C19
H
5 5
O
15.16, S 6.94%. Found: C 50.01, H 3.50, N 15.29, S 6.99%.
N-(3-Chloro-2-oxo-(4-o-tolyl)azetidin-1-yl)-2-((6-
N-(3-Chloro-2-(4-methoxyphenyl)-4-oxoazetidin-1-yl)-2-
methylbenzo[d]thiazol-2-yl)amino)acetamide (5i)
((6-methylbenzo[d]thiazol-2-yl)amino)acetamide (5n)
ꢀ
1
ꢀ1
Yield:88%;IR(KBr)n (cm ):3420 (NH), 1710(C –– O), 1660(C –– N);
Yield:69%;IR(KBr)n (cm ):3500 (NH), 1720(C –– O), 1585(C –– N);
1
1
H NMR (DMSO-d
.50(s,1H,CHCl),5.08(s,1H,CH-Ar),7.16(brs1H,NH),6.94–7.90
m, 7H, Ar-H, and benzothiazole-H), 10.02 (s, 1H, CONH);
6
) d ppm: 2.36 (s, 6H, 2CH
3
), 3.72 (s, 2H, CH
2
),
HNMR(DMSO-d
), 5.01(s, 1H, CH-Ar), 5.46(s, 1H, CHCl), 6.99(brs, 1H,
NH), 6.80–7.99 (m, 7H, Ar-H, and benzothiazole-H), 11.00 (s, 1H,
6 3 2
)dppm:2.34(s,3H,CH ),3.73(s,2H,CH ),3.82
4
(s, 3H, OCH
3
(
1
3
13
C NMR (CDCl
34.3,130.8,130.1,125.7,125.2,114.9,64.7,57.3,20.1;MS(m/z):
19ClN S: C 57.90, H 4.62,
3
) d ppm: 173.9, 170.1, 163.2, 153.9, 144.0, 134.9,
CONH); CNMR(CDCl
140.8, 131.7, 128.0, 123.6, 114.8, 65.0, 57.8, 55.0, 23.8; MS (m/z):
19ClN S: C 55.75, H 4.44, N
3
)dppm:173.5, 170.1, 163.9, 159.0, 152.8,
1
4
14.06 (Mþ1). Anal. calcd. for C20
H
O
4 2
430.09 (Mþ1). Anal. calcd. for C20
H
4 3
O
N 13.52, S 7.73%. Found: C 57.79, H 4.60, N 13.48, S 7.70%.
13.00, S 7.44%. Found: C 55.77, H 4.42, N 13.03, S 7.46%.
N-(3-Chloro-2-(4-methoxyphenyl)-4-oxoazetidin-1-yl)-2-
N-(3-Chloro-2-(4-methoxyphenyl)-4-oxoazetidin-1-yl)-2-
(
(6-methylbenzo[d]thiazol-2-yl)amino)acetamide (5j)
((6-methoxybenzo[d]thiazol-2-yl)amino)acetamide (5o)
ꢀ
1
ꢀ1
Yield:85%;IR(KBr)n (cm ):3345 (NH), 1725(C –– O), 1599(C –– N);
Yield:78%;IR(KBr)n (cm ):3325 (NH), 1640(C –– O), 1620(C –– N);
1
1
HNMR(DMSO-d
), 5.08(s, 1H, CH-Ar), 5.40(s, 1H, CHCl), 7.49(brs, 1H,
NH), 6.92–8.39 (m, 7H, Ar-H, and benzothiazole-H), 10.25 (s, 1H,
6 3 2
)dppm:2.34(s,3H,CH ),3.77(s,2H,CH ),3.83
6 2 3
H NMR (DMSO-d ) d ppm: 3.70 (s, 2H, CH ), 3.88 (s, 6H, 2OCH ),
(
s, 3H, OCH
3
5.10 (s, 1H, CH-Ar), 5.50 (s, 1H, CHCl), 7.98 (brs, 1H, NH), 6.99–
8.01 (m, 7H, Ar-H, and benzothiazole-H), 10.52 (s, 1H, CONH);
13
13
CONH); CNMR(CDCl
42.8, 133.4, 130.1, 129.8, 125.2, 114.0, 64.7, 57.3, 55.8, 20.9; MS
m/z): 430.09 (Mþ1). Anal. calcd. for C20 19ClN S: C 50.26, H
.55, N 12.41, S 7.19%. Found: C 50.30, H 3.62, N 12.56, S 7.15%.
3
)dppm:173.5, 170.2, 163.6, 158.2, 151.9,
3
C NMR(CDCl ) d ppm:174.56, 173.9, 170.1, 163.5, 151.4, 145.9,
1
(
3
133.8, 129.2, 128.7, 126.9, 117.0, 67.5, 64.2, 55.6; MS (m/z):
19ClN S: C 53.75, H 4.29,
H
O
4 3
446.19 (Mþ1). Anal. calcd. for C20
H
4 4
O
N 12.54, S 7.17%. Found: C 53.77, H 4.30, N 12.55, S 7.20%.
N-(3-Chloro-2-(4-methoxyphenyl)-4-oxoazetidin-1-yl)-2-
N-(3-Chloro-2-(2-chlorophenyl)-4-oxoazetidin-1-yl)-2-((6-
(
(6-chlorobenzo[d]thiazol-2-yl)amino)acetamide (5k)
chlorobenzo[d]thiazol-2-yl)amino)acetamide (5p)
ꢀ
1
ꢀ1
Yield:79%;IR(KBr)n (cm ):3355 (NH), 1700(C –– O), 1602(C –– N);
Yield: 70%; IR (KBr) n (cm ): 3368 (NH), 1699 (C–O), 1578
1
1
6 2
H NMR (DMSO-d ) d ppm: 3.75 (s, 2H, CH ), 3.83 (s, 3H, OCH
3
),
(C–N); H NMR (DMSO-d
6
) d ppm: 3.75 (s, 2H, CH
2
), 5.10 (s, 1H,
5
8
.06 (s, 1H, CH-Ar), 5.50 (s, 1H, CHCl), 7.35 (brs, 1H, NH), 6.90–
CH-Ar), 5.55 (s, 1H, CHCl), 6.28 (br s, 1H, NH), 7.15–8.99 (m, 7H,
1
3
.30 (m, 7H, Ar-H, and benzothiazole-H), 10.15 (s, 1H, CONH);
Ar-H, and benzothiazole-H), 10.56 (s, 1H, CONH); C NMR
(CDCl ) d ppm: 173.9, 170.1, 163.5, 151.5, 145.9, 133.8, 129.2,
128.5, 126.9, 125.8, 117.0, 67.5, 64.2, 55.6. MS (m/z): 455.98
S: C 47.44, H 4.48,
1
3
C NMR (CDCl
33.4, 130.1, 129.8, 125.2, 114.0, 64.7, 57.5, 55.8; MS (m/z):
S: C 50.56, H 3.57,
3
) d ppm: 173.9, 170.1, 163.6, 158.2, 151.9, 142.8,
3
1
4
58.09 (Mþ1). Anal. calcd. for C19
H16Cl N O
2 4 3
(Mþ1). Anal. calcd. for C18
3 4 2
H13Cl N O
N 12.40, S 7.10%. Found: C 50.60, H 3.60, N 12.50, S 7.12%.
N 12.29, S 7.04%. Found: C 47.45, H 4.40, N 12.31, S 7.05%.
N-(3-Chloro-2-(4-methoxyphenyl)-4-oxoazetidin-1-yl)-2-
N-(3-Chloro-2-(2-chlorophenyl)-4-oxoazetidin-1-yl)-2-((6-
(
(6-fluorobenzo[d]thiazol-2-yl)amino)acetamide (5l)
fluorobenzo[d]thiazol-2-yl)amino)acetamide (5q)
ꢀ
1
ꢀ1
Yield: 86%; IR (KBr) n (cm ): 3360 (NH), 1685 (C–O), 1610
Yield: 80%; IR (KBr) n (cm ): 3358 (NH), 1685 (C–O), 1590
1
1
(
C–N); H NMR (DMSO-d
6
) d ppm: 3.77 (s, 2H, CH
2
), 3.83 (s, 3H,
(C–N); H NMR (DMSO-d
6
) d ppm: 3.70 (s, 2H, CH
2
), 5.09 (s, 1H,
OCH
3
), 5.08 (s, 1H, CH-Ar), 5.50 (s, 1H, CHCl), 7.21 (br s, 1H, NH),
CH-Ar), 5.52 (s, 1H, CHCl), 7.50 (br s, 1H, NH), 6.99–8.90 (m, 7H,
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Arch. Pharm. Chem. Life Sci. 2015, 348, 254–265
R. Ali and N. Siddiqui
ARC HH PHARM
Archiv der Pharmazie
1
3
Ar-H, and benzothiazole-H), 10.37 (s, 1H, CONH); C NMR
CDCl ) d ppm: 173.8, 170.9, 163.0, 150.5, 140.8, 131.5, 128.2,
28.0, 125.8, 118.2, 67.9, 64.0, 55.6. MS (m/z): 499.08 (Mþ1).
Anal. calcd. for C18 FN S: C 46.36, H 2.81, N 15.02,
groups. For induction of seizures in mice, a 60 Hz alternating
current of 50 mA intensity was used. The current was applied
for 0.2 s using ear clip electrodes, coated with an electrolyte
solution containing an anesthetic agent. Abolition of the hind
limb and tonic maximal extension was regarded as end point
protection against MES-induced seizures. The observations
were taken at two different time intervals (0.5 h in one group
and 4.0 h in other group, respectively).
(
1
3
H13Cl
2
4 2
O
S 6.88%. Found: C 46.38, H 2.85, N 15.20, S 6.90%.
N-(3-Chloro-2-(2-chlorophenyl)-4-oxoazetidin-1-yl)-2-((6-
nitrobenzo[d]thiazol-2-yl)amino)acetamide (5r)
ꢀ
1
Yield: 78%; IR (KBr) n (cm ): 3350 (NH), 1680 (C–O), 1608
1
(
C–N); H NMR (DMSO-d
6
) d ppm: 3.73 (s, 2H, CH
2
), 5.01 (s, 1H,
Subcutaneous pentylenetetrazole-induced seizure
test [21]
CH-Ar), 5.59 (s, 1H, CHCl), 6.99 (br s, 1H, NH), 7.09–8.20 (m, 7H,
13
Ar-H, and benzothiazole-H), 9.87 (s, 1H, CONH); C NMR
CDCl ) d ppm: 174.8, 170.5, 162.0, 150.3, 141.8, 133.5, 128.9,
28.0, 126.8, 118.9, 67.8, 64.3, 55.6. MS (m/z): 465.01 (Mþ1).
Anal. calcd. for C18 S: C 52.42, H 3.70, N 12.87,
This model primarily identifies those compounds that raise
seizure threshold. The subcutaneous dose of PTZ (85 mg/kg) at
which 97% of the animals showed clonic seizure induction
was calculated using dose response method. Animals were
divided into different groups and test drugs were adminis-
tered. The test compounds were administered intraperitone-
ally at three different doses, that is, 30, 100, and 300 mg/kg.
At the anticipated time of testing, PTZ was administered
subcutaneously as 0.5% solution in the posterior midline of
mice. Animals were observed after 30 min and 4.0 h. The
absence of clonic spasm in half or more animals was regarded
as endpoint protection against scPTZ-induced clonic seizures.
(
3
1
2 5 4
H13Cl N O
S 7.37%. Found: C 52.44, H 3.77, N 12.90, S 7.40%.
N-(3-Chloro-2-(2-chlorophenyl)-4-oxoazetidin-1-yl)-2-((6-
methylbenzo[d]thiazol-2-yl)amino)acetamide (5s)
Yield: 69%; IR (KBr) n (cm ): 3310 (NH), 1710 (C–O), 1615
ꢀ
1
1
(
C–N); H NMR (DMSO-d
6
) d ppm: 2.40 (s, 3H, CH
3
), 3.70 (s, 2H,
CH
2
), 5.05 (s, 1H, CH-Ar), 5.40 (s, 1H, CHCl), 7.55 (br s, 1H, NH),
.99–7.60 (m, 7H, Ar-H, and benzothiazole-H), 10.43 (s, 1H,
) d ppm: 174.0, 170.1, 163.5, 158.1,
44.8, 131.5, 128.9, 126.9, 118.0, 67.5, 64.3, 55.7. MS (m/z):
S: C 50.56, H 3.57,
6
13
CONH); C NMR (CDCl
3
1
4
Rotarod test [22]
35.04 (Mþ1). Anal. calcd. for C19
H
16Cl
2
4
N O
2
Mice were divided into different experimental groups and
trained to stay on a knurled rotarod of diameter 3.2 cm
rotating at 10 rpm. Trained animals were injected with the
test compounds. Motor impairment 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.
N 12.41, S 7.10%. Found: C 50.60, H 3.60, N 12.45, S 7.19%.
N-(3-Chloro-2-(2-chlorophenyl)-4-oxoazetidin-1-yl)-2-((6-
methoxybenzo[d]thiazol-2-yl)amino)acetamide (5t)
Yield:72%;IR(KBr)n (cm ):3340 (NH), 1780(C –– O), 1599(C –– N);
ꢀ
1
1
6 2 3
H NMR (DMSO-d ) d ppm: 3.72 (s, 2H, CH ), 3.83 (s, 3H, OCH ),
5
7
.04 (s, 1H, CH-Ar), 5.44 (s, 1H, CHCl), 7.50 (brs, 1H, NH), 6.95–
Quantification studies
.85 (m, 7H, Ar-H, and benzothiazole-H), 10.50 (s, 1H, CONH);
For the determination of effective dose ED50, that is the dose
of the drug required to elicit the biological response in 50% of
animals and TD50 values that is median toxic dose, groups of
six mice were given a range of intraperitoneal doses of the
test drug until at least three points were established in the
range of 10–90% 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 computer program [23].
1
3
C NMR (CDCl
26.0, 124.8, 117.9, 67.5, 64.9, 55.7, 58.3. MS (m/z): 450.04
S: C 50.60, H 3.50, N 12.45,
3
) d ppm: 173.9, 170.5, 163.8, 157.9, 144.0, 132.8,
1
(
Mþ1). Anal. calcd. for C19
2 4 3
H16Cl N O
S 7.12%. Found: C 50.69, H 3.55, N 12.55, S 7.15%.
Pharmacology
Pharmacological experiments were approved by Institutional
Animal Ethics committee (IAEC, approval no. 784). Animals
were procured from Central Animal House Facility (Hamdard
University, New Delhi, India). Swiss albino mice of same age
and weight were used as experimental animals. The screening
for anticonvulsant activity was carried out by MES test and
scPTZ test whereas neurotoxicity evaluation was done by the
rotarod method. The tested compounds (5a–t) were injected
intraperitoneally at a dose of 30, 100, and 300 mg/kg for
both methods. Phenytoin and carbamazepine were used as
standard drugs for comparison.
Liver toxicity [24–27]
To find out the toxic effects, if any, of the synthesized
compounds on liver, the test compounds were administered
to mice. Twenty-four hours later, serum and tissue samples
were taken for estimation of SGOT, SGPT, ALP, albumin, and
total bilirubin using commercially available kits. Thirty-six
hours after selected active compounds administration, blood
was withdrawn from the tail vein for serum estimations.
Followed by this, mice were sacrificed under high dose of
anesthesia and liver tissue was excised out washed with ice
cold saline and stored for biochemical and histopathological
studies.
Maximal electroshock seizure test [20]
MES test is a model for generalized tonic–clonic seizures and
identifies those compounds which prevent seizure spread.
Animals were randomly divided into different treatment
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264

Arch. Pharm. Chem. Life Sci. 2015, 348, 254–265
New Benzo[d]thiazol-2-yl-acetamides as Anticonvulsants
ARC HH PHARM
Archiv der Pharmazie
Histopathology
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The excised liver tissues were fixed in 10% neutral buffered
formalin and sections of maximum 5 mm thickness were cut.
Further, sections were stained with hematoxylin and eosin for
histopathology. The histomorphological evaluation of the
liver sections was done by a pathologist unacquainted with
the treatment groups.
Statistical analysis
The data were represented as mean ꢁ standard deviation.
One-way analysis of variance (ANOVA) was used to compare
the means of all groups. The value of p < 0.05 was considered
to be statistically significant. GraphPad Prism was used for
statistical analysis.
[13] R. Ali, N. Siddiqui, J. Chem. Hindawi 2013, in press. DOI:
10.1155/2013/345198
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1
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Pharmacokinetic parameters
All the synthesized compounds were assessed using Molinspi-
ration software for the estimation of some important
pharmacokinetic descriptors like molecular weight, number
of rotatable bonds, partition coefficient, total polar surface
area, and number of hydrogen bond donors and acceptors.
[16] N Siddiqui, A. Rana, S. A. Khan, M. A. Bhat, S. E. Haque,
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One of the authors (Ruhi Ali) is thankful to the University
Grants Commission (MANF), Ministry of Human Resource
Development, Govt. of India for financial support.
[19] H. Van de Waterbeemd, G. Camenisch, G. Folkers,
J. R. Chretien, O. A. Raevsky, J. Drug Target. 1998, 6,
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The authors have declared no conflict of interest.
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[
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ß 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.archpharm.com
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