Synthesis and anticonvulsant activity of 3-(6-substituted-benzothiazol-2-yl)-6-phenyl-[1,3]-oxazinane-2-thiones

Article abstract of DOI:10.1002/1521-4184(200211)335:8<381::AID-ARDP381>3.0.CO;2-S

A new series of 3-(6-substituted-benzothiazol-2-yl)-6-phenyl-[1,3] -oxazinane-2-thiones (4a-j) has been synthesised using an appropriate synthetic route (Scheme 1) and characterised by elemental analyses and spectral (IR, ¹H NMR, ¹³C NMR, and El MS) data. The anticonvulsant activity of all the title compounds (4 a-j) was evaluated against Maximal Electroshock (MES) induced seizures and furthermore the most potent compounds were evaluated against subcutaneous pentylenetetrazole (sc PTZ) induced seizures model in mice. The neurotoxicity was assessed using the rotorod procedure. All the test compounds were administered intraperitoneally at various dose levels ranging from 30-200 mg/kg body wt and the median effective dose (ED₅₀), median toxic dose (TD₅₀), and protection index (PI) values were determined (Table 2). Among the compounds tested, the 3-(6-dimethylaminobenzothiazol-2-yl)-6-phenyl-[1,3]-oxazinane-2-thiones (4j) was found to be the most potent (ED₅₀: 9.85 and 14.8 in MES model and 12 and 17 in scPTZ model at t = 0.5 h and 4 h, respectively, and TD₅₀ 42.8 and 44 at t = 0.5 h and 4 h, respectively, which has been found to be significant at p < 0.01 with respect to reference standard phenytoin) with protection index (PI) 4.85.

Full text of DOI:10.1002/1521-4184(200211)335:8<381::AID-ARDP381>3.0.CO;2-S

Arch. Pharm. Pharm. Med. Chem. 2002, 8, 381–388
3-(Benzothiazol-2-yl)-6-phenyl-[1,3]oxazinanethiones 381
Rajendra S. Chopadea,
Synthesis and Anticonvulsant Activity of
3-(6-Substituted-benzothiazol-2-yl)-6-phenyl-[1,3]-
oxazinane-2-thiones
Rajesh H. Bahekarb,
Pramod B. Khedekarc,
Kishore P. Bhusaric,
Akkinpalli Raghu Ram Raod
A new series of 3-(6-substituted-benzothiazol-2-yl)-6-phenyl-[1,3]-oxazinane-2-
a
Department of
Pharmaceutical Sciences,
Nagpur University
Nagpur-440010 (M.S), India
King’s College London,
Department of Pharmacy,
Franklin-Wilkin’s Building,
150 Stamford Street,
London SE1 9NN, UK
Nagpur College of
thiones (4 a–j) has been synthesised using an appropriate synthetic route
(Scheme 1) and characterised by elemental analyses and spectral (IR, 1H NMR, 13
C
NMR, and EI MS) data.The anticonvulsant activity of all the title compounds (4 a–j)
was evaluated against Maximal Electroshock (MES) induced seizures and further-
more the most potent compounds were evaluated against subcutaneous pentylene-
tetrazole (sc PTZ) induced seizures model in mice.The neurotoxicity was assessed
using the rotorod procedure. All the test compounds were administered intraperito-
neally at various dose levels ranging from 30–200 mg/kg body wt and the median ef-
fective dose (ED50), median toxic dose (TD50), and protection index (PI) values were
determined (Table 2). Among the compounds tested, the 3-(6-dimethylaminoben-
zothiazol-2-yl)-6-phenyl-[1,3]-oxazinane-2-thiones (4 j) was found to be the most
potent (ED50: 9.85 and 14.8 in MES model and 12 and 17 in scPTZ model at
t = 0.5 h and 4 h, respectively, and TD50 42.8 and 44 at t = 0.5 h and 4 h, respec-
tively, which has been found to be significant at p < 0.01 with respect to reference
standard phenytoin) with protection index (PI) 4.85.
b
c
Pharmacy, Wanadongari,
Hingana Road, Nagpur 441
110 (M.S.), India
d
University College of
Pharmaceutical Sciences,
Kakatiya University,
Warangal 506009 (A.P.),
India
Keywords: Anticonvulsant; Synthesis; 3-(Benzothiazol-2-yl)-6-phenyl-[1,3]-oxazi-
nane-2-thiones; Maximal Electroshock Seizures (MES); Subcutaneous pentylene-
tetrazole (sc PTZ); Neurotoxicity
Received: February 28, 2002 [FP677]
oxy)-2-benzothiazolamine) was reported to be a potent
anticonvulsant agent that functions by action on voltage-
Introduction
Epilepsy is a complex and multigenic disease affecting
about 30–40 million people worldwide [1–3]. It is mainly
due to an electrical hyperexcitability in the central nerv-
ous system [4]. Although there are a number of antiepi-
leptic drugs currently available, uncontrolled seizures
and medication toxicity are still major problems of antiep-
ileptic drug treatment [5]. The development of novel
agents, particularly compounds effective against com-
plex seizures, remains a major focus of antiepileptic drug
research [6].In recent years much effort has been devot-
ed to the development of novel approaches by elucidat-
ing the cellular and molecular mechanisms of the hyper-
excitability to provide specific targets for novel therapies
and as a result several new drugs such as vigabatrin,
lamotrigine, gabapentin, tiagabine, felbamate, topiram-
ate, fosphenytoin, and levetiracetam have appeared on
the market [5]. Literature survey reveals that 2-ami-
nobenzothiazole derivatives possessed potent anticon-
vulsant activity [7]. In 1985, Riluzole, (6-(triflurometh-
dependent sodium channels [8–10].Modulation of sodi-
um channels is a mechanism shared by other clinically
useful anticonvulsants like phenytoin and carbamaze-
pine [11]. Similarly substituted-[1,3]-oxazine-2-thiones
exhibit potential anticonvulsant activity [12]. Previously
we reported some 2-aminobenzothiazoles derivatives
as potentially active antimicrobial and anti-inflammatory
agents [13–15]. In continuation of our work on substitut-
ed 2-aminobenzothiazoles and to explore the potential
of this nucleus as useful anticonvulsant agent, we report
herein the synthesis and anticonvulsant activity of a new
series of 3-(6-substituted-benzothiazol-2-yl)-6-phenyl-
[1,3]-oxazinane-2-thiones (4 a–j).Compounds 4a-j have
been designed by incorporating aminobenzothiazoles
and oxazinethiones together to get potent anticonvul-
sant activity.
Results and discussion
Correspondence: Rajesh H. Bahekar, Department of
Pharmacy, Franklin-Wilkin’s Building, 150 Stamford Street,
London SE1 9 NN, UK. Phone: +44 20 7848 4833, Fax:
+44 20 7848 4800, e-mail: rajesh.bahekar@kcl.ac.uk.
In the present investigation, ten different derivatives of
3-(6-substituted-benzothiazol-2-yl)-6-phenyl-[1,3]-ox-
azinane-2-thiones (4 a–j) were synthesised and evaluat-
© 2002 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
0365-6233/08/0381 $ 17.50+.50/0

382 Chopade et al.
Arch. Pharm. Pharm. Med. Chem. 2002, 335, 381–388
Scheme 1
ed for their anticonvulsant activity.Synthesis of title com-
pounds 4 a–j has been carried out as depicted in
Scheme 1. Various derivatives of 6-substituted-2-ami-
nobenzothiazoles (1 a–j) were prepared by a reported
procedure [16]. The compounds 1 a–j were converted
into various derivatives of 3-(6-substituted-benzothia-
zol-2-ylamino)-1-phenylpropan-1-one (2 a–j) by treating
with formaldehyde and acetophenone according to the
Mannich reaction. The Mannich reaction or α-amino-
methylation involves the condensation of the active
methyl groupin acetophenone with formaldehyde and
2-aminobenzothiazole (in the form of its hydrochloride).
The probable mechanism of the reaction involves the in-
termediate formation of the hydroxy-methyl-aminoben-
zothiazole, which eliminates water to form the carboca-
tion.This reactive species condenses with the α-carbon
atom of acetophenone to yield compound 2 a–j. Further
the compounds 2 a–j were reduced to 3-(6-substituted-
mation) and 3460–3500 cm–1 (N–H stretching). Com-
pounds 2 a–j showed absorption bands at 1550–
1630 cm–1 (N–H deformation), 1700–1720 cm–1 (C=O
stretching), and ca. 3450 cm–1 (N–H stretching), due to
conversion of primary amine into secondary amine.
Compounds 3 a–j showed strong bands at ca. 3450
cm–1 (N–H stretching) and 3590–3650 cm–1 (O–H
stretching) and the absence of a band at 1700–1720
cm–1 (C=O), due to reduction of carbonyl groupto hy-
droxyl group.While compounds4 a–j showed disappear-
ance of bands at ca. 3450 cm–1 (N–H stretching) and
3590–3650 cm–1 (O–H stretching) but shows a promi-
nent band at 1200–1270 cm–1 (C=S stretching).Halogen
containing compounds (2 d, 2 e, 3 d, 3 e, 4 d, and 4 e)
showed the absorption band at 590–760 cm–1 (C–X
stretching) and nitro compounds (2 h, 3 h, and 4 h)
showed band at 1490–1550 cm–1 (NO2 stretching). The
EI MS 1H NMR and 13C NMR spectral data of all the syn-
thesised compounds were in conformity with the struc-
ture assigned.
benzothiazol-2-ylamino)-1-phenylpropan-1-ol
(3 a–j)
using sodium borohydride as a mild reducing agent. In
this stepnucleophilic addition of the hydride ion to the
electrophilic carbon atom of the carbonyl group results
in the reduction of ketone to secondary alcohol.
Finally compounds 3 a–j were cyclised to give title com-
pounds 3-(6-substituted-benzothiazol-2-yl)-6-phenyl-
[1,3]-oxazinane-2-thiones (4 a–j) using carbon disul-
phide.
In the EI-MS spectra, molecular ion (M+) peaks, which
appeared at different intensities, confirmed the molecu-
lar weights of the examined compounds (2 a–j,3 a–j, and
4 a–j). Molecular ion peaks were the base peak for the
compound 2 b, 2 c, 2 h, 2 j, 3 a, 3 b, 3 f, 3 h, 4 a, 4 b, 4 c,
4 h, and 4 i. Appearance of an isotope peak (M+ + 2) as
intense as the molecular ion peak confirmed the pres-
ence of halogen atom in compounds 2 d,2 e,3 d,3 e,4 d,
and 4 e. The corresponding 1H NMR, 13C NMR, and
mass spectral data are presented in the experimental
section.
All of the synthesised compounds were characterised by
their physical, analytical, and spectral data (Table 1).
The IR spectra of 1 a–j showed the presence of charac-
teristic absorption peaks at 1600–1650 cm–1 (N–H defor-

Arch. Pharm. Pharm. Med. Chem. 2002, 335, 381–388 3-(Benzothiazol-2-yl)-6-phenyl-[1,3]oxazinanethiones 383
Table 1. Physical and analytical data of compounds 2 a–j, 3 a–j, and 4 a–j.
b
CompR
Mol. formula
(Mol. wt)
Mp
[°C]
Yielda
[%]
Mass
(M+)
2 a
2 b
2 c
2 d
2 e
2 f
2 g
2 h
2 i
H
C16H14ON2S (282)
C17H16ON2S (296)
C18H18ON2S (310)
C16H13ON2SCl (316)
C16H13ON2SBr (361)
C17H16O2N2S(312)
C18H18O2N2S (324)
C16H15O3N3S (337)
C16H14O2N2S (298)
C18H19ON3S (325)
C16H16ON2S (284)
C17H18ON2S (298)
C18H20ON2S (312)
C16H15ON2SCl (318)
C16H10ON2SBr (363)
C17H18O2N2S (314)
C18H20O2N2S (326)
C16H15O3N3S (339)
C16H16O2N2S (300)
C18H21ON3S (327)
C17H14ON2S2 (326)c
C18H18ON2S2 (342)
C19H20ON2S2 (356)
C17H14ON2S2Cl (360)
C17H14ON2S2Br (405)
C18H16O2N2S2 (356)
C19H18O2N2S2 (370)
C17H15O3N3S2 (381)
C17H14O2N2S2 (342)
C19H19ON3S2 (369)
188–90
206–08
208–09
210–12
221–14
240–42
148–50
252–54
242–03
266–07
196–98
212–14
216–17
218–20
220–22
248–50
154–56
260–62
242–43
236–37
207–209
172–74
178–79
184–86
188–90
228–30
132–34
240–41
166–67
192–93
76
58
55
64
69
70
55
68
58
61
72
68
63
67
69
80
78
74
68
66
77
72
69
67
70
60
72
69
66
71
282
296
310
318d
363d
312
324
337
298
325
284
298
312
320d
365d
314
326
339
300
327
326
342
356
362d
407d
356
370
381
342
369
CH3
C2H5
Cl
Br
OCH3
OC2H5
NO2
OH
N(CH3)2
H
CH3
C2H5
Cl
2 j
3 a
3 b
3 c
3 d
3 e
3 f
3 g
3 h
3 i
Br
OCH3
OC2H5
NO2
OH
N(CH3)2
H
CH3
C2H5
Cl
3 j
4 a
4 b
4 c
4 d
4 e
4 f
4 g
4 h
4 i
Br
OCH3
OC2H5
NO2
OH
4 j
N(CH3)2
a
Compounds 2 a–j and 3 a–j were recrystallised from methanol, and compounds 4 a–j from benzene-petroleum ether
60–40 °C (6 : 4).
b
c
d
CHN analyses were found to be within the limit of 0.4 %.
Lit mp: 208–210 °C, Ref.[19]
.
values represent (M+ + 2) due to appearance of an isotopic peak.
The anticonvulsant activity of all the title compounds
(4 a–j) was evaluated against Maximal Electroshock
(MES) induced seizures and furthermore the most po-
tent compounds were evaluated against subcutaneous
pentylenetetrazole (sc PTZ) induced seizures model in
mice [17]. Using the rotorod procedure the neurotoxicity
was assessed [18]. All the test compounds were admin-
istered intraperitoneally at various dose level ranging
from 30 to 200 mg/kg body wt and the median effective
dose (ED50), median toxic dose (TD50), and protection
index (PI) values were determined. Suspensions of the
test compounds in propylene glycol were administered
to mice at half and hour or 4 hours before evaluation of
their activity. The results of anticonvulsant activity and
neurotoxicity are presented in Table 2.
The anti MES activity (ED50 values in Table 2) indicated
significant anticonvulsant activity for all of the test com-
pounds 4 a–j.However, they were found to be less potent
when compared with the reference standard phenytoin

384 Chopade et al.
Arch. Pharm. Pharm. Med. Chem. 2002, 335, 381–388
Table 2. Anticonvulsant and neurotoxicity of compounds 4 a–j in micea.
CompMES
0.5 h
scPTZ
0.5 h
Toxicity
0.5 h
PI
4.0 h
4.0 h
ND
4.0 h
110
4 a
4 b*
4 c*
4 d
4 e
4 f
53
(46–61)
65.5
(60–71)
ND
20
88.5
(79–98)
1.66
3.13
3.58
1.27
1.39
1.6
(109–111)
16.9
(14.2–19.3)
22
(20–24)
29.5
(28–31)
53.5
(47–60)
70
(19–21)
(68–72)
14.8
(12.9–16.6)
20
(19–21)
18
27.6
(25.2–30)
53.5
(45–62)
71
(15.6–20.4)
(70–72)
86
(83–88)
95
(89–101)
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
110
(106–114)
130
(125–135)
88
(79–98)
99
(81–121)
123
(120–126)
150
(146–154)
70
82
(79–85)
112
(110–114)
140
(59–83)
(135–145)
4 g
4 h
4 i
77
(68–88)
86
(80–92)
118
(110–126)
135
1.53
1.41
1.37
4.85
6.60
(130–140)
99
(81–121)
110
(109–111)
140
(139–141)
175
(174–176)
95
107
131
156
(89–101)
(99–115)
(126–136)
(140–172)
4 j**
Std
9.85
(8.77–10.7)
14.8
(13–16)
12
17
47.8
(39.2–59.2)
60
(56–64)
(11.4–12.6)
(15.6–18.4)
6.48
7.1
7.5
8.2
42.8
44
(PTN) (5.65–7.24)
(5.9–8.3)
(6.4–8.6)
(7.8–8.6)
(36.4–47.5)
(37–51)
a
All compounds were administered by ip injection at doses spanning the range 30–200 mg kg–1, 30 min and 4 h before
evaluation of activity and at least 6 animals were used to calculate each ED50 andTD50 values.In scPTZ induced sei-
zures test, 200 µL/kg body wt. of 10 µM solution of PTZ was administered by subcutaneous route 15 min after the ip
injection of test compounds;the anticonvulsant activity was recorded at t = 0.5 and 4 h and rep resented in terms of the
ED50, i.e., dose of test compounds required to assure anticonvulsant protection in 50 % of animals from hind limb
tonic extension (tonic phase);theTD50, dose eliciting minimal neurological toxicity in 50 % of animals as assessed by
the rotorod test (locomotor deficit); the PI, protection index (PI = TD50/ED50) from MES induced seizures after 0.5 h;
ED50 andTD50values are expected as mg kg–1;All data were calculated according to the method of Litchfield andWil-
coxon [20], and significant differences between ED50 values of the test compounds with respect to std PTN (pheny-
toin) are denoted as *p < 0.05 and ** p < 0.01; ND: activity not determined.
(ED50: 6.48 and 7.1 at t = 0.5 and 4 h in MES model).
The different substituents on the aromatic ring exert a
significant influence on the biological activity by modu-
lating the lipophilicity and thereby facilitating penetration
across the blood-brain barrier.The presence of electron-
withdrawing groups (halogen, alkoxy, hydroxy, and nitro
substituents) on the aromatic ring in general decreases
the potency of test compounds compared to compounds
having electron-donating groups (alkyl and dialkylamino
substituents).This is because of decreased lipophilicity,
which in turn inhibits permeability across biological
membranes.Further, it has been found that the ED50 and
TD50 values of test compounds increase significantly at
t = 4 h, compared to t = 0.5 h, in contrast to the refer-

Arch. Pharm. Pharm. Med. Chem. 2002, 335, 381–388 3-(Benzothiazol-2-yl)-6-phenyl-[1,3]oxazinanethiones 385
ence standard, indicating that the test compounds were
metabolised with time in the biological environment.This
trend was found to be more pronounced in compounds
4 d, 4 e, 4 f, 4 g, 4 h, and 4 i (having electron-withdrawing
groups) compare to compounds 4 b, 4 c, and 4 j (having
Scheme 2
electron-donating groups). In order to confirm this fact in
vitro, the most potent compound 4 j was incubated in
phosphate buffer solution (pH 7.4) at 37 °C and after
every hour 10 µL of aliquot was analysed by analytical
ED50 and TD50 values of compounds 4 d, 4 e, 4 f, 4 g, 4 h,
and 4 i was therefore found at t = 4 h.These results also
RP-HPLC (Reverse Phase High Performance Liquid
reflect that the oxazinane-2-thione ring is necessary for
Chromatography) over a period of 6 h. Further the indi-
anticonvulsant activity; in turn, it may be essential to
vidual peaks were collected from HPLC, freeze-dried,
maintain the lipophilicity of the test compounds. Similar
and characterised by Matrix Assisted Laser Desorption
results were found when some of the most potent com-
Ionisation Time of Flight Mass Spectrometry (MALDI
pounds were evaluated for anticonvulsant activity
TOF MS). The results of this study (Figure 1) show that
against the sc PTZ model. Further, to confirm this phe-
after 2 h compound 4 j (parent peak, retention time:
nomenon in vivo, a kinetic study should be carried out in
36 min) has been hydrolysed (appearance of second
an animal model. Based upon the results it will also be
peak at 30 min). The hydrolysis product (metabolite of
necessary to optimise the lead compound by substitut-
compound 4 j) was found to be less lipophilic compared
ing a series of electron-donating groups on aromatic ring
and selectively modifying the oxazinane-2-thione ring it-
to the parent compound as it elutes before the parent
peak from a C18 column in RP HPLC. As shown in
self. The protection index (PI) values are found to be
Scheme 2, at physiological pH, the test compound 4 j
more significant for determining the relation between li-
pophilicity and toxicity. Table 2 shows that PI values > 3
undergo hydrolysis across the oxazinane-2-thione ring
(as the observed mass, Figure 2 was found to be in
were found for more potent compounds in contrast to
agreement with the hydrolysis product of compound 4 j).
less lipophilic compounds. Thus, as the lipophilicity in-
creases so does the toxicity and therefore also the pro-
tection index (PI). In the series, 3-(6-dimethylaminoben-
As in the case of 4 j, all the test compounds may possibly
undergo hydrolysis and therefore the ED50 and TD50 val-
ues increase with time. In particular, electron-withdraw-
ing substituents favour this hydrolysis compares to elec-
tron-donating groupand a significant increase in the
Figure 2. Matrix assisted laser desorption ionisation
Figure 1. Analytical reverse phase high performance liq-
uid chromatogram of compound 4 j and its metabolite:
RP-HPLC Conditions: Beckman Gold Nouveau System
equipped with a 168 photodiode-array detector.Column;
Vydac 218TP53 (C18, 300 Å, 5 mm, 3.2 mm i.d. × 250
mm). 0.5 mL min–1, Buffer A = 0.1 % TFA in water. Buffer
B = 90 % ACN containing 10 % buffer A. Linear gradient
from 0 % B to 90 % B over 30 min, total run time 50 min.
Retention time (Rt) for parent peak 36 Min, metabolite Rt
= 30 min.
time of flight mass spectrum of 4 j metabolite: MALDI
TOF MS Conditions; Lasermat 2000 (Thermo Bioanaly-
sis Ltd., UK). The test material (ca. 0.2 mg mL–1) dis-
solved in a mixture of water and methanol (9 : 1) and
2 µL was applied to the sample plate and allowed to dry
at room temperature prior to analysis.The spectrum was
acquired in positive mode without matrix at laser power
20 and typically 10–12 shots were obtained per spec-
trum. Expected mass: 387 (M+); Observed: 409
(M + Na+).

386 Chopade et al.
Arch. Pharm. Pharm. Med. Chem. 2002, 335, 381–388
3-(6-Ethyl-benzothiazol-2-ylamino)-1-phenylpropan-1-one
(2 c):White crystals; Rf: 0.57 (chloroform); IR (KBr): 1568 (N–H
deformation), 1710 (C=O stretching), 3440 (N–H stretching),
cm–1; 1H NMR (CDCl3): δ 1.1–1.28 (t, 3 H, CH3–CH2–C6H5–),
1.9–1.98 (d, 2 H, CH3–CH2–C6H5–), 2.2–2.3 (d, 4 H, –NH–
CH2–CH2–CO–), 4.21 (s, 1 H, –NH–CH2–CH2–CO–), 7.2–8.0
(m, 8 H, Aromatic) ppm; EI MS (m/z, %): 310 (M+, 100 %).
zothiazol-2-yl)-6-phenyl-[1,3]-oxazinane-2-thiones (4 j)
was found to be the most potent (ED50: 9.85 and 14.8 in
MES model and 12 and 17 in the scPTZ model at
t = 0.5 h and 4 h, respectively, and TD50 42.8 and 44 at
t = 0.5 h and 4 h, respectively, which have been found
to be significant at p < 0.01 with respect to reference
standard phenytoin) with a protection index (PI) of 4.85.
Further studies are in progress to optimise this lead
compound and fully characterise the mode of action.
3-(6-Bromo-benzothiazol-2-ylamino)-1-phenylpropan-1-one
(2 e):White crystals; Rf: 0.66 (chloroform); IR (KBr): 700 (Ar–Br
stretching),1580 (N–H deformation), 1700 (C=O stretching),
3450 (N–H stretching), cm–1; 1H NMR (CDCl3): δ 2.23–2.35 (d,
4 H, –NH–CH2–CH2–CO–), 4.21 (s, 1 H, –NH–CH2–CH2–
CO–), 7.1–8.0 (m, 8 H, Aromatic) ppm; EI MS (m/z, %): 363
([M+ + 2], 100 %).
Acknowledgments
3-(6-Nitro-benzothiazol-2-ylamino)-1-phenylpropan-1-one
(2 h):White crystals; Rf: 0.61 (chloroform); IR (KBr): 1490 (NO2
stretching), 1560 (N–H deformation), 1720 (C=O stretching),
3450 (N–H stretching), cm–1; 1H NMR (CDCl3): δ 2.22–2.34 (d,
4 H, –NH–CH2–CH2–CO–), 4.20 (s, 1 H, –NH–CH2–CH2–
CO–), 7.1–8.0 (m, 8 H, Aromatic) ppm;EI MS (m/z, %):337 (M+,
100 %).
The authors wish to thank the Regional Sophisticated In-
strumentation Center (Central Drug Research Institute),
Lucknow for recording spectra, the Principals of the De-
partment of Pharmaceutical Sciences, Nagpur Universi-
ty Nagpur (India), Nagpur College of Pharmacy, for pro-
viding laboratory facilities, and the University Grant
Commission for financial assistance.
3-(6-Dimethylaminobenzothiazol-2-ylamino)-1-phenylpropan-
1-one (2 j):White crystals; Rf: 0.63 (chloroform); IR (KBr): 1580
(N–H deformation), 1710 (C=O stretching), 3450 (N–H stretch-
ing), cm–1; 1H NMR (CDCl3): δ 1.1–1.30 (t, 6 H, (CH3)2N–
C6H5–), 2.2–2.3 (d, 4 H, –NH–CH2–CH2–CO–), 4.1 (s, 1 H,
–NH–CH2–CH2–CO–), 7.1–8.1 (m, 8 H, Aromatic) ppm; EI MS
(m/z, %): 325 (M+, 100 %).
Experimental
Melting points were determined in open capillaries using a
Thermonik precision melting point cum boiling point apparatus,
Model C-PMB-2 (Mumbai, India) and are uncorrected.Purity of
the compounds was checked by precoated TLC plates (E.
Merck Kieselgel 60 F254, Mumbai, India). IR spectra were re-
corded using KBr pellets on a Perkin-Elmer 337 Spectropho-
tometer from Perkin Elmer International Incorporation,
Synthesis of 3-(6-substituted-benzothiazol-2-ylamino)-1-phe-
nylpropan-1-ol 3 a–j
To a solution of 3-(6-substituted benzothiazol-2-ylamino)-1-
phenylpropan-1-one (0.01 mole) in methanol (100 mL), sodi-
um borohydride (0.01 mole) was added in fraction with con-
stant stirring over the period of 3 hours. After stirring for
3 hours, the reaction mixture was allowed to stand overnight.
The separated solid was filtered off, dried, and recrystallised
from methanol. Using the above procedure ten such com-
pounds 3 a–j were synthesised and characterised and their
physical data have been listed in Table 1.
1
Rorkreuz, Switzerland (νmax in cm–1). H NMR and 13C NMR
spectra on a Bruker W.M. 400 Spectrometer (Bruker AG, Fal-
landen, Switzerland) at 360 MHz using TMS as internal stand-
ard (chemical shifts in δ ppm) and mass spectra (EI-MS) were
recorded at 70 eV on a Jeol D-300 spectrometer (Jeol Ltd, To-
kyo, Japan). Elemental analyses were carried out using
Heraeus Carlo Erba 1180 CHN analyser (from Heraeus Instru-
ment GmbH, Hanau, Germany). All the chemicals were pur-
chased from Aldrich Company Ltd, Dorset (UK).
Some representative spectral data for compounds 3:
3-(Benzothiazol-2-ylamino)-1-phenylpropan-1-ol (3 a): Pale
white crystals; Rf: 0.66 (chloroform); IR (KBr): 3450 (N–H
Synthesis of 3-(6-substituted-benzothiazol-2-ylamino)-1-phe-
nylpropan-1-one 2 a–j; General procedure
1
stretching), 3590 (O–H stretching) cm–1; H NMR (CDCl3): δ
1.8–1.83 (m, 1 H, Ar–CH(OH)–), 2.2–2.3 (d, 4 H, –NH–CH2–
CH2–CO–), 4.2 (s, 1 H, –NH–CH2–CH2(OH)–), 7.2–8.1 (m, 9 H,
Aromatic) and 8.9 (bs, 1 H, Ar–CH(OH)–) ppm;EI MS (m/z, %):
284 (M+, 100 %).
To a solution of 2-aminobenzothiazole (0.01 mole) in metha-
nol (150 mL), acetophenone (0.01 mole), formaldehyde
(0.01 mole) and a few drops of concentrated hydrochloric acid
were added dropwise with constant stirring. The reaction mix-
ture was heated under reflux for 2 hours on a water bath. The
reaction mixture was filtered and cooled. The separated solid
was filtered off, dried, and recrystallised from methanol. Using
the above procedure, ten such compounds 2 a–j were synthe-
sised and characterised and their physical data are listed in
Table 1.
3-(6-Methyl-benzothiazol-2-ylamino)-1-phenylpropan-1-ol
(3 b): Pale white crystals; Rf: 0.68 (chloroform); IR (KBr): 3450
(N–H stretching), 3600 (O–H stretching) cm–1; 1H NMR
(CDCl3):δ 1.1–1.27 (t, 3 H, CH3–C6H5–), 1.81–1.84 (m, 1 H, Ar–
CH(OH)–), 2.1–2.3 (d, 4 H, –NH–CH2–CH2–CO–), 4.2 (s, 1 H,
–NH–CH2–CH2(OH)–), 7.2–8.0 (m, 8 H, Aromatic) and 8.88
(bs, 1 H, Ar–CH(OH)–) ppm; EI MS (m/z,%): 298 (M+, 100 %).
Some representative spectral data for compounds 2:
3-(6-Chloro-benzothiazol-2-ylamino)-1-phenylpropan-1-ol
(3 d): Pale white crystals; Rf: 0.62 (chloroform); IR (KBr): 710
(Ar–Cl stretching), 3452 (N–H stretching), 3590 (O–H stretch-
ing) cm–1;1H NMR (CDCl3):δ 1.81–1.83 (m, 1 H, Ar–CH(OH)–),
2.1–2.33 (d, 4 H, –NH–CH2–CH2–CO–), 4.22 (s, 1 H, –NH–
CH2–CH2(OH)–), 7.2–8.0 (m, 8 H, Aromatic) and 9.0 (bs, 1 H,
Ar-CH(OH)–) ppm; EI MS (m/z, %): 320 ([M+ + 2], 100 %).
3-(6-Methylbenzothiazol-2-ylamino)-1-phenylpropan-1-one
(2 b):White crystals; Rf: 0.56 (chloroform); IR (KBr): 1560 (N–H
deformation), 1720 (C=O stretching), 3450 (N–H stretching),
cm–1;1H NMR (CDCl3):δ 1.1–1.28 (t, 3 H, CH3–C6H5–), 2.2–2.3
(d, 4 H, –NH–CH2–CH2–CO–), 4.2 (s,1 H, –NH–CH2–CH2–
CO–), 7.2–8.1 (m, 8 H, Aromatic) ppm;EI MS (m/z, %):296 (M+,
100 %).

Arch. Pharm. Pharm. Med. Chem. 2002, 335, 381–388 3-(Benzothiazol-2-yl)-6-phenyl-[1,3]oxazinanethiones 387
(q, 4 H, –N–CH2–CH2–CH–Ar), 7.2–8.0 (m, 8 H, Aromatic)
ppm; 13C NMR (360 MHz, CDCl3) δ: 24.5, 25.0 (–CH2–CH2–,
oxazinanethione), 42.73 (CH, benzothiazole), 52.6 (–CH–Ar,
oxazinanethione), 122–126 (CH, Aromatic), 132 (Ar–Cl), and
182 (C=S); EI MS (m/z, %): 362 ([M+ + 2], 100 %) 248 (80 %),
188 (20 %), 172 (30 %), 77 (52 %).
3-(6-Methoxy-benzothiazol-2-ylamino)-1-phenylpropan-1-ol
(3 f): Pale white crystals; Rf: 0.68 (chloroform); IR (KBr): 3450
(N–H stretching), 3605 (O–H stretching) cm–1; 1H NMR
(CDCl3): δ 1.1–1.28 (t, 3 H, CH3O–C6H5–), 1.81–1.83 (m, 1 H,
Ar–CH(OH)–), 2.1–2.3 (d, 4 H, –NH–CH2–CH2–CO–), 4.2 (s,
1 H, –NH–CH2–CH2(OH)–), 7.2–8.0 (m, 8 H, Aromatic) and
8.88 (bs, 1 H, Ar–CH(OH)–) ppm; EI MS (m/z, %): 314 (M+,
100 %).
3-(6-Nitro-benzothiazol-2-yl)-6-phenyl-[1,3]-oxazinane-2-
thiones (4 h): White crystals; Rf: 0.35 (chloroform); IR (KBr):
1
1250 (C=S stretching), 1490 (NO2 stretching) cm–1; H NMR
3-(6-Nitro-benzothiazol-2-ylamino)-1-phenylpropan-1-ol (3 h):
Pale white crystals; Rf: 0.69 (chloroform); IR (KBr): 1496 (NO2
stretching), 3450 (N–H stretching), 3590 (O–H stretching)
(CDCl3): δ 1.19–1.90 (t, 1 H, –N–CH2–CH2–CH–Ar), 2.1–2.33
(q, 4 H, –N–CH2–CH2–CH–Ar), 7.2–8.1 (m, 8 H, Aromatic)
ppm; 13C NMR (360 MHz, CDCl3) δ: 24.5, 25.0 (–CH2–CH2–,
oxazinanethione), 42.73 (CH, benzothiazole), 52.6 (–CH–Ar,
oxazinanethione), 124–128 (CH, Aromatic), 142 (Ar–NO2) and
182 (C=S); EI MS (m/z, %): 381 (M+, 100 %) 265 (79 %), 205
(22 %), 189 (32 %), 78 (49 %).
1
cm–1; H NMR (CDCl3): δ 1.81–1.83 (m, 1 H, Ar–CH(OH)–),
2.1–2.33 (d, 4 H, –NH–CH2–CH2–CO–), 4.22 (s, 1 H, –NH–
CH2–CH2(OH)–), 7.2–8.0 (m, 8 H, Aromatic) and 9.0 (bs, 1 H,
Ar–CH(OH)–) ppm; EI MS (m/z, %): 339 (M+, 100 %).
Synthesis of 3-(6-substituted-benzothiazol-2-yl)-6-phenyl-
3-(6-Hydroxybenzothiazol-2-yl)-6-phenyl-[1,3]-oxazinane-2-
thiones (4 i): White crystals; Rf: 0.39 (chloroform); IR (KBr):
1265 (C=S stretching), cm–1; 1H NMR (CDCl3): δ 1.89–1.90 (t,
1 H, –N–CH2–CH2–CH–Ar), 2.1–2.33 (q, 4 H, –N–CH2–CH2–
CH–Ar), 7.2–8.1 (m, 8 H, Aromatic), 9.2–9.4 (bs, 1 H, Ar–OH)
ppm; 13C NMR (360 MHz, CDCl3) δ: 24.5, 25.0 (–CH2–CH2–,
oxazinanethione), 42.73 (CH, benzothiazole), 52.6 (–CH–Ar,
oxazinanethione), 124–126 (CH, Aromatic),151 (Ar–OH) and
182 (C=S); EI MS (m/z, %): 342 (M+, 100 %) 226 (80 %), 166
(22 %), 150 (30 %), 77 (42 %).
[1,3]-oxazinane-2-thiones 4 a–j
To a solution of 3-(6-substituted-benzothiazol-2-ylamino)-1-
phenylpropan-1-ol (0.01 mole) in dry chloroform (50 mL), car-
bon disulphide (0.01 mole) was added dropwise. The reaction
mixture was heated under reflux for 7 hours on a water bath.
Excess of the solvent was distilled-off in vacuo.The residue so
obtained was recrystallised from a mixture of benzene-petrole-
um ether (60–80 °C;6 : 4).Using the above procedure ten such
compounds 4 a–j were synthesised and characterised and
their physical data have been listed in Table 2.
Some representative spectral data for compounds 4:
Pharmacology
3-(Benzothiazol-2-yl)-6-phenyl-[1,3]-oxazinane-2-thiones
(4 a):White crystals; Rf: 0.36 (chloroform); IR (KBr): 1200 (C=S
stretching), cm–1; 1H NMR (CDCl3): δ 1.89–1.90 (t, 1 H,
–N–CH2–CH2–CH–Ar), 2.1–2.33 (q, 4 H, –N–CH2–CH2-CH-
Ar), 7.2–8.1 (m, 9 H, Aromatic) ppm; 13C NMR (360 MHz,
CDCl3) δ: 24.5, 25.0 (–CH2–CH2–, oxazinanethione), 42.73
(CH, benzothiazole), 52.6 (–CH–Ar, oxazinanethione), 122
(CH, Aromatic) and 182 (C=S). EI MS (m/z, %): 326 (M+,
100 %), 210 (86 %), 150 (25 %), 134 (33 %), 78 (56 %).
Maximal Electroshock Seizures (MES) method was used to
check the anticonvulsant activity of all the title compounds 4 a–j
[17]. This study was conducted on albino mice of either sex
weighing between 20 to 25 g. The animals were divided into
two groups (control and standard) and each experimental
groupconsisted of six animals. All the animals were left for 2
days under laboratory conditions for acclimatisation and main-
tained on a standard pellet diet and water ad libitum before the
day of the experiment. On the last day food was withdrawn and
they were given water only.A 12 hours dark:light cycle was also
maintained. All the experimental protocols were approved by
the institutional review committee and experiments were con-
ducted in accordance with the standard guidelines.The homo-
geneous suspension of the test compounds (4 a–j) and stand-
ard drug (phenytoin) were prepared in polyethylene glycol and
distilled water (1 : 9/mL). All the test compounds were adminis-
tered intraperitoneally (ip) at a dose of 30–200 mg/kg body wt.,
30 min prior to the start of experiments. The Maximal Electro-
shock Seizures (MES) were induced by an electroconvulsome-
ter (Techno Instruments, Lucknow), using a technique de-
scribed earlier [17]. The animals were subjected to electro-
shock (60 mA/0.2 s) via the transauricular electrodes. Further
the most potent compounds 4 b, 4 c, and 4 j were evaluated
against the sc PTZ model in mice. The anticonvulsant effect
was assessed by recording the Tonic Hind-limb Extension
(THE) at various dose level at t = 0.5 and 4 h. Absence of sei-
zure component like hind leg tonic extension with drug treat-
ment was considered to be evidence of protection. Median ef-
fective dose (ED50) was calculated for each compound and are
presented in Table 2.
3-(6-Methyl-benzothiazol-2-yl)-6-phenyl-[1,3]-oxazinane-2-
thiones (4 b): White crystals; Rf: 0.38 (chloroform); IR (KBr):
1250 (C=S stretching), cm–1; 1H NMR (CDCl3): δ 1.1–1.27 (t,
3 H, CH3–C6H5–),1.89–1.90 (t, 1 H, –N–CH2–CH2–CH–Ar),
2.1–2.33 (q, 4 H, –N–CH2–CH2–CH–Ar), 7.2–8.1 (m, 8 H, Aro-
matic) ppm; 13C NMR (360 MHz, CDCl3) δ: 19.6 (CH3, benzo-
thiazole), 24.5, 25.0 (–CH2–CH2–, oxazinanethione), 42.73
(CH, benzothiazole), 52.6 (–CH–Ar, oxazinanethione), 122–
124 (CH, Aromatic) and 182 (C=S); EI MS (m/z, %): 342 (M+,
100 %), 226 (80 %), 166 (22 %), 150 (32 %), 77 (52 %).
3-(6-Ethyl-benzothiazol-2-yl)-6-phenyl-[1,3]-oxazinane-2-
thiones (4 c): White crystals; Rf: 0.38 (chloroform); IR (KBr):
1270 (C=S stretching), cm–1; 1H NMR (CDCl3): δ 1.1–1.27 (t,
3 H, CH3–CH2–C6H5–), 1.87–1.89 (t, 1 H, –N–CH2–CH2–CH–
Ar), 1.9–1.96 (d, 2 H, CH3–CH2–C6H5–), 2.1–2.33 (q, 4 H,
–N–CH2–CH2–CH–Ar), 7.2–8.1 (m, 8 H, Aromatic) ppm; 13C
NMR (360 MHz, CDCl3) δ: 19.6 (CH3–CH2–, benzothiazole),
24.5, 25.0 (–CH2–CH2–, oxazinanethione), 35.0 (CH3–CH2–,
benzothiazole), 42.73 (CH, benzothiazole), 52.6 (–CH–Ar, ox-
azinanethione), 122–125 (CH, Aromatic) and 182 (C=S);EI MS
(m/z, %): 356 (M+, 100 %), 240 (80 %), 180 (22 %), 164 (32 %),
77 (50 %).
Acute neurotoxicity of all the test compounds was assessed in
mice by evaluating the Rolling Roller Performance (RRP) ac-
cording to the method described by Dunham and Miya
(1957) [18].Briefly, groupof animals (mice) were trained to bal-
ance on a rotating rod (3 cm diameter and 6 rpm speed) and
3-(6-Chloro-benzothiazol-2-yl)-6-phenyl-[1,3]-oxazinane-2-
thiones (4 d):White crystals;Rf:0.32 (chloroform);IR (KBr):710
(Ar–Cl stretching),1260 (C=S stretching) cm–1; 1H NMR
(CDCl3): δ 1.89–1.90 (t, 1 H, –N–CH2–CH2–CH–Ar), 2.1–2.33

388 Chopade et al.
Arch. Pharm. Pharm. Med. Chem. 2002, 335, 381–388
[9] J. Benavides, J. C. Camelin, N. Mitrani, F. Flamand, A.
Uzan, J.J.Legrand, C.Gueremy, G.LeFur, Neuropharma-
cology 1985, 24, 1085–1092.
was allowed three attempts to remain on the rotating rod for
20 s. Such trained animals were treated with the test com-
pounds at various dose level ranging from 30–200 mg/kg body
wt., by intraperitoneal administration. Test compounds were
considered to be neurotoxic at a particular dose level if the
trained animal showed lack of Rolling Roller Performance.
Each of the trained animals was tested in this manner at 30 min
and 4 h after the drug administration, and the neurotoxic effect
was recorded in terms of TD50 and based upon these results PI
values were calculated as shown in Table 2.
[10] S.J. Hays, R. D. Schwarz, L. L. Coughenour, D.K. Boyd, R.
J. Anderson, P. A. Boxer, 201st National ACS Meeting.
Atlanta, GA, MEDI 6, 1991.
[11] D. S. Ragsdale, T. Scheuer, W. A. Catterall, Mol. Pharma-
col. 1991, 40, 756–765.
[12] C. Singh, H. K. Parwana, G. Singh, Indian J. Pharm. Sci.
1995, 57, 198.
[13] P. B. Khedekar, K. P. Bhusari, R. H. Bahekar, A. R. R. Rao,
S. N. Umathe, Indian J. Heterocycl Chem. 2001, 10, 231–
234.
References
[1] E. A. Swinyard in Antiepileptic Drugs, 2nd ed (Ed: D. M.
Woodbury, J. K. Penry, C. E. Pippenger), Reven Press,
New York 1982, pp. 5–20.
[14] P. B. Khedekar, K. P. Bhusari, R. H. Bahekar, A. R. R. Rao,
S. N. Umathe, Indian J. Heterocycl Chem. 2000, 9,
275–278.
[2] W. Loscher, D. Schmidt, Epilepsy Res. 1994, 17, 95–134.
[3] J. O. McNamara in The Pharmacological Basis of Thera-
peutics, 9th ed (Ed: J. G. Hardman, L. E. Limbird, P. B. Mo-
linoff, R.W.Ruddon, A.G.Gilman), McGraw Hill, NewYork,
1990, pp. 461–486.
[15] P. B. Khedekar, K. P. Bhusari, R. H. Bahekar, A. R. R. Rao,
S. N. Umathe, Indian J. Heterocycl Chem. 2000, 9,
213–216.
[16] J.Trefouel, M.Trefouel, F. Nitti, D. Bovet , Chem. Res. Soc.
Bio. 1935, 120, 756.
[4] Z. Lin, P. K. Kadaba, Med. Res. Rev. 1997, 17, 537–572.
[5] J. F. Wolfe, T. D. Greenwood, J. M. Mulheron, Exp. Opin.
Ther. Patents 1998, 8, 361–381.
[17] E. A. Swinyard, J. Woodhead , H. S. White, M. R. Franklin,
in: Antiepileptic Drugs 3rd Ed. (Eds: R. H. Levy, F. C. Drei-
fuss, R. H. Mattson, B. S. Meldrum, J. K. Penry), Raven
Press, New York, 1989, 85–102.
[6] N. D. P. Cosford, I. A. McDonald, E. J. Schweiger, Annu.
Rep. Med. 1998, 33, 61–70.
[18] N.W. Dunham, T. S. Miya, J. Am. Pharmacol. Assoc. 1957,
46, 208–209.
[7] S. J. Hays, M. J. Rice, D. F. Ortwine, G. Johnson, R. D.
Schwarz, D. K. Boyd, L. F. Copeland, M. G.Vartanian, P. A.
Boxer, J. Pharm. Sci. 1994, 83, 1425–1432.
[19] C. Podesva, K.Vagi, Can. J. Chem. 1966, 44, 1872–1875.
[8] J. Mizoule, B. Meldrum, M. Martine, M. Croucher, C. Ollak,
A. Uzan, J. J. Legrand, C. Gueremy, G. LeFur, Neurophar-
macology, 1985, 24, 767–773.
[20] J. Litchfield, F. Wilcoxon, J. Pharmacol. Exp. Ther. 1949,
96, 99–115.