Synthesis, crystal structure and antidiabetic activity of substituted (E)-3-(Benzo [d]thiazol-2-ylamino) phenylprop-2-en-1-one

Article abstract of DOI:10.1016/j.ejmech.2012.11.020

A novel series of substituted (E)-3-(Benzo [d]thiazol-2-ylamino)phenylprop- 2-en-1-onewere synthesized starting from 2-aminobenzothiazole and 1-aryl-3,3-bis- (methylsulfanyl)-2-propen-1-onesin the presence of a catalytic amount of sodium hydride in THF. The synthesised compounds' structures were confirmed by IR, Mass spectrometry, ¹H NMR, ¹³C NMR and HRMS spectral data. These compounds were evaluated for their antidiabetic activity, and most of the derivatives of (E)-3-(Benzo [d]thiazol-2-ylamino) phenylprop-2-en-1-one displayed significant antidiabetic activity.

Full text of DOI:10.1016/j.ejmech.2012.11.020

European Journal of Medicinal Chemistry 59 (2013) 304e309
Contents lists available at SciVerse ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Synthesis, crystal structure and antidiabetic activity of substituted (E)-3-(Benzo
[d]thiazol-2-ylamino) phenylprop-2-en-1-one
,
,e,
Vijay S. Patil a c, Kamalakar P. Nandre b, Sougata Ghosh d, Vaidya Jayathirtha Rao c, Balu A. Chopade d
**
,
***
Balasubramanian Sridhar f, Sheshanath V. Bhosale g , Sidhanath V. Bhosale
,
a,b,
*
a Department of Organic Chemistry, North Maharashtra University, Jalgaon 425001, India
b Polymers and Functional Materials Division, CSIR-Indian Institute of Chemical Technology, Hyderabad 500607, India
c Division of Crop Protection Chemicals, CSIR-Indian Institute of Chemical Technology, Hyderabad 500607, India
d Institute of Bioinformatics and Biotechnology, University of Pune, Pune 411007, India
e Department of Microbiology, University of Pune, Pune 411007, India
f Crystallography Division, CSIR-Indian Institute of Chemical Technology, Hyderabad 500607, India
g School of Applied Sciences, RMIT University, GPO Box 2476V, Melbourne, Vic. 3001, Australia
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel series of substituted (E)-3-(Benzo [d]thiazol-2-ylamino)phenylprop-2-en-1-onewere synthesized
starting from 2-aminobenzothiazole and 1-aryl-3,3-bis- (methylsulfanyl)-2-propen-1-onesin the pres-
ence of a catalytic amount of sodium hydride in THF. The synthesised compounds’ structures were
confirmed by IR, Mass spectrometry, 1H NMR, 13C NMR and HRMS spectral data. These compounds were
evaluated for their antidiabetic activity, and most of the derivatives of (E)-3-(Benzo [d]thiazol-2-ylamino)
phenylprop-2-en-1-one displayed significant antidiabetic activity.
Received 31 July 2012
Received in revised form
29 October 2012
Accepted 14 November 2012
Available online 20 November 2012
Ó 2012 Elsevier Masson SAS. All rights reserved.
Keywords:
2-Aminobenzothiazole
a
-Aroylketene dithioacetals
Antidiabetic
1. Introduction
Pattan et al. reported antidiabetic activity of 2-amino[50(4-
sulphonylbenzilidine)-2,4-thiazolidinedione]-7-chloro-6-
A variety of heterocyclic compounds can be synthesised using 2-
aminobenzothiazoles, as the functional group NH2 is suitably sit-
uated in the moiety. A literature survey reveals that several deriv-
atives of 2-aminobenzothiazoles have useful biological activity i.e.
antibacterial [1], antifungal [2], antimalarial [3], antitubercular [4],
antihelmintic [5], viral infection [6] as well as antitumour activity
[7e13].The antidiabetic properties shown by benzothiazole deriv-
atives i.e. N-(6-chlorobenzothiazol-2-yl)-2-(substituted amino)
acetamide were reported by Mariappan et al. [14] Furthermore, 2-
arylsulfonylaminobenzothiazole derivatives were prepared and
subjected for evaluation of their in vitro activity against protein
tyrosine phosphatase 1B (PTP-1B) by Gabriel and co-workers [15].
fluorobenzothiazole [16]. Recently, the synthesis of nine ethyl 2-(6-
substituted benzo[d]thiazol-2-ylamino)-2-oxoacetate derivatives
and their protein tyrosine phosphatase 1B inhibitory activities were
studied by Gabriel et al. [17] Protein tyrosine phosphatase 1B
inhibitors like Ertiprotafib are found to have immense adverse
effects [18]. Hereby, there is a need to search for alternate targets.
However, till date there are no detailed reports on the study of the
benzothiazole derivatives on the inhibition of the enzymes taking
part in the carbohydrate metabolism. a-amylase and a-glucosidases
are the key players in the postprandial hyperglycaemia observed in
case of non insulin dependent diabetes mellitus (NIDDM). Hence
inhibition of these enzymes can act as a potent target that can serve
as a powerful strategy in the treatment of NIDDM [19].
In continuation of our on-going research into antidiabetic herein
we report the synthesis, characterization and antidiabetic activity of
(E)-3-(Benzo [d]thiazol-2-ylamino)phenylprop-2-en-1-onestarting
from 2-aminobenzothiazole and 1-aryl-3,3-bis-(methylsulfanyl)-
2-propen-1-ones. In the synthesis the catalytic system employed
was a small amount of sodium hydride in THF. These compounds
* Corresponding author. Polymers and Functional Materials Division, CSIR-Indian
Institute of Chemical Technology, Hyderabad 500607, India. Tel.: þ91 40 27191474.
** Corresponding author. School of Applied Sciences, RMIT University, GPO Box
2476V, Melbourne, Vic. 3001, Australia.
*** Corresponding author. Institute of Bioinformatics and Biotechnology, Univer-
sity of Pune, Pune 411007, India. Tel.: þ91 20 2569 0643.
E-mail addresses: bachopade@gmail.com (B.A. Chopade), bsheshanath@
gmail.com (S.V. Bhosale), sidhanath2003@yahoo.co.in (S.V. Bhosale).
were screened for their antidiabetic activity by using
a-amylase
0223-5234/$ e see front matter Ó 2012 Elsevier Masson SAS. All rights reserved.
http://dx.doi.org/10.1016/j.ejmech.2012.11.020

V.S. Patil et al. / European Journal of Medicinal Chemistry 59 (2013) 304e309
305
inhibition assay as well as glucosidase inhibition assay with murine
pancreatic, small intestinal and liver extracts and also the pure
glucosidase.
a-
2. Results and discussion
2.1. Chemistry
A novel series of substituted (E)-3-(Benzo[d]thiazol-2-ylamino)
phenylprop-2-en-1-one (3, ael) was prepared using mild base i.e.
NaH through substitution reaction of suitably functionalized
aroylketene dithioacetals (AKDTAs) (1, aef) with 2-aminoben-
zothiazole (2, aed) in THF(Scheme 1). The precursors, -aroylke-
tene dithioacetals (AKDTAs) (1, aef) were prepared from readily
available substituted acetophenone, carbon disulfide, and an alky-
lating agent, using literature procedures [20,21].
The IR spectrum shows the carbonyl stretching vibrations were
below 1600 cmꢀ1due to the characteristic conjugation effect of the
amino group. In 1H NMR spectra, S,N-ketals showed a characteristic
a-
Fig. 1. Single crystal X-ray structure of 3h (E-isomer).
a
pancreatic glucosidase where as derivatives 3c (IC50 ¼ 20.85
m
mM)
M),
3d (IC50 ¼ 21.72
m
M), 3j (IC50 ¼ 23.51
m
M) and 3k (IC50 ¼ 23.16
exhibited moderate inhibition. Furthermore activities shown by
compounds 3a (IC50 ¼ 26.94 M), 3f (IC50 ¼ 24.71 M) and 3h
(IC50 ¼ 26.49 M) are moderate. The derivatives 3g and 3i exhibited
m
m
m
a further reduced level of activity as compare to 3a, 3f and 3h.
Inhibitory activity of synthesised compounds against murine
intestinal glucosidase is as shown in Table 1. Compound 3h
NH proton at
d 15.2 ppm, assigned to the eNH2 group. The amino
group participated in a strong hydrogen bonding with the oxygen
of the carbonyl group (NHeO]C). The 13C NMR spectrum showed
(IC50 ¼ 14.72
3b and 3f were showed reduced activity. The derivatives 3a
M) were found to be
mM) showed excellent activity. However compounds
a signal for the carbonyl carbon of the ketone near
d 185. Further-
(IC50 ¼ 29.99
m
M) and 3k (IC50 ¼ 29.29
m
more, crystals of (E)-1-(4-Chlorophenyl)-3-(6-ethoxybenzo[d]
thiazol-2-ylamino)-3-(methylthio)-prop-2-en-1-one suitable for
X-ray analysis were grown by vapour diffusion of MeOH into
a CHCl3 solution. The structure of the compound 3h was confirmed
from X-ray crystallographic analysis [CCDC 885525] and the
configuration is E (Fig. 1).
inferior inhibitor for the intestinal glycosidase. Furthermore, the
compound 3e showed no inhibition where as rest of the derivatives
3c (IC50 ¼ 31.88
(IC50 ¼ 32.14
inhibition. While acarbose failed to show any inhibition.
m
M), 3d (IC50 ¼ 31.88
m
M), 3g (IC50 ¼ 44.50
mM), 3i
m
M) and 3j (IC50 ¼ 49.36
m
M) showed very little
In the inhibition of murine liver glucosidase a variation was
observed among the tested compounds. The derivatives 3c
2.2. Biology
(IC50 ¼ 15.74
m
M), 3d (IC50 ¼ 15.39
m
M), 3f (IC50 ¼ 16.74
mM) and 3g
(IC50 ¼ 15.03
m
M) showed excellent inhibitory activity. Whereas
The antidiabetic activities were examined by the standard a-
compound 3h (IC50 ¼ 17.36) showed significant activity. The acar-
amylase inhibition and glucosidase inhibition assay. The activity
results expressed as IC50 are summarised in Table 1. The IC50values
were the average of three independent measurements. The
protease inhibitor used was phorbol-12-myristate-13-acetate.
The a-amylase inhibition activity was carried out by using re-
ported method with a slight modification. The (E)-3-(Benzo [d]
bose exhibited inhibitory activity in micro-molar range
(IC50 ¼ 0.99
3i (IC50 ¼ 21.66
activity as compare to 3c, 3f, 3g and 3h. In case of 3b
(IC50 ¼ 24.21 M) and 3j (IC50 ¼ 24.19 M) observed inhibition is
reduced as compare to 3a, 3i and 3k while 3e shows no inhibition.
-glucosidase (E.C. 3.2.1.20) inhibitory activity against pure
enzyme showed compound 3a (IC50 ¼ 21.05 M) to selectively
inhibit the pure enzyme. Other derivatives tested failed to show
inhibition unlike acarbose (IC50 ¼ 102 M) which was used as
a standard inhibitor against pure alpha glucosidase indicating the
m
M). Furthermore, the derivatives 3a (IC50 ¼ 22.49
mM),
m
M) and 3k (IC50 ¼ 21.38 M) exhibited moderate
m
m
m
thiazol-2-ylamino) phenylprop-2-en-1-one derivatives tested, as
a
compare to acarbose (IC50 ¼ 35.5
significant level of inhibition. The
study revealed that the derivatives 3c (IC50 ¼ 15.87
(IC50 ¼ 16.32 M), 3f (IC50 ¼ 16.87 M), 3d (IC50 ¼ 17.84 M) and 3h
(IC50 ¼ 17.85 M) showed excellent inhibition. Furthermore, the
derivatives 3i (IC50 ¼ 19.85 M), 3b (IC50 ¼ 18.88 M), 3k
(IC50 ¼ 18.63 M) and 3j (IC50 ¼ 18.35 M) were found to be superior
as compared to 3a derivative whereas less potent to 3c, 3e, 3f, 3d and
m
M). These derivatives showed
-amylase inhibition activity
M), 3e
m
a
m
m
m
m
m
m
selectivity of the compounds towards the
murine glucosidases.
a-amylase and the crude
m
m
m
m
3h derivatives. In case of the 3a derivative (IC50 ¼ 20.59
mM) showed
3. Experimental section
moderate activity similar to that of the 3i derivatives.
In vitro efficacy of compounds was evaluated for their antidia-
3.1. Chemistry
betic activity using glucosidase inhibition assay. The results are
tabulated in Table 1. Compounds 3b (IC50 ¼ 19.93
m
M) and 3c
Melting points of compounds were determined by a Kofler
micro melting point apparatus and were uncorrected. IR spectra
(IC50 ¼ 18.04 M) were shows excellent inhibition of murine
m
R2
N
R2
H
SC
3
O
N
R1
HN
S
,
NaH THF
O
+
Ar
H
SC
3
H2N
R1
N2 Reflux
,
S
Ar
H
SC
3
1 (a-f)
2 (a-d)
3 (a-k)
Scheme 1. General synthetic pathway for the preparation of compounds 3aek; Ar ¼ C6H5, 4-CH3C6H4, 4-BrC6H4, 4-ClC6H4, 4-FC6H4; 4-OCH3C6H4; R1 ¼ H, 6-OC2CH3, 6-CH3; R2 ¼ H,
5-CH3.

306
V.S. Patil et al. / European Journal of Medicinal Chemistry 59 (2013) 304e309
Table 1
Enzyme inhibition activity of compounds 3aek. The results summarized are the mean values of n ¼ 3 for IC50 values; NI e No inhibition.
Sr.
Code
Structure
Enzyme inhibition IC50 values (mM)
No.
Porcine
pancreatic
Murine
pancreatic
glucosidase
Murine
intestinal
glucosidase
Murine
liver
glucosidase
a
-amylase
1.
3a
20.59
26.94
29.99
22.49
2.
3.
4.
3b
3c
3d
18.88
15.87
17.84
19.93
20.85
21.72
23.50
31.88
45.31
24.21
15.74
15.39
5.
6.
7.
3e
3f
16.32
16.87
20.33
18.04
24.71
32.35
NI
NI
25.85
44.50
16.74
15.03
3g
8.
9.
3h
3i
17.85
19.85
26.49
33.57
14.72
32.14
17.36
21.66
10.
3j
18.35
23.51
49.36
24.19
11.
12.
3k
18.63
35.50
23.16
29.29
NI
21.38
Acarbose
>100
>100

V.S. Patil et al. / European Journal of Medicinal Chemistry 59 (2013) 304e309
307
were recorded on a Thermo Nicolet Nexus 670 spectrometer using
KBr pellets. 1H NMR spectra were recorded on AVANCE 300 MHz
spectrometer using tetramethylsilane (TMS) as an internal standard
and a13C NMR (75 MHz) Varian instrument. Mass spectra were
recorded on VG-7070H Micromass at 200 ꢁC, 70 eV.
115.3, 122.2, 126.4, 128.8, 129.8, 131.7, 133.4, 137.9, 145.2, 156.3,
156.7, 165.8, 185.0; HRMS (ESI)m/z: Calculated for C19H18BrN2O2S2:
[M þ H]þ 448.9989, Found: 448.9993.
3.1.5. (E)-3-(Benzo [d]thiazol-2-ylamino)-1-(4-bromophenyl)-3-
(methylthio)prop-2-en-1 one (3d)
3.1.1. Typical procedure for synthesis of substituted (E)-3-(Benzo [d]
thiazol-2-ylamino) phenylprop-2-en-1-one(3, ael)
IR (KBr ymax/cmꢀ1): 3159, 3061, 2985, 2920, 2829, 2717, 2659,
2619, 2482,1591,1568,1564,1537,1489,1463,1436,1423,1328,1278,
1259, 1224,1178, 1076, 935, 842, 804, 657; Mass [ESI, 70 eV] m/z (%):
In a 100 mL two neck round bottom flask, of which one neck is
fitted with a reflux condenser, the mixture of 0.01 mol of
substituted 2-aminobenzothiazole (2, aed), 0.02 mol sodium
hydride under N2 atmosphere in 5e10 mL of dry THF was added
through the other neck, and the reaction mixture was stirred at
room temperature for 10e15 min. Into the reaction mixture
0.01 mol 1-aryl-3,3-bis-(methylsulfanyl)-2-propen-1-ones (1, aef)
i.e. aroyl ketene dithioacetal in 10 mL dry THF was added and the
mixture was refluxed. Progress of the reaction was monitored by
TLC (hexane: EtOAc, 8:2). After completion of the reaction, the
reaction mixture was poured into crushed ice (250 mL of ice-water)
with vigorous stirring and then stirred at room temperature for
another 30 min. The reddish or yellow precipitate formed was
filtered, washed with cold water and dried. The crude product was
recrystalized from MeOH or CHCl3: MeOH. The recrystalized
product was characterized by various spectroscopic techniques.
405 (98), 407 (100), 408 (25); 1H NMR (300 MHz, CDCl3)
d ppm: 2.53
(s, 3H, SCH3), 5.98 (s, 1H, CH]C), 7.22e7.25 (dd, J ¼ 1.8 & 7.2 Hz, 1H,
PhH), 7.36e7.39 (t, J ¼ 6.3 and 7.2 Hz, 1H, PhH), 7.69e7.71 (d,
J ¼ 8.2 Hz,2H, PhH), 7.75e7.79 (m, 3H, PhH); 13C NMR (75 MHz,
CDCl3): d ppm 15.9, 92.0,121.0,121.6,124.2,126.3,126.6,128.8,130.1,
131.7, 137.8, 138.0, 143.6, 165.8, 169.9, 182.7; HRMS (ESI)m/z: Calcu-
lated for C17H14BrN2OS2: [M þ H]þ 404.9713, Found: 404.97130.
3.1.6. (E)-3-(6-Ethoxybenzo[d]thiazol-2-ylamino)-3-(methylthio)-
1-phenylprop-2-en-1-one (3e)
IR (KBr ymax/cmꢀ1): 3149, 3089, 3068, 2974, 2933, 2883, 2841,
2623, 2532, 2285, 2160, 1901, 1600, 1548, 1456, 1438, 1417, 1390,
1301, 1253, 1220, 1111, 1053, 931, 732, 682, 651; Mass [ESI, 70 eV] m/
z (%): 371 (98), 372 (25), 373 (12); 1H NMR (300 MHz, CDCl3)
d ppm:
1.42e1.46 (t, 3H, CH2CH3), 2.52 (s, 3H, SCH3), 4.01e4.08 (q, 2H,
CH3CH2), 6.03 (s, 1H, CH]C), 6.92e6.96 (dd, J ¼ 2.2 and 6.0 Hz, 1H,
PhH), 7.163e7.169 (d, J ¼ 2.2 Hz, 1H, PhH), 7.39e7.48 (m, 3H, PhH),
7.65e7.68 (d, J ¼ 9.0 Hz,1H, PhH), 7.87e7.89 (m, 2H, PhH), 15.21 (s,
3.1.2. (E)-3-(Benzo [d]thiazol-2-ylamino)-3-(methylthio)-1-p-
tolylprop-2-en-1-one (3a)
IR (KBr ymax/cmꢀ1): 3143, 3059, 2989, 2922, 2852, 2744, 2299,
1595, 1568, 1556, 1489, 1454, 1315, 1255, 1182, 1076, 837, 754, 694;
Mass [ESI, 70 eV] m/z (%): 341 (100), 342 (26), 343 (12), 376 (29); 1H
1H, NH); 13C NMR (75 MHz, CDCl3):
d ppm 14.8, 15.7, 64.0, 92.04,
105.0, 115.2, 122.0, 127.2, 128.2, 128.4, 131.6, 133.2, 133.4, 139.0,
145.2, 156.2, 156.9, 165.2, 186.3; HRMS (ESI) m/z: Calculated for
C19H19N2O2S2: [M þ H]þ 371.0870, Found: 371.0887.
NMR (300 MHz, CDCl3)
d ppm: 2.42 (s, 3H, ArCH3), 2.53 (s, 3H,
SCH3), 6.04 (s, 1H, CH]C), 7.17e7.23 (m, 3H, PhH), 7.34e7.39(m, 1H,
PhH), 7.68e7.71 (d, J ¼ 7.5 Hz, 1H, PhH), 7.76e7.80 (m, 3H, PhH),
3.1.7. (E)-1-(4-Bromophenyl)-3-(5,6-dimethylbenzo[d]thiazol-2-
ylamino)-3 (methylthio) prop-2-en-1-one (3f)
15.16 (s, 1H, NH); 13C NMR (75 MHz, CDCl3):
d ppm 15.8, 21.5, 92.4,
120.9, 121.4, 123.9, 125.7, 126.1, 127.3, 128.3, 129.2, 132.1, 136.2,
Yellow solid; IR (KBr ymax/cmꢀ1): 3142, 2976, 2916, 2852, 2648,
2571, 2466, 2283, 1591, 1539, 1531, 1487, 1456, 1433, 1273, 1259,
1224, 1174, 1076, 918, 869, 840, 761; Mass [ESI, 70 eV] m/z (%): 433
142.4, 151.1, 159.2, 164.6, 186.5; HRMS (ESI)m/z: Calculated for
C18H
17eN2OS2: [M þ H]þ 341.0767, Found: 341.0782.
(96), 435 (100); 1H NMR (300 MHz, CDCl3)
d ppm: 2.43 (s, 3H,
3.1.3. (E)-3-(6-Ethoxybenzo [d] thiazol-2-ylamino)-3-(methylthio)-
1-p-tolylprop-2-en-1-one (3b)
ArCH3), 2.35 (s, 3H, ArCH3), 2.51 (s, 3H, SCH3), 5.95 (s, 1H, CH]C),
7.45 (s,1H, PhH), 7.54 (s,1H, PhH), 7.57e7.58 (d, J ¼ 8.4 Hz, 2H, PhH),
7.74e7.76 (d, J ¼ 8.4 Hz, 2H, PhH), 15.15 (s, 1H, NH); 13C NMR
IR (KBr ymax/cmꢀ1): 3066, 2985, 2978, 2887, 2860, 2736, 2673,
2609, 2534, 2439, 2277, 2158, 1600, 1539, 1519, 1475, 1456, 1435,
1392, 1303, 1290, 1261, 1222, 1182, 1111, 1056, 933, 819, 758; Mass
[ESI, 70 eV] m/z (%): 385 (100), 386 (29), 387 (15); 1H NMR
(75 MHz, CDCl3):
d ppm 15.8, 20.01, 20.08, 91.5, 121.1, 122.0, 126.4,
128.7, 129.4, 131.0, 131.6, 133.3, 135.5, 137.8, 149.5, 158.0, 165.8,
185.0; HRMS (ESI) m/z: Calculated for C19H18BrN2OS2: [M þ H]þ
432.9990, Found: 432.9805.
(300 MHz, CDCl3) d ppm: 1.38 (s, 3H, ArCH3), 1.42e1.47 (t, 3H, CH2e
CH3), 2.52 (s, 3H, SCH3), 4.01e4.08 (q, 2H, CH3eCH2), 5.96 (s, 1H,
CH]C), 6.93e6.96 (dd, J ¼ 2.4 and J ¼ 6.6 Hz 1H, PhH), 7.16e7.17(d,
J ¼ 2.4 Hz, 1H, PhH), 7.55e7.58 (d, d, J ¼ 8.4 Hz, 2H, PhH), 7.65e7.68
(d, J ¼ 8.8 Hz, 1H, PhH), 7.74e7.77 (d, J ¼ 8.4 Hz, 2H, PhH), 15.16 (s,
3.1.8. (E)-3-(Benzo [d]thiazol-2-ylamino)-1-(4-chlorophenyl)-3-
(methylthio)prop-2-en-1-one (3g)
IR (KBr ymax/cmꢀ1): 3149, 3070, 3005, 2920, 2848, 2659, 2569,
1591, 1568, 1547, 1537, 1494, 1463, 1435, 1425, 1328, 1282, 1259,
1222, 1089, 846, 765, 756; Mass [ESI, 70 eV] m/z (%): 361 (100), 363
1H, NH); 13C NMR (75 MHz, CDCl3):
d ppm 14.1, 15.1, 20.8, 91.3,
104.4, 114.5, 121.3, 126.6, 128.5, 132.0, 135.6, 141.6, 144.6, 155.5,
156.3, 164.0, 185.5; HRMS (ESI)m/z: Calculated for C20
H21eN2O2S2:
(42); 1H NMR (300 MHz, CDCl3)
d ppm: 2.53 (s, 3H, SCH3), 5.99 (s,
[M þ H]þ 385.1033, Found: 385.1044.
1H, CH]C), 7.21e7.28 (dd, J ¼ 1.5 Hz, 1H, PhH), 7.35e7.42 (m,3H,
PhH), 7.69e7.72 (d, J ¼ 7.5 Hz, 1H, PhH), 7.77e7.80 (d, J ¼ 8.3 Hz, 1H,
PhH), 7.82-7.85 (d, J ¼ 8.3 Hz, 2H, PhH), 15.19 (s, 1H, NH); 13C NMR
3.1.4. (E)-1-(4-Bromophenyl)-3-(6-ethoxybenzo[d]thiazol-2-
ylamino)-3-(methylthio)prop-2-en-1-one (3c)
(75 MHz, CDCl3):
d ppm 15.9, 92.1, 121.1, 121.6, 126.3, 128.7, 132.2,
IR (KBr ymax/cmꢀ1): 3149, 2997, 2895, 2735, 2571, 2534, 2297,
1876, 1602, 1573, 1543, 1504, 1483, 1456, 1427, 1319, 1284, 1261,
1224, 1074, 1058, 920, 883, 817, 758; Mass [ESI, 70 eV] m/z (%): 449
138.1, 151.1, 159.0, 165.7, 185.3; HRMS (ESI) m/z: Calculated for
C17H14N2OS2Cl: [M þ H]þ 361.0225, Found: 361.0236.
(82), 451 (82); 1H NMR (300 MHz, CDCl3)
d
ppm: 1.42e1.47 (t, 3H,
3.1.9. (E)-1-(4-Chlorophenyl)-3-(6-ethoxybenzo[d]thiazol-2-
ylamino)-3-(methylthio)prop-2-en-1-one (3h)
CH2eCH3), 2.52 (s, 3H, SCH3), 4.01e4.08 (q, 2H, CH3eCH2), 5.96 (s,
1H, CH]C), 6.93-6.96 (dd, J ¼ 2.4 and 6.6 Hz, 1H, PhH), 7.16e7.17 (d,
J ¼ 2.4 Hz, 1H, PhH), 7.55e7.58 (d, J ¼ 8.4 Hz, 2H, PhH), 7.65e7.68 (d,
J ¼ 8.8 Hz, 1H, PhH), 7.74e7.77 (d, J ¼ 8.4 Hz, 2H, PhH), 15.16 (s, 1H,
IR (KBr ymax/cmꢀ1): 3155, 3093, 2974, 2926, 2879, 2763, 2735,
2663, 2574, 2547, 2295, 1602, 1554, 1506, 1489, 1460, 1433, 1284,
1253, 1224, 1178, 1112, 1085, 1056, 920, 813, 761; Mass [ESI, 70 eV]
NH); 13C NMR (75 MHz, CDCl3):
d
ppm 14.8, 15.8, 64.1, 91.6, 105.1,
m/z (%): 405 (100), 407 (42); 1H NMR (300 MHz, CDCl3)
d ppm:

308
V.S. Patil et al. / European Journal of Medicinal Chemistry 59 (2013) 304e309
1.42e1.47 (t, 3H, OCH2CH3), 2.52 (s, 3H, SCH3), 4.01e4.08 (q, 2H,
CH3CH2O), 5.96 (s,1H, CH]C), 6.93e6.96 (dd, J ¼ 2.2 and 6.0 Hz,1H,
PhH), 7.16e7.17 (d, J ¼ 2.2 Hz, 1H, PhH), 7.39e7.42 (d, J ¼ 8.3 Hz, 2H,
PhH), 7.65-7.68 (d, J ¼ 9.0 Hz, 1H, PhH), 7.82e7.84 (d, J ¼ 8.3 Hz, 2H,
incubated with 100
[22]. 500 L of starch (1%) was added to initiate the
activity. -amylase without any compound was used as control. The
DNSA assay was employed to estimate reducing sugar at A540 nm
and the enzyme units were expressed as micro-molar per minute.
Under the used assay conditions, one unit of enzyme was defined as
m
L of samples (1 mg mlꢀ1) at 37 ꢁC for 10 min
-amylase
m
a
a
PhH), 15.16 (s, 1H, NH); 13C NMR (75 MHz, CDCl3):
d ppm 14.8, 15.8,
64.0, 91.6105.0, 115.3, 122.1, 128.6, 128.7, 129.7, 133.4, 137.4, 137.9,
145.3, 146.9,156.30,156.37, 156.7, 184.8; HRMS (ESI) m/z: Calculated
for C19H18N2O2S2Cl: [M þ H]þ 405.0495, Found: 405.0498.
the amount of enzyme required to liberate 1 mM of maltose. The
final inhibition shown by different samples were compared with
the standard inhibitor, acarbose [19]. The following formula was
used to estimate inhibitory activity:
3.1.10. (E)-3-(Benzo [d]thiazol-2-ylamino)-1-(4-fluorophenyl)-3-
(methylthio)prop-2-en-1-one (3i)
IR (KBr ymax/cmꢀ1): 3170, 3122, 3059, 2991, 2924, 2873, 2806,
2748, 2611, 1597, 1566, 1543, 1508, 1494, 1456, 1438, 1427, 1319,
1276, 1247, 1186, 1159, 1072, 864, 823, 771, 725; Mass [ESI, 70 eV] m/
z (%): 345 (100), 346 (25) 347 (10); 1H NMR (300 MHz, CDCl3)
% Inhibition ¼ ðA540Control ꢀ A540TestÞ=A540Control ꢂ 100
3.2.2. Glucosidase inhibition assay with murine pancreatic, small
intestinal and liver extracts
d
ppm: 2.53 (s, 3H, SCH3), 5.98 (s, 1H, CH]C), 7.08e7.13 (t,
Fromthe National Toxicology Centre, Pune, 10-week-old male
Swiss mice weighing 20 g were procured. The entire procedure of
activity was carried out following the guidelines of the Institutional
Animal Ethical Committee. The obtained Swiss mice from the
national toxicology centre, Pune, were starved for 12 h. Pancreas,
liver and small intestine tissues were excised and homogenized
with 10 mM ice cold phosphate buffer containing 6 mM NaCl (1:10
dilution; w/v) and appropriate amount of protease inhibitors. At
10,000 rpm tissue homogenates were centrifuged for 10 min. After
10 min, the supernatant was taken as a source of enzyme and was
diluted so as to get an absorbance of 0.4 (at 280 nm). The assay of
enzyme inhibition was carried out as described above. The method
employed by Bhat et al. was used to calculate percentage inhibition
of the samples against pancreatic, small intestinal and liver
glucosidases [23].
J ¼ 8.3 Hz, 2H, PhH), 7.21e7.24 (t, J ¼ 3.0 and 7.5 Hz, 1H, PhH), 7.35e
7.40 (t, J ¼ 7.5 and 8.3 Hz, 2H, PhH), 7.69e7.71 (d, J ¼ 7.5 Hz, 1H,
PhH), 7.77e7.79 (d, J ¼ 7.5 Hz, 1H, PhH), 7.89e7.94 (dd, J ¼ 3.0 and
6.0 Hz, 2H, PhH); 13C NMR (75 MHz, CDCl3):
d ppm 15.8, 92.0, 115.5,
115.6, 121.0, 121.5, 124.1, 126.2, 129.6, 129.7, 132.1, 135.2, 151.0, 159.0,
165.2, 163.3, 166.7, 185.2; HRMS (ESI)m/z: Calculated for
C17H14FN2OS2: [M þ H]þ 345.0518, Found: 345.0531.
3.1.11. (E)-3-(6-Ethoxybenzo[d]thiazol-2-ylamino)-1-(4-
fluorophenyl)-3-(methylthio)prop-2-en-1-one (3j)
IR (KBr ymax/cmꢀ1): 3057, 2980, 2926, 2879, 2735, 2598, 1602,
1550, 1498, 1460, 1433, 1298, 1255, 1222, 1165, 821, 599; Mass [ESI,
70 eV] m/z (%): 389 (10), 371 (100), 372 (25), 373 (15); 1H NMR
(300 MHz, CDCl3)
d ppm: 1.42e1.46 (t, 3H, OCH2CH3), 2.52 (s, 3H,
SCH3), 4.01e4.08 (q, 2H, CH3CH2O), 5.96 (s, 1H, CH]C), 6.92e6.96
(dd, J ¼ 2.2 and 8.3 Hz, 1H, PhH), 7.08e7.14 (t, J ¼ 8.3 and 9.0 Hz,
2H, PhH), 7.16e7.17 (d, J ¼ 2.2 Hz, 1H, PhH), 7.65e7.68 (d, J ¼ 8.3 Hz,
1H, PhH), 7.88e7.93 (m, 2H, PhH), 15.13 (s, 1H, NH); 13C NMR
3.2.3.
Glucosidase inhibition assay of benzothiazole derivatives was
carried out as per Sanap et al., 2010 [24]. In brief, 100 L of
glucosidase (0.1 unit/ml; Sigma Aldrich, USA) was mixed with each
of the samples (200
L) and incubated for 1 h at 37 ꢁC. Enzyme
action for -glucosidase was initiated by addition of 100 L of
10 mM p-nitrophenyl- -glucopyranoside in 100 mM phosphate
buffer of pH 6.8 and stopped by adding 2 mL of 0.1 M Na2CO3 after
an incubation of 10 min at 37 ꢁC.
-Glucosidase inhibitory activity
a-Glucosidase inhibition assay
m
a-
(75 MHz, CDCl3):
d ppm 14.8, 15.7, 64.0, 91.6, 105.1, 115.32, 115.36,
115.6, 122.1, 129.5, 129.6, 135.2, 135.3, 145.2, 156.2, 156.8, 163.2,
165.3, 166.6, 184.9; HRMS (ESI)m/z: Calculated for C19H18FN2O2S2:
[M þ H]þ 389.0778, Found: 389.0793.
m
a
m
a-D
3.1.12. (E)-3-(6-Ethoxybenzo[d]thiazol-2-ylamino)-1-(4-
a
methoxyphenyl)-3-(methylthio) prop-2-en-1-one (3k)
was determined by measuring absorbance of the p-nitrophenol
released from pNPG at 420 nm using Shimadzu Spectrophotometer
UV-1601 using the following formula:
IR (KBr ymax/cmꢀ1): 2980, 2933, 2891, 2833, 2738, 2692, 1600,
1573, 1556, 1516, 1504, 1462, 1431, 1319, 1301, 1244, 1226, 1170,1172,
1074, 1022, 840, 812, 769; Mass [ESI, 70 eV] m/z (%): 401 (100), 402
(25), 403 (15), 383 (7); 1H NMR (300 MHz, CDCl3)
d ppm: 1.41e1.46
% Inhibition ¼ ðA420Control ꢀ A420TestÞ=A420Control ꢂ 100
(t, 3H, OCH2CH3), 2.51 (s, 3H, SCH3), 3.86(s, 3H, OCH3), 4.00e4.07 (q,
2H, CH3CH2O), 5.98 (s, 1H, CH]C), 6.88e6.95 (dd, J ¼ 2.6 and
9.0 Hz, 3H, PhH), 7.15e7.16 (d, J ¼ 2.6 Hz, 1H, PhH), 7.63e7.66 (d,
J ¼ 8.8 Hz, 1H, PhH), 7.85e7.88 (d, J ¼ 8.8 Hz, 2H, PhH), 15.19 (s, 1H,
4. Conclusion
NH); 13C NMR (75 MHz, CDCl3):
d ppm 14.8, 15.7, 55.4, 64.0, 91.7,
Thus, in the present study, we have synthesized series of novel
(E)-3-(Benzo [d]thiazol-2-ylamino)phenylprop-2-en-1-one start-
ing from 1-aryl-3,3-bis-(methylsulfanyl)-2-propen-1-ones and 2-
aminobenzothiazole and screened as new class of antidiabetic
agents. The benzothiazole derivatives 3c, 3e, 3f, 3d and 3h showed
105.0, 113.7, 115.1, 121.9, 129.3, 130.6, 131.5, 133.3, 145.3, 156.1, 157.1,
162.5, 164.1, 185.5; HRMS (ESI)m/z: Calculated for C20H21N2O3S2:
[M þ H]þ 401.0975, Found: 401.0993.
excellent inhibitory activity against a-amylase. We also found that
3.2. Biology
the derivatives 3b, 3c, 3d, 3f, 3g and 3h are promising glycosidase
inhibitors. The results of the present investigation indicate the
importance of these novel compounds as potential lead candidates.
The pharmacological evaluations of the products were carried
out in the pharmacological unit, Institute of Bioinformatics and
Biotechnology, (University of Pune, INDIA.)
Acknowledgements
3.2.1.
Benzothiazole derivatives were employed to check the
amylase inhibitory activity using the Bernfeld method (1955) with
a slight modification in the substrate. The 100 L of porcine
pancreatic -amylase 50
g mlꢀ1 (O.D. 0.4 at 280 nm) was
a-Amylase inhibition assay
a
-
The authors are thankful to the Director, IICT, Hyderabad for
providing necessary instrumental facilities. Sid. V. Bhosale would
like to thank the DAE-BRNS, Mumbai and CSIR, New Delhi, India for
financial support under XIIth five year plan. S. Ghosh thanks
m
a
m

V.S. Patil et al. / European Journal of Medicinal Chemistry 59 (2013) 304e309
309
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