Synthesis of some thiazolyl aminobenzothiazole derivatives as potential antibacterial, antifungal and anthelmintic agents

Article abstract of DOI:10.3109/14756360903555258

A series of 4-(6-substituted-1,3-benzothiazol-2-yl)amino-2-(4- substitutedphenyl)-amino-1,3-thiazoles, 9-24 have been synthesised from 2-chloro-N-(6-substituted-1,3-benzothiazol-2-yl)acetamides, 5-8. The structures of these compounds have been elucidated by spectral (IR, ¹H NMR, Mass) and elemental (C, H, N) analysis data. All the newly synthesised compounds (9-24) were screened for their antibacterial, antifungal and anthelmintic activities. Almost all of these compounds showed moderate to good antimicrobial activity against two gram negative bacteria (E. coli, P. aeruginosa), two gram positive bacteria (S. aureus, B. subtilis), pathogenic fungal strains (C. albicans, A. niger) and good anthelmintic activity against earthworm species (P. corethruses). Compounds 18 and 20 exhibited good antibacterial and antifungal activities, while compound 22 displayed the most significant anthelmintic activity.

Full text of DOI:10.3109/14756360903555258

Journal of Enzyme Inhibition and Medicinal Chemistry, 2011; 26(1): 22–28
Copyright © 2011 Informa UK, Ltd.
ISSN 1475-6366 print/ISSN 1475-6374 online
DOI: 10.3109/14756360903555258
RESEARCH ARTICLE
Synthesis of some thiazolyl aminobenzothiazole derivatives as
potential antibacterial, antifungal and anthelmintic agents
Nikhil D. Amnerkar, and Kishore P. Bhusari
Department of Medicinal Chemistry, Sharad Pawar College of Pharmacy, Rashtrasant Tukadoji Maharaj Nagpur
University, Nagpur, Maharashtra, India
Abstract
A series of 4-(6-substituted-1,3-benzothiazol-2-yl)amino-2-(4-substitutedphenyl)- amino-1,3-thiazoles, 9–24 have
been synthesised from 2-chloro-N-(6-substituted-1,3-benzothiazol-2-yl)acetamides, 5–8. The structures of these
compounds have been elucidated by spectral (IR, 1H NMR, Mass) and elemental (C, H, N) analysis data. All the newly
synthesised compounds (9–24) were screened for their antibacterial, antifungal and anthelmintic activities. Almost all
of these compounds showed moderate to good antimicrobial activity against two gram negative bacteria (E. coli, P.
aeruginosa), two gram positive bacteria (S. aureus, B. subtilis), pathogenic fungal strains (C. albicans, A. niger) and good
anthelmintic activity against earthworm species (P. corethruses). Compounds 18 and 20 exhibited good antibacterial
and antifungal activities, while compound 22 displayed the most significant anthelmintic activity.
Keywords: Aminobenzothiazole, thiazole, antibacterial activity, antifungal activity, anthelmintic activity
Introduction
e scaffold benzothiazole and its analogue are impor-
tant pharmacophores that are found in many marine
compounds or natural plants [6,7]. In the past decades,
2-aminobenzothiazole and its derivatives have received
much attention due to their chemotherapeutic value in
the development of novel anthelmintics and antimicro-
bial agents [8−12]. In addition, many 2-aminobenzo-
thiazole derivatives exhibit a wide variety of biological
activities such as diuretic [13], anticancer [14], anticon-
vulsant [15,16], antihistamine [17] and anti-inflammatory
[18]. Moreover, the thiazole ring is an important building
block in medicinal chemistry and endowed with antimi-
crobial, anthelmintic and various other pharmacologi-
cal activities [19−21]. In addition, there are a number of
antimicrobial and anthelmintic thiazoles available in
clinical practice (Cefixime, Ceftizoxime, Cefotaxime,
Ceftazidime, Ceftibuten, Aztreonam, Tigemonam,
iabendazole) that make less use of the amino group.
Inviewofthehighdegreeofbioactivityshownbythetwo
heterocyclic compounds mentioned above and in our con-
tinued search for antimicrobial and anthelmintic agents,
we aimed to construct a system combining both these vital
Nowadays helminth infections are a major medical
problem worldwide and there has been a considerable
increase in its incidence [1]. It is one of the most frequent
sources of human infections particularly in tropical coun-
tries like India [2,3]. Chemotherapy is important in the
treatment of parasitic infections [4]. Helminth infections
often have a connection to some other disease (especially
those caused by microorganisms), whenever the body
system gets debilitated. Diseases caused by microbial
infection are a serious menace to the health of human
beings [5]. Despite the important advances in the field
of anthelmintic and antimicrobials, together with the
availability of drugs for these infections, there is a con-
tinuing increase in the incidence of these infectious dis-
eases, together with a gradual rise in resistance. is has
resulted in an increased morbidity and mortality with an
overall increase in healthcare costs. is scenario high-
lights the urgent need for the design of new and effective
entities with chemical structures that are different from
the traditional drugs which will act both as anthelmintic
and antimicrobials.
Address for Correspondence: K. P. Bhusari, Department of Medicinal Chemistry, Sharad Pawar College of Pharmacy, Rashtrasant Tukadoji
Maharaj Nagpur University, Nagpur-441 110, Maharashtra, India. Tel.: +91 7104 236352, Fax: +91 7104 235084 E-mail addresses: kishore.
bhusari@gmail.com, nikhilamnerkar@gmail.com.
(Received 23 August 2009; revised 08 December 2009; accepted 13 December 2009)
22

Synthesis of some thiazolyl aminobenzothiazole derivatives
23
1
moieties in a single molecular framework, together with an
exploration of the additive effects of their biological activi-
ties. In the present paper, we report the synthesis of some
hitherto unreported 4-(6-substituted-1,3-benzothiazol-2
-yl)amino-2-(4-substituted-phenyl)-amino-1,3-thiazole
derivatives and also to evaluate them biologically for their
antibacterial, antifungal and anthelmintic activities.
(C=N), 1108 (C−N); H NMR (CDCl3, ppm): δ 7.87−8.26
(m, 9H, Ar-H), 12.22 (s, 1H, NH); EI-MS: m/z [M+H]+ 360;
Anal. calcd for C16H11ClN4S2: C, 53.55; H, 3.09; N, 15.61.
Found: C, 53.48; H, 3.11; N, 15.59.
4-(1,3-benzothiazol-2-yl)amino-2-(4-hydroxyphenyl)amino-
1,3-thiazole (11)
Brown solid; Yield: 64%; mp 181–182°C; Rf 0.56 (ethyl
acetate:ammonia); IR (KBr, cm−1): 3620 (OH), 3382
(NH), 1546 (C=N), 1098 (C−N); 1H NMR (CDCl3, ppm): δ
7.63−8.12 (m, 9H, Ar-H), 9.8 (s, 1H, OH), 12.68 (s, 1H, NH);
EI-MS: m/z [M+H]+ 341; Anal. calcd for C16H12N4OS2: C,
56.45; H, 3.55; N, 16.46. Found: C, 56.42; H, 3.53; N, 16.48.
Experimental
Chemistry
All the chemicals and solvents employed in the synthesis
were supplied by Merck (Darmstadt, Germany), Fluka
(Seelze, Germany) and SD Fine chemicals (Mumbai,
India) and used without purification. Melting points
were determined on a digital melting point apparatus
Electrothermal 1A 9200 (Electrothermal Engineering Ltd.,
Southend-on-sea, Essex, UK) and were uncorrected. All
thereactionsweremonitoredbyTLCperformedon2−6cm
aluminium sheets precoated with silica gel 60 (HF-254, E.
Merck, Mumbai, India). e IR spectra were recorded on
a Shimadzu FTIR 8400S spectrophotometer (Kyto, Japan)
using KBr optics. 1H NMR spectra were recorded in CDCl3
on a Varian Mercury YH-300 MHz spectrophotometer
(Palo Alto, CA) and chemical shifts (δ) are given in ppm
relative to TMS. Mass spectra were recorded at 70eV on a
Jeol D-300 spectrometer (Tokyo,) and a 3200 QTRAP LC/
MS/MS spectrophotometer (Applied Biosystems, Foster
City, CA). Elemental analyses were carried out using a
FLASH EA 1112 CHN analyser (ermo Finnigan, Milan,
Italy), VARIO EL (Elementar, Hanau, Germany) and found
within 0.4% of theoretical values.
4-(1,3-benzothiazol-2-yl)amino-2-(4-methoxyphenyl)amino-
1,3-thiazole (12)
Light yellow crystals; Yield: 69%; mp 193–195°C; Rf 0.63
(ethyl acetate:ammonia); IR (KBr, cm−1): 3336 (NH), 1580
(C=N), 1084 (C−N); 1H NMR (CDCl3, ppm): δ 3.78 (s, 3H,
OCH3), 7.88−8.31 (m, 9H, Ar-H), 13.11 (s, 1H, NH); EI-MS:
m/z [M+H]+ 355; Anal. calcd for C17H14N4OS2: C, 57.61; H,
3.98; N, 15.81. Found: C, 57.65; H, 3.96; N, 15.79.
4-(6-Methyl-1,3-benzothiazol-2-yl)amino-2-phenylamino-1,3-
thiazole (13)
Brown solid; Yield: 60%; mp 208–210°C; Rf 0.52 (ethyl
acetate:ammonia); IR (KBr, cm−1): 3284 (NH), 1552
(C=N), 1124 (C−N); 1H NMR (CDCl3, ppm): δ 2.48 (s, 3H,
CH3), 7.76−8.23 (m, 9H, Ar-H), 12.84 (s, 1H, NH); EI-MS:
m/z [M+H]+ 339; Anal. calcd for C17H14N4S2: C, 60.33; H,
4.17; N, 16.55. Found: C, 60.27; H, 4.15; N, 16.57.
4-(6-Methyl-1,3-benzothiazol-2-yl)amino-2-(4-chlorophenyl)
amino-1,3-thiazole (14)
Synthesis
General synthesis of 4-(6-substituted-1,3-benzothiazol-2-yl)
amino-2-(4-substituted-phenyl)amino-1,3-thiazole (9–24)
A mixture of 2-chloro-N-(6-substituted-1,3-benzothizol-
2-yl)acetamides (5–8), substituted phenylthiourea
(0.01mol),absoluteethanol(15mL)andanhydrouspotas-
sium carbonate (0.01mol) were heated under reflux in a
water bath for 12h. e excess substituted phenylthiourea
and ethanol were removed by distillation and the residue
treated with 5% sodium carbonate solution to remove acid
impurities, filtered then washed with water and dried. e
crude product was crystallised from ethanol.
White crystals; Yield: 52%; mp 202–204°C; Rf 0.46 (ethyl
acetate:ammonia); IR (KBr, cm−1): 3324 (NH), 1574
(C=N), 1105 (C−N); 1H NMR (CDCl3, ppm): δ 2.34 (s, 3H,
CH3), 7.64−7.98 (m, 8H, Ar-H), 12.08 (s, 1H, NH); EI-MS:
m/z [M+H]+ 374; Anal. calcd for C17H13ClN4S2: C, 54.76; H,
3.51; N, 15.02. Found: C, 54.72; H, 3.53; N, 14.99.
4-(6-Methyl-1,3-benzothiazol-2-yl)amino-2-(4-
hydroxyphenyl)amino-1,3-thiazole (15)
Brown solid; Yield: 58%; mp 233–235°C; Rf 0.55 (ethyl
acetate:ammonia); IR (KBr, cm−1): 3570 (OH), 3295 (NH),
1
1568 (C=N), 1092 (C−N); H NMR (CDCl3, ppm): δ 2.56
4-(1,3-benzothiazol-2-yl)amino-2-phenylamino-1,3-thiazole (9)
Yellow solid; Yield: 68%; mp 171–173°C; Rf 0.54 (ethyl
acetate:ammonia); IR (KBr, cm−1): 3284 (NH), 1552 (C=N),
1086 (C−N); 1H NMR (CDCl3, ppm): δ 7.69−8.12 (m, 10H,
Ar-H), 11.86 (s, 1H, NH); EI-MS: m/z [M+H]+ 325; Anal.
calcd for C16H12N4S2: C, 59.23; H, 3.73; N, 17.27. Found: C,
59.27; H, 3.71; N, 17.28.
(s, 3H, CH3), 7.74−8.05 (m, 8H, Ar-H), 10.2 (s, 1H, OH),
11.76 (s, 1H, NH); EI-MS: m/z [M+H]+ 355; Anal. Calcd
for C17H14N4OS2: C, 57.61; H, 3.98; N, 15.81. Found: C,
57.64; H, 3.96; N, 15.81.
4-(6-Methyl-1,3-benzothiazol-2-yl)amino-2-(4-
methoxyphenyl)amino-1,3-thiazole (16)
4-(1,3-benzothiazol-2-yl)amino-2-(4-chlorophenyl)amino-
1,3-thiazole (10)
Light yellow crystals; Yield: 59%; mp 188–190°C; Rf 0.38
(ethyl acetate:ammonia); IR (KBr, cm−1): 3330 (NH), 1574
White crystals; Yield: 64%; mp 213–215°C; Rf 0.61 (ethyl
acetate:ammonia); IR (KBr, cm−1): 3330 (NH), 1552
1
(C=N), 1122 (C−N); H NMR (CDCl3, ppm): δ 2.35 (s,
3H, CH3), 3.84 (s, 3H, OCH3), 7.68−7.94 (m, 8H, Ar-H),
© 2011 Informa UK, Ltd.

24
N. D. Amnerkar and K. P. Bhusari
12.33 (s, 1H, NH); EI-MS: m/z [M+H]+ 355; Anal. Calcd
for C18H16N4OS2: C, 58.67; H, 4.38; N, 15.21. Found: C,
58.63; H, 4.38; N, 15.22.
[M+H]+ 403; Anal. Calcd for C18H15ClN4OS2: C, 53.66; H,
3.75; N, 13.91. Found: C, 53.63; H, 3.72; N, 13.92.
4-(6-Ethoxy-1,3-benzothiazol-2-yl)amino-2-(4-
4-(6-Fluoro-1,3-benzothiazol-2-yl)amino-2-phenylamino-1,3-
thiazole (17)
hydroxyphenyl)amino-1,3-thiazole (23)
Grey solid; Yield: 61%; mp 262–264°C; Rf 0.35 (ethyl
Brown solid; Yield: 54%; mp 245–247°C; Rf 0.52 (ethyl
acetate:ammonia); IR (KBr, cm−1): 3640 (OH), 3286
acetate:ammonia); IR (KBr, cm−1): 3308 (NH), 1574 (C=N),
(NH), 1538 (C=N), 1125 (C−N); H NMR (CDCl3, ppm):
1
1
1096 (C−N); H NMR (CDCl3, ppm): δ 7.72−8.16 (m, 9H,
δ 1.54 (t, J=8.12, 3H, OCH2-CH3, methyl), 4.22 (q, 2H,
OCH2), 7.64−8.11 (m, 8H, Ar-H), 10.4 (s, 1H, OH), 13.06
(s, 1H, NH); EI-MS: m/z [M+H]+ 385; Anal. Calcd for
C18H16N4O2S2: C, 56.23; H, 4.19; N, 14.57. Found: C, 56.28;
H, 4.17; N, 14.56.
Ar-H), 11.98 (s, 1H, NH); EI-MS: m/z [M+H]+ 343; Anal.
Calcd for C16H11FN4S2: C, 56.12; H, 3.24; N, 16.36. Found:
C, 56.16; H, 3.22; N, 16.35.
4-(6-Fluoro-1,3-benzothiazol-2-yl)amino-2-(4-chlorophenyl)
amino-1,3-thiazole (18)
4-(6-Ethoxy-1,3-benzothiazol-2-yl)amino-2-(4-
Brown solid; Yield: 66%; mp 222–224°C; Rf 0.49 (ethyl
methoxyphenyl)amino-1,3-thiazole (24)
acetate:ammonia); IR (KBr, cm−1): 3274 (NH), 1556
Greenish-grey solid; Yield: 74%; mp 283–285°C; Rf 0.72
1
(C=N), 1108 (C−N); H NMR (CDCl3, ppm): δ 7.68−8.06
(ethyl acetate:ammonia); IR (KBr, cm−1): 3342 (NH), 1574
(m, 8H, Ar-H), 12.65 (s, 1H, NH); EI-MS: m/z [M+H]+ 378;
Anal. Calcd for C16H10ClFN4S2: C, 50.99; H, 2.67; N, 14.87.
Found: C, 50.92; H, 2.69; N, 14.87.
(C=N), 1085 (C−N); H NMR (CDCl3, ppm): δ 1.46 (t,
1
J=8.87, 3H, OCH2-CH3, methyl), 3.94 (s, 3H, OCH3), 4.17
(q, 2H, OCH2), 7.75−8.19 (m, 8H, Ar-H), 13.12 (s, 1H, NH);
EI-MS: m/z [M+H]+ 399; Anal. Calcd for C19H18N4O2S2:
C, 57.27; H, 4.55; N, 14.06. Found: C, 57.21; H, 4.53; N,
14.05.
4-(6-Fluoro-1,3-benzothiazol-2-yl)amino-2-(4-hydroxyphenyl)
amino-1,3-thiazole (19)
Yellow solid; Yield: 72%; mp 254–256°C; Rf 0.61 (ethyl
acetate:ammonia); IR (KBr, cm−1): 3475 (OH), 3326
(NH), 1543 (C=N), 1121 (C−N); 1H NMR (CDCl3, ppm): δ
7.64−7.92 (m, 8H, Ar-H), 9.6 (s, 1H, OH), 12.24 (s, 1H, NH);
EI-MS: m/z [M+H]+ 359; Anal. Calcd for C16H11FN4OS2:
C, 53.62; H, 3.09; N, 15.63. Found: C, 53.59; H, 3.09; N,
15.61.
Biological activity
Antibacterial activity
All the newly synthesised compounds were screened
for their antibacterial activity against two different
strains of Gram-negative (Escherichia coli ATCC 25922
and Pseudomonas aeruginosa ATCC 27853) and Gram-
positive (Staphylococcus aureus ATCC 25923 and Bacillus
subtilis ATCC 6633) bacteria. e minimum inhibitory
concentration (MIC) was determined by the test tube
dilution technique using Muller-Hinton nutrient broth
[22]. e MIC values were also tested for the well-known
antibiotics (ciprofloxacin and ampicillin) to compare
the antibacterial activity of our test compounds with
currently used antibiotics. e stock solution of the test
compounds (2−4 μg/ mL) was prepared in dimethylsul-
phoxide (DMSO). e stock solution was sterilised by
passing through a 0.2mm polycarbonate sterile mem-
brane (Nucleopore Corporation, Pleasanton, CA, USA)
filters. Serial dilution of the test compounds was carried
out and the following concentrations were used: 1000,
500, 250, 125, 62, 32, 16, 8, 4, down to 1 μg/mL. Test com-
pounds at various concentrations were added to culture
medium in a sterilised borosilicate test tube and different
bacterial strains were inoculated at concentration of 106
bacilli/mL. e tubes were incubated at 37°C for 24h and
then examined for the presence or absence of growth of
the test organisms. All experiments were performed in
triplicate. e MIC values were obtained from the low-
est concentration of the test compounds where the tubes
remained clear (i.e. no turbidity), indicating that the
bacterial growth was completely inhibited at this con-
centration. e MIC values were expressed in μg/mL and
summarised in Table 1.
4-(6-Fluoro-1,3-benzothiazol-2-yl)amino-2-(4-
methoxyphenyl)amino-1,3-thiazole (20)
Orange-browncrystallinesolid;Yield:56%;mp231–233°C;
Rf 0.53 (ethyl acetate:ammonia); IR (KBr, cm−1): 3284 (NH),
1562 (C=N), 1110 (C−N); 1H NMR (CDCl3, ppm): δ 3.86 (s,
3H, OCH3), 7.78−8.21 (m, 8H, Ar-H), 11.92 (s, 1H, NH);
EI-MS: m/z [M+H]+ 373; Anal. Calcd for C17H13FN4OS2: C,
54.82; H, 3.52; N, 15.04. Found: C, 54.85; H, 3.53; N, 15.01.
4-(6-Ethoxy-1,3-benzothiazol-2-yl)amino-2-phenylamino-1,3-
thiazole (21)
Brown solid; Yield: 63%; mp 256–258°C; Rf 0.35 (ethyl
acetate:ammonia); IR (KBr, cm−1): 3328 (NH), 1544 (C=N),
1
1077 (C−N); H NMR (CDCl3, ppm): δ 1.42 (t, J=8.4, 3H,
OCH2-CH3, methyl), 4.09 (q, 2H, OCH2), 7.72−8.14 (m, 9H,
Ar-H), 12.43 (s, 1H, NH); EI-MS: m/z [M+H]+ 369; Anal.
Calcd for C18H16N4OS2: C, 58.67; H, 4.38; N, 15.21. Found:
C, 58.62; H, 4.36; N, 15.23.
4-(6-Ethoxy-1,3-benzothiazol-2-yl)amino-2-(4-chlorophenyl)
amino-1,3-thiazole (22)
White crystalline solid; Yield: 56%; mp 279–281°C; Rf
0.62 (ethyl acetate:ammonia); IR (KBr, cm−1): 3342 (NH),
1
1580 (C=N), 1074 (C−N); H NMR (CDCl3, ppm): δ 1.34
(t, J=7.72, 3H, OCH2-CH3, methyl), 4.09 (q, 2H, OCH2),
7.89−8.36 (m, 8H, Ar-H), 13.12 (s, 1H, NH); EI-MS: m/z
Journal of Enzyme Inhibition and Medicinal Chemistry

Synthesis of some thiazolyl aminobenzothiazole derivatives
25
Table 1. Antimicrobial activity data for the tested compounds.
Gram negative bacteriaa
Gram positive bacteriaa
Fungia
C. albicans
Compound
E. coli
15
12
22
27
37
28
44
59
13
6
P.aeruginosa
S. aureus
B. subtilis
A. niger
72
52
34
32
44
32
61
22
12
4
9
21
13
16
29
26
21
33
54
15
8
39
21
27
18
53
39
51
32
28
18
19
8
28
18
23
12
62
42
54
38
21
11
17
6
81
41
63
29
57
35
48
26
14
9
10
11
12
13
14
15
16
17
18
19
16
22
56
42
64
76
3
21
29
49
36
78
84
4
11
4
8
20
3
21
74
48
56
41
6
95
56
74
42
2
29
17
24
12
−
43
13
19
9
22
23
24
Ciprofloxacin
−
Ampicillin
2
2
1
1
−
−
Fluconazole
−
−
−
−
1
2
aData are given as MIC (μg/mL).
Antifungal activity
Table 2. Anthelmintic activity of tested compounds.
Mean death time
Mean paralysing time (min)a (min)a
e newly synthesised compounds were screened
for their antifungal activity against Candida albicans
(NCIM no. 3471) and Aspergillus niger (NCIM no. 1196)
in DMSO by the serial plate dilution method [23]. Sabour
and Dextrose Agar (Merck) media were used for the
cultivation of the fungi. A spore suspension was made
for each fungal strain using normal saline. A loopful of
fungal strain was transferred to 3 mL saline to produce a
suspension. Agar media (20 mL) were poured into each
petri dish and the excess suspension was decanted. e
plates were dried by placing in an incubator at 37°C for
1h. e MIC values were noted and the activity of each
compound was compared with fluconazole as the stan-
dard drug. e MIC values were in μg/mL and shown
in Table 1.
Compound
9
69.63 0.41
62.56 0.31
64.58 0.37
75.09 0.51
41.87 0.40
34.79 0.33
38.60 0.32
47.08 0.30
55.26 0.13
50.94 0.39
53.98 0.36
58.92 0.41
30.82 0.37
22.26 0.58
28.00 0.30
32.74 0.60
19.84 1.24
82.61 0.77
75.83 0.29
73.63 0.46
82.57 0.27
49.12 0.60
50.92 0.36
48.61 0.46
61.00 0.44
65.16 0.56
68.46 0.33
71.46 0.35
68.25 0.15
47.28 0.14
35.83 0.34
40.55 0.41
39.93 0.61
31.39 0.34
10
11
12
13
14
15
16
17
18
19
20
21
22
23
Anthelmintic activity
24
The in vitro trial for anthelmintic activity was car-
ried out against earthworm Pontoscotex corethruses
(ICARBC 408) species [24]. The test compound sus-
pensions were prepared by triturating the newly syn-
thesised compounds with 0.5% Tween 80 and distilled
water. The resulting mixture was stirred for 30 minutes
using a mechanical stirrer. The suspensions were
diluted to contain 0.2% w/v of test samples. A suspen-
sion of the standard drug, mebendazole, was prepared
at the same concentration in a similar way. Three sets
of five earthworms of almost similar sizes were placed
in petri plates of 4 inch diameter containing 50 mL of
suspension of the test sample and the standard drug
at room temperature. Another set of five earthworms
were kept as controls in a 50 mL suspension of dis-
tilled water and 0.5% Tween 80. The paralysing and
Mebendazole
aData are given as mean S.E.M. (n=3) against earthworm P.
corethruses species
death times were noted and their mean was calculated
for triplicate sets. The death time was ascertained by
placing the earthworms in warm water at 50°C, which
stimulated movement if the worm was still alive. The
results are depicted in Table 2.
Results and discussion
In the present work a series of 16 new aminobenzothiazole
derivatives were synthesised. e synthetic route leading
to the formation of 4-(6-substituted-1,3-benzothiazol-
© 2011 Informa UK, Ltd.

26
N. D. Amnerkar and K. P. Bhusari
O
N
N
Cl
N
H
NH2
a
S
S
R1
R1
5–8
1–4
R2
NH2
b
N
S
H
N
S
NH
N
R1
S
N
H
R2
R1
9–24
R1
R1
R2
R2
Compound
Compound
Compound
1
5
6
7
8
9
17
18
19
20
21
22
23
24
H
H
H
H
Cl
F
F
F
F
H
Cl
CH3
2
3
4
10
11
12
13
14
15
16
F
H
OH
OH
OC2H5
OCH3
OCH3
H
CH3
CH3
CH3
CH3
OC2H5
OC2H5
OC2H5
OC2H5
H
Cl
H
Cl
OH
OH
OCH3
OCH3
Scheme 1. General scheme for the synthesis of compounds 9-24. Reagents and conditions: (a) dry benzene, ClCOCH2Cl, TEA, reflux, 3h,
80°C; (b) dry EtOH, RNHCSNH2, reflux, 10-12h.
2-yl)amino-2-(4-substitutedphenyl)amino-1,3-thiazole
9–24isshowninScheme1. ecompounds6-substituted-
1,3-benzothiazol-2-amines 1–4 were synthesised with an
excellent yield following the methodology as described by
Jimonet et al. [25] from aryl amines. e compounds 1–4
on reaction with chloracetyl chloride afforded 2-chloro-
N-(6-substituted-1,3-benzothiazol-2-yl)acetamide 5–8
on refluxing the reaction mixture at 120°C for 5h [26].
Final compounds 4-(6-substituted-1,3-benzothiazol-2-yl)
amino-2-(4-substituted- phenyl)amino-1,3-thiazole 9–24
were obtained by the cyclisation of 2-chloroacetamides
5–8 with commercially available 4-substitued phenyl thio-
ureas in absolute ethanol. All the reaction products were
obtained in moderate to very good yield. e structures
of the final compounds were elucidated by elemental
analyses, Fourier transform infrared spectroscopy (FTIR),
1H NMR and electron impact mass spectrometry (EI-MS)
analyses.
e IR spectra of the compounds 9–24 showed, in
each case, stretching band of N−H and C=N group in the
region 3342−3270 and 1580−1538 cm−1, respectively. e
1H NMR spectra showed, in each case, the signals as mul-
tiplet at δ 7.64−8.36 ppm attributed to Ar−H in addition to
the singlet of N−H group in the region 11.34−13.12 ppm.
e disappearance of the C=O band at 1732−1685cm−1,
provided confirmatory evidence for ring closure from
1
the 2-chloracetamides (5–8). e H NMR spectra also
lacked the CO−CH2 signal at δ 4.38−4.74 ppm. EI-MS of
all compounds displayed the (M+H+) which confirmed
their molecular weights.
e MIC (μg/mL) of tested compounds are shown in
Table 1. e antibacterial test results indicated that most
title compounds exhibited noticeable activities against
all the strains of bacteria tested (Gram-negative, Gram-
positive) in vitro. Seven compounds of the newly synthe-
sised series showed high in vitro antimicrobial activity.
Journal of Enzyme Inhibition and Medicinal Chemistry

Synthesis of some thiazolyl aminobenzothiazole derivatives
27
Compound 18 (MIC of 6−8 µg/mL) exhibited remark-
able antibacterial activity against Gram-negative (E. coli
and P. aeroginosa) bacteria. Compound 20 (MIC of 6−8
µg/mL) showed excellent activity against Gram-positive
(S. aureus and B. subtilis) bacteria, while compounds
18 (MIC of 11−18 µg/mL) and 12 (MIC of 12−18 µg/mL)
showed respectable antibacterial activity. Most of the
compounds were found to be between 2- and 50- fold less
active on comparison with the standard. Investigation of
the structure- activity relationship revealed that the com-
pounds with electron withdrawing (fluoro) substitutents
at the 6-position of benzothiazole ring favours the activity
against both Gram-negative and Gram-positive bacteria.
e substitutions with an electron withdrawing groups
(chloro) at the 4-position of phenyl ring showed more
potency against Gram-negative bacteria whereas the elec-
tron donating groups (methoxy) exhibited better activity
against Gram-positive bacteria.
Many of the newly synthesised compounds were
found to show good antifungal activity. From the anti-
fungal activity data (Table 2), it was observed that 18
(MIC of 4−9 µg/mL) and 20 (MIC of 3−4 µg/mL) were the
most active compounds against both the tested patho-
gens (C. albicans and A. niger). Compounds 17 (MIC
of 12−14 µg/mL), 19 (MIC of 8−11 µg/mL) and 22 (MIC
of 13−17 µg/mL) showed moderate to good antifungal
activity. Substitution with an electron withdrawing
group (fluoro) at 6-position of benzothiazole increases
the antifungal activity compared with an electron donat-
ing group (methyl and ethoxy) and unsubstituted ben-
zothiazoles. Introduction of an electron donating group
(methoxy) on the 4-position of the phenyl ring shows
marginal enhancement of activity compared to other
groups and the unsubstituted phenyl ring against both
the species.
Conclusion
is study reports the successful synthesis of 4-(6-
substituted-1,3-benzothiazol-2-yl)amino-2-(4-sub-
stitutedphenyl)amino-1,3-thiazoles through an easy,
convenient and efficient synthetic method. All these
new compounds were confirmed by IR, NMR, MS spec-
tra and elemental analyses and were evaluated for their
antibacterial, antifungal and anthelmintic activities. e
results showed that most of the synthesised aminoben-
zothiazole derivatives exhibited significant antibacte-
rial, antifungal and anthelmintic activities. e 6-fluoro
substituted aminobenzothiazoles exhibited good anti-
bacterial and antifungal activities. Substitution with a
chloro group in the phenyl ring confers greater antibac-
terial activity against Gram-negative bacteria whereas
derivatives having a methoxy group possessed more
antibacterial activity against Gram-positive bacteria
and fungal strains. e results of anthelmintic studies
revealed that substitution with an ethoxy group on amin-
obenzothiazole and a chloro group on the phenyl ring
exhibited greater activity. us, 2-aminobenzothiazole
serves as important pharmacophore for the design of
new antibacterial, antifungal and anthelmintic agents
and may lead to compounds with better pharmacologi-
cal profiles than the standard drugs.
Acknowledgements
e authors are thankful to Dr. Bhoomendra Bhongade,
International Medical University, Kuala Lumpur, Malaysia
for his help and valuable suggestions and SAIL, School of
Pharmaceutical Sciences, RGPV, Bhopal for mass spectra
and CHN analysis.
All newly synthesised derivatives 9–24 showed good
anthelmintic activity at 0.2% w/v. Compound 22, with a
mean paralysing time of 22.26min, showed maximum
activity against P. corethruses species of earthworm
on comparison with standard mebendazole (mean
paralysing time of 19.84min) at the same concentration.
Compounds 14 (mean paralysing time of 34.79min),
23 (mean paralysing time of 28.00min) and 24 (mean
paralysing time of 32.74min) showed moderate activity
while compound 12 (mean paralysing time of 75.09min)
showed least activity amongst all the tested compounds.
e substitution of an electron donating group (ethoxy)
on the 6-position of benzothiazole increases the activity
compared to an electron withdrawing group (fluoro) and
unsubstituted benzothiazoles. On the other hand, substi-
tution with an electron withdrawing group (chloro) on the
4-position of phenyl ring shows a remarkable increase in
activity compared to other groups and the unsubstituted
phenyl ring.
Declaration of interest
e authors report no conflicts of interest. e authors
alone are responsible for the content and writing of the
paper.
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