Studies of antimicrobial activity of N-alkyl and N-acyl 2-(4-thiazolyl)-1H-benzimidazoles

Article abstract of DOI:10.1016/j.ejps.2003.09.001

Various N-alkyl and N-acyl derivatives of 2-(4-thiazolyl)-1H-benzimidazole, an anthelmintic and systemic fungicide, were synthesized by polymer-supported reactions and screened for their antifungal and antibacterial potency to establish structure-activity

Full text of DOI:10.1016/j.ejps.2003.09.001

European Journal of Pharmaceutical Sciences 21 (2004) 115–118
Studies of antimicrobial activity of N-alkyl and N-acyl
2-(4-thiazolyl)-1H-benzimidazolesଝ
N.S. Pawar, D.S. Dalal, S.R. Shimpi, P.P. Mahulikar∗
School of Chemical Sciences, North Maharashtra University, Jalgaon 425 001, India
Received 19 March 2003; received in revised form 12 August 2003; accepted 3 September 2003
Abstract
Various N-alkyl and N-acyl derivatives of 2-(4-thiazolyl)-1H-benzimidazole, an anthelmintic and systemic fungicide, were synthesized by
polymer-supported reactions and screened for their antifungal and antibacterial potency to establish structure-activity relationships.
© 2003 Elsevier B.V. All rights reserved.
Keywords: Antimicrobial activity; Fungicides; Heterocycles
1. Introduction
and systemic fungicide. Fungicidal properties (Robinson,
1964) and its systemic properties in plants (Tomlin, 1991)
have already been well documented. Its mode of action is
systemic fungicide with protective and curative action. It is
used to control of Aspergillus, Botrytis, Ceratocystis, Cer-
cospora, Colletotrichum, Corticium, Diaporthe, Diplodia,
Fusarium, Gibberella, Gloeosporium, Oospora, Penicillium,
Phoma, Rhizoctonia, Sclerotinia, Septoria, Thielaviopsis,
Verticillium spp., etc. in asparagus, avocados, bananas, bar-
ley, beans, cabbage, celery, chicory, cherries, citrus, cotton,
some cucurbits, flax, mangoes, mushrooms, oats, onions,
ornamentals, pawpaws, pome fruit, potatoes, rice, soya-
beans, strawberries, sugar beet, sweet potatoes, tobacco,
tomatoes, turf, vines and wheat. Also used for control of
storage diseases of fruits and vegetables and for control
of Dutch elm disease. It is also used as an anthelmintic in
human and veterinary medicine.
Thiabendazole has significant anthelmintic activity for
gastrointestinal parasites in sheep, goats, cattle, horses,
swine, dogs, and poultry. This compound is well-tolerated
and does not stain the skin, hair or wool of animals. It may
be given orally for therapeutic use or in feed or mineral
supplements for the prophylactic control of parasites in
domestic animals (Grenda et al., 1965; Brown et al., 1961).
Benzimidazole and thiazole analogues have found appli-
cations in medicine and agriculture. Therefore, development
of a simple, fast and flexible method to generate libraries of
such compounds was desirable (Bogdal et al., 1997).
The main emphasis of our work was the designing and
development of new synthetic methods and application of
The benzimidazole compounds have been proved to be the
most important group of fungicides with systemic activity
and are well known for their pronounced ability to control a
large number of fungal diseases (Foye et al., 1995; Kadam
et al., 1997). Benomyl, thiabendazole and thiophnate methyl
are main examples of this fungicide class. Because of their
systemic activity, they can help to control some diseases
after infection also. Benzimidazole fungicides are also used
to prevent post-harvest rots and as soil-drench treatments.
Sulfur and/or nitrogen heterocycles have acquired an
immense importance among the heterocycles, possess-
ing pharmaceutical activities and widely occur in nature
in the form of alkaloids, vitamins, pigments and as con-
stituents of plant and animal cells. The utility of thia-
zoles in curative treatment has been firmly established.
They exhibit anti-bacterial, anti-hypertensive, anti-anginal,
anti-arrhythmetic, anti-histaminic, narcotic, antagonistic,
etc. activities. Thiazole nucleus is found in many antibiotics
and vitamins in one or another form (Foye et al., 1995;
Kadam et al., 1997).
The 2-(4-thiazolyl)-1H-benzimidazoles are structurally
analogous to benzimidazoles, well known as an anthelmintic
ଝ
This paper is dedicated to Dr. P.M. Gurav, Department of Biochem-
istr∗y, Shivaji University, Kolhapur 416 004 (M.S.), India.
Corresponding author. Fax: +1-0257-2252183.
E-mail addresses: nileshpawar1329@rediffmail.com (N.S. Pawar),
mahulikarpp@rediffmail.com (P.P. Mahulikar).
0928-0987/$ – see front matter © 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.ejps.2003.09.001

116
N.S. Pawar et al. / European Journal of Pharmaceutical Sciences 21 (2004) 115–118
products as biologically active molecules. In this connec-
tion, we have been attempted the synthesis N-alkyl and
N-acyl derivatives of 2-(4-thiazolyl)-1H-benzimidazole by
polymer-supported reactions using Amberlite IRA-400 (Cl−
form) resin as a support for 2-(4-thiazolyl)-1H-benzimidazole
nucleophile. The resin could be reactivated simply by wash-
ing with dilute HCl solution. Simple work-up and isolation
of product by removal of solvent was a crucial feature of
this reaction for the library generation of biologically active
compounds of thiabendazole.
and placed on the seeded agar plates. Paper discs moist-
ened with ethanol, were placed on the surface of seeded
petriplates as a control. The plates were incubated at 27 ◦C
for 2–3 days. A clear zone of inhibition around the paper
disc demonstrated the relative susceptibility of the fungi
to the synthesized derivatives. The fungicidal potency is
proportional to the diameter (in mm) of the zone of inhibi-
tion. The experiments were performed in duplicate and the
average of the measured zones of inhibition was considered.
Percent change in antifungal activity of different deriva-
tives over parent compound, 2-(4-thiazolyl)-1H-benzimi-
dazole was calculated using following formula:
2. Materials and methods
D − P
percent change in antifungal activity =
× 100
P
Various N-alkyl and N-acyl derivatives of 2-(4-thiazolyl)-
1H-benzimidazoles were prepared by reacting polymer-
supported anion of 2-(4-thiazolyl)-1H-benzimidazoles with
alkyl halides and acid chlorides, respectively in dry methanol
(Pawar et al., 2003), which are listed in Table 1. All syn-
thesized derivatives were evaluated for their antimicrobial
activities, namely antifungal activity against Aspergillus
niger, Aspergillus flavous, Alternaria alternata and Fusar-
ium oxysporum and antibacterial actions against Bacillus
mecarium, Bacillus japonecum, Pseudomonas fluorescence
and Pseudomonas putida using paper disc agar method. For
antimicrobial study, fungi were grown on Sabouraud’s broth
(Alice and Sivaprakasam, 1996) and bacteria on nutrient
Agar (Patil et al., 2000).
To each petriplate 20 ml of sterilized medium was added.
After the agar had set, 10% of inoculum (suspension cul-
ture) was added to each petriplate and spread thoroughly
by rotatory motion of the plate. Sterilized Whatman No. 1
filter paper discs (6 mm dia.) were thoroughly moistened
with a 5 mg/ml solution of the compound(s) in ethanol
where D is the zone of inhibition for derivatives and P zone
of inhibition for parent compound.
The results of antifungal activity are presented in Fig. 1(a)
and (b).
The methodology for evaluation of antibacterial activity
has performed same as described for antifungal activity, only
the plates were incubated at 37 ◦C for 24 h. The results of
antibacterial activity are presented in Fig. 2.
3. Results and discussion
The derivatization of 2-(4-thiazolyl)-1H-benzimidazoles
was found to be more effective towards the antimicrobial
activities. In antifungal activity studies, an introduction of
isopropyl group (II d) reflected better activity followed in
decreasing order by carboxymethyl (II h) and benzyl (II g)
and then benzoyl (III b) groups. All other derivatives ex-
hibited lower antifungal activities than parent molecule (I)
against all test fungi species. In contrast, surprisingly the
parent molecule (I) was found to be totally inactive against
all test bacteria species, however, its all derivatives showed
better antibacterial potency and efficacy. The highest an-
tibacterial action was reflected by butyl (II e) and cinnamate
(III c) derivatives. In normal alkyl substituents, addition of
methylene group (II a, b, c, e) boosted the activity, whereas,
branching (isopropyl; II d), olefinic double bond (allyl; II
f), aromatic benzene ring (benzyl; II g) and also carboxylic
group (carboxymethyl; II h) conferred average antibacterial
activities. In case of esters, cinnamate (III c) exhibited the
highest antibacterial action followed by phenyl acetate (III
d), acetate (III a) and benzoate (III b). In general, struc-
tural modification of 2-(4-thiazolyl)-1H-benzimidazoles was
found to be more effective against test bacteria species than
the fungi species.
Table 1
N-alkyl and N-acyl derivatives of 2-(4-thiazolyl)-1H-benzimidazole
Substituent R
Yield (%)
Physical constants
mp/bp (+12 ◦C)
I H
II a CH3
II b CH3CH2
II c CH3CH2CH2
II d (CH3)2CH
II e CH3(CH2)2CH2
–
302
139
78
66
98
90
92
92
94
93
93
91
90
90
96
92
94
70
78
=
II f CH2 CHCH2
Such study of structure-activity relationships (SAR) es-
tablished on the basis of bioassay could be useful to eluci-
date the moderately toxic or non toxic new groups of pest
management agents through the biorational design of the
derivatives. Many instances have demonstrated the impor-
tance of SAR study in drug and pesticide discovery. The
II g C6H5CH2
II h HO2CCH2
III a CH3CO
III b C6H5CO
III c C6H5CH CHCO
III d C6H5CH2CO
175
268
224
147
180
150+
=

N.S. Pawar et al. / European Journal of Pharmaceutical Sciences 21 (2004) 115–118
117
A. niger
A. flavous
A. alternata
F. oxysporum
60
50
40
30
20
10
0
(a)
Compounds
A. niger
A. flavous
A. alternata
40
30
F. oxysporum
20
10
0
-10
-20
-30
-40
-50
-60
(b)
Compounds
Fig. 1. (a) Antifungal activity of thiabendazole and its derivatives. (b) Percent change in antifungal activity of thiabendazole derivatives over parent
compound.
B. mecarium
B. Japonecum
P. fluorescence
P. putida
20
18
16
14
12
10
8
6
4
2
0
Compounds
Fig. 2. Antibacterial activity of thiabendazole and its derivatives.

118
N.S. Pawar et al. / European Journal of Pharmaceutical Sciences 21 (2004) 115–118
Brown, H.D., Matzulc, A.R., Ilves, I.R., Peterson, L.H., Harries, S.A.,
Sarrate, L.H., Egerton, J.R., Yakstis, J.J., Campbell, W.C., Cuckler,
A.C., 1961. Antiparasitic drugs. IV. 2-(4ꢀ-Thiazolyl)-benzimidzole, a
new anthelmintic. J. Am. Chem. Soc. 83, 1764–1765.
Foye, W.O., Thomas, L.L., David, A., Williams, B.I., 1995. Principles of
Medicinal Chemistry, fourth ed., Waverly Pvt. Ltd., New Delhi.
Grenda, V.J., Joner, R.E., Gal, G., Sletzinger, M., 1965. Novel preparation
of benzimidazoles from N-arylamididines. new synthesis of thiaben-
dazole. J. Org. Chem. 30, 259–261.
development of pyrethroids is an extremely successful ex-
ample (Tsao and Coats, 1995). The present investigation
may help to explore new possible pest management agents
through the biorational approach.
Acknowledgements
Kadam, S.S., Mahadik, K.R., Bothara, K.G., 1997. Principles of Medicinal
Chemistry, vols. I and II.
Patil, S.G., Patil, M.G., Mendki, P.S., Maheshwari, V.L., Kothari, R.M.,
2000. Study of antimicrobial and pesticidal activity of nerium indicum.
Pestology 24 (5), 37–39.
This work was presented at 21st Annual National Confer-
ence of Indian Council of Chemists, Jabalpur, India, OP-27,
2002, p. 95.
Pawar, N.S., Dalal, D.S., Mahulikar, P.P., 2003. Synthesis of biologically
active N-alkyl and N-acyl 2-(4-thiazolyl)-1H-benzimidazoles, Chem-
istry of Heterocyclic Compounds, communicated.
References
Robinson, H.J., 1964. Antimycotic properties of thiabendazole. J. Invest.
Dermatol. 42, 479–482.
Tomlin, C., 1991. Pesticide Manual, ninth ed., p. 11500.
Tsao, R., Coats, J.R., 1995. Starting from nature to make better insecti-
cides. Chem. Tech. 25, 23–28.
Alice, D., Sivaprakasam, K., 1996. Fungicidal, bactericidal and nemati-
cidal effect of garlic clove extract. J. Ecobiol. 8 (2), 99–103.
Bogdal, D., Pielichowski, J., Jaskotk, 1997. Remarkable fast N-alkylation
of azaheterocycles under microwave irradiation in dry media, Hetero-
cycles 45, 715–722.