Antimicrobial activity of Schiff bases of coumarin-incorporated 1,3,4-oxadiazole derivatives: An in vitro evaluation

Article abstract of DOI:10.1007/s00044-012-0452-9

A series of 3-{5-[(E)-(substituted benzylidene) amino]-1,3,4-oxadiazol-2- yl}-2H-chromen-2-ones (4a-r) were synthesized by the reaction of 3-(5-amino]-1,3,4-oxadiazol-2-yl}-2H-chromen-2-one with different substituted benzaldehydes to form Schiff bases of coumarin-incorporated 1,3,4-oxadiazole derivatives. The structures of the compounds were confirmed on the basis of their elemental analysis and spectral data. The compounds were screened against bacterial strains Staphylococcus aureus NCTC (10418), Escherichia coli NCTC (6571), and fungal strain Candida albicans ATCC (10231). Ciprofloxacin and Ketoconazole were used as standards. The test compounds and standards were evaluated at 100 μg/ml concentration. DMF (N,N-dimethylformamide) was used as solvent and control. Most of the synthesized compounds possess significant antimicrobial activity. Compound (4m) without any substitution of the phenyl ring which is attached to 1,3,4-oxadiazole moiety showed highly significant in vitro growth inhibition against S. aureus and E. coli, while as compound (4g) with para N(CH₃)₂ showed highly significant in vitro growth inhibition against C. albicans.

Full text of DOI:10.1007/s00044-012-0452-9

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res (2013) 22:4455–4458
DOI 10.1007/s00044-012-0452-9
ORIGINAL RESEARCH
Antimicrobial activity of Schiff bases of coumarin-incorporated
1,3,4-oxadiazole derivatives: an in vitro evaluation
•
Mashooq Ahmad Bhat Mohamed A. Al-Omar
•
Nadeem Siddiqui
Received: 12 September 2012 / Accepted: 26 December 2012 / Published online: 10 January 2013
Ó Springer Science+Business Media New York 2013
Abstract A series of 3-{5-[(E)-(substituted benzylidene)
amino]-1,3,4-oxadiazol-2-yl}-2H-chromen-2-ones (4a–r)
were synthesized by the reaction of 3-(5-amino]-1,3,4-ox-
adiazol-2-yl}-2H-chromen-2-one with different substituted
benzaldehydes to form Schiff bases of coumarin-incorpo-
rated 1,3,4-oxadiazole derivatives. The structures of the
compounds were confirmed on the basis of their elemental
analysis and spectral data. The compounds were screened
against bacterial strains Staphylococcus aureus NCTC
(10418), Escherichia coli NCTC (6571), and fungal strain
Candida albicans ATCC (10231). Ciprofloxacin and
Ketoconazole were used as standards. The test compounds
and standards were evaluated at 100 lg/ml concentration.
DMF (N,N-dimethylformamide) was used as solvent and
control. Most of the synthesized compounds possess sig-
nificant antimicrobial activity. Compound (4m) without
any substitution of the phenyl ring which is attached to
1,3,4-oxadiazole moiety showed highly significant in vitro
growth inhibition against S. aureus and E. coli, while as
compound (4g) with para N(CH3)2 showed highly signif-
icant in vitro growth inhibition against C. albicans.
Keywords Coumarin Á 1,3,4-Oxadiazoles Á Schiff base Á
Antimicrobial activity
Introduction
The name coumarin originates from caribbian word
‘‘coumaron’’ for the tonka tree, which was known botani-
cally at one time as Caumarouna odorata. Coumarins are
reported to possess important pharmacological activities
like antimicrobial (Bhat et al., 2009), anticonvulsant (Bhat
et al., 2008a), antitumor (Chimichi et al., 2002), and anti-
inflammatory (Cruzzocrea et al., 2000). 1,3,4-Oxadiazole
derivatives are reported to show a broad spectrum of bio-
logical activities which include COX inhibitor (Boschelli
et al., 1993), anticonvulsant (Zarghi et al., 2005), anti-
bacterial (Bhat et al., 2005), and antifungal (Nizamuddin
et al., 2001). Biocidal activities of Schiff bases have been
well established. These have been attributed to the toxo-
phoric C=N linkage in them. Schiff base acquired broad
spectrum of biological activities like antibacterial (Iqbal
et al., 2007), antifungal (Mishra et al., 2005), anti-inflam-
matory (Sharma et al., 2002), antiproliferative (Vicini
et al., 2006), antitubercular (Lourenco et al., 2007),
and anticonvulsant (Ragavendran et al., 2007). The cou-
marin-incorporated 1,3,4-oxadiazoles have been reported
as potential antimicrobial agents (Cacic et al., 2006;
Mashelkar and Audi, 2006).The main idea of this work was
to design mutual prodrugs which contain coumarin and
1,3,4-oxadiazole moieties, using Schiff base (C=N) as
linkage group to produce synergistic antimicrobial activity.
This prompted us to synthesize and study the antimi-
crobial activity of compounds incorporating coumarin and
1,3,4-oxadiazoles Schiff bases to get the synergistic effect.
Electronic supplementary material The online version of this
article (doi:10.1007/s00044-012-0452-9) contains supplementary
material, which is available to authorized users.
M. A. Bhat (&) Á M. A. Al-Omar
Department of Pharmaceutical Chemistry, College of Pharmacy,
King Saud University, P.O. Box 2457, Riyadh 11451,
Kingdom of Saudi Arabia
e-mail: mashooqbhat@rediffmail.com
N. Siddiqui
Department of Pharmaceutical Chemistry, Faculty of Pharmacy,
Jamia Hamdard (Hamdard University), New Delhi 110062, India
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Med Chem Res (2013) 22:4455–4458
Scheme 1 Synthesis of Schiff
bases of coumarin-incorporated
1,3,4-oxadiazole derivatives
(4a–r) i piperidine, C2H5OH,
reflux 5 h. ii NH2NH2ÁH2O,
C2H5OH, reflux 10 h. iii CNBr,
C2H5OH, 55–60 °C for 90 min.
iv Glacial CH3COOH, 1,4-
dioxan, substituted
O
O
O
O
O
(iii)
NH
N
NH2
N
2
O
3
NH2
(ii)
benzaldehydes, reflux 8 h; 4a:
R = 3-NO2; 4b: R = 3,4-
O
O
O
(iv)
(OCH3)2; 4c: R = 4-OH; 4d:
R = 2-OH; 4e: R = 2-NO2; 4f:
R = 3-OH; 4g: R = 4-N(CH3)2;
4h: R = 4-F; 4i: R = 4-OCH3;
4j: R = 2-Cl; 4k: 3-Cl; 4l: 4-Cl;
4m: R = H; 4n: R = 4-NO2;
4o: R = 3-F; 4p: R = 2-F; 4q:
R = 2-OCH3; 4r: R = 3-OCH3
O
CH3
O
O
1
O
R
N
O
(i)
N
N
O
O
(4 a-r)
H3C
O
+
OH
O
CH3
Chemistry
The structures of the synthesized compounds were
confirmed on the basis of spectral data and elemental
analysis. The additional data of synthesis and analytical
data of all the intermediates (1–3) and 3-{5-[(E)-(substi-
tuted benzylidene) amino]-1,3,4-oxadiazol-2-yl}-2H-chro-
men-2-ones (4a–r) are given in Online Resource 1.
Synthesis of ethyl-2-oxo-2H-chromene-3-carbxylate (1)
(m. p. 120–122 °C), 2-oxo-2H-chromene-3-carbohydrazide 2
(m. p. 136–138 °C), and 3-(5-amino-1,3,4-oxadiazole-2-yl)-
2H-chromen-2-one (3) (m. p. 200–202 °C) were performed
according to reported methods (Bhat et al., 2008; Khan and
Mymmona, 2003). 3-{5-[(E)-(substituted benzylidene)
amino]-1,3,4-oxadiazol-2-yl}-2H-chromen-2-ones (4a–r)
were synthesized by reacting different substituted benzal-
dehydes with 3-(5-amino-1,3,4-oxadiazole-2-yl)-2H-chro-
men-2-one (3) to form Schiff bases (Scheme 1).
Antimicrobial activity
The compounds were screened against bacterial strains
Staphylococcus aureus NCTC (10418), Escherichia coli
NCTC (6571) and fungal strain Candida albican ATCC
(10231) by cup plate method [agar diffusion method]
(Barry, 1976). Ciprofloxacin and Ketoconazole were used
as standards. The test compounds and standards were
evaluated at 100 lg/ml concentration. DMF (N,N-dimeth-
ylformamide) was used as solvent and negative control.
Data are represented as % inhibition with reference to
standards in (Table 1). The microbial strains and standards
(Ciprofloxacin and Ketoconazole) were obtained from
Biochemistry Department, Majeedia Hospital, Jamia
Hamdard, New Delhi.
Experimental
All the solvents were of laboratory grade (LR) and were
obtained from Merck, Central Drug House Private Ltd.
(CDH) and S. D. Fine Chemicals. Melting points were
determined in open capillary tubes and thermometer is
uncorrected. The elemental analysis (C, H, and N) of all
compounds were performed on the CHN Elementar
(Analysen systeme GmbH, Germany) and Vario EL III
(Elementar Amricas Corporation) and were within limit of
0.4 % of the theoretical values. Thin layer chromatog-
raphy was performed on silica gel G (Merck). The FT-IR
spectra were recorded in KBr pellets on a (BIO-RAD FTS
Results and discussions
It has been observed that most of the compounds showed
inhibition against S. aureus, E. coli, and C. albicans. Com-
pound 4m without any substitution showed 80 % growth
inhibition against S. aureus which was comparable to Cip-
rofloxacin while as compounds (4a, 4e and 4n) showed 64 %
growth inhibition against S. aureus. Compounds (4j, 4k and
4l) were devoid of growth inhibition against S. aureus.
1
135) WIN-IR spectrophotometer. H NMR and 13C NMR
spectra were recorded on a Bruker model DPX 300 FT
NMR spectrometer in (CDCl3) using tetramethylsilane
(Me4Si, TMS) as an internal standard. Mass spectra were
recorded on a Jeol JMS-D instrument fitted with a JMS
2000 data system at 70 eV.
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Med Chem Res (2013) 22:4455–4458
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Table 1 Antibacterial and antifungal activity of synthesized compounds (4a–r)
Compounds
Diameter of zone of inhibition (mm)
% Inhibition with reference to standarda
S. aureus
E. coli
C. albicans
S. aureus
E. coli
C. albicans
4a
17
12
10
10
17
10
12
12
14
–
12
10
10
12
14
15
12
15
10
17
17
17
20
12
10
10
15
15
09
25
–
–
10
9
64
48
40
40
64
40
48
48
56
–
48
40
40
48
56
60
48
60
40
64
64
64
80
48
40
40
60
60
36
100
–
–
50
45
50
–
4b
4c
4d
10
–
4e
4f
11
16
10
12
13
14
15
12
–
55
80
50
60
65
70
75
60
–
4g
4h
4i
4j
4k
–
–
4l
–
–
4m
20
17
12
12
14
14
10
25
–
80
64
48
48
56
56
40
100
–
4n
4o
11
13
13
14
08
–
55
65
65
70
40
–
4p
4q
4r
2
Ciprofloxacinb
Ketoconazoleb
20
100
Ketoconazole (100 lg/ml), zone of inhibition: 20 mm
a
The percentage zone of inhibition was calculated against the bacterial strains Staphylococcus aureus NCTC (10418), Escherichia coli NCTC
(6571), and fungal strain Candida albicans ATCC (10231). Solvent and negative control: DMF (N,N-dimethyl formamide)
b
Standards: Ciprofloxacin (100 lg/ml), zone of inhibition: 25 mm
Compound 4m without any substitution showed 80 %
growth inhibition against E. coli, which was comparable to
Ciprofloxacin. Compounds (4j, 4k, 4l) and (4j, 4k, 4l)
showed 64 and 60 % growth inhibition against Gram-nega-
tive E. coli, respectively. Compound 4g with para N(CH3)2
substitution showed 80 % growth inhibition against
C. albicans which was comparable to Ketoconazole. Com-
pound 4l, (4k, 4r), (4j, 4p, 4q), and (4i, 4m) showed 75, 70,
65, and 60 % growth inhibition against C. albicans,
respectively. Since all the test compounds and standarddrugs
were prepared in freshly distilled DMF, its zone of inhibition
was found to be very negligible and taken as zero mm. All the
synthesized compounds were more active than start, 2-oxo-
2H-chromene-3-carbohydrazide (2) against S. aureus,
E. coli and C. albicans when compared with standard drugs
Ciprofloxacin and Ketoconazole.
with nitro substitution presented moderate growth inhibition
against S. aureus. (c) Compounds with chloro substitution
presented moderate growth inhibition against E. coli.
(d) Compound with para dimethyl amino substitution
showed highest growth inhibition against C. albicans.
(e) Compounds containing Chloro and methoxy substitution
also showed moderated activity against C. albicans.
Conclusion
Compound 4m without any substitution of the phenyl ring
which is attached to 1,3,4-oxadiazole moiety showed highly
significant in vitro growth inhibition against S. aureus and
E. coli, while as compound 4g with para N(CH3)2 showed
highly significant in vitro growth inhibition against C. albi-
cans. It can be concluded from this study that unsubstituted
compound 4m and para N(CH3)2 substituted compound 4g
showed highest in vitro growth inhibition against S. aureus,
E. coli, and C. albicans, respectively, compared to Cipro-
floxacin and Ketoconazole.
Structure activity relationship
(a) Compound without any substitution presented highest
growth inhibition against S. aureus, E. coli. (b) Compounds
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Med Chem Res (2013) 22:4455–4458
Acknowledgments The author is thankful to Department of Phar-
maceutical Chemistry, Hamdard University, New Delhi, India for
carrying out the antimicrobial activities.
coumarin derivative, protects against collagen-induced arthritis
in Lewis rats. Brit J Pharmacol 131:1399–1407
Iqbal A, Siddiqui HL, Ashraf CM, Ahmad M, Weaver GW (2007)
Synthesis, characterization and antibacterial activity of azome-
thine derivatives derived from 2-formylphenoxyacetic acid.
Molecules 12:245–254
Khan MSY, Mymmona A (2003) Synthesis of some new 2,
5-disubstituted 1,3,4-oxadiazole derivatives and their biological
activity. Indian J Chem 42B:900–904
References
Barry AL (1976) The antimicrobial susceptibility test: principle and
practices. Lea and Febiger, Philadelphia, p 180
Bhat MA, Khan SA, Siddiqui N (2005) Synthesis and antibacterial
activity of coumarin incorporated 1,3,4-oxadiazoles. Indian J
Heterocycl Chem 14(3):271–272
Bhat MA, Siddiqui N, Khan SA (2008a) Synthesis of novel 3-(4-
acetyl-5H) methyl-5-substituted phenyl-4,5-dihydro-1,3,4-oxa-
diazol-2-yl)-2H-chromen-2 ones as potential anticonvulsant
agents. Acta Pol Pharm 65:235–239
Bhat MA, Siddiqui N, Khan SA (2008b) Synthesis, anticonvulsant and
neurotoxicity screening of 2-(substitutedphenyl)-3-[3-(2-oxo-2H-
chromen-3-yl)-5-thioxo-1,5-dihydro-4H-1,2,4-triazol-4-yl]-1,3-
thiazolidin-4-ones. Indian J Heterocycl Chem 17:287–288
Bhat MA, Siddiqui N, Khan SA, Mohamed MI (2009) Synthesis of
triazolothiazolidinone derivatives of coumarin with antimicro-
bial activity. Acta Pol Pharm 66(6):625–632
Boschelli HD, Conner TD, Bornemeier DA, Dyer RD, Kennedy JA,
Kuipers PJ, Okonkwo GC, Dchrier DJ, Wright CD (1993) 1,3,4-
Oxadiazole, 1,3,4-thiadiazole, and 1,2,4-triazole analogs of the
fenamates: in vitro inhibition of cyclooxygenase and 5-lipoxy-
genase activities. J Med Chem 36:1802–1810
Cacic M, Trkovnek M, Cacic F, Has-Schon E (2006) Synthesis and
antimicrobial activity of some derivatives of (7-hydroxy-2-oxo-
2H-chromen-4-yl)-acetic acid hydrazide. Molecules 11:134–147
Chimichi S, Boccalini M, Cosimelli B, Viola G, Vedali D, Dall’
Acqua F (2002) New geiparvarin analogues from 7-(2-oxoeth-
oxy) coumarins as efficient in vitro antitumoral agents. Tetra-
hedron Lett 43:7473–7476
Lourenco MCS, Souza MVN, Pinheiro AC, Ferreira ML, Goncalves
RSB, Nogueira TCM, Peraltab MA (2007) Evaluation of anti-
tubercular activity of nicotinic and isoniazid analogues. Arkivoc
15:181–191
Mashelkar UC, Audi AA (2006) Synthesis of some novel 4-substi-
tuted coumarins having potential biological activity (Part III).
Indian J Chem 45B:1463–1469
Mishra P, Rajak H, Mehta A (2005) Synthesis of Schiff bases of
2-amino-5-aryl-1,3,4-oxadiazoles and their evaluation for anti-
microbial activities. J Gen Appl Microbiol 51:133–141
Nizamuddin M, Mishra M, Srivastava MK, Khan MH (2001)
Synthesis and fungicidal activity of 3,6,9-triaryl-2-thioxothia-
zolo[4,5-d][1,3,4]oxadiazolo[2,3-b]pyrimidine and 3,10-diaryl-
2-thioxothiazolo[4,5-d] pyrimido [2,1-b] pyrimidines. Indian J
Chem 40B:49–53
Ragavendran JV, Sriram D, Patel SK, Reddy IV, Bharathwajan N,
Stables JP, Yogeeswari P (2007) Design and synthesis of
anticonvulsants from a combined phthalimide-GABA-anilide
and hydrazone pharmacophore. Eur J Med Chem 42:146–151
Sharma S, Srivastava VK, Kumar A (2002) Newer N-substituted
anthranilic acid derivatives as potent anti-inflammatory agents.
Eur J Med Chem 37:689–697
Vicini P, Incerti M, Doytchinova IA, Colla PL, Busonera B, Loddo R
(2006) Synthesis and antiproliferative activity of benzo[d]iso-
thiazole hydrazones. Eur J Med Chem 41:624–632
Zarghi A, Tabatabhi SA, Faizi M, Ahadian A, Navabi P, Zanganeh V,
Shafiee A (2005) Synthesis and anticonvulsant activity of new
2-substituted-5-(2-benzyloxyphenyl)-1,3,4-oxadiazoles. Bioorg
Med Chem Lett 15:1863–1865
Cruzzocrea S, Mazzon E, Bevilaqua C, Constantino G, Britti D,
Mazzullo G, De Sarro A, Caputi AP (2000) Cloricromene, a
123