Synthesis and antimicrobial activity of some new 3-[5-(4-substituted) phenyl-1,3,4-oxadiazole-2yl]-2- styrylquinazoline-4(3H)-ones

Article abstract of DOI:10.1007/s00044-007-9054-3

Several 3-[5-(4-substituted)phenyl-1,3,4-oxadiazole-2-yl]-2-styryl quinazoline-4(3H)-one were synthesized and screened for antibacterial activity against Staphylococcus aureus , Bacillus subtilis, Pseudomonas aeruginosa, and Escherichia coli and antifungal activity against Aspergillus niger and Fusariumoxysporum by the serial dilution technique. Compounds were prepared by reacting corresponding 2-methtyl quinazolinone and 4-subustituted benzaldehydes in glacial acetic acid. Physicochemical and spectral data were consistent with newly synthesized compounds. The prepared compounds were compared with previously synthesized 2-methyl-3-[5-(4-substituted)phenyl-1,3,4-oxadiazole-2- yl]-quinazoline-4(3H)-ones for antimicrobial activity. The present study revealed that styryl moiety at the second position of 4(3H) quinazolinone marginally increased the biological activity and exhibited better antibacterial than antifungal activities.

Full text of DOI:10.1007/s00044-007-9054-3

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res (2008) 17:205–211
DOI 10.1007/s00044-007-9054-3
ORIGINAL RESEARCH
Synthesis and antimicrobial activity of some new
3–[5-(4-substituted) phenyl-1,3,4-oxadiazole-2yl]-2-
styrylquinazoline-4(3H)-ones
Vivek Gupta Æ Sushil K. Kashaw Æ Varsha Jatav Æ
Pradeep Mishra
Received: 31 October 2007 / Accepted: 6 November 2007 / Published online: 3 January 2008
¨
Ó Birkhauser Boston 2007
Abstract Several 3-[5-(4-substituted)phenyl-1,3,4-oxadiazole-2-yl]-2-styryl qui-
nazoline-4(3H)-one were synthesized and screened for antibacterial activity against
Staphylococcus aureus , Bacillus subtilis, Pseudomonas aeruginosa, and Esche-
richia coli and antifungal activity against Aspergillus niger and Fusariumoxysporum
by the serial dilution technique. Compounds were prepared by reacting corre-
sponding 2-methtyl quinazolinone and 4-subustituted benzaldehydes in glacial
acetic acid. Physicochemical and spectral data were consistent with newly syn-
thesized compounds. The prepared compounds were compared with previously
synthesized 2-methyl-3-[5-(4-substituted)phenyl-1,3,4-oxadiazole-2-yl]-quinazo-
line-4(3H)-ones for antimicrobial activity. The present study revealed that styryl
moiety at the second position of 4(3H) quinazolinone marginally increased the
biological activity and exhibited better antibacterial than antifungal activities.
Introduction
One of the most frequently encountered heterocyclic molecules in medicinal
chemistry is 4(3H)-quinazolinone with wide applications including antibacterial,
antifungal, anticonvulsant, and anti-inflammatory activities (Armarego 1979;
Gravier et al., 1992; Fisnerova et al., 1986). An increase in its antimicrobial
activity by substituting different heterocyclic ring at the third position is also well
documented in the literature. The increased antimicrobial activity obtained by
V. Gupta Á S. K. Kashaw (&) Á V. Jatav Á P. Mishra
Pharmaceutical Chemistry Division, Department of Pharmaceutical Sciences, Dr. H.S.G. University,
Sagar, India
e-mail: sushilkashaw@gmail.com

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Med Chem Res (2008) 17:205–211
placing a styryl moiety at the second position has also been reported. In our research
we found that oxadiazole and substituted oxadiazole itself possessed antibacterial
and antifungal activities (Mishra et al., 2005). In an effort to observe the synergistic
effect of both of these effects we synthesized new 4(3H)-qunazolinone analogues
incorporating the styryl moiety and substituted oxadiazole at the second and third
position of 4(3H)-qunazolinone, respectively. The present paper reports the
synthesis and antimicrobial activity of 3-[5-(4-substituted) phenyl-1,3,4-oxadiaz-
ole-2-yl]-2-styryl quinazoline-4(3H)-one.
Material and methods
Chemistry
Melting points were determined in one-end-open capillary tubes on a Buchi 530
melting point apparatus and are uncorrected. Infrared (IR) and 13C nuclear
magnetic resonance (13C NMR) spectra were recorded for the compounds on
Perkin Elmer Spectrum RXI spectrophotometer in KBr pettels and a 13C
Advance Bruker (300 MHz) instrument, respectively. Chemical shifts are
reported in parts per million (ppm) using tetramethylsilane (TMS) as an internal
standard. Elemental analysis (C, N, and S) were undertaken with an Elemental
Vario EL III Carlo Erba 1108 analyzer. The purity of the compounds was
confirmed by thin-layer chromatography using silica gel glass plates and a
benzene:ethanol (8:2) solvent system. The spots were developed in an iodine
chamber and visualized under an ultraviolet lamp.
3-[5-(4-substituted)phenyl-1,3,4-oxadiazole-2-yl]-2-styrylquinazoline-4(3H)-
ones (7a–o), were obtained (Fig. 1) by refluxing equimolar amounts of opportune 2-
methyl-3-[5-(4-substituted)phenyl-1,3,4-oxadiazole-2-yl]-quinazoline-4(3H)-ones
(6a–e) and benzaldehyde in glacial acetic acid. The structure of new compounds
1
was elucidated by analytical as well as spectroscopic measurements. The H NMR
spectra of compounds 7 are consistent with a trans olefinic structure: b-olefinic
protons appeared as doublets at d 6.296–6.980 (J = 16.2 Hz, as required for a trans
structure) while the a-olefinic hydrogen were found along with an aromatic
multiplet because of the deshielding effect of the two quinazolinone nitrogens.
Synthesis of 3-[5-(4-substituted)phenyl-1,3,4-oxadiazole-2yl]-2-styrylquinazo-
line-4(3H)-ones was achieved based on the following procedures.
Synthesis of 4-substituted benzaldehyde semicarbazone (2)
Semicarbazide hydrochloride (0.01M) and sodium acelate (0.02M) were dissolved
in 15–20 ml of distilled water placed in a flat-bottomed flask. The required aromatic
aldehyde (0.01M) was dissolved in aldehyde-free alcohol. This solution was added
slowly to the solution of semicarbazide hydrochloride. The separated precipitate
was filtered, dried, and recrystallized from hot ethanol (95%).

Med Chem Res (2008) 17:205–211
207
CH3COONa
R1
CH=N-NHCONH2
R1
CHO + H2NNHCONH2
2
1
CH3COONa
Br2, CH3COOH
N
N
R1
O
NH2
3
O
COOH
AC2O
O
Reflux
N
NH2
CH3
4
5
N
O
N
N
R1
NH2
N
O
N
R1
H
H
H
R2
H
CH3
Cl
R1
a
b
c
d
e
f
O
6
N
CH3
Cl
Cl
Cl
H
CH3
Cl
R2
CHO
g
h
i
j
k
l
m
n
o
CH3
CH3
CH3
OCH3
OCH3
OCH3
N(CH3)2
H
CH3
Cl
H
CH3
Cl
O
N
N
N
R1
N
O
H
R2
N(CH3)2 CH3
N(CH3)2 Cl
7
Fig. 1 Scheme for the synthesis of the title compounds (7a–o)
Synthesis of 2-amino-5-aryl-1,3,4-oxadiazols (3)
Semicarbazone (2) (0.01M) and sodium acetate (0.02M) was dissolved in 30–40
ml of glacial acetic acid with continuous stirring. Bromine (0.7 ml in 5 ml of
GAA) was added slowly, and the solution was stirred for 1 h and then poured
onto crushed ice. The resulting solid was separated, dried, and recrystallized
from hot ethanol (95%).

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Med Chem Res (2008) 17:205–211
Synthesis of 2-methyl benzoxazin -4(3H)-one (5)
Anthranilic acid (4) (0.01M, 1.8g) was taken in acetic anhydride and refluxed under
anhydrous conditions for 4 h. Excess acetic anhydride was then distilled off under
reduced pressure. The obtained product was immediately used for next step.
Synthesis of 2-methyl-3-[5-(4-substituted)phenyl-1,3,4-oxadiazole-2-yl]-
quinazoline-4(3H)-ones (6)
To the mixture of benzoxazinone (5) 2-amino-5-aryl -1,3,4-oxadiazole (0.01M) in
10 ml of glacial acetic acid was added and refluxed under anhydrous condition for 4
h. After cooling it was poured into crushed ice. The solid separated out was filtered
thoroughly washed with cold distilled water, dried, and recrystallized from hot
ethanol (95%).
Synthesis of the title compounds (7)
Equimolar amounts (0.012M) of 2-methyl-3-[5-(4-substituted)phenyl-1,3,4-oxadi-
azole-2-yl]-quinazoline-4(3H)-one and opportune benzaldehyde were reacted in
glacial acetic (5.2 mL) under reflux for 18 h. A sticky oily matter was obtained,
which was then purified to remove impurities to obtain the final product, which was
dried and recrystallized from hot ethanol. The physicochemical and spectral
properties of the title compounds are presented in Tables 1 and 2 respectively.
Table 1 Physicochemical properties of 3-[5-substituted 1,3,4-thiadiazole -2 yl] quinazoline-4(3H)-ones
Comp.
Molecular formula
Mol. wt.
m.p. (°C)
% yield
7a
7b
7c
7d
7e
7f
C24H16N4O2
392
210
23.29
12.74
8.9
C25H18N4O2
406
240*
C24H15N4O2Cl
426.5
426.5
440.5
461
238–240
195*
C24H15N4O2Cl
19.8
17.3
22.05
21.94
15.15
46.93
6.65
9.2
C
C
C
C
C
C
C
C
C
C
C
25H17N4O2Cl
24H14N4O2Cl2
25H18N4O2
215
185*
7g
7h
7i
406
195–197
185*
26H20N4O2
420
25H17N4O2Cl
25H18N4O3
440.5
422
260*
7j
210*
7k
7l
26H20N4O3
436
218–220
215*
25H17N4O3Cl
26H21N5O2
456.5
435
27.47
4
7m
7n
7o
180*
27H23N5O2
449
183–185
180*
5.8
26H20N5O2Cl
469.5
3.7
*Compound decomposed at mentioned temperature.

Med Chem Res (2008) 17:205–211
209
Table 2 Spectroscopic data of the title compounds (7–o)
Comp. IR spectra (cm-1
)
1H NMR
7a
7b
7c
7d
7e
7f
1672 (C=O), 1590 (C=N),
1145 (C-O-C)
6.9 (1H, bCH),
7.05–8.45 (m,15H, 2Ph & H5–8, aCH)
2.47 (s, 3H, Me); 6.9 (d, 1H, bCH);
7.11–8.47 (m, 14H, 2Ph & H5–8, aCH)
6.92 (1H, bCH),
1674.2 (C=O),1585 (C=N),
1142.5 (C-O-C)
1662.8 (C=O), 1594.5 (C=N),
1149.8 (C-O-C)
7.10–8.46 (m,14H, 2Ph & H5–8, aCH)
6.90 (1H, bCH),
1670.8 (C=O), 1601.8 (C=N),
1146.5 (C-O-C)
7.11–8.44 (m,14H, 2Ph & H5–8, aCH)
1650 (C=O), 1590.7 (C=N), 1150 2.35 (s, 3H, Me); 6.93 (d, 1H, bCH);
(C-O-C)
7.05–8.48 (m, 13H, 2Ph & H5–8, aCH)
1678 (C=O), 1585.5 (C=N), 1145 6.90 (d, 1H, bCH);
(C-O-C)
7.90–8.48 (m, 13H, 2Ph & H5–8, aCH)
7g
7h
7i
1671.3 (C=O), 1603.2 (C=N),
1154.2 (C-O-C)
2.35 (s, 3H, Me); 6.92 (d, 1H, bCH);
7.06–8.49 (m, 14H, 2Ph & H5–8, aCH)
2.28 (s, 6H, 2Me); 6.93 (d, 1H, bCH);
7.11–8.48 (m, 13H, 2Ph & H5–8, aCH)
2.35 (s, 3H, Me); 6.9 (d, 1H, bCH);
7.10–8.45 (m, 13H, 2Ph & H5–8, aCH)
3.89 (s, 3H, OMe); 6.92 (d, 1H, bCH);
7.09–8.47 (m, 14H, 2Ph & H5–8, aCH)
1658.9 (C=O), 1573.6 (C=N),
1150 (C-O-C)
1676.6 (C=O), 1584.7 (C=N),
1145 (C-O-C)
7j
1657.8 (C=O), 1599.1 (C=N),
1168.9 (C-O-C)
7k
7l
1671.5 (C=O), 1589.7 (C=N),
1142 (C-O-C)
2.37 (s, 3H, Me); 3.88 (s, 3H, OMe) 6.92 (d, 1H, bCH);
7.03–8.17 (m, 14H, 2Ph & H5–8, aCH)
3.88 (s, 3H, OMe); 6.91 (d, 1H, bCH);
7.11–8.45 (m, 13H, 2Ph & H5–8, aCH)
3.12 (s, 6H, NMe2); 6.90 (d, 1H, bCH);
7.05–8.44 (m, 14H, 2Ph & H5–8, aCH)
2.36 (s, 3H, Me); 3.10 (s, 6H, NMe2); 6.91 (d, 1H, bCH);
7.08–8.48 (m, 13H, 2Ph & H5–8, aCH)
3.11 (s, 6H, NMe2) 6.90 (d, 1bCH);
1672.4 (C=O), 1597.1 (C=N),
1172 (C-O-C)
7m
7n
7o
1687 (C=O), 1588.5 (C=N),
1163.3 (C-O-C)
1686.4 (C=O), 1591.3 (C=N),
1164 (C-O-C)
1685.8 (C=O), 1592.5 (C=N),
1162.6 (C-O-C)
7.07–8.47 (m, 13H, 2Ph & H5–8, aCH)
Microbiological evaluation
All the glass apparatus used was sterilized before use. The liquid dilution technique
was used to determine the minimum inhibitory concentration (MIC) of the
synthesized compounds. Bacterial strain of Staphylococcus aureus (MTCC no. 96),
Bacillus subtilus (MTCC no. 619), Pseudomonas aeruginosa (MTCC no. 424) and
Escherichia coli (MTCC no. 40) and fungal strains of Aspergillus niger (MTCC no.
1344) and Fusarium oxysporum obtained from Institute of Microbial Technology,
Chandigarh were used in the present study. Nutrient broth (beef extract 1 g, yeast
extract 2 g, peptone 5 g, sodium chloride 5 g, distilled water q.s. 1000 ml) was used
as growth medium for bacteria and Sabouraund’s medium (dextrose 40 g, peptone

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Med Chem Res (2008) 17:205–211
Table 3 Antibacterial and antifungal activity of synthesized compounds (7a–o)
Code
Antibacterial (lg/ml)
Antifungal (lg/ml)
S. aureus
B. subtilis
P. aeruginosa
E. coli
A. niger
F. oxysporum
7a
7b
7c
7d
7e
7
82
80
90
76
143
NA
NA
130
NA
NA
NA
145
NA
NA
NA
NA
NA
155
NA
NA
–
152
NA
NA
141
NA
NA
NA
156
NA
NA
NA
NA
NA
166
NA
NA
–
NA
NA
79
NA
NA
75
NA
NA
86
NA
NA
70
NA
NA
NA
85
NA
NA
NA
83
NA
NA
NA
92
NA
NA
NA
81
7f
7g
7h
7i
NA
NA
NA
NA
NA
88
NA
NA
NA
NA
NA
83
NA
NA
NA
NA
NA
94
NA
NA
NA
NA
NA
79
7j
7k
7l
7m
7n
7o
NF
CT
NA
NA
6
NA
NA
5
NA
NA
8
NA
NA
4
–
–
–
–
6
8
NA = not significantly active
10 g, distilled water q.s. 1000 ml) was used for fungus growth. Cook’s procedure of
serial dilution and observation for presence of growth was used in the determining
the MIC. Dimethylformamide was used as the solvent for the compounds. A blank
test was done to check the antimicrobial activity of DMF. Norfloxacin (NF) and
clotrimazole (CT) were used as the standard drugs for antibacterial and antifungal
activity, respectively, because these compounds are easily soluble in DMF.
Results and discussion
The synthesized 2-styryl quinazolinones 7a–o were screened for their antimicrobial
activity by the serial dilution method to evaluate the minimum inhibitory
concentration Table 3.
All of the precursors (6a–e) of the title compounds showed antibacterial activity
in the range of 88–130 lg/mL for Staphylococcus aureus, 84–129 lg/mL for
Bacillus subtilis, 95–138 lg/mL for Pseudomonas aeruginosa, and 80–120 lg/mL
for Escherichia coli. It was observed that styrylation of 2-methyl-3-[5-phenyl-1,3,4-
oxadiazole-2-yl]quinazoline-4(3H)-one marginally increased its antimicrobial
activity Table 4. Only nonsubstituted styryl compounds showed activity. Substitu-
tion either by electron-releasing or electron-attracting moieties at the styryl group
resulted in loss of activity. Compound 7d was found to be the most active compound

Med Chem Res (2008) 17:205–211
211
Table 4 Antibacterial and antifungal activity of compounds (6a–e)
Code
Antibacterial (lg/ml)
Antifungal (lg/ml)
S. aureus
130
B. subtilis
P. aeruginosa
135
E. coli
120
A. niger
185
F. oxysporum
192
6a
127
122
84
(R=H)
6b
127
89
138
98
115
82
165
172
165
170
180
184
175
179
(R=Me)
6c
(R=Cl)
6d
90
85
100
95
80
(R=OMe)
6e
88
88
84
(R=N(CH3)2
NF
6
–
5
–
8
–
4
–
–
6
–
8
CT
of the prepared series. All active compounds showed better antibacterial than
antifungal activity in the range 70–195 lg/ml. In conclusion the presented results
reveal that synthesized 2-styryl-quinazoline-4(3H)-one exhibited better antibacterial
than antifungal activity and that styrylation slightly increases the biological activity.
Acknowledgements Thanks are due to SAIF, Lucknow for performing spectroscopic studies.
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