Synthesis and antibacterial activity of some 5-(4-biphenylyl)-7-aryl[3,4-d] [1,2,3]-benzothiadiazoles

Article abstract of DOI:10.1016/j.ejmech.2005.01.005

A series of 5-(4-biphenylyl)-7-aryl[3,4-d] [1,2,3]-benzothiadiazoles were synthesized, characterized by IR, NMR and elemental analysis and evaluated for in vitro antibacterial activity against some Gram-positive and Gram-negative bacteria. The antibacterial data revealed that compounds 7a-j had better activity against tested Gram-positive organisms than the reference ciprofloxacin and norfloxacin. However, the compounds were nearly inactive against Gram-negative bacteria. Compound 7c and 7d were the most active compounds against Gram-positive bacteria.

Full text of DOI:10.1016/j.ejmech.2005.01.005

European Journal of Medicinal Chemistry 40 (2005) 728–731
www.elsevier.com/locate/ejmech
Synthesis and antibacterial activity of some 5-(4-biphenylyl)-7-aryl[3,4-d]
[1,2,3]-benzothiadiazoles
T. Balasankar, M. Gopalakrishnan, S. Nagarajan *
Department of Chemistry, Annamalai University, Annamalainagar 608002, Tamil Nadu, India
Received 23 October 2004; received in revised form 21 January 2005; accepted 24 January 2005
Available online 02 March 2005
Abstract
A series of 5-(4-biphenylyl)-7-aryl[3,4-d] [1,2,3]-benzothiadiazoles were synthesized, characterized by IR, NMR and elemental analysis
and evaluated for in vitro antibacterial activity against some Gram-positive and Gram-negative bacteria. The antibacterial data revealed that
compounds 7a–j had better activity against tested Gram-positive organisms than the reference ciprofloxacin and norfloxacin. However, the
compounds were nearly inactive against Gram-negative bacteria. Compound 7c and 7d were the most active compounds against Gram-
positive bacteria.
© 2005 Elsevier SAS. All rights reserved.
Keywords: Thiadiazoles; 1,2,3-Benzothiadiazoles; Synthesis; Antibacterial activity
1. Introduction
3 [11]. These ketones on treatment with ethyl acetoacetate in
the presence of sodium ethoxide, 6-ethoxycarbonyl-3-(4-
biphenyl)-5-substituted arylcyclohex-2-en-1-ones 4 are
formed. The above compounds are subjected to decarboxy-
lation; 3-(4-biphenylyl)-7-substituted arylcyclohex-2-en-1-
ones 5 are obtained. The ketones are converted into their semi-
carbazones 6 that on further treatment with SOCl2 5-(4-
biphenylyl)-7-aryl [3,4-d][1,2,3]-benzothiadiazoles 7 are
formed (Fig. 1).
The IR spectra of the compound 6 displayed primary bands
(cm–1) at 3442, 3240 (–NHCO, –CONH2), 1720 (–CONH2)
and 1426 (–C=N). IR spectra of 7 exhibited bands at 1582
(N=N) and 685 (C–S). The absence of bands in the region
3442, 3240 and 1426 and the presence of bands in the region
1582, 685 are regarded as positive evidence for the formation
of 7.
In 1955, Hurd and Mori [1] first reported the synthesis of
1,2,3-thiadiazoles from the reaction of a-methylene (or ethyl)
hydrazones. 1,2,3-Thiadiazoles are an important class of bio-
logically active compounds [2–7] as well as useful interme-
diates in organic synthesis [8]. For example, 4,5-bis(4′-
methoxyphenyl)-1,2,3-thiadiazole was found to be an active
inhibitor of collagen-induced platelet aggregation in vitro [9].
Many methods have been developed for the synthesis of 1,2,3-
thiadiazoles [10,11], of which the Hurd–Mori cyclization of
a-methylene ketones is the most convenient methodology
[12–16]. We report here the synthesis of biphenyl substituted
1,2,3-thiadiazole and their antibacterial activity.
The antibacterial activity of 7a–j was assessed in side-by-
side comparison with ciprofloxacin and norfloxacin against
some Gram-positive (Staphylococcus aureus, and Bacillus
subtilis) and Gram-negative (Escherichia coli, Klebsiella
peneumoniae, and Pseudomonas aeruginosa) bacteria using
conventional agar dilution procedure and the results are sum-
marized in Table 1. The antibacterial data indicated that com-
pounds 7a–j had a better activity against tested Gram-
positive organisms. However, all the compounds were nearly
inactive against tested Gram-negative bacteria. The antibac-
2. Results and discussion
The 4-acetylbiphenyl 2 [17] is obtained form acetylation
of biphenyl 1 in the presence of anhydrous aluminum chlo-
ride. 4-Acetylbiphenyl on treatment with different aromatic
aldehydes in the presence of base gives styryl biphenyl ketones
* Corresponding author. Tel.: +91 4144 23 8734.
E-mail address: drsn@sify.com (S. Nagarajan).
0223-5234/$ - see front matter © 2005 Elsevier SAS. All rights reserved.
doi:10.1016/j.ejmech.2005.01.005

T. Balasankar et al. / European Journal of Medicinal Chemistry 40 (2005) 728–731
729
Fig. 1. Synthetic pathways to compounds 7a–j.
terial data revealed that the 1,2,3-thiadiazole derivatives 7a–j
possesses similar antibacterial profiles. The selective antibac-
terial activity against Gram-positive bacteria is in contrast to
the good antibacterial activity of ciprofloxacin against both
Gram-positive and Gram-negative bacteria. The compounds
7c and d are more active than the rest of the compounds tested.
Among the methyl substituted compounds 4-methyl 7h is
more effective than 2- and 3-methyl substituted compounds.
Thus the nature of the functional group and position of the
substituent has strong influence on the spectrum and extent
of antibacterial activity.
Table 1
In vitro antibacterial activity of 7a–j and standards (MIC µg ml−1
)
Compounds
S.
B.
E.
K.
P.
3. Experimental
aureus subtilis coli peneumoniae aeruginosa
7a
7b
7c
7d
7e
7f
7g
7h
7i
0.55
0.40
0.19
0.20
0.48
0.45
0.43
0.22
0.40
0.41
0.50
0.40
0.024
0.024
0.50
0.45
0.44
0.13
0.32
0.35
0.02
0.05
32
8
>60
24
>60
32
Melting points are determined in open capillaries and are
uncorrected. Infrared spectra were recorded on Perkin–
Elmer (FT-IR-8300) in KBr pellets. 1H NMR and 13C NMR
were recorded on Bruker (AMX-400) using CDCl3 as sol-
vent. TMS was used as internal reference for 1H NMR.
40
32
8
>60
>60
>60
>60
44
>60
>60
>60
>60
55
37
28
26
32
38
>60
>60
>60
>60
>60
>60
1
3.1. General procedure for the synthesis of 6-ethoxycarbo-
nyl-3-(4-biphenylyl)-5-substituted arylcyclohex-2-en-1-one
4(a–j)
7j
Ciprofloxacine 0.45
Norfloxacin
0.13 0.03
0.48 0.12
1
3.5
A mixture of sodium ethoxide (2 g sodium in 60 ml etha-
nol), freshly distilled ethyl aceto acetate (0.01 mol) and styryl
biphenyl ketone 3 (0.01 mol) was dissolved in absolute etha-
nol (20 ml) and refluxed for 2 h on a steambath and cooled.
The MIC values of compounds 7a–j indicated that the 7c and 7d were the
most active compounds. The strong antibacterial activity of this compounds
against tested Gram-positive bacteria suggested further investigation on this
compounds.

730
T. Balasankar et al. / European Journal of Medicinal Chemistry 40 (2005) 728–731
Table 2
Physical and analytical data of 7(a–j)
Compound numbers
M.p. (°C)
Yield Molecular formula
(%)
Elemental analysis
Carbon (found/calcd) Hydrogen (found/calcd)
Nitrogen (found/calcd)
7.69/7.46
7a
7b
7c
7d
7e
7f
7g
7h
7i
166–167
125–127
135–138
141–142
138–140
159–160
167–169
125–128
139–141
172–174
25
30
27
38
20
29
37
32
35
33
C
C
C
C
C
C
C
C
C
C
24H16N2S
79.12/79.24
76.14/76.01
72.36/72.02
70.4/70.20
4.39/4.82
4.56/4.71
3.76/3.26
3.66/3.81
4.39/4.20
3.51/3.26
3.91/3.80
4.29/4.76
4.91/4.76
4.51/4.76
25H18N2S
7.10/7.05
24H15N2ClS
24H15N3O2S
24H18N3O2S
24H15N2ClS
25H15N3O2S
24H18N2S
7.03/7.37
10.20/10.11
7.69/7.82
79.12/79.48
72.91/72.02
71.34/70.20
79.81/79.36
78.12/79.36
80.02/79.36
7.41/7.37
10.18/10.11
7.89/7.40
24H18N2S
7.68/7.40
7j
24H18N2S
7.28/7.40
The separated solid was filtered, washed with water and
recrystallized from ethanol to get 4.
(C-9), 146.34 (C-8), 143.82 (C-5), 141.99 (C-7), 138.84,
140.71, 141.07 (ipso carbons), 122.02 (C-4), 127.51–130.07
(C-6 and aromatic carbons).
3.2. General procedure for the synthesis of 3-(4-bipheny-
lyl)-5-arylcyclohex-2-en-1-one 5(a–j)
3.4.2. 7b
1H NMR, d = 8.80 (1H, d, H-4, J = 1.2 Hz): 8.01 (1H, d,
H-6, J = 1.2 Hz), 3.91 (3H, s, CH3), d7.10–7.86 (m, aromatic
protons), 13C NMR, d = 160.90 (C-9), 141.95 (C-8), 141.81
(C-5), 141.02 (C-7), 120.52 (C-4), 139.1, 134.91, 133.07 (ipso
carbons), 127.77–131.54 (C-6 and aromatic carbons).
A mixture of an appropriate ketone 4 (0.01 mol) in glacial
acetic acid (25 ml) and concentrated hydrochloric acid (12 ml)
was refluxed for 10 h over a water bath. The reaction mixture
was poured into crushed ice and stirred well. The separated
product 5 was recrystallized from aqueous ethanol.
3.4.3. 7c
1H NMR, d = 8.85 (1H, d, H-4, J = 1.2 Hz): 8.02 (1H, d,
H-6, J = 1.2 Hz), 7.04–7.785 (m, aromatic protons), 13C
NMR, d = 160.87 (C-9), 142.10 (C-8), 140.94 (C-5), 140.11
(C-7), 135.79, 138.78, 139.11 (ipso carbons), 121.44 (C-6),
127.77–133.97 (C-6 and aromatic carbons).
3.3. General procedure for the synthesis of 3-(4-bipheny-
lyl)-5-arylcyclohex-2-en-1-one semicarbazone 6(a–j)
A mixture of ketone 5 (0.01 mol), semicarbazide hydro-
chloride (0.01 mol) and sodium acetate (0.015 mol) in etha-
nol (40 ml) was refluxed for 2 h on a steam bath and cooled.
The separated solid said was filtered, washed with water and
recrystallized from ethanol.
3.4.4. 7d
1H NMR, d = 8.93 (1H, d, H-4, J = 1.2 Hz): 8.10 (1H, d,
H-6, J = 1.2 Hz), 7.26–7.93 (m, aromatic protons), 13C NMR,
d = 161.12 (C-9), 148.68 (C-8), 146.84 (C-5), 142.32 (C-7),
122.6 (C-4), 138.36, 140.82, 140.04 (ipso carbons), 122.34–
132.77 (C-6 and aromatic carbons).
3.4. General procedure for the synthesis
of 5-(4-biphenylyl)-7-aryl[3,4-d] [1,2,3] benzothiadiazole
7(a–j)
3.4.5. 7e
1H NMR, d = 8.84–8.85 (1H, d, H-4, J = 1.2 Hz), 8.10–
8.02 (1H, d, H-6, J = 1.2 Hz), 3.8 (3H, s, OCH3), 7.00–7.86
(m, aromatic protons), 13C NMR, d = 159.45 (C-9), 141.08
(C-8), 140.65 (C-5), 140.45 (C-7), 121.21 (C-4), 156.32,
138.60 (ipso carbons), 127.32–31.60 (ipso carbons), 127.16–
131.73 (C-6 and aromatic carbons).
Semicarbazone 6 (0.001 mol) was added portion wise to
the thionyl chloride (1.5 ml) at 0–5 °C and then kept at room
temperature for 1–2 h. Dichloromethane (10 ml) was added
to the reaction mixture and decomposed with an ice-cold
sodium carbonate solution. The organic layer was washed with
water (four to five times each with 10 ml) and dried over
anhydrous sodium sulfate. After evaporation of the solvent a
gummy substance was obtained, which was solidified on treat-
ment with cyclohexane and purified by column chromatog-
raphy using silica gel (60–120 mesh, BDH) with benzene-
pet-ether (60–80) (10:1) as elutents. The yield, melting point
and elemental composition of 7(a–j) are given in Table 2.
3.4.6. 7f
1H NMR, d = 8.91 (1H, d, H-4, J = 1.1 Hz): 8.12 (1H, d,
H-6, J = 1.1 Hz), 7.12–7.98 (m, aromatic protons), 13C NMR,
d = 162.71 (C-9), 143.34 (C-8), 141.22 (C-5), 141.3 (C-7),
140.4, 139.1, 134.07 (ipso carbons), 141.4 120.2 (C-4),
123.51–133.17 (C-6 and aromatic carbons).
3.4.1. 7a
1H NMR (400 MHz, CDCl3), d = 8.84 (1H, d, H-4,
J = 1.2 Hz): 8.06 (1H, d, H-6, J = 1.3 Hz), 7.10–7.86 (m, aro-
matic protons), 13C NMR (100 MHz), CDCl3), d = 160.84
3.4.7. 7g
1H NMR, d = 8.80 (1H, d, H-4, J = 2 Hz): 8.02 (1H, d,
H-6, J = 2 Hz), 7.02–7.90 (m, aromatic protons), 13C NMR,

T. Balasankar et al. / European Journal of Medicinal Chemistry 40 (2005) 728–731
731
d = 163.81 (C-9), 144.29 (C-8), 141.2 (C-5), 141.8 (C-7),
140.7, 139.8, 136.09 (ipso carbons), 122.2 (C-4), 124.1–
131.19 (C-6 and aromatic carbons).
solution was diluted with water (9 ml). Further progressive
double dilution with melted Muller–Hinton agar was per-
formed to obtain the required concentrations. The minimum
inhibitory concentration (MIC) was the lowest concentration
of the test compound, which resulted in no visible growth on
the plate. To ensure that the solvent had no effect on bacterial
growth, a control test was performed with test medium supple-
mented with DMSO at the same dilutions as used in the
experiment.
3.4.8. 7h
1H NMR, d = 2.32(3H,s, CH3), 8.82 (1H, d, H-4,
J = 1.3 Hz): 8.10 (1H, d, H-6, J = 1.3 Hz), 7.08–7.93 (m, aro-
matic protons), 13C NMR, d = 21.2 (CH3), 161.21 (C-9), 145.2
(C-8), 142.7 (C-5), 140.8 (C-7), 156.2, 140.2, 137.8,136.2
(ipso carbons), 121.6 (C-4), 123.4–129.9 (C-6 and aromatic
carbons).
References
3.4.9. 7i
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1H NMR, d = 2.41 (3H,s, CH3), 8.83 (1H, d, H-4,
J = 1.3 Hz): 8.16 (1H, d, H-6, J = 1.3 Hz), 7.10–7.89 (m, aro-
matic protons), 13C NMR, d = 21.7 (CH3), 160.82 (C-9), 146.2
(C-8), 141.9 (C-5), 140.5 (C-7), 155.2, 139.8, 139.2,135.2
(ipso carbons), 122.1 (C-4), 124.2–130.4 (C-6 and aromatic
carbons).
3.4.10. 7j
1H NMR, d = 2.37(3H,s, CH3), 8.91 (1H, d, H-4,
J = 1.3 Hz): 8.21 (1H, d, H-6, J = 1.3 Hz), 7.18–7.91 (m, aro-
matic protons), 13C NMR, d = 21.4 (CH3), 161.41 (C-9),
144.02 (C-8), 142.1 (C-5), 140.1 (C-7), 156.2, 140.4,
138.1,137.2 (ipso carbons), 121.9 (C-4), 122.6–130.1 (C-
6 and aromatic carbons).
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3.5. Antibacterial activity
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The in vitro antibacterial activity of the synthesized com-
pounds against Gram-positive organisms (S. aureus, and B.
subtilis) and Gram-negative (E. coli, K. peneumoniae and P.
aeruginosa) organisms by the conventional agar dilution pro-
cedures [18] and compared with that of ciprofloxacin and nor-
floxacin. Twofold serial dilutions of the compounds and ref-
erence drugs were prepared in Muller–Hinton agar. Drugs
were dissolved in dimethylsulfoxide (DMSO; 1 ml) and the
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