Synthesis and bioassay of aminosulfonyl-1,3,4-oxadiazoles and their interconversion to 1,3,4-thiadiazoles

Article abstract of DOI:10.1016/j.ejmech.2010.06.022

A new class of oxadiazoles is prepared by treating aminosulfonylacetic acids with different carboxylic acid hydrazides. Interconversion of oxadiazoles to thiadiazoles is carried out with thiourea. The compounds are screened for antimicrobial and antioxidant activities.

Full text of DOI:10.1016/j.ejmech.2010.06.022

European Journal of Medicinal Chemistry 45 (2010) 4246e4251
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Synthesis and bioassay of aminosulfonyl-1,3,4-oxadiazoles and their
interconversion to 1,3,4-thiadiazoles
*
V. Padmavathi , S. Nagi Reddy, G. Dinneswara Reddy, A. Padmaja
Department of Chemistry, Sri Venkateswara University, Tirupati, Andhra Pradesh 517 502, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A new class of oxadiazoles is prepared by treating aminosulfonylacetic acids with different carboxylic
acid hydrazides. Interconversion of oxadiazoles to thiadiazoles is carried out with thiourea. The
compounds are screened for antimicrobial and antioxidant activities.
Received 17 February 2010
Received in revised form
10 June 2010
Accepted 15 June 2010
Available online 22 June 2010
Ó 2010 Elsevier Masson SAS. All rights reserved.
Keywords:
1,3,4-oxadiazole
1,3,4-thiadiazole
Phosphorus oxychloride
Thiourea
Antimicrobial activity
Antioxidant activity
1. Introduction
with the synthesis and bioassay of arylaminosulfonylmethyl-5-aryl-
1,3,4-oxadiazoles and their conversion to thiadiazoles.
Heterocyclic compounds containing five-membered rings gained
importance because of their versatile biological properties. In
particular, compounds bearing 1,3,4-oxadiazole nucleus are known
to have unique antioedema and anti-inflammatory activities [1].
Differently substituted oxadiazole molecules possess other inter-
esting properties such as analgesic [1], antimicrobial [2], antituber-
cular [3], anticonvulsant [4] and antihepatitis B virus activities [5].
The advent of sulfur drugs and the later discovery of mesoionic
compounds in fact accelerated the rate of interest in the field of sulfur
containing heterocycles. Substituted oxadiazole and thiadiazole
derivatives are potent cyclooxygenase/5-lipooxygenase inhibitors
[6]. Indeed, 5-unsubstituted 1,3,4-thiadiazoles are used as interme-
diates in the synthesis of therapeutically potent antibiotic cefazolin
[7]. Remarkable progress has been made by our group in the
development of biologically potent heterocycles [8]. Replacement of
-O- by -S- in some heterocycles was reported viz., transformation of
epoxide to episulfides by the action of thiocyanates or thiourea.
However, there are few reports about the conversion of 1,3,4-oxa-
diazoles to 1,3,4-thiadiazoles [9]. The present communication deals
2. Chemistry
The general synthetic pathway for the synthesis of arylamino-
sulfonylmethyl oxadiazoles and thiadiazoles is depicted in Scheme 1.
Experimental data and spectroscopic analysis of the compounds 4e7
are compiled in experimental section. The synthetic intermediate,
arylaminosulfonylacetic acid methyl ester 2 is prepared by the
condensation of substituted aniline with methyl chlor-
osulfonylacetate. The latter compound is obtained from methyl
bromoacetate [10]. Hydrolysis of 2 in the presence of KOH in meth-
anol gave the corresponding acid, arylaminosulfonylacetic acid 3
[10]. The cyclocondensation of 3 with different aryl acid hydrazides
in the presence of phosphorus oxychloride afforded 2-arylamino-
sulfonylmethyl-5-aryl-1,3,4-oxadiazoles 4. Similarly the reaction of 3
with arylsulfonylacetic acid hydrazide in the presence of phosphorus
oxychloride produced 2-arylaminosulfonylmethyl-5-arylsulfo-
nylmethyl-1,3,4-oxadiazole 5. The 1H NMR spectrum of 4a displayed
a singlet at
d
5.04 for methylene protons and another broad singlet at
4.08
10.45 ppm for NH. However 5a exhibited two sharp singlets at
d
and 4.42 ppm for two methylene protons. The signal at downfield
region is assigned to methylene protons adjacent to SO2NH group.
* Corresponding author. Tel.: þ91 877 2289303; fax: þ91 877 2249532.
E-mail address: vkpuram2001@yahoo.com (V. Padmavathi).
Apart from these, a broad singlet is observed at
d 10.54 ppm due to
0223-5234/$ e see front matter Ó 2010 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2010.06.022

V. Padmavathi et al. / European Journal of Medicinal Chemistry 45 (2010) 4246e4251
4247
H
H
N
O
N
OH
NH2
i
S
ii
S
CH3
O
O
O
O
O
O
R
R
R
3
1
2
3
iv
O
iii
N
N
O
N
N
H
H
O
N
N
S
R
S
S
O
O
O
O
O
R
R
5
R
4
v
v
N
N
O
H
N
N
H
O
N
N
S
S
R
S
S
S
O
O
O
O
R
R
R
6
7
R
a = H
b = Me
c = Cl
i. ClSO2CH2CO2CH3/Et3N/Benzene (70-75%)
ii. KOH/H2O/MeOH (72-76%)
iii. RC6H4CONHNH2/POCl3 (70-75%)
iv. RC6H4SO2CH2CONHNH2/POCl3 (68-78%)
v. H2NCSNH2/THF (70-78%)
Scheme 1. Synthesis of arylaminosulfonylmethyl oxadiazoles and thiadiazoles.
NH. Compounds 4 and 5 are treated with two-fold excess thiourea in
tetrahydrofuran to give 2-arylaminosulfonylmethyl-5-aryl-1,3,4-
thiadiazole 6 and 2-arylaminosulfonylmethyl-5-arylsulfonylmethyl-
1,3,4-thiadiazole 7, respectively. The 1H NMR spectrum of 6a showed
control drugs. The observed data on the antimicrobial activity of the
compounds and control drugs are given in Tables 1e3.
3.2. Antioxidant testing
two singlets at d 5.05 and 10.42 ppm for methylene and NH protons
while for 7a three singlets at 4.03, 4.47 and 10.56 ppm for two
methylene and NH protons. The structures of 4e7 were evidenced by
13C NMR spectroscopy.
The compounds 4e7 are tested for antioxidant property by
nitric oxide [13,14] and DPPH [15] methods. The observed data on
the antioxidant activity are given in Table 4.
4. Result and discussion
3. Biology
We have synthesized 2-arylaminosulfonylmethyl-5-aryl-
1,3,4-oxadiazole (4) and 2-arylaminosulfonylmethyl-5-arylsul-
fonylmethyl-1,3,4-oxadiazole (5) by the cyclocondensation of
2-arylaminosulfonylacetic acid with acid hydrazides and arylsulfo-
nylacetic acid hydrazides in the presence of POCl3. The interconver-
sionof4and5to2-arylaminosulfonylmethyl-5-aryl-1,3,4-thiadiazole
(6) and 2-arylaminosulfonylmethyl-5-arylsulfonylmethyl-1,3,4-thia-
diazole (7), respectively was effected with thiourea as presented in
Scheme 1.
3.1. Antimicrobial activity
The compounds 4e7 were tested for in vitro antimicrobial
activity against the Gram-positive bacteria Staphylococcus aureus
(NCIM No. 5021), Bacillus subtilis (NCIM No. 2063), the Gram-
negative bacteria Klebsiella pneumoniae (NCIM No. 2957), Proteus
vulgaris (NCIM No. 2027) and fungi Fusarium solani (NCIM No.
1330), Curvularia lunata (NCIM No. 716), Aspergillus niger (NCIM No.
596). The primary screen was carried out by agar disc-diffusion
method [11] using nutrient agar medium. The minimum inhibitory
concentration for the most active compounds 6c, 7a, 7b and 7c
against the same microorganisms used in the preliminary
screening was carried out using microdilution susceptibility
method [12]. Chloramphenicol and Ketoconazole were used as
4.1. Biological results
The results of preliminary antibacterial testing of compounds
4e7 are presented in Table 1. The results revealed that the

4248
V. Padmavathi et al. / European Journal of Medicinal Chemistry 45 (2010) 4246e4251
Table 1
Table 2
Antibacterial activity of 4e7.
Antifungal activity of 4e7.
Compound
Concentration
g/disc)
Zone of inhibition (mm)
Compound
Concentration Zone of inhibition (mm)
(
m
(mg/disc)
Fusarium
solani
Curvularia
lunata
Aspergillus
niger
Gram-positive
bacteria
Gram-negative
bacteria
4a
100
200
100
200
100
200
100
200
100
200
100
200
100
200
100
200
100
200
100
200
100
200
100
200
100
200
11
13
12
15
14
16
13
16
14
18
17
19
22
24
19
22
27
30
31
33
27
35
33
37
38
42
e
13
15
14
16
13
15
16
20
15
17
14
18
24
25
21
24
25
27
30
32
25
33
34
36
41
44
e
12
16
10
12
11
13
14
17
13
15
16
18
19
21
17
18
20
23
29
30
22
26
32
33
36
39
e
Staphylococcus Bacillus Klebsiella
Proteus
aureus
subtilis pneumoniae vulgaris
4b
4a
4b
4c
5a
5b
5c
6a
6b
6c
7a
7b
7c
100
200
100
200
100
200
100
200
100
200
100
200
100
200
100
200
100
200
100
200
100
200
100
200
10
13
10
12
12
14
13
14
12
15
13
15
19
22
20
23
25
27
27
30
25
28
31
33
35
41
e
09
11
09
10
11
13
12
15
11
13
12
14
18
20
22
24
23
26
29
31
27
29
28
32
38
44
e
07
09
07
08
09
10
11
12
10
12
11
13
14
17
18
19
19
22
27
29
25
27
28
30
37
42
e
06
08
07
09
10
11
12
14
10
12
13
14
15
16
13
15
18
20
23
26
24
26
25
28
42
45
e
4c
5a
5b
5c
6a
6b
6c
7a
7b
7c
Ketoconazole
Control (DMSO)
Chloramphenicol 100
200
Control (DMSO)
(Table 3). The structureeantimicrobial activity relationship of the
synthesized compounds revealed that the compounds having
thiadiazole moiety exhibited higher antimicrobial activity than the
compounds with oxadiazole unit. Further the compound having
arylsulfonylmethane moiety 7 showed excellent antimicrobial
activity. The presence of chloro substituent in the aromatic ring
enhanced the activity.
compounds 6c, 7a, 7b and 7c displayed excellent activity against
Gram-positive bacteria (inhibitory zone >26 mm) and good
activity against Gram-negative bacteria (inhibitory zone
>20 mm). The compound 6a displayed moderate to high activity
towards gram (þve) bacteria and moderate activity towards
gram (ꢀve) bacteria. The compounds 4 and 5 are less active
against both bacteria. All the tested compounds except 4 and 5
showed moderate to high inhibitory effect towards tested fungi
(Table 2).
4.2. Antioxidant testing
The compounds 4e7 are tested for antioxidant property by
nitric oxide and DPPH methods. The results revealed that the
compounds having oxadiazole moiety exhibited good antioxidant
The MIC values represent the lowest concentration that
completely inhibited visible growth of the microorganisms

V. Padmavathi et al. / European Journal of Medicinal Chemistry 45 (2010) 4246e4251
mg/ml of 6c, 7a, 7c.
4249
Table 3
Minimum inhibitory concentration (MIC),
Compound
Minimum inhibitory concentration MIC,
m
g/ml
K. pneumoniae
S. aureus
B. subtilis
P. vulgaris
F. solani
C. lunata
A. niger
6c
7a
7b
7c
100
50
50
100
25
50
200
50
100
50
200
100
100
50
200
100
50
100
100
100
50
200
50
100
50
25
25
50
Chloramphenicol
Ketoconazole
6.25
e
6.25
e
12.5
e
12.5
e
e
e
e
12.5
6.25
6.25
property when compared with those having thiadiazole unit. In
6. Experimental
fact, the compounds 4a, 4c, 5a and 5c exhibited high antioxidant
property in both nitric oxide and DPPH methods at a 100
concentration (Table 4).
mM
6.1. Chemistry
Melting points were determined in open capillaries on a Mel-
Temp apparatus and are uncorrected. The purity of the compounds
was checked by TLC (silica gel H, BDH, 1:3 ethyl acetateehexanes).
The IR spectra were recorded on a Thermo Nicolet IR200 FT-IR
spectrometer as KBr pellets and the wave numbers were given in
cmꢀ1. The NMR spectra were recorded in DMSO-d6 on a Bruker
spectrospin operating at 400 MHz. All chemical shifts are reported
5. Conclusion
In conclusion, a new class of heterocycles, 1,3,4-oxadiazoles and
1,3,4-thiadiazoles are developed adopting simple, elegant and well-
versed methodologies. The preliminary antimicrobial activity
studies revealed that the compounds having thiadiazole moiety
in
d (ppm) using TMS as an internal standard. The microanalyses
were performed on a Perkin-Elmer 240 C elemental analyzer. The
starting compound arylaminosulfonylacetic acid 3 was prepared by
the literature procedure [10].
exhibited
a higher antimicrobial activity in comparison to
compounds having oxadiazole unit. On the other hand, compounds
with oxadiazole unit showed a good antioxidant property.
6.1.1. General procedure for the synthesis of 2-arylaminosulfonyl-
methyl-5-aryl-1,3,4-oxadiazole 4aec/2-arylaminosulfonylmethyl-5-
arylsulfonylmethyl-1,3,4-oxadiazole 5aec
Table 4
Antioxidant property of 4e7.
To an equimolar solution (5 mmol) of arylaminosulfonylacetic
acid and benzoic acid hydrazide/arylsulfonylacetic acid hydrazide,
POCl3 (4 ml) is added and refluxed for 5e8 h. The excess POCl3 is
removed under vacuum and the residue is poured onto crushed ice.
The resulting precipitate is filtered, washed with saturated sodium
bicarbonate solution and then with water, dried and recrystallized
from ethanol to get 4aec/5aec.
6.1.1.1. 2-Phenylaminosulfonylmethyl-5-phenyl-1,3,4-oxadiazole(4a).
White solid (1.18 g, 75%); m.p. 147e149 ꢁC; IR (KBr): 1329, 1135
(SO2), 1589 (C]N), 3334 (NH) cmꢀ1; 1H NMR (DMSO-d6)
d
5.04 (s,
2H, SO2eCH2), 7.25e7.88 (m, 10H, AreH), 10.45 (bs, 1H, NH) ppm;
13C NMR (DMSO-d6)
47.2, 121.7, 123.1, 128.4, 129.2, 130.2, 130.5,
d
137.1,137.8,157.8,164.3 ppm; Anal. Calcd. For C15H13N3O3S: C, 57.13;
H, 4.16; N, 13.33; Found: C, 57.10; H, 4.22; N, 13.43%.
6.1.1.2. 2-(p-methylphenylaminosulfonylmethyl)-5-(p-methylphenyl)-
1,3,4-oxadiazole (4b). White solid (1.25 g, 72%); m.p. 161e163 ꢁC; IR
(KBr): 1318, 1138 (SO2), 1593 (C]N), 3341 (NH) cmꢀ1 1H NMR
;
(DMSO-d6)
SO2eCH2), 7.20e7.94 (m, 8H, AreH), 10.51 (bs, 1H, NH) ppm; 13C
NMR (DMSO-d6) 22.5, 22.9, 47.6, 121.2, 123.4, 127.9, 129.9, 130.7,
131.2, 137.2, 138.3 159.2, 165.1 ppm; Anal. Cacld. For C17H17N3O3S:
Anal. Calcd. For C, 59.46; H, 4.99; N, 12.24; Found: C, 59.57; H, 5.04;
N, 12.32%.
d
2.28 (s, 3H, AreCH3), 2.31 (s, 3H, Ar0eCH3), 4.98 (s, 2H,
Compound
NO scavenging (%)
DPPH scavenging (%)
d
4a
4b
4c
5a
5b
5c
6a
6b
6c
7a
7b
7c
63.52
54.33
70.54
66.78
57.19
69.39
25.45
29.39
35.66
22.64
20.26
28.19
96.90
62.27
58.10
69.61
64.71
58.64
70.98
27.80
32.28
34.58
23.82
21.74
29.93
95.37
6.1.1.3. 2-(p-chlorophenylaminosulfonylmethyl)-5-(p-chlorophenyl)-
1,3,4-oxadiazole (4c). White solid (1.34 g, 70%); m.p. 182e184 ꢁC; IR
(KBr): 1320, 1143 (SO2), 1608 (C]N), 3343 (NH) cmꢀ1 1H NMR
;
(DMSO-d6):
d
5.09 (s, 2H, SO2eCH2), 7.23e7.91 (m, 8H, AreH), 10.47
47.8,121.9,122.2,128.8,128.9,
(bs,1H, NH) ppm;13C NMR (DMSO-d6)
d
129.7, 130.2, 136.8, 137.5, 158.5, 164.8 ppm; Anal. Calcd. For
C15H11Cl2N3O3S: C, 46.89; H, 2.89; N, 10.94; Found: C, 46.82; H, 2.93;
N, 10.90%
Ascorbic acid

4250
V. Padmavathi et al. / European Journal of Medicinal Chemistry 45 (2010) 4246e4251
6.1.1.4. 2-phenylaminosulfonylmethyl-5-phenylsulfonylmethyl-1,3,4-
C15H11Cl2N3O2S2: C, 45.01; H, 2.77; N, 10.50; Found: C, 45.09; H,
2.74; N, 10.44%.
oxadiazole (5a). White solid (1.34 g, 68%); m.p. 172e174 ꢁC; IR
(KBr): 1331, 1130 (SO2), 1582 (C]N), 3347 (NH) cmꢀ1 1H NMR
;
(DMSO-d6)
7.18e7.72 (m, 10H, AreH), 10.54 (bs, 1H, NH) ppm; 13C NMR (DMSO-
d6) 54.3, 59.0, 122.8, 129.2, 130.3, 129.8, 130.6, 137.9, 138.7, 139.5,
d
4.08 (s, 2H, SO2eCH2), 4.42 (s, 2H, CH2eSO2),
6.1.2.4. 2-phenylaminosulfonylmethyl-5-phenylsulfonylmethyl-1,3,4-
thiadiazole (7a). White solid (1.49 g, 73%); m.p. 185e187 ꢁC; IR
d
(KBr): 1331, 1133 (SO2), 1583 (C]N), 3346 (NH) cmꢀ1 1H NMR
;
158.5, 160.2 ppm; Anal. Cald. For C16H15N3O5S2; C, 48.84; H, 3.84; N,
10.68; Found: C, 48.91; H, 3.80; N, 10.53%.
(DMSO-d6):
7.22e7.91 (m,10H, AreH),10.56 (bs,1H, NH) ppm; 13C NMR (DMSO-
d6): 53.1, 59.3, 122.3, 127.8, 128.8, 128.1, 130.4, 136.7, 137.6, 138.9,
d 4.03 (s, 2H, SO2eCH2), 4.47 (s, 2H, CH2eSO2),
d
6.1.1.5. 2-(p-methylarylaminosulfonylmethyl-5-(p-methylphenylsul-
fonylmethyl)-1,3,4-oxadiazole (5b). White solid (1.64 g, 78%); m.p.
196e198 ꢁC; IR (KBr): 1334, 1132 (SO2), 1592 (C]N), 3342 (NH)
157.9, 152.9 ppm; Anal. Calcd. For C16H15N3O4S3: C, 46.93; H, 3.69;
N, 10.26: Found: C, 47.03; H, 3.74; N, 10.20%.
cmꢀ1
;
1H NMR (DMSO-d6)
d
2.35 (s, 3H, AreCH3), 2.38 (s, 3H,
Ar0eCH3), 3.98 (s, 2H, SO2eCH2), 4.48 (s, 2H, CH2eSO2), 7.12e7.82
(m, 8H, AreH), 10.48 (bs, 1H, NH) ppm; 13C NMR (DMSO-d6)
23.1,
6.1.2.5. 2-(p-methylphenylaminosulfonylmethyl-5-(p-methylphenyl-
sulfonylmethyl)-1,3,4-oxadiazole (7b). White solid (1.71 g, 78%); m.
p. 216e218 ꢁC; IR (KBr): 1336, 1135 (SO2), 1592 (C]N), 3341 (NH)
d
23.4, 54.1, 59.2, 121.8, 127.8, 129.7, 130.5, 131.8, 136.5, 137.9, 138.7,
157.8, 158.7 ppm; Anal. Calcd. For C18H19N3O5S2: C, 51.29; H, 4.54;
N, 9.97; Found: C, 51.38; H, 4.49; N, 9.94%.
cmꢀ1
;
1H NMR (DMSO-d6):
d
2.27 (s, 3H, AreCH3), 2.30 (s, 3H,
Ar0eCH3), 4.10 (s, 2H, SO2eCH2), 4.52 (s, 2H, CH2eSO2), 7.25e7.95
(m, 8H, AreH), 10.60 (bs, 1H, NH) ppm; 13C NMR (DMSO-d6):
23.5,
d
23.7, 55.3, 60.4, 123.3, 127.9, 129.3, 130.5, 128.8, 137.5, 139.3, 140.2,
158.9, 160.4 ppm; Anal. Calcd. For C18H19N3O4S3: C, 49.41; H, 4.38;
N, 9.60; Found: C, 49.49, H, 4.34, N, 9.68%.
6.1.1.6. 2-(p-chlorophenylaminosulfonylmethyl-5-(p-chlorophenylsul-
fonylmethyl)-1,3,4- oxadiazole (5c). White solid (1.73 g, 75%); m.p.
221e223 ꢁC; IR (KBr): 1336, 1134 (SO2), 1606 (C]N), 3344 (NH)
cmꢀ1
;
1H NMR (DMSO-d6)
d
4.05 (s, 2H, SO2eCH2), 4.45 (s, 2H,
CH2eSO2), 7.27e7.89 (m, 8H, AreH), 10.59 (bs, 1H, NH) ppm; 13C
NMR (DMSO-d6) 54.7, 58.5, 122.5, 128.5, 129.5, 129.7, 130.6,
6.1.2.6. 2-(p-chlorophenylaminosulfonylmethyl-5-(4-chlorophenylsul-
fonylmethyl)-1,3,4-thiadiazole (7c). White solid (1.82 g, 76%); m.p.
238e240 ꢁC; IR (KBr): 1338, 1136 (SO2), 1602 (C]N), 3345 (NH)
d
137.3, 138.5, 139.2, 158.9, 159.4 ppm; Anal. Cacld. For
C16H13Cl2N3O5S2: C, 41.57; H, 2.83; N, 9.07; Found: C, 41.66; H,
2.87; N, 9.15%.
cmꢀ1
;
1H NMR (DMSO-d6):
d
4.06 (s, 2H, SO2eCH2), 4.44 (s, 2H,
CH2eSO2), 7.19e7.88 (m, 8H, AreH), 10.58 (bs, 1H, NH) ppm; 13C
NMR (DMSO-d6): 55.2, 59.2, 123.2, 129.4, 130.1, 130.5, 131.3, 136.8,
d
138.1, 140.5, 160.3, 161.2 ppm; Anal. Calcd. For C16H13Cl2N3O4S3: C,
40.17; H, 2.74; N, 8.78; Found: C, 40.10; H, 2.78; N, 8.86%.
6.1.2. Generalprocedureforthesynthesisofarylaminosulfonylmethyl-
5-aryl-1,3,4-thiadiazole 6aec/arylaminosulfonylmethyl-5-arylsul-
fonylmethyl-1,3,4-thiadiazole 7aec
6.2. Biological assays
In a sealed test tube, a mixture of 4/5 (5 mmol), thiourea
(20 mmol) dissolved in tetrahydrofuran (5 ml) is taken and refluxed
at 120e150 ꢁC in an oil bath for 22e26 h. After the reaction is
completed, it is extracted with dichloromethane. The organic layer
is washed with water, brine solution and dried over anhydrous
Na2SO4. The resultant solid is recrystallized from methanol to get
6aec/7aec.
6.2.1. Compounds
The compounds 4e7 are dissolved in DMSO at different
concentrations of 100, 200 and 800 mg/ml.
6.2.2. Cells
Bacterial strains S. aureus, B. subtilis, E. coli, K. pneumoniae and
fungi F. solani, C. lunata and A. niger were obtained from National
Collection of Industrial Microorganisms (NCIM), National Chemical
Laboratory, Pune, India.
6.1.2.1. 2-phenylaminosulfonylmethyl-5-phenyl-1,3,4-thiadiazole (6a).
White solid (1.16 g, 70%); m.p. 162e164 ꢁC; IR (KBr): 1318, 1140
(SO2), 1580 (C]N), 3339 (NH) cmꢀ1
;
1H NMR (DMSO-d6)
d
5.05
(s, 2H, SO2eCH2), 7.21e7.87 (m, 10H, AreH), 10.42 (bs, 1H, NH)
ppm; 13C NMR (DMSO-d6)
47.4, 121.7, 122.2, 128.5, 129.7, 130.9,
6.2.3. Antibacterial and antifungal assays
d
Preliminary antimicrobial activities of compounds 4e7 are
tested by Agar disc-diffusion method. Sterile filter paper discs
(6 mm diameter) moistened with the test compound solution in
131.5, 137.3, 138.1, 58.3, 164.9 ppm; Anal. Calcd. For
C15H13N3O2S2: C, 54.36; H, 3.95; N, 12.68; Found: C, 54.29; H,
4.00; N, 12.78%.
DMSO of specific concentration 100
mg and 200 mg/disc were
carefully placed on the agar culture plates that had been previously
inoculated separately with the microorganisms. The plates were
incubated at 37 ꢁC and the diameter of the growth inhibition zones
were measured after 24 h in case of bacteria and after 48 h in case of
fungi. All determinations were made in triplicate for each
compound. Average of three independent readings for each
organism was recorded.
6.1.2.2. 2-(p-methylphenylaminosulfonylmethyl-5-(p-methylphenyl)-
1,3,4-thiadiazole (6b). White solid (1.29 g, 72%); m.p. 187e189 ꢁC;
IR (KBr): 1324, 1142 (SO2), 1594 (C]N), 3342 (NH) cmꢀ1 1H NMR
;
(DMSO-d6)
2H, SO2eCH2), 7.25e7.92 (m, 8H, AreH), 10.51 (bs, 1H, NH) ppm;
13C NMR (DMSO-d6)
22.8, 23.2, 47.9, 121.8, 123.5, 127.7, 128.8,
d
2.32 (s, 3H, AreCH3), 2.36 (s, 3H, Ar0eCH3), 5.08 (s,
d
130.1, 130.2, 136.5, 136.9, 158.1, 164.5 ppm; Anal. Calcd. For
C17H17N3O2S2: C, 56.80; H, 4.77; N, 11.69; Found: C, 56.75; H, 4.81;
N, 11.76%.
The MIC values were carried out using microdilution suscepti-
bility method. Chloramphenicol was used as reference antibacterial
agent. Ketoconazole was used as reference antifungal agent. The
test compounds, chloramphenicol and ketoconazole were dis-
6.1.2.3. 2-(p-chlorophenylaminosulfonylmethyl-5-(p-chlorophenyl)-
solved in DMSO at a concentration of 800
dilution of the solution was prepared (400, 200, 100,., 6.25
The microorganism suspensions were inoculated to the corre-
sponding wells. The plates were incubated at 36 ꢁC for 24 and 48 h
for bacteria and fungi, respectively. The minimum inhibitory
concentrations of the compounds represent as the lowest
m
g/ml and two-fold
1,3,4-thiadiazole (6c). White solid (1.50 g, 75%); m.p. 161e163 ꢁC; IR
m
g/ml).
(KBr): 1322, 1144 (SO2), 1603 (C]N), 3344 (NH) cmꢀ1
;
1H NMR
(DMSO-d6):
(bs, 1H, NH) ppm; 13C NMR (DMSO-d6):
129.3, 130.4, 130.7, 136.9, 137.7, 158.7, 165.3 ppm; Anal. Calcd. For
d
5.12 (s, 2H, SO2eCH2), 7.21e7.89 (m, 8H, AreH), 10.52
d
48.3, 121.3, 122.3, 128.9,

V. Padmavathi et al. / European Journal of Medicinal Chemistry 45 (2010) 4246e4251
4251
concentration of each chemical compounds in the tubes with no
Acknowledgements
turbidity (i.e. no growth) of inoculated bacteria/fungi.
The authors are thankful to CSIR, New Delhi, India for the
6.2.4. Antioxidant testing
financial assistance under major research project.
The compounds 4e7 were tested for antioxidant property by
nitric oxide and DPPH methods.
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