Synthesis and in vitro antimicrobial activity of 1,3,4-oxadiazole-2-thiol and its analogs

Article abstract of DOI:10.1002/jhet.2042

The present communication deals with the synthesis of 1,3,4-oxadiazole-2-thiol derivatives containing cyclic secondary amines such as morpholine, N-methyl piperizine, and piperizine. The structural elucidation is based on the spectral data (IR, ¹H NMR, and ¹³C NMR).The newly synthesized compounds were then tested for their antimicrobial activity against a representative panel of micro-organisms such as Bacillus subtilis, Escherichia coli and Candida albicans by using ciprofloxacin and fluconazole as reference drugs for bacteria and fungi, respectively. These synthesized compounds showed moderate to potential antibacterial and antifungal activity in the range of 6-50 μM against the selected bacteria and 12-50 μM against the most common fungi, respectively.

Full text of DOI:10.1002/jhet.2042

Month 2014 Synthesis and In Vitro Antimicrobial Activity of 1,3,4-Oxadiazole-2-thiol
and its Analogs
R. Galge, A. Raju, M. S. Degani, and B. N. Thorat
a
b
b
a
*
aDepartment of Chemical Engineering, Institute of Chemical Technology, Nathalal Parekh Road, Matunga (E), Mumbai,
Maharashta 400019, India
bDepartment of Pharmaceutical Sciences and Technology, Institute of Chemical Technology, Nathalal Parekh Road,
Matunga (E), Mumbai, Maharashta 400019, India
*
E-mail: galgesantosh@gmail.com
Additional Supporting Information may be found in the online version of this article.
Received March 19, 2013
DOI 10.1002/jhet.2042
Published online 00 Month 2014 in Wiley Online Library (wileyonlinelibrary.com).
The present communication deals with the synthesis of 1,3,4-oxadiazole-2-thiol derivatives containing
cyclic secondary amines such as morpholine, N-methyl piperizine, and piperizine. The structural elucidation
1
is based on the spectral data (IR, H NMR, and 13C NMR) .The newly synthesized compounds were then
tested for their antimicrobial activity against a representative panel of micro-organisms such as Bacillus
subtilis, Escherichia coli and Candida albicans by using ciprofloxacin and fluconazole as reference drugs
for bacteria and fungi, respectively. These synthesized compounds showed moderate to potential
antibacterial and antifungal activity in the range of 6–50 mM against the selected bacteria and 12–50 mM
against the most common fungi, respectively.
J. Heterocyclic Chem., 00, 00 (2014).
INTRODUCTION
cyclic amines such as morpholine, N-methyl piperizine,
piperizine, and substituted piperizine. The few drugs
present in market containing 1,3,4-oxadiazole and cyclic
amines are such as raltegravir, furamizole, tiodazosin, and
nesapadil. To the best of our knowledge the synthesis
and antimicrobial activity of synthesized compounds have
not been reported so far in the open literature.
The chemistry of heterocyclic compounds are known to be
useful as a key starting material for their application as active
pharmaceutical ingredients. Amongst them, 1,3,4-oxadiazole
and its derivative are known to be important in the develop-
ment of medicinal chemistry. The heterocyclic compounds
are known to possess a broad spectrum of antimicrobial
activity [1–6]. The 20th century saw a leap jump in the
synthesis and manufacturing of several antimicrobial drugs.
Interestingly, several bacteria have developed resistance
against most of these drugs soon after or even before their
introduction to the market. To overcome some of the issues
related to the antibiotic resistance, there is an urgent need
for the development of new class of antibacterial compounds.
2,5 Disubstituted 1,3,4-oxadiazole are known to exhibit
highly desirable properties such as anticonvulsant [7,8],
analgesic, anti-inflammatory, antiplatelet activity [9–26],
and antitubercular activity [27–32].
RESULTS AND DISCUSSIONS
Chemistry. In this investigation, the starting raw material
1,3,4-oxadiazole-2-thiol was synthesized from a cheap and
readily available 4-chlorobenzoic acid.1,3,4-Oxadiazole-2-
thiol can be synthesized by several methods as reported in
the open literature [33–36]. For the present study, 1,3,4-
oxadiazole-2-thiol (4) was synthesized by the method
described in reference [37]. 1,3,4-Oxadiazole-2-thiol was
then subjected to nitration by a known experimental
procedure of nitration to obtain 5-(4-chloro-3-nitrophenyl)-
1,3,4-oxadiazole-2-thiol [38]. 5-(4-Chloro-3-nitrophenyl)-
1,3,4-oxadiazole-2-thiol (5) was then alkylated using
various alkylating reagents to get thio alkylated products
(6a–d) (Scheme 1). Then the thio alkylated products
(6a–d) were condensed with morpholine, N-methyl
The focus of the present study is the synthesis of novel,
biologically active heterocyclic compounds starting with
1,3,4-oxadiazole-2-thiol and condensing it with cyclic sec-
ondary amines such as morpholine, N-methyl piperizine,
and piperizine. The use of cyclic amine was thought as
there are several active drugs in the market that contains
© 2014 HeteroCorporation

R. Galge, A. Raju, M. S. Degani, and B. N. Thorat
Vol 000
piperizine, and piperizine to obtain (7a–d), (8a–d), and
(9a–d), respectively (Scheme 2). The compounds
synthesized compounds are shown in Table 1, along with
C, H, and N values in percentage.
1
synthesized were confirmed using HNMR, 13C NMR,
Antimicrobial Activity.
The newly synthesized
and elemental analysis. The physical properties of the
compounds (6a–d), (7a–d), (8a–d), and (9a–d) were
screened against gram-positive bacteria (Staphylococcus
aureus), gram-negative bacteria (Escherichia coli), and
fungus (Candida albicans) by using the twofold dilution
technique to determine the actual minimum inhibitory
concentration (MIC) by using resazurin microtiter assay
(REMA) [39]. Ciprofloxacin and Fluconazole were used
as standard drugs against bacteria and fungus,
respectively. The DMSO was used both as a solvent and
as a control. The inhibition zone was not observed in the
control sample (DMSO).
Scheme 1. Reagents and conditions: (i) KOH/EtOH; (ii) reflux 8 h; (iii)
aq. HCl; and (iv) HNO3 + H2SO4, 90–95o C, 4 h; (v) Alkyl halide, K2CO3/
DMF 80–85ꢀC, 4 h.
The series of compounds (6a–d), (7a–7d), (8a–d), and
(9a–d) shown in Table 2, were screened against S. aureus,
E. coli, and C. albicans by using the twofold dilution
technique to determine the actual MIC. MIC is the lowest
concentration at which the complete inhibition of microbial
activity was observed, and it was found by visual inspec-
tion (color change from blue to pink in case of growth).
The minimum inhibitory concentration of ciprofloxacin
was found to be <1 mM against S. aureus and E. coli.
The compounds 7a, 7c, 7d, 8b, 9a, 9c, and 9d have least
antimicrobial activity against all the microbes used,
whereas, the compound 8a possess potential activity
against all the microbes. The compounds 7b, 8d, and 9b
were found to be the most effective against S. aureus with
MIC < 12 mM. In addition, all these compounds showed
better antibacterial activity than antifungal activity.
Scheme 2. Reagents and conditions (i) K2CO3, DMF, morpholine 85–90ꢀC,
4 h; (ii) K2CO3, DMF, N-methyl piperizine, 85–90ꢀC, 4 h; and (iii) K2CO3,
DMF, piperizine, 85–90ꢀC, 4 h.
In conclusion, 1,3,4-oxadiazole derivatives were
successfully synthesized in appreciable yields and screened
Table 1
Physical and analytical data of synthesized compounds.
Elemental analysis a (calculated/found)
Compounds
R
X
Mol. for
mp (ꢀC)
C%
H%
N%
5
–H
Ph–CH2–
—
—
—
—
—
O
O
O
O
C8H4ClN3O3S
C15H10ClN3O3S
C10H8ClN3O3S
C11H10ClN3O3S
C13H14ClN3O3S
C19H18N4O4S
C14H16N4O4S
C15H18N4O4S
C17H22N4O4S
C20H21N5O3S
C15H19N5O3S
C16H21N5O3S
C18H25N5O3S
C19H19N5O3S
C14H17N5O3S
C15H19N5O3S
C17H23N5O3S
179–182
86–89
68–71
65–67
—
67–69
55–58
69–72
—
—
—
—
—
37.29/37.35
51.80/51.71
42.04/42.03
44.08/44.08
47.63/47.59
57.27/57.23
49.9/49.96
51.42/51.38
53.95/53.94
58.38/58.34
51.56/51.55
52.88/52.86
55.22/55.19
57.42/57.39
50.14/50.10
51.56/51.51
54.09/54.05
1.56/1.59
2.90/2.95
2.82/2.87
3.36/3.39
4.30/4.35
4.55/4.57
4.79/4.82
5.18/5.21
5.86/5.91
5.14/5.16
5.48/5.49
5.82/5.86
6.44/6.48
4.82/4.92
5.11/5.15
5.48/5.53
6.14/6.17
16.31/16.35
12.08/12.12
14.71/14.75
14.02/14.10
12.82/12.84
14.06/14.09
16.66/16.69
15.99/16.03
14.80/14.43
17.02/17.08
20.04/20.08
19.27/19.24
17.89/17.91
17.62/17.65
20.88/20.92
20.04/20.07
18.55/18.56
6a
6b
6c
6d
7a
7b
7c
7d
8a
8b
8c
8d
9a
9b
9c
9d
CH3CH2–
(CH3)2CH–
CH3(CH2)4–
Ph–CH2–
CH3CH2–
(CH3)2CH–
CH3(CH2)4–
Ph–CH2–
CH3CH2–
(CH3)2CH–
CH3(CH2)4–
Ph–CH2–
CH3CH2–
(CH3)2CH–
CH3(CH2)4–
–NCH3
–NCH3
–NCH3
–NCH3
–NH
–NH
–NH
–NH
103–105
87–92
135–138
98–101
aElemental analysis value limit = Æ0.4% of the theoretical value.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2014
Synthesis and In Vitro Antimicrobial Activity of
1,3,4-Oxadiazole-2-thiol and its Analogs
Table 2
Synthesized 1,3,4-oxadiazole-2-thiol and its analogs with their minimum inhibitory concentration (MIC) values.
MIC* (mM)
Code
MW
Staphylococcus aureus
Escherichia coli
Candida albicans
6a
6b
6c
6d
7a
7b
7c
7d
8a
8b
8c
8d
9a
9b
9c
9d
347.77
285.70
299.73
327.78
398.45
336.36
350.39
378.44
411.47
349.40
363.43
391.48
397.45
335.38
349.40
377.46
331.4
21.75
35.71
37.46
20.48
49.80
10.51
43.79
47.30
12.85
43.67
11.35
6.11
49.68
11.1
43.67
47.18
<1.0
—
21.75
35.71
37.46
20.48
49.80
42.04
43.79
47.30
12.85
43.67
11.35
48.93
49.68
44.42
43.67
47.18
<1.0
—
21.75
35.71
37.46
20.48
49.80
42.04
43.79
47.30
12.85
43.67
22.71
48.93
49.68
44.42
43.67
47.18
—
Std (ciprofloxacin)
Std (fluconazole)
306.3
0.25
*Compounds were tested against the mentioned micro-organisms using resazurin microtiter assay method.
purification. The benzoate intermediate was then reacted with
Hydrazine hydrate in ethanol at its reflux temperature for 8 h.
Subsequently, the reaction mixture was cooled to room temperature
and 4-chlorobenzohydrazide was filtered by using a Büchner
funnel. The filtrate was diluted with hexane and cooled further to
obtain second crop product. This 4-chlorobenzohydrazide (3) was
used further without any purification. The yield obtained from both
these reactions were quantitative (95%). 4-Chlorobenzohydrazide
(3) was, added to the ethanolic solution containing carbon
disulfide (CS2), and the resulting reaction mixture was refluxed
for 8 h. The reaction was monitored using TLC, which on
completion showed the absence of starting material, and hence it
can be considered as 100% conversion. The reaction mixture was
then cooled to the room temperature and filtered through the
Büchner funnel. The residue cake was acidified with aqueous HCl
solution to obtain the white solid that was again filtered through
the Büchner funnel. The product 1,3,4-oxadiazole-2-thiol was
finally crystallized from ethanol. Yellow solid, mp 171–175ꢀC; IR
(KBr, cmÀ1): 2941(ÀC = C–H), 1610 (C = N); 1H NMR
(300 MHz, CDCl3): d 7.8 (d, 2H, J = 9.06 Hz, Ar–H), 7.5 (d, 2H,
J = 8.3Hz, Ar–H).
in vitro for their antimicrobial activities against both strains
of gram-positive and gram-negative bacteria and also against
a fungus. The enhanced activity may be attributed to the
presence cyclic amines such as morpholine, N-methyl
piperizine piperizine, and various substitutions on the
mercapto group. The importance of such work lies in the
possibility that the new compounds might be more
efficacious drugs against bacteria and fungi, which could
be helpful in designing more potent antibacterial and antifun-
gal agents for therapeutic use. Further evaluation is expected
to open the frontiers in the area of medical chemistry to use
these compounds as new lead in clinical trials.
EXPERIMENTAL
General. All the chemicals used in synthesis were procured
from Sigma Aldrich. All the chemicals used were of analytical
grade. The melting point of the synthesized compounds was
determined by open end capillary method by using apparatus
supplied by local manufacturer. For monitoring the chemical
reactions and the purity of the intermediates and final compounds,
TLC was carried out using Silica gel G coated plates with the
appropriate solvent system of different ratios. The TLC plates
were visualized under ultraviolet light at a wavelength (k) of
254 nm to determine the Rf value. The IR spectrum was recorded
on a Perkin Elmer spectrophotometer by using KBr, cmÀ1 pellets.
5-(4-Chloro-3-nitrophenyl)-1,3,4-oxadiazole-2-thiol (5).
Sulphuric acid 9.80g was added to 6.03g of nitric acid at 0–5ꢀC.
This nitrating mixture was stirred for 10 to 15min then to this
nitrating mixture 10g of 1,3,4-oxadiazole-2-thiol (4) was added
portion wise in 30 min. After the complete addition, the
temperature of the reaction mixture was gradually increased to
90–95ꢀC and maintained for 4 h. The completion of reaction was
confirmed using TLC. The reaction mixture was then cooled to
the room temperature, and it was then poured in the crushed ice
slowly. The off-white solid thus obtained was filtered through the
Büchner funnel, and it was washed with the cold water to obtain
5-(4-chloro-3-nitrophenyl)-1,3,4-oxadiazole-2-thiol (5). Off-white
solid, yield 60%, mp 179–182ꢀC; IR (KBr, cmÀ1): 2562 (ÀSH ),
1
The structures of all the compounds were confirmed by using H
NMR and 13C NMR spectra. (DMSO-d6, CDCl3, and TMS).
1,3,4-Oxadiazole-2-thiol (4). To synthesize 1,3,4-oxadiazole-
2-thiol, 4-chloro benzoic acid was esterified with ethanol in the
presence of H2SO4. The reaction product ethyl 4-chloro benzoate
was confirmed using IR. This ester was used further without any
1
1610 (C = N), 1547(ÀNO2); H NMR (300MHz, CDCl3): d 8.59
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

R. Galge, A. Raju, M. S. Degani, and B. N. Thorat
Vol 000
(d, 1H, J = 1.5 Hz, Ar–H ), 8.2 (dd, 1H J = 1.5 Hz and J = 8.3 Hz,
Ar–H ), 7.7 (d, 1H, J = 8.3 Hz, Ar–H); Anal. Calcd. for
C8H4ClN3O3S: C, 37.29; H, 1.56; N, 16.31. Found: C, 37.35; H,
1.59; N, 16.35.
carried out. If the precipitate was obtained, then it was filtered
through the Büchner funnel, and if there was no precipitate, then
it was extracted with ethyl acetate. The final product was then
purified by column chromatography by using suitable proportions
of Hexane and ethyl acetate.
General procedure for the synthesis of 6(a–d). 5-(4-Chloro-
3-nitrophenyl)-1,3,4-oxadiazole-2-thiol (5) was dissolved in DMF.
To this solution, an equimolar K2CO3 was added. The resulting
solution was stirred for 10 to 15 min and a suitable equimolar
alkyl halide was added to this solution. The resulting reaction
mixture was heated to 80–85ꢀC for 4 h. The reaction mixture was
then cooled to room temperature, and it was then poured in the
crushed ice. Depending upon the nature of reaction product,
further work up was decided. For example, if the precipitate was
obtained, it was filtered through the Büchner funnel, and if there
was no precipitate then it was extracted with ethyl acetate. The
product obtained was used as it is for further reactions. Benzyl
chloride, 1-iodo ethane, 2-bromo propane, and 1-bromo pentane
were used to obtain 6a, 6b, 6c, and 6d, respectively.
2-(Benzylsulfanyl)-5-(4-chloro-3-nitrophenyl)-1,3,4-oxadiazole
(6a). Yellow solid, yield 72%, mp 86–89ꢀC; IR (KBr, cmÀ1):
3099–2961 (Ar–H), 1712 (C = N ), 1534 (ÀNO2); 1H NMR
(300MHz, CDCl3): d 8.6 (d, 1H, Ar–H), 8.2 (dd, 1H Ar–H), 7.7
(d, 1H, Ar–H), 7.5 (m, 5H Ar–H), 2.5 (s, 2H, PhCH2); 13C NMR:
d 182.7, 167.1, 154.1, 152.8, 151.3, 150.9, 149.2, 147.9, 147.7,
145.8, 48.8; Anal. Calcd. for C15H10ClN3O3S: C, 51.80; H, 2.90;
N, 12.08. Found: C, 51.71; H, 2.95; N, 12.12.
4-{4-[5-(Benzylsulfanyl)-1,3,4-oxadiazol-2-yl]-2-nitrophenyl}
morpholine (7a). Yellow solid, yield 78%, mp 67–69ꢀC; IR
(KBr, cmÀ1): 2958–2848 (Ar–H), 1714 (C = N str), 1529
1
(ÀNO2), 1385–1351 (ÀNO2) ; H NMR (300 MHz, CDCl3): d
8.46 (d, 1H, J = 2.26 Hz, Ar–H), 8.01 (dd, 1H, J = 2.26 Hz and
J = 8.3 Hz, Ar–H), 7.4 (m, 5H, Ar–H), 7.1 (d, 1H, J = 9.05 Hz,
Ar–H), 5.35 (s, 2H, PhCH2), 3.85 (apparent t, 4H, –2CH2), 3.15
(apparent t, 4H, –2CH2); 13C NMR: d 164.4, 148.5, 140.6,
135.6, 134.5, 128.6, 128.4, 128.2, 122, 119.2, 67, 66.3,51;
Anal. Calcd. for C19H18N4O4S: C, 57.27; H, 4.55; N, 14.06.
Found: C, 57.23; H, 4.57; N, 14.09.
4-{4-[5-(Ethylsulfanyl)-1,3,4-oxadiazol-2-yl]-2-nitrophenyl}
morpholine (7b). Yellow solid, yield 69%, mp 55–58ꢀC; IR
(KBr, cmÀ1): 2973–2857 (Ar–H), 1716 (C = N ), 1525
1
(ÀNO2), 1383–1330 (ÀNO2); H NMR (300 MHz, CDCl3): d
8.42 (d, 1H, J = 2.26 Hz, Ar–H), 8.1 (dd, 1H, J = 2.26 Hz and
J = 9.06, Ar–H), 7.1 (d, 1H, J = 9.06, Ar–H), 4.4 (q, 2H, CH2),
3.82 (apparent t, 4H, –2CH2), 3.19 (apparent t, 4H, –2CH2), 1.4
(t, 3H, CH3); 13C NMR: d 164.6, 148.4, 140.6, 134.3, 128.2,
122.5, 119.2, 66.3, 61.3, 51,14.2; Anal. Calcd. for C14H16N4O4S:
C, 49.99; H, 4.79; N, 16.66. Found: C, 49.96; H, 4.82; N, 16.69.
4-{2-Nitro-4-[5-(propan-2-ylsulfanyl)-1,3,4-oxadiazol-2-yl]
phenyl}morpholine (7c). Yellow solid, yield 62, mp 69–72ꢀC,
IR (KBr, cmÀ1): 2973–2857 (Ar–H), 1716 (C= N ), 1525 (ÀNO2),
2-(4-Chloro-3-nitrophenyl)-5-(ethylsulfanyl)-1,3,4-oxadiazole
(6b). Yellow solid, yield 71%, mp 68–71ꢀC, IR (KBr, cmÀ1):
3101–2939 (Ar–H), 1713 (C = N), 1534 (ÀNO2), 1387–1357
1
1
1383–1330 (ÀNO2); H NMR (300 MHz, CDCl3): d 8.42 (d, 1H,
(ÀNO2); H NMR (300 MHz, CDCl3): d 8.5 (d, 1H, J = 1.88 Hz,
J = 2.26 Hz, Ar–H), 8.1 (dd, 1H, J = 2.26 Hz and J = 9.06 Hz,
Ar–H), 7.1 (d, 1H, J = 9.06 Hz, Ar–H), 5.22 (m, 1H, –CH), 3.82
(apparent t, 4H, –2CH2), 3.19 (apparent t, 4H, –2CH2), 1.35 (d,
6H, –C(CH3)2); 13C NMR: d 164, 148.3, 140.7, 134.3, 128,
122.9, 119.8, 68.8, 66.3, 51, 21.8; Anal. Calcd. for C15H18N4O4S:
C, 51.42; H, 5.18; N, 15.99. Found: C, 51.38; H, 5.21; N, 16.03.
4-{2-Nitro-4-[5-(pentylsulfanyl)-1,3,4-oxadiazol-2-yl]phenyl}
morpholine (7d). Yellow liquid, yield 67%, IR (KBr, cmÀ1):
2959–2860 (Ar–H), 1715 (C = N), 1528 (ÀNO2), 1346 (ÀNO2);
1H NMR (300MHz, CDCl3): d 8.43 (d, 1H, J = 2.26, Ar–H), 8.1
(dd, 1H, J = 2.26 Hz and J = 9.06 Hz, Ar–H), 7.1 (d, 1H,
J = 9.06 Hz, Ar–H), 4.3 (t, 2H, –S–CH2), 3.85 (apparent t, 4H, –
2CH2), 3.15 (apparent t, 4H, –2CH2), 1.36 (m, 6H, –CH2), 0.9 (t,
3H, CH3); 13C NMR: d 184.1, 167.8, 160.1, 153.8, 147.6, 147.5,
142.6, 138.7, 88.3, 85.8, 84.9, 70.5, 47.5, 41.7, 41.3, 33.3; Anal.
Calcd. for C17H22N4O4S: C, 53.95; H, 5.86; N, 14.80. Found: C,
53.94; H, 5.91; N, 14.43.
Ar–H), 8.2 ( dd, 1H, J = 2.0 Hz and J = 8.4 Hz, Ar–H), 7.6 (d, 1H,
J = 8.3 Hz, Ar–H), 4.4 (q, 2H, –CH2), 1.4 (t, 3H, –CH3); 13C
NMR: d 183.1, 167.3, 152.9, 151.5, 150.8, 149.8, 145.9, 81.5,
33.6; Anal. Calcd. for C10H8ClN3O3S: (%): C, 42.04; H, 2.82; N,
14.71 Found: C, 42.03; H, 2.87; N, 14.75.
2-(4-Chloro-3-nitrophenyl)-5-(propan-2-ylsulfanyl)-1,3,4-
oxadiazole (6c). Pale yellow solid, yield 62%, mp 65–67ꢀC,
IR (KBr, cmÀ1): 3101–2925 (Ar–H), 1709 (C = N), 1533
(ÀNO2), 1387–1357 (ÀNO2); 1HNMR (300 MHz, CDCl3): d
8.4 (d, 1H, J = 2.26, Ar–H), 8.05 (dd, 1H, J = 2.26 Hz and
J=8.3, Ar–H ), 7.06 (d, 1H, J= 8.30, Ar–H), 5.2 (m, 1H,–CH),1.37
(d, 6H,–C(CH3)2); 13C NMR: d 164, 148.3, 140.7, 134.3,
128.0, 122.9, 119.1, 68.8, 21.8; Anal. Calcd. for C11H10ClN3O3S:
C, 44.08; H, 3.36; N, 14.02. Found: C, 44.06; H, 3.39; N,
14.10.
2-(4-Chloro-3-nitrophenyl)-5-(pentylsulfanyl)-1,3,4-oxadiazole
(6d). Yellow liquid, yield 65%, IR (KBr, cmÀ1): 3101–2958
1
General procedure for the synthesis of 8(a–d). 0.5 g of
N-methyl piperizine, equimolar quantity of both K2CO3 and
2-(4-chloro-3-nitrophenyl)-5-(alkylsulfanyl)-1,3,4-oxadiazole
(6a–6d) was dissolved in DMF. This solution was heated to
85–90ꢀC for 4 h. The reaction mass was cooled to the room
temperature, and later it was poured in the crushed ice. This
aqueous solution was then extracted with ethyl acetate thrice. The
organic layer was dried over anhydrous Na2SO4 followed by the
vacuum evaporation. The final products, viz., 8a–8d were then
purified by acid base treatment.
(Ar–H), 1725 (C = N), 1539 (ÀNO2), 1353–1357 (ÀNO2); H
NMR (300 MHz, CDCl3): d 8.5 (d, 1H, J = 1.88Hz, Ar–H), 8.2
(dd, 1H , J = 1.88Hz and J = 8.4 Hz, Ar–H), 7.6 (d, 1H, J = 8.3Hz,
Ar–H), 4.4 (t, 2H,), 1.8 (quintet, 2H, CH2), 1.4(m, 4H (ÀCH2)2),
0.9 (t, 3H, CH3); 13C NMR: d 163.7, 147.8, 133.5, 132.0, 131.4,
130.4, 126.4, 66.2, 28.2, 28.0, 22.2, 13.8; Anal. Calcd. for
C13H14ClN3O3S: C, 47.63; H, 4.30; N, 12.82. Found: C, 47.59;
H, 4.35; N, 12.84.
General procedure for the synthesis of 7(a–d).
0.5 g
of morpholine, equimolar quantity of both K2CO3 and respective
2-(4-chloro-3-nitrophenyl)-5-(alkylsulfanyl)-1,3,4-oxadiazole
(6a–6d) was dissolved in DMF. This solution was heated to
85–90ꢀC for 4 h. The reaction was then cooled to room
temperature, and it was poured in the crushed ice. Depending
upon the nature of the reaction product, further work-up was
1-{4-[5-(Benzylsulfanyl)-1,3,4-oxadiazol-2-yl]phenyl}-4-
methylpiperazine (8a).
Yellow liquid, yield 69%, IR
(KBr, cmÀ1): 2939–2798 (Ar–H), 1713 (C= N ), 1527 (ÀNO2),
1377–1347 (ÀNO2); 1H NMR (300 MHz, CDCl3): d 8.42 (d, 1H,
J = 2.07Hz, Ar–H), 8.1 (dd, 1H, J = 2.07 Hz and J = 8.6 Hz,
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2014
Synthesis and In Vitro Antimicrobial Activity of
1,3,4-Oxadiazole-2-thiol and its Analogs
Ar–H), 7.4 (m, 5H, Ar–H), 7.1 (d, 1H, J = 8.6 Hz, Ar–H), 5.38
(s, 2H, PhCH2), 3.2 (apparent t, 4H, –2CH2), 2.6 (apparent t,
4H, –2CH2), 2.38 (s, 3H, –NCH3); 13C NMR: d 184, 168,
159.7, 155.2, 153.8, 148, 147.9, 147.8, 147.7, 140.8, 138.8,
86.3, 73.9, 70, 65.4; Anal. Calcd. for C20H21N5O3S: C,
58.38; H, 5.14; N, 17.02. Found: C, 58.34; H, 5.16; N,
17.08.
(d, 1H, J = 2.26Hz, Ar–H) , 8.1 (dd, 1H, J = 9.06 Hz and
J = 2.26 Hz, Ar–H), 7.0 (d, 1H, J = 9.06Hz, Ar–H ), 4.37 (q, 2H,
–CH2), 3.8 (apparent t, 4H, –2CH2), 3.1 (apparent t, 4H, –2CH2),
1.39 (t, 3H, –CH3); Anal. Calcd. for C14H17N5O3S: C, 50.14; H,
5.11; N, 20.88. Found: C, 50.10; H, 5.15; N, 20.92.
1-{2-Nitro-4-[4-(propan-2-ylsulfanyl)cyclopenta-1,3-dien-1-yl]
phenyl}piperazine (9c).
Yellow solid, yield 70.5%, mp
135–138ꢀC, IR (KBr, cmÀ1): 3401 (ÀNH), 2987 (aromatic
C–H Str), 1711 (C = N str), 1532 (ÀNO2), 1342 (ÀNO2), 1112
(C–O–C Str), 1H NMR (300 MHz, DMSO-d6): d8.35 (d, 1H,
J = 2.07 Hz, Ar–H), 8.02 (dd, 1H, J = 2.07 Hz and J = 8.6 Hz,
Ar–H), 7.2 (d, 1H, J = 8.6 Hz, Ar–H), 5.2 (m, 1H, –CH), 3.2
(bs, 4H, –2CH2), 2.7 (bs, 4H, –2CH2), 1.4 (d, 6H, –(CH3)2);
Anal. Calcd. for C15H19N5O3S: C, 51.56; H, 5.48; N, 20.04.
Found: C, 51.51; H, 5.53; N, 20.07.
1-{4-[5-(Ethylsulfanyl)-1,3,4-oxadiazol-2-yl]phenyl}-4-
methylpiperazine (8b).
Yellow liquid, yield 62%, IR
(KBr, cmÀ1): 2940–2842 (Ar–H), 1729 (C = N), 1528 (ÀNO2),
1386–1348 (ÀNO2) ; 1H NMR ( 300MHz, CDCl3): d 8.42
(d, 1H, J = 1.8 Hz, Ar–H), 8.1 (dd, 1H, J = 1.8 Hz and J = 8.6 Hz,
Ar–H), 7.1 (d, 1H, J = 8.6 Hz, Ar–H ), 4.38 (q, 2H, –CH2), 3.2
(apparent t, 4H, –2CH2), 2.6 (apparent t, 4H, –2CH2), 2.35 (s, 3H,
–NCH3), 1.4 (t, 3H, –CH3); 13C NMR: d 164.5, 148.3, 140.1,
134.1, 128.1, 121.6, 119.2, 61, 54.3, 50.4, 45.8, 14.1; Anal.
Calcd. for C15H19N5O3S: C, 51.56; H, 5.48; N, 20.04. Found: C,
1-{4-[4-(pentylsulfanyl)cyclopenta-1,3-dien-1-yl]-2-nitrophenyl}
piperazine (9d).
Yellow solid, yield 72%, mp 98–101ꢀC; IR
(KBr,cmÀ1): 3401(ÀNH ), 2987 (Ar–H), 1711 (C = N) , 1532
(ÀNO2), 1342 (ÀNO2), 1H NMR (300 MHz, DMSO-d6): d8.4
(s, 1H, Ar–H), 8.1 (d,1H, J= 8.6 Hz, Ar-H), 7.2 (d, 1H, J=8.6Hz,
Ar–H), 4.3 (t, 2H), 3.5 (m, 4H, –2CH2), 3.2 (m, 4H, –2CH2), 1.8
(t, 2H, –CH2), 1.4 (m, 4H, –2CH2), 0.9 (t, 3H, –CH3); Anal. Calcd.
for C17H23N5O3S: C, 54.09; H, 6.14; N, 18.55. Found: C, 54.05;
H, 6.17; N, 18.56.
51.55; H, 5.49; N, 20.08.
1-Methyl-4-{4-[5-(propan-2-ylsulfanyl)-1,3,4-oxadiazol-2-yl]
phenyl}piperazine (8c).
Yellow liquid, yield 59%, IR
(KBr, cmÀ1): 2979–2798 (Ar–H), 1708 (C = N), 1528 (ÀNO2),
1
1375–1348 (ÀNO2); H NMR (300 MHz, CDCl3): d 8.4 (d, 1H,
J = 2.2 Hz, Ar–H ), 8.1 (dd, 1H, J = 2.2 Hz and J = 8.3 Hz, Ar–H),
7.1 (d, 1H, J = 8.3 Hz, Ar–H) , 5.2 (septet, 1H, –CH), 3.2
(apparent t, 4H, –2CH2), 2.6 (apparent t, 4H, –2CH2), 2.39 (s, 3H,
–NCH3), 1.39 (d, 6H, –(CH3)2); 13C NMR: d 164.1, 148.3, 140.3,
134.1, 128, 122.2, 119.2, 68.7, 54.4, 50.6, 45.8, 21.8; Anal.
Calcd. for C16H21N5O3S: C, 52.88; H, 5.82; N, 19.27. Found: C,
52.86; H, 5.86; N, 19.24.
Acknowledgments. One of the authors is thankful to University
Grand Commission Special Assistance Programme for providing
financial support in the form of Senior Research fellowship.
We also thank the staff of Sophisticated Analytical Instrument
Facility, Indian Institute of Technology, Bombay for their
analytical support.
1-Methyl-4-{4-[5-(pentylsulfanyl)-1,3,4-oxadiazol-2-yl]
phenyl}piperazine (8d).
Yellow liquid, yield 64%, IR (KBr,
cmÀ1): 2959–2860 (Ar–H), 1715 (C= N), 1528 (ÀNO2),1346
(ÀNO2); 1H NMR (300 MHz, CDCl3): d 8.4(d, 1H, J=1.8Hz,
Ar–H ), 8.1(dd, 1H, J=1.8Hz and J=8.6 Hz, Ar–H), 7.1 (d, 1H,
J=8.6 Hz, Ar–H ), 4.3 (t, 2H, –CH2), 3.2 (apparent t, 4H, –2CH2),
2.6 (apparent t, 4H, –2CH2), 2.35 (s, 3H, –NCH3), 1.8 (t, 3H, –
CH3), 1.4 (m, 4H, (ÀCH2)2), 0.9 (t, 3H, –CH3); 13C NMR:
d164.6, 148.3, 140.2, 134.1, 128.1, 121.7, 119.3, 65.2, 54.4,
50.5, 45.8, 28.2, 28, 22.2,13.8; Anal. Calcd. for C19H19N5O3S:
C, 57.42; H, 4.82; N, 17.62. Found: C, 57.39; H, 4.92; N, 17.65.
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General procedure for the synthesis of 9(a–d).
0.5 g
of piperizine, equimolar quantity of both K2CO3 and respective
2-(4-chloro-3-nitrophenyl)-5-(alkylsulfanyl)-1,3,4-oxadiazole
(6a–6d) was dissolved in DMF. This solution was heated to 85–90
ꢀC for 4 h. The reaction mass was cooled to the room temperature,
and later it was poured in the crushed ice. The precipitate obtained
was filtered through the Büchner funnel, and it was then purified
through column chromatography by using suitable proportions of
dichloromethane and methanol.
1-{4-[4-(Benzylsulfanyl)cyclopenta-1,3-dien-1-yl]-2-nitrophenyl}
piperazine (9a). Yellow solid, yield 67.7%, mp 103–105ꢀC, IR
(KBr, cmÀ1): 3441(ÀNH), 2930–2881 (Ar–H), 1711 (C = N),
1
1527 (ÀNO2),1338 (ÀNO2); H NMR (300 MHz, DMSO-d6): d
8.46 (d, 1H, J = 2.26 Hz, Ar–H), 8.1(dd, 1H, J = 2.26Hz and
J = 9.06Hz, Ar–H), 7.4 (m, 5H, Ar–H), 7.06 (d, 1H, J = 9.06Hz,
Ar–H), 5.3 (s, 2H, PhCH2), 3.8 (apparent t, 4H, –2CH2), 3.1
(apparent t, 4H, –2CH2); Anal. Calcd. for C19H19N5O3S: C,
57.42; H, 4.82; N, 17.62. Found: C, 57.39; H, 4.92; N, 17.65.
1-{4-[4-(Ethylsulfanyl)cyclopenta-1,3-dien-1-yl]-2-nitrophenyl}
piperazine (9b).
Yellow solid, yield 67.7%, mp 87–92ꢀC, IR
(KBr, cmÀ1): 3401(ÀNH), 2987 (Ar–H), 1711 (C= N), 1532
1
(ÀNO2), 1342 (ÀNO2); H NMR (300MHz, DMSO-d6): d 8.4
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

R. Galge, A. Raju, M. S. Degani, and B. N. Thorat
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