Multicomponent synthesis of novel 2-aryl-5-((1-aryl-1H-1,2,3-triazol-4-yl) methylthio)-1,3,4-oxadiazoles using CuI as Catalyst and their antimicrobial evaluation

Article abstract of DOI:10.1071/CH13082

A series of novel 2-aryl-5-((1-aryl-1H-1,2,3-triazol-4-yl)methylthio)-1,3, 4-oxadiazoles have been synthesised by C-S bond formation and azide-alkyne cyclocondensation between [5-(aryl)-[1,3,4]oxadiazol-2-yl]methanethiol, propargyl bromide, and substituted aryl azides in one pot with an aim to explore their effect on the in vitro growth of microorganisms causing microbial infection. In vitro antibacterial activity was determined against four strains, namely Staphylococcus aureus, Bacillus subtilis, Escherichia coli, and Pseudomonas aeruginosa and antifungal activity against two fungal strains, namely Aspergillus niger and Aspergillus flavus.

Full text of DOI:10.1071/CH13082

CSIRO PUBLISHING
Aust. J. Chem.
Full Paper
http://dx.doi.org/10.1071/CH13082
Multicomponent Synthesis of Novel 2-Aryl-5-((1-aryl-1H-
1,2,3-triazol-4-yl)methylthio)-1,3,4-oxadiazoles using
CuI as Catalyst and their Antimicrobial Evaluation
A
A
A C
,
Jayant Sindhu, Harjinder Singh, Jitender Mohan Khurana,
B
B
Chetan Sharma, and Kamal Rai Aneja
A
Department of Chemistry, Delhi University, Delhi 110007, India.
Department of Microbiology, Kurukshetra University Kurukshetra,
Kurukshetra 136119, Haryana, India.
B
C
Corresponding author. Email: jmkhurana@chemistry.du.ac.in
A series of novel 2-aryl-5-((1-aryl-1H-1,2,3-triazol-4-yl)methylthio)-1,3,4-oxadiazoles have been synthesised by C–S
bond formation and azide–alkyne cyclocondensation between [5-(aryl)-[1,3,4]oxadiazol-2-yl]methanethiol, propargyl
bromide, and substituted aryl azides in one pot with an aim to explore their effect on the in vitro growth of microorganisms
causing microbial infection. In vitro antibacterial activity was determined against four strains, namely Staphylococcus
aureus, Bacillus subtilis, Escherichia coli, and Pseudomonas aeruginosa and antifungal activity against two fungal strains,
namely Aspergillus niger and Aspergillus flavus.
Manuscript received: 19 February 2013.
Manuscript accepted: 2 April 2013.
Published online: 27 May 2013.
Introduction
activity by participating in hydrogen-bonding interactions with
receptors.[11] Substituted 1,3,4-oxadiazoles have been found to
exhibit anti-inflammatory,[12–15] hypoglycemic,[16,17] antianxi-
ety, antidepressant,[18] and antimitotic[19] activities. In addition
to these, several researchers have also reported antimicrobial
activities of 1,3,4-oxadiazoles.[20–24] 1,2,3-Triazoles are also
important pharmacologically due to their latent ability for the
formation of hydrogen bonds with other active molecules. 1,2,3-
Triazoles exhibit antitumour,[25] anti-HIV,[26,27] cytostatic,[28]
and anti-bacterial[29] activities. They can also act as gamma-
aminobutyric acid[30] and glycosidase inhibitors.[31] This
heterocycle has been compared with amide bonds and may
serve as a bioisoster of peptide bonds due its electronic
features.[32,33] Some of the lead compounds having oxadiazole
and triazole moieties (i, ii, and iii) acting as antifungal agents are
shown in Fig. 1.[34]
It has also been reported that sulfur is an important bridge for
combining two heterocyclic moieties covalently in a single
compound.[35] It was believed from a literature survey that
oxadiazoles having aryl, alkyl, and one or more methylene
groups as a linker exhibit different biological activities like
anticancer, anti-inflammatory, and antimicrobial activities
by playing an important role in their penetration into the
microbial cell.[36,37] Based on the abovementioned observa-
tions, we decided to develop a new approach for the synthesis
of novel 2-aryl-5-((1-aryl-1H-1,2,3-triazol-4-yl)methylthio)-
1,3,4-oxadiazoles by C–S bond formation and an azide–alkyne
cycloaddition reaction in one pot and to study their antimicro-
bial activity on different pathogen strains.
The resistance of many microbial organisms, particularly Gram-
positive bacteria Staphylococcus aureus and species of the genus
Enterococcus, towards anti-microbial agents has increased.[1]
Microbes have developed resistance against many existing
agents and therefore focus has been on the development of
alternative new more effective antimicrobial agents with novel
modes of action and a broad spectrum of activities. Molecular
hybridisation is the approach of designing new chemical entities
based on the fusion/coupling of two heterocyclic rings in a single
compound wherein both active compounds/units are derived
from known bioactive molecules.[2] Pharmacophore hybridisa-
tion is believed to be analogous to conventional combination
therapy, with the exception that the two drugs are covalently
linked and available as a single entity.[3]
The multicomponent reaction (MCR) approach offers major
advantages such as atom economy, introduction of structural
complexity and diversity, and high efficiency, etc, over conven-
tional linear-type syntheses and have played an important role in
modern drug discovery.[4–6] Similarly click chemistry has also
played a very significant role in drug discovery, because alkyne
and azide components can be incorporated into a wide range of
substrates.[7] The combination of MCR with click reactions has
been shown to be a powerful strategy to yield complex structures
in a single step.[8,9]
1,3,4-Oxadiazoles have been established as a privileged
structure class.[10] Oxadiazoles occur frequently in drug-like
molecules and act as bioisosteric replacements for ester and
amide functionalities thus enhancing the pharmacological
Journal compilation Ó CSIRO 2013
www.publish.csiro.au/journals/ajc

B
J. Sindhu et al.
O
N
N
N
N
N
O
N
N
N
N
N
N
N
N
N
N
N
N
S
SR
O
N
N
R
N
i
R
iii
ii
Fig. 1. Some of the lead compounds having antimicrobial activity.
N3
N
N
3a
Br
S
O
OMe
2a
K2CO3,
MeO
.
CuSO4 5H2O,
DMF, 60ЊC, 2h
Path Ia
Sodium ascorbate,
THF/water (70:30, v/v),
60Њ
C, 4h
Path Ib
Br
N
N
N
N
OMe
N
S
O
.
SH
K2CO3, CuSO4 5H2O
Sodium ascorbate,
N
MeO
N
O
1a
DMF, 60
Њ
C,15 min
5a
N3
MeO
3a
Br
OMe
.
K2CO3, CuSO4 5H2O, Sodium ascorbate,
DMF, 60 C, 35 min
Path II
Њ
Scheme 1. Synthesis of 2-(4-methoxyphenyl)-5-((1-(4-methoxyphenyl)-1H-1,2,3-triazol-4-yl)methylthio)-1,3,4-oxadiazole (5a) by different paths.
Results and Discussion
the reaction of 1a (2.2 mmol) and propargyl bromide (2.8 mmol)
in the presence of K2CO3 (3.3 mmol) in DMF (10 mL) at 608C.
After 2 h, the reaction was found to be complete. The solid so
obtained was filtered and recrystallised from ethanol to afford
pure product which was identified as 2-(4-methoxyphenyl)-5-
(prop-2-ynylthio)-1,3,4-oxadiazole (2a) (90 % yield). Subse-
quently the intermediate compound 2a (1.2 mmol) was reacted
with 1-azido-4-methoxybenzene (3a) (1.2 mmol) in THF/water
(70 : 30, v/v) in a round-bottomed flask at 608C in the presence
of an aqueous solution of CuSO4ꢀ5H2O (10 mol-%) and sodium
ascorbate (20 mol-%). The reaction was complete after 4 h as
monitored by TLC using ethyl acetate/hexane (70 : 30, v/v) as
eluent. A crude mass was obtained after work up which was
purified by flash chromatography to yield the desired 5a as a
white solid in 85 % yield and an overall yield of 77 % (path Ia).
The reaction of 1a and propargyl bromide was also carried
out using K2CO3 (3.3 mmol), CuSO4ꢀ5H2O (10 mol-%), and
sodium ascorbate (20 mol-%) as catalyst at 608C. The reaction
time improved significantly from 2 h to 15 min and the yield of
the product also increased from 90 to 95 % (path Ib). The same
reaction was also attempted in the presence of CuSO4ꢀ5H2O
Chemistry
The present manuscript reports the synthesis of targeted 2-aryl-
5-((1-aryl-1H-1,2,3-triazol-4-yl)methylthio)-1,3,4-oxadiazoles
5a–m, by a one-pot three-component approach using 5-aryl-
1,3,4-oxadiazole-2-thiols 1, substituted phenyl azides 3, and
propargyl bromide, which involves an azide–alkyne cyclo-
addition reaction and C–S bond formation in the presence of
CuSO4ꢀ5H2O, sodium ascorbate, and K2CO3 in DMF at 608C.
The starting molecules 5-aryl-1,3,4-oxadiazole-2-thiols 1 and
substituted phenyl azides 3 were prepared from substituted
benzoic acid and substituted amines, respectively, by the
reported procedures.[38]
The synthesis of compounds 5a–m can be achieved by
different paths as shown in Scheme 1. The reaction of 5-(4-
methoxyphenyl)-1,3,4-oxadiazole-2-thiol (1a), propargyl bro-
mide, and 1-azido-4-methoxybenzene (3a) was attempted by
two different paths summarised in Scheme 1. First, we attempted
the synthesis of targeted compound 2-(4-methoxyphenyl)-5-((1-
(4-methoxyphenyl)-1H-1,2,3-triazol-4-yl)methylthio)-1,3,4-
oxadiazole (5a) by sequential reactions. The first path involved

Synthesis and Antimicrobial Evaluation of Triazole
C
SH Br
N
N
O
N
O
N
N3
R1
N
N
N
K2CO3 (1.5 equiv.), CuSO4 (10 mol-%),
Na ascorbate (20 mol-%),
S
R2
R4
DMF, 60ЊC, 35–45 min
R2
R3
R3
R1
R4
1
3
5a–m
Scheme 2. Synthesis of compounds 5a–m.
Table 2. Physical data of the synthesised compounds 5a m
]
Table 1. Optimisations of reaction conditions for the synthesis
2-(4-methoxyphenyl)-5-((1-(4-methoxyphenyl)-1H-1,2,3-triazol-4-yl)
methylthio)-1,3,4-oxadiazole (5a)
Compound
R1
R2
R3
R4
Time [min]
Yield [%]
5a
5b
5c
5d
5e
5f
OMe
OMe
H
H
H
H
H
H
H
H
H
H
H
H
Cl
H
OMe
H
H
H
Cl
H
Cl
H
H
Cl
H
Cl
H
H
H
35
37
42
40
38
40
35
42
40
38
35
38
45
94
90
84
88
86
88
92
81
80
90
87
83
79
Entry
Solvent
Time [min]
Temp [8C]
Yield [%]
F
1
2
3
4
5
6
7
8
DMF
35
80
60
30
80
60
60
60
60
60
94
H
Br
DMF
78
OMe
OMe
OMe
H
F
DMF
35
89
Ethanol
t-BuOH
THF
THF/waterB
t-BuOH/waterB
160
120
75
48A
54A
70
F
5g
5h
5i
Me
H
H
F
90
60
38A
5j
OMe
H
H
190
5k
5l
OMe
OMe
NO2
AIncomplete reaction.
B(70 : 30, v/v).
H
5m
OMe
(10 mol-%) and sodium ascorbate (20 mol-%) but in the absence
of K2CO3. This reaction required 60 min for completion. CuI
polarises the C–Br bond which makes the carbon more suscep-
tible to attack by thiol thus increasing the rate of reaction.
Therefore, keeping in mind the role of CuI in both azide–
alkyne cycloaddition reactions and also in catalysing C–S bond
formation, we decided to attempt both steps in one pot. The
reaction of 1a (1.2 mmol), propargyl bromide (1.2 mmol), and
3a (1.2 mmol) was carried out in DMF in the presence of K2CO3
(1.8 mmol), CuSO4ꢀ5H2O (10 mol-%), and sodium ascorbate
(20 mol-%) at 308C. The reaction was found to be complete after
80 min. The reaction mixture was poured onto crushed ice. The
solid so obtained was filtered and purified by flash chromato-
graphy to give the target compound 5a in 78 % yield. The
reaction was then repeated at 608C under otherwise similar
conditions in DMF. The reaction was found to be complete in
35 min and the desired compound 5a was obtained in 94 % yield
(path II) (Scheme 2).
Thus path II was found to be the most efficient as the isolation
of intermediate compounds formed during reaction and their
purification is not required. It also helps to increase the overall
yield of the product. By using CuI as a common catalyst in both
sequential steps, a multicomponent approach was developed for
the synthesis of S-tethered 1H-[1,2,3]-triazoles. This approach
utilises the well known catalytic activities of CuI in both click
chemistry and C–S bond formation. Therefore, this strategy can
be adopted as a general path for the synthesis of a series of 1,2,3-
triazoles. A focussed library of 13 compounds, 2-aryl-5-((1-
aryl-1H-1,2,3-triazol-4-yl)methylthio)-1,3,4-oxadiazoles 5a–m,
were synthesised (Table 2). All the novel compounds were
characterised by 1H NMR, 13C NMR, and IR spectroscopy and
electrospray ionisation (ESI) and high resolution mass spectro-
metry (HRMS). The formation of the triazole ring was confirmed
by the resonance of H-5 of the triazole ring in the aromatic region
in the 1H NMR spectra. The structures were further supported by
the 13C NMR spectra, which confirmed the C-skeleton of the
triazole derivatives 5a–m. ESI-MS/HRMS of all compounds
showed [M þ Na]þ, [Mþ], or [Mþ H]þ. All these compounds
were then screened for their anti-bacterial and anti-fungal
activity.
No improvement in the reaction time and product yield was
observed at higher temperatures. The reaction was also
attempted in ethanol, t-BuOH, THF, THF/water (70 : 30, v/v),
and t-BuOH/water (70 : 30, v/v) at 608C but the best results were
obtained in DMF at 608C as mentioned in Table 1.
A complete spectroscopic study (1H NMR, 13C NMR, and IR
spectroscopy and mass spectrometry) of the product 5a con-
firmed the formation of the expected 2-(4-methoxyphenyl)-
5-((1-(4-methoxyphenyl)-1H-1,2,3-triazol-4-yl)methylthio)-
1,3,4-oxadiazole (Scheme 2) only. A careful examination of the
1H NMR spectrum of 5a showed a singlet at d 8.12 for 1 proton
present at the C-5 carbon of the triazole ring. This higher value
justifies the substitution of the aryl group on N-1. Similarly a
singlet at d 4.62 confirms the presence of a S–CH2 group apart
from other characteristics signals (see Supplementary Material).
Biological Results and Discussion
In Vitro Antibacterial Activity
A total of 13 chemical compounds were screened for their
antibacterial and antifungal activity. The tested chemical com-
pounds possessed variable antibacterial activity against Gram-
positive (Staphylococcus aureus and Bacillus subtilis) bacteria.
However, they did not exhibit any activity against Gram-
negative (Escherichia coli and Pseudomonas aeruginosa)

D
J. Sindhu et al.
bacteria. Positive controls produced significantly sized inhibi-
tion zones against the tested bacteria and fungi. However,
negative controls did not show an observable inhibitory effect
against any of the test organisms as shown in Table 3.
Four compounds, 5b, 5f, 5j, and 5m were found to be best as they
exhibited the lowest MIC of 128 mg mLꢁ1 against S. aureus
whereas three compounds, 5b, 5f, and 5m were found to be best
against B. subtilis with the lowest MIC of 64 mg mLꢁ1 (Table 4,
Fig. 3).
The tested chemical compounds showed a zone of inhibition
ranging between 13.6 and 18.6 mm against the Gram-positive
bacteria. On the basis of the zone of inhibition produced against
the test bacterium, three compounds, namely, 5b, 5f, and 5m
were found to be most active against S. aureus and B.subtilis
with a zone of inhibition of 16.3 and 18.6 mm, respectively.
However other tested compounds showed moderate anti-
bacterial activity (Table 3, Fig. 2). The minimum inhibitory
concentration (MIC) of all compounds 5a–m was measured
against Gram-positive bacteria, as shown in Table 4. In the
whole series, the MIC of the chemical compounds ranged
between 64 and 512 mg mLꢁ1 against Gram-positive bacteria.
Antifungal Activity
All the 13 compounds 5a–m were also tested for their in vitro
antifungal activity against two fungal strains, namely, A. niger
and A. flavus species through poisoned food method. The
standard drug fluconazole was used for comparison of the
antifungal activity shown by the compounds and results were
recorded as a percentage of mycelial growth inhibition. It can be
inferred from Table 5 that all the compounds 5a–m showed
variable antifungal activity against the two pathogens. From a
careful comparison of the results, it is observed that three
compounds, namely 5l, 5f, and 5m showed high antifungal
activity with .50 % inhibition of mycelial growth against
the two fungi in comparison with the standard drug. Other
Table 3. Antibacterial activity of chemical compounds 5a m through
]
agar well diffusion method
Compound
Diameter of growth of inhibition zone [mm]A
Table 4. Minimum inhibitory concentration (MIC) of compounds
Staphylococcus
Bacillus
subtilise
Escherichia Pseudomonas
coliB
5a m
]
aureus
aeruginosaB
5a
14.6
16.3
14.3
13.6
14.3
15.6
13.6
14.3
14.6
15.3
14.3
13.6
16.3
26.6
15.3
18.6
14.6
15.3
15.0
18.3
14.3
15.6
15.3
15.6
14.6
14.3
18.6
24.0
–
–
–
–
Compound
MIC [mg mLꢁ1
]
5b
Staphylococcus aureus
Bacillus subtilis
5c
–
–
5d
–
–
5a
256
128
256
512
256
128
512
256
256
128
256
512
128
6.25
128
64
5e
–
–
5b
5f
–
–
5c
256
128
128
64
5g
–
–
5d
5h
–
–
5e
5i
–
–
5f
5j
–
–
5g
256
128
128
128
256
256
64
5k
–
–
5h
5l
–
–
5i
5m
–
–
5j
Ciprofloxacin
25.0
22.0
5k
5l
AValues, including diameter of the well (8 mm), are means of three
5m
replicates.
BNo activity.
Ciprofloxacin
6.25
30
Staphylococcus aureus
Bacillus subtilis
Pseudomonas aeruginosa
Escherichia coli
25
20
15
10
5
0
Compounds/Antibiotic
Fig. 2. Comparisons of diameter of growth of inhibition zone (mm) of compounds 5a–m with the standard
drug ciprofloxacin. Superscript a represents the zone of inhibition, also including the diameter of the well
(8 mm).

Synthesis and Antimicrobial Evaluation of Triazole
E
compounds also showed good antifungal activities as sum-
marised in Table 5. Comparisons of antifungal activity of all the
synthesised compounds with the reference drug in terms of
percentage mycelial growth inhibition are also shown in Fig. 4.
Among all the tested chemical compounds, compound 5m
showed good antibacterial and antifungal activity and this will
be explored further.
was stirred at 608C on a magnetic stirrer for an appropriate time
as shown in Table 2. The progress of the reaction was monitored
by TLC using ethyl acetate/petroleum ether (70 : 30, v/v) as
eluent. After completion of the reaction, the reaction mixture
was poured into a beaker containing crushed ice. The precipitate
formed was collected by vacuum filtration. The solid obtained
was purified by flash column chromatography using silica gel
(230–400 mesh size).
Conclusion
In conclusion, the present study offers an application of CuI in an
efficient and convenient synthesis of 2-aryl-5-((1-aryl-1H-
1,2,3-triazol-4-yl)methylthio)-1,3,4-oxadiazoles 5a–m. Bio-
logical evaluation of these compounds shows that some of the
compounds possess good antimicrobial activity.
Spectroscopic Data
2-(4-Methoxyphenyl)-5-((1-(4-methoxyphenyl)-1H-
1,2,3-triazol-4-yl)methylthio)-1,3,4-oxadiazole (5a)
White solid. Mp 1638C. nmax (KBr)/cmꢁ1 3124, 2994, 1610,
1516, 1475, 1260. dH (400 MHz, CDCl3) 8.12 (s, 1H, Ar-H),
7.90–7.88 (m, 2H, Ar-H), 7.58–7.56 (m, 2H, Ar-H), 6.97–6.94
(m, 4H, Ar-H), 4.62 (s, 2H, S–CH2), 3.84 (s, 3H, OMe), 3.83 (s,
3H, OMe). dc (100 MHz, CDCl3) 166.1, 163.1, 162.3, 159.8,
143.5, 130.2, 128.4, 122.2, 121.7, 115.9, 114.6, 114.4, 55.6,
55.4, 26.8. m/z (ESI) 395.1050 [M þ H]þ.
Experimental
Chemistry
Structures of all of the compounds were identified by their
spectroscopic data. Silica gel 60 F254 (precoated aluminum
plates) from Merck were used to monitor the reaction progress.
Melting points were determined on a melting point apparatus
and are uncorrected. IR (KBr) spectra were recorded on a
Perkin–Elmer FTIR spectrophotometer and the values are
expressed as nmax in cmꢁ1. The NMR (1H and 13C) spectra were
recorded on a Jeol JNM ECX-400P at 400 and 100 MHz,
respectively. The chemical shift values are recorded on the d
scale and the coupling constants (J) are in Hertz. Mass spectra
were recorded on a Bruker Micro TOF Q–II.
2-(4-Methoxyphenyl)-5-((1-phenyl-1H-1,2,3-triazol-
4-yl)methylthio)-1,3,4-oxadiazole (5b)
White solid. Mp 1228C. nmax (KBr)/cmꢁ1 3134, 2934, 1613,
1504, 1481, 1258. dH (400 MHz, CDCl3) 8.21 (s, 1H, Ar-H),
Table 5. Antifungal activity of compounds 5a m through poisoned
]
food method
Compound
Mycelial growth inhibition [%]
Characterisation of Compounds 1
Aspergillus niger
Aspergillus flavus
5-(4-Methoxy-phenyl)-[1,3,4]oxadiazole-2-thiol (1a): mp
2028C (lit.[39] 2048C).
5a
41.1
45.5
37.7
33.3
38.8
47.7
33.3
42.2
36.6
43.3
35.5
46.6
51.1
81.1
44.4
48.8
42.2
35.5
41.1
52.2
38.8
45.5
38.8
47.7
41.1
48.8
53.3
77.7
5-Phenyl-[1,3,4]oxadiazole-2-thiol (1b): mp 2168C (lit.[40]
217–2198C).
5b
5c
5d
5-(3-Chloro-phenyl)-[1,3,4]oxadiazole-2-thiol (1c): mp
1638C (lit.[40] 1618C).
5e
5f
5g
General Procedure for the Synthesis of Compounds 5a–m
5h
5i
A mixture of 1b (1.0 mmol), propargyl bromide (1.0 mmol),
substituted phenyl azide (1.0 mmol), and K2CO3 (1.5 mmol)
was dissolved in DMF (10 mL) in a 50 mL round-bottomed
flask. An aqueous solution of CuSO4ꢀ5H2O (10 mol-%) was
added to the above mixture, followed by addition of an aqueous
solution of sodium ascorbate (20 mol-%). The reaction mixture
5j
5k
5l
5m
Fluconazole
600
Staphylococcus aureus
Bacillus subtilis
500
400
300
200
100
0
Compounds/Antibiotic
Fig. 3. Comparison of minimum inhibitory concentration of the compounds 5a–m.

F
J. Sindhu et al.
90
80
Aspergillus flavus
Aspergillus niger
70
60
50
40
30
20
10
0
Compounds/Antifungal
Fig. 4. Graphical representation of antifungal activity of compounds 5a–m with the standard drug
fluconazole.
7.90–7.88 (m, 2H, Ar-H), 7.69–7.67 (m, 2H, Ar-H), 7.49–7.39
(m, 3H, Ar-H), 6.96–6.94 (m, 3H, Ar-H), 4.64 (s, 2H, S–CH2),
3.83 (s, 3H, OMe). dc (100 MHz, CDCl3) 166.1, 163.8, 159.8,
143.5, 131.7, 130.2, 129.0, 126.6, 123.3, 122.2, 121.7, 114.6,
55.5, 26.8. m/z (ESI) 366.1298 [M þ H]þ.
7.19–7.15 (m, 2H, Ar-H), 6.97–6.95 (m, 2H, Ar-H), 4.63 (s, 2H,
S–CH2), 3.84 (s, 3H, OMe). dc (100 MHz, CDCl3) 166.1, 163.0,
162.3, 143.9, 128.4, 128.4, 122.6, 122.5, 121.9, 114.6, 114.3,
54.9, 26.6. m/z (ESI) 384.1173 [M þ H]þ.
2-(4-Methoxyphenyl)-5-((1-p-tolyl-1H-1,2,3-triazol-
4-yl)methylthio)-1,3,4-oxadiazole (5g)
2-((1-(3-Chloro-4-fluorophenyl)-1H-1,2,3-triazol-4-yl)
methylthio)-5-phenyl-1,3,4-oxadiazole (5c)
Off-white solid. Mp 1428C. nmax (KBr)/cmꢁ1 3137, 2924,
1611, 1501, 1481, 1254, 1167, 1033. dH (400 MHz, CDCl3) 8.16
(s, 1H, Ar-H), 7.89–7.87 (m, 2H, Ar-H), 7.55–7.53 (m, 2H,
Ar-H), 7.26 (m, 2H, Ar-H), 6.95–6.93 (m, 2H, Ar-H), 4.63
(s, 2H, S–CH2), 3.82 (s, 3H, OMe), 2.36 (s, 3H, Ar-Me). dc
(100 MHz, CDCl3) 166.1, 163.0, 162.3, 143.9, 133.1, 128.4,
122.6, 122.5, 121.8, 116.7, 116.5, 115.8, 114.4, 54.9, 30.9, 26.6.
m/z (ESI) 380.1438 [M þ H]þ.
White solid. Mp 1258C. nmax (KBr)/cmꢁ1 3146, 3006, 1511,
1472, 1245, 1197. dH (400 MHz, CDCl3) 8.21 (s, 1H, Ar-H),
7.97–7.94 (m, 2H, Ar-H), 7.81–7.79 (m, 1H, Ar-H), 7.59–7.46
(m, 4H, Ar-H), 7.28–7.25 (m, 1H, Ar-H), 4.64 (s, 2H, S–CH2). dc
(100 MHz, CDCl3) 166.2, 163.7, 159.1, 156.5, 144.1, 131.8,
129.0, 126.5, 123.0, 121.7, 120.2, 120.2, 26.5. m/z (ESI)
388.1071 [M þ H]þ.
2-((1-(4-Bromophenyl)-1H-1,2,3-triazol-4-yl)
methylthio)-5-phenyl-1,3,4-oxadiazole (5d)
2-((1-(3-Chlorophenyl)-1H-1,2,3-triazol-4-yl)
methylthio)-5-phenyl-1,3,4-oxadiazole (5h)
White solid. Mp 1908C. nmax (KBr)/cmꢁ1 3119, 3093, 2985,
1560, 1492, 1233, 1064. dH (400 MHz, CDCl3) 8.22 (s, 1H,
Ar-H), 7.97–7.95 (m, 2H, Ar-H), 7.62–7.47 (m, 7H, Ar-H), 4.65
(s, 2H, S–CH2). dc (100 MHz, CDCl3) 166.1, 144.0, 135.7,
132.8, 131.8, 129.0, 126.6122.5, 121.9, 121.4, 26.5. m/z (ESI)
413.2883 [M þ H]þ.
Light pink solid. Mp 1358C. nmax (KBr)/cmꢁ1 3138, 2925,
1596, 1474, 1195, 1047. dH (400 MHz, CDCl3) 8.23 (s, 1H,
Ar-H), 7.97–7.94 (m, 2H, Ar-H), 7.75–7.74 (m, 1H, Ar-H),
7.60–7.58 (m, 1H, Ar-H), 7.49–7.38 (m, 5H, Ar-H), 4.65 (s, 2H,
S–CH2). dc (100 MHz, CDCl3) 166.0, 163.0, 162.2, 143.5,
138.9, 134.4, 130.1, 128.3, 121.5, 120.4, 115.8, 114.4, 55.3,
26.6. m/z (ESI) 370.44 [M þ H]þ.
2-((1-(3-Chloro-4-fluorophenyl)-1H-1,2,3-triazol-4-yl)
methylthio)-5-(4-methoxyphenyl)-1,3,4-oxadiazole (5e)
2-((1-(4-Fluorophenyl)-1H-1,2,3-triazol-4-yl)
methylthio)-5-phenyl-1,3,4-oxadiazole (5i)
White solid. Mp 1268C. nmax (KBr)/cmꢁ1 3145, 2926, 1613,
1508, 1478, 1268, 1175. dH (400 MHz, CDCl3) 8.21 (s, 1H,
Ar-H), 7.90–7.87 (m, 2H, Ar-H), 7.82–7.79 (m, 1H, Ar-H),
7.60–7.56 (m, 1H, Ar-H), 7.28–7.26 (m, 1H, Ar-H), 6.97–6.95
(m, 2H, Ar-H), 4.63 (s, 2H, S–CH2), 3.84 (s, 3H, OMe). dc
(100 MHz, CDCl3) 166.1, 162.9, 162.3, 159.1, 156.6, 144.2,
133.2, 128.3, 123.0, 122.3, 121.7, 120.2, 120.2, 117.6, 117.4,
115.7, 114.4, 55.4, 26.5. m/z (ESI) 417.0403 [M þ H]þ.
Off-white solid. Mp 1458C. nmax (KBr)/cmꢁ1 3137, 3093,
1514, 1474, 1227, 1191, 1050. dH (400 MHz, CDCl3) 8.23 (s,
1H, Ar-H), 7.97–7.94 (m, 2H, Ar-H), 7.75–7.74 (m, 1H, Ar-H),
7.60–7.58 (m, 1H, Ar-H), 7.49–7.38 (m, 5H, Ar-H), 4.65 (s, 2H,
S–CH2). dc (100 MHz, CDCl3) 166.0, 163.0, 162.2, 143.5,
138.9, 134.4, 130.1, 128.3, 121.5, 120.4, 115.8, 114.4, 55.3,
26.6. m/z (ESI) 354.48 [M þ H]þ.
2-((1-(4-Fluorophenyl)-1H-1,2,3-triazol-4-yl)
methylthio)-5-(4-methoxyphenyl)-1,3,4-oxadiazole (5f)
2-((1-(3-Chlorophenyl)-1H-1,2,3-triazol-4-yl)
Off-white solid. Mp 1758C. nmax (KBr)/cmꢁ1 3135, 2927,
1617, 1502, 1267, 1171, 1031. dH (400 MHz, CDCl3) 8.18 (s,
1H, Ar-H), 7.90–7.88 (m, 2H, Ar-H), 7.69–7.64 (m, 2H, Ar-H),
methylthio)-5-(4-methoxyphenyl)-1,3,4-oxadiazole (5j)
Light pink solid. Mp 1608C. nmax (KBr)/cmꢁ1 3119, 1615,
1597, 1482, 1266, 1175, 1047. dH (400 MHz, CDCl3) 8.12

Synthesis and Antimicrobial Evaluation of Triazole
G
(s, 1H, Ar-H), 7.96–7.95 (m, 2H, Ar-H), 7.58–7.44 (m, 5H,
Ar-H), 4.65 (s, 2H, S–CH2), 3.82 (s, 3H, OMe). dc (100 MHz,
CDCl3) 166.0, 163.0, 162.2, 143.5, 138.9, 134.4, 130.1, 128.3,
121.5, 120.4, 115.8, 114.4, 55.3, 26.6. m/z (ESI) 400.0870
[M þ H]þ.
with a 100 mL volume with concentration of 2.0 mg mLꢁ1 of
each compound reconstituted in dimethyl sulfoxide (DMSO).
All the plates were incubated at 378C for 24 h. The antibacterial
activity of each compound was evaluated by measuring the zone
of growth inhibition against the test organisms with a zone
reader (HiAntibiotic zone scale). DMSO was used as a negative
control whereas ciprofloxacin was used as a positive control.
This procedure was performed in three replicate plates for each
organism and the mean values of the diameter of inhibition
zones ꢃ standard deviations were calculated.[42]
2-((1-(4-Methoxyphenyl)-1H-1,2,3-triazol-4-yl)
methylthio)-5-phenyl-1,3,4-oxadiazole (5k)
Off-white solid. Mp 1258C. nmax (KBr)/cmꢁ1 3134, 2934,
1613, 1504, 1481, 1258. dH (400 MHz, CDCl3) 8.12 (s, 1H,
Ar-H), 7.96–7.95 (m, 2H, Ar-H), 7.58–7.44 (m, 5H, Ar-H),
6.97–6.95(m, 2H, Ar-H), 4.65 (s, 2H, S–CH2), 3.82(s, 3H,
OMe). dc (100 MHz, CDCl3) 166.1, 163.8, 159.8, 143.4,
131.7, 130.2, 129.0, 126.6, 123.3, 122.2, 121.7, 114.6, 55.5,
30.9. m/z (ESI) 366.1294 [M þ H]þ.
Determination of MIC of Chemical Compounds
The MIC is the lowest concentration of an antimicrobial
compound that will inhibit the visible growth of a microorgan-
ism after overnight incubation. The MIC of the various com-
pounds against bacterial strains was tested through a modified
agar well diffusion method.[42] In this method, a two-fold serial
dilution of each chemically synthesised compound was prepared
by first reconstituting the compound in DMSO followed by
dilution in sterile distilled water to achieve a decreasing con-
centration range of 512 to 1 mg mLꢁ1. A 100 mL volume of each
dilution was introduced into wells (in triplicate) in the agar
plates already seeded with 100 mL of standardised inoculum
(106 cfu mLꢁ1) of the test microbial strain. All test plates were
incubated aerobically at 378C for 24 h and observed for the
inhibition zones. The MIC, taken as the lowest concentration of
the chemical compound that completely inhibited the growth of
the microbe, shown by a clear zone of inhibition, was recorded
for each test organism. Ciprofloxacin was used as a positive
control.
2-(3-Chlorophenyl)-5-((1-(4-methoxyphenyl)-1H-1,2,3-
triazol-4-yl)methylthio)-1,3,4-oxadiazole (5l)
Light pink solid. Mp 1308C. nmax (KBr)/cmꢁ1 3119, 1615,
1597, 1482, 1266, 1175, 1047. dH (400 MHz, CDCl3) 8.15 (s,
1H, Ar-H), 7.95–7.84 (m, 2H, Ar-H), 7.58–7.38 (m, 4H, Ar-H),
6.98–6.95 (m, 2H, Ar-H), 4.65 (s, 2H, S-CH2), 3.82 (s, 3H,
OMe). dc (100 MHz, CDCl3) 164.9, 164.4, 159.8, 135.1, 131.7,
130.4, 126.5, 124.9, 124.6, 122.1, 114.6, 55.5, 29.6. m/z (ESI)
400.0868 [M þ H]þ.
2-(4-Methoxyphenyl)-5-((1-(4-nitrophenyl)-1H-1,2,3-
triazol-4-yl)methylthio)-1,3,4-oxadiazole (5m)
Light pink solid. Mp 1408C. nmax (KBr) cmꢁ1 3139, 3087,
1610, 1597, 1525, 1505, 1483, 1341, 1261, 1170. dH (400 MHz,
CDCl3) 8.38–8.37 (s, 2H, Ar-H), 7.95–7.88 (m, 4H, Ar-H), 7.56
(s, 1H, Ar-H), 6.97–6.96 (m, 2H, Ar-H), 4.65 (s, 2H, S–CH2),
3.85(s, 3H, OMe). dc (100 MHz, CDCl3) 166.1, 162.9, 162.3,
149.4, 144.1, 130.7, 128.8, 128.4, 121.5, 120.7, 118.4, 115.7,
114.4, 55.5, 30.9. m/z (ESI) 410.0868 [M]þ.
Antifungal Activity
The antifungal activity of the 13 chemical compounds was
evaluated by a poisoned food technique.[43] The moulds were
grown on Sabouraud’s dextrose agar (SDA) at 258C for 7 days
and used as inocula. Molten SDA (458C, 15 mL) was poisoned
by the addition of 100 mL of each compound having a concen-
tration of 2.0 mg mLꢁ1 reconstituted in DMSO, poured into a
sterile Petri plate, and allowed to solidify at room temperature.
The solidified poisoned agar plates were inoculated at the centre
with fungal plugs (8 mm diameter) obtained from the colony
margins and incubated at 258C for 7 days. DMSO was used as
the negative control whereas fluconazole was used as the
positive control. The experiments were performed in triplicate.
The diameter of fungal colonies was measured and expressed as
the percentage inhibition of myelial growth by the following
calculation: percentage inhibition of myelial growth ¼ (dc ꢁ
dt)/dc ꢂ 100 (%), where dc is the average diameter of the fungal
colony in negative control sets and dt is the average diameter of
the fungal colony in experimental sets.
Antimicrobial Assay
Test Microorganisms
A total of six microbial strains were selected on the basis of
their clinical importance in causing diseases in humans. Two
Gram-positive bacteria (Staphylococcus aureus MTCC 96 and
Bacillus subtilis MTCC 121), two Gram-negative bacteria
(Escherichia coli MTCC 1652 and Pseudomonas aeruginosa
MTCC 741), and two fungi (Aspergillus niger and A. flavus[41]
)
were used in the present study for evaluation of antimicrobial
activity of the chemical compounds. All the bacterial cultures
were procured from the Microbial Type Culture Collection
(MTCC), IMTECH, Chandigarh. The bacteria were subcultured
on nutrient agar whereas fungi were subcultured on Sabouraud’s
dextrose agar.
Supplementary Material
Antibacterial Activity
Spectral data are available on the Journal’s website.
The antibacterial activity of 13 chemical compounds was
evaluated by the agar well diffusion method. All the microbial
cultures were adjusted to 0.5 McFarland standard, which is
visually comparable to a microbial suspension of ,1.5 ꢂ 106
cfu mLꢁ1. Mueller Hinton agar medium (20 mL) was poured
into each Petri plate and plates were swabbed with a 100 mL
inocula of the test microorganisms and kept for 15 min for
adsorption. Using a sterile cork borer of 8 mm diameter, wells
were bored into the seeded agar plates and these were loaded
Acknowledgement
JS and HS thank UGC, New Delhi, India for the grant of Junior Research
Fellowships.
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