Design, synthesis, antibacterial evaluation and molecular docking studies of novel pyrazole/1,2,4-oxadiazole conjugate ester derivatives

Article abstract of DOI:10.1007/s00044-021-02710-z

The development of new antimicrobial drugs is most needed due to rapid growth in global antimicrobial resistance. Thus, in this context, a series of novel pyrazole/1,2,4-oxadiazole conjugate ester derivatives (7a–j) was synthesized. All the derivatives we

Full text of DOI:10.1007/s00044-021-02710-z

MEDICINAL
CHEMISTRY
RESEARCH
Medicinal Chemistry Research (2021) 30:1087–1098
https://doi.org/10.1007/s00044-021-02710-z
ORIGINAL RESEARCH
Design, synthesis, antibacterial evaluation and molecular docking
studies of novel pyrazole/1,2,4-oxadiazole conjugate ester
derivatives
Navaneetha Depa1 Harikrishna Erothu1,2
●
Received: 27 September 2020 / Accepted: 30 January 2021 / Published online: 18 February 2021
© The Author(s), under exclusive licence to Springer Science+Business Media, LLC part of Springer Nature 2021
Abstract
The development of new antimicrobial drugs is most needed due to rapid growth in global antimicrobial resistance. Thus, in
this context, a series of novel pyrazole/1,2,4-oxadiazole conjugate ester derivatives (7a–j) was synthesized. All the
derivatives were evaluated for their in vitro antibacterial activity against Gram-positive (Enterococcus, Bacillus subtilis and
Staphylococcus aureus) and Gram-negative (Salmonella, Klebsiella and Escherichia coli) bacteria and their minimum
inhibitory concentration (MIC) was determined. Some of the derivatives have shown significant biological activity with a
potency comparable to standard drug Streptomycin. Moreover, molecular docking studies, pharmacokinetic properties
ADMET (absorption, distribution, metabolic, excretion and toxicity), molecular properties and TOPKAT analysis were
predicted through in silico method. In vitro and in silico studies revealed that among all the compounds, compound (7a) has
shown a significant biological activity with a good LibDock score 162.751 kcal/mol. All the synthesized derivatives were
1
confirmed by FTIR, H NMR, 13C NMR and mass spectrometry.
Graphical Abstract
Supplementary information The online version contains
supplementary material available at https://doi.org/10.1007/s00044-
021-02710-z.
* Harikrishna Erothu
2
Centre for Advanced Energy Studies (CAES), Department of
harikrishnaiitm@gmail.com
Chemistry, Koneru Lakshmaiah Education Foundation (KLEF),
Guntur, Andhra Pradesh, India
1
Department of Chemistry, Koneru Lakshmaiah Education
Foundation (KLEF), Guntur, Andhra Pradesh, India

1088
Medicinal Chemistry Research (2021) 30:1087–1098
●
●
●
●
Keywords ADMET Antibacterial activity Molecular docking 1,2,4-oxadiazole Pyrazole
Introduction
five-membered heterocyclic molecules containing oxygen
and two nitrogen atoms. Oxadiazole scaffolds are wide
range natural products with diverse therapeutic properties.
Oxadiazole-containing compounds i.e., 1,2,4-oxadiazole
derivatives are well known for their anti-inflammatory,
analgesic, agonists fatty acid receptors, anti-tumour and
antimicrobial properties [28, 29].
Bacteria and other pathogenic microbes develop resistance
to antibiotics treatments through diverse adaptations and
mechanisms [1]. Anti-microbial resistance (AMR), acquir-
ing resistance to the existing antibiotics and therapies by
pathogenic bacteria and other microbes, is the global
health concern [2, 3]. Drug-resistant microbial infections are
hard to cure and affect the global economy, especially the
low-income and developing countries. Growing AMR
among diverse pathogenic bacteria, microbes and the non-
availability of potent antimicrobial agents in general and
antibacterial agents in particular has drawn the attention of
the global science community and the pharma industry
[4, 5]. In recent years, significant developments were wit-
nessed in terms of understanding the probable reasons and
mechanism of growing AMR, prevention and treatment of
drug-resistant infections. Significant progress was made in
combating AMR to develop potent molecules/antibiotics
mostly through novel heterocyclic compounds [5–11].
Heterocyclic compounds are a rich source of active
functional molecules with diverse biological functions
ranging from oxygen carriers (haemoglobin), the storehouse
of energy (adenosine triphosphate), genetic materials
(DNA), active components of protein synthesis machinery
(RNA) neurotransmitters and natural antimicrobial agents
(diketopiperazines) [12]. Owing to the various biological
activities, heterocyclic compounds with varying functional
moieties have been studied for their antibacterial properties.
Molecules containing nitrogen-rich five-membered hetero-
cyclic structures, pyrazoles and 1,2,4-oxadiazoles are the
indispensable stock of biologically active compounds for a
myriad of applications [13–20].
It is evident from the presence in natural products and
the recent findings that pyrazole and oxadiazole deriva-
tives are medicinally important moieties with diverse
biological activities, especially, antibacterial properties
[30–34]. We anticipated that the amalgamation of the two
active moieties i.e., pyrazoles and oxadiazoles with
appropriate chemistry would result the novel and potent
class of antibacterial compounds. However, there are
barely any systematic studies reporting development
and antibacterial activities of such substituted pyrazole/
1,2,4-oxadiazole conjugate ester compounds. Recently,
1,2,4-oxadiazole/2-imidazoline hybrids were successfully
developed to treat infectious diseases and certain cancers
[35]. In this endeavour, we have prepared a library of
rationally designed and selectively substituted pyrazole/
1,2,4-oxadiazole conjugate ester derivatives (7a–j). The
synthesized compounds were screened for superior anti-
bacterial activity against three Gram-positive and three
Gram-negative bacteria. Molecular docking studies,
ADMET, TOPKAT study and molecular properties were
also performed to study the interaction modes of synthe-
sized compounds with the active site of the protein. The
results of in vitro and in silico studies showed that sub-
stituted pyrazole/1,2,4-oxadiazole conjugate ester deriva-
tives may serve as new antibacterial agents.
Pyrazoles are five-membered heterocyclic molecules with
two nitrogens in the structure and are chemically 1,2-dia-
zoles. Pyrazole-moiety-containing compounds have suc-
cessfully been developed and studied for their anti-
inflammatory, anti-convulsant, anti-cancer, ACE inhibitor,
anti-viral and anti-microbial studies [21–26]. Apart from the
synthetically made pyrazole-containing biologically active
compounds, a handful of natural products showcase the
presence of pyrazole nucleus with diverse properties ranging
from anti-diabetic to anti-cancer activities [27]. Pyrazole-3
(5)-carboxylic acid, Fluviols A-E, Pyrazofurin and Formycin
are a few to list medicinally active natural compounds
pyrazole-moiety embedded into the integral structure.
Aminophenazone, phenazone, sulfinpyrazone and phe-
nylbutazone are examples of drugs that contain embedded
pyrazole moiety in their structure. Similarly, oxadiazoles are
Results and discussion
The molecules under study i.e., substituted pyrazole/1,2,4-
oxadiazole conjugate ester derivatives (7a–j) were synthe-
sized (Schemes 1 and 2) with moderate to good yields
(Table 1). Pyrazalone (3-methyl-1-phenyl-1H-pyrazol-5
(4H)-one (3)) was obtained by refluxing ethyl acetoacetate
with phenyl hydrazine (2) in acetic acid. Pyrazole car-
boxylic acid intermediate (5-chloro-3-methyl-1-phenyl-1H-
pyrazole-4-carboxylic acid (5)) was then prepared from (3)
in successive reactions with POCl3 in dry DMF followed by
the oxidation of aldehyde moiety to acid in acetic acid
(Scheme 1) [36]. The chloromethyl oxadiazole derivatives
(6) were synthesized using previously reported method
[37–42]. The final compounds under study i.e., pyrazole/

Medicinal Chemistry Research (2021) 30:1087–1098
1089
Table 1 Synthesis of pyrozole/1,2,4-oxadiazole conjugate ester
derivatives (7a–j)
Compound number
Structure
Yield (%)a
7a
78%
7b
7c
90%
83%
Scheme 1 Synthesis of pyrazole carboxylic acid intermediate 5
(5-chloro-3-methyl-1-phenyl-1H-pyrazole-4-carboxylic acid)
7d
7e
7f
82%
85%
74%
Scheme 2 Preparation of pyrazole–oxadiazole conjugate ester deri-
vatives (7a–j) through esterification of 5 (5-chloro-3-methyl-1-phenyl-
1H-pyrazole-4-carboxylic acid) with chloromethyl oxadiazoles
(5-(chloromethyl)-3-phenyl-1,2,4-oxadiazole) derivatives
1,2,4-oxadiazole conjugate ester derivatives (7a–j) were
obtained by Cs2CO3-mediated esterification of (5) with
corresponding chloromethyl oxadiazoles (6) under dry
conditions in moderate to good yields (Scheme 2 and Table
1) [43–47]. Thus, obtained target compounds were purified
using standard chromatography techniques and character-
ized by infra-red, NMR and mass spectroscopic data. Pyr-
azole and oxadiazole conjugation were realized with a
biocompatible and biodegradable ester linkage (Scheme 2).
The assignment of antibacterial properties was achieved
using the zone of inhibition testing and MIC method. The
zone of inhibition testing was judiciously chosen owing to
the advantages the technique offers for the antibacterial
screening of the wide range of candidate molecules. The
quick turnaround time, economic experimental setup,
applicability to diverse chemical and natural product
screening are the advantages of the zone of inhibition
technique. All the synthesized pyrazole–oxadiazole con-
jugate ester derivatives (7a–j) were screened for their
in vitro antibacterial activity against three Gram-positive
bacteria (Enterococcus, Bacillus subtilis and Staphylo-
coccus aureus) and three Gram-negative bacteria (Salmo-
nella, Klebsiella and Escherichia coli). The anticipated
antibacterial properties were evaluated against a standard
antibacterial compound by using the zone of inhibition and
7g
79%
7h
7i
82%
80%
7j
81%
aYield calculated after purification
MIC method. The average zone of inhibition with the
standard at 10-µg/ml concentration and minimum inhibitory
concentration (MIC) with the standard at 1 mg/ml against
each bacterium were studied and measured for all the
compounds (7a–j) and the obtained results are summarized
in Tables 2 and 3.
The unsubstituted derivative (7a) demonstrated anti-
bacterial activity against both Gram-positive ((Enterococcus

1090
Medicinal Chemistry Research (2021) 30:1087–1098
Table 2 Antibacterial activity
(zone of inhibition) of pyrozole/
1,2,4-oxadiazole conjugate ester
derivatives (7a–j) (µg/ml
concentration)
Compound
Zone of inhibition (mm)
Gram-positive
Gram-negative
Enterococcus Bacillus subtilis S. aureus Salmonella Klebsiella E. coli
7a
7b
7c
7d
7e
7f
32
32
-
21
30
-
27
26
-
-
-
-
-
-
-
-
-
-
-
-
27
28
-
26
29
9
33
30
-
25
29
-
26
29
-
28
22
-
30
30
-
7g
7h
7i
33
35
-
22
25
-
29
28
-
27
29
-
24
25
-
7j
-
-
-
-
21
35
Standard (Streptomycin) 37
31
32
30
- denotes no activity
Table 3 Minimum inhibitory
concentration (MIC) data for
antibacterial activity of
pyrozole/1,2,4-oxadiazole
conjugate ester derivatives
(7a–j) obtained by micro
dilution method
Compound
Zone of inhibition in MIC in µg/ml
Gram-positive
Gram-negative
Enterococcus Bacillus subtilis S. aureus Salmonella Klebsiella E. coli
7a
7b
7c
7d
7e
7f
32
32
-
21
30
-
27
26
-
-
27
28
-
26
29
13
30
30
-
-
-
33
30
-
25
22
-
26
29
-
-
28
29
-
-
-
7g
7h
7i
33
35
-
22
25
-
29
28
-
-
27
29
-
24
25
-
-
-
7j
-
-
-
-
-
-
Standard (Streptomycin) 37
31
32
36
30
35
- denotes no activity
(32 mm), Bacillus subtilis (21 mm) and Staphylococcus
aureus (27 mm)) and Gram-negative (Klebsiella (27 mm),
and Escherichia coli (26 mm)) bacteria as demonstrated by
the presence of a zone of inhibition (Table 2). Similar
antibacterial activity that was observed with the 4-bromo
(7b), 4-methoxy (7d), 4-fluoro (7e), 2-chloro (7g) and 3-
chloro (7h) on the oxadiazole phenyl ring of the pyrazole/
1,2,4-oxadiazole conjugates was observed (Table 2).
Contrastingly, antibacterial screening of compounds with
2-bromo (7c), 3-nitro (7f), p-tolyl (7i) and o-tolyl (7j)
substituted phenyl moiety on the oxadiazole indicated that
the compounds are not active against Gram-positive and
Gram-negative bacteria. Though, o-tolyl (7j) substituted
phenyl moiety on the oxadiazole demonstrated relatively
good activity against Gram-negative E. coli bacteria
(Table 2). The graphical representation of antibacterial
activity of the synthesized compounds as well as standard
drug Streptomycin has shown in Figs. 1 and 2. To further
evaluate antibacterial potential, we determined the MIC
for the synthesized compounds. The results (Table 3)
show that the tested compounds (7a, 7b, 7d, 7e, 7g, 7h)
possess significant antibacterial activity compared to the
standard drug. The graphical representation of anti-
bacterial activity of the synthesized compounds as well as
standard drug Streptomycin has shown in Figs. 3 and 4.
Apparently, observed antibacterial properties of pyrazole/
1,2,4-oxadiazole conjugate molecules are specific to the
substitution the oxadiazole moiety. Overall, antibacterial
screening of pyrazole/1,2,4-oxadiazole conjugate ester
molecules demonstrated the anticipated synergic effect of
individual pyrazole and oxadiazole moieties. Further, the
observed substitution-specific differential antibacterial

Medicinal Chemistry Research (2021) 30:1087–1098
1091
40
35
30
25
20
15
10
5
0
Salmonella
Klebsiella
E.coli
Compounds
Fig. 4 Graphical representation of MIC values of synthesized pyr-
azole/1,2,4-oxadiazole conjugate ester derivatives and standard drug
(Streptomycin) against Gram-negative bacterial strains
Fig. 1 Zone of inhibition in mm of synthesized pyrazole/1,2,4-oxa-
diazole conjugate ester derivatives and standard drug (Streptomycin)
against Gram-positive bacterial strains
Molecular docking studies
Molecular docking studies were carried out to understand the
ligand orientation and the inhibitory ability toward human
DNA gyrase by using LibDock module in Accelrys Dis-
covery studio 2.1. The 3D structure of DNA gyrase was
retrieved from protein Data Bank (PDBID:5CDP) and it is
imported into Accelrys Discovery studio 2.1. Docking was
carried out for the synthesized derivatives and later with
known inhibitor drug streptomycin. The best ligand con-
formation was investigated based on high LibDock score,
calculated binding energy and higher interaction amino acid
residues. The docking information of all synthesized com-
pounds is given in Table 4 and from the docking analysis, the
compounds (7a) that is active in vitro has shown a good
docking score 162.751 kcal/mol as compared to Streptomy-
cin 187.377 kcal/mol. The docking results indicate that the
compound (7a) fitted good in active site pocket with the good
docking score. The best conformation with H-bond interac-
tions for the compounds (7a) is shown in Fig. 5. In this study,
for the docking validation, co-crystallised ligand etoposide is
redocked and evaluated for their effectiveness in binding.
Fig. 2 Zone of inhibition in mm of synthesized pyrazole/1,2,4-oxa-
diazole conjugate ester derivatives and standard drug (Streptomycin)
against Gram-negative bacterial strains
40
35
30
25
20
15
10
5
Molecular properties
0
The drug-likeness of the synthesized compounds was pre-
dicted by using Lipinski’s rule of 5 which means mol.wt
≤500, logp ≤5, H-bond donors ≤5 and H-bond acceptor ≤10.
This rule explains about molecular properties important for
pharmacokinetics in the human body. The molecular
properties of all compounds are tabulated in Table 5. All the
synthesized derivatives obeyed the Lipinski’s rule.
Enterococcus
Bacillus subꢀlis
Compounds
S.aureus
Fig. 3 Graphical representation of MIC values of synthesized pyr-
azole/1,2,4-oxadiazole conjugate ester derivatives and standard drug
(Streptomycin) against Gram-positive bacterial strains
ADMET studies
activity strongly supports the need for rational designing
of molecules for countering AMR and validates our
hypothesis.
The pharmacokinetic studies were examined by ADMET
analysis by using Accelrys Discovery studio 2.1. The

1092
Medicinal Chemistry Research (2021) 30:1087–1098
Table 4 Docking conformation of synthesized compounds (7a–j)
Name
LibDock score
Calculate BE (kcal/
mol)
Interacting amino acids
Interacting atoms
H-bond count
2
H-distance
7a
162.751
−34.44779
−31.4895
Asp437,Arg458
Gly459,Gly436
Ser84,DC2013
DG2012,DT2010
DG8
B:ASP437:HN - 7a.mol:O18
B:ASP437:HN - 7a.mol:N19
2.257000
2.282000
7b
151.012
151.558
153.52
Asp437,Arg458
Gly459,Gly436
Ser84,DC2013
DG2012,DT2010
DG8
B:ASP437:HN - 7b.mol:N19
7b.mol:H35 - H:DC2012:C2
1
1
1
3
3
2.151000
2.208000
7c
−27.69448
−49.22423
−55.40352
−35.35721
−59.43023
−34.70153
−53.80486
−57.92473
−102.86163
−34.15795
Asp437,Arg458
Gly459,Gly436
Ser84,DC2013
DG2012,DT2010
DG8
B:ASP437:HN - 7c.mol:N2
7c.mol:C1 - B:ASP437:HN
7c.mol:H30 - B:ASP437:HN
7c.mol:H30 - B:ASP437:CB
2.393000
2.216000
1.725000
2.138000
7d
Asp437,Arg458
Gly459,Gly436
Ser84,DC2013
DG2012,DT2010
DG8
G:DG2009:H21 - 7d.mol:Cl14
B:ASP437:HN - 7d.mol:O18
7d.mol:H45 - E:DG8:HO3′
7d.mol:H39 - B:ASP437:HN
2.145000
2.251000
1.788000
1.748000
7e
163.475
176.174
162.886
165.810
159.036
150.071
187.377
209.244
Asp437,Arg458
Gly459,Gly436
Ser84,DC2013
DG2012,DT2010
DG8
B:ARG458:HH21 - 7e.mol:N19
B:ARG458:HH21 - 7e.mol:O18
G:DG2009:H21 - 7e.mol:O18
7e.mol:H30 - B:ASP437:OD2
2.128000
2.494000
2.423000
1.986000
7f
Asp437,Arg458
Gly459,Gly436
Ser84,DC2013
DG2012,DT2010
DG8
G:DG2009:H21 - 7f.mol:N19
B:ARG458:HH21 - 7f.mol:N19
B:ARG458:HH21 - 7f.mol:O18
2.480000
2.499000
7g
Asp437,Arg458
Gly459,Gly436
Ser84,DC2013
DG2012,DT2010
DG8
B:ARG458:HH21 - 7g.mol:N19
B:ARG458:HH21 - 7g.mol:O18
2.351000
2.291000
7h
Asp437,Arg458
Gly459,Gly436
Ser84,DC2013
DG2012,DT2010
DG8
B:ASP437:HN - 7h.mol:O18
B:ASP437:HN - 7h.mol:N19
E:DG8:O3′ - 7h.mol:H42
E:DG8:HO3′ - 7h.mol:H42
2
3
1
4
3
2.048000
2.198000
2.008000
1.714000
7i
Asp437,Arg458
Gly459,Gly436
Ser84,DC2013
DG2012,DT2010
DG8
G:DG2009:H21 - 7i.mol:O18
G:DG2009:H21 - 7i.mol:N19
B:ARG458:HH21 - 7i.mol:N19
7i.mol:H41 - H:DC2013:O4′
2.094000
1.460000
2.334000
1.938000
7j
Asp437,Arg458
Gly459,Gly436
Ser84,DC2013
DG2012,DT2010
DG8
B:ASP437:HN - 7J.mol:O18
7J.mol:H46 - E:DG8:HO3′
7J.mol:H46 - E:DG8:O3′
2.117000
1.840000
1.873000
Streptomycin
Etoposide
Asp437,Arg458
Gly459,Gly436
Ser84,DC2013
DG2012,DT2010
DG8
Streptomycin:H42 - E:DG8:O3′
Streptomycin:H47 - E:DG8:N7
Streptomycin:H50 - E:DG8:OP1
Streptomycin:H52 - E:DG8:OP2
Streptomycin:H54 - B:GLU435:O
1.959000
2.388000
1.931000
2.444000
2.064000
DG8, Gly459
Arg458, Ser84
Gly436, DG2009
DT2010, DC2012
Asp437, DC2013
B:ASP437:HN - Etoposide: O13
Etoposide:H44 - E:DG8: O6
H: DC2013:H41 - Etoposide: O8
Etoposide:H45 - B:ASP437:HN
Etoposide:H44 - H:DC2013:H41
1.995000
2.242000
2.157000
1.642000
1.409000
properties like absorption, blood–brain barrier, aqueous
solubility, hepatotoxicity, hepatotoxicity probability,
cytochrome P450 CYP2D6 and probability enzyme inhi-
bition study are tabulated in Table 6. Figure 6 represents
the plot of predicted values of drug absorption for the
synthesized derivatives.
In silico toxicity assessment
The drug potential toxicity was predicted by TOPKAT by
using Accelrys Discovery studio 2.1. The impact of drug
consumption of synthesized compounds have been
assessed by using TOPKAT, which determines the

Medicinal Chemistry Research (2021) 30:1087–1098
1093
toxicological final points using quantitative structure
toxicity relationship. The TOPKAT data of all com-
pounds are tabulated in Table 7.
Structure-based pharmacophore modelling
Structure-based pharmacophore modelling is performed for
better understanding of the key features that may be
responsible for biological function of synthesized deriva-
tives. Figure 7 represents the generated structure-based
pharmacophore model with location constrains. Based on
the fit value, the compound (7a) fitted well on the generated
pharmacophore with a fit value 2.877, and Fig. 8 shows the
mapping of the high active compound 7a on the pharma-
cophore model.
Conclusion
In summary, we have synthesized a novel series of pyr-
azole/1,2,4-oxadiazole ester derivatives using simple reac-
tion schemes with moderate to good yields. The
antibacterial activity of the synthesized compounds was
screened against both Gram-positive (Enterococcus, Bacil-
lus subtilis and Staphylococcus aureus) and Gram-negative
(Salmonella, Klebsiella and Escherichia coli) bacteria by
employing zone of inhibition and MIC technique. The
unsubstituted derivative (7a), 4-bromo (7b), 4-methoxy
Fig. 5 Hydrogen bonding interactions of 7a compound with active site
residues of (5CDP), green dotted lines indicating hydrogen bonds and
pink colour-bumps (colour figure online)
Table 5 Molecular properties of
synthesized derivatives (7a–j)
Name
ALogP Molecular weight
Num_H_Acceptors
Num_H_Donors Num_Rotatable bonds
7a
7b
7c
7d
7e
7f
3.82
394.811
473.707
473.707
424.837
412.802
439.809
429.256
429.256
408.838
408.838
5
5
5
6
5
7
5
5
5
5
0
0
0
0
0
0
0
0
0
0
6
6
6
7
6
7
6
6
6
6
4.568
4.568
3.804
4.025
3.714
4.484
4.484
4.306
4.306
7g
7h
7i
7j
Table 6 Absorption,
distribution, metabolism,
excretion and toxicity (ADMET)
of synthesized derivatives (7a–j)
Name BBB Absorption Solubility Hepatotoxicity Hepatotoxicity
probability
CYP2D6 CYP2D6
probability
7a
7b
7c
7d
7e
7f
2
1
1
2
2
4
2
2
2
2
0
0
0
0
0
1
0
0
0
0
2
2
2
2
2
2
2
2
2
2
1
1
1
1
1
1
1
1
1
1
0.86
0
0
0
0
0
0
0
0
0
0
0.465
0.376
0.485
0.336
0.386
0.217
0.415
0.445
0.297
0.485
0.867
0.86
0.867
0.867
0.761
0.874
0.867
0.867
0.86
7g
7h
7i
7j

1094
Medicinal Chemistry Research (2021) 30:1087–1098
(7d), 4-fluoro (7e), 2-chloro (7g) and 3-chloro (7h) on the
oxadiazole phenyl ring of the pyrazole/1,2,4-oxadiazole
conjugates exhibited promising antibacterial activity against
various microorganisms. Based on in vitro and in silico
studies (docking, molecular properties, ADMET, fit value
and structure-based pharmacophore modelling), it was
confirmed that (7a) has shown a significant biological
activity. Therefore, we strongly believe that the promising
antibacterial properties exhibited by the rationally designed
compounds will inspire the development of novel anti-
bacterial compounds, aiding the combat against global
AMR threat.
chromatography carried on precoated silica gel 60F254
plates (Merck). The IR spectra were recorded on a Perkin-
Elmer 683 or a FTIR 1310 spectro-photometers using KBr
pellets. 13C NMR spectra using CDCl3 as internal standard
were recorded on a Varian Unity 100 MHz. NMR spectra
using TMS as an internal standard were recorded on a
Varian Unity 500 MHz and BRUKER AMX 300 spectro-
meters. Mass spectra were performed on a VG Micromass
7070H and a Finnigan Mat 1020B mass spectrometer at
70 eV. NMR, FTIR and mass characterization spectra of all
the final compounds are provided in the Supplementary
Material.
Antibacterial studies
Experimental
Gram-positive (Enterococcus, Bacillus subtilis and Sta-
phylococcus aureus) and Gram-negative (Salmonella,
Klebsiella and Escherichia coli) were received from Lavin
Laboratories, Hyderabad, India. Nutrient agar medium was
used for the bacterial cultures under study and for screening
the antibacterial properties of developed compounds. Bac-
terial stock cultures were prepared and maintained in
nutrient agar media. Respective subcultures each bacterium
under study were prepared and employed for the anti-
bacterial screening.
All the reagents and commercial solvents were used without
further purification. Melting points were determined by
using a Buchi 535 melting point apparatus and were
uncorrected. The visualization of compounds was per-
formed with UV light at 254 and 365 nm, I2 and heating
plates dipping in 2% phosphomolybdic acid in 15% aq.
H2SO4 solution. The reactions were monitored by thin layer
Antibacterial activity of each compound prepared
against the bacteria under study was evaluated using the
zone of inhibition radius measurements. Pyrazole/1,2,4-
oxadiazole conjugates were introduced to the agar plates
with bacteria and incubated for a period of overnight 12 h
and the resulting zone of inhibition is measured. Multiple
copies of culture plates per each compound against each
bacteria were used to rule out any experimental errors,
and the average zone of inhibition values obtained at the
end of the incubation period was compared against the
standard.
Fig. 6 Plot of polar surface area (PSA) versus LogP for the compounds
showing the 95 and 99% confidence limit ellipses corresponding to the
blood–brain barrier and intestinal absorption models
Table 7 Predicted fit values of synthesized derivatives (7a–j)
Name
Acceptor 40
Acceptor 94
Donor 161
Donor 97
Fit Value
Hydro-phobe 28
Hydro-phobe 70
Pharm print
7a
1
1
1
1
1
0
0
1
1
1
0
1
0
0
0
0
0
1
1
0
0
0
1
0
0
0
0
0
0
0
0
0
0
0
1
1
0
0
0
0
0
0
0
0
0
0
1
0
2.877
2.566
2.686
2.546
2.554
2.872
2.668
2.577
2.581
2.617
3.692
3
1
1
1
1
1
1
1
1
1
1
0
1
1
1
1
1
1
1
1
1
1
1
1
1
'100011'
'100011'
'100011'
'100011'
'100011'
'010011'
'010011'
'100011'
'100011'
'100011'
'011101'
'100111'
7b
7c
7d
7e
7f
7g
7h
7i
7j
Streptomycin
Etoposide

Medicinal Chemistry Research (2021) 30:1087–1098
1095
(25 mL), then the mixture was refluxed for 3 h, then the
ethanol was removed under reduced pressure to give com-
pound (3) as a yellow solid (11.34 g, yield 85%, m.p.:
123–124 °C).
5-Chloro-3-methyl-1-phenyl-1H-pyrazole-4-carbaldehyde
(4)
Phosphorus oxychloride (144 mmol) was added drop wise
into N,N-dimethylformamide (172.4 mmol) at 0–5 °C. After
the mixture was stirred for 30 min, 3-methyl-1-phenyl-1H-
pyrazol-5(4H)-one (3) (10.0 g, 57.5 mmol) was added portion
wise. Then mixture was heated to 60 °C for another 2 h. The
reaction mixture was poured slowly into crushed ice, and the
precipitated solid was filtered and dried, to give (4) as a light-
yellow solid (9.98 g, yield: 79%, m.p.: 135–138 °C).
Fig. 7 Generated structure-based pharmacophore model with inter
featured distances
5-Chloro-3-methyl-1-phenyl-1H-pyrazole-4-carboxylic acid
(5)
A solution of NaClO2 (3.15 g, 70 mmol) in 10-ml H2O was
added drop wise into a stirred solution of 5-chloro-3-
methyl-1-phenyl-1H-pyrazole-
4-carbaldehyde
(2.4 g,
36 mmol) in AcOH 10 ml and NaH2PO4 (4.2 g, 70 mmol) in
10 ml of H2O stirred at room temperature for 1.5 h, by
monitoring TLC completion the reaction, diluted with water
and extracted into ethyl acetate (3 × 10 ml), combined the
organic layers dried over Na2SO4, concentrated under
reduced pressure obtained crude product was purified by
column chromatography to give 5 as a white solid (3.1 g,
yield: 72%, m.p.: 233–234 °C).
Fig. 8 Structure-based pharmacophore modelling of (7a) compound.
Green colour represents the hydrogen-bond donor, magenta colour
represents the hydrogen-bond acceptor and light blue represents the
hydrophobic regions (colour figure online)
General procedure for the preparation of (3-phenyl-
1,2,4-oxadiazol-5-yl) methyl 5-chloro-3-methyl-1-
phenyl-1H-pyrazole-4-carboxylate derivatives
(5a–m)
For MIC assays, a stock solution was prepared in DMSO
for each test compound. The bacterial strains from stock
cultures were reactivated by transferring into Mueller Hin-
ton Broth. The tubes are incubated at 37 °C for 18 h. A final
bacteria inoculum containing 105 colony-forming units was
added to MHA medium and poured into petri dishes. Dif-
ferent test compounds at a concentration of 1 mg/ml were
added to wells. Antibiotic such as streptomycin at a con-
centration of 1 mg/ml was used as positive reference to
determine the sensitivity of tested microorganisms. The
MIC number is a lowest concentration of the compound that
inhibits that the bacterial growth was observed.
To a solution of 5-chloro-3-methyl-1-phenyl-1H-pyrazole-
4-carboxylic acid (5.7 mmol) and Cs2CO3 (7.5 mmol) in dry
DMF (5 ml), a substituted 5-(chloromethyl)-3-phenyl-1,2,4-
oxadiazole (7.50 mmol) was added. Then the mixture was
stirred at room temperature for 3 h, the mixture was
extracted with EtOAc. The organic layer was dried over
MgSO4 and evaporated. The residue was purified by chro-
matography on a silica gel column using petroleum ether
and ethyl acetate as the effluent to give pure product (7a–j).
All the compounds were synthesized according to this
procedure (Scheme 2).
3-Methyl-1-phenyl-1H-pyrazol-5(4H)-one (3)
1. (3-phenyl-1,2,4-oxadiazol-5-yl) methyl 5-chloro-3-
methyl-1-phenyl-1H-pyrazole-4-carboxylate
(7a):
Ethyl acetoacetate (10.0 g, 77 mmol) was added to a solu-
tion of phenyl hydrazine (8.31 g, 77 mmol) in ethanol
White solid (307 mg, 78%), m.p. 145–147 °C; 1H
NMR (CDCl3, 500 MHz): δ 2.58 (s, 3H, CH3), 5.60

1096
Medicinal Chemistry Research (2021) 30:1087–1098
(s, 2H, CH2), 7.29 (d, J = 8.4 Hz, 1H, Ar-H),
7.46–7.55 (m, 6H, Ar-H), 7.79 (d, J = 8.4 Hz, 1H,
Ar-H), 7.97–8.01 (m, 1H, Ar-H), 8.10 (t, J = 1.7 Hz);
13C NMR (75 MHz, CDCl3): δ 174.34, 167.61,
161.16, 152.62, 143.10, 139.93, 137.27, 134.96,
132.35, 131.45, 130.20, 129.54, 129.16, 127.95,
127.58, 126.95, 125.56, 125.48, 108.70, 56.23,
14.85; IR (KBr): ν 2828, 2856, 1720, 1659, 1499,
1246, 1095, 760 cm−1; ESI–MS: m/z 395 (M + H).
131.25, 129.76, 128.69, 128.09, 126.85, 126.17,
118.39, 113.68, 112.35, 58.18, 13.09; IR (KBr): ν
2931, 2860, 1718, 1600, 1548, 1446, 1251, 1168,
1090, 756 cm−1; ESI–MS: m/z 413 (M + H).
6. (3-(3-nitrophenyl)-1,2,4-oxadiazol-5-yl) methyl 5-
chloro-3-methyl-1-phenyl-1H-pyrazole-4-carboxylate
(7f): Yellow solid (324 mg, 74%), m.p. 170–172 °C;
1H NMR (CDCl3, 400 MHz): δ 2.49 (s, 3H, CH3),
5.50 (s, 2H, CH2), 7.45–7.59 (m, 7H, Ar-H), 8.0 (d,
J = 8.5 Hz, 2H, Ar-H); 13C NMR (75 MHz, CDCl3): δ
170.93, 148.76, 147.74, 138.17, 137.50, 137.20,
135.76, 135.40, 134.33, 133.66, 130.55, 129.63,
129.56, 129.43, 129.32, 128.06, 116.48, 125.59,
61.87, 14.10; IR (KBr): ν 2924, 2854, 1707, 1497,
1372, 1240, 1168, 1081, 770 cm−1; ESI–MS: m/z 440
(M + H).
7. (3-(2-chlorophenyl)-1,2,4-oxadiazol-5-yl) methyl 5-
chloro-3-methyl-1-phenyl-1H-pyrazole-4-carboxylate
(7g): White solid (338 mg, 79%), m.p. 168–170 °C;
1H NMR (CDCl3, 400 MHz): δ 2.58 (s, 3H, CH3),
5.60 (s, 2H, CH2), 7.42–7.57 (m, 7H, Ar-H), 8.08-
8.13 (m, 2H, Ar-H); 13C NMR (75 MHz, CDCl3): δ
173.16, 163.70, 157.35, 157.16, 145.24, 136.27,
133.27, 128.79, 122.69, 122.60, 121.03, 118.68,
116.82, 116.58, 114.83, 114.11, 112.82, 57.03,
13.76; IR (KBr): ν 2930, 2857, 1724, 1605, 1404,
1359, 1256, 1117,1044, 755 cm−1; ESI–MS: m/z 429
(M + H).
2. (3-(4-bromophenyl)-1,2,4-oxadiazol-5-yl) methyl 5-
chloro-3-methyl-1-phenyl-1H-pyrazole-4-carboxylate
(7b): Brown solid (426 mg, 90%), m.p. 155–157 °C;
1H NMR (CDCl3, 500 MHz): δ 2.57 (s, 3H, CH3),
5.60 (s, 2H, CH2), 7.45–7.55 (m, 5H, Ar-H), 7.63 (d,
J = 8.5 Hz, 2H, Ar-H), 7.97 (d, J = 8.5 Hz, 2H, Ar-
H); 13C NMR (75 MHz, CDCl3): δ 170.69, 141.45,
140.01, 137.29, 134.74, 134.23,130.22, 129.10,
128.53, 128.27, 126.39, 124.42, 123.31, 119.04,
114.02, 62.40, 14.09; IR (KBr): ν 2929, 2851, 1595,
1490, 1389, 1252, 1173, 1119, 1025, 819, 752 cm−1
;
ESI–MS: m/z 474.90 (M + H).
3. (3-(2-bromophenyl)-1,2,4-oxadiazol-5-yl) methyl 5-
chloro-3-methyl-1-phenyl-1H-pyrazole-4-carboxylate
(7c): Brown solid (393 mg, 83%), m.p. 168–170 °C;
1H NMR (CDCl3, 500 MHz): δ 2.58 (s, 3H, CH3),
5.59 (s, 2H, CH2), 7.18 (d, J = 8.5 Hz, 2H, Ar-H),
7.45–7.55 (m, 5H, Ar-H), 7.80 (d, J = 7.91 Hz, 2H,
Ar-H); 13C NMR (75 MHz, CDCl3): δ 161.34, 157.40,
157.10, 152.80, 145.33, 136.31, 135.41, 134.59,
129.90, 128.88, 128.77, 128.71, 121.75, 120.75,
118.74, 114.79, 114.05, 133.27, 61.98, 14.09; IR
(KBr): ν 2982, 2927, 1716, 1497, 1317, 1242, 1154,
773 cm−1; ESI–MS: m/z 474.90 (M + H).
8. (3-(3-chlorophenyl)-1,2,4-oxadiazol-5-yl) methyl 5-
chloro-3-methyl-1-phenyl-1H-pyrazole-4-carboxylate
(7h): White solid (351 mg, 82%), m.p. 167–169 °C;
1H NMR (CDCl3, 500 MHz): δ 2.57 (s, 3H, CH3),
5.60 (s, 2H, CH2), 7.47–7.54 (m, 7H, Ar-H), 8.07-
8.14 (m,2H, Ar-H); 13C NMR (75 MHz, CDCl3): δ
179.27, 174.26, 162.70, 158.87, 154.39, 149.66,
136.46, 134.92, 131.25, 130.24, 129.22, 128.75,
121.11, 120.11, 115.32, 114.25, 112.93, 111.44,
56.34, 14.10; IR (KBr): ν 2929, 1724, 1640, 1450,
1278, 1127, 1021 cm-1; ESI–MS: m/z 429 (M + H).
9. (3-(p-tolyl)-1,2,4-oxadiazol-5-yl) methyl 5-chloro-3-
methyl-1-phenyl-1H-pyrazole-4-carboxylate (7i): Pale
4. (3-(4-methoxyphenyl)-1,2,4-oxadiazol-5-yl) methyl
5-chloro-3-methyl-1-phenyl-1H-pyrazole-4-carboxy-
late (7d): Pale yellow solid (347 mg, 82%), m.p.
1
140–142 °C; H NMR (CDCl3, 500 MHz): δ 2.56 (s,
3H, CH3), 3.96 (s, 3H, OCH3), 5.60 (s, 2H, CH2),
7.40–7.60 (m, 5H, Ar-H), 7.62 (d, J = 8.2 Hz, 2H, Ar-
H), 8. 36 (d, J = 8.2 Hz, 2H, Ar-H); 13C NMR
(75 MHz, CDCl3): δ 174.13, 167.76, 161.17, 152.42,
139.28, 132.35, 129.73, 129.76, 129.65, 129.16,
129.11, 129.02, 125.02, 116.25, 116.21, 116.03,
115.98, 56.78, 46.28, 14.84; IR (KBr): ν 2929,
2859, 1688, 1592, 1442, 1296, 1130,1023, 792,
743 cm−1; ESI–MS: m/z 425 (M + H).
1
red solid (326 mg, 80%), m.p. 155–157 °C; H NMR
(CDCl3, 500 MHz): δ 2.42 (s, 3H, CH3), 2.57 (s, 3H,
CH2), 5.59 (s, 2H, CH2), 7.29 (d, J = 7.94 Hz, 2H, Ar-
H); 7.47–7.56 (m, 5H, Ar-H), 7.98 (d, J = 8.19 Hz,
2H, Ar-H); 13C NMR (75 MHz, CDCl3): δ 161.30,
157.40, 157.12, 144.34, 136.27, 133.43, 130.55,
129.39, 128.85, 128.75, 128.53, 128.26, 124.67,
118.71, 114.84, 114.08, 61.90, 50.65, 14.17; IR
(KBr): ν 2929, 2860, 1747, 1600, 1519, 1338, 1258,
1173, 1027, 752 cm−1; ESI–MS: m/z 409 (M + H).
10. (3-(o-tolyl)-1,2,4-oxadiazol-5-yl) methyl 5-chloro-3-
methyl-1-phenyl-1H-pyrazole-4-carboxylate (7j): Pale
5. (3-(4-fluorophenyl)-1,2,4-oxadiazol-5-yl) methyl 5-
chloro-3-methyl-1-phenyl-1H-pyrazole-4-carboxylate
(7e): Pale red solid (350 mg, 85%), m.p. 152–154 °C;
1H NMR (CDCl3, 400 MHz): δ 2.58 (s, 3H, CH3), 5.59
(s, 2H, CH2), 7.18–7.21 (m, 3H, Ar-H), 7.46–7.54
(m,6H, Ar-H); 13C NMR (75 MHz, CDCl3): δ 170.44,
158.07, 139.65, 133.99, 133.50, 131.84, 131.62,

Medicinal Chemistry Research (2021) 30:1087–1098
1097
1
red solid (330 mg, 81%), m.p. 169–171 °C; H NMR
(CDCl3, 500 MHz): δ 2.40 (s, 3H, CH3), 2.57 (s, 3H,
CH2), 5.60 (s, 2H, CH2), 7.47–7.57 (m, 3H, Ar-H),
7.92–8.04 (m, 6H, Ar-H); 13C NMR (75 MHz, CDCl3):
δ 173.74, 168.51, 162.44, 161.12, 152.55, 141.74,
137.25, 132.26, 129.52, 129.09, 128.98, 127.34,
125.43, 123.36, 108.74, 56.29, 21.50, 14.80; IR
(KBr): ν 2925, 2847, 1680, 1595, 1551, 1483, 1252,
1177, 1033, 745 cm−1; ESI–MS: m/z 409 (M + H).
quinazolin-4-ones linked to 1,2,3-triazol hybrids as Mycobacter-
ium tuberculosis H37Rv inhibitors besides antimicrobial activity.
Med Chem Res. 2019;28:559–70.
12. MA A. A review: biological importance of heterocyclic com-
pounds. Der Pharma Chem. 2017;9:141–7.
13. Depa N, Erothu H. One‐pot three‐component synthesis of 3‐
aminoalkyl indoles catalyzed by molecular iodine. Chemis-
trySelect. 2019;4:9722–5.
14. Ansari A, Ali A, Asif M, Shamsuzzaman S. Review: biologically
active pyrazole derivatives. N J Chem. 2017;41:16–41.
15. Hassan AS, Askar AA, Naglah AM, Almehizia AA, Ragab A.
Discovery of new schiff bases tethered pyrazole moiety: design,
synthesis, biological evaluation, and molecular docking study as
dual targeting DHFR/DNA gyrase inhibitors with immunomodu-
latory activity. Molecules. 2020;25:2593.
16. Cunha F, Nogueira J, de Aguiar A. Synthesis and antibacterial
evaluation of 3,5-Diaryl-1,2,4-oxadiazole derivatives. J Braz
Chem Soc. 2018;29:2405–2416.
Acknowledgements The authors are gratefully acknowledged to the
Department of Chemistry and Centre for Advanced Energy Studies
(CAES), KLEF (Deemed to be University), Vaddeswaram, Andhra
Pradesh, India for providing the research facilities and also Averin
Biotech Pvt. Ltd, Hyderabad for in silico studies.
17. Biernacki K, Daśko M, Ciupak O, Kubiński K, Rachon J, Dem-
kowicz S. Novel 1,2,4-oxadiazole derivatives in drug discovery.
Pharmaceuticals. 2020;13:111.
Compliance with ethical standards
18. Parikh PH, Timaniya JB, Patel MJ, Patel KP. Design, synthesis,
and characterization of novel substituted 1,2,4-oxadiazole and
their biological broadcast. Med Chem Res. 2020;29:538–48.
19. Dasari SR, Tondepu S, Vadali LR, Seelam N. PEG-400 mediated
an efficient eco-friendly synthesis of new isoxazolyl pyrido[2,3-d]
pyrimidines and their anti-inflammatory and analgesic activity.
Synth Commun. 2020;50:2950–61.
Conflict of interest The authors declare no competing interests.
Publisher’s note Springer Nature remains neutral with regard to
jurisdictional claims in published maps and institutional affiliations.
References
20. Perla P, Seelam N, Bera R. Design and synthesis of novel 1a,3,4-
oxadiazole derivatives as cytotoxic agents: a combined experi-
mental and docking study. Russ J Org Chem. 2020;56:924–34.
21. Alam O, Naim M, Nawaz F, Alam MJ, Alam P. Current status of
pyrazole and its biological activities. J Pharmacy Bioallied Sci.
2016;8:2–17.
22. El Shehry MF, Abbas SY, Farrag AM, Fouad SA, Ammar YA.
Synthesis and biological evaluation of 3-(2,4-dichlorophenox-
ymethyl)-1-phenyl-1H-pyrazole derivatives as potential antitumor
agents. J Iran Chem Soc. 2020;17:2567–75.
23. Liu H, Yang G-S, Liu C-B, Lin Y, Yang Y, Gong Y-N. Syntheses,
crystal structures, and antibacterial activities of helical M(II)
phenyl substituted pyrazole carboxylate complexes. J Coord
Chem. 2014;67:572–87.
24. Hassan S. Synthesis, antibacterial and antifungal activity of some
new pyrazoline and pyrazole derivatives. Molecules. 2013;18:
2683–711.
25. Dasari SR, Tondepu S, Vadali LR, Seelam N. Design, synthesis and
molecular docking studies of novel pyrazole benzimidazole deriva-
tives as potent antibacterial agents. Asian J Chem. 2019;31:2733–9.
26. Koteswara Rao CP, Rao TB, Charan GK, Srinu B, Maturi SR.
Synthesis and anticancer evaluation of 2-{4-[5-(5-substituted
arylpyrimidin-2-yl)-1H-pyrazol-3-yl]-phenyl}thiazolo[4,5-b]pyr-
idine derivatives. Russ J Gen Chem. 2019;89:1023–8.
27. Karrouchi K, Radi S, Ramli Y, Taoufik J, Mabkhot Y, Al-aizari F.
et al. Synthesis and pharmacological activities of pyrazole deri-
vatives: a review. Molecules. 2018;23:134.
28. Kumar D, Patel G, Chavers AK, Chang K-H, Shah K. Synthesis of
novel 1,2,4-oxadiazoles and analogues as potential anticancer
agents. Eur J Med Chem. 2011;46:3085–92.
29. Caneschi W, Enes KB, Carvalho de Mendonça C, de Souza
Fernandes F, Miguel FB, da Silva Martins J, et al. Synthesis and
anticancer evaluation of new lipophilic 1,2,4 and 1,3,4-oxadia-
zoles. Eur J Med Chem. 2019;165:18–30.
1. Frieri M, Kumar K, Boutin A. Antibiotic resistance. J Infect
Public Health. 2017;10:369–78.
2. Aslam B, Wang W, Arshad MI, Khurshid M, Muzammil S,
Rasool MH, et al. Antibiotic resistance: a rundown of a global
crisis. Infect Drug Resist. 2018;11:1645–58.
3. Årdal C, Balasegaram M, Laxminarayan R, McAdams D, Outterson
K, Rex JH, et al. Antibiotic development—economic, regulatory
and societal challenges. Nat Rev Microbiol. 2019;18:267–74.
4. Lomazzi M, Moore M, Johnson A, Balasegaram M, Borisch B.
Antimicrobial resistance—moving forward?BMC Public Health.
2019;19:858.
5. Laws M, Shaaban A, Rahman KM. Antibiotic resistance breakers:
current approaches and future directions. FEMS Microbiol Rev.
2019;43:490–516.
6. Richardson LA. Understanding and overcoming antibiotic resis-
tance. PLOS Biol. 2017;15.
7. Mannam MR, S S, Kumar P, Chamarthi NR, K. RSP. Synthesis of
novel 3-[(2R*)-2-[(2S*)-6-fluoro-3,4-dihydro-2H-chromen-2-yl]-
2-hydroxyethyl]-urea/thiourea derivatives and evaluation of their
antimicrobial activities. Phosphorus, Sulfur, Silicon Relat Ele-
ments. 2019;195:65–74..
8. Naresh VSSP, Somarothu P. Synthesis and antimicrobial activity
of some novel fused heterocyclic moieties. Organic. Commu-
nications. 2013;6:78–85.
9. Mannam MR, Devineni SR, Pavuluri CM, Chamarthi NR, Kot-
tapalli RSP. Urea and thiourea derivatives of 3-(trifluoromethyl)-
5,6,7,8-tetrahydro-[1, 2, 4]triazolo[4,3-a]pyrazine: synthesis,
characterization, antimicrobial activity and docking studies.
Phosphorus, Sulfur, Silicon Relat Elements. 2019;194:922–32.
10. Mannam MR, S S, Kumar P, K RSP. Synthesis of novel 1‐(5‐
(Benzylsulfinyl)‐3‐methyl‐1,3,4‐thiadiazol‐2(3
thiourea/urea derivatives and evaluation of their antimicrobial
activities. J Heterocycl Chem. 2019;56:2179–91.
H)‐ylidene)‐
30. Suhail HD, Mazin NM, Ekhlas Qanber J, Rawaa MOH. Synthesis,
characterization and antibacterial evaluation of 1,3,4-oxadiazole
derivatives. Int J Res Pharm Sci. 2019;10:2342–50.
11. Maddali NK, Viswanath IVK, Murthy YLN, Bera R, Takhi M,
Rao NS, et al. Design, synthesis and molecular docking studies of

1098
Medicinal Chemistry Research (2021) 30:1087–1098
31. Neeraja P, Srinivas S, Mukkanti K, Dubey PK, Pal S. 1H-1,2,3-
Triazolyl-substituted 1,3,4-oxadiazole derivatives containing struc-
tural features of ibuprofen/naproxen: their synthesis and anti-
bacterial evaluation. Bioorganic Med Chem Lett. 2016;26:5212–7.
32. Titi A, Messali M, Alqurashy BA, Touzani R, Shiga T, Oshio H.
et al. Synthesis, characterization, X-Ray crystal study and bioctivities
of pyrazole derivatives: Identification of antitumor, antifungal and
antibacterial pharmacophore sites. J Mol Struct. 2020;1205:127625.
33. Anand Mohan J, Md. Mansoor A. Design, synthesis and anti-
bacterial evaluation of hybrid curcumin based pyrazole deriva-
tives. Int J pharma Bio Sci. 2020;10:L94–101.
34. Baral N, Mohapatra S, Raiguru BP, Mishra NP, Panda P, Nayak
S, et al. Microwave-assisted rapid and efficient synthesis of new
series of chromene-based 1,2,4-oxadiazole derivatives and eva-
luation of antibacterial activity with molecular docking investi-
gation. J Heterocycl Chem. 2019;56:552–65.
35. Shetnev A, Baykov S, Kalinin S, Belova A, Sharoyko V, Rozhkov
A. et al. 1,2,4-Oxadiazole/2-imidazoline hybrids: multi-target-
directed compounds for the treatment of infectious diseases and
cancer. Int J Mol Sci. 2019;20:1699.
36. Wang B-L, Zhang L-Y, Zhan Y-Z, Zhang Y, Zhang X, Wang L-Z,
et al. Synthesis and biological activities of novel 1,2,4-triazole
thiones and bis(1,2,4-triazole thiones) containing phenylpyrazole
and piperazine moieties. J Fluor Chem. 2016;184:36–44.
37. Dürüst Y, Karakuş H, Kaiser M, Tasdemir D. Synthesis and anti-
protozoal activity of novel dihydropyrrolo[3,4-d][1,2,3]triazoles.
Eur J Med Chem. 2012;48:296–304.
groups by 1,3-dipolar cycloaddition of some organic azides and
their biological activities. Turk J Chem. 2014;38:739–55.
40. Pitasse-Santos P, Sueth-Santiago V, Lima M. 1,2,4- and 1,3,4-
Oxadiazoles as scaffolds in the development of antiparasitic
agents. J Braz Chem Soc. 2017;29:435–456.
41. Cai J, Wei H, Hong KH, Wu X, Cao M, Zong X, et al. Discovery
and preliminary evaluation of 2-aminobenzamide and hydro-
xamate derivatives containing 1,2,4-oxadiazole moiety as potent
histone deacetylase inhibitors. Eur J Med Chem. 2015;96:1–13.
42. Mohammadi-Khanaposhtani M, Shabani M, Faizi M, Aghaei I,
Jahani R, Sharafi Z, et al. Design, synthesis, pharmacological
evaluation, and docking study of new acridone-based 1,2,4-oxa-
diazoles as potential anticonvulsant agents. Eur J Med Chem.
2016;112:91–8.
43. Quadri M, Silnović A, Matera C, Horenstein NA, Stokes C, De
Amici M, et al. Novel 5-(quinuclidin-3-ylmethyl)-1,2,4-oxadia-
zoles to investigate the activation of the α7 nicotinic acetylcholine
receptor subtype: synthesis and electrophysiological evaluation.
Eur J Med Chem. 2018;160:207–28.
44. Parrish JP, Dueno EE, Kim S-I, Jung KW. Improved Cs2CO3 pro-
moted O-alkylation of acids. Synth Commun. 2011;30:2687–700.
45. Panday AK, Ali D, Choudhury LH. Cs2CO3-Mediated rapid
room-temperature synthesis of 3-amino-2-aroyl benzofurans and
their copper-catalyzed N-arylation reactions. ACS Omega.
2020;5:3646–60.
46. Zhang Q, Song C, Huang H, Zhang K, Chang J. Cesium carbonate
promoted cascade reaction involving DMF as a reactant for the
synthesis of dihydropyrrolizino[3,2-b]indol-10-ones. Org Chem
Frontiers. 2018;5:80–7.
47. Castillo J-C, Orrego-Hernández J, Portilla J. Cs2CO3-promoted
direct N-alkylation: highly chemoselective synthesis of N-
38. Sağırlı A, Dürüst Y. Reactions of 3-(p-substituted-phenyl)-5-
chloromethyl-1,2,4-oxadiazoles with KCN leading to acetonitriles
and alkanes via a non-reductive decyanation pathway. Beilstein J
Org Chem. 2018;14:3011–7.
39. DÜRÜSt Y, KarakuŞ H, Yavuz MZ, GepdİRemen AA. Synthesis
of novel triazoles bearing 1,2,4-oxadiazole and phenylsulfonyl
alkylated benzylamines and anilines. Eur J Org Chem.
2016;2016:3824–35.