A novel five-step synthetic route to 1,3,4-oxadiazole derivatives with potent α-glucosidase inhibitory potential and their in silico studies

Article abstract of DOI:10.1002/ardp.201900095

A series of new N-aryl/aralkyl derivatives of 2-methyl-2-{5-(4-chlorophenyl)-1,3,4-oxadiazole-2ylthiol}acetamide were synthesized by successive conversions of 4-chlorobenzoic acid (a) into ethyl 4-chlorobenzoate (1), 4-chlorobenzoylhydrazide (2) and 5-(4-chlorophenyl)-1,3,4-oxadiazole-2-thiol (3), respectively. The required array of compounds (6a–n) was obtained by the reaction of 1,3,4-oxadiazole (3) with various electrophiles (5a–n) in the presence of DMF (N,N-dimethylformamide) and sodium hydroxide at room temperature. The structural determination of these compounds was done by infrared, ¹H-NMR (nuclear magnetic resonance), ¹³C-NMR, electron ionization mass spectrometry, and high-resolution electron ionization mass spectrometry analyses. All compounds were evaluated for their α-glucosidase inhibitory potential. Compounds 6a, 6c–e, 6g, and 6i were found to be promising inhibitors of α-glucosidase with IC₅₀ values of 81.72 ± 1.18, 52.73 ± 1.16, 62.62 ± 1.15, 56.34 ± 1.17, 86.35 ± 1.17, 52.63 ± 1.16 μM, respectively. Molecular modeling and ADME (absorption, distribution, metabolism, excretion) predictions supported the findings. The current synthesized library of compounds was achieved by utilizing very common raw materials in such a way that the synthesized compounds may prove to be promising drug leads.

Full text of DOI:10.1002/ardp.201900095

Received: 30 May 2019
Revised: 10 August 2019
Accepted: 1 September 2019
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|
DOI: 10.1002/ardp.201900095
F U L L P A P E R
A novel five‐step synthetic route to 1,3,4‐oxadiazole
derivatives with potent α‐glucosidase inhibitory potential
and their in silico studies
1
1
1
1
Muhammad Iftikhar
|
Shahnawaz
|
|
Muhammad Saleem
|
Naheed Riaz
|
|
2
3
1
1
Aziz‐ur‐Rehman
|
Ishtiaq Ahmed
Jameel Rahman
|
Muhammad Ashraf
1
4
4
Muhammad S. Sharif
|
Shafi U. Khan
|
Thet T. Htar
1
Department of Chemistry, Baghdad‐ul‐
Abstract
Jadeed Campus, The Islamia University
of Bahawalpur, Bahawalpur, Pakistan
A series of new N‐aryl/aralkyl derivatives of 2‐methyl‐2‐{5‐(4‐chlorophenyl)‐1,3,4‐
oxadiazole‐2ylthiol}acetamide were synthesized by successive conversions of
4‐chlorobenzoic acid (a) into ethyl 4‐chlorobenzoate (1), 4‐chlorobenzoylhydrazide
2
Department of Chemistry, Government
College University Lahore, Lahore, Pakistan
3
Institute for Biological Interfaces (IBG‐1),
Karlsruhe Institute of Technology (KIT),
(
2) and 5‐(4‐chlorophenyl)‐1,3,4‐oxadiazole‐2‐thiol (3), respectively. The required
Karlsruhe, Germany
array of compounds (6a–n) was obtained by the reaction of 1,3,4‐oxadiazole (3) with
various electrophiles (5a–n) in the presence of DMF (N,N‐dimethylformamide) and
sodium hydroxide at room temperature. The structural determination of these
4
School of Pharmacy, Monash University
Malaysia, Subang Jaya, Malaysia
Correspondence
1
13
Naheed Riaz, Department of Chemistry,
Baghdad‐ul‐Jadeed Campus, The Islamia
University of Bahawalpur, Bahawalpur
compounds was done by infrared, H‐NMR (nuclear magnetic resonance), C‐NMR,
electron ionization mass spectrometry, and high‐resolution electron ionization
mass spectrometry analyses. All compounds were evaluated for their α‐glucosidase
inhibitory potential. Compounds 6a, 6c–e, 6g, and 6i were found to be promising
inhibitors of α‐glucosidase with IC50 values of 81.72 ± 1.18, 52.73 ± 1.16,
6
3100, Pakistan.
Email: nrch322@yahoo.com;
nrch322@iub.edu.pk
6
2.62 ± 1.15, 56.34 ± 1.17, 86.35 ± 1.17, 52.63 ± 1.16 µM, respectively. Molecular
modeling and ADME (absorption, distribution, metabolism, excretion) predictions
supported the findings. The current synthesized library of compounds was
achieved by utilizing very common raw materials in such a way that the synthesized
compounds may prove to be promising drug leads.
K E Y W O R D S
4
‐chlorobenzoic acid, mercapto‐N‐aryl/aralkyl propionamide oxadiazoles, N‐substituted‐2‐
bromopropionamide, α‐glucosidase inhibition
1
|
INTRODUCTION
nucleus is present in several drug molecules. For example, furamizole
[3]
is an antibiotic,
nesapidil is a calcium channel blocker and a
[
4]
Oxadiazoles are classified as five‐membered heterocyclic ring
systems containing one oxygen and two nitrogen atoms in the ring
system. Amongst the four possible isomers of oxadiazoles, the isomer
vasodilating agent,
raltegravir is anti‐HIV and inhibits HIV
[
5]
integrase enzyme,
and tiodazosin is an antihypertensive drug
[6]
(Figure 1). Several other derivatives of oxadiazoles have shown
[7–9]
[1,2]
1,3,4‐oxadiazole is the most widely studied.
The capability of the
biological activities, which include antimicrobial,
anti‐inflamma-
[10]
[1,11]
[12,13]
[14–17]
1,3,4‐oxadiazole nucleus to undergo a variety of chemical reactions
tory,
antitubercular,
antioxidant,
anticancer,
[21,22]
anti-
[18]
[19,20]
has made it a medicinal backbone, and thus it has drawn attention for
proliferative,
antiviral,
anticonvulsant,
[24]
antiacetylcholi-
[25]
[23]
consideration in a wide range of applications. 1,3,4‐Oxadiazole
nesterase,
antihistone deacetylase,
antixanthine oxidase,
Arch Pharm Chem Life Sci. 2019;e1900095.
wileyonlinelibrary.com/journal/ardp © 2019 Deutsche Pharmazeutische Gesellschaft
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https://doi.org/10.1002/ardp.201900095

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IFTIKHAR ET AL.
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O
N
OH
N
N
N
N
O
O
H N
2
OCH3
O
NO2
Furamizole
N
Nesapidal
O
N
O
N
O
OH
F
N
N
H
N
H3CS
H
N
N
N
N
OCH3
OCH3
N
N
O
N
O
O
Tiodazosin
Raltegravir
NH2
FIGURE 1 Available drugs containing oxadiazole moiety in their structures
potent inhibition of Dengue and West Nile virus NS2B/NS3
glucose causes postprandial hyperglycemia in diabetes mellitus type
[35]
[
26]
[27,28]
[29]
proteases,
antidiabetic,
5‐HT
4
receptor partial agonistic,
[31,32]
2 patients.
Acarbose, voglibose, and miglitol are known antidia-
[
30]
benzodiazepine receptor agonistic,
and analgesic.
It has been
betic drugs, which inhibit α‐glucosidase activity. However, these
drugs have several side‐effects including diarrhea, abdominal
discomfort, and so on. Thus, there is a significant need to keep
observed that alkyl or aryl halide derivatives of oxadiazoles have
better biological activities than the unsubstituted 1,3,4‐oxadia-
[
33]
[35]
zole.
Besides, it is reported that compounds bearing 1,3,4‐
searching for new antidiabetic drugs with minimum side‐effects.
[34]
oxadiazole core are good inhibitors of the enzyme α‐glucosidase.
The present study focuses on the synthesis, characterization, and in
vitro enzyme inhibition along with docking studies and the absorp-
tion, distribution, metabolism, and excretion (ADME) properties of
compounds in search for potent antidiabetic lead molecules.
The enzyme α‐glucosidase (EC.3.2.1.20) is produced by the brush
border of small intestine. It catalyzes hydrolysis of α‐1 → 4‐glycoside
bond in oligosaccharides to produce glucose. The absorption of
TABLE 1 R‐groups in aryl/aralkyl substituted amines
Compound
a
–R
Compound
f
–R
Compound
k
–R
b
c
g
h
l
m
d
e
i
j
n
–
–

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SCHEME 1 Synthesis of N‐substituted
O
O
O
_
_
5
‐(4‐chlorophenyl)‐1,3,4‐oxadiazole‐2‐yl‐
EtOH, 3 4 hr
NH2-NH2, 4 5 hr
OH
OEt
NH-NH2
sulphanyl‐2″‐methylacetamides (6a–n)
Reflux
Stirring, RT
Cl
Cl
Cl
2
1
a
EtOH/KOH/CS2,
Reflux, 4 hr
N
N
O
SH
3
Cl
DMF, NaOH
30 min at RT
_
Stirring 2 3 hr
2
-Bromopropionyl bromide,
_
CH3
Br
H
Basic medium, pH 9 10
N
R
R
NH2
_
O
4
a n
_
3
5
a n
3′
N
N
CH3
H
1
O
N
1′′
2′ 1′
5
5′′
S
R
O
Cl
3′′
_
a n
6
2
2
|
RESULTS AND DISCUSSION
Chemistry
separately. Compound 3 was prepared starting with reflux of 4‐
chlorobenzoic acid (a) in ethanol catalyzed by concentrated H SO to
2
4
.1
|
get the corresponding ethyl ester (1), which upon reaction with
hydrated hydrazine in methanol produces carbohydrazide (2), which in
turn was refluxed with carbon disulfide in the presence of ethanolic
potassium hydroxide to get the cyclized product 5‐(4‐chlorophenyl)‐
N‐(Aryl/aralkyl)‐2‐methyl‐(2‐[5‐(4‐chlorophenyl)‐1,3,4‐oxaiazole‐2yl‐
thiol]acetamides (6a–n) with their substituted aryl/aralkyl groups (Table
1
) were synthesized as shown in Scheme 1. The synthesized compounds
1
,3,4‐oxadiazol‐2‐thiol (3). The other precursors (5a–n) of the target
compounds were prepared through coupling of aryl/aralkyl amines
4a–n) with 2‐bromopropionyl bromide in basic media (pH 9–10). The
were screened against yeast α‐glucosidase and were found to be good
inhibitors of the enzyme (Table 2).
(
The target compounds 6a–n were synthesized in a number of steps.
First, the two main precursors 5‐(4‐chlorophenyl‐1,3,4‐oxadiazol‐2‐thiol
target compounds (6a–n) were finally produced in a good yield by
reacting precursor 3 with electrophiles 2‐bromo‐N‐[aryl/aralkyl]propio-
namide (5a–n; Scheme 1). Structures of compounds 6a–n were
(
3) and 2‐bromo‐N‐[aryl/aralkyl]propionamide (5a–n) were prepared
1
established through IR, H‐NMR (nuclear magnetic resonance) and
1
3
TABLE 2 α‐Glucosidase inhibition potential of compounds 6a–n
C‐NMR spectroscopy, electron ionization mass spectrometry (EI‐MS),
and high‐resolution electron ionization mass spectrometry (HR‐EI‐MS).
Compound
Inhibition (%) at 0.5 mM
97.57 ± 1.24
75.35 ± 1.26
96.72 ± 1.24
94.64 ± 1.26
95.32 ± 1.25
74.84 ± 1.29
91.52 ± 1.23
86.42 ± 1.28
96.36 ± 1.25
85.38 ± 1.23
68.45 ± 1.21
38.45 ± 1.19
17.45 ± 1.13
24.45 ± 1.16
65.73 ± 1.93
IC50 (µM)
81.72 ± 1.18
275.45 ± 1.21
52.73 ± 1.16
62.62 ± 1.15
56.34 ± 1.17
275.72 ± 1.25
86.35 ± 1.17
124.52 ± 1.24
52.63 ± 1.16
124.32 ± 1.19
–
6
6
6
6
6
6
6
6
6
6
6
6
6
6
a
b
c
d
e
f
2
.1.1 | Spectral characterization of compound 6a
The IR spectrum of compound 6a showed absorption bands for
several functions as 3,020 (Ar‐H), 2,920 (C–H), 1,696 (C═O),
−1
1
,597–1,535 (C═C, C═N), 1,237 (C–O), 1,063 (C–N) cm . Reso-
nances of a doublet methyl at δ 1.73 (J = 6.7 Hz) and a methine
1
g
h
i
quartet at δ 4.52 (J = 6.7 Hz) in H‐NMR spectrum were attested for
1
S‐substituted propamide function in 6a. The H signals for p‐
chlorophenyl attached to 1,3,4‐oxadiazole moiety appeared as two
doublets at δ 7.48 (2H, J = 8.5 Hz), 7.91 (2H, J = 8.5 Hz), whereas the
signals for the N‐phenyl group displayed their position at δ 7.07–7.15
j
k
l
(5H, m). Quaternary carbons of the oxadiazole ring resonated at δ
–
1
3
1
65.1 (C‐5) and 165.3 (C‐2) in the C‐NMR spectrum, whereas
m
n
–
carbonyl carbon of amide function displayed its position at δ 168.1
C‐1). The signals due to carbons of 4‐chlorophenyl moiety
were observed at δ 141.1 (C‐4″), 138.4 (C‐1″), 129.0 (C‐2″,6″), and
–
(
Acarbose
375.82 ± 1.76

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FIGURE 2 Comparison of SAR (structure–activity relationship) of the most active compounds
1
1
24.0 (C‐3″,5″). The N‐phenyl group appeared at δ 138.4 (C‐1‴),
2.3 Homology model of Saccharomyces cerevisiae
|
α‐glucosidase
19.8 (C‐2‴), 136.2 (C‐3‴), 137.7 (C‐4‴), 129.6 (C‐5‴), 129.0 (C‐6‴).
+
The EI‐MS spectrum of 6a afforded the molecular ion peak [M] at
m/z 359.3 with some characteristic fragments at m/z 268.0 and 111.0
due to p‐aminophenyloxadiazole and chlorophenyloxadiazole moi-
eties, respectively. This spectral analysis led to the structure of 6a;
along with this compound, the data of other analogues 6b–n have
been provided in the experimental part.
The homology model three‐dimensional (3D) structure of the
target S. cerevisiae α‐glucosidase was constructed. The sequence
alignments between isomaltase from S. cerevisiae (PDB ID: 3A4A)
and S. cerevisiae α‐glucosidase showed that there was a high
sequence identity and a sequence similarity of 71.4% and 86.9%,
respectively. The crystal structure of isomaltase was selected as a
template structure and downloaded from the Protein Database
Bank (PDB). Twenty different model structures were built,
and on the basis of the DOPE score, the best model was
selected. Validation of the model structure was performed via
Ramachandran plot and showed that about 98.1% residues
2
.2
|
α‐Glucosidase inhibitory activity
As yeast α‐glucosidase shows structural and functional resemblance with
the human α‐glucosidase, it was used for routine screening of molecules
possessing antidiabetic potential. All the synthesized oxadiazole amides
(6a–n) showed promising inhibitory potential against α‐glucosidase with
IC50 values between 52.63 ± 1.16 and 275.72 ± 1.25 µM, which are all
comparable with the inhibitory potential (IC50 375.82 ± 1.76 µM) of
standard acarbose (Table 2). The products derived from phenylamine
showed significant activity, 6a with IC50 = 81.72 ± 1.18 µM. The analysis
of the structural features and activity potentials reveals that the
presence of phenyl or mono‐ or dimethylated phenyl amines has a strong
pharmacophoric effect in enhanced antiglucosidase activity. Among the
substituted phenyl amines, the target compounds derived from mono‐ or
di‐substitution at meta‐positions showed significant α‐glucosidase
inhibitory potential, that is, 6i (IC50 52.63 ± 1.16 µM), 6c (IC50
5
2.73 ± 1.15 µM), 6e (IC50 56.34 ± 1.17 µM), and 6g (IC50
6.35 ± 1.17 µM; Figure 2). Besides, para‐methylated phenylamine‐
8
derived compound 6d also displayed potent inhibitory activity with an
IC50 value of 62.62 ± 1.15 µM. However, the compounds derived from
mono‐substituted ethyl or ethoxy amines (6k–n) were found inactive.
The decrease in enzyme inhibition potential is observed as 6i = 6c >
6e > 6d > 6a > 6g. Compounds 6h and 6j showed good and 6b and 6f
showed moderate enzyme inhibition profiles.
TABLE 3 Ramachandran plot analysis of Saccharomyces cerevisiae
α‐glucosidase
FIGURE 3 Three‐dimensional overlapped orientation of template
structure (PDB: 3A4A in green color) superimposed on modeled
structure of α‐glucosidase (pink color)
Favored region
69 (98.1%)
Allowed region
Outlier region
5
11 (1.9%)
0 (0.0%)

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FIGURE 4 Validation of the homology model of α‐glucosidase using the RAMPAGE Ramachandran plot
were in the favored region, 1.9% residues in the allowed region,
whereas no outlier residue was found in structure a (Table 3)
which indicated the good stereochemistry of the model structure
and it was found fit for further docking studies. The 3D
overlapped structure of the template structure and the modeled
structure of α‐glucosidase and the Ramachandran plot are shown
in Figures 3 and 4.
2
.4 Molecular docking studies
|
Molecular modeling is widely used to illustrate the potential
interaction modes of the active inhibitors binding to the protein
target. Molecular docking was performed on the synthesized
compounds (6a–n) to identify that plausible binding mode can
explain their inhibitory activity. To validate the docking protocol,
first‐bound cocrystal ligand, α‐D‐glucose, was docked in the
modeled structure, which exhibited a very good root‐mean‐square
deviation of 0.73 (Figure 5), reflecting the crystal and redocked
α‐D‐glucose within active site of target structure. Figure 5 shows
FIGURE 5 Validation of docking protocol, cocrystal bound α‐D‐
glucose (green) and redocked α‐D‐glucose (cyan) in model structure
(RMSD = 0.73)

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FIGURE 6 Orientation of all docked compounds 6a–n within the active site of modeled structure of yeast α‐glucosidase. Different
interacting amino acids within the active site of α‐glucosidase are shown in stick form
the overlapped binding orientation of all docked compounds
within the active site of modeled structures. The best position
was selected based on cluster analysis of docking‐binding position
having the highest probability with reference to stability of the
ligand–substrate complex. Docking showed that all compounds
were docked well within the active site of the target enzyme
and 6i exhibited the highest inhibitory potential with a Chem-
gauss4 score of −10.42 and −10.95, respectively. Different amino
acid residues of target enzyme were involved in making binding
interactions with the side chains of both compounds 6c and 6i
(Figures 7 and 8).
Amino acid residues Asp408 and Arg439 were involved in
forming two hydrogen bonds with two nitrogen atoms in acetamide
and oxadiazole moiety of both compounds 6c and 6i as shown in the
green dotted line in Figures 7 and 8. In addition, Glu276 and Asp349
were involved in making two π‐anion interactions with oxadiazole
moiety and adjacent benzene moiety, while the same benzene was
involved in making π–π T‐shaped with Phe300 (Figures 7 and 8).
Apart from hydrogen bonding and electrostatic interaction, hydro-
phobic interactions were also involved by side chain of compound 6c
with different amino acid residues of Phe157, Leu218, His239,
His245, Ala278, and Arg312 target, whereas in case of compound 6i,
two additional hydrophobic interactions were also formed by the
addition of methyl group (Figure 8).
(
Figure 6) and the Chemgauss4 score of docked compounds is
shown in Table 4. Difference in binding interactions was due to the
attached side chain differences in the corresponding compounds.
Detailed analysis of binding interaction of potent compounds 6c
TABLE 4 Chemgauss4 score of compounds 6a–n against α‐
glucosidase modeled structures
Sr. No.
Compound
Chemgauss4 score
−11.60
1
2
3
4
5
6
7
8
9
6a
6b
6c
6d
6e
6f
−10.85
−10.42
−11.63
−10.62
2
.4.1 | ADME properties of compounds 6a–n
−10.47
6g
6h
6i
−11.08
The ADME properties of molecules were investigated by Med-
[
36]
−10.85
Chem Designer
and are given in Table 5. It has been reported
−10.95
that the computational methods could be used for the prediction
of intestinal drug permeability in rats as in the experimental
1
1
1
1
1
0
1
2
3
4
6j
−10.04
[
37]
methods.
The four parameters of Lipinski rule, that is,
6k
6l
−10.54
molecular weight, logP, number of hydrogen‐bond acceptors and
donors, are thought to be linked with the permeability and
solubility, two basic requirements for a drug to have good
pharmacokinetic parameters. The properties like polar surface
−10.88
6m
6n
−10.03
−10.32

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FIGURE 7 Three‐dimensional (left) and two‐dimensional (right) binding interactions of 6c within the active site of α‐glucosidase. Interacting
amino acid residues are shown in light green color, whereas 6c is shown in golden color. Hydrogen bonding is shown in green dotted form while
π–π interaction is shown in pink dotted line, other halogen interactions are shown in cyan color
area and molecular flexibility were considered to have an impact
on oral bioavailability. From the table, it can be observed that
the compounds having higher logD and logP values and a lower
number of hydrogen bonds predict higher bioavailability of
these molecules have drug‐like properties in silico. TPSA is the
topological polar surface area. A molecule with a TPSA value
2
exceeding 140 Å predicts the decreased bioavailability of
[
37]
molecule.
In the present studies, all molecules showed
[
37]
2
drugs.
S + logP and MlogP are octanol‐water distribution
excellent TPSA values between 68.02 and 77.25 Å . Thus, all
coefficients and their values are below 5, which indicates that
these molecules have desirable drug‐like TPSA properties.
FIGURE 8 Three‐dimensional (left) and two‐dimensional (right) binding interactions of 6i within the active site of α‐glucosidase. Interacting
amino acid residues are shown in light green color, whereas 6i is shown in golden color. Hydrogen bonding is shown in green dotted form while
π–π interaction is shown in pink dotted line, other halogen interactions are shown in cyan color

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TABLE 5 Calculated values of ADME (absorption, distribution, metabolism, excretion) properties of compounds
Compound
MlogP
3.278
3.510
3.510
3.510
3.738
3.738
3.738
3.738
3.738
3.738
3.738
3.738
3.745
3.234
S + logP
3.856
4.121
4.170
4.250
4.437
4.540
4.508
4.421
4.552
4.560
4.503
4.655
4.511
4.319
S + logD
3.856
4.121
4.170
4.250
4.437
4.540
4.508
4.421
4.552
4.560
4.502
4.655
4.511
4.319
MWt
MNO
TPSA
68.02
68.02
68.02
68.02
68.02
68.02
68.02
68.02
68.02
68.02
68.02
68.02
77.25
77.25
HBDH
6
6
6
6
6
6
6
6
6
6
6
6
6
6
a
b
c
d
e
f
359.836
373.863
373.863
373.863
387.890
387.890
387.890
387.890
387.890
387.890
387.890
387.890
403.890
403.890
5
5
5
5
5
5
5
5
5
5
5
5
6
6
1
1
1
1
1
1
1
1
1
1
1
1
1
1
g
h
i
j
k
l
m
n
Note: S + logP and MlogP are octanol‐water distribution coefficients (<5.0). S + logD is pH‐dependent octanol‐water distribution coefficient. HBDH
indicates number of hydrogen‐bond donors (<5). MNO value indicates the total number of hydrogen‐bond acceptor (sum of N and O atoms; <10). MWt is
2
molecular weight (180–480 Da). TPSA is the topological polar surface area expressed in square angstroms (<140 Å ).
3
|
CONCLUSIONS
4.1.2 | Synthesis of ethyl 4‐chlorobenzoate (1)
4
‐Chlorobenzoic acid (a, 0.03 M; 6.0 g) was dissolved in 50 ml of
absolute ethanol with further addition of 5 ml of conc. H SO in
50 ml round‐bottom. The reaction mixture was refluxed for 2–3 hr.
The targeted new N‐aryl/aralkyl derivatives (6a–n) of 2‐methyl‐2‐{5‐
4‐chlorophenyl)‐1,3,4‐oxadiazole‐2ylthiol}acetamides were synthe-
sized and characterized by spectroscopic methods. Compounds 6a,
c–e, 6g, and 6i were found as potent inhibitors of α‐glucosidase with
IC50 values of 81.72 ± 1.18, 52.73 ± 1.16, 62.62 ± 1.15, 56.34 ± 1.17,
6.35 ± 1.17, 52.63 ± 1.16 µM, respectively. Molecular docking
2
4
(
2
The progress and finally the completion of reaction were monitored
by TLC. After completion, the reaction mixture was poured into a
separating funnel containing 50 ml of distilled water and was
extracted with diethyl ether. The organic layer was condensed under
vacuum to get transparent ester 1.
6
8
and ADME studies supported the mode of binding interactions and
drug‐like properties of the active molecules.
Colorless oil; yield: 71%; B.P. 237–239°C; IR (KBr): v = 2,928,
−
1 1
1
,755, 1,597 cm ; H‐NMR (500 MHz, CDCl
3
): δ = 1.20 (t, J = 6.5 Hz,
3
H, CH –CH –O), 4.40 (q, J = 6.5 Hz, 2H, O–CH
3
2
2
1
–CH
3
3
), Ar‐H 7.48 (d,
4
|
EXPERIMENTAL
Chemistry
J = 8.0 Hz, 2H), and 7.91 (d, J = 8.0 Hz, 2H); C‐NMR (125 MHz,
3 3 2
CDCl ): δ = 21.0 (CH ), 63.0 (CH ), Ar‐C [128.0 (CH), 128.0 (CH),
4
4
.1
|
131.4 (CH), 131.4 (CH), 137.1 (C), and 134.1 (C)], and 166.0 (C═O);
+
HR‐EI‐MS m/z: 184.0291 [M] calculated for C
H
9 9
2
ClO ; 184.0281.
.1.1 | General
All the chemicals and solvents of analytical grade were purchased
from a local supplier of Sigma‐Aldrich and Alfa Aesar. Melting points
were measured by Gallenkamp electrothermal apparatus. The purity
of the synthesized compounds was confirmed by using silica‐coated
4
.1.3 | Synthesis of 4‐chlorobenzohydrazide (2)
Ethyl 4‐chlorobenzoate (1, 0.02 M; 6.0 ml) and 30 ml of methanol
were placed in a 100‐ml round‐bottom flask. Ten milliliters of 0.02 M
hydrazine hydrate (80%) was added to the reaction mixture and was
refluxed for 4–5 hr. The solvent was distilled off and cold distilled
water was added with shaking till the appearance of precipitates
of 4‐chlorobenzohydrazide (2) which was then filtered, washed with
distilled water and dried.
1
thin‐layer chromatography (TLC) plates F256 20 × 20 cm. H‐NMR
spectra were recorded on the 400 MHz Bruker spectrometer
13
while C‐NMR spectra were scanned at 100 MHz on the same
instrument. The chemical shift values δ were presented on ppm scale
using tetramethylsilane as internal standard. Infrared (IR) spectra
were recorded as KBr pallets on a Jasco‐320‐A spectrophotometer.
EI‐MS and HR‐EI‐MS spectra were measured on a JMS‐HX‐110
spectrometer.
Yellow crystals; yield 76%; M.P.: 162–165°C; IR (KBr): v = 3,410,
−1 1
3,305, 2,925, 1,688, 1,520 cm
; H‐NMR (500 MHz, CDCl ): δ 4.06
3
(s, –NH , 1H), Ar‐H, 7.55 (d, 2H, CH, J = 8.5 Hz), 7.80 (d, 2H, CH,
2
1
3
The InChI codes of the investigated compounds together with
some biological activity data are provided as Supporting Information.
J = 8.5 Hz), 8.90 (s, –NH, 1H); C‐NMR (125 MHz, CDCl ): δ Ar‐C
3
[127.3 (CH), 128.0 (CH), 129.8 (CH), 129.9 (CH), 133.1 (C), 136.3 (C)],

IFTIKHAR ET AL.
9 of 12
|
+
1
64.9 (C═O); HR‐EI‐MS (m/z): 170.0247 [M] calculated for
3H, H‐3ʹ), 4.52 (q, J = 7.5 Hz, 1H, H‐2ʹ), Ar‐H 7.07–7.11 (m, 5H, CH),
7.48 (d, J = 8.5 Hz, 2H, H‐3″,5″), 7.91 (d, J = 8.5 Hz, 2H, H‐2″,6″), 9.21
C
7 7 2
H ClN O; 170.0237.
1
3
3
(s, 1H, NH); C‐NMR (125 MHz, CDCl ): δ = 16.8 (C‐3ʹ), 44.6 (C‐2ʹ),
Ar‐C [119.8 (C‐2‴), 121.5 (C‐2″,6″), 126.5 (C‐3″,5″), 129.6 (C‐5‴),
4
.1.4 | Synthesis of 5‐(4‐chlorophenyl)‐1,3,4‐
1
1
34.7 (C‐6‴), 136.2 (C‐3‴), 137.7 (C‐4‴), 138.4 (C‐1‴), 138.4 (C‐1″),
oxadiazole‐2‐thiol (3)
41.1 (C‐4″), 165.1 (C‐5), 165.3 (C‐2), and 168.2 (C‐1ʹ)]; HR‐EI‐MS
+
4
‐Chlorobenzohydrazide (2; 0.025 M; 4.0 g) was dissolved in 30 ml of
(m/z): 359.0497 [M] calculated for C17
H14SN
3 2
O Cl; 359.0485.
absolute ethanol and placed in a 100‐ml round‐bottom flask. Carbon
disulfide (0.025 M; 6.5 ml) was added to the flask followed by the
addition of potassium hydroxide (0.03 M; 2.0 g). The mixture was
refluxed for 6–7 hr with stirring. After completion of the reaction, the
mixture was diluted with 30 ml of distilled water and acidified with
dilute HCl to pH 2.0. The precipitates of 5‐(4‐chlorophenyl)‐1,3,4‐
oxadiazole‐2‐thiol (3) were filtered, washed with distilled water, and
crystallized from ethanol.
2‐[{5‐(4‐Chlorophenyl)‐1,3,4‐oxadiazol‐2‐yl}thio]‐N‐(2‐methylphen‐
yl)propanamide (6b)
Yield: 69%; M.P.: 131–133°C; IR (KBr): v = 3,029, 2,920, 1,701, 1,590,
−
1 1
and 1,530 cm
3H, H‐3ʹ), 1.77 (s, 3H, Ar‐CH
7.16–7.21 (m, 4H), 7.40 (d, J = 8.5 Hz, 2H, H‐3″,5″), 7.88 (d, J = 8.5 Hz,
;
H‐NMR (500 MHz, CDCl
3
): δ = 1.45 (d, J = 7.0 Hz,
3
), 4.35 (q, J = 7.0 Hz, 1H, H‐2ʹ), Ar‐H
1
3
2H, H‐2″,6″), and 8.55 (s, 1H, NH); C‐NMR (125 MHz, CDCl
3
):
Amorphous pink solid; yield 66%; M.P.: 135–138°C; IR (KBr):
δ = 16.0 (C‐3ʹ), 21.1 (CH ), 42.8 (C‐2ʹ), Ar‐C [120.8 (C‐2‴), 121.9
3
−1
1
v = 3,417, 3,325, 2,910, 1,520 cm
.
H‐NMR (500 MHz, CDCl
3
):
(C‐2″,6″), 125.0 (C‐3″,5″), 129.6 (C‐5‴), 132.5 (C‐6‴), 136.2 (C‐3‴),
136.3 (C‐4‴), 136.4 (C‐1‴), 138.4 (C‐1″), 141.1 (C‐4″), 142.1 (C‐5),
δ = Ar‐H, 7.45 (d, J = 8.5 Hz, 1H), 7.80 (d, J = 8.5 Hz, 2H, H‐2″,6″), and
13
+
1
2.31 (s, 1H, –SH); C‐NMR (125 MHz, CDCl
3
): δ = Ar‐C [126.3 (CH),
149.3 (C‐2), and 160.2 (C‐1ʹ); HR‐EI‐MS (m/z): 373.0655 [M]
127.0 (CH), 128.8 (CH), 128.9 (CH), 133.1 (C), 134.3 (C), 145.1 (C),
3 2
calculated for C18H16SN O Cl; 373.0642.
+
and 159.8 (C)]; HR‐EI‐MS (m/z): 211.9811 [M] calculated for
8
C H
5
ClN
2
OS; 211.9801.
2‐[{5‐(4‐Chlorophenyl)‐1,3,4‐oxadiazol‐2‐yl}thio]‐N‐(3‐methylphen‐
yl)propanamide (6c)
Yield: 70%; M.P.: 132–134°C; IR (KBr): v = 3,032, 2,940, 1,690, 1,605,
4
.1.5 | Synthesis of compounds (5a–n)
−
1 1
and 1,550 cm
;
3
H‐NMR (500 MHz, CDCl ): δ = 1.49 (d, J = 7.0 Hz,
The calculated amount of aryl/aralkyl amines (4a–n, 11.0 mM each)
3
3H, H‐3ʹ), 1.74 (s, 3H, CH ), 4.45 (q, J = 7.0 Hz, 1H, H‐2′), Ar‐H 7.42
was added to 10 ml of distilled water in an iodine flask containing
(s, 1H, H‐2‴), 7.55 (d, J = 8.0 Hz, 1H, H‐4‴), 7.60 (dd, J = 8.5, 7.0 Hz,
1H, H‐5‴), 7.62 (d, J = 8.0 Hz, 1H, H‐6‴), 7.72 (d, J = 8.5 Hz, 2H,
H‐3ʹ,5ʹ), 7.96 (d, J = 8.5 Hz, 2H, H‐2ʹ,6ʹ), and 9.96 (s, 1H, NH);
5
% Na
was stirred for 10 min and then 2‐bromopropionyl bromide (1.0 ml,
1.0 mM) was poured into the reaction mixture drop‐wise in 2–5 min
2 3
CO solution to adjust the pH 9–10. The reaction mixture
1
3
1
C‐NMR (125 MHz, CDCl
3
): δ = 19.8 (C‐3ʹ), 21.1 (CH ), 39.8 (C‐2ʹ),
3
with constant stirring. The flask was shaken vigorously untill the
precipitates formed and the room temperature was achieved.
The precipitates were further stirred for 45 min. The reaction
progress was monitored by TLC (n‐hexane/ethylacetate; 7:3).
The final products were filtered, washed with distilled water,
dried to get the respective N‐aralkyl/aryl‐substituted‐2‐bromopro-
pionamides (5a–n).
Ar‐C [117.8 (C‐2‴), 120.1 (C‐2″,6″), 127.0 (C‐3″,5″), 128.7 (C‐5‴),
129.3 (C‐6‴), 130.0 (C‐3‴), 132.4 (C‐4‴), 135.3 (C‐1‴), 136.9 (C‐1″),
140.7 (C‐4″), 142.3 (C‐5), 147.3 (C‐2), and 166.0 (C‐1ʹ)]; HR‐EI‐MS
+
(m/z): 373.0658 [M] calculated for C18
H16SN
3 2
O Cl; 373.0642.
2‐[{5‐(4‐Chlorophenyl)‐1,3,4‐oxadiazol‐2‐yl}thio]‐N‐(4‐methylphen‐
yl)propanamide (6d)
Yield: 79%; M.P.: 135–137°C; IR (KBr): v = 3,020, 2,920, 1,696, 1,597,
−
1 1
and 1,535 cm
;
3
H‐NMR (500 MHz, CDCl ): δ = 1.38 (d, J = 7.0 Hz,
4
.1.6 | Synthesis of compounds (6a–n)
3H, H‐3ʹ), 2.50 (s, 3H, CH
3
), 4.38 (q, J = 7.0 Hz, 1H, H‐2ʹ), Ar‐H 7.42
Compound 3 (0.002 g, 0.1 mM) was dissolved in N,N‐dimethylforma-
mide (DMF, 10 ml) in a 50‐ml round‐bottom flask followed by the
addition of sodium hydride (0.002 g, 0.1 mM). The mixture was
stirred for 30 min at room temperature and then electrophiles (5a–n
each, respectively) were added slowly with further stirring for 2–3 hr.
Distilled water was added to the flask and the products were
recovered by filtration or solvent extraction according to the product
nature.
(d, J = 8.5 Hz, 2H, H‐2‴,6‴), 7.55 (d, J = 8.5 Hz, 2H, H‐3‴,5‴), 7.61
(d, J = 8.5 Hz, 2H, H‐3″,5″), 7.70 (d, J = 8.5 Hz, 2H, H‐2″,6″), 9.25
1
3
(s, 1H, NH); C‐NMR (125 MHz, CDCl
3 3
): δ = 20.8 (C‐3ʹ), 21.9 (CH ),
37.6 (C‐2ʹ), Ar‐C [119.3 (C‐2‴), 120.1 (C‐2″,6″), 126.0 (C‐3″,5″), 129.9
(C‐5‴), 130.3 (C‐6‴), 130.7 (C‐3‴), 131.4 (C‐4‴), 134.3 (C‐1‴), 137.9
(C‐1″), 142.1 (C‐4″), 142.8 (C‐5), 149.3 (C‐2), and 166.1 (C‐1ʹ)];
+
HR‐EI‐MS (m/z): 373.0658 [M] calculated for C18
H16SN
3 2
O Cl;
373.0642.
2
‐[{5‐(4‐Chlorophenyl)‐1,3,4‐oxadiazol‐2‐yl}thio]‐N‐phenylpropana-
2‐[{5‐(4‐Chlorophenyl)‐1,3,4‐oxadiazol‐2‐yl}thio]‐N‐(2,3‐dimethyl-
phenyl)propanamide (6e)
mide (6a)
Yield: 78%; M.P.: 135–136°C; IR (KBr): v = 3,020, 2,920, 1,696, 1,597,
Yield: 73%; M.P.: 127–139°C; IR (KBr): v = 3,029, 2,918, 1,688, 1,591,
−1 1
−1
1
and 1,535 cm
;
H‐NMR (500 MHz, CDCl
3
): δ = 1.73 (d, J = 7.0 Hz,
and 1,529 cm
;
3
H‐NMR (500 MHz, CDCl ): δ = 1.39 (d, J = 7.0 Hz,

10 of 12
IFTIKHAR ET AL.
|
3
H, H‐3ʹ), 1.78 (s, 3H, CH
3
), 2.10 (s, 3H, CH
3
), 4.45 (q, J = 7.0 Hz, 1H,
2‐[{5‐(4‐Chlorophenyl)‐1,3,4‐oxadiazol‐2‐yl}thio]‐N‐(3,4‐dimethyl-
phenyl)propanamide (6i)
H‐2ʹ), Ar‐H 7.42–7.46 (m, 1H, CH), 7.45 (d, J = 8.5 Hz, 2H, H‐3″,5″),
1
3
and 7.68 (d, J = 8.5 Hz, 2H, H‐2″,6″); C‐NMR (125 MHz, CDCl
δ = 21.7 (C‐3ʹ), 23.1 (CH ), 25.1 (CH ), 34.6 (C‐2ʹ), Ar‐C [117.3 (C‐2‴),
20.1 (C‐2″,6″), 128.0 (C‐3″,5″), 128.9 (C‐5‴), 130.5 (C‐6‴), 130.9
3
):
Yield: 70%; M.P.: 138–140°C; IR (KBr): v = 3,035, 2,925, 1,696, 1,590,
−
1 1
3
3
and 1,535 cm
;
H‐NMR (500 MHz, CDCl ): δ = 1.45 (d, J = 7.0 Hz,
3
), 1.72 (s, 3H, CH ), 4.39 (q, J = 7.5 Hz, 1H,
3
1
3H, H‐3ʹ), 1.68 (s, 3ʹH, CH
3
(
C‐3‴), 133.4 (C‐4‴), 138.3 (C‐1‴), 139.9 (C‐1″), 142.7 (C‐4″), 142.8
H‐2′), Ar‐H 7.55 (s, 1H, H‐2‴), 7.67 (d, J = 8.5 Hz, 1H, H‐5‴), 7.72
(d, J = 8.5 Hz, 1H, H‐6‴), 7.88 (d, J = 8.5 Hz, 2H, H‐3″,5″), and 7.70
+
(
C‐5), 149.3 (C‐2), and 168.0 (C‐1ʹ)]; HR‐EI‐MS (m/z): 387.0812 [M]
1
3
calculated for C19
H18SN
3 2
O Cl; 387.0798.
(d, J = 8.5 Hz, 2H, H‐2″,6″); C‐NMR (125 MHz, CDCl
3
): δ = 21.1
), 34.7 (C‐2ʹ), Ar‐C [120.5 (C‐2‴), 121.1
C‐2″,6″), 126.4 (C‐3″,5″), 127.9 (C‐5‴), 129.5 (C‐6‴), 132.5 (C‐3‴),
3 3
(C‐3ʹ), 22.1 (CH ), 23.9 (CH
(
2
‐[{5‐(4‐Chlorophenyl)‐1,3,4‐oxadiazol‐2‐yl}thio]‐N‐(2,4‐dimethyl-
phenyl)propanamide (6f)
Yield: 65%; M.P.: 139–140°C; IR (KBr): v = 3,045, 2,945, 1,710,
1
33.4 (C‐4‴), 134.5 (C‐1‴), 138.1 (C‐1″), 142.7 (C‐4″), 147.8 (C‐5),
+
1
49.3 (C‐2), and 160.0 (C‐1ʹ)]; HR‐EI‐MS (m/z): 387.0812 [M]
3 2
calculated for C19H18SN O Cl; 387.0798.
−
1
1
1
,605, and 1,545 cm
d, J = 7.0 Hz, 3H, H‐3ʹ), 1.69 (s, 3H, CH
q, J = 7.0 Hz, 1H, H‐2ʹ), Ar‐H, 7.35 (s, 1H, H‐3‴), 7.42 (d, J = 8.5 Hz,
H, H‐5‴), 7.47 (d, J = 8.5 Hz, 1H, H‐6‴), 7.58 (d, J = 8.5 Hz, 2H,
;
H‐NMR (500 MHz, CDCl
3
): δ = 1.40
(
(
3
), 1.70 (s, 3H, CH
3
), 4.40
2
‐[{5‐(4‐Chlorophenyl)‐1,3,4‐oxadiazol‐2‐yl}thio]‐N‐(3,5‐dimethyl-
phenyl)propanamide (6j)
Yield: 75%; M.P.: 133–135°C; IR (KBr): v = 3,025, 2,929, 1,696, 1,588,
1
1
3
H‐3″,5″), and 7.68 (d, J = 8.5 Hz, 2H, H‐2″,6″); C‐NMR (125 MHz,
CDCl ): δ = 23.1 (C‐3ʹ), 23.5 (CH ), 25.7 (CH ), 34.0 (C‐2ʹ), Ar‐C
118.5 (C‐2‴), 121.7 (C‐2″,6‴), 126.0 (C‐3″,5″), 127.9 (C‐5‴),
−1 1
and 1,545 cm
H, H‐3ʹ), 1.77 (s, 3H, CH
H‐2ʹ), Ar‐H 7.21 (s, 1H, H‐2‴), 7.29 (s, 1H, H‐4‴), 7.31 (s, 1H, H‐6‴),
;
H‐NMR (500 MHz, CDCl
3
): δ = 1.76 (d, J = 7.0 Hz,
3
3
3
3
3
), 2.13 (s, 3H, CH
3
), 4.45 (q, J = 7.0 Hz, 1H,
[
1
29.5 (C‐6‴), 132.5 (C‐3‴), 133.9 (C‐4‴), 134.3 (C‐1‴), 138.1
7
8
.42 (d, J = 8.5 Hz, 2H, H‐3″,5″), 7.60 (d, J = 8.5 Hz, 2H, H‐2″,6″), and
(
C‐1″), 142.7 (C‐4″), 142.8 (C‐5), 144.3 (C‐2), and 162.0 (C‐1ʹ)];
13
.75 (s, 1H, NH); C‐NMR (125 MHz, CDCl ): δ = 19.7 (C‐3ʹ), 21.1
3
+
HR‐EI‐MS (m/z): 387.0812 [M] calculated for C19
H
18SN
3
O
2
Cl;
3
(CH ), 23.1 (CH
3
), 33.6 (C‐2ʹ), Ar‐C [119.7 (C‐2‴), 120.1 (C‐2″,6″),
3
87.0798.
127.0 (C‐3″,5″), 128.9 (C‐5‴), 130.5 (C‐6‴), 130.9 (C‐3‴), 133.4
(
(
C‐4‴), 138.3 (C‐1‴), 139.9 (C‐1″), 141.7 (C‐4″), 142.8 (C‐5), 149.3
+
C‐2), and 160.0 (C‐1ʹ)]; HR‐EI‐MS (m/z): 387.0812 [M] calculated
2
‐[{5‐(4‐Chlorophenyl)‐1,3,4‐oxadiazol‐2‐yl}thio]‐N‐(2,5‐dimethyl-
3 2
for C19H18SN O Cl; 387.0798.
phenyl)propanamide (6g)
Yield: 71%; M.P.: 157–159°C; IR (KBr): v = 3,020, 2,920, 1,696, 1,597,
−1
1
2‐[{5‐(4‐Chlorophenyl)‐1,3,4‐oxadiazol‐2‐yl}thio]‐N‐(2‐ethylphenyl)‐
propanamide (6k)
and 1,535 cm
H, H‐3′), 1.69 (s, 3H, CH
J = 7.0 Hz), Ar‐H 7.35 (s, 1H, H‐6‴), 7.41 (d, J = 8.5 Hz, 1H, H‐3‴), 7.45
;
H‐NMR (500 MHz, CDCl
3
): δ = 1.60 (d, J = 7.0 Hz,
3
3
), 1.70 (s, 3H, CH
3
), 4.42 (q, 1H, H‐2′,
Yield: 71%; M.P.: 133–135°C; IR (KBr): v = 3,029, 2,920, 1,701, 1,590,
−
1 1
and 1,540 cm
3H, CH –CH
CH –CH ), 4.35 (q, J = 7.0 Hz, 1H, H‐2ʹ), Ar‐H 7.21–7.26 (m, 4H, CH),
.48 (d, J = 8.5 Hz, 2H, H‐3″,5″), 7.93 (d, J = 8.5 Hz, 2H, H‐2″,6″), and
;
H‐NMR (500 MHz, CDCl
3
): δ = 1.16 (t, J = 6.5 Hz,
(
(
(
(
d, J = 8.5 Hz, 1H, H‐4‴), 7.59 (d, J = 8.5 Hz, 2H, H‐3″,5″), and 7.70
1
3
3
2
), 1.39 (d, J = 7.0 Hz, 3H, H‐3ʹ), 2.60 (q, J = 6.5 Hz, 2H,
d, J = 8.5 Hz, 2H, H‐2″,6″); C‐NMR (125 MHz, CDCl
C‐3ʹ), 22.5 (CH ), 25.9 (CH ), 34.1 (C‐2ʹ), Ar‐C [120.5 (C‐2‴), 121.1
C‐2″,6″), 126.4 (C‐3″,5″), 127.9 (C‐5‴), 129.5 (C‐6‴), 130.5 (C‐3‴),
3
): δ = 20.1
2
3
3
3
7
8
1
3
.75 (s, 1H, NH); C‐NMR (125 MHz, CDCl
), 24.5 (CH ), 44.5 (C‐2ʹ), Ar‐C [121.5 (C‐2‴), 123.4 (C‐2″,6″),
26.5 (C‐3″,5″), 128.7 (C‐5‴), 129.6 (C‐6‴), 134.8 (C‐3‴), 135.3
3
): δ = 14.1 (C‐3ʹ), 17.0
1
33.9 (C‐4‴), 134.3 (C‐1‴), 138.1 (C‐1″), 142.7 (C‐4″), 142.8 (C‐5),
+
(CH
3
2
1
44.3 (C‐2), and 162.0 (C‐1ʹ)]; HR‐EI‐MS (m/z): 387.0812 [M]
1
3 2
calculated for C19H18SN O Cl; 387.0798.
(
(
C‐4‴), 138.3 (C‐1‴), 139.9 (C‐1″), 149.7 (C‐4″), 165.0 (C‐5), 165.4
+
C‐2), and 168.7 (C‐1ʹ)]; HR‐EI‐MS (m/z): 387.0812 [M] calculated
2
‐[{5‐(4‐Chlorophenyl)‐1,3,4‐oxadiazol‐2‐yl}thio]‐N‐(2,6‐dimethyl-
phenyl)propanamide (6h)
Yield: 70%; M.P.: 140–142°C; IR (KBr): v = 3,030, 2,929, 1,692,
3 2
for C19H18SN O Cl; 387.0798.
2‐[{5‐(4‐Chlorophenyl)‐1,3,4‐oxadiazol‐2‐yl}thio]‐N‐(4‐ethylphenyl)‐
propanamide (6l)
−
1
1
1
,589, and 1,525 cm
;
H‐NMR (500 MHz, CDCl
3
): δ = 1.34
), 4.45
(
(
(
d, J = 7.0 Hz, 3H, H‐3ʹ), 1.66 (s, 3H, CH
3
), 2.19 (s, 3H, CH
3
Yield: 73%; M.P.: 138–141°C; IR (KBr): v = 3,025, 2,920, 1,696, 1,605,
−
1 1
q, 1H, H‐2ʹ, J = 7.0 Hz), Ar‐H 7.42–7.46 (m, 1H, 3CH), 7.49
d, J = 8.5 Hz, 2H, H‐3″,5″), and 7.60 (d, J = 8.5 Hz, 2H, H‐2″,6″);
and 1,532 cm
3H, CH –CH
CH –CH ), 4.21 (q, J = 7.0 Hz, 1H, H‐2ʹ), Ar‐H 7.10 (d, J = 8.5 Hz, 2H,
;
H‐NMR (500 MHz, CDCl
3
): δ = 1.28 (t, J = 6.4 Hz,
3
2
), 1.40 (d, J = 7.0 Hz, 3H, H‐3ʹ), 2.19 (q, J = 6.4 Hz, 2H,
1
3
C‐NMR (125 MHz, CDCl
3
): δ = 21.7 (C‐3ʹ), 23.1 (CH
3
), 25.1 (CH
3
),
2
3
3
1
4.6 (C‐2ʹ), Ar‐C [117.3 (C‐2‴), 120.1 (C‐2″,6″), 128.0 (C‐3″,5″),
28.9 (C‐5‴), 130.5 (C‐6‴), 130.9 (C‐3‴), 133.4 (C‐4‴), 138.3
H‐2‴,6‴), 7.18 (d, J = 8.5 Hz, 2H, H‐3‴,5‴), 7.48 (d, J = 8.5 Hz, 2H,
H‐3″,5″), 7.93 (d, J = 8.5 Hz, 2H, H‐2″,6″), and 8.75 (s, 1H, NH);
1
3
(
C‐1‴), 139.9 (C‐1″), 142.7 (C‐4″), 142.8 (C‐5), 149.3 (C‐2), and
C‐NMR (125 MHz, CDCl
3
): δ = 14.1 (CH
3 2
), 17.0 (C‐3ʹ), 24.5 (CH ),
+
1
68.0 (C‐1ʹ)]; HR‐EI‐MS [M] (m/z): 387.0812 calculated for
44.5 (C‐2ʹ), Ar‐C [121.5 (C‐2‴), 123.4 (C‐2″,6″), 126.5 (C‐3″,5″), 128.7
(C‐5‴), 129.6 (C‐6‴), 134.8 (C‐3‴), 135.3 (C‐4‴), 138.3 (C‐1‴), 139.9
19 3 2
C H18SN O Cl; 387.0798.

IFTIKHAR ET AL.
11 of 12
|
(
C‐1″), 149.7 (C‐4″), 165.0 (C‐5), 165.4 (C‐2), and 168.7 (C‐1ʹ)];
The IC50 values of the active compounds were calculated from
the data obtained by measuring inhibitory activities of compounds
after their suitable dilutions using Ez‐Fit Perella Scientific software.
+
HR‐EI‐MS (m/z): 387.0812 [M] calculated for C19
H18SN
O
3 2
Cl;
3
87.0798.
2
‐[{5‐(4‐Chlorophenyl)‐1,3,4‐oxadiazol‐2‐yl}thio]‐N‐(2‐ethoxyphen‐
4
.3
|
Homology modeling of yeast α‐glucosidase
yl)propanamide (6m)
The homology model of α‐glucosidase from S. cerevisiae was built
because to date no crystal structure of α‐glucosidase has been
reported in PDB. The amino acid sequence of α‐glucosidase
was retrieved from using UniProt ID P53341 and aligned with
the best selected template of isomaltase from S. cerevisiae (PDB
Yield: 65%; M.P.: 140–142°C; IR (KBr): v = 3,029, 2,929, 1,710,
−
1
1
1
,592, and 1,529 cm
t, J = 6.6 Hz, 3H, CH
q, J = 7.0 Hz, 2H, CH
.16–7.19 (m, 4H, CH), 6.81 (d, J = 8.5 Hz, 2H, H‐3″,5″), 7.92
;
H‐NMR (500 MHz, CDCl
), 1.72 (d, J = 7.5 Hz, 3H, H‐3ʹ), 3.99
), 4.35 (q, J = 7.5 Hz, 1H, H‐2ʹ), Ar‐H
3
): δ = 1.37
(
(
3
–CH
2
3
–CH
2
7
[
39]
1
3
ID: 3A4A).
Sequence alignment was carried using “zAlign
(
(
(
(
(
d, J = 8.5 Hz, 2H, H‐2″,6″), and 8.75 (s, 1H, NH);
125 MHz, CDCl ): δ = 14.8 (CH ), 16.9 (C‐3ʹ), 63.6 (CH
C‐NMR
2
), 44.7
sequence to template” tool in Discovery Studio Client vs 16.1
3
3
program and homology modeling was also performed out using
C‐2′), Ar‐C [113.2 (C‐2‴), 121.5 (C‐2″,6″), 121.6 (C‐5‴), 125.5
C‐3″,5″), 128.0 (C‐6‴), 129.5 (C‐3‴), 130.7 (C‐4‴), 138.4
[
40]
built in Modeler v. 9.15 in DS software.
The best homology
model was selected on the basis of the DOPE score while
validation and assessment were conducted via Ramachandran
C‐1‴), 155.8 (C‐1″), 165.1 (C‐4″), 165.3 (C‐5), 165.4 (C‐2), and
+
1
68.0 (C‐1ʹ)]; HR‐EI‐MS (m/z): 403.0759 [M] calculated for
[
41]
plot using RAMPAGE.
19 3 3
C H18SN O Cl; 403.0747.
2‐[{5‐(4‐Chlorophenyl)‐1,3,4‐oxadiazol‐2‐yl}thio]‐N‐(4‐ethoxyphen‐
4.4 Molecular docking studies
|
yl)propanamide (6n)
Molecular docking calculations were performed using FRED tool in
Yield: 77%; M.P.: 133–134°C; IR (KBr): v = 3,035, 2,920, 1,690, 1,590,
[42,43]
Open Eye software.
All the compounds were first drawn in
−
1 1
and 1,545 cm
H, CH –CH
O–CH –CH ), 4.35 (q, J = 7.0 Hz, 1H, H‐2ʹ), Ar‐H 7.12 (d, J = 8.5 Hz,
H, H‐2‴,6‴), 7.21 (d, J = 8.5 Hz, 2H, H‐3‴,5‴), 7.54 (d, J = 8.5 Hz, 1H,
H‐3″,5″), 7.88 (d, J = 8.5 Hz, 2H, H‐2″,6″), and 8.75 (s, 1H, NH);
;
H‐NMR (500 MHz, CDCl
3
): δ = 1.35 (t, J = 6.6 Hz;
[44]
Chemdraw Professionals ver. 15.1
and then were imported into
3
3
2
–O), 1.39 (d, J = 7.0 Hz, 3H, H‐3ʹ), 3.45 (q, J = 6.6 Hz, 2H,
Discovery Studio for 3D structure generation and energy minimiza-
tion. OMEGA 2.5 tool of Open Eye software was used for generation
2
3
2
[45,46]
of conformers of compounds.
Active site was selected on the
basis of modeled cocrystal ligand α‐glucose. Before molecular
docking studies, docking protocol was optimized for cocrystal ligand
and then final docking was carried out for all the compounds as well
as the reference compound for comparison. During docking calcula-
tions, 20 different poses were generated and sorted out based on
the lowest Chemgauss4 score. Binding orientations were also
1
3
C‐NMR (125 MHz, CDCl
4.7 (C‐2ʹ), Ar‐C [113.2 (C‐2‴), 121.5 (C‐2″,6″), 121.6 (C‐5‴), 126.7
C‐3″,5″), 129.0 (C‐6‴), 129.5 (C‐3‴), 131.7 (C‐4‴), 136.4 (C‐1‴),
3
): δ = 14.8 (CH
3
2
), 16.9 (C‐3ʹ), 59.3 (CH ),
4
(
142.3 (C‐1″), 160.1 (C‐4″), 161.3 (C‐5), 165.4 (C‐2), and 168.7 (C‐1ʹ)];
+
HR‐EI‐MS (m/z): 403.0759 [M] calculated for C19
H18SN
O
3 3
Cl;
403.0747.
[39]
visualized using Discovery Studio software.
4
.2
|
α‐Glucosidase inhibition assay
ACKNOWLEDGMENT
Yeast αglucosidase inhibition assay was performed according to
We are thankful to Open Eye Scientific for providing free academic
license of Open Eye Suite.
[
38]
the method used by Tariq et al.
Total reaction volume of 100 µl
contained 70 µl of 50 mM phosphate buffer pH 6.8, 10‐µl (0.5 mM)
test compound, followed by the addition of 10 µl (0.057 units)
yeast enzyme (Sigma Inc.). The contents were mixed, preincubated
for 10 min at 37°C, and preread at 400 nm. The reaction was
initiated by the addition of 10 µl of 0.5 mM substrate (p‐
nitrophenyl‐α‐D‐glucopyranoside). After 25–30 min of incubation
at 37°C, absorbance was measured using Synergy HST microplate
reader (BioTek). All experiments were carried out in triplicates and
the data are presented as mean ± standard error of the mean.
Acarbose was used as positive control. The percentage inhibition
of the enzyme was calculated using the following formula.
ORCID
Naheed Riaz
http://orcid.org/0000-0002-6890-882X
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How to cite this article: Iftikhar M, Shahnawaz, Saleem M,
et al. A novel five‐step synthetic route to 1,3,4‐oxadiazole
derivatives with potent α‐glucosidase inhibitory potential
and their in silico studies. Arch Pharm Chem Life Sci.
[
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29] R. Nirogi, A. R. Mohammed, A. K. Shinde, S. R. Gagginapally,
D. M. Kancharla, V. R. Middekadi, N. Bogaraju, S. R. Ravella, P. Singh,
2019;e1900095. https://doi.org/10.1002/ardp.201900095