Synthesis, in vitro α-glucosidase inhibitory potential and molecular docking study of thiadiazole analogs

Article abstract of DOI:10.1016/j.bioorg.2018.03.022

α-Glucosidase is a catabolic enzyme that regulates the body's plasma glucose levels by providing energy sources to maintain healthy functioning. 2-Amino-thiadiazole (1–13) and 2-amino-thiadiazole based Schiff bases (14–22) were synthesized, characterized by ¹H NMR and HREI-MS and screened for α-glucosidase inhibitory activity. All twenty-two (22) analogs exhibit varied degree of α-glucosidase inhibitory potential with IC₅₀ values ranging between 2.30 ± 0.1 to 38.30 ± 0.7 μM, when compare with standard drug acarbose having IC₅₀ value of 39.60 ± 0.70 μM. Among the series eight derivatives 1, 2, 6, 7, 14, 17, 19 and 20 showed outstanding α-glucosidase inhibitory potential with IC₅₀ values of 3.30 ± 0.1, 5.80 ± 0.2, 2.30 ± 0.1, 2.70 ± 0.1, 2.30 ± 0.1, 5.50 ± 0.1, 4.70 ± 0.2, and 5.50 ± 0.2 μM respectively, which is many fold better than the standard drug acarbose. The remaining analogs showed good to excellent α-glucosidase inhibition. Structure activity relationship has been established for all compounds. The binding interactions of these compounds were confirmed through molecular docking.

Full text of DOI:10.1016/j.bioorg.2018.03.022

Accepted Manuscript
Synthesis, in vitro α-glucosidase inhibitory potential and molecular docking
study of thiadiazole analogs
Muhammad Tariq Javid, Fazal Rahim, Muhammad Taha, Haseeb Ur Rehman,
Mohsan Nawaz, Abdul wadood, Syahrul Imran, Imad Uddin, Ashik Mosaddik,
Khalid Mohammed Khan
PII:
S0045-2068(18)30048-8
DOI:
https://doi.org/10.1016/j.bioorg.2018.03.022
YBIOO 2312
Reference:
To appear in:
Bioorganic Chemistry
Received Date:
Revised Date:
Accepted Date:
17 January 2018
15 March 2018
18 March 2018
Please cite this article as: M. Tariq Javid, F. Rahim, M. Taha, H. Ur Rehman, M. Nawaz, A. wadood, S. Imran, I.
Uddin, A. Mosaddik, K. Mohammed Khan, Synthesis, in vitro α-glucosidase inhibitory potential and molecular
docking study of thiadiazole analogs, Bioorganic Chemistry (2018), doi: https://doi.org/10.1016/j.bioorg.
2
018.03.022
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Synthesis, in vitro α-glucosidase inhibitory potential and molecular docking study of
thiadiazole analogs
a
a
b
a
Muhammad Tariq Javid , Fazal Rahim , Muhammad Taha , Haseeb Ur Rehman , Mohsan
a
c
d
a
b
Nawaz , Abdul wadood , Syahrul Imran , Imad Uddin , Ashik Mosaddik , Khalid Mohammed
e
Khan
a
Depatment of Chemistry, Hazara University, Mansehra-21300, Pakistan
Department of clinical pharmacy, Institute for Research and Medical Consultations (IRMC),
b
Imam Abdulrahman Bin Faisal University, P.O. Box 1982, Dammam 3144,, Saudi Arabia.
c
Department of Biochemistry, Abdul Wali Khan University Mardan, Mardan-23200, Pakistan.
Atta-ur-Rahman Institute for Natural Product Discovery, Universiti Teknologi MARA (UiTM),
d
Puncak Alam Campus, 42300 Bandar Puncak Alam, Selangor D. E. Malaysia.
e
H. E. J. Research Institute of Chemistry, International Center for Chemical and Biological
Sciences, University of Karachi, Karachi-75270, Pakistan.
Abstract
α-Glucosidase is a catabolic enzyme that regulates the body’s plasma glucose levels by providing
energy sources to maintain healthy functioning. 2-Amino-thiadiazole (1-13) and 2-amino-
1
thiadiazole based Schiff bases (14-22) were synthesized, characterized by HNMR and HREI-
MS and screened for α-glucosidase inhibitory activity. All twenty two (22) analogs exhibit
varied degree of α-glucosidase inhibitory potential with IC50 values ranging between 2.30 ± 0.1
to 38.30 ± 0.7 μM, when compare with standard drug acarbose having IC50 value of 39.60 ± 0.70
μM. Among the series eight derivatives 1, 2, 6, 7, 14, 17, 19 and 20 showed outstanding α-
glucosidase inhibitory potential with IC50 values of 3.30 ± 0.1, 5.80 ± 0.2, 2.30 ± 0.1, 2.70 ± 0.1,
2
.30 ± 0.1, 5.50 ± 0.1,4.70 ± 0.2, and 5.50 ± 0.2μM respectively, which is many fold better than
the standard drug acarbose. The remaining analogs showed good to excellent α-glucosidase
inhibition. Structure activity relationship has been established for all compounds. The binding
interactions of these compounds were confirmed through molecular docking.
Keywords: Synthesis, thiadiazole, α-glucosidase, molecular docking study, SAR.
*Corresponding Author: fazalstar@gmail.com, Tel.: 0092-335-9528343
1

1
. Introduction
Diabetes mellitus (DM) is one of the most serious and chronic metabolic diseases all over the
world characterized by hyperglycemia resulting from defects in insulin secretion, insulin action,
or both [1, 2]. Normalization of blood glucose levels, especially postprandial hyperglycemia is
important to prevent the complications of diabetes which include retinopathy, neuropathy,
nephropathy, coronary heart disease, stroke, and peripheral arteriopathy [3]. α-Glucosidase
catalyzes the final step in the digestive process of carbohydrates to effect postprandial blood
glucose levels [4]. Patients with type-2 diabetes mellitus (T2DM) mostly suffer from
hyperglycemia, need to maintain normal blood glucose level to control the development of type
2
diabetes [5, 6]. In this regard α-glucosidase inhibitors play a critical role to prevent or delay the
digestion or absorption of carbohydrates and suppress postprandial hyperglycemia, making such
inhibitors useful in management of type 2 diabetes [7]. In addition, α-glucosidase inhibitors have
been thought to prevent postprandial endothelial dysfunction and cardio metabolic disorders, as
well as tumor growth and metastasis [8-11]. Thus, the study of α-glucosidase inhibition has
broad aspects and many potentially useful applications.
Heterocyclic compounds are of special interest to medicinal chemists because of their
exceptional chemical and versatile biological profiles. Despite significant research progress on
heterocyclic ring systems, efforts are on-going to identify novel heterocyclic compounds with
potent bioactivities. The 1,3,4-thiadiazole scaffold has drawn special interest because of its
inherent and diverse biological response [12].
1
,3,4-Thiadiazole, a privileged structure, represents a key motif in heterocyclic chemistry and
occupies a prime place in medicinal chemistry due its wide range of pharmacological activities
13]. Recently, derivatives of 1,3,4-oxadiazole/thiadiazole have been reported for their
[
antibacterial [14, 15], antifungal [16], antiviral [17], anti-inflammatory [18], antianxiety [19],
antimicrobial [20], anticonvulsant [21], anticancer [22], anti-depressant [23] and anti-tubercular
activities [24]. Some other thiadiazole containing drugs present in the market include
acetazolamide, methazolamide, cefazedone, timolol and xanomeline [25].
2

Fig-1: Thiadiazole containing drugs
Our research group has been working on design and synthesis of heterocyclic compounds
including thiadiazole, oxadiazole and oxazole derivatives in search of potential lead compounds
since few years and had found promising results [26-35]. Here in this study we are reporting
synthesis and α-glucosidase inhibition of thiadiazole derivatives.
2
2
. Results and Discussion
.1. Chemistry
Synthesis of 2-amino-1,3,4-thiadiazole analogs was carried out in two steps. In step-1, equimolar
thiosemicarbazide was mixed with different substituted benzaldehyde in ethanol in the presence
of 2-3ml of HCl as a catalyst and refluxed for 3-4 hrs. In step-2, these Schiff base intermediate
was cyclized by treating it with iodine and potassium carbonate using 1,4-dioxane as a solvent
and refluxed for 4 hrs. After reaction completion it was cooled at room temperature then reacted
with Na
2
S
2
3
O and extracts the desired organic compound from the reaction mixture using ethyl
acetate to get the corresponding solid product of 2-amino-1,3,4-thiadiazole analogs.
3

In step-3, equimolar 2-amino-1,3,4-thiadiazole was further reacted with substituted
benzaldehydes in methanol in the presence of few drops of acetic acid to give us the desired
thiadiazole based Schiff bases analogs (14-22).
Scheme-1: Synthesis of 2-amino-1,3,4-thiadiazole based Schiff bases analogs
Fig-2: General structure of (a) 2-amino-1,3,4-thiadiazole analogs (1-13) and (b) 2-amino-1,3,4-
thiadiazole based Schiff bases analogs (14-22)
Table-1: Different substituents of 2-amino-1,3,4-thiadiazole analogs (1-13) and 2-amino-1,3,4-
thiadiazole based Schiff bases analogs (1-22)
Sr. No.
R
1
R
2
1
2
3
4

4
5
6
7
8
9
1
0
1
1
1
2
3
1
2
.2. α-Glucosidase activity
2
-Aminothiadiazole (1-13) and thiadiazole based Schiff bases (14-22) were illustrated for α-
glucosidase inhibitory potential. All the synthesized analogs showed potent inhibitory potential
ranging between (2.70 ± 0.1µM to 38.30 ± 0.7µM) against standard drug acarbose with IC50
value of (38.45 ± 0.80 µM). Structure activity relationship shows that the activity of synthesized
5

analogs depends upon substituents attached to phenyl ring. 1,3,4-thiadiazole analogs having
substituent with phenyl ring i.e, 4-hydroxy analog (6) (IC50 = 2.30 ± 0.1 µM), 2,4-dichloro
analog (7) (IC50 = 2.70 ± 0.1 µM) and 2-nitro analog (1) (IC50 = 3.30 ± 0.1 µM) showed potent α-
glucosidase inhibitory potential. 4-hydroxy analog shows the best activity then that of 2,4-
dichloro and 2-nitro analogs this may be due to the hydroxy substituent. 2-nitro analog having
less IC50 value then 4-hydroxy and 2,4-dichloro analogs.
Figure 3: Most potent analogs6, 7 and 1
1
0
,3,4-thiadiazole analogs having 4-chloro analog (2) (5.80 ± 0.2), 4-nitro analogue (8) (6.40 ±
.2),3-nitro analog (13) (8.40 ± 0.2) and naphthalen-2-ol analog (10) (9.30 ± 0.3) showed
outstanding inhibitory potential due to the different substituents on phenyl part. Other 1,3,4-
thiadiazole analogs having substituents as 4-N,N-dimethylamine analog (4), 2-methoxy-5-bromo
analog (3), 2,3-dimethoxy analog (5), 3-benzyloxy-4-chloro analog (12), 4-benzyloxy analog
(
11), anthracenyl analog (9) with IC50 values of 11.70 ± 0.3, 15.90 ± 0.3, 20.10 ± 0.4, 25.30 ±
.4, 35.30 ± 0.6 and 38.30 ± 0.7μM, respectively showed excellent inhibitory potential.
0
Thiadiazole based Schiff bases analogs (14-22) were showed potent α-glucosidase inhibitory
potential. Thus these analogs having substituents on phenyl ring i.e, 4-hydroxy with 4-chloro
(
14) (2.30 ± 0.1µM), 2,4-dichloro with 4-chloro analog (19) (4.70 ± 0.2µM), 4-chloro with 2-
6

nitro analog (17) (5.50 ± 0.1µM) and 3-nitro with 2,4-dichloro (20) (5.50 ± 0.2µM) showed
important α-glucosidase inhibitory activity.
Figure-4: Most potent analogs 14 and 19
Other thiadiazole based Schiff bases analogs having 4-chloro with 4-nitro analog (15) (11.60 ±
0
.3), 5-bromo-2-methoxy with 3-nitro analog (21) (15.30 ± 0.3), 4-benzyloxy with 4-chloro
analog (18) (17.6 ± 0.4), 4-benzyloxy-3-methoxy with 4-hydroxy analog (22) (10.20 ± 0.2)5-
bromo-2-methoxy with 4-chloro analog (16) (25.30 ± 0.5), substituents on phenyl ring showed
excellent inhibitory potential.
The synthesized analogs are more active than the standard acarbose. Analogs with nitro, chloro
and hydroxy substituents possess outstanding activity.
Table-2: α-Glucosidase inhibition of thiadiazole derivatives (1-22)
a
a
Comp. No. IC50 ± SEM
Comp. No. IC50 ± SEM
1
2
3
4
5
6
7
8
9
3.30 ± 0.1
5.80 ± 0.2
15.90 ± 0.3
11.70 ± 0.3
20.10 ± 0.4
2.30 ± 0.1
2.70 ± 0.1
6.40 ± 0.2
38.30 ± 0.7
13
14
15
16
17
18
19
20
21
8.40 ± 0.2
2.30 ± 0.1
11.60 ± 0.3
25.30 ± 0.5
5.50 ± 0.1
17.6 ± 0.4
4.70 ± 0.2
5.50 ± 0.2
15.30 ± 0.3
7

1
1
1
0
1
2
9.30 ± 0.3
35.30 ± 0.6
25.30 ± 0.4
22
10.20 ± 0.2
Acarbose
39.60 ± 0.70
2
.3. Molecular docking analysis
In order to get insight into the binding interactions of the 2-amino-1,3,4-thiadiazole derivatives
with the active site amino acids of α-glucosidase the docking study was carried out. Although the
crystal structure of all eukaryotic α-glucosidase enzyme is still unavailable, so the 3D homology
model was used in this work for docking study. All the optimized compounds were docked into
the binding pocket of α-glucosidase. All the compounds showed good docking results as
experimental results. The top ranked conformations of the most active compounds were selected
for further studies and visual inference. Interaction detail of compounds and protein
To discuss the interaction detail of compounds and α-glucosidase, all the twenty-two synthesized
compounds were classified into two groups on the basis of their IC50 value.
i.
Interactions of the most active compounds
The compounds which have IC50 values between 2.30 ± 0.1 and 9.30 ± 0.3 exhibit varying
degree of α-glucosidase inhibitory activity. From the molecular docking study (docking score -
5
2
.231) it was observed that the top ranked conformation of the most active compound 06 (IC50
.30 ± 0.1mM) (Fig. 5a) established three hydrogen bonds through amine and hydroxyl group
with the binding site residues Glu276 and Asp408. The sulfur atom of thiadiazole group of
compound formed a hydrogen bond with Asn347 residues. Where as the compound shows an
arene-hydrogen interaction with the Arg439 and shows some hydrophobic interactions towards
Phe300 and His348 residues.
The docking results, of second most active compound 14 which have the same experimental
results as compound 6 with IC50 2.30 ± 0.1 μM (docking score -5.743) (Fig. 5b) revealed that the
chlorobenzene moiety of the compound establishes a hydrogen donor interaction with the oxygen
atom of Pro309 residue. Whereas three arene-H bonds were observed with Tyr71, Phe157 and
Arg312 and hydrophobic interactions with Tyr313 residue.
Compound 07 (2.70 ± 0.1) can be seen clearly in Figure 5c forming four interactions with the
residues Asp68, Asp214 and Asp349. Asp68 was involved in side chain hydrogen donor
interaction with the sulfur of thiadiazol group and amine group. The Asp214 shows a side chain
8

hydrogen donor interaction with the chlorine atom of chlorophenyl moiety and Asp349 also
involved in hydrogen bond with the sulfur of thiadiazol group of the compound.
Compound 1 which the third most active compound with IC50 value 3.30 ± 0.1 (docking score -
5
.783) (Fig. 5d) established six hydrogen bonds with the binding site residues of enzyme.
Arg212 and His348 formed hydrogen bonds with the nitro group of nitrobenzene moiety. Glu276
and Arg439 show hydrogen bonds with the thiadiazol moiety and Asp214 makes a hydrogen
bond with the benzene. Where as Phe177 and Phe300 involved in hydrophobic interactions.
The interaction of the compound with the active site of the enzyme may be due to the strong
electron withdrawing group like halogen and nitro (NO
2
) groups and electron donating groups
hydroxyl and amine (OH and NH ) groups in the compound.
2
Figure 5: Representation of most active compounds (green, cyan, pink and brown) in the
binding site (lemon yellow) of α-glucosidase (a) compound 6 (b) compound 14 (c) compound 7
(
d) compound 1. Interactions are represented as dotted lines, H-bonds black, arene-H bonds
green.
9

ii.
Binding interactions of moderate active compounds
Compounds having IC50 value between 10.20 ± 0.2 μM and 38.30 ± 0.7 μM exhibit varying
degree of α-glucosidase inhibitory activity and good docking results. The molecular docking
study of the top ranked compound of this series shows various interactions with the binding site
residues. Compound 22 with IC50 value 10.20 ± 0.2 μM (docking score -6.126) shows four
interactions. The benzene hydrogen formed one hydrogen bond with Gln181 and the phenol
group and benzene ring establishes three arene-hydrogen interactions with Phe177, Phe311 and
Arg312 residues of the enzymes (Fig. 6a).
Compound 15 with IC50 value of 11.60 ± 0.3 μM (docking score -6.492) also showed
considerable interactions with the binding site residues. The binding mode of compound 15
shown in figure (15C). The nitrophenyl moiety of the compound formed two hydrogen bonds
with Arg212 and His348. While the chlorophenyl moiety forms a hydrogen bond with Pro309
and two arene-hydrogen interactions with Phe157 and Arg312 residues (Fig. 6b).
The thiadiazol-2-amine moiety of compound 4 shows two hydrogen bonds (docking score -
5
.207) with the Phe157 residue of enzyme. Where as the Arg439 shows arene-hydrogen bond
with the thiadiazole ring of the compound (Fig. 6c). While compound 21 with IC50 value 15.30 ±
.3 (docking score -6.216) exhibited two hydrogen bonds with the Arg212 and His348 residues.
0
The compound also shows few hydrophobic interactions with residues Tyr71, Phe177 and
Phe300 (Fig. 6d). The moderate inhibitory activity of this group of compound may be due to the
presence of bulky methoxy groups. The brief interaction detail of the compounds is given in
Table-3.
10

Figure 6: Predicted binding interactions of moderately active compounds (green, pink, cyan and
brown) in the binding site (lemon yellow) of α-glucosidase. (a) compound22 (b) compound 15
(
c) compound 4 (d) compound 21. Interactions are represented as dotted lines, H-bonds black,
arene-H bonds green.
Table-3: Interaction detail of all twenty-two compounds.
CompNo.
Docking
score
Interaction detail (Ligands/α-glucosidase)
0
1
-5.783
Ligand
Receptor
Interaction Distance E(kcal/mol)
S 11 OE1 GLU 276
H-donor
3.55
3.26
3.22
3.33
-1.2
-1.6
-2.6
-1.3
N 8 NH1 ARG 439 H-acceptor
O 14 NH2 ARG 212 H-acceptor
O 15 NH2 ARG 212 H-acceptor
11

O 15 NE2 HIS 348
Ligand Receptor
H-acceptor
3.05
-1.8
0
0
2
3
-4.505
-5.895
Interaction Distance E(kcal/mol)
S 11 OD2 ASP 408
N 12 OD2 ASP 408
CL 13 OD1 ASP 214
H-donor
H-donor
H-donor
pi-H
3.70
2.95
3.30
4.25
-0.7
-3.7
-1.0
-0.8
5
-ring
CB PHE 157
Receptor
Ligand
S 11
Interaction
H-donor
H-donor
H-donor
H-acceptor
pi-pi
Distance E(kcal/mol)
OD2 ASP 68
3.61
3.62
3.12
3.09
3.93
-4.1
-1.8
-4.9
-1.2
-0.0
S 11 OD2 ASP 349
N 12 OD2 ASP 68
O 14 NH2 ARG 212
5
-ring 6-ring PHE 177
0
4
-5.207
Ligand
S 11
N 12
Receptor
PHE 157
PHE 157
Interaction
H-donor
H-donor
pi-H
Distance E(kcal/mol)
O
O
3.58
3.30
4.62
-0.4
-1.7
-0.4
5
-ring
CD ARG 439
Receptor
0
0
5
6
-5.695
-5.231
Ligand
N 12
Interaction Distance E(kcal/mol)
O
PHE 157
H-donor
H-donor
Interaction
H-donor
H-donor
H-donor
H-donor
pi-H
3.12
2.97
-0.9
-0.8
N 12 OD2 ASP 408
Ligand
O 8
Receptor
Distance E(kcal/mol)
OD2 ASP 408
2.83
4.02
3.03
3.08
3.64
-2.3
-0.5
-2.7
-0.6
-0.8
S 12 OD1 ASN 347
N 13 OE1 GLU 276
N 13 OE2 GLU 276
6
-ring CD ARG 439
0
7
-5.446
Ligand
S 11
Receptor
Interaction
H-donor
H-donor
H-donor
H-donor
pi-pi
Distance E(kcal/mol)
OD2 ASP 68
3.45
4.00
3.08
3.19
3.78
-2.9
-0.6
-4.7
-0.2
-0.0
S 11 OD2 ASP 349
N 12 OD2 ASP 68
CL 14 OD1 ASP 214
5
-ring
6-ring PHE 177
12

0
0
1
8
9
0
-5.327
-6.115
-5.477
Ligand
Receptor
Interaction
H-donor
H-donor
H-acceptor
H-acceptor
Interaction
H-donor
H-donor
pi-H
Distance E(kcal/mol)
S 11 OD2 ASP 408
N 12 OD2 ASP 408
O 14 NH2 ARG 212
O 15 NH2 ARG 212
4.02
2.96
3.37
3.01
-0.8
-2.0
-0.9
-1.9
Ligand
S 6
Receptor
Distance E(kcal/mol)
OD2 ASP 68
OD2 ASP 68
3.87
3.43
4.29
3.86
-3.6
-2.3
-0.8
-0.0
N 7
6
5
-ring CD ARG 439
-ring
6-ring PHE 177
Receptor
pi-pi
Ligand
S 11
Interaction
H-donor
H-donor
H-donor
pi-H
Distance E(kcal/mol)
OD2 ASP 68
3.54
3.76
3.41
3.95
3.93
-4.8
-0.5
-1.8
-0.6
-0.0
S 11 OD2 ASP 349
N 12 OD2 ASP 68
6
5
-ring CD ARG 439
-ring 6-ring PHE 177
pi-pi
1
1
1
1
1
2
3
4
-6.222
-6.121
-5.529
-5.743
Ligand
Receptor
Interaction
H-donor
H-donor
pi-H
Distance E(kcal/mol)
S 11 OD2 ASP 408
N 12 OD2 ASP 408
3.55
2.99
4.36
-0.4
-4.1
-1.2
5
-ring
CB PHE 157
Receptor
Ligand
S 1
Interaction
H-donor
H-donor
H-donor
Interaction
H-donor
H-donor
H-acceptor
Interaction
H-donor
H-pi
Distance E(kcal/mol)
OD1 ASP 214
OE1 GLU 276
OD1 ASP 214
Receptor
3.88
3.99
3.10
-3.0
-1.4
-3.9
S 1
N 6
Ligand
Distance E(kcal/mol)
S 11 OD1 ASP 214
N 12 OE1 GLN 181
O 15 ND2 ASN 347
3.92
3.53
3.21
-1.7
-0.8
-0.8
Ligand
CL 13
O 21
Receptor
PRO 309
6-ring TYR 71
Distance E (kcal/mol)
O
3.48
3.86
-0.5
-0.2
13

5
6
-ring
-ring
CB PHE 157
CB ARG 312
Receptor
pi-H
pi-H
4.36
3.72
-0.8
-0.5
1
5
-6.492
Ligand
CL 13
Interaction
H-donor
Distance E(kcal/mol)
O
PRO 309
3.22
2.96
3.24
4.60
3.53
-0.8
-3.2
-0.7
-1.2
-0.5
O 22 NH2 ARG 212 H-acceptor
O 23 NE2 HIS 348 H-acceptor
5
-ring
-ring CB ARG 312
Receptor
BR 20 OD2 ASP 68
CB PHE 157
pi-H
6
pi-H
1
1
1
6
7
8
-6.579
-6.621
-7.851
Ligand
Interaction
H-donor
H-donor
pi-H
Distance E (kcal/mol)
3.51
3.72
4.71
-0.6
-0.4
-1.2
CL 21
-ring CB
Ligand
O
PRO 309
PHE 157
5
Receptor
Interaction
H-acceptor
H-acceptor
Distance E (kcal/mol)
O 22 NH2 ARG 212
O 23 NH2 ARG 212
3.45
3.23
3.17
-0.9
-1.9
-1.1
O 23 NE2 HIS 348 H-acceptor
Ligand
CL 20
Receptor
PRO 309
Interaction
H-donor
H-pi
Distance E (kcal/mol)
O
2.99
3.57
3.84
3.56
-0.4
-0.5
-0.4
-0.3
C 27 6-ring PHE 177
6
6
-ring
N
ARG 312
pi-H
-ring CB ARG 312
pi-H
1
2
9
0
-6.216
-6.751
Ligand
CL 20
Receptor
PRO 309
Interaction
H-donor
H-acceptor
pi-H
Distance E (kcal/mol)
O
3.43
3.70
4.61
3.53
-0.7
-0.4
-1.2
-0.5
CL 21 NH2 ARG 212
5
6
-ring
CB PHE 157
-ring CB ARG 312
pi-H
Ligand
C 7
Receptor
Interaction
H-donor
H-donor
H-donor
pi-H
Distance E (kcal/mol)
OD2 ASP 408
3.61
3.30
3.48
4.84
-0.4
-0.1
S 11
O
PHE 157
S 11 OD2 ASP 408
-ring CB PHE 157
-0.2
-0.3
5
14

2
2
1
2
-6.216
-6.126
Ligand
Receptor
Interaction Distance E (kcal/mol)
O 24 NH2 ARG 212 H-acceptor
O 25 NE2 HIS 348 H-acceptor
3.20 -3.3
2.87 -2.9
Ligand
Receptor
Interaction
H-donor
H-pi
Distance E (kcal/mol)
H 11 OE1 GLN 181
C 25 6-ring PHE 177
2.77
3.54
4.51
3.97
-0.8
-0.5
-0.6
-1.3
6
6
-ring
-ring
CA PHE 311
ARG 312
pi-H
N
pi-H
2
.4. Conclusion
In conclusion we have synthesized and evaluated α-glucosidase inhibition of 2-Aminothiadiazole
1-13) and 2-Aminothiadiazole based Schiff base analogs (14-22). All compounds showed varied
(
degree of α-glucosidase inhibition ranging between 1.73 ± 0.001 to 69.65 ± 0.12 μM when
compared with the standard inhibitor acarbose having IC50 value 21.25 ± 0.15 μM. Among the
series, analogs 1, 2, 6, 7, 14, 17, 19 and 20 showed outstanding α-glucosidase inhibitory potential
which were more active than standard acarbose. The remaining analogs also showed good to
excellent α-glucosidase inhibition. SAR has been established for all compounds.
3
3
. Experimental
.1. Materials and Methods
The NMR spectra of concerned analogs of thiadiazole were recorded by on Avance Av-500 MHz
NMR spectrometers in which DMSO-d were used as a solvent. Chemical shift values of spectra
6
are assigned in δ (ppm). Tetramethylsilane act as internal standard. Jeol JMS-600H instrument
were used to obtained Electron Ionization Mass Spectra. The probability of reactions was
checked by TLC on pre-coated silica gel aluminum plates (kieselgel 60,254, E. Merck,
Germany). UV lamp at range of 254 and 365nm were used to observe the spots on TLC plate.
3
.2. Reaction procedure for the synthesis of 2-amino-1,3,4-thiadiazole
Synthesis of 2-amino-1,3,4-thiadiazole analogs was carried out in two steps. In first step various
benzaldehyde (1 mmol) was mixed with thiosemicarbazide (1 mmol) in ethanol. 2-3ml of HCl
was added as a catalyst and refluxes the reaction mixture for 3-4 hrs. The color change indicates
15

reaction progress. Reaction completion was monitored by TLC. On completion, reaction mixture
was filtered, washed with hexane followed by ethanol to get Schiff base intermediate.
In step-2, these Schiff base intermediate was cyclized by treating it with iodine and potassium
0
carbonate at 80 C using 1,4-dioxane as a solvent. The reaction mixture was refluxed for 4 hrs.
Reaction completion was monitored by TLC. After reaction completion it was cooled at room
temperature then reacted with 5% Na
2
S
2
3
O (20 mL) and extract the desired organic compound
from the reaction mixture using ethyl acetate. Upper layer with desired organic compound will
be collected and on evaporation get the corresponding solid product of 2-amino-1,3,4-thiadiazole
analogs.
3
.2.1. 5-(2-nitrophenyl)-1, 3, 4-thiadiazol-2-amine
1
Pale Yellow solid , Yield: 75%; H-NMR: (500 MHz, DMSO-d
6
): δ 10.2 (s, 2H, -NH ), 8.2 (d, J
2
=
6.4 HZ, 1H, Ar), 8.0(d, J= 8.2 HZ, 1H,Ar), 7.9 (dd, J = 7.2 HZ, J = 7.8 HZ, 1H,Ar), 7.6 (m,
1
3
1
1
3
H, Ar); C-NMR (125 MHz, DMSO-d
23.9; HR-EI-MS: m/z calcd for C
6
):δ 171.4, 158.2, 146.2, 135.0, 131.1, 129.2, 128.0,
+
8
H
6
N
4
O
2
S, [M] 222.0201; found 222.0200.
.2.2. 5-(4-chlorophenyl)-1,3,4-thiadiazole-2-amine
1
White solid, Yield: 85%; H-NMR (500 MHz, DMSO-d
6
): δ 10.1 (s, 2H, -NH ), 7.82 (d, J = 8.2
2
1
3
Hz, 2H, Ar), 7.60 (d, J = 8.6Hz, 2H, Ar); C-NMR (125 MHz, DMSO-d
6
):δ 173.4, 161.2, 134.0,
+
1
2
3
31.2, 128.7, 128.7, 128.1, 128.1; HR-EI-MS: m/z calcd for C
8
H
6
ClN
3
S, [M] 210.9971; found
10.9973.
.2.3. 5-(5-bromo-2-methoxyphenyl)-1,3,4-thiadiazol-2-amine
1
White solid, Yield: 70%; H-NMR (500 MHz, DMSO-d
6
): δ 10.0 (s, 2H, -NH ), 7.5 (d, J= 2.3
2
Hz, 1H, Ar), 7.2 (dd, J = 2.9 Hz, J = 8.9 Hz 1H, Ar), 7.1 (d, J = 8.8 Hz, 1H, Ar), 6.4(s, 3H, -
1
3
OCH3); C-NMR (125 MHz, DMSO-d
6
):δ 173.6, 161.1, 156.0, 133.5, 132.1, 124.0, 116.4,
+
1
14.0, 55.8; HR-EI-MS:m/z calcd for C
9
H
8
BrN
3
OS, [M] 284.9571; found 284.9575.
3
.2.4. 5-(4-(dimethylamino)phenyl)-1,3,4-thiadiazol-2-amine
1
White solid, Yield: 83%., H-NMR (500 MHz, DMSO-d
6
): δ 9.7 (s, 2H, -NH2), 7.4 (d, J= 8.2
1
3
Hz, 2H, Ar), 6.6 (d, J = 8.8 Hz, 2H, Ar), 3.14 (s, 6H, -CH
3
); C-NMR (125 MHz, DMSO-d
6
):δ
1
73.5, 161.3, 155.0, 129.1, 129.1, 122.4, 112.2, 112.2, 40.7, 40.7; HR-EI-MS: m/z calcd for
+
C
10
H
12
N S, [M] 220.0784; found 220.0781.
4
3
.2.5. 5-(2,3-dimethoxyphenyl)-1,3,4-thiadiazol-2-amine
16

1
Pale yellow, Yield: 80%. H-NMR (500 MHz, DMSO-d
6
): δ 10.1 (s, 2H, -NH2), 7.5 (dd, J = 1.7
Hz, J = 7.7Hz, 1H, Ar), 7.2 (t, J = 8.2 Hz, J = 7.0 Hz, 1H, Ar), 7.0 (dd, J = 1.7 Hz, J = 6.2 Hz,
1
3
1
1
H, Ar), 3.5 (s, 3H, -OCH
3
), 3.3 (s, 3H, -OCH
3
); C-NMR (125 MHz, DMSO-d ):δ 173.7, 161.2,
6
51.8, 147.6, 122.7, 122.2, 120.3, 114.8, 60.1, 55.4; HR-EI-MS: m/z calcd for C10
H
11
N
3
2
O S,
+
[
M] 237.0571; found 237.0570.
3
.2.6. 5-(4-hydroxy phenyl)-1,3,4-thiadiazole-2-amine
1
White, Yield: 75%; H-NMR (500 MHz, DMSO-d
6
): δ 10.0 (s, 1H, -OH) 8.5 (s, 2H, -NH2), 8.3
1
3
(
d, J = 7.7 Hz, 2H, Ar), 7.6 (d, J = 8.5 Hz, 2H, Ar); C-NMR (125 MHz, DMSO-d
6
): δ 173.4,
+
1
61.2, 158.1, 128.4, 128.4, 125.6, 116.0, 116.0; HR-EI-MS:m/z calcd for C
93.0311; found 193.0313.
8
H
7
3
N OS, [M]
1
3
.2.7. 5-(2,4-dichlorophenyl)-1,3,4-thiadiazole-2-amine
1
Solid white, Yield: 78%, H-NMR (500 MHz, DMSO-d
6
):δ 10.3 (s, 2H, -NH2), 8.1 (d, J= 8.2
1
3
Hz, 1H,Ar), 7.5 (d, J = 1.6 Hz, 1H, Ar), 7.3 (dd, J = 1.5 Hz, J = 8.3 Hz, 1H, Ar); C-NMR (125
MHz, DMSO-d
for C Cl
6
):δ 174.0, 161.1, 135.4, 134.3, 133.1, 130.4, 129.7, 127.0; HR-EI-MS: m/z calcd
+
8
H
5
2
N
3
S, [M] 244.9581; found, 244.9584.
3
.2.8. 5-(4-nitrophenyl)-1,3,4-oxadiazol-2-amine
1
Yellow. Yield: 70%, H-NMR (500 MHz, DMSO-d ): δ 8.431−8.267 (m, 2H, Ar), 8.132−8.044
6
1
3
(
m, 2H, Ar), 7.5 (s, 2H, -NH2); C-NMR (125 MHz, DMSO-d
6
):δ 169.0, 164.2, 147.3, 131.6,
+
1
2
3
30.4, 130.4, 128.2, 128.2; HR-EI-MS: m/z calcd for C
06.0438.
8
H
6
N
4
O
2
S, [M] 206.0440; found,
.2.9. 5-(anthracen-9-yl)-1,3,4-oxadiazol-2-amine
1
Green, Yield: 68%, H-NMR (500 MHz, DMSO-d
6
): δ 10.4 (s, 2H, -NH2), 8.4 (d, J = 10.6 Hz,
2
H, Ar), 7.7 (d, J = 10.1 Hz, 2H, Ar), 7.4 (t, J = 7.1 Hz, J = 7.6 Hz, 2H,Ar), 7.548-7.227 (m, 2H,
1
3
Ar), 7.1 (s, 1H, Ar); C-NMR (125 MHz, DMSO-d
6
):δ 173.5, 161.3, 133.8, 131.7, 131.7, 130.0,
1
30.0, 129.3, 127.7, 127.7, 125.2, 125.2, 125.1, 125.1, 123.5, 123.5; HR-EI-MS: m/z calcd for
+
C
16
H
11
N S, [M] 261.0902; found, 261.0905.
3
3
.2.10. 3-(5-amino-1,3,4-thiadiazol-2-yl)naphthalen-2-ol
1
Yellow, Yield: 65%, H-NMR (500 MHz, DMSO-d
6
): δ 10.2 (s, 1H, -OH), 8.6 (s, 2H, -NH2), 8.1
(
dd, J = 10.0 Hz, J = 11.2Hz, 1H, Ar), 7.91 (d,J = 9.6 Hz, 1H, Ar), 7.7 (dd, J = 3.5 Hz, J = 9.4
Hz, 1H, Ar), 7.305-7.217 (m, 1H, Ar), 7.1 (t, J = 10.6 Hz, J = 10.0 Hz, 1H, Ar), 7.0 (d, J = 10.4
1
3
Hz, 1H, Ar); C-NMR (125 MHz, DMSO-d ):δ 173.7, 161.2, 151.3, 134.0, 128.1, 127.3, 127.0,
6
17

+
1
26.2, 126.0, 125.3, 123.3, 109.6; HR-EI-MS: m/z calcd for C12
43.0465.
H
9
N OS, [M] 243.0466; found,
3
2
3
.2.11. 5-(4-(benzyloxy)phenyl)-1,3,4-thiadiazol-2-amine
1
White, Yield: 75%, H-NMR (500 MHz, DMSO-d
6
): δ 10.0 (s, 2H, -NH2), 7.5 (d, J = 10.1 Hz,
1
3
2
H, Ar), 7.4 (d, J = 10.1 Hz, 2H, Ar), 7.454-7.367 (m, 5H, Ar), 5.0 (s, 2H, -OCH ); C-NMR
2
(
125 MHz, DMSO-d
6
):δ 173.4, 161.3, 158.5, 136.2, 128.5, 128.5, 128.1, 128.1, 127.2, 126.7,
+
1
2
3
26.7, 125.3, 114.3, 114.3, 70.3; HR-EI-MS:m/z calcd for C15
83.0777.
H
13
N
3
OS, [M] 283.0779; found,
.2.12. 5-(3-(benzyloxy)-4-chlorophenyl)-1,3,4-thiadiazol-2-amine
1
White, Yield: 88%, H-NMR (500 MHz, DMSO-d
6
): δ 10.4 (s, 2H, -NH2), 7.5 (s, 1H, Ar),
7
2
1
.563-7.221 (m, 5H, Ar), 7.2 (dd, J = 1.80 Hz, J = 8.3Hz, 1H, Ar), 7.1 (d, J = 7.5 Hz, 1H, Ar),
1
3
.5 (s, 2H, -OCH
2
); C-NMR (125 MHz, DMSO-d ):δ 173.2, 161.1, 154.6, 136.2, 132.2, 130.0,
6
28.4, 128.4, 127.1, 126.5, 126.5, 122.1, 120.7, 112.3, 70.0; HR-ESI-MS: m/z calcd for
+
C
15
H12ClN
3
OS, [M] 317.0390; Found 317.0393.
3
.2.13. 5-(3-nitrophenyl)-1, 3, 4-thiadiazol-2-amine
1
Yellow solid, Yield: 79%, H-NMR (500 MHz, DMSO-d
6
):δ 10.2 (s, 2H, -NH2) 8.22 (t, J =2.0
Hz, 1H, Ar), 8.24 (m, J = 8.2, J =2.2, J =0.7 Hz, 1H, Ar), 8.22−8.10 (m, 1H, Ar), 7.44 (t, J = 8.0
1
3
Hz, 1H, Ar); C-NMR (125 MHz, DMSO-d
6
):δ 173.4, 161.1, 148.0, 136.5, 134.0, 129.5, 123.4,
+
1
22.3; HR-EI-MS:m/z calcd for C
8
H
6
N
4
O
2
S [M] 222.0211; Found, 222.0210.
3
.3.
Synthetic
procedure
of
(E)-4-((5-(4-chlorophenyl)-1,3,4-thiadiazol-2-
ylimino)methyl)phenol
In step-3, equimolar 2-amino-1,3,4-thiadiazole was further reacted with substituted
benzaldehydes in the presence of methanol and 2-3 drops of acetic acid. The reaction mixture
was refluxed for 2-3 hrs. Reaction completion was monitored by TLC. After reaction completion
desired organic compound was collected and washed with hexane. On evaporation get the
corresponding solid product of thiadiazole based Schiff bases analogs.
3
.3.14. (E)-4-((5-(4-chlorophenyl)-1,3,4-thiadiazol-2-ylimino)methyl)phenol
1
White solid, Yield: 71%, ( H-NMR (500 MHz, DMSO-d
6
), δ 9.76 (s, 1H, -CH=N), 7.82 (d, J=
8
.2 Hz, 2H, Ar), 7.75 (d, J = 8.1 Hz, 2H, Ar), 7.51 (d, J = 7.8, 2H, Ar), 6.91 (d, J = 7.1, 2H, Ar),
18

1
3
5
1
.41 ( s, 1H, -OH). C-NMR (125 MHz, DMSO-d ):δ 173.7, 161.1, 160.3, 159.5, 133.8, 131.1,
6
13.4, 130.1, 130.1, 128.8, 128.8, 128.5, 128.3, 128.3, 115.5;HR-EI-MS:m/z calcd for
+
C
15
H10ClN
3
OS [M] 315.0233; Found, 315.0235.
3
.3.15. (E)-5-(4-chlorophenyl)-N-(4-nitrobenzylidene)-1,3,4-thiadiazol-2-amine
1
Pale yellow solid, Yield: 74%, H-NMR (500 MHz, DMSO-d
6
), δ 10.15 (s, 1H, -CH=N), 8.68 (d,
J = 8.8, 2H, Ar), 8.53 (d, J = 8.7, 2H, Ar), 8.34 (d, J = 8.5 Hz, 2H, Ar), 7.91 (d, J = 8.1, 2H, Ar);
1
3
C-NMR (125 MHz, DMSO-d
6
):δ 173.5, 161.2, 159.5, 149.6, 142.0, 133.7, 131.0, 129.0, 129.0,
+
1
3
3
28.5, 128.5, 127.3, 127.3, 123.6, 123.6;HR-EI-MS:m/z calcd for C15
44.0135; Found, 344.0133.
H
9
N
4
ClN
4
2
O S [M]
.3.16. (E)-N-(5-bromo-2-methoxybenzylidene)-5-(4-chlorophenyl)-1,3,4-thiadiazol-2-amine
1
Light yellow solid, Yield: 77%, H-NMR (500 MHz, DMSO-d
6
), δ10.27 (s,1H, -CH=N), 7.84 (d,
J = 8.91, 2H, Ar), 7.74 (s, 1H, Ar), 7.51 (d, J = 7.8, 1H, Ar), 7.25 (d, J = 7.5, 2H, Ar), 7.23 (d, J =
1
3
7
1
.4, 1H, Ar), 3.92 (s, 3H, -CH
3
). C-NMR (125 MHz, DMSO-d ):δ 173.6, 161.0, 159.5, 156.1,
6
34.5, 134.0, 131.1, 131.1, 128.8, 128.8, 128.4, 128.4, 118.6, 112.5, 109.7, 55.6;HR-EI-MS:m/z
+
calcd for C16
H
11BrClN
3
OS [M] 406.9495; Found, 406.9493.
3
.3.17. (E)-5-(4-chlorophenyl)-N-(2-nitrobenzylidene)-1,3,4-thiadiazol-2-amine
1
White solid,Yield: 78%, H-NMR (500 MHz, DMSO-d
6
), δ 10.24 (s,1H, -CH=N), 8.07 (d, J =
8
1
1
.3, 2H, Ar), 7.85 (d, J = 8.1, 1H, Ar), 7.75 (d, J = 7.8, 1H, Ar), 7.72 (d, J = 7.7, 2H, Ar), 7.63 (t,
1
3
H, Ar), 7.45 (t, 1H, Ar); C-NMR (125 MHz, DMSO-d ):δ 173.5, 161.1, 159.4, 147.3, 134.4,
6
33.9, 131.4, 131.1, 129.5, 128.8, 128.8, 128.4, 128.4, 127.8, 123.5;HR-EI-MS:m/z alcd for
+
C
15
H
9
ClN
4
O
2
S [M] 344.0136; Found, 344.0135.
3
.3.18. (E)-N-(4-(benzyloxy)benzylidene)-5-(4-chlorophenyl)-1,3,4-thiadiazol-2-amine
1
Greenish solid, Yield: 72%, H-NMR (500 MHz, DMSO-d
6
), δ 10.27 (s,2H, -O-CH ), 9.59 (s,
2
1
H, -HC=N), 7.85 (d, J = 7.6, 2H, Ar), 7.83 (d, J =7.5 Hz, 2H, Ar), 7.75 (d, J = 7.3, 2H, Ar), 7.51
1
3
(
d, J = 7.6, 2H, Ar), 7.25 (t, 3H, Ar), 7.08 (d, J = 6.8, 2H, Ar); C-NMR (125 MHz, DMSO-d
6
):δ
1
1
73.6, 161.0, 160.8, 159.5, 136.2, 133.8, 131.1, 129.7, 129.7, 129.0, 129.0, 128.4, 128.4, 128.4,
28.4, 128.2, 127.1, 126.7, 126.7, 114.0, 114.0, 70.3;HR-EI-MS:m/z calcd for C22
H
16ClN OS
3
+
[
M] 405.0704; Found, 405.0702.
3
.3.19. (E)-5-(4-chlorophenyl)-N-(2,4-dichlorobenzylidene)-1,3,4-thiadiazol-2-amine
1
Light grey solid,Yield: 68%, H-NMR (500 MHz, DMSO-d
6
), δ 10.27 (s,1H, -HC=N), 7.88 (d, J
=
7.7, 2H, Ar), 7.84 (d, J = 7.6, 1H, Ar), 7.72 (s, 1H, Ar), 7.64 (d, J = 7.4, 2H, Ar), 7.62 (d, J =
19

1
3
7
1
.3 Hz, 1H, Ar); C-NMR (125 MHz, DMSO-d ):δ 173.5, 161.1, 159.4, 133.8, 131.1, 131.0,
6
30.5, 128.8, 128.8, 128.6, 128.5, 128.4, 128.4, 127.8, 126.5;HR-EI-MS:m/z calcd for
+
C
15
H
8
Cl
3
N
3
S [M] 366.9505; Found, 366.9503.
3
.3.20. (E)-N-(2,4-dichlorobenzylidene)-5-(3-nitrophenyl)-1,3,4-thiadiazol-2-amine
1
White solid,Yield: 76%, H-NMR (500 MHz, DMSO-d
6
), δ 10.28 (s,1H, -CH-N), 8.66 (s, 1H,
Ar), 8.33 (d, J = 8.5 Hz, 1H, Ar), 8.22 (d, J = 8.3 Hz, 1H, Ar), 7.85 (d, J = 8.1 Hz, 1H, Ar), 7.70
1
3
(
s, 1H, Ar), 7.64 (t, 1H, Ar), 7.53 (d, J = 7.6 Hz, 1H, Ar); C-NMR (125 MHz, DMSO-d
6
):δ
1
1
3
73.4, 161.1, 159.5, 148.0, 136.5, 133.8, 131.0, 130.5, 129.6, 128.6, 128.5, 127.8, 127.5, 123.4,
+
22.3;HR-EI-MS:m/z calcd for C15
H
8
Cl
2
N
4
O S [M] 377.9745; Found, 377.9743.
2
.3.21. (E)-N-(5-bromo-2-methoxybenzylidene)-5-(3-nitrophenyl)-1,3,4-thiadiazol-2-amine
1
Light green solid, Yield: 68%, H-NMR (500 MHz, DMSO-d
6
), δ 10.26 (s,1H, -CH=N), 8.65 (s,
1
H, Ar), 8.33 (d, J = 8.4 Hz, 1H, Ar), 8.23 (d, J = 8.3 Hz, 1H, Ar), 7.83 (s, 1H, Ar), 7.73 (d, J =
.8 Hz, 1H, Ar), 7.67 (d, J = 7.7 Hz, 1H, Ar), 7.24 (d, J = 7.3 Hz, 1H, Ar), 3.92 (s, 3H, -
7
1
3
OCH
3
); C-NMR (125 MHz, DMSO-d ):δ 173.5, 161.2, 159.5, 156.1, 147.9, 136.5, 134.4,
6
1
34.0, 131.1, 129.6, 123.4, 122.2, 118.6, 112.7, 109.6, 55.2;HR-EI-MS:m/z calcd for
+
C
16
H11BrN
4
O S [M] 417.9734; Found, 417.9736.
3
3
.3.22. (E)-4-((5-(4-(benzyloxy)-3-methoxyphenyl)-1,3,4-thiadiazol-2-ylimino)methyl)phenol
1
Light brown solid,Yield: 79%, H-NMR (500 MHz, DMSO-d
6
), δ 9.78 (s,1H, -CH=N), 7.76 (d, J
=
7.9 Hz, 2H, Ar), 7.50 (d, J = 7.7, 2H, Ar), 7.41 (t, 3H, Ar), 7.29 (s, 1H, Ar), 7.27 (d, J = 7.4 Hz,
1
H, Ar), 7.12 (d, J = 7.2 Hz, 1H, Ar), 6.92 (d, J = 7.1 Hz, 2H, Ar), 5.39 (s, 1H,-OH), 5.19 (s, 2H,
1
3
-
CH
2
), 3.93 (s, 3H, -OCH
3
); C-NMR (125 MHz, DMSO-d ):δ 173.6, 161.1, 160.3, 159.5, 149.7,
6
1
1
4
3
49.2, 136.2, 130.1, 130.1, 128.5, 128.3, 128.3, 127.1, 126.6, 126.6, 126.4, 120.3, 115.6, 115.6,
+
11.8, 110.5, 70.6, 55.6;HR-EI-MS:m/z calcd for C23
H
19
N
3
O
3
S [M]
417.1147; Found,
71.1145.
.4. α-Glucosidase assay
α-Glucosidase inhibitory activities was determined as per reported methods [36].10 μL of test
samples (5 mg/mL DMSO solution)were reconstituted in 100 μL of 100 mM-phosphate buffer
(
pH6.8) in 96-well microplate and incubated with 50 μL of crude intestinal α-glucosidase for 5
min before 50 μL substrate (5 mM, p-nitrophenyl-α-D-glucopyranoside prepared in same buffer)
was added. Release of p-nitrophenol was measured at 405 nm spectrophotometrically
(
SpectraMax® plus384) for5 min after incubation with substrate. Individual blanks for test
20

samples were prepared to correct background absorbance where substrate was replaced with
0μL of buffer. Control sample contained 10 μL DMSO in place of test samples. Percentage of
5
enzyme inhibition was calculated as (1-B/A) x 100 whereA represents absorbance of control
without test samples, and B represents absorbance in presence of test samples.
Acknowledgements
Authors would like to acknowledge the Higher Education of Pakistan for financial support under
the National Research Program for Universities, project number 5721.
References
[
1] Centers for Disease Control and Prevention. Diabetes, Working to Reverse the US Epidemic.
2016).
(
[
[
2] World Health Organization. Diabetes Fact Sheet. June (2016).
3] A. J.Scheen, Is there a role for α-glucosidase inhibitors in the prevention of type 2 diabetes
mellitus, Drugs. (63) (2003) 933-951.
[
4] S. Poovitha, M. Parani, In vitro and in vivo α-amylase and α-glucosidaseinhibiting activities
of the protein extracts from two varieties of bitter gourd(Momordicacharantia L.), BMC
Complement. Altern. Med. (16) (S1) (2016) 185–199.
[
[
[
[
[
5] F. Zaccardi, D.R. Webb, T. Yates, M.J. Davies, Pathophysiology of type 1 and type 2
diabetes mellitus: a 90-year perspective, Postgrad. Med. J. (92) (2016) 63–69.
6] G.S. Chadha, M.E. Morris, Monoclonal antibody pharmacokinetics in type 2diabetes mellitus
and diabetic nephropathy, Curr. Pharmacol. Rep. (2) (2016) 45–56.
7] D. S. Bell, Type 2 diabetes mellitus: what is the optimal treatment regimen? Am. J. Med.
(
116) (2004) 23-29.
8] T. Kato, K. Node, Therapeutic potential of α-glucosidase inhibitors to prevent postprandial
endothelial dysfunction, Int. Heart. J. (55) (2014) 386-390.
9] S. Yamagishi, T. Matsui, S. Ueda, K. Fukami, S. Okuda, Clinical utility of acarbose, an
alpha-glucosidase inhibitor in cardiometabolic disorders, Curr. Drug.Metab.(10) (2009) 159-
1
63.
21

[
[
[
10] R. Pili, J. Chang, R.A. Partis, R.A. Mueller, F.J. Chrest, A. Passaniti, The alphaglucosidase I
inhibitor castanospermine alters endothelial cell glycosylation, prevents angiogenesis, and
inhibits tumor growth, Cancer. Res. (55) (1995) 2920-2926.
11] S. Atsumi, C. Nosaka, Y. Ochi, H. Iinuma, K.Umezawa, Inhibition of experimental
metastasis by an alpha-glucosidase inhibitor, 1,6-epi-cyclophellitol, Cancer. Res. (53) (1993)
4
896-4899.
12]. (a) B. S. Holla, N. K. Poorjary, S. B. Rao, M. K. Shivananda, Synthesis and antiviral
activity of novel [1,2,4]triazolo[3,4-b][1,3,4]thiadiazoles. Eur. J. Med. Chem. (37) (2002)
5
11; (b) S. M. S. Atta, N. M. Fazwy, F. A. Ahmed, A. H. Abdel-Rahman, Phosphorus,
Sulfur, and Silicon and the Related Elements (177) (2002) 863.
[
[
[
[
[
[
[
13] M. Taha, M. T. Javid, S. Imran, M. Selvaraj, S. Chigurupati, H. Ullah, F. Rahim, F. Khan, J.
I. Mohammad, K. M. Khan. Synthesis and study of the α-Amylase Inhibitory Potential of
Thiadiazole Quinoline Derivatives. Bioorg. Chem. (74) (2017) 179.
14] P. Li, J. Yin, W. M. Xu, J. Wu, M. He, D. Y. Hu, S. Yang, B. A. Song, Design, Synthesis,
and Evaluation of New Sulfone Derivatives Containing a 1,3,4-Oxadiazole Moiety as Active
Antibacterial Agents. Chem. Biol. Drug. Des. (82) (2013) 546-556.
15] W. M. Xu, F. F. Han, M. He, D. Y. Hu, J. He, S. Yang, B. A. Song, Synthesis and
Biological Evaluation of Novel Sulfone Derivatives Containing 1,3,4-Oxadiazole Moiety. J.
Agric. Food Chem. (60) (2012) 1036-1041.
16] F. Liu, X. Q. Luo, B. A. Song, P. S. Bhadury, S. Yang, L. H. Jin, W. Xue, D. Y. Hu, Design,
Synthesis, and Evaluation of New Sulfone Derivatives Containing a 1,3,4-Oxadiazole Moiety
as Active Antibacterial Agents. Bioorg. Med. Chem. Lett. (16) (2008) 3632-3640.
17] B. Song, L Dong, J. Wu, Z. Wu, Y. Zhu, X. Chen, D. Hu, Synthesis and antiviral activity of
novel thioether derivatives containing 1,3,4-oxadiazole/thiadiazole and emodin moieties.
(
191) (2016) 904-907.
18] E. Palaska, G. Sahin, P. Kelicen, N. T. Durlu, Altinok, G. Farmaco. Synthesis and anti-
inflammatory activity of 1-acylthiosemicarbazides, 1,3,4-oxadiazoles, 1,3,4-thiadiazoles and
1
,2,4-triazole-3-thiones. (57) (2002) 101-107.
19] M. Harfenist, D. J. Heuser, C. T. Joyner, J. F. Batchelor, H. L. White. Selective Inhibitors of
Monoamine Oxidase. 3. Structure−Activity Relationship of Tricyclics Bearing Imidazoline,
Oxadiazole, or Tetrazole Groups. J. Med. Chem. (39) (1996) 1857-1863.
22

[
20] (a) N. N. Farshori, M. R. Banday, A. Ahmad, A. U. Khan, A. Rauf. Synthesis,
characterization, and in vitro antimicrobial activities of 5-alkenyl/hydroxyalkenyl-2-
phenylamine-1,3,4-oxadiazoles and thiadiazoles. Bioorg. Med. Chem. Lett. (20) (2010) 1933.
(
b) I. Chaaban, E. L. Khwass, E. L. Sayeda, M. Mahran, E. L. Sayed, A. Ola, E. L. Saidi, A.
E. Hassan, Alex J Pharm Sci. (20) (2006) 107.
[
[
[
[
[
[
21] V. Jatav, P. Mishra, S. Kashaw, J. P. Stables, CNS depressant and anticonvulsant activities
of some novel 3-[5-substituted 1,3,4-thiadiazole-2-yl]-2-styryl quinazoline-4(3H)-ones. Eur.
J. Med. Chem. (43) (2008) 1945-54.
22] X. Yang, L. Xiang, X. Li, T.- Zhao, H. Zhang,W. Zhou, X.Wang, H. Gong, H. Zu,
Synthesis, biological evaluation, and molecular docking studies of 1,3,4-thiadiazol-2-amide
derivatives as novel anticancer agents. Bioorg. Med. Chem. (20) (2012) 2789-95.
23] N. Siddiqui, N. Andalip, S. Bawa, R. Ali, O. Afzal, M. Akhtar, B. Azad, R. Kumar,
Antidepressant potential of nitrogen-containing heterocyclic moieties: An updated review. J.
Pharm. Bio. Allied. Sci. 3 (2011) 194-212.
24] E. Oruç, S. Rollas, F. Kandemirli, N. Shvets, A. Dimoglo, 1,3,4-thiadiazole derivatives.
Synthesis, structure elucidation, and structure-antituberculosis activity relationship
investigation. J. Med. Chem. (47) (2004) 6760-7.
25] Y. Hu, C.-Y.Li, X.-M.Wang, Y.-H.Yang, H.-L. Zhu, 1,3,4-Thiadiazole: synthesis, reactions,
and applications in medicinal, agricultural, and materials chemistry. Chem. Rev. (114) (2014)
5
572-610.
26] F. Rahim, K. Ullah, H. Ullah, A. Wadood, M. Taha, A. U. Rehman, I. uddin, M. Ashraf, A.
Shaukat, W. Rehman, S. Hussain, K.M. Khan. Triazinoindole analogs as potent inhibitors of
α-glucosidase: Synthesis, biological evaluation and molecular docking studies. Bioorg.
Chem(58) (2015) 81-87.
[
[
27]F. Rahim, H.Ullah, M. T. Javid, A.Wadood, M. Taha, M. Ashraf, A.Shaukat, M. Junaid, S.
Hussain, W.Rehman, R.Mehmood, M. Sajid, M. N. Khan, and K. M. Khan. Synthesis, in
vitro evaluation and molecular docking studies of thiazole derivatives as new inhibitors of α-
glucosidase. Bioorg.Chem(62) (2015) 15-21.
28] F. Rahim, F. Malik, H.Ullah, A.Wadood, F. Khan, M. T. Javid, M.Taha, W.Rehman, A.
U.Rehman, K. M. Khan, Isatin based Schiff bases as inhibitors of α-glucosidase: Synthesis,
23

characterization, in vitro evaluation and molecular docking studies. Bioorg.Chem(60) (2015)
2-48.
4
[
[
[
[
[
[
29] F. Rahim, K. Zaman, H.Ullah, M.Taha, A.Wadood, M. T.Javed, W.Rehman, M. Ashraf, R.
Uddin, I.uddin, H.Asghar, A. A. Khan, K. M. Khan. Synthesis of 4-thiazolidinone analogs as
potent in vitro anti-urease agents. Bioorg. Chem. (63) (2015) 123-131.
30] M. Taha, N. H. Ismail, S. Imran, A.Wadood, M. Ali, F. Rahim, A. A. Khan, M. Riaz. Novel
thiosemicarbazide–oxadiazole hybrids as unprecedented inhibitors of yeast α-glucosidase and
in silico binding analysis. RSC Adv. (6) (2016) 33733-33742.
31] M. Taha, S. A. A. Shah, M. Afifi, S. Imran, S. Sultan, F.l Rahim, N. H. Ismail, K. M. Khan,
Synthesis, Molecular Docking Study and Thymidine Phosphorylase Inhibitory Activity of 3-
Formylcoumarin Derivatives. Bioorg. Chem. (78) (2018) 17-23.
32] M. Taha, M. Arbin, N. Ahmat, S. Imran F. Rahim, Synthesis: Small Library of Hybrid
Scaffolds of Benzothiazole Having Hydrazone and evaluation of their β-glucuronidase
activity. Bioorg. Chem. (77) (2018) 47-55.
33] M. Taha, H. Ullah, L. M. R. A. Muqarrabun, N. Khan, F. Rahim, N. Ahmat, M. T. Javid, M.
Ali, K. M. Khan, Bisindolylmethane thiosemicarbazides as potential inhibitors of urease:
Synthesis and molecular modeling studies. Bioorg. Med. Chem. (26) (2018) 152-160.
34] M. Taha, H. Ullah, L. M. R. A. Muqarrabun, N. Khan, F. Rahim, N. Ahmat, M. Ali, S.
Perveen, Synthesis of bis-indolylmethanes as new potential inhibitors of β-glucuronidase and
their molecular docking studies. Eur. J. Med. Chem. (143) (2018) 1757-1767.
35] M.Taha, S. Imran, F. Rahim, A. Wadood, K. M. Khan, Oxindole based oxadiazole hybrid
analogs: Novel α-glucosidase inhibitors. Bioorg. Med. Chem. (76) (2018) 273-280.
36] L.R. Guerreiro, E.P. Carriero, L. Fernandes, T.A. Cardote, R. Moreira, A.T. Caldeira, R. C.
Guedes, A. J. Burke, Bioorg. Med. Chem. (21) (2013) 1911.
[
[
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Highlights:





Synthesis of Thiadiazole derivatives
In vitro α-Glucosidase activity
Identification of a new class of α-Glucosidase inhibitor
Structure Activity Relationship established
Molecular docking
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