Synthesis, and In Vitro and In Silico α-Glucosidase Inhibitory Studies of 5-Chloro-2-Aryl Benzo[d]thiazoles

Article abstract of DOI:10.1016/j.bioorg.2018.02.013

Twenty-five derivatives of 5-chloro-2-aryl benzo[d]thiazole (1–25) were synthesized and evaluated for their α-glucosidase (S. cerevisiae EC 3.2.1.20) inhibitory activity in vitro. Among them eight compounds showed potent activity with IC₅₀ values between 22.1 ± 0.9 and 136.2 ± 5.7 μM, when compared with standard acarbose (IC₅₀ = 840 ± 1.73 μM). The most potent compounds 4, 9, and 10 showed IC₅₀ values in the range of 22.1 ± 0.9 to 25.6 ± 1.5 μM. Compounds 2, 5, 11, and 19 showed IC₅₀ values within the range of 40.2 ± 0.5 to 60.9 ± 2.0 μM. Compounds 1 and 3 were also found to be good inhibitors with IC₅₀ values 136.2 ± 5.7 and 104.8 ± 9.9 μM, respectively. Their activities were compared with α-glucosidase inhibitor drug acarbose (standard) (IC₅₀ = 840 ± 1.73 μM). The remaining compounds were inactive. Structure-activity relationships (SAR) have also been established. Kinetics studies indicated compounds 2, 3, 10, 19, and 25 to be non-competitive, while 1, 5, 9, and 11 as competitive inhibitors of α-glucosidase enzyme. All the active compounds (1–5, 9–11, and 19) were also found to be non-cytotoxic, in comparison to the standard drug i.e., doxorubicin (IC₅₀ = 0.80 ± 0.12 μM) in MTT assay. Furthermore, molecular interactions of active compounds with the enzyme binding sites were predicted through molecular modeling studies.

Full text of DOI:10.1016/j.bioorg.2018.02.013

Accepted Manuscript
Synthesis, α-Glucosidase Inhibitory Potential, In Vitro, and In Silico Studies on
5-Chloro-2-Aryl Benzo[d]thiazoles
Shazia Shah, Arshia, Kulsoom Javaid, Humaira Zafar, Khalid Mohammed
Khan, Ruqaiya Khalil, Zaheer Ul-Haq, Shahnaz Perveen, M. Iqbal Choudhary
PII:
S0045-2068(17)30691-0
DOI:
https://doi.org/10.1016/j.bioorg.2018.02.013
YBIOO 2273
Reference:
Bioorganic Chemistry
To appear in:
Received Date:
Revised Date:
Accepted Date:
6 September 2017
2 February 2018
10 February 2018
Please cite this article as: S. Shah, Arshia, K. Javaid, H. Zafar, K. Mohammed Khan, R. Khalil, Z. Ul-Haq, S. Perveen,
M. Iqbal Choudhary, Synthesis, α-Glucosidase Inhibitory Potential, In Vitro, and In Silico Studies on 5-Chloro-2-
Aryl Benzo[d]thiazoles, Bioorganic Chemistry (2018), doi: https://doi.org/10.1016/j.bioorg.2018.02.013
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Synthesis, α-Glucosidase Inhibitory Potential, In Vitro, and In Silico Studies on 5-Chloro-2-
Aryl Benzo[d]thiazoles
Shazia Shah,a Arshia,a Kulsoom Javaid,a Humaira Zafar,b Khalid Mohammed Khan,*a
Ruqaiya Khalil,b Zaheer Ul-Haqb Shahnaz Perveen,c M. Iqbal Choudhary*a,b,d
aH. E. J. Research Institute of Chemistry, International Center for Chemical and Biological
Sciences, University of Karachi, Karachi-75270, Pakistan
bDr. Panjwani Center for Molecular Medicine and Drug Research, International Center for
Chemical and Biological Sciences, University of Karachi, Karachi-75270, Pakistan
cPCSIR Laboratories Complex, Karachi, Shahrah-e-Dr. Salimuzzaman Siddiqui, Karachi-75280,
Pakistan
dDepartment of Biochemistry, Faculty of Sciences, King Abdulaziz University, Jeddah-21412, Saudi
Arabia
Abstract: Twenty-five derivatives of 5-chloro-2-aryl benzo[d]thiazole (1-25) were synthesized and
evaluated for their α-glucosidase inhibitory activity in vitro. Among them eight compounds showed
potent activity with IC50 values between 22.1 ± 0.9 to 136.2 ± 5.7 μM, when compared with standard
acarbose (IC50 = 840 ± 1.7 µM). The most potent compounds 4, 9, and 10 showed IC50 values within
the range of 22.1 ± 0.9 to 25.6 ± 1.5 μM. Compounds 2, 5, 11, and 19 showed IC50 values within the
range of 40.2 ± 0.5 to 60.9 ± 2.0 μM. Compounds 1 and 3 were also found to be good inhibitors with
IC50 values 136.2 ±5.7 and 104.8 ± 9.9 μM, respectively. The remaining compounds were inactive.
Structure-activity relationships (SAR) have also been established. Kinetics studies indicated
compounds 2, 3, 10, 19, and 25 to be non-competitive, while 1, 5, 9, and 11 as competitive inhibitors
of α-glucosidase enzyme. Furthermore, molecular interactions of active compounds with the enzyme
binding sites were predicted through molecular modelling studies.
Keywords: 5-Chloro-2-aryl benzo[d]thiazole; α-glucosidase; diabetes mellitus; hyperglycemia; in
silico studies.
1
Introduction
α-Glucosidase inhibitors are antidiabetic drugs used for the prevention of post-prandial
hyperglycemia in type-II diabetes [1]. Diabetes mellitus type II is a metabolic disorder that is
characterized by high blood glucose in the context of insulin resistance, and relative insulin
deficiency. The classic symptoms are excessive thirst, frequent urination, and constant hunger.
Obesity is now recognized as the primary cause of type II diabetes in people who are genetically
predisposed to the disease [2]. α-Glucosidase inhibitors are used to maintain high glycemic control
along with other insulin secretagogues [3].
1

Absolute or relative deficiency in insulin secretions and/or insulin resistance results in
hypoglycaemia, which is associated with diabetes mellitus [4]. It is estimated that by the year of
2025 diabetes mellitus will affect 300 million people worldwide [5], thus there is an urgent need to
develop improved therapies for this chronic disorder. One of the approaches to manage this disease
is to control the activity of α-glucosidase (EC.3.2.1.20), which is an enzyme positioned at small
intestine. This enzyme is responsible for the cleavage of α-1-4 bond linkage in starch or
oligosaccharides into monosaccharides such as glucose [6]. Therefore, inhibition of α-glucosidase
can help in the post-prandial hyperglycemia, and associated complications.
Benzothiazole is a class of heterocyclic compounds containing nitrogen and sulphur as heteroatoms.
Structurally, benzothiazole skeleton is a fusion of benzene ring and thiazole moiety. They are
pharmacologically active compounds with a wide spectrum of activities, such as anti-tuberculosis
[7], anti-tumor [8], anti-cancer [9], antiviral [10], analgesic [11], LTD4 receptor antagonist [11]
anticonvulsant [12], and antifungal [13]. Benzothiazoles also have importance in the field of
polymer chemistry [14], medicines [15], and dyes [16, 17].
As discussed earlier, diabetes is a rapidly spreading disease, and its prevalence increases day by day.
Benzothiazole nucleus has the ability to control diabetes mellitus. Since, it is involved in inhibition
of 11-hydroxysteroid dehydrogenase type 1 [18], it has the ability to stimulate insulin secretion [19]
and has known hypoglycaemic mechanism [20], etc.
Rationale of the current study:
Previously, our research group reported in vitro activity of benzothiazole Schiff bases against α-
glucosidase enzyme [21] (Figure-1). In continuation of our studies on benzothiazole derivatives, we
synthesized some new analogues, and evaluated their α-glucosidase activity. Compounds 1, 3, 4, 8,
9, 13, 18, 19, 21, and 25 were identified as new while remaining compounds have been reported
previously [22-28].
2

Figure-1: Rationale of Current Study.
2
Results and discussion
Chemistry
2.1
A library of 5-chloro-2-substituted benzothiazoles (1-25) were synthesized by reacting 4-chloro-2-
aminothiophenol with different aromatic aldehydes in the presence of sodium metabisulfite
(Na2S2O5) in N,N-dimethylformamide (DMF) under reflux for 2 h. The mixture was cooled at room
temperature, and poured on to cold water for precipitation. Filtration of precipitate, followed by
washing with cool water resulted in pure benzothiazoles (1-25) (Scheme-1). Structures of the
3

synthetic compounds were identified by spectroscopic techniques, such as 1H-NMR and EI-MS, and
HREI-MS.
Schemes-1: Synthesis of 5-Chloro-2-aryl benzo[d]thiazole Derivatives.
2.3
α-Glucosidase inhibition Studies
All synthetic 5-chloro-2-aryl benzo[d]thiazole (1-25) were evaluated for their in vitro α-glucosidase
inhibitory activity. Among them, eight compounds showed potent activity, with IC50 values between
22.1 ± 0.9 to 136.2 ± 5.7 μM, as compared to standard acarbose ( IC50 = 840 ± 1.7 µM) (Table-1).
Compounds 4 (IC50 = 22.1 ± 0.9 µM), 9 (IC50 = 24.8 ± 0.4 µM), and 10 (IC50 = 25. 6± 1.5 µM) were
found to be the most potent inhibitors in the series. Compounds 2, 5, 11, and 19 also showed
prominent IC50 values within the range of 40.2 ± 0.5 to 60.9 ± 2.0 μM. Compound 1 (IC50 = 136.2
±5.7 µM) and 3 (IC50 = 104.8 ± 9.9 μM) were also found to be good inhibitors of α-glucosidase.
Remaining compounds were found to be inactive. To study the substituent effects on benzothiazoe
moiety with respect to α-glucosidase inhibitory activity a structure-activity relationship (SAR) has
also been established. Furthermore, molecular interactions of active compounds with the enzyme
binding sites were predicted through molecular modelling studies.
Table-1: α-Glucosidase inhibitory activity of 5-chloro-2-aryl benzo[d]thiazole derivatives 1-25.
Compounds
1
Aryl part
IC50 ± SEMa [μM]
136.2 ± 5.7
60.9 ± 2.0
2
4

104.8 ± 9.9
22.1 ± 0.9
3
4
53.4 ± 4.3
N.A.b
5
6
7
8
N.A.b
N.A.b
24.8 ± 0.4
25. 6± 1.5
52.7 ± 1.0
9
10
11
N.A.b
12
5

N.A.b
N.A.b
13
14
N.A.b
N.A.b
15
16
N.A.b
17
N.A.b
18
19
40.2 ± 0.5
N.A.b
N.A.b
N.A.b
20
21
22
N.A.b
N.A.b
23
24
6

180 ± 1.25
25
SEMa means Standard Error of the Mean; N.A.b means Not Active; Standard: Acarbose, IC50 ± SEM = 840 ± 1.73 µM.
Structure-activity relationship (SAR) studies of twenty-five derivatives of 5-chloro-2-aryl
benzo[d]thiazole towards α-glucosidase inhibition indicates that different substituents at the aryl part
of 5-chloro-2-aryl benzo[d]thiazole are responsible for their varying degree of activities. We have
hypothetically divided the 5-chloro-2-aryl benzo[d]thiazole molecule in two parts (benzothiazole and
aryl part) for better understanding the SAR (Figure-2).
Among the synthetic compounds, compound 4, having hydroxyl at C-2' and bromo groups at C-5'
positions, was found to be the most active member of the series (IC50 = 22.1 ± 0.92 μM), which is
thirty-folds more active than the standard drug acarbose (IC50 = 840 ± 1.73 μM). Compound 1
having only hydroxyl group at C-2', showed a decreased activity (IC50 = 136.2 ± 5.7 μM); however,
compound 2 (IC50 value of 60.9 ± 2.07 μM), having a hydroxyl group at C-4', showed an increased
activity. Substituting the hydroxyl group at C-3' position resulted in decreased activity, as in
compound 3 (IC50 = 104.8 ± 9.92 μM) (Figure-3).
7

Figure-3: SAR of Hydroxyl and Bromo Substituted Aryl Part.
Interestingly, compound 10 with a hydroxyl at C-2' and a methoxy at C-5’, displayed a good activity
with an IC50 value of 25.6 ± 1.50 μM, while, compound 11 with a hydroxyl group at C-4' and
methoxy group at C-5', displayed a decreased activity (IC50 = 52.7 ± 1.07 μM). Other combinations
of hydroxyl and methoxy substituents (compounds 12 and 13) were found to be inactive (Figure-4).
Figure-4: SAR of Hydroxyl And Methoxy Substituted Aryl Part.
8

Substitution of ethoxy group at C-4', as in compound 9, resulted in a good inhibitory activity, with
an IC50 value of 24.8 ± 0.40 μM. Amongst the compounds having only methoxy group at the phenyl
moiety, compound 5 which has one methoxy substituent at C-4' was found to be active ( IC50 = 53.4
± 4.3 μM), whereas compounds 6, 7, and 8 each with two or three methoxy groups on the phenyl
ring, were found to be inactive (Figure-5). Compound 25, with phenoxy pentyl group, was found to
be moderately active with IC50 value of 180 ± 1.25 μM.
Figure-5: SAR of Alkoxy Substituted Aryl Part.
Good activity was observed when phenyl group was replaced with indole moiety, as in compound
19, which displayed an IC50 value of 40.2 ± 0.5 μM (Figure-6).
Figure-6: SAR of hetero-atomic substituted aryl part
9

Compounds 15-18, and 20-24 were found to be completely inactive.
2.4 Kinetic studies
Active compounds of 5-chloro-2-arylbenzo[d]thiazole series (i.e. 1-5, 9-11, 19, and 25) were
analyzed for kinetic studies (Figure-7, and 8). Among them, compounds 2, 3, 10, 19, and 25 were
found to be non-competitive inhibitors of ɑ-glucosidase, as these derivatives were able to decrease
the Vmax, while Km remained unaffected. Compounds 1, 5, 9, and 11 increased the Km values
while Vmax remains unaffected, hence considered as competitive inhibitor of the ɑ -glucosidase
enzyme(Table-2).
6
80
4
60
40
2
0
-2
20
0
-20
-40
-4
-6
-60
-80
-80 -60 -40 -20
0
20 40 60 80
-10 -8 -6 -4 -2
0
2
4
6
8
10
Inhibitor (Compound 9)
1/S
A
B
80
60
40
20
0
-20
-40
-60
-80
-80 -60 -40 -20
0
20 40 60 80
Inhibitor (Compound 9)
C
Figure-7: The mode of inhibition of α-glucosidase by compound 9, (A) Lineweaver-Burk plot
of reciprocal rate of reaction (velocities) vs reciprocal of substrate in the absence ( ), and in
the presence of 80 µM (□), 40 µM (■), 20 µM (∆), 10 µM (▲), and 5 µM (▼) of 9. (B)
Secondary replot of Lineweaver-Burk plot between the slopes of each line on Lineweaver-Burk
plot vs different concentrations of 9, and (C) Dixon plot of reciprocal rate of reaction
(velocities) vs different concentrations of 9.
10

1
0.5
0
10
5
0
-5
-10
-0.5
-1
-10 -8 -6 -4 -2
0
2
4
6
8
10
-100 -80 -60 -40 -20
0
20 40 60 80 100
1/S
Inhibitor (Compound 25)
A
B
10
5
0
-5
-10
-100 -80 -60 -40 -20
0
20 40 60 80 100
Inhibitor (Compound 25)
C
Figure-8: The mode of inhibition of α-glucosidase by compound 25, (A) Lineweaver-Burk plot
of reciprocal rate of reaction (velocities) vs reciprocal of substrate in the absence (▼), and in
the presence of 125 µM (□), 62.5 µM (■), 31.25 µM (∆), 15.625 µM (▲), and 7.8125 µM ( ) of
25. (B) Secondary replot of Lineweaver-Burk plot between the slopes of each line on
Lineweaver-Burk plot vs different concentrations of 25, and (C) Dixon plot of reciprocal rate
of reaction (velocities) vs different concentrations of 25.
Table-2: Kinetic studies of active compounds.
Ki ± SEMa [μM]
Compounds
Type of Inhibition
14.1 ± 0.100
25.8 ± 0.006
26.6 ± 0.0001
16.03 ± 0.0411
25.5 ± 0.115
Competitive
Non-competitive
Non-competitive
Non-competitive
Competitive
1
2
3
4
5
11

12.39 ± 0.04
5.70 ± 0.021
59.75 ± 0.005
10.55 ± .00017
44.78 ± 0.005
Competitive
Non-competitive
Competitive
Non-competitive
Non-competitive
9
10
11
19
25
2.5 Computational modeling studies
Molecular modeling studies were carried out in order to investigate the binding mode of active
compounds against α-glucosidase. In this connection, a homology model of the α-glucosidase (S.
cerevisae) was developed, and the active compounds of the series were docked using Glide software
[29].
Yeast α-glucosidase (EC 3.2.1.20) has been widely used to screen bioactive compounds targeting α-
glucosidase. The lack of crystal structure was compensated using homology model developed using
Yeast isomaltase (PDB 3AJ7) from the same specie [30], which was further refined using Prime.
The quality of model was assessed using the Ramachandran plot which is a gold standard for the
assessment of three-dimensional structures of protein [31]. A brief review of the plot shows that
most of the residues lie in favored regions (92.2%) with only two outliers (Figure S1).
Molecular docking studies of selected compounds were carried out to elaborate the observed α-
glucosidase inhibitory activity of the newly synthesized compounds. In order to challenge the ability
of Glide to reproduce the crystal pose control docking experiments were carried out using PDBs
3A4A [32], and 3W37 [33]. The complex 3W37 represents the coordinates of Sugar Beet α-
glucosidase and acarbose. While, the coordinates of the native ligand α-D-glucose in the active site
of isomaltase are deposited as PDB 3A4A. The RMSD values between the crystal pose and docked
poses in both cases was found to be less than 2 Å (Figure S2). The results of control docking validate
the predictive ability of Glide to establish the binding mode of the inhibitors in the active site of the
target enzyme.
Molecular docking studies of the newly synthesized benzothiazole derivatives 1-5, 9-10, 19, and 25
was carried out using already validated protocol. The active site of the α-glucosidase is part of a
larger pocket that is virtually separated by Phe157 and Phe300. The analysis of kinetic profile of the
compounds suggests that the ligand binds in the close proximity of the substrate, thus variation in the
position of the same moiety results in different inhibitory profile. Among the hydroxl substituted
12

derivatives (1-4), compound 4 bearing the hydroxyl and bromide substitution at C-2' and C-5' is the
most active member of the series. The top ranked docked pose of the compound 4 is presented in
Figure-9(a). The benzothiazole ring of the compound anchors the binding site by hydrophobic
interactions with His279 and Glu304. The hydroxl moiety is involved in hydrogen bonding with the
Arg312, in the active site of the protein. As mentioned earlier in the SAR analysis, the introduction
of Bromide at with the C-5' position significantly increased the observed α-glucosidase inhibitory
potential. The docking study suggests that the bromide moiety depicts halogen bond with Lys155.
We hypothesize that the halogen interaction unique to compound 4 among the hydroxl derivatives is
responsible for its activity.
Figure-9: The top ranked docking pose of the compounds 4,9,10,19. The binding site is
presented as tan wires and sticks, in case of native contacts and interactions, respectively. The
panel (a) presents the docking pose of compound 4, (b) shows the pose of compound 9.
Whereas, compounds 10 and 19 poses are presented in panel (b) and (c), respectively.
13

In case of the ligands with alkoxy substituted aryl part only compounds 5 and 9 bearing single
substitution at C-4' positions were found to be active. Both these compounds were found to be
competitive inhibitors of α-glucosidase. A cursory look at the Figure-9(b) shows that the compound
9 anchors the active site via hydrophobic interactions with the residues in active site; Phe157,
Pro240, His279 and Glu304. The π-stacking interaction between the benzothiazole ring of the
compound and the residues of Phe157 might be the reason of the observed inhibition. Since, the
residues of the hydrophobic patch partake in the catalysis by holding the terminal ring of acarbose
[34].
Compound 10 bearing hydroxy and methoxy substitution on the aryl part is the most active member
among the relevant derivatives 10-13. The top ranked docked pose of the compound 10 showed
similarity with the docked pose of compound 9 (Figure S3). The compound mediate hydrophobic
interaction with Pro240 and Arg312 in the active site. The protein-inhibitor contact is further
stabilized by π-stacking interaction between the compound and residues; Phe157 and His239
(Figure-9 (c)).
The binding mode of indole substituted aryl derivative 19 suggests that the compound is
accommodated near the hydrophobic patch of the active site (Figure-9 (d)). The compound interact
via hydrophobic interactions with the amino acids in the native contacts including; Phe157, Leu176,
Pro240, Arg312, and His239. A halogen bond between Arg312 and the chloride moiety at the
benzothiazole ring further stabilizes the contacts.
3. Conclusion
In this study in vitro α-gluocosidase inhibitory activity of twenty-four derivatives of 5-chloro-2-aryl
benzo[d]thiazole was evaluated. Amongst them derivatives 1-5, 9-11, and 19 showed potent α-
gluocosidase inhibitory activity than the drug acarbose used as a standard. The kinetics data
indicated compounds 2-3, 10, 19, and 25 as non-competitive, while 1, 5, 9, and 11 as competitive
inhibitors of α-gluocosidase. Moreover, in silico studies of active compounds with enzyme binding
sites also employed to validate its the successful interactions with ligand proteins. These preliminary
results identified compounds 1-5, 9-11, and 19 as lead molecules for further studies.
4. Experimental
14

4.1 Material and Methods
2-amino-4-cholorobenzenethiol, different aromatic aldehydes and solvents were purchased from
Sigma-Aldrich USA and of analytical grade and were as used as without any further purification.
Pre-coated silica gel, GF-254 (Merck, Germany) was used for thin layer chromatography.
Visualization of TLC was performed under ultraviolet light at 254 and 366 nm. Mass spectra were
1
carried out on a Finnigan MAT-311A (Germany) mass spectrometer. The H-NMR were carried out
on Avance Bruker AM spectrometers, operating at 300, and 400 MHz. The chemical shift values are
presented in ppm (δ), relative to tetramethylsilane (TMS) as an internal standard and the coupling
constant (J) are in Hz.
15

4.2. Bioassay for α-glucosidase inhibitory activity
α-Glucosidase inhibitory activity was evaluated by 0.1 M phosphate buffer (pH 6.8) at 37 °C. The
enzyme (S. cerevisiae EC 3.2.1.20) was dissolved in phosphate buffer saline and incubated with
different concentrations of test compounds at 37 °C for 15 min. p-Nitrophenyl-α-D-glucopyranoside
(0.7 mM) was added, and change in absorbance at 400 nm was recorded for 30 min by multiplate
reader. Test compounds were replaced with DMSO (7% final) in control. Acarbose was used as the
standard inhibitor [35].
4.3. Statistical analyses
The IC50 values were estimated by using EZ-Fit Enzyme Kinetic Program (Perrella Scientific Inc.,
Amherst, USA) and the percent inhibition was calculated by using the subsequent formula
% Inhibition = 100 (100-OD test well/ OD control) X 100
4.3. Kinetic studies
The kinetic parameters of the α-glucosidase were analyzed by incubating the enzyme with different
concentrations of test compounds. The concentrations of substrate were also varied (0.1- 0.8 mM) in
order to evaluate the change in Km values.
4.4. Molecular docking Interaction
In order to predict the binding mode of newly synthesized benzothiazole derivatives, molecular
docking studies were carried out with α-glucoronidase of S. cerevisae (yeast) using Glide software
[29]. In order to compensate the non-availability of crystal structure, homology modeling was
carried out using SWISS-MODEL web-server [36]. The FASTA sequence of α-glucosidase
(P53051.1) of S. cerevisiae was obtained from NCBI protein database. The most reliable model was
made using isomaltase (MAL12) from S. cerevisiae (PDB 3AJ7) exhibiting more than 85%
similarity and 71% identity [32]. The developed model was submitted to server RAMPAGE for
geometric analysis using the Ramachandran plot [31].
The builder module in MOE 2016.08 was used to draw the compounds. All the compounds were
energy minimized, following the addition of partial charges as per Merck Molecular Force Field
(MMFF94). The compounds were docked using Glide software. A receptor grid was generated suing
the coordinates of the residues spanning the active site (Table-S1). All the compounds were docked
using the default docking protocol in Glide and after post-docking minimization 10 poses of each
16

ligand were recoded for analysis. The resulting poses of the compounds were visually inspected to
comprehend protein ligand interactions. The interactions were analyzed with the help of PLIP web
server (https://projects.biotec.tu-dresden.de/plip-web/plip). All the visuals were recorded using
Chimera [37].
4.5. General procedure for the syntheses of compounds 1-25
Synthesis of 2-amino-4-cholorobenzenethioles was carried out by reaction of 2-amino-4-
cholorobenzenethiol with different aromatic aldehydes. In a representative reaction different
aromatic aldehydes (1 mmol) and 2-amino-4-cholorobenzenethiol (1 mmol) were stirred in N,N-
dimethylformamide (10 mL) as solvent for 30 minutes, then sodium metabisulfite (Na2S2O5) 0.61 g
was added into the mixture, and refluxed for 2 h. Progress of reaction was monitored by TLC. After
completion of reaction, it was cooled and precipitated by addition of cool water. Filtration of
precipitate, followed by washing with cool water, resulted in pure benzothiazoles 1-25.
2-(5-Chlorobenzo[d]thiazol-2-yl)phenol (1)
White crystal, Yield: 83 %, M.P.: 198 °C, 1H-NMR (300 MHz, CD3OD) δ: 7.97 (d, 1H, J4,5 = 2.0 Hz,
H-4), 7.83 (d, 1H, J7,6 = 8.7 Hz, H-7), 7.41 (dd, 1H, J6,7 = 8.7 Hz, J6,4 = 2.0 Hz, H-6), 7.38 (m, 2H,
H-4', H-5'), 7.10 (d, 1H, J6', 5' = 8.4 Hz, H-6'), 6.94 (d, 1H, J3',4' = 6.0 Hz, H-3'); EI-MS: m/z (rel.
abund. %), 263 (M+ +2, 37), 261 (M+, 100), 233 (48), 206 (8), 198 (13), 142 (7), 107 (20). HREI-MS
m/z : 261.0016, [M]+ (Calcd for C13H8ClNOS, 261.0015).
4-(5-Chlorobenzothiazol-2-yl)phenol (2)
1
White solid, Yield: 70%, M.P.: 265 °C, H-NMR: (300 MHz, CD3OD): δ 7.87 (d, 1H, J7,6 = 8.7 Hz,
H-7), 7.26 (dd, 1H, J6,7 = 8.7 Hz, J6,4 = 1.8 Hz, H-6), 7.94 (d, 1H, J4,5 = 1.8 Hz, H-4), 7.69 (d, 2H,
J2',3', J 2', 6' = 8.7 Hz, H-2', H-6'), 6.85 (d, 2H, J3',2', J 5', 6' = 8.7 Hz, H-3', H-5'). EI-MS: m/z (rel. abund.
%), 263(M+ +2, 37), 261 (M+, 94), 233(8), 142 (17), 107 (15). HREI-MS m/z : 261.0015 [M]+ (Calcd
for C13H8ClNOS, 261.0015).
3-(5-Chloro-2-benzothiazolyl)phenol (3)
White solid, Yield: 70%, M.P.: 196 °C, 1H-NMR: (300 MHz, CD3OD): δ 7.80 (d, 1H, J 7,6 = 8.4 Hz,
H-7), 7.32 (dd, 1H, J6,7 = 8.4 Hz, J6,4 = 2.1 Hz, H-6), 8.09 (d, 1H, J4,6 = 2.1 Hz, H-4), 7.68 (s, 1H, H-
2'), 7.03 (d, 1H, J4',5' = 7.8 Hz, H-4′), 7.37 (dd, 1H, J5',4' = 7.8 Hz, J5',6' = 7.5 Hz, H-5′), 7.56 (d, 1H,
17

J6',5' = 7.5 Hz, H-6′). EI-MS: m/z (rel. abund. %), 263 (M+ +2, 37.8), 261 (M+, 100), 232 (13), 142
(20), 130 (13), 107 (15). HREI-MS m/z: 261.0016 [M]+ (Calcd for C13H8ClNOS, 261.0015).
4-Bromo-2-(5-chlorobenzothiazol-2-yl)phenol (4)
White crystal, Yield: 63%, M.P.: 210 °C, 1H-NMR: (300 MHz, CD3OD): δ 7.81 (d, 1H, J7,6 = 8.7 Hz,
H-7), 7.39 (dd, 1H, J6,7 = 8.7, J6,4 =1.8 Hz, H-6), 7.97 (d, 1H, J4,5 = 1.8 Hz, H-4), 6.97 (d, 1H, J3',4'
=
9.0 Hz, H-3'), 7.44 (dd, 1H, J4',3'= 9.0, J4',6' = 2.2 Hz, H-4'), 7.74 (d, 1H, J6',4' = 2.2 Hz, H-6'). EI-MS:
m/z (rel. abund. %), 343 (M++4, 28), 341 (M+ +2, 100), 339 (M+ 74.1), 261 (12), 232 (80), 197(30).
HREI-MS m/z : 338.9120 [M]+ (Calcd for C13H7BrClNOS, 338.9120).
5-Chloro-2-(4-methoxyphenyl)-benzothiazole (5)
White crystal, Yield: 82%, M.P.: 148 °C, 1H-NMR: (300 MHz, CD3OD): δ 7.77 (d, 1H, J7,6 = 8.4 Hz,
H-7), 7.31 (dd, 1H, J6,7 = 8.6 Hz, J6,4 = 2.0 Hz, H-6), 8.02 (d, 1H, J4,5 = 1.8 Hz, H-4), 7.00 (d, 2H,
J2′,3′, J6′,5′ = 8.7 Hz, H-2',H-6'), 7.99 (d, 2H, J3′,2′, J5′,6′ = 8.7 Hz, H-3', H-5′), 3.87 (s, 3H, OCH3) . EI-
MS: m/z (rel. abund. %), 277 (M++2, 38), 275 (M+, 100), 262 (19), 260 (49), 234 (19), 232 (52), 197
(25). HREI-MS m/z : 275.0174 [M]+ (Calcd for C14H10ClNOS, 275.0172).
5-Chloro-2-(3,4-dimethoxyphenyl)-benzothiazole (6)
1
White solid, Yield: 80%, M.P.: 164 °C, H-NMR: (300 MHz, CD3OD): δ 7.75 (d, 1H, J7,6 = 8.5 Hz,
H-7), 7.57 (dd, 1H, J6,7 = 8.5, J 6,4 = 2.0 Hz, H-6), 8.07 (d, 1H, J 4,6= 2.0 Hz, H-4), 7.67 (d, 1H, J2',6'
=
2.0 Hz, H-2'), 6.90 (d, 1H, J5',6' = 8.5 Hz, H-5′), 7.32 (dd, 1H, J6',5' = 8.5, J6',2' = 2.0 Hz, H-6′) . EI-
MS: m/z (rel. abund. %), 307 (M++2, 38), 305 (M+, 100), 290 (3), 262 (29), 219 (14), 152 (9). HREI-
MS m/z: 305.0277 [M]+ (Calcd for C15H12ClNO2S 305.0278).
5-Chloro-2-(3,4,5-trimethoxyphenyl)benzo[d]thiazole (7)
1
White crystal, Yield: 89 %, M.P.: 159 °C, H-NMR: (300 MHz, CD3OD): δ 7.74 (d, 1H, J7,6 = 8.4
Hz, H-7), 7.34 (dd, 1H, J6,7 = 8.4 Hz, J6,4 = 2.0 Hz, H-6), 8.07 (d, 1H, J4,5 = 2.0 Hz, H-4), 7.24 (s,
2H, H-2', H-6'). EI-MS: m/z (rel. abund. %), 337(M+ +2, 39), 335 (M+, 100), 322 (38), 320 (96), 294
(15), 277 (25), 262 (56), 249 (10). HREI-MS m/z : 335.0383 [M]+ (Calcd for C16H14ClNO3S,
335.0383).
18

5-Chloro-2-(2,3,4-trimethoxyphenyl)-benzothiazole (8)
1
White crystal, Yield: 75%, M.P.: 125 °C, H-NMR: (300 MHz, CD3OD): δ 8.25 (d, 1H, J6′,5′ = 9.0
Hz, H-6'), 8.04 (d, 1H, J4,5 = 1.8 Hz, H-4), 7.86 (d, 1H, J7,6 = 8.4 Hz, H-7), 7.32 (dd, 1H, J6,7 = 8.7,
J6,4 = 1.8 Hz, H-6), 6.83 (d, 1H, J5′,6′ = 9.0 Hz, H-5'); EI-MS: m/z (rel. abund. %), 337 (M++2, 34),
335 (M+, 80), 319 (100), 306 (28), 289 (28), 277 (38), 262 (22). HREI-MS m/z : 335.0385 [M]+
(Calcd for C16H14ClNO3S, 335.0383).
5-Chloro-2-(4-ethoxyphenyl)-benzothiazole (9)
Yellow solid, Yield: 41%, M.P.: 128 °C, 1H-NMR: (300 MHz, CD3OD): δ 7.75 (d, 1H, J7,6 = 8.7 Hz,
H-7), 7.32 (dd, 1H, J6,7 = 8.7 Hz, J6,4 = 1.8 Hz, H-6), 8.05 (d, 1H, J4,5 = 1.8 Hz, H-4), 8.01 (d, 2H,
J2',3', J 6', 5' = 8.7 Hz, H-2', H-6'), 6.98 (d, 2H, J3',2', J 5',6' = 8.7 Hz, H-3',H-5'), 4.11 (q, 2H, OCH2), 1.44
(t, 3H, CH3). EI-MS: m/z (rel. abund. %), 291(M+ +2, 38), 289.0 (M+, 60), 261 (100), 232 (17), 197
(15), 142 (19), 107 (19). HREI-MS m/z : 289.0328 [M]+ (Calcd for C15H12ClNOS, 289.0328).
2-(5-Chlorobenzothiazol-2-yl)-4-methoxyphenol (10)
White crystal, Yield: 81%, M.P.: 130 °C, 1H-NMR: (300 MHz, CDCl3): δ 7.76 (d, 1H, J7,6 = 8.4 Hz,
H-7), 7.36 (dd, 1H, J6,7 = 8.4 Hz, J6,4 =1.8 Hz, H-6), 7.96 (d, 1H, J4,5 = 1.8 Hz, H-4), 6.97 (d, 1H, J3',
4' = 8.0 Hz, H-3'), 7.06 (dd, 1H, J4', 3' = 8.0 Hz, J4', 6' = 2.4 Hz, H-4'), 7.16 (d, 1H, J6', 4' = 2.4 Hz, H-6').
EI-MS: m/z (rel. abund. %), 293(M+ +2, 38), 291 (M+, 53), 278 (37), 276 (100), 220 (18), 194(16),
159 (10). HREI-MS m/z : 291.0121 [M]+ (Calcd for C14H10ClNO2S, 291.0121).
4-(5-Chlorobenzo[d]thiazol-2-yl)-2-methoxyphenol (11)
1
White solid, Yield: 86%, M.P.: 138 °C, H-NMR: (300 MHz, CD3OD): δ 7.79 (d, 1H, J7,6 = 8.4 Hz,
H-7), 7.33 (dd, 1H, J6,7 = 8.4 Hz, J6,4 = 1.8 Hz, H-6), 8.01 (d, 1H, J4,5 = 1.8 Hz, H-4), 7.51 (dd, 1H,
J6′,5′ = 8.1 Hz, J6′,2′= 1.8 Hz, H-6'), 6.99 (d, 1H, J5′,6 ′ = 8.4 Hz, H-5'), 7.74 (d, 1H, J2′,6′ = 1.8 Hz, H-
2'). EI-MS: m/z (rel. abund. %), 293 (M++2, 38), 291 (M+, 100), 290 (40), 276 (16), 248 (28), 233
(6), 220 (8). HREI-MS m/z : 291.0121 [M]+ (Calcd for C14H10ClNO2S,, 291.0121).
5-(5-Chlorobenzothiazol-2-yl)-2-methoxyphenol (12)
White solid, Yield: 90 %, M.P.: 140 °C, 1H-NMR: (300 MHz, CD3OD): δ 8.01 (d, 1H, J4,5 = 1.8 Hz,
H-4), 7.76 (d, 1H, J7,6 = 8.7 Hz, H-7), 7.69 (d, 1H, J2', 6' = 2.1 Hz, H-2'), 7.33 (dd, 1H, J6,7 = 8.7, J6,4
19

= 1.8 Hz, H-6), 7.68 (dd, 1H, J6',5'= 8.1 Hz, J 6', 2' = 2.0 Hz, H-6'), 6.94 (d, 1H, J5', 6' = 8.1 Hz, H-5');
EI-MS: m/z (rel. abund. %), 293(M+ +2, 38), 291 (M+, 10), 276 (8), 248 (8), 235 (13), 197 (5), 155
(6). HREI-MS m/z : 291.0121 [M]+ (Calcd C14H10ClNO2S, 291.0121).
2-(5-Chlorobenzothiazol-2-yl)-6-methoxyphenol (13)
1
White solid, Yield: 89%, M.P.: 194 °C, H-NMR: (300 MHz, CD3OD): δ 8.01 (d, 1H, J4,5 = 1.8 Hz,
H-4), 7.78 (d, 1H, J7,6 = 8.7 Hz, H-7), 7.38 (d, 1H, J6′,5′ = 8.4 Hz, H-6'), 7.34 (dd, 1H, J6,7 = 8.7, J6,4
=1.8 Hz, H-6), 6.98 (d, 1H, J4′,5′ = 7.8 Hz, H-4'), 6.90 (t, 1H, J5′,6,4′ = 7.9 Hz, H-5'), EI-MS: m/z (rel.
abund. %), 293 (M++2, 38), 291(M+, 92), 290 (44), 273 (51), 220 (30), 194 (16), 170 (11). HREI-MS
m/z : 291.0121 [M]+ (Calcd for C14H10ClNO2S, 291.0121).
5-Chloro-2-phenylbenzothiazole (14)
1
White crystal, Yield: 92 %, M.P.: 135 °C, H-NMR: (300 MHz, CD3OD): δ 7.80 (d, 1H, J7,6 = 8.7
Hz, H-7), 7.34 (dd, 1H, J6,7 = 8.4, J6,4 = 2.0 Hz, H-6), 8.01 (d, 1H, J4,5 = 2.0 Hz, H-4), 8.07 (d, 2H,
J2′,3′, J6′,5′ = 8.6 Hz, H-2',6'), 7.49 (m, 3H, H-3',H-4', H-5'). EI-MS: m/z (rel. abund. %), 247 (M++2,
37), 245 (M+, 100), 218 (6), 210 (10), 142 (56), 122 (15), 107 (35). HREI-MS m/z : 245.0066 [M]+
(Calcd for C13H8ClNS,, 245.0066).
5-Chloro-2-(4-chlorophenyl)-benzothiazole (15)
1
White solid, Yield: 73%, M.P.: 158 °C, H-NMR: (300 MHz, CD3OD): δ 7.79 (d, 1H, J7,6 = 8.7 Hz,
H-7), 7.35 (dd, 1H, J6,7 = 8.4 Hz, J6,4 = 1.8 Hz, H-6), 8.02 (d, 1H, J4,5 = 1.8 Hz, H-4), 7.98 (d, 2H,
J2',3', J 6', 5' = 8.7, Hz, H-2',H-6'), 7.46 (d, 2H, J3',2', J 5',6' = 8.7 Hz, H-3', H-5'). EI-MS: m/z (rel. abund.
%), 281(M+ +2, 69.5), 279 (M+, 100), 244 (44), 273 (51), 142 (30), 137 (12), 107 (25). HREI-MS
m/z : 278.9677 [M]+ (Calcd for C13H7Cl2NS, 278.9676).
5-Chloro-2-(2,4-dichlorophenyl)-benzothiazole (16)
1
White solid, Yield: 59%, M.P.: 203 °C, H-NMR: (300 MHz, CD3OD): δ 8.05 (d, 1H, J7,6 = 8.4 Hz,
H-7), 7.55 (dd, 1H, J6,7 = 8.7 Hz, J6,4 = 2.1 Hz, H-6), 8.09 (d, 1H, J4,6 = 2.1 Hz, H-4), 7.73 (d, 1H,
J3',5' = 2.1 Hz, H-3'), 7.50 (dd, 1H, J5',6' = 8.4 Hz, J5',3' = 1.8 Hz, H-5′), 8.25 (d, 1H, J6',5' = 8.4 Hz, H-
6′). EI-MS: m/z (rel. abund. %), 316 (M+ +2, 35.6), 314 (M+, 100), 312 (92), 277 (5.0), 142 (20), 107
(11). HR-EIMS m/z: 314.9257 [M]+ (Calcd for C13H6Cl3NS, 314.9257).
20

4-(5-Chlorobenzothiazol-2-yl)-N,N-dimethylaniline (17)
1
White solid, Yield: 68%, M.P.: 172 °C, H-NMR: (300 MHz, CD3OD): δ 7.71 (d, 1H, J7,6 = 8.7 Hz,
H-7), 7.26 (dd, 1H, J6,7 = 8.7 Hz, J6,4 = 2.0 Hz, H-6), 7.99 (d, 1H, J4,5 = 2.0 Hz, H-4), 7.94 (d, 2H,
J2′,3′, J6′,5′ = 8.6 Hz, H-2',6'), 6.76 (d, 2H, J3′,2′, J5′,6′ = 8.6 Hz, H-3', H-5′), 3.06 (s, 6H,(CH3)2). EI-MS:
m/z (rel. abund. %), 290 (M++2, 36), 288 (M+, 100), 287 (99), 274 (15), 272 (20), 259 (25), 244 (11),
143 (23). HREI-MS m/z : 288.0489 [M]+ (Calcd for C15H13ClN2S, 288.0488).
5-Chloro-2-(naphthalen-2-yl)-benzothiazole (18)
White crystal ,Yield: 59 %, M.P.: 152 °C, 1H-NMR: (300 MHz, CD3OD): δ 7.83 (d, 1H, J7,6 = 8.5 Hz
H-7), 7.37 (dd, 1H, J6,7 = 8.5 Hz, J6,4 = 2.0 Hz, H-6), 8.07 (d, 1H, J4,6 = 2.0 Hz, H-4), 7.90 (d, 1H,
J1',3' = 1.5 Hz, H-1'), 8.17 (dd, 1H, J3',4' 8.5 Hz, J3',1' = 1.5 Hz, H-3′), 7.95 (d, 1H, J4',3' = 8.5 Hz, H-4′),
7.98 (d, 1H, J5',6' = 8.0 Hz, H-5′), 7.87 (t, 1H, H-6′), 7.56 (m, 2H, H-7′, H-8'). EI-MS: m/z (rel.
abund. %), 297 (M+ +2, 38), 295 (M+, 100), 235 (18), 233 (49), 207 (9), 198 (13), 107(16). HREI-
MS m/z : 295.0224 [M]+ (Calcd for C17H10ClNS, 295.0222).
5-Chloro-2-(1H-indol-3-yl)-benzothiazole (19)
Brown solid, Yield: 69%, M.P.: 200 °C, 1H-NMR: (300 MHz, CD3OD): δ 7.74 (d, 1H, J7,6 = 8.4 Hz,
H-7), 7.34 (m, 2H, H-6, 5'), 8.28 (brs, 2H, H-4, H-7'), 8.06 (s, 1H, H-2′), 7.52 (d, 1H, J4′,5 = 8.2 Hz,
H-4′), 8.09 (t, 1H, J6′,5′,7' = 8.3 Hz, H-6′). EI-MS: m/z (rel. abund. %), 286 (M++ 2, 38), 284(M+, 99),
259 (257), 22 (5), 158 (100), 124 (30). HREI-MS m/z : 284.0176 [M]+ (Calcd for C15H9ClN2S,
284.0175).
5-Chloro-2-(furan-2-yl)-benzothiazole (20)
White crystal, Yield: 82%, M.P.: 121 °C, 1H-NMR: (300 MHz, CD3OD): δ 7.79 (d, 1H, J7,6 = 8.7 Hz,
H-7), 7.35 (dd, 1H, J6,7 = 8.4, Hz J6,4 = 1.8 Hz, H-6), 8.01 (d, 1H, J4,5 = 1.8 Hz, H-4), 7.21 (d, 1H,
J2',3 '= 0.9 Hz, H-2'), 6.59 (q, 1H, H-3'), 7.60 (d, 1H, J4',3 '= 3.0 Hz, H-2'). EI-MS: m/z (rel. abund. %),
237(M+ +2, 37), 235 (M+, 100), 244 (44), 273 (51), 142 (30), 137 (12), 107 (25). HREI-MS m/z :
234.9859 [M]+ (Calcd for C11H6ClNOS, 234.9859).
21

5-Chloro-2-(5-methylfuran-2-yl)benzothiazole (21)
1
White solid, Yield: 46%, M.P.: 164 °C, H-NMR: (300 MHz, CD3OD): δ 7.74 (d, 1H, J7,6 = 8.7 Hz,
H-7), 7.30 (dd, 1H, J6,7 = 8.4 Hz, J6,4 = 1.8 Hz, H-6), 7.97 (d, 1H, J4,5 = 1.8 Hz, H-4), 7.09 (d, 1H,
J3',4' = 3.0 Hz, H-3'), 6.19 (d, 1H, J4',3' = 2.4 Hz, H-4'), 2.42 (s, 3H, CH3). EI-MS: m/z (rel. abund. %),
251(M+ +2, 37), 249 (M+, 100), 248 (35), 234 (29), 220 (60), 206 (28), 179 (5). HREI-MS m/z :
249.0015 [M]+ (Calcd for C12H8ClNOS, 249.0015).
5-Chloro-2-(thiophen-2-yl)-benzothiazole (22)
White solid, Yield: 86 %, M.P.: 120 °C, 1H-NMR: (300 MHz, CD3OD): δ 7.74 (d, 1H, J7,6 = 8.4 Hz,
H-7), 7.33 (dd, 1H, J6,7 = 8.4 Hz, J6,4 = 1.8 Hz, H-6), 7.99 (d, 1H, J4,5 = 1.8 Hz, H-4), 7.66 (d, 1H,
J2′,3′ = 3.0 Hz, H-2'), 7.13 (t, 1H, H-3'), 7.52 (d, 1H, J4′,3′= 4.8 Hz, H-4'). EI-MS: m/z (rel. abund. %),
253 (M++2, 41), 251 (M+, 100), 218(5), 207 (8), 142 (27), 125 (7), 107 (18). HREI-MS m/z :
250.9631 [M]+ (Calcd for C11H6ClNS2, 250.9630).
5-Chloro-2-(pyridin-3-yl)-benzothiazole (23)
1
White solid, Yield: 93%, M.P.: 172 °C, H-NMR: (300 MHz, CD3OD): δ 7.83 (d, 1H, J7,6 = 8.4 Hz,
H-7), 7.39 (dd, 1H, J6,7 = 8.4, J6,4 = 1.8 Hz, H-6), 8.05 (d, 1H, J4,5 = 1.8 Hz, H-4), 9.27 (d, 1H, J2′,6′
=
1.8 Hz, H-2'), 8.73 (d, 1H, J4′,5′ = 3.9 Hz, H-4'), 7.50 (dd, 1H, J5′,4′ = 5.0 Hz, J5′,6′ =7.8 Hz, H-5'), 8.42
(dd, 1H, J6′,2′, = 1.8 Hz, J6′,5′ =6.6 Hz, H-6'). EI-MS: m/z (rel. abund. %), 248 (M++2, 37.5), 246 (M+,
100), 220 (25), 211(5), 194 (4), 142 (12), 107 (20). HREI-MS m/z : 246.0019 [M]+ (Calcd for
C12H7ClN2S, 246.0018).
5-Chloro-2-(pyridin-4-yl)-benzothiazole (24)
White crystalline solid, Yield: 87%, M.P.: 185 °C, 1H-NMR: (300 MHz, CD3OD): δ 7.83 (d, 1H, J7,6
= 8.7 Hz, H-7), 7.41 (dd, 1H, J6,7 = 8.7 Hz, J6,4 = 2.0 Hz, H-6), 8.08 (d, 1H, J4,5 = 2.0 Hz, H-4), 8.76
(d, 2H, J2',3', J 2', 6' = 6.0 Hz, H-2', 6'), 7.93 (d, 2H, J3', 2', J 6',2' = 6.0 Hz, H-3', 6'). EI-MS: m/z (rel.
abund. %), 248 (M+ + 2, 37), 246 (M+, 100), 235 (18), 233 (47), 207 (9), 198 (15), 117 (9). HREI-
MS m/z : 246.0019, [M]+ (Calcd for C12H7ClN2S, 246.0018).
22

5-Chloro-2-(4-(pentyloxy)phenyl)benzothiazole (25)
1
White solid, Yield: 41%, H-NMR: (400 MHz, DMSO): δ 8.21 (d, 1H, J7,8 = 8.8 Hz, H-7), 8.19 (m,
2H, H-2', H-3'), 8.13 (s, 1H, H-5), 7.53 (dd, 1H, J8,7 = 8.4 Hz, J8,5 = 2.0 Hz, H-8), 7.36 (d, 2H, J5',6', J
6',5' = 8.4 Hz, H-5',H-6'), 4.12 (q, 2H, 4''-CH2), 3.16 (m, 2H, 2''-CH2). 2.62 (m, 2H, 3''-CH2), 2.62 (m,
2H, 1''-CH2), 1.00 (t, 3H, 5''-CH3), EI-MS: m/z (rel. abund. %), 333 (M+ +2, 2.5), 331.0 (M+, 8.9),
261 (100.0), 232 (4.6), 197 (3.1), 142 (3.5), 107 (2.4), HREI-MS m/z : 331.0798, [M]+ (Calcd for
C18H18ClNOS, 331.0799)
Conflict of Interest
Authors declare no conflict of interest.
Acknowledgement: The authors are thankful to Higher Education Commission (HEC) Pakistan, for
financial support under the National Research Program for Universities, Project No. 20-2073.
References
[1]
[2]
[3]
[4]
M. Shivashankar, and D. Mani, A brief overview of diabetes, Int. J. Pharm. Pharm. Sci. 3
(2011) 22-27.
A.E. Butler, J. Janson, S. Bonner-Weir, R. Ritzel, R.A. Rizza, and P.C. Butler, β-Cell deficit
and increased β-cell apoptosis in humans with type 2 diabetes, Diabetes. 52 (2003) 102-110.
O.A. Fasanmade, I.A. Odeniyi, A.O. Ogbera, Diabetic ketoacidosis: diagnosis and
management, Afr. J Med. Med. Sci. 37 (2008) 99-105.
K.G.M.M. Alberti, P.F. Zimmet, Definition, diagnosis and classification of diabetes mellitus
and its complications. Part 1: diagnosis and classification of diabetes mellitus, Diabetic
Med. 15 (1998) 539-553.
[5]
[6]
H. King, R.E. Aubert, W.H. Herman, Global burden of diabetes, 1995–2025: prevalence,
numerical estimates, and projections. Diabetes Care, 21 (1998) 1414-1431.
K. Nakagawa, Studies targeting α-glucosidase inhibition, antiangiogenic effects, and lipid
modification regulation: background, evaluation, and challenges in the development of food
ingredients for therapeutic purposes. Biosci, Biotechnol, Biochemistry, 77 (2013) 900-908.
[7]
S. Landge, A.B. Mullick, K. Nagalapur, J. Neres, V. Subbulakshmi, K. Murugan, J.
Mahadevaswamy, Discovery of benzothiazoles as antimycobacterial agents: Synthesis,
structure-activity relationships and binding studies with Mycobacterium tuberculosis
decaprenylphosphoryl-β-d-ribose 2′-oxidase, Bioorg. Med. Chem. 23 (2015) 7694-7710.
23

[8]
[9]
E.L. Stone, F. Citossi, R. Singh, B. Kaur, M. Gaskell, P.B. Farmer, M. Stocks, Antitumour
benzothiazoles. Part 32: DNA adducts and double strand breaks correlate with activity;
synthesis of 5F203 hydrogels for local delivery, Bioorg. Med. Chem. 23 (2015), 6891-6899.
E.B. Lindgren, M.A. de Brito, T.R. Vasconcelos, M.O. de Moraes, R.C. Montenegro, J.D
Yoneda, K.Z. Leal, Synthesis and anticancer activity of (E)-2-benzothiazole hydrazones
Europ. J. Med. Chem. 86 (2014) 12-16.
[10] T. Akhtar, S. Hameed, N. Al-Masoudi, R. Loddo, P. Colla, In vitro antitumor and antiviral
activities of new benzothiazole and 1, 3, 4-oxadiazole-2-thione derivatives, Acta. Pharm. 58
(2008) 135-149.
[11] N. Siddiqui, M. Alam, A.A. Siddiqui, Synthesis and analgesic activity of some 2-[{4-(alkyl
thioureido) phenyl sulphonamido]-6-substituted benzothiazoles, Asian. J. Chem. 16 (2004)
1005.
[12] N. Siddiqui, S.N. Pandeya, S.A. Khan, J. Stables, A. Rana, M. Alam, M.A. Bhat, (2007).
Synthesis and anticonvulsant activity of sulfonamide derivatives-hydrophobic domain,
Bioorg. Med. Chem. Lett. 17 (2007) 255-259.
[13] H. Bujdáková, T. Kuchta, Sidóová, E., and Gvozdjaková, A., Anti-Candida activity of four
antifungal benzothiazoles, FEMS Microbiology Letters, 112, (1993) 329-333.
[14] C.K. Lau, C. Dufresne, Y. Gareau, R. Zamboni, M. Labelle, R.N. Young, L. Charette,
Evolution of a series of non-quinoline leukotriene D 4 receptor antagonist; synthesis and sar
of benzothiazoles and thiazoles substituted benzyl alcohols as potent LTD 4 antagonists,
Bioorg. Med. Chem. Lett. 5 (1995) 1615-1620.
[15] H. Kokelenberg, C.S. Marvel, Polymers containing anthraquinone units: Benzimidazole and
benzothiazole polymers, J. Polymer Sci Part A‐1: Polymer Chem. 8 (1970) 3199-3209.
[16] R.O. McCracken, K.B. Lipkowitz, Structure-activity relationships of benzothiazole and
benzimidazole anthelmintics: a molecular modeling approach to in vivo drug efficacy, J.
Parasitol, 76 (1990) 853-864.
[17] S.Y. Gwon, S.Y. Lee, Y.A. Son, S.H. Kim, Benzothiazole and indole based dye sensor:
Optical switching functions with pH stimuli, Fibers and Polymers. 13 (2012) 1101-1104.
[18] Su, X., Vicker, N., Ganeshapillai, D., Smith, A., Purohit, A., Reed, M. J., Potter, B. V. Mol
cell endocrinol, benzothiazole derivatives as novel inhibitors of human 11β-hydroxysteroid
dehydrogenase type 1, 248 (2006), 214-217.
[19] L. Pasternak, E. Meltzer-Mats, G. Babai-Shani, G. Cohen, O. Viskind, J. Eckel, A.
Gruzman, Benzothiazole derivatives augment glucose uptake in skeletal muscle cells and
stimulate insulin secretion from pancreatic β-cells via AMPK activation, Chem. Commun.
50 (2014) 11222-11225.
[20] E. Meltzer-Mats, G. Babai-Shani, L. Pasternak, N. Uritsky, T. Getter, O. Viskind, A.
Gruzman, Synthesis and mechanism of hypoglycemic activity of benzothiazole derivatives,
J. Med. Chem, 56 (2013), 5335-5350.
24

[21] M. Taha, N.H. Ismail, S. Lalani, M.Q. Fatmi, S. Siddiqui, K.M. Khan, M.I. Choudhary,
Synthesis of novel inhibitors of α-glucosidase based on the benzothiazole skeleton
containing benzohydrazide moiety and their molecular docking studies, Eur. J. Med. Chem.
92 (2015) 387-400.
[22] W.H. Zhong, Y.M. Zhang, and X.Y. Chen, Samarium diiodide promoted reductive
cyclization of nitrodisulfides with nitriles: a new route to benzothiazoles, ChemInform, 33
(2002) 316-318.
[23] Y.M. Ha, Y. Uehara, D. Park, H.O. Jeong, J.Y. Park, Y.J. Park, J.Y. Lee, H.J. Lee, Y.M.
Song, H.R. Moon, and H.Y. Chung, Synthesis and preliminary in vitro biological evaluation
of 5-chloro-2-(substituted phenyl) benzo [d] thiazole derivatives designed as novel
antimelanogenesis agents, Appl. Biochem. Biotechnol. 168 (2012) 1416-1433.
[24] P. Namjin, H. Yumi, K.M. Rajesh, K. Yong, S.H Kwang, L. Sunwoo, Synthesis of
benzothiazoles through copper‐catalyzed one‐pot three‐component reactions with use of
sodium hydrosulfide as a sulfur surrogate, Eur. J. Org. Chem. 10 (2012) 1984-1993.
[25] F. Xuesen, W. Yangyang, H. Yan, Z. Xinying, W. Jianji, Ru (III)-catalyzed oxidative
reaction in ionic liquid: an efficient and practical route to 2-substituted benzothiazoles and
their hybrids with pyrimidine nucleoside, Tetrahedron Lett, 51 (2010) 3493-3496.
[26] T. Yao, P. Qiang, J. Zengqiang, M. Dazhuang, S. Xuesong, H. Shiqing, , Preparation and
oxidation of α-nitro alcohols with supported reagents, Tetrahedron Lett. 55 (2014) 5499-
5503.
[27] L. Hee-Jong, D. Myung, L.I. Young-Choi, M.H. Jung, Microwave-assisted synthesis of
benzimidazoles, benzoxazoles, and benzothiazoles from resin-bound esters, J. Comb. Chem.
10 (2008) 501-503.
[28] S. Yousuf, S. Shah, A. Nida. K.M. Khan, 2-(5-Chloro-1, 3-benzothiazol-2-yl)-4-
methoxyphenol Acta Crystallogr. Sect. E. 68 (2012) 2877.
[29] R.A. Friesner, J.L. Banks, R.B. Murphy, T.A. Halgren, J.J. Klicic, D.T. Mainz, M.P.
Repasky, E.H. Knoll, M. Shelley, J.K. Perry, D.E. Shaw, P. Francis, P.S. Shenkin, Glide: A
New Approach for Rapid, Accurate Docking and Scoring. 1. Method and Assessment of
Docking Accuracy, J. Med. Chem. 47 (2004) 1739-1749. doi:10.1021/jm0306430.
[30] X.-Y. Qin, J. Lee, L. Zheng, J.-M. Yang, Y. Gong, Y.-D. Park, Inhibition of α-glucosidase
by 2-thiobarbituric acid: Molecular dynamics simulation integrating parabolic
noncompetitive
inhibition
kinetics,
Process
Biochem.
(2017)
0–1.
doi:10.1016/j.procbio.2017.10.016.
[31] R.W. Hooft, C. Sander, G. Vriend, Objectively judging the quality of a protein structure
from Ramachandran plot., Comput. Appl. Biosci. 13 (1997) 425–430.
doi:10.1093/bioinformatics/13.4.425.
a
25

[32] K. Yamamoto, H. Miyake, M. Kusunoki, S. Osaki, Crystal structures of isomaltase from
Saccharomyces cerevisiae and in complex with its competitive inhibitor maltose, FEBS J.
277 (2010) 4205-4214. doi:10.1111/j.1742-4658.2010.07810.x.
[33] T. Tagami, K. Yamashita, M. Okuyama, H. Mori, M. Yao, A. Kimura, Molecular basis for
the recognition of long-chain substrates by plant α-glucosidases, J. Biol. Chem. 288 (2013)
19296-19303. doi:10.1074/jbc.M113.465211.
[34] K. Bharatham, N. Bharatham, K.H. Park, K.W. Lee, Binding mode analyses and
pharmacophore model development for sulfonamide chalcone derivatives, a new class ofꢀ??-
glucosidase
inhibitors,
J.
Mol.
Graph.
Model.
26 (2008)
1202-1212.
doi:10.1016/j.jmgm.2007.11.002.
[35] A. Farooq, L. Shahazadi, M. Bajda, N. Ullah, A. Rauf, S.A. Shahzad, A.F. Khan, M. Ashraf,
M. Yar, Organo catalyzed Novel Synthetic Methodology for Highly Functionalized
Piperidines as Potent α‐Glucosidase Inhibitors, Archiv der Pharmazie 349 (2016) 724-732.
[36] T. Schwede, J. Kopp, N. Guex, M.C. Peitsch, SWISS-MODEL: An automated protein
homology-modeling
server,
Nucleic
Acids
Res.
31
(2003)
3381-3385.
doi:10.1093/nar/gkg520.
[37] E.F. Pettersen, T.D. Goddard, C.C. Huang, G.S. Couch, D.M. Greenblatt, E.C. Meng, T.E.
Ferrin, UCSF Chimera - A visualization system for exploratory research and analysis, J.
Comput. Chem. 25 (2004) 1605-1612. doi:10.1002/jcc.20084.
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27

Research Highlight
 Synthesis of 5-chloro-2-aryl benzo[d]thiazoles has been performed
 α-Glucosidase Inhibitory potential of synthetic compounds has been evaluated.
 In silico studies of 5-chloro-2-aryl benzo[d]thiazoles have been accomplished
 All synthetic compounds were spectroscopically characterized.
 Structure-activity relationship has been evaluated.
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