One-Pot Three Component Synthesis of 2-(1H-Benzo[d]thiazole-2-yl)-N-Arylbenzamides in Glycerol Medium

Article abstract of DOI:10.14233/ajchem.2020.22538

In this work, a series of 2-(1H-benzo[d]thiazole-2-yl)-N-arylbenzamides is synthesized by using diethyl phthalate, anilines and 2-amino-benzenethiol by one-pot three component synthesis in glycerol medium. Phosphoric acid is used as an effective reagent for this one-pot three component reaction. This reaction got completed in a short time, easy workup and gave an excellent yield in glycerol medium. The N-arylbenzamides was found to have significant cytotoxic potentials against various cancer cells viz., A549 (lung cancer), HeLa (cervical cancer) and MCF-7 (breast cancer) using MTT assay. The molecular docking study is also employed to understand the binding mechanism of N-arylbenzamides against the antibacterial target. The docking result shows the binding energy of compound 4a is -8.6 kcal/mol. The binding affinity is a major concern and it shows that Asn and Thr residues have an interaction with compound 4a.

Full text of DOI:10.14233/ajchem.2020.22538

Asian Journal of Chemistry; Vol. 32, No. 6 (2020), 1343-1351
A
SIAN
J
OURNAL OF HEMISTRY
C
https://doi.org/10.14233/ajchem.2020.22538
One-Pot Three Component Synthesis of 2-(1H-Benzo[d]thiazole-2-yl)-
N-Arylbenzamides in Glycerol Medium
1,2,
2,*,
2,
3,
3,
SWATHI THUMULA
,VENKATESAN SRINIVASADESIKAN
, RAVI K. KOTTALANKA , S. REX JEYA RAJKUMAR and BALAJEE RAMCHANDRAN
1
Division of Chemistry, Department of Science and Humanities, Sreenidhi Institute of Science and Technology, Ghatkesar, Hyderabad-501301,
India
2
Division of Chemistry, Department of Sciences and Humanities, Vignan′s Foundation for Science, Technology and Research, Vadlamudi-522213,
India
3
Department of Biotechnology, Vignan′s Foundation for Science, Technology and Research, Vadlamudi-522213, India
*
Corresponding author: Tel.: +91 863 2344700 Extn: 121; E-mail: vsdgun@gmail.com
Received: 19 November 2019; Accepted: 20 January 2020; Published online: 30 May 2020;
AJC-19880
In this work, a series of 2-(1H-benzo[d]thiazole-2-yl)-N-arylbenzamides is synthesized by using diethyl phthalate, anilines and 2-amino-
benzenethiol by one-pot three component synthesis in glycerol medium. Phosphoric acid is used as an effective reagent for this one-pot
three component reaction. This reaction got completed in a short time, easy workup and gave an excellent yield in glycerol medium. The
N-arylbenzamides was found to have significant cytotoxic potentials against various cancer cells viz., A549 (lung cancer), HeLa (cervical
cancer) and MCF-7 (breast cancer) using MTT assay. The molecular docking study is also employed to understand the binding mechanism
of N-arylbenzamides against the antibacterial target. The docking result shows the binding energy of compound 4a is -8.6 kcal/mol. The
binding affinity is a major concern and it shows that Asn and Thr residues have an interaction with compound 4a.
Keywords: Glycerol, Diethyl phthalate, Anilines, 2-Aminobenzenethiol, Green chemistry.
the synthesis of pharmaceutically active ingredients, in which
the toxicity and residue of solvent have to be carefully cont-
rolled [11]. Because of these properties, there are a large
number of reports available in literature on the applications of
glycerol as an efficient and convenient solvents in organic
transformations [11,12]. On the other hand, benzothiazoles
have attracted much attention as important structural motifs
in medicinal chemistry. Many compounds bearing this
heterocyclic unit have revealed diverse and interesting biolo-
gical activities, such as anti-inflammatory, anti-microbial, anti-
tumour, neuroprotective and anti-convulsant activities [13-17].
Due to their importance, various synthetic strategies have been
developed. Commonly used methods include: (a) condensation
of o-amino benzenethiol with carboxylic acids by dehydration
catalyzed by acids [18,19]; (b) copper- or palladium-catalyzed
intramolecular cyclization of 2-halobenzothioureas [20,21];
(c) coupling of amylamines with 2-halobenzothiazoles [22]
or o-amino benzothiazoles with aryl halides [23-25]; (d) oxi-
dative cyclization of intermediates generated by o-amino
INTRODUCTION
Green chemistry [1] state that chemical reactions are
experiencing a deep change to meet environmentally benign
criteria. This indicates that the “Green Chemistry” process
involves the choice of a safe, non-toxic and low-cost solvents
[
2-4]. However, these green solvents have to be low-cost and
easy to handle. In the past decade, water [5-7], glycerol [8],
ionic liquids [9], polyethylene glycol [10] have appeared as
the most promising options for current solvents. Glycerol was
an environmental and biodegradable solvent is produced as a
byproduct in the biodiesel industries [11]. Moreover, glycerol
is non-volatile under normal atmospheric pressure and has a
high boiling point (290 ºC), thus making the distillation of the
reaction products a feasible separation technique. Reactions
in glycerol is carried out at high temperature, thus allowing
acceleration of the reaction or making possible reactions that
do not proceed in low boiling point solvents [11]. In particular,
low toxicity of glycerol has allowed to utilize as a solvent in
This is an open access journal, and articles are distributed under the terms of the Attribution 4.0 International (CC BY 4.0) License. This
license lets others distribute, remix, tweak, and build upon your work, even commercially, as long as they credit the author for the original
creation. You must give appropriate credit, provide a link to the license, and indicate if changes were made.

1
344 Thumula et al.
Asian J. Chem.
thiophenols with isothiocyanates [26]; and (e) Cu(I)- or Fe(III)-
catalyzed cross-coupling reactions of o-halo anilines with
isothiocyanates [27,28]. We now report our synthetic studies
on reactions of diethyl phthalate with anilines and 2-amino-
thiophenol. This is probably the first report to synthesize 2-
water (10 mL) twice and dried at 50 ºC under above 650 mmHg
vacuum for 10-12 h. The crude compound was purified by
recrystallization method using methanol as a solvent to get
the desired compound 5a.
Synthesis of compound 4a by step-wise synthesis:
Charged compounds 5 (5 mmol) and 3 (5 mmol) in glycerol
(20 mL) and heated at 100 ºC for 120 min in the presence of
(
1H-benzo[d]thiazole-2-yl)-N-aryl benzamides in glycerol.
Furthermore, the antibacterial and antifungal activities of
reported compounds were also evaluated in present work.
H
3
PO (5 mmol). Reaction progress was monitored by TLC.
4
After completion of the reaction water (50 mL) was added
and stirred for 10-15 min to separate out colourless solid from
the reaction mixture, which was collected by filtration. The
isolated solid was washed with water (10 mL) twice and dried
at 50 ºC under above 650 mmHg vacuum for 10-12 h. The
crude compound was purified by recrystallization method using
methanol as a solvent to get the desired compound 4a.
Synthesis of compound 6a: Charged compounds 1 (5
mmol) and 3 (5 mmol) in glycerol (20 mL) and heated at 100
EXPERIMENTAL
Melting points were uncorrected and found in H
in open capillary tubes. TLC was run on silica gel-G and visua-
lizations were found using UV light. Infrared spectra were
done by instrument Elmer-Perkin 1000 in KBr pellets. H NMR
spectra were recorded using TMS as standard in DMSO-d
with 400 MHz. Mass spectra were recorded byAgilent instru-
ment. Starting materials were received from commercial sources
and treated as such for reactions.
2
SO bath
4
1
6
ºC for 20 min in the presence of H
3
PO (5 mmol). Reaction
4
Synthesis of compound 4 from compounds 1, 2 and 3
by one-pot reaction: Charged compounds 1 (5 mmol), 2 (5
mmol) and 3 (5 mmol) in glycerol (20 mL) and heated at 100
progress was monitored by TLC. After completion of the
reaction added water (50 mL) and stirred for 10-15 min to
separate out colourless solid from the reaction mixture which
was collected through filtration. The isolated solid was washed
with 10 mL water twice and dried at 50 ºC under above 650
mmHg vacuum for 10-12 h. The crude compound was purified
by recrystallization method using methanol as a solvent to get
the desired compound 6a.
ºC for 120-150 min in the presence of H
3
PO (5 mmol).
4
Reaction progress was monitored by TLC. After completion
of the reaction water (50 mL) was added and stirred for 10-15
min to separate out colourless solid from the reaction mixture,
which was collected by filtration. The isolated solid was washed
with water (10 mL) twice and dried at 50 ºC under above 650
mmHg vacuum for 10-12 h. The crude compound was purified
by recrystallization method using methanol as a solvent to get
the desired compound 4 (Scheme-I).
Synthesis of compound 4a by step-wise synthesis:
Charged compounds 6 (5 mmol) and 2a (5 mmol) in glycerol
(20 mL) and heated at 100 ºC for 120 min in the presence of
H
3
PO (5 mmol). Reaction progress was monitored by TLC.
4
Synthesis of compound 5a: Charged compounds 1 (5
mmol) and 2a (5 mmol) in glycerol (20 mL) and heated at
After completion of the reaction added water (50 mL) and
stirred for 10-15 min to separate out colourless solid from the
reaction mixture which was collected by filtration. The isolated
solid was washed with water (10 mL) twice and dried at 50º C
under above 650 mmHg vacuum for 10-12 h. The crude com-
pound was purified by recrystallization method using methanol
as a solvent to get the desired compound 4a.
1
00 ºC for 20 min in the presence of H
3
PO (5 mmol). Reaction
4
progress was monitored by TLC. After completion of the
reaction water (50 mL) was added and stirred for 10-15 min
to separate out colourless solid from the reaction mixture which
was collected by filtration. The isolated solid was washed with
Scheme-I: Synthesis of various 2-(1H-benzo[d]thiazole-2-yl)-N-phenylbenzamides (4a–l) in glycerol medium via one-pot synthesis

Vol. 32, No. 6 (2020)
One-Pot Three Component Synthesis of 2-(1H-Benzo[d]thiazole-2-yl)-N-Arylbenzamides 1345
-(1H-Benzo[d]thiazole-2-yl)-N-phenylbenzamide 2-(1H-Benzo[d]thiazole-2-yl)-N-(2-hydroxyphenyl)-
-1
2
(
3
(
9
1
1
4a):Yield 90%, m.p.: 217-219 ºC; IR (KBr, νmax, cm ): 3429-
benzamide (4h):Yield 90%, m.p.: 218-220 ºC; IR (KBr, νmax,
1
-1
050 (br, medium, -NH-), 1643 (s, strong, -CO-NH-); H NMR
cm ): 3455-3045 (br, medium, -NH-), 1645 (s, strong, -CO-
1
400 MHz, DMSO-d , TMS): δ 6.7-7.9 (m, 13H, aromatic-H),
6
NH-); H NMR (400 MHz, DMSO-d
aromatic-H), 8.30 (s, 1H, -OH), 9.8(s,1H,-NH-); C NMR (100
MHz, DMSO-d ): δ 116.6, 118.8, 119.6, 123.8, 127.0, 128.4,
128.8, 130.4, 131.4, 131.8, 134.5, 134.8, 151.1, 165.8; HRMS
6
, TMS):δ6.7-7.9 (m, 12H,
13
13
.7 (s, 1H, -NH-); C NMR (100 MHz, DMSO-d
18.8, 119.1, 123.3, 127.3, 128.1, 1128.5, 130.3, 131.5, 131.6,
34.4, 134.5, 151.9, 165.1; HRMS calcd. (found) for C20
6
): δ 116.4,
6
H
N O
14 2 2
+
+
[
M+H] : 331.0460 (331.0423).
-(1H-Benzo[d]thiazole-2-yl)-N-(4-chlorophenyl)-
benzamide (4b):Yield 89%, m.p.: 196-198 ºC; IR (KBr, νmax
cm ): 3455-3045 (br, medium, -NH-), 1648(s, strong, -CO-
, TMS): δ6.7-7.9 (m, 12H,
aromatic-H), 9.8 (s, 1H, -NH-); C NMR (100 MHz, DMSO-
calcd. (found) for C20
2-(1H-Benzo[d]thiazole-2-yl)-N-(4-nitrophenyl)-
benzamide (4i):Yield 88%, m.p.: 156-158 ºC; IR (KBr, νmax
H
14
N
2
O [M+H] : 347.4685 (347.4621).
3
2
,
,
-
1
-1
cm ): 3458-3042 (br, medium, -NH-), 1654 (s, strong, -CO-
1
1
NH-); H NMR (400 MHz, DMSO-d
6
NH-); H NMR (400 MHz, DMSO-d
6
, TMS): δ 6.7-7.9 (m, 12H,
aromatic-H), 9.8 (s,1H,-NH-); C NMR (100 MHz, DMSO-
): δ 116.4, 118.1, 119.4, 123.5, 127.6, 128.0, 128.2, 130.2,
131.6, 131.5, 134.2, 134.8, 151.4, 165.9; HRMS calcd. (found)
13
13
d
1
6
): δ 116.3, 118.6, 119.3, 123.4, 127.5, 128.3, 128.7, 130.2,
31.6, 131.9, 134.1, 134.2, 151.3, 165.3; HRMS calcd. (found)
d
6
+
+
for C20
H
13
N O
2 2
Cl[M+H] : 365.3513 (365.3818).
-(1H-Benzo[d]thiazole-2-yl)-N-(4-methylphenyl)-
benzamide (4c):Yield 90%, m.p.: 204-205 ºC; IR (KBr, νmax
for C20
H
13
N O
3 4
[M+H] : 376.3526 (376.3562).
2-(1H-Benzo[d]thiazole-2-yl)-N-(3-nitrophenyl)-
benzamide (4j):Yield 89%, m.p.: 160-162 ºC; IR (KBr, νmax
2
,
,
-1
-1
cm ): 3458-3046 (br, medium, -NH-), 1642 (s, strong, -CO-NH-);
cm ): 3475-3042 (br, medium, -NH-), 1655 (s, strong, -CO-
1
1
H NMR (400 MHz, DMSO-d
.7-7.9 (m, 12H, aromatic-H), 9.8 (s, 1H, -NH-); C NMR (100
MHz, DMSO-d ):δ23.0, 116.1, 118.1, 119.1, 123.0, 127.1, 128.0,
28.3, 130.0, 131.8, 131.9, 134.5, 134.9, 151.1, 165.2; HRMS
6
, TMS): δ 2.3 (s, 3H, -CH
3
),
NH-); H NMR (400 MHz, DMSO-d
6
, TMS): δ6.7-7.9 (m, 12H,
aromatic-H), 9.8 (s, 1H, -NH-); C NMR (100 MHz, DMSO-
): δ 116.6, 118.6, 119.1, 123.8, 127.3, 128.1, 128.2, 130.3,
131.8, 131.9, 134.1, 134.3, 151.2, 165.4; HRMS calcd. (found)
13
13
6
6
d
6
1
+
+
calcd. (found) for C21
H
16
N O
2 2
[M+H] : 345.2887 (345.2843).
-(1H-Benzo[d]thiazole-2-yl)-N-(2-methylphenyl)-
benzamide (4d):Yield 88%, m.p.: 208-210 ºC; IR (KBr, νmax
cm ): 3451-3041 (br, medium, -NH-), 1649 (s, strong, -CO-
for C20
H
13
N O
3 4
[M+H] : 376.3516 (376.3563).
2-(1H-Benzo[d]thiazole-2-yl)-N-(2-chlorophenyl)-
benzamide (4k):Yield 88%, m.p.: 205-207 ºC; IR (KBr, νmax
2
,
,
-1
-1
cm ): 3452-3043 (br, medium, -NH-), 1649 (s, strong, -CO-
1
1
NH-); H NMR (400 MHz, DMSO-d
CH ), 6.7-7.9 (m, 12H, aromatic-H), 9.7 (s,1H,-NH-);
NMR(100 MHz, DMSO-d
6
, TMS): δ 2.2(s, 3H,
NH-); H NMR (400 MHz, DMSO-d
6
,TMS): δ6.7-7.9 (m, 12H,
aromatic-H), 9.8 (s, 1H, -NH-); C NMR (100 MHz, DMSO-
): δ 116.0, 118.9, 119.1, 123.2, 127.3, 128.3, 128.6, 130.0,
131.3, 131.5, 134.3, 134.6, 151.0, 165.1; HRMS calcd. (found)
13
13
-
3
C
6
): δ 22.3, 116.4, 118.6, 119.1,
d
6
1
1
3
23.0, 127.0, 128.6, 128.9, 130.3, 131.5, 131.9, 134.2, 134.4,
+
+
51.2, 165.4; HRMS calcd. (fond) for C21
45.2897 (345.2844).
H
16
N
2
O
2
[M+H] :
for C20
H
13
N O
2 2
Cl [M+H] : 349.2610 (349.2644).
2-(1H-Benzo[d]thiazole-2-yl)-N-(4-fluorophenyl)-
benzamide (4l):Yield 86%, m.p.: 156-158 ºC; IR (KBr, νmax
2
-(1H-Benzo[d]thiazole-2-yl)-N-(4-bromophenyl)-
benzamide (4e): Yield 86%, m.p.: 205-207 ºC; IR (KBr, νmax
cm ): 3459-3040 (br, medium, -NH-), 1650 (s, strong, -CO-NH-);
H NMR (400 MHz, DMSO-d , TMS): δ 6.7-7.9 (m, 12H,
aromatic-H), 9.8 (s, 1H, -NH-); C NMR (100 MHz, DMSO-
): δ 116.2, 118.1, 119.9, 123.8, 127.8, 128.3, 128.7, 130.2,
31.4, 131.9, 134.1, 134.0, 151.3, 165.8; HRMS calcd. (found)
Br [M+H] : 408.3774 (408.3727).
-(1H-Benzo[d]thiazole-2-yl)-N-(4-iodophenyl)-
benzamide (4f): Yield 85%, m.p.: 210-212 ºC; IR (KBr, νmax
cm ): 3420-3030 ( br, medium, -NH-), 1652 (s, strong, -CO-NH-);
H NMR (400 MHz, DMSO-d , TMS): δ 6.7-7.9 (m, 12H,
aromatic-H), 9.8 (s,1H, -NH-); C NMR (100 MHz, DMSO-
,
-1
,
cm ): 3456-3048 (br, medium, -NH-), 1643 (s, strong, -CO-
-1
1
NH-); H NMR (400 MHz, DMSO-d
6
,TMS):δ6.7-7.9 (m, 12H,
aromatic-H), 9.8 (s, 1H, -NH-); C NMR (100 MHz, DMSO-
): δ 116.3, 118.0, 119.4, 123.1, 127.5, 128.3, 128.5, 130.1,
131.4, 131.6, 134.2, 134.9, 151.1, 165.3; HRMS calcd. (found)
1
13
6
13
d
6
d
1
6
+
for C20
H
13
N
2
O F [M+H] : 333.3625 (333.3649).
2
+
for C20
H
13
N O
2 2
Computational studies: The Schrodinger molecular model-
ling suite was employed to carry out the molecular docking
protocols.
Ligand background: The binding affinity plays a crucial
role to determine the biological activity between the receptor
and inhibitor. It was influenced by the geometrical positions,
steric and the physical properties. The small molecule was
synthesized in a laboratory. It was redrawn usingACD/Chem-
sketch ver 12.0 and was geometrically optimized and converted
into 3D format.
Preparation methodologies:A small molecule was similar
to ciproflaxcin. Hence, the PDBID:3G7B was extracted from
Protein Data Bank (www.rcsb.org). Later, the protein molecule
was prepared using Protein preparation wizard, Schrodinger.
The molecule was optimized, and it was minimized with the
OPLS-2005 force field.
2
,
-1
1
6
13
d
1
C
6
): δ116.8, 118.8, 119.2, 123.1, 127.3, 128.4, 128.7, 130.1, 131.4,
31.9, 134.8, 134.9, 151.4, 165.5; HRMS calcd. (found) for
+
20
H
2
13
N O
2 2
I [M+H] : 456.2781 (456.2735).
-(1H-Benzo[d]thiazole-2-yl)-N-(4-methoxyphenyl)-
benzamide (4g):Yield 90%, m.p.: 162-164 ºC; IR (KBr, νmax
,
-1
cm ): 3040-3463 (br, medium, -NH-), 1655 (s, strong, -CO-NH-);
1
H NMR (400 MHz, DMSO-d
.7-7.9 (m, 12H, aromatic-H), 9.8 (s, 1H, -NH-); C NMR
): δ56.5, 116.1, 118.3, 119.4, 123.5, 127.1,
28.2, 128.6, 130.7, 131.1, 131.2, 134.4, 134.6, 151.9, 165.1;
6
, TMS): δ 3.7 (s, 3H, -OCH
3
)
1
3
6
(
1
100 MHz, DMSO-d
6
+
HRMS calcd. (found) for C21
361.2826).
H
16
N
2
O
3
[M+H] : 361.2852
Docking methodologies: The molecular docking was per-
formed using GLIDE, Schrödinger with the vdW scaling of
(

1
346 Thumula et al.
Asian J. Chem.
0
.8 and partial cut-off of 0.15 to soften the potential for non-
at different temperatures in the presence of H
3
PO (1 eq.).
4
polar sites and implemented without the constraints. The
docking was performed using GLIDE-SP. An attention paid
to obtain the better GLIDE energy and Interactions to favour
the outcome.
Table-1 shows that at room temperature no product is obtained
(entry 1, 8, 10 & 14). However at higher temperature, required
compound 4a was obtained in moderate to good yield (65-
90%) under different solvent medium. Higher yield was obtained
while performing the reaction at 100 ºC (entry 3). While there
was an increase in the reaction temperature, decrement in yield
was observed (entry 4). On contrary, there was no product
formation when the reaction temperature was performed at
room temperature (entry 1, 8, 10 & 14). A number of solvents
such as polar protic and polar aprotic solvents were screened
and found that the maximum yield was obtained with glycerol
(entry 2). Exploration of various acids such as acetic acid,
RESULTS AND DISCUSSION
The feasibility of three component reaction between diethyl
phthalate (1), aniline (2a) and 2-aminobenzene thiol (3) was
examined with H
3
PO
4
in glycerol. Initially with H
3
PO (0.5
4
equiv.) at 100 ºC afforded 2-(1H-benzo[d]thiazole-2-yl)-N-
phenylbenzamide (4a) with 75% yield. The structure and
chemical composition of 2-(1H-benzo[d]thiazole-2-yl)-N-
phenylbenzamide (4a) was confirmed by spectroscopic and
analytical techniques.
2
H SO
4
and H
3
PO were studied and found that the phosphoric
4
acid is the optimum choice (entry 3, 6 and 7) for this reaction.
Having optimized three component reaction condition in
hand, the scope and limitations with a series of substituted
The reaction was further optimized with different solvents
such as glycerol, PEG-600, ethylene glycol, DMF and DMSO
TABLE-1
OPTIMIZATION OF REACTION CONDITIONS
Entry
Solvent
Glycerol
Glycerol
Glycerol
Glycerol
Glycerol
Glycerol
Glycerol
PEG-600
PEG-600
Ethylene glycol
Ethylene glycol
DMF
Temperature (°C)
Catalyst
Reaction time (h)
Yield (%)
1
2
3
4
5
6
7
8
9
RT
100
100
150
100
100
100
RT
100
RT
100
RT
1 eq. of H PO
5
3
2
2
1.5
2
3
5
2.5
5
2.5
5
–
3
4
0.5 eq of H PO
75
90
80
80
75
84
–
80
–
75
20
65
–
3
4
1 eq. of H PO
3
4
1 eq. of H PO
3
4
2 eq of H PO
3
4
1 eq of H SO
2
4
1 eq of AcOH
1 eq. of H
3
PO
4
1 eq. of H PO
3
4
1
1
0
1
1 eq. of H PO
3
4
1 eq. of H PO
3
4
1
1
1
1
2
3
4
5
1 eq. of H PO
3
4
DMF
DMSO
DMSO
100
RT
100
1 eq. of H PO
1.5
5
2.5
3
4
1 eq. of H PO
3
4
1 eq. of H PO
63
3
4
TABLE-2
LIST OF VARIOUS BENZOTHIAZOLE DERIVATIVES OBTAINED BY THE
ONE-POT THREE COMPONENT REACTION AND THEIR YIELDS
S. No.
1
Reactant 1
Reactant 2
Reactant 3
Product 4
Yield (%)
90
O
O
NH2
H N
2
N
H
N
OEt
OEt
HS
S
O
O
Cl
NH2
O
H N
2
N
H
N
OEt
OEt
2
3
89
90
HS
S
O
O
Cl
CH3
NH2
O
H N
2
N
H
N
OEt
OEt
HS
S
O
CH3

Vol. 32, No. 6 (2020)
One-Pot Three Component Synthesis of 2-(1H-Benzo[d]thiazole-2-yl)-N-Arylbenzamides 1347
O
O
NH2
H N
2
N
H
N
OEt
OEt
CH3
4
CH3
88
86
HS
S
O
O
Br
NH2
O
S
H N
2
N
OEt
OEt
H
5
6
N
HS
O
O
Br
I
NH2
O
S
H N
2
N
OEt
OEt
H
85
90
90
N
HS
O
O
I
OCH3
NH2
O
S
H N
2
N
OEt
OEt
H
7
8
9
N
HS
O
O
OCH3
NH2
OH
O
H N
2
N
OEt
OEt
H
N
HS
S
O
O
OH
NO2
NH2
O
H N
2
N
H
OEt
OEt
88
89
88
N
HS
S
O
O
NO2
O
NH2
H N
2
N
H
NO2
OEt
OEt
1
0
1
N
HS
S
NO2
O
O
O
S
NH2
H N
2
N
H
N
OEt
OEt
Cl
1
Cl
HS
O
O
F
NH2
O
H N
2
N
OEt
OEt
H
12
86
N
HS
S
O
F

1
348 Thumula et al.
Asian J. Chem.
anilines 2a-l was explored. Therefore, synthesis of compounds
a-l was carried out by using diethyl phthalate (1), different
substituted anilines (2a-l) and 2-aminobenzenethiol (3) in
glycerol at 100 ºC in the presence of 1 eq. H PO for 120 min
Table-2). It was found that both electron-deficient and electron-
rich anilines were applicable for this optimized condition and
afforded the corresponding benzothiazole derivatives in good
yield (85-90%).
2-aminobenezenthiol (3) to form the compound such as 2-(2-
mercaptophenyl)-isoindoline-1,3-dione (6a) as an intermediate
compound. The 2-(2-mercaptophenyl)-isoindoline-1,3-dione
(6a) was further reacted with aniline (2) to form a desired benzo-
thiazole derivative (4) as a major product. To confirm the above
stated mechanism in Scheme-III, an intermediate compound
6a was isolated in good yield separately by the reaction between
diethyl phthalate (1) and 2-aminobenzenethiol (3) in the presence
4
3
4
(
The plausible mechanism for the formation of benzothia-
zole derivatives (4a-l) from the reactants 1, 2a-l and 3 by one-
pot three component reaction is presented in Scheme-II. As
shown, diethyl phthalate (1) first reacted with aniline (2) in
of H
3
PO in glycerol medium. The obtained compound 6a was
4
then further treated with aniline (2) under the similar reaction
conditions to afford the desired compound 4 in a stepwise
method.
the presence of H
mediate compound 2-phenylisoindoline-1,3-dione (5a) and
ethanol was eliminated as byproduct. The further reaction of
3
PO
4
in glycerol medium to afford the inter-
Biological activity: The benzothiazole compound (4a)
was screened for their in vitro antibacterial and antifungal activity
against pathogenic bacterial species (Staphylococcus aureus,
Streptococcus pneumoniae, Pseudomonas aeruginosa, Acineto-
bacter baumannii) and pathogenic fungal species (Candida
albicans, Trichophyton rubrum, Aspergillus niger, Aspergillus
fumigatus, Candida tropicalis) at three different concentrations
using standard disc diffusion method described elsewhere [29].
The antibacterial and antifungal activity of compound 4a was
determined using sterile 2 µL 96-well plates [30]. The screening
solution of compound 4a was prepared in 10% aqueous DMSO
and the results of the antibacterial and antifungal activities
were expressed in terms of zone of inhibition and minimum
inhibitory concentration (MIC). From these results (Tables 3
and 4), it is concluded that the newly synthesized benzothiazole
compound 4a has a significant antibacterial and antifungal
action but they did not match the effectiveness of conventional
bactericide gentamicin and fungicide ketoconazole.
2-phenylisoindoline-1,3-dione (5a) with 2-aminobenezenthiol
(
3) in the presence of H PO and glycerol by simple conden-
3
4
sation and cyclization mechanism produces the desired comp-
ound 4 as major product via the formation (5b) as an inter-
mediate compound. To confirm the above stated mechanism
in Scheme-II, an intermediate compound (5a) was isolated in
good yield separately by the reaction between diethyl phthalate
(1) and aniline (2) in the presence of H
3
PO in glycerol medium.
4
The obtained compound (5a) was then further treated with 2-
aminobenzenethiol (3) under the similar reaction conditions
to afford the desired compound 4 in a step-wise synthetic
method.
However, the selective formation of desired benzothiazole
derivatives (4a-l) from the reactants 1, 2a-l and 3 could also
be possible through one-pot three component reaction via an
alternative mechanism as shown in Scheme-III.According to
alternative approach, diethyl phthalate (1) initially reacts with
in vitro Cytotoxicity activity of benzothiazole derivative
(4a): All cancer cell lines used in this study were procured
Scheme-II: Plausible mechanism of one-pot three reaction of 1, 2 and 3 to obtain benzothiazole compound (4)

Vol. 32, No. 6 (2020)
One-Pot Three Component Synthesis of 2-(1H-Benzo[d]thiazole-2-yl)-N-Arylbenzamides 1349
Scheme-III: Plausible mechanism of one-pot three reaction of 1, 3 and 2 to obtain benzothiazole compound (4)
TABLE-3
a
ANTIBACTERIAL AND ANTIFUNGAL ACTIVITY OF BENZOTHIAZOLE COMPOUND (4a)
Zone of inhibition (mm)
Microbial pathogen
S, 10 µg
25 µg
50 µg
100 µg
Staphylococcus aureus
Streptococcus pneumoniae
Pseudomonas aeruginosa
Acinetobacter baumannii
Candida albicans
Trichophyton rubrum
Aspergillus niger
Aspergillus fumigatus
21.02 ± 0.11
20.29 ± 0.55
20.22 ± 0.54
20.87 ± 0.59
21.43 ± 0.52
20.39 ± 0.93
20.21 ± 0.33
20.24 ± 0.14
20.39 ± 0.43
12.12 ± 0.15
08.14 ± 0.36
06.01 ± 0.41
11.41 ± 0.23
11.22 ± 0.98
08.44 ± 0.36
07.52 ± 0.85
07.53 ± 0.96
06.97 ± 0.81
16.11 ± 0.43
12.16 ± 0.25
14.41 ± 0.32
15.78 ± 0.34
15.55 ± 0.23
15.13 ± 0.35
13.44 ± 0.65
14.34 ± 0.35
14.24 ± 0.32
21.54 ± 0.55
18.11 ± 0.21
20.51 ± 0.23
21.17 ± 0.24
21.08 ± 0.03
19.11 ± 0.42
18.61 ± 0.61
18.67 ± 0.56
19.33 ± 0.12
Candida tropicalis
a
Gentamicin for bacterial strains and Ketoconazole for fungal strains was used as positive controls.
TABLE-4
ANTIBACTERIAL AND ANTIFUNGAL ACTIVITY OF BENZOTHIAZOLE COMPOUND (4a)
Microbial pathogen
Staphylococcus aureus
Streptococcus pneumoniae
Pseudomonas aeruginosa
MIC
06.34
13.56
10.32
Microbial pathogen
Acinetobacter baumannii
Candida albicans
MIC
08.25
09.14
14.05
Microbial pathogen
Aspergillus niger
Aspergillus fumigatus
Candida tropicalis
MIC
13.26
13.89
10.65
Trichophyton rubrum
from NCCS, Pune, India and maintained with their selective
medium (HiMedia, India). To ensure growth and viability of
the cells, the mediums were supplemented with 10% FBS
Absorbance was recorded at 595 nm and sensitivity to cisplatin
and the compounds were calculated based on cell proliferation
measurements at 24 h. Compound 4a was evaluated for their
cytotoxicity with three human derived cell lines namely human
cervical carcinoma (HeLa), human lung carcinoma (A549) and
human breast cancer cells (MCF-7) by using standard MTT
assay. For comparison purpose, the commercially available
drug, cisplatin was used as a positive control. The dose depen-
dent response of compound 4a against the various cancer cells
tested is represented in Fig. 1. Furthermore, the IC50 values
for the complex for MCF-7, HeLa and A549 showed that the
(
HiMedia, India) and incubated in a humidified atmosphere
with 5% CO at 37 ºC.
2
MTT assay: All the cells were seeded in 96-well plates
and allowed to adhere overnight at 37 ºC. Briefly, following
treatment of cells with cisplatin and all the other compounds
for 24 h, MTT reagent [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-
tetrazolium bromide] was added to each well and incubated
for 4 h at 37 ºC. Dimethyl sulphoxide was used as control.

1
350 Thumula et al.
Asian J. Chem.
HaCaT
1
00
100
50
0
A549
Test drug
Cisplatin
Test drug
5
0
0
100
MCF 7
100
Cisplatin
Test drug
HeLa
50
Cisplatin
Test drug
50
0
0
Fig. 1. in vitro Cytotoxicity activity of compound 4a and standard drug (i.e., cisplatin)
4
4
a compound was cytotoxic to these cells (Fig. 2). Compound
a was also screened for their cytotoxic potential on the human
crystal structure of 3G7B. The hydrogen bonding interactions
have been observed from the in-sights of the conformation.
The complex results of docking score shows -6.6 kcal/mol
and hydrogen bonding withAsn54 andAsp81 with the distance
of 1.9 Å, respectively (Table-5). Therefore, the residues are
considered as an active-sites to proceed further. The docking
was performed with ciprofloaxcin and observed the interaction
with Asp81 and Ser129 with the distance ~2.0 Å. The test
molecule was docked with the reference molecules. The test
molecule shows the interaction with Thr173 and Asn54 with
the distance of 1.9 and 2.4 Å, respectively, and the docking
score has observed to be -8.6 kcal/mol. The test molecule clearly
shows as more stable among the earlier molecules with respect
to the docking score and strong hydrogen bonding of O–H···O
normal keratinocyte cells (HaCaT), in order to investigate the
selectivity of the compound. In the non-cancerous cell line,
compound 4a showed its non-toxic nature.
1.5
1.0
0.5
0
Cisplatin
Test drug
(
Fig. 3).
Conclusion
A facile and diverse one-pot three component method is
A549
MCF7
HeLA
Fig. 2. IC50 values of compound 4a and cisplatin onA549, MCF7 and HeLA
cell lines
developed for the synthesis of benzothiazole derivatives by
using low-cost and conveniently available starting materials
in glycerol medium. The one-pot reaction takes short time and
easy work up. Compound 4a was obtained with good yield
while performing the reaction at 100 ºC in the presence of
H PO in glycerol medium. The dose dependent response of
Molecular docking analysis: The molecular docking was
carried out to identify the mechanism of action of small mole-
cule with protein. The study aimed to identify the significance
of the synthesized small molecule against anti-bacterial target.
The molecular docking has initiated with reproducing the
3
4
compound 4a against the various cancer cells have shown the
TABLE-5
MOLECULAR DOCKING RESULTS
Complex
G7B_X-ray_structure
G7B_reproduced crystal structure
G7B_test_molecule
Interactions
Docking score (Kcal/mol)
3
3
3
3
N54 (N–H···O) 1.87 Å; D81 (O···H–N) 1.9
N54 (N–H···O) 1.9 Å; D81 (O···H–N) 1.9
T173 (O–H···O) 1.9; N54 (O···H–N) 2.4
–
-6.6
-8.6
-6.9
G7B_ciproflaxcin
D81 (N–H···O) 2.3; D81 (N–H···O) 2.1; S129 (O–H···O) 1.8

Vol. 32, No. 6 (2020)
One-Pot Three Component Synthesis of 2-(1H-Benzo[d]thiazole-2-yl)-N-Arylbenzamides 1351
1
0. J. Chen, S.K. Spear, J.G. Huddleston and R.D. Rogers, Green Chem.,
, 64 (2005);
7
https://doi.org/10.1039/b413546f
Thr173
1
1
1. J. Francos and V. Cadierno, Green Chem., 12, 1552 (2010);
https://doi.org/10.1039/c0gc00169d
2. A.A. Hamid M. Abd-Elmonem, A.M. Hayallah F.A. Abo Elsoud and
K.U. Sadek, ChemistrySelect, 2, 10689 (2017);
https://doi.org/10.1002/slct.201702011
Ser129
13. C. Beaulieu, Z. Wang, D. Denis, G. Greig, S. Lamontagne, G. O’Neill,
D. Slipetz and J. Wang, Bioorg. Med. Chem. Lett., 14, 3195 (2004);
https://doi.org/10.1016/j.bmcl.2004.04.005
1
1
1
1
4. N. Siddiqui, S. Pandeya, S. Khan, J. Stables, A. Rana, M. Alam, M.
Arshad and M. Bhat, Bioorg. Med. Chem. Lett., 17, 255 (2007);
https://doi.org/10.1016/j.bmcl.2006.09.053
5. N. Siddiqui, A. Rana, S. Khan, M. Bhat and S. Haque, Bioorg. Med.
Chem. Lett., 17, 4178 (2007);
https://doi.org/10.1016/j.bmcl.2007.05.048
6. M. Subramanyam, R. Sreenivasulu, R. Gundla, M.V.B. Rao and K.P.
Rao, Lett. Drug Des. Discov., 15, 1299 (2018);
Asp81
Asn54
3
G7B – TEST MOLECULE
Fig. 3. Binding interactions of benzothiazole compound 4a with protein
molecule having non-covalent interactions with Asp81, Asn54,
Ser129 and Thr173
https://doi.org/10.2174/1570180815666180219165119
7. B. Srinivas, J. Suryachandram, Y.K. Devi and K.P. Rao, J. Heterocycl.
Chem., 54, 3730 (2017);
good results compared with standard drug. The results of mole-
cular docking for compound 4a have observed with a docking
score of -8.6 kcal/mol and the strong hydrogen bonding with
the Asn54 and Thr173 in the binding site.
https://doi.org/10.1002/jhet.2960
18. A. Ben-Alloum, S. Bakkas and M. Soufiaoui, Tetrahedron Lett., 38,
6395 (1997);
https://doi.org/10.1016/S0040-4039(97)01490-1
9. B.S. Londhe, U.R. Pratap, J.R. Mali and R.A. Mane, Bull. Korean Chem.
Soc., 31, 2329 (2010);
1
CONFLICT OF INTEREST
https://doi.org/10.5012/bkcs.2010.31.8.2329
2
2
0. J.M. Sprague and A.H. Land, ed.: R.C. Elderfield, Heterocyclic
Compounds, Wiley: New York, 5, 484-722 (1957).
1. A.D. Jordan, C. Luo and A.B. Reitz, J. Org. Chem., 68, 8693 (2003);
https://doi.org/10.1021/jo0349431
The authors declare that there is no conflict of interests
regarding the publication of this article.
REFERENCES
22. H.F. Motiwala, R. Kumar and A.K. Chakraborti, Aust. J. Chem., 60, 369
2007);
(
1
2
3
4
5
6
.
.
.
.
.
.
C.-J. Li and B.M. Trost, Proc. Natl. Acad. Sci. USA, 105, 13197 (2008);
https://doi.org/10.1073/pnas.0804348105
U.K. Lindström, Chem. Rev., 102, 2751 (2002);
https://doi.org/10.1021/cr010122p
C.J. Li, Chem. Rev., 105, 3095 (2005);
https://doi.org/10.1021/cr030009u
J.N. Tan, H. Li and Y. Gu, Green Chem., 12, 1772 (2010);
https://doi.org/10.1039/c0gc00274g
C. Capello, U. Fischer and K. Hungerbühler, Green Chem., 9, 927 (2007);
https://doi.org/10.1039/b617536h
https://doi.org/10.1071/CH06391
2
3. L.-X. Xiao, K. Li and D.-Q. Shi, Phosphorus Sulfur Silicon Rel. Elem.,
1
83, 3156 (2008);
https://doi.org/10.1080/10426500802070270
2
2
4. Q. Shen, T. Ogata and J.F. Hartwig, J. Am. Chem. Soc., 130, 6586 (2008);
https://doi.org/10.1021/ja077074w
5. J.J. Yin, M.M. Zhao, M.A. Huffman and J.M. McNamara, Org. Lett., 4,
3481 (2002);
https://doi.org/10.1021/ol0265923
2
2
2
6. D. Fajkusova and P. Pazdera, Synthesis, 1297 (2008);
https://doi.org/10.1055/s-2008-1067008
7. G. Shen, X. Lv and W. Bao, Eur. J. Org. Chem., 33, 5897 (2009);
https://doi.org/10.1002/ejoc.200900953
Y.D. Reddy, C.V. Ramana Reddy and P.K. Dubey, RSC Adv., 4, 2974
(
2014);
https://doi.org/10.1039/C3RA44423F
7
8
.
.
R. Ratnam, J. Sci. Ind. Res. B, 21, 45 (1962).
C.J. Li and L. Chen, Chem. Soc. Rev., 35, 68 (2006);
https://doi.org/10.1039/B507207G
H.R. Safaei, M. Shekouhy, S. Rahmanpur and A. Shirinfeshan, Green
Chem., 14, 1696 (2012);
8. Y.J. Guo, R.Y. Tang, P. Zhong and J.H. Li, Tetrahedron Lett., 51, 649
(
2010);
https://doi.org/10.1016/j.tetlet.2009.11.086
9
.
2
3
9. C.H. Collins, P.M. Lyne and J.M. Grange, Microbiological Methods,
Butterworths & Co. Ltd.: London, p. 543 (1987).
0. I. Wiegand, K. Hilpert and R.E. Hancock, Nat. Protoc., 3, 163 (2008);
https://doi.org/10.1038/nprot.2007.521
https://doi.org/10.1039/c2gc35135h