Synthesis and biological evaluation of new 2-aryl-4-((4-aryl-1H-1,2,3-triazol-1-yl)methyl)thiazole derivatives

Article abstract of DOI:10.1007/s11164-017-3164-4

A series of 2-aryl-4-((4-aryl-1H-1,2,3-triazol-1-yl)methyl)thiazole derivatives (8a–p) have been synthesized. The structure of the newly synthesized compounds was determined by spectral analysis. The title compounds were screened for their preliminary ant

Full text of DOI:10.1007/s11164-017-3164-4

Res Chem Intermed
DOI 10.1007/s11164-017-3164-4
Synthesis and biological evaluation of new 2-aryl-4-((4-
aryl-1H-1,2,3-triazol-1-yl)methyl)thiazole derivatives
1
1
2
•
Vikas Shinde
Laxman Nawale
•
Pramod Mahulikar
3
•
Pravin C. Mhaske
3
•
Dhiman Sarkar
Received: 17 June 2017 / Accepted: 4 October 2017
Ó Springer Science+Business Media B.V. 2017
Abstract A series of 2-aryl-4-((4-aryl-1H-1,2,3-triazol-1-yl)methyl)thiazole
derivatives (8a–p) have been synthesized. The structure of the newly synthesized
compounds was determined by spectral analysis. The title compounds were
screened for their preliminary antitubercular activity against Mycobacterium
tuberculosis H37Ra (MTB, ATCC 25177) and Mycobacterium bovis BCG (BCG,
ATCC 35743). Further, the synthesized compounds were screened for antimicrobial
activity against standard Gram-negative bacteria Escherichia coli (NCIM 2576) and
Pseudomonas flurescence (NCIM 2059) and Gram-positive bacteria Staphylococcus
aureus (NCIM 2602) and Bacillus subtilis (NCIM 2162). Among all the synthesized
compounds, 8a–c, f–h, m exhibited good activity against dormant M. bovis BCG
strain. Compounds 8h, j exhibited good activity against all tested bacterial strains.
All active compounds were screened for cytotoxicity and found inactive. Their high
potency and promising antimycobacterial activity suggest that these compounds
could serve as good leads for further optimization and development.
Keywords 1,2,3-Triazole Á Thiazole Á Antitubercular activity Á Antibacterial
activity
Electronic supplementary material The online version of this article (doi:10.1007/s11164-017-3164-
4) contains supplementary material, which is available to authorized users.
&
&
Pramod Mahulikar
mahulikarpp@rediffmail.com
Pravin C. Mhaske
mhaskepc18@gmail.com
1
2
School of Chemical Sciences, North Maharashtra University, Jalgaon, India
Post Graduate Department of Chemistry, S. P. Mandali’s Sir Parashurambhau College
(Affiliated to Savitribai Phule Pune University), Tilak Road, Pune 411 030, India
3
CombiChemBio Resource Centre, CSIR-National Chemical Laboratory, Pune 411 008, India
123

V. Shinde et al.
Introduction
Mycobacterium tuberculosis (MTB) is among the most challenging bacterial
infections. TB was one of the top 10 causes of death worldwide in 2015, responsible
for more deaths than human immunodeficiency virus (HIV) and malaria [1]. In
addition, M. bovis BCG is among the most commonly administered vaccines
worldwide [2]. Due to emerging infectious diseases and the increasing number of
multidrug-resistant microbial pathogens in recent decades, new classes of antimi-
crobial agents are required. The increase in antibiotic resistance due to multiple
factors has encouraged the search for new compounds which are active against
multidrug-resistant pathogens.
Synthesis of motifs containing more than one heterocycle ring has received much
attention in recent years. Triazole and its derivatives are an important class of
bioactive molecules, exhibiting significant pharmacological activities including
antimicrobial [3, 4], antiinflammatory, anesthetic [5], antineoplastic [6], anticon-
vulsant [7], antiproliferative [8], anticancer [9], antimalarial [10], and antiviral
activity [11]. Also, they show phosphodiesterase enzyme inhibition [12], anti-
hepatitis C [13], b-lactamase inhibition [14], fungicidal [15], insecticidal [16], and
plant growth inhibition [17] activity, as well as many more. Among heterocyclic
derivatives, triazole compounds were reported to be the most promising candidates
towards anti-TB activity [18–33].
Thiazole and its derivatives are important structures in medicinal chemistry that
could provide a rich spectrum of biological activities [34–59]. The structural
diversity and biological importance of triazole and thiazoles have made them
attractive targets for synthesis. 1,2,3-Triazole and thiazole rings present in the same
molecule could represent a convenient model for investigation of their biological
activity. Bearing in mind the biological significance of triazole and thiazole
derivatives and in continuation of our study on synthesis and biological evaluation
of various compounds [58, 59], we report herein synthesis of 2-aryl-4-((4-aryl-1H-
1,2,3-triazol-1-yl)methyl)thiazole derivatives 8a–p as potential antimycobacterial
agents.
Experimental
All reactions were monitored and the purity of products checked by thin-layer
chromatography (TLC) on Merck 60 F-254 silica gel plates with visualization by
ultraviolet (UV) light. Melting points were determined in capillary tubes in silicone
1
13
oil bath using a Veego melting point apparatus and are uncorrected. H and
C
nuclear magnetic resonance (NMR) spectra were recorded on Bruker Avance II 500
NMR spectrometer (Bruker Instruments Inc., Billerica, MA, USA) at either
1
00 MHz ( H NMR) or 126 MHz ( C NMR). Chemical shifts are reported from
13
5
internal tetramethylsilane standard and are given in d units. Column chromatog-
raphy was performed on silica gel (100–200 mesh) supplied by Acme Chemical Co.
(
Mumbai, Maharashtra, India). Starting (2-arylthiazol-4-yl)methanol compounds
1
23

Synthesis and biological evaluation of new 2-aryl-4-((4-…
3a–d were synthesized by known literature method [56]. Chemicals and solvents
used were of laboratory grade and purified as per literature methods.
Synthesis of (2-phenylthiazol-4-yl)methyl methanesulfonate (5a)
To a mixture of (2-phenylthiazol-4-yl)methanol (3a, 2 g, 0.01 mol), triethylamine
(
2.02 mL, 0.02 mol) in dichloromethane (DCM, 20 mL) at 0 °C, and methanesul-
fonyl chloride (1.71 g, 0.015 mol) was added dropwise at 0 °C and the reaction
mixture stirred for 3 h. After completion of reaction (TLC), the mixture was
extracted with water. Organic layer was dried over sodium sulfate and evaporated
on rotary evaporator to obtain (2-phenylthiazol-4-yl)methyl methanesulfonate (5a)
as thick oil in yield of 2.42 g (90 %).
Synthesis of 4-(azidomethyl)-2-phenylthiazole (6a)
A mixture of (2-phenylthiazol-4-yl)methyl methanesulfonate (5a, 2.0 g, 0.007 mol)
and sodium azide (0.58 g, 0.009 mol) in dimethyl sulfoxide (DMSO) was stirred for
3
h at 70 °C. After completion of reaction (TLC), the mixture was quenched in
water and the product extracted by ethyl acetate (3 9 25 mL); organic layer was
dried over sodium sulfate and evaporated under vacuum to give 4-(azidomethyl)-2-
phenylthiazole (6a) as thick oil in yield of 1.3 g (86 %).
General procedure for synthesis of 2-phenyl-4-((4-phenyl-1H-1,2,3-triazol-
1
-yl)methyl)thiazole (8a)
A reaction mixture of 4-(azidomethyl)-2-phenylthiazole (6a, 0.2 g, 0.0009 mol),
ethynylbenzene (0.094 g, 0.0009 mol), copper sulfate (0.035 g, 0.00022 mol), and
sodium ascorbate (0.045 g, 0.00022 mol) in dimethylformamide (DMF):water
(
6 mL, 3:1) was stirred overnight. After completion of reaction (TLC), the reaction
mixture was quenched in water and extracted by ethyl acetate (3 9 15 mL).
Organic layer was dried over sodium sulfate and evaporated on rotary evaporator.
The crude product was purified by column chromatography (ethyl acetate:hexane)
to furnish target compound 2-phenyl-4-((4-phenyl-1H-1,2,3-triazol-1-yl)methyl)thi-
azole (8a). Compounds 8b–p were synthesized by similar procedure.
2
-Phenyl-4-((4-phenyl-1H-1,2,3-triazol-1-yl)methyl)thiazole (8a) Yield: 70 %;
1
m.p.: 138 °C; H NMR (500 MHz, CDCl ): d ppm = 5.76 (s, 2H), 7.25 (s, 1H),
7
3
H
.37–7.43 (m, 3H), 7.45–7.51 (m, 3H), 7.85–7.87 (m, 2H), 7.99–7.93 (m, 2H), 8.02
1
3
(
s, 1H); C NMR (126 MHz, CDCl ): d ppm = 50.0, 117.7, 120.1, 125.8, 126.6,
3
C
1
28.2, 128.8, 129.1, 130.5, 130.6, 133.1, 148.1, 150.6, 169.5; HRMS: 319.1021
?
M ? H) , 341.0840 (M ? Na) .
?
(
4
-((4-(4-Fluorophenyl)-1H-1,2,3-triazol-1-yl)methyl)-2-phenylthiazole (8b) Yield: 76 %;
1
m.p.: 146 °C; H NMR (500 MHz, CDCl ): d ppm = 5.75 (s, 2H), 7.11 (t,
3
H
J = 8.7 Hz, 2H), 7.26 (s, 1H), 7.49–7.44 (m, 3H), 7.82 (dd, J = 8.8 and 3.3 Hz, 2H),
1
3
7
.97–7.92 (m, 2H), 7.98 (s, 1H); C NMR (126 MHz, CDCl ): d ppm = 50.0, 115.7,
3
C
123

V. Shinde et al.
1
1
15.9, 117.8, 119.9, 126.6, 126.8, 127.5, 127.5, 129.1, 130.6, 133.1, 147.3, 150.5,
?
61.7,163.7, 169.5; HRMS: 337.0930 (M ? H) , 359.0748 (M ? Na) .
?
4
-((4-(4-Methoxyphenyl)-1H-1,2,3-triazol-1-yl)methyl)-2-phenylthiazole (8c) Yield:
1
7
J = 0.5 Hz, 2H), 6.98–6.93 (m, 2H), 7.23 (s, 1H), 7.48–7.43 (m, 3H), 7.80–7.74 (m,
4 %; m.p.: 120 °C; H NMR (500 MHz, CDCl ): d ppm = 3.84 (s, 3H), 5.74 (d,
3
H
1
3
H), 7.93 (s, 1H), 7.95 (dd, J = 4.7 and 2.3 Hz, 2H); C NMR (126 MHz, CDCl3):
2
d ppm = 50.0, 55.3, 114.2, 117.6, 119.3, 123.3, 126.6, 127.1, 129.1, 130.5, 133.1,
C
?
48.0, 150.7, 159.6, 169.4; HRMS: 349.1124 (M ? H) , 371.0942 (M ? Na) .
?
1
4
-((4-(3,4-Dimethoxyphenyl)-1H-1,2,3-triazol-1-yl)methyl)-2-phenylthiazole (8d) Yield:
1
8
3
1
2
1
1
0 %; m.p.: 138 °C; H NMR (500 MHz, CDCl ): d ppm = 3.90 (s, 3H), 3.95 (s,
3
H
H), 5.74 (s, 2H), 6.90 (d, J = 8.3 Hz, 1H), 7.23 (s, 1H), 7.29 (dd, J = 8.1 and
.8 Hz, 1H), 7.44–7.46 (m, 3H), 7.50 (d, J = 1.8 Hz, 1H), 7.94 (dd, J = 6.8 and
1
3
.7 Hz, 3H); C NMR (126 MHz, CDCl ): dC ppm = 50.0, 56.0, 56.0, 109.0,
3
11.3, 117.6, 118.3, 119.5, 123.6, 126.6, 129.1, 130.5, 133.1, 148.0, 149.1, 149.3,
?
50.7, 169.4; HRMS: 379.1231 (M ? H) , 401.1050 (M ? Na) .
?
2
7
1
-(4-Bromophenyl)-4-((4-phenyl-1H-1,2,3-triazol-1-yl)methyl)thiazole (8e) Yield:
1
2 %; m.p.: 122 °C; H NMR (500 MHz, CDCl ): d ppm = 5.76 (s, 2H), 7.29 (s,
3
H
H), 7.35 (d, J = 7.6 Hz, 2H), 7.62 - 7.56 (m, 3H), 7.89–7.84 (m, 2H), 7.91 (d,
1
3
J = 7.9 Hz, 2H), 8.13 (s, 1H); C NMR (126 MHz, CDCl ): d ppm = 49.9,
3
C
1
18.3, 120.1, 125.2, 125.8, 128.0, 128.9, 129.4, 130.6, 132.3, 133.4, 148.2, 150.9,
?
67.6; HRMS: 397.0124 (M ? H) , 418.9942 (M ? Na) .
?
1
2
-(4-Bromophenyl)-4-((4-(4-fluorophenyl)-1H-1,2,3-triazol-1-yl)methyl)thiazole (8f)
1
Yield: 75 %; m.p.: 98 °C; H NMR (500 MHz, CDCl ): d ppm = 5.76 (s, 2H),
7
3
H
.12 (t, J = 8.6 Hz, 2H), 7.32 (s, 1H), 7.35 (d, J = 8.7 Hz, 2H), 7.75–7.78 (m, 2H),
1
3
7
ppm = 49.9, 115.8, 115.9, 118.4, 119.9, 125.2, 127.5, 127.6, 129.4, 130.6, 132.3,
.89 (d, J = 8.7 Hz, 2H), 8.13 (s, 6H); C NMR (126 MHz, CDCl ): d
3
C
?
33.4, 147.4, 150.8, 161.7, 163.7, 167.6; HRMS: 415.0030 (M ? H) , 436.9848
1
?
M ? Na) .
(
2
-(4-Bromophenyl)-4-((4-(4-methoxyphenyl)-1H-1,2,3-triazol-1-yl)methyl)thiazole (8g)
1
Yield: 80 %; m.p.: 98 °C; H NMR (500 MHz, CDCl ): d ppm = 3.84 (s, 3H),
3
H
5
.74 (s, 2H), 6.96 (d, J = 8.6 Hz, 2H), 7.27 (s, 1H), 7.33 (d, J = 7.9 Hz, 2H), 7.79
1
d, J = 7.9, Hz, 2H), 7.91 (d, J = 7.9 Hz, 2H), 8.12 (s, 1H); C NMR (126 MHz,
3
(
CDCl ): d ppm = 49.9, 55.3, 114.3, 118.2, 119.3, 123.2, 123.2, 125.2, 127.1,
3
C
?
29.4, 130.6, 133.3, 148.1, 151.0, 159.7, 167.5; HRMS: 427.0226 (M ? H) ,
1
?
49.0041 (M ? Na) .
4
2
6
2
-(4-Bromophenyl)-4-((4-(p-tolyl)-1H-1,2,3-triazol-1-yl)methyl)thiazole (8h) Yield:
1
8 %; m.p.: 110 °C; H NMR (500 MHz, CDCl ): d ppm = 2.84 (s, 3H), 5.74 (s,
3
H
H), 7.15 (d, J = 8.6 Hz, 2H), 7.24 (s, 1H), 7.35 (d, J = 8.1 Hz, 2H), 7.77 (d,
1
3
J = 8.6 Hz, 2H), 7.87 (d, J = 8.1 Hz, 2H), 7.92 (s, 1H); C NMR (126 MHz,
CDCl ): d ppm = 21.3, 49.9, 118.2, 119.7, 125.2, 125.7, 129.5, 130.6, 132.3,
3
C
?
33.3, 134.9, 138.1, 148.3, 151.0, 167.5; HRMS: 411.0269 (M ? H) , 433.0083
1
?
M ? Na) .
(
1
23

Synthesis and biological evaluation of new 2-aryl-4-((4-…
2
7
1
-(4-Chlorophenyl)-4-((4-phenyl-1H-1,2,3-triazol-1-yl)methyl)thiazole (8i) Yield:
1
2 %; m.p.: 138 °C; H NMR (500 MHz, CDCl ): d ppm = 5.75 (s, 2H), 7.26 (s,
3
H
H), 7.34 (d, J = 7.3 Hz, 2H), 7.42-7.44 (m, 3H), 7.85 (d, J = 8.0 Hz, 2H), 7.88 (d,
1
3
J = 7.3 Hz, 2H), 8.00 (s, 1H); C NMR (126 MHz, CDCl ): d ppm = 50.0,
3
C
1
17.9, 120.1, 125.8, 127.8, 128.2, 128.9, 129.3, 130.5, 131.6, 136.5, 148.2, 150.8,
?
68.1; HRMS: 353.0630 (M ? H) , 375.0448 (M ? Na) .
?
1
2
-(4-Chlorophenyl)-4-((4-(4-fluorophenyl)-1H-1,2,3-triazol-1-yl)methyl)thiazole (8j)
1
Yield: 66 %; m.p.: 120 °C; H NMR (500 MHz, CDCl ): d ppm = 5.73 (s, 2H),
7
3
H
.08 (t, J = 8.6 Hz, 2H), 7.25 (s, 1H), 7.34 (d, J = 8.7 Hz, 2H), 7.76–7.78 (m, 2H),
3
1
7
ppm = 50.0,115.7, 115.9, 118.0, 119.8, 126.8, 127.5, 127.5, 127.8, 129.3, 131.5,
.88 (d, J = 8.7 Hz, 2H), 7.91 (s, 1H); C NMR (126 MHz, CDCl ): d
3
C
?
36.6, 147.3, 150.7, 161.7, 163.7, 168.1; HRMS: 371.0534 (M ? H) , 393.0352
1
?
M ? Na) .
(
2
-(4-Chlorophenyl)-4-((4-(4-methoxyphenyl)-1H-1,2,3-triazol-1-yl)methyl)thiazole
1
(
8k) Yield: 76 %; m.p.: 122 °C; H NMR (500 MHz, CDCl ): d ppm = 3.83 (s,
3
H
3
7
H), 5.74 (s, 2H), 6.96 (d, J = 8.9 Hz, 2H), 7.25 (s, 1H), 7.3 (d, J = 8.1 Hz, 2H),
1
.77 (d, J = 8.9 Hz, 2H), 7.88 (d, J = 8.1 Hz, 2H), 7.91 (s, 1H); C NMR
3
(
126 MHz, CDCl ): d ppm = 49.9, 55.3, 114.3, 117.8, 119.3, 123.2, 127.1, 127.8,
3
C
?
29.3, 131.6, 136.5, 148.0, 150.9, 159.7, 168.0; HRMS: 383.0735 (M ? H) ,
1
4
?
05.0553 (M ? Na) .
2
-(4-Chlorophenyl)-4-((4-(3,4-dimethoxyphenyl)-1H-1,2,3-triazol-1-yl)methyl)thia-
1
zole (8l) Yield: 80 %; m.p.: 120 °C; H NMR (500 MHz, CDCl ): d ppm = 3.89
3
H
(
J = 8.3 Hz and 1.5 Hz, 2H), 7.40 (d, J = 8.5 Hz, 2H), 7.47 (d, J = 1.5 Hz, 1H),
s, 3H), 3.94 (s, 3H), 5.72 (s, 2H), 6.88 (d, J = 8.3 Hz, 1H), 7.25 (s, 1H),7.27 (dd,
1
3
7
ppm = 49.9, 55.9, 56.0, 109.0, 111.3, 117.9, 118.2, 119.5, 123.5, 127.8, 129.3,
.85 (d, J = 8.5 Hz, 2H), 7.92 (s, 1H); C NMR (126 MHz, CDCl ): d
3
C
?
31.5, 136.5, 148.0, 149.1, 149.3, 150.8, 168.0; HRMS: 413.0840 (M ? H) ,
?
35.0658 (M ? Na) .
1
4
2
-(4-Fluorophenyl)-4-((4-phenyl-1H-1,2,3-triazol-1-yl)methyl)thiazole (8m) Yield:
1
7
J = 12.6 and 4.7 Hz, 2H), 7.24 (s, 1H), 7.37–7.31 (m, 1H), 7.43 (m, 2H), 7.85 (m,
0 %; m.p.: 96 °C; H NMR (500 MHz, CDCl ): d ppm = 5.75 (s, 2H),7.16 (dd,
3
H
1
3
2
ppm = 50.0, 116.1, 116.3, 117.6, 120.1, 125.8, 128.2, 128.5, 128.6, 128.9, 129.5,
H), 7.97–7.91 (m, 2H), 8.01 (s, 1H); C NMR (126 MHz, CDCl ): d
3
C
?
30.5, 148.2, 150.6,163.1, 165.1, 168.2; HRMS: 373.0930(M ? H) , 359.0748
1
?
M ? Na) .
(
2
-(4-Fluorophenyl)-4-((4-(4-fluorophenyl)-1H-1,2,3-triazol-1-yl)methyl)thiazole (8n)
1
Yield: 66 %; m.p.: 154 °C; H NMR (500 MHz, CDCl ): d ppm = 5.74 (s, 2H),
3
H
7
1
1
1
.13–7.15 (m, 4H), 7.26 (s, 1H), 7.84–7.78 (m, 2H), 7.95–7.91 (m, 2H), 7.96 (s,
1
3
H); C NMR (126 MHz, CDCl ): dC ppm = 50.0, 115.7, 115.9, 116.1, 116.3,
3
17.7, 119.8, 126.8, 127.5, 127.5, 128.5, 128.6, 129.4, 147.3, 150.5, 161.7, 163.1,
?
63.7,165.1, 168.3; HRMS: 355.0831 (M ? H) , 377.0649 (M ? Na) .
?
123

V. Shinde et al.
2
-(4-Fluorophenyl)-4-((4-(4-methoxyphenyl)-1H-1,2,3-triazol-1-yl)methyl)thiazole
1
(
8o) Yield: 74 %; m.p.: 118 °C; H NMR (500 MHz, CDCl ): d ppm = 3.84 (s,
3
H
3
H), 5.73 (s, 2H), 6.98–6.94 (m, 2H), 7.15 (t, J = 8.6 Hz, 2H), 7.23 (s, 1H),
1
.79–7.75 (m, 2H), 7.91 (s, 1H), 7.96–7.92 (m, 2H); C NMR (126 MHz, CDCl3):
3
7
d ppm = 49.9, 55.3, 114.2, 116.1, 116.3, 117.6, 119.3, 123.3, 127.1, 128.5, 128.6,
C
?
29.5, 148.0, 150.8, 159.64, 163.1, 165.1, 168.2; HRMS: 367.1031 (M ? H) ,
1
?
89.0849 (M ? Na) .
3
4
-((4-(3,4-Dimethoxyphenyl)-1H-1,2,3-triazol-1-yl)methyl)-2-(4-fluorophenyl)thia-
1
zole (8p) Yield: 76 %; m.p.: 136 °C; H NMR (500 MHz, CDCl ): dH
3
ppm = 3.91 (s, 3H) 3.96 (s, 3H), 5.74 (s, 2H), 6.91 (d, J = 8.3 Hz, 1H), 7.15 (t,
J = 8.6 Hz, 2H), 7.23 (s, 1H), 7.29 (t, J = 4.1 Hz, 2H), 7.50 (d, J = 1.8 Hz, 1H),
1
3
7
1
1
.97–7.90 (m, 2H); C NMR (126 MHz, CDCl ): d ppm = 50.0, 55.9, 56.0,
3
C
09.0, 111.3, 116.1, 116.3, 117.6, 118.2, 119.5, 123.5, 128.5, 128.6, 129.4, 148.1,
?
49.1, 149.3, 150.7, 163.1, 165.1, 168.2; HRMS: 397.1136 (M ? H) , 419.0954
?
(
M ? Na) .
Experimental protocol for biological activity
Antitubercular activity
All synthesized compounds were screened for their in vitro activity against
M. tuberculosis H37Ra (ATCC 25177) and M. bovis BCG (ATCC 35743) using
twofold dilution technique to determine the actual minimum inhibitory concentra-
tion (MIC). Activity against MTB was determined through XTT reduction
menadione assay (XRMA), reading absorbance at 470 nm as per the protocol
described in literature [60–64]. Nitrate reductase (NR) assay was performed to
estimate inhibition of M. bovis BCG [60–64], measuring absorbance at 540 nm. In
vitro activity against MTB and M. bovis BCG at dormant (12 days) stage was
performed using the XRMA and NR assay, respectively, as described above.
Percentage inhibition was calculated using the following formula:
%
inhibition ¼ ½ðcontrolÀCMPÞ=ðcontrolÀblankފ  100;
where ‘‘control’’ is the activity of mycobacteria without compounds, ‘‘CMP’’ is the
activity of mycobacteria in presence of compound, and ‘‘blank’’ is the activity of
culture medium without mycobacteria.
Cytotoxicity
To check the selectivity, selected 2-aryl-4-((4-aryl-1H-1,2,3-triazol-1-yl)methyl)thi-
azole derivatives (8a–p) were assayed for their cytotoxic effects in two different cell
lines (HeLa, HCT) using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium
bromide (MTT) assay [65, 66]. The cell lines were maintained under standard
cell culture conditions under 5 % CO at 37 °C in 95 % air humidified environment.
2
Each concentration was tested in duplicates in a single experiment.
1
23

Synthesis and biological evaluation of new 2-aryl-4-((4-…
Antibacterial activity
All bacterial cultures were first grown in Luria–Bertani medium at 37 °C at
1
80 rpm. Once the culture reached 1 OD, it was used for antibacterial assay.
Bacterial strains Escherichia coli (NCIM 2576), Pseudomonas flurescence (NCIM
059) as Gram-negative and Staphylococcus aureus (NCIM 2602) and Bacillus
subtilis (NCIM 2162) as Gram-positive were obtained from NCIM (NCL, Pune) and
2
grown in Luria–Bertani medium from HiMedia, India. The assay was performed in
9
6-well plates after 8 and 12 h for Gram-negative and Gram-positive bacteria,
respectively. Screening was carried out using 0.1 % of 1-OD culture at 620 nm.
Inoculated culture was added into each well of 96-well plate containing the
compounds to be tested. Optical density for each plate was measured at 620 nm
after 8 h for Gram-negative bacteria and after 12 h for Gram-positive bacteria.
Results and discussion
A series of 2-aryl-4-((4-aryl-1H-1,2,3-triazol-1-yl)methyl)thiazole derivatives (8a–
p) were synthesized according to Scheme 1. Ethyl 3-bromo-2-oxopropanoate 2 on
cyclocondensation reaction with aryl thioamides 1a–d gave ethyl 2-arylthiazole-4-
carboxylates 3a–d. Ester 3a–d on reduction with lithium aluminum hydride in
tetrahydrofuran (THF) gave (2-arylthiazol-4-yl)methanol 4a–d; subsequent reaction
with methanesulfonyl chloride and triethylamine in DCM furnished (2-phenylth-
iazol-4-yl)methyl methanesulfonate 5a–d, which on reaction with sodium azide in
DMSO gave 4-(azidomethyl)-2-arylthiazole 6a–d. Azide 6a–d, on click reaction
with substituted alkynes 7a–d, furnished target compounds 2-aryl-4-((4-aryl-1H-
1
,2,3-triazol-1-yl)methyl)thiazole 8a–p.
The structure of the title compounds 8a–p was confirmed by NMR and high-
resolution mass spectrometry (HRMS). As a representative analysis of compound
1
4
-((4-(4-fluorophenyl)-1H-1,2,3-triazol-1-yl)methyl)-2-phenylthiazole (8b), the H
NMR spectrum of compound 8b displayed one singlet in aliphatic region at d 5.75
thiazole-CH -triazole). A triplet at d 7.11 and multiplet at d 7.80–7.83 were
(
2
attributed to protons of fluoro-substituted phenyl ring, while multiplet at d 7.44–7.49
and d 7.92–7.97 corresponds to protons of phenyl ring. Thiazole and triazole protons
1
3
resonated as singlet at d 7.26 and 7.98, respectively. The C NMR spectrum of
compound 8b showed one signal of thiazole-CH -N carbon at d 50.0. Aromatic
2
carbons of fluoro-substituted phenyl showed typical fluoro-coupling [C –F d 163.66,
1
1
2
1
61.69 ( J = 248 Hz), C -F d 115.89, 115.72 ( J = 21.42 Hz), C -F d 127.54,
2
3
3
27.48 ( J = 7.56 Hz)]. Structure of compound 8b was further confirmed by
1
HRMS, which showed molecular ion peak at m/z 337.0930 (M ? H) , 359.0748
?
?
M ? Na) . Structures of all derivatives were ascertained similarly.
(
123

V. Shinde et al.
Scheme 1 Synthetic route for 2-aryl-4-((4-aryl-1H-1,2,3-triazol-1-yl)methyl)thiazoles 8a–p
Biological evaluation
Antitubercular activity
The antitubercular activity of each synthesized compound was determined by
measuring inhibition of growth against a virulent dormant-stage strain of
M. tuberculosis H37Ra (MTB, ATCC 25177) and M. bovis (BCG, ATCC 35743)
in liquid medium. In preliminary screening, the antimycobacterial activity of these
compounds was assessed at concentrations of 30, 10, and 3 lg/mL using first-line
antitubercular drug rifampicin as reference standard. In vitro activity studies against
dormant stage of MTB and M. bovis BCG were performed using XRMA [60–63]
and NR assay [60–63], respectively. The results of antitubercular activity are
reported in Table 1.
The in vitro antitubercular assay against M. tuberculosis H37Ra and M. bovis
BCG revealed that compounds 8a–c, f–h, m (MIC 0.03–2.47 lg/mL) exhibited
good activity against dormant-stage BCG strain. The preliminary structure–activity
relationship study revealed that replacement of hydrogen atom of phenyl ring A and
B (Fig. 1) by substituent groups such as Br, Cl, F, OMe, and CH affected the
3
antitubercular activity.
Further, it was also noted that, among the compounds 8a–d with unsubstituted
1
phenyl ring A and substituted phenyl ring B, compound 8a (R = H) showed good
activity against M. tuberculosis H37Ra (MIC 9.28 lg/mL) and M. bovis (MIC
1
0
.88 lg/mL), compound 8b (R = 4-F) exhibited good activity against H37Ra
(
MIC 8.99 lg/mL) and M. bovis (MIC 1.69 lg/mL), whereas compound 8c
R = 4-OMe) showed good activity against M. bovis (MIC 1.37 lg/mL). Among
1
(
the compounds 8e–h with 4-bromo-substituted phenyl ring A and substituted phenyl
1
ring B, compound 8f (R = 4-F) and 8h (R = 3,4-OMe) showed excellent activity
1
1
23

Synthesis and biological evaluation of new 2-aryl-4-((4-…
Table 1 Antitubercular
Compound
M. tuberculosis H37Ra
M. bovis BCG
(dormant stage) activity (MIC in
lg/mL) of compounds 8a–p
IC50
MIC90
IC50
MIC90
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
a
b
c
d
e
f
1.4
9.28
8.99
[30
[30
[30
[30
[30
[30
[30
[30
[30
[30
[30
[30
[30
[30
0.015
0.24
0.15
0.08
30
0.88
1.69
1.37
[30
[30
0.67
2.25
0.35
[30
[30
[30
[30
2.47
[30
[30
[30
0.021
0.92
[30
[30
22.01
18.33
[30
4.85
[30
0.05
1.51
0.03
[30
[30
[30
[30
0.25
[30
[30
[30
0.77
g
h
i
16.88
23.16
[30
12.62
[30
25.52
[30
[30
0.85
j
k
l
m
n
o
MIC90 minimum inhibitory
concentration, IC50 50 %
inhibitory concentration
8p
Rifampicin
Fig. 1 Compounds 8a–p
S
N
N
A
N
R
N
R1
B
1
against M. bovis (MIC 0367 and 0.35 lg/mL respectively) and 8g (R = 4-OMe)
exhibited good activity with MIC of 2.25 lg/mL Among the compounds 8i–l with
4
-chloro-substituted phenyl ring A and substituted phenyl ring B, all compounds
were found less active. From the compounds 8m–p with 4-fluoro-substituted phenyl
ring A and substituted phenyl ring B, compound 8m exhibited good activity against
M. bovis (MIC 2.47 lg/mL), whereas compounds 8n–p were found less active. It
was notable that compounds with unsubstituted or 4-bromo-substituted phenyl
ring A and substituted phenyl ring B showed good antitubercular activity against
BCG.
Compounds 8a–p were further evaluated against two human cancer cell lines
HeLa and HCT116) and against primary human umbilical vein endothelial cells
HUVECs) to check the toxicity of these compounds (Table S-2). All active
(
(
compounds were relatively nontoxic up to 100 lg/mL against HUVECs; the results
of cytotoxicity screening are presented in Table 2.
According to the study on drug susceptibility of TB, the antimycobacterial
activity was considered to be specific for selectivity index [10. The selectivity
123

V. Shinde et al.
1
23

Synthesis and biological evaluation of new 2-aryl-4-((4-…
index (SI) was calculated by dividing GI50 for cell lines (HeLa, HCT 116, and
HUVEC) by the MIC for in vitro activity against dormant MTB and M. bovis BCG.
For dormant state of M. bovis BCG, all compounds showed SI higher than [40
against primary HUVEC cells (Table 2).
Cytotoxic activity evaluation
The results of this evaluation are presented in Table 2.
Antibacterial activity
The antibacterial activity of synthesized compounds was determined against
standard Gram-negative bacteria E. coli (NCIM 2576) and P. flurescence (NCIM
2059) and Gram-positive bacteria S. aureus (NCIM 2602) and B. subtilis (NCIM
2162). Ampicillin served as positive control for antibacterial activity [64]. The
in vitro preliminary screening values (% inhibition) against the tested microorgan-
isms are summarized in Table S-2. The antibacterial activity results are reported as
minimum inhibitory concentration in Table 3.
Analysis of the antibacterial activity results presented in Table 3 provides some
lead molecules with good antibacterial activity. Among the compounds 8a–p tested,
it was observed that the synthesized compounds showed moderate to good activity.
1
It is worthwhile to mention that compounds 8h (R = Br, R = CH ) and 8j
3
1
(
R = Cl, R = F) exhibited good activity with MIC values of 4.5 to 20.2 lg/mL
Table 3 Antibacterial activity
in MIC90 (lg/mL) of compounds
Comp.
E. coli
P. flurescence
S. aureus
B. subtilis
8a–p
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
a
b
c
d
e
f
[30
[30
[30
[30
[30
[30
[30
9.5
[30
[30
[30
[30
[30
[30
[30
7.2
[30
[30
[30
[30
[30
[30
[30
6.7
[30
[30
[30
[30
[30
[30
[30
12.2
[30
12.5
[30
[30
[30
[30
[30
[30
10.32
1.35
g
h
i
[30
4.5
[30
5.4
[30
20.2
[30
25.6
[30
[30
28.5
[30
1.0
j
k
l
[30
[30
[30
[30
23.3
[30
1.46
1.62
[30
[30
[30
[30
[30
[30
4.36
0.49
m
n
o
p
Ampicillin
Kanamycin
[30
123

V. Shinde et al.
1
against all tested strains. Compounds 8l (R = Cl, R = CH ) and 8o (R = F,
3
1
R = OCH ) showed good antibacterial activity against S. aureus with MIC of 25.6
3
and 28.5 lg/mL, respectively, while compound 8o also exhibited good activity
against E. coli with MIC of 23.3 lg/mL. Thus, it is concluded that compounds with
R = Br, R = CH and R = Cl, R = F group showed good antibacterial activity.
1
1
3
Conclusions
We describe synthesis and biological screening of 2-aryl-4-((4-aryl-1H-1,2,3-
triazol-1-yl)methyl)thiazole derivatives 8a–p. Most of the synthesized compounds
with unsubstituted or 4-bromo-substituted phenyl ring at 2-position of thiazole and
substituted phenyl ring at 4-position of 1,2,3-triazole showed good antitubercular
activity against M. bovis. Most of the synthesized compounds exhibited good
antibacterial activity. These results warrant synthesis of similar libraries with other
substituents to confirm the trend described herein.
Acknowledgements The authors are grateful to CSIR-NCL, Pune for supporting the biological activity
investigation. Central Analysis Facility, Savitribai Phule Pune University, Pune is also acknowledged for
spectral analysis.
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