Novel tetrazoloquinoline-thiazolidinone conjugates as possible antitubercular agents: Synthesis and molecular docking

Article abstract of DOI:10.1039/c6md00278a

A novel approach for the synthesis of a new 4-thiazolidinone scaffold was developed by a one-pot three-component cyclocondensation of various tetrazolo quinoline aldehydes 1a-f, acid hydrazide 2a-c, and thioglycolic acid 3 in the presence of [DBUH][OAc] as a catalyst in high yields. All the conjugates were screened for their antimycobacterial activity against MTB H37Ra and M. bovis BCG strains, with the MIC values ranging from 0.99-13.55 μmol mL^-1 and 0.14-20.11 μmol mL^-1, respectively. The 4-thiazolidinone-incorporated tetrazoloquinoline derivatives 4a, 4d, 4g, 4j, 4m, and 4p were highly potent against MTB H37Ra and M. bovis BCG strains. The most active compounds were also evaluated for their cytotoxicity against MCF-7, A549, and HCT 116 cell lines and were found to be non-cytotoxic. Further, molecular docking studies into the active site of the InhA enzyme revealed a similar binding mode to the native ligand in the crystal structure, thereby helping us to understand the ligand-protein binding interaction and establish a structural basis for the inhibition of mycobacterium tuberculosis. The results suggest that the tetrazoloquinoline-thiazolidinone conjugates 4a, 4d, 4g, 4j, 4m, and 4p are promising antitubercular agents.

Full text of DOI:10.1039/c6md00278a

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RESEARCH ARTICLE
Novel tetrazoloquinoline–thiazolidinone
conjugates as possible antitubercular agents:
Cite this: DOI: 10.1039/c6md00278a
synthesis and molecular docking†‡
a
a
a
Dnyaneshwar D. Subhedar, Mubarak H. Shaikh, Bapurao B. Shingate,*
b
b
c
Laxman Nawale, Dhiman Sarkar and Vijay M. Khedkar
A novel approach for the synthesis of a new 4-thiazolidinone scaffold was developed by a one-pot three-
component cyclocondensation of various tetrazolo quinoline aldehydes 1a–f, acid hydrazide 2a–c, and
thioglycolic acid 3 in the presence of [DBUH]ijOAc] as a catalyst in high yields. All the conjugates were scre-
ened for their antimycobacterial activity against MTB H37Ra and M. bovis BCG strains, with the MIC values
−1
−1
ranging from 0.99–13.55 μmol mL and 0.14–20.11 μmol mL , respectively. The 4-thiazolidinone-
incorporated tetrazoloquinoline derivatives 4a, 4d, 4g, 4j, 4m, and 4p were highly potent against MTB
H37Ra and M. bovis BCG strains. The most active compounds were also evaluated for their cytotoxicity
against MCF-7, A549, and HCT 116 cell lines and were found to be non-cytotoxic. Further, molecular
docking studies into the active site of the InhA enzyme revealed a similar binding mode to the native ligand
in the crystal structure, thereby helping us to understand the ligand–protein binding interaction and estab-
lish a structural basis for the inhibition of mycobacterium tuberculosis. The results suggest that the tetra-
zoloquinoline–thiazolidinone conjugates 4a, 4d, 4g, 4j, 4m, and 4p are promising antitubercular agents.
Received 22nd May 2016,
Accepted 1st July 2016
DOI: 10.1039/c6md00278a
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halve the mortality risk; however, its effect was not very effec-
tive for decreasing deaths by tuberculosis. Due to these rea-
1
. Introduction
9
Tuberculosis (TB) is a major global health issue and is ranked
as the second leading cause of death from an infectious dis-
ease worldwide. According to a WHO report, nine million
sons, there is an ongoing need for new effective and safe anti-
tubercular drugs.
Over the last decade, the 4-thiazolidinones scaffold has
attracted great interest among researchers because of its
promising potency in a number of areas, including antimi-
1
new cases of TB and an estimated two million deaths occur
2
each year and more than 30 million lives will be claimed by
3
,4
10
11
12
TB between 2000 and 2020. A combination of four first-line
drugs, namely isoniazid, pyrazinamide, rifampicin, and eth-
ambutol, are utilized the development and dissemination of
multidrug-resistance and extensive drug resistance. Mycobac-
terium tuberculosis (MTB) strains, together with co-infection
with HIV, have intensified the urgent need for new anti-TB
crobial, anti-inflammatory, COX-2 inhibitor, nematici-
1
3
14
15
16
dal, HIV inhibitors, hypertensive, anticonvulsant, anti-
1
7
18
19
20
cancer,
CNS-penetrant,
antiparasitic,
hepatitis,
2
1
22
hyperglycemic, antibiofilm, and monoamine oxidase A in-
2
3
hibitors. Compounds with the 4-thiazolidinone scaffold in
2
4
their skeleton (Fig. 1) display better antitubercular activity.
5
,6
drug discovery. The M. bovis BCG (Bacille Calmette-Guerin)
Isoniazid (INH) is an NADH-dependent 2-trans enoyl-acyl
vaccination is among the most commonly administered
worldwide and the only attenuated live vaccine. In a recent
review commissioned by WHO, its effect was estimated to
carrier protein (ACP) reductase of the type II fatty acid
synthase (FASII) pathway in MTB. There is a strong body of
7
8
25
evidence indicating that it is the primary target of the front-
2
6
line antitubercular drug INH. The 4-thiazolidinone ring with
2
7
an INH scaffold also exhibits antitubercular activity. The fu-
sion of quinoline to the tetrazole ring is known to increase
a
Department of Chemistry, Dr. Babasaheb Ambedkar Marathwada University,
Aurangabad, 431 004, India. E-mail: bapushingate@gmail.com;
Fax: (91) 240 2403113; Tel: (91) 240 2403312
2
8
the biological activity in areas such as anticancer, anti-
b
29
30
31
32
Combichem Bioresource Centre, National Chemical Laboratory, Pune, 411 008,
bacterial,
antinflammatory, antioxidant and antitubercular agents
Fig. 2).
Multicomponent reactions (MCRs) have led to a rapid gen-
antifungal,
antimicrobial,
anticonvulsant,
2
9
33
34
India
c
School of Health Sciences, University of KwaZulu Natal, Westville Campus,
(
Durban, 4000, South Africa
†
‡
The authors declare no competing interests.
eration of diverse sets of complex molecules, particularly in
drug discovery. The use of MCRs and ionic liquids is a
Electronic supplementary information (ESI) available. See DOI: 10.1039/
c6md00278a
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Fig. 1 Reported anti-TB agents and our designed molecules.
Fig. 2 Tetrazoloquinoline-based bioactive compounds.
3
5
perfect synergy for eco-compatible heterocyclic synthesis. In
the context of green chemistry, the reactions, assisted by
their remarkable catalytic behavior, display significant merits
bovis BCG strain. In addition, we also performed a molecular
docking study for the most active compounds.
3
6
of reduced reaction time and improved yields. The ionic
2
. Results and discussion
3
7
liquid DBU acetate has been used for various organic
3
8
2.1 Chemistry
transformations.
The diverse applications of 4-thiazolidinone scaffolds in
medicinal chemistry have attracted considerable interest dur-
ing the last few years from synthetic chemists keen to expand
useful green synthetic routes; as a result, a number of
methods have already been reported, but they have several
disadvantages. Therefore, in continuation of our efforts
based on the synthesis and bioevaluation of various com-
pounds, a search for a more general, eco-friendly, and effi-
cient high-yielding route to the synthesis of 4-thiazolidinone
scaffolds remains a valid exercise. Herein, the newly synthe-
sized tetrazoloquinoline–thiazolidinone conjugates exhibited
good antitubercular activity against MTB H37Ra and the M.
The synthesis of new 4-thiazolidinone-incorporated tetrazolo
quinoline derivatives (4a–r) was achieved via a facile condensa-
tion reaction between tetrazolo[1, 5-a]quinoline-4-carbaldehydes
(1a–f), acid hydrazide (2a–c), and thioglycolic acid (3) in the
presence of [HDBU]ijOAc] as a catalyst. The present “one-pot
synthesis” protocol provides easy access to the synthesis of de-
sired products in excellent yields (80–90%) with high purity
and was investigated to establish the feasibility and scope for
broader substrate choice. The required starting materials, tetra-
zolo[1, 5-a]quinoline-4 carbaldehydes 1a–f, were prepared by the
reaction of 2-chloroquinoline-3-carbaldehyde derivatives with
sodium azide in DMF (Scheme S1, ESI‡).
3
9
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Table 1 Optimization of the reaction conditionsa
In order to explore the optimum conditions for the synthe-
sis of the 4-thiazolidinone conjugates, the reaction of tetra-
zolo[1, 5-a]quinoline-4-carbaldehyde 1a (1 mmol), acid hydra-
zide (isoniazid) 2a (1 mmol), and thioglycolic acid 3 (2 mmol)
was selected as the model reaction (Scheme 1).
The effect of various reaction conditions and different cat-
alysts, concentration of catalyst, and temperature were stud-
ied to optimize the reaction conditions. At first, we studied
the effect of various organic solvents at different temperature
for the model reaction in the presence of [DBUH]ijOAc] as a
catalyst; also various solvents, such as ethanol, methanol,
b
Entry
Solvent
Temp (°C)
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
9
Ethanol
Methanol
H O
2
2 2
CH Cl
CH CN
3
THF
DMF
PhMe
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
100
1
1
1
1
1
1
1
1
1
55
58
48
60
75
54
55
59
90
Reflux
80
Solvent-free
a
Reaction conditions: 1a (1 mmol), 2a (1 mmol), 3 (2 mmol) and
H
2
O, CH
3
2 2
CN, THF, CH Cl , DMF, and toluene, were screened.
b
[
DBUH]ijOAc] (20 mol%). Isolated yield.
In each case, the rate of the reaction was very slow and
resulted in a lower yield of product (Table 1, entries 1–8). We
thus performed the same reaction under solvent-free condi-
tions, which led to an improvement in both the reaction rate
as well as the yield of product (Table 1, entry 9). We were sat-
isfied to find that, the reaction proceeded smoothly and al-
most a complete conversion of reactants was observed at 80
saturation of the [DBUH]ijOAc]. The above results signify that,
20 mol% of [DBUH]ijOAc] is the optimum concentration in
terms of efficient yield and reaction time.
The reusability of the catalyst was also explored for the se-
lected model reaction. The catalyst was reused four times,
and the results demonstrated that the catalyst can be reused
without a significant reduction in the yield. After the first
fresh run with a 90% yield, cold water was added to the reac-
tion mixture and the products were isolated by filtration. The
ionic liquid was recovered from the filtrate by removing the
water under reduced pressure. The recovered ionic liquid was
further tested in up to three more reaction cycles. Recycling
and reuse of the ionic liquid showed a minimal decrease in
the yields of product. The product 4a was obtained in 88%,
°C, which afforded the desired product 4a in 90% yield
within 1 h (Table 1, entry 9).
Further optimization related to the temperature, revealed
that the temperature had a pronounced effect on the rate
of the reaction. Cyclocondensation was not achieved when
the model reaction was conducted at room temperature
(ESI,‡ Table S1, entry 1) and increasing the reaction tem-
perature up to 70 °C was required, with several hours re-
quired for completion of the reaction (ESI,‡ Table S1, en-
tries 2–4). The maximum yield of the product was obtained
in shortest time period when the reaction was performed at
83%, and 80% yields after successive cycles (Table S3, ESI‡).
1
8
0 °C (ESI,‡ Table S1, entry 5). However, no further en-
The formation of compound 4a was confirmed by
NMR,
H
1
3
1
hancement in the yield of product 4a was observed when
the reaction temperature was raised from 80 °C to 90 °C
C NMR, and HRMS analysis. In the H NMR
spectrum of compound 4a, the methylene protons of
4-thiazolidinone ring appeared as two distinct doublet of dou-
blets at δ 4.10 and 3.99 ppm, indicating that both the protons
were magnetically non-equivalent. The C–H proton of the
4-thiazolidinone ring appeared as a singlet at δ 6.73 ppm. The
formation of the 4-thiazolidinone ring was also proven by the
(ESI,‡ Table S1, entry 6).
In order to achieve a better yield of the desired product,
the model reaction was optimized by varying the amount of
catalyst (ESI,‡ Table S2). The model reaction was then subse-
quently tested for different concentrations, namely 5, 10, 15,
2
0, and 25 mol% (ESI,‡ Table S2, entries 1–5) of [DBUH]ijOAc]
2
appearance of the peaks at 35.3, 57.7, and 167.8 (CH, CH ,
1
3
at 80 °C under solvent-free conditions. It was evident that 20
mol% of the [DBUH]ijOAc] was adequate to obtain the opti-
mum yield in the shortest reaction time (1 h). When using
less than 20 mol% of catalyst, moderate yields of the product
and CO, respectively) ppm in the C NMR spectrum of
compound 4a. Further, the formation of compound 4a was
+
confirmed by HRMS spectrum, with a calculated [M + H] at
392.0929 and observed at 392.0933.
(
48–80%) were obtained with extended reaction times, while
To examine the substrate scope of the one-pot three-com-
ponent cyclocondensation reaction for the construction of a
library of novel 4-thiazolidinones (4a–r), the three different
with an excess mol% of catalyst (25 mol%), there was no fur-
ther increase in the yield of the product, possibly due to the
Scheme 1 Standard model reaction.
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Scheme 2 Synthesis of new 4-thiozolidinone-incorporated tetrazoloquinoline derivatives 4a–r.
Scheme 3 Plausible mechanistic pathway for the synthesis of N-(4-oxo-2-(tetrazoloij1,5-a]quinolin-4-yl)thiazolidin-3-yl)isonicotinamide by
DBUH]ijOAc].
[
acid hydrazide, thioglycolic acid, and various tetrazolo quino-
line aldehydes were used under the optimized reaction condi-
tions. The results are shown in Scheme 2. It could be seen
that the reaction proceeded successfully and gave the
expected products in good to excellent yields in short reac-
tion times.
A plausible mechanistic pathway (Scheme 3) is proposed
to illustrate the synthesis of N-(4-oxo-2-(tetrazoloij1,5-
a]quinolin-4-yl)thiazolidin-3-yl)isonicotinamide derivatives cat-
alyzed by [DBUH]ijOAc]. It can be speculated that the DBUH
group favors interacting with an oxygen atom of the carbonyl
group of the aldehyde, while the OAc group interacts with the
hydrazide proton, facilitating the formation of the imine
intermediate III by increasing the electrophilicity of the car-
bonyl group of the aldehyde as well as the nucleophlicity of
the hydrazide. Then, free OAc ions interact with thioglycolic
acid protons and attack the imine group of the intermediate
III, with the simultaneous removal of a water molecule from
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intermediate III and the formation of N-(4-oxo-2-(tetrazoloij1,5-
a]quinolin-4-yl)thiazolidin-3-yl)isonicotinamide 4a together
with regeneration of the catalyst.
pared with 4e and 4f, with MIC values greater than 66.75
μmol mL against MTB H37Ra.
−
1
In the 4j–l series, the position of the methyl group is on
the tetrazolo quinoline at R . Compound 4j, with an iso-
1
nicotinohydrazide unit, shows enhanced antimycobacterial
2
.2 Biological activity
.2.1. In vitro antimycobacterial activity evaluation. The
activity against MTB H37Ra, with an MIC value of 2.14 μmol
−
1
2
mL , as compared to 4a, 4d, and 4g. Similarly, compounds
4k and 4l, with nicotinohydrazide and 4-nitrobenzohydrazide
moieties, respectively, did not show any significant change in
antitubercular activity when compared with compounds hav-
ing a methyl group on the tetrazoloquinolines, i.e., 4e, 4f, 4k,
and 4l.
newly synthesized 4-thiazolidinone incorporated tetrazolo[1,5-
a]quinoline derivatives (4a–r) were screened for in vitro anti-
tubercular activity against MTB H37Ra (ATCC 25177) and M.
bovis BCG (ATCC 35743) in liquid medium. In a preliminary
4
0
screening (ESI,‡ Tables S4 and S5), the antimycobacterial
activity of these compounds were assessed at concentrations
In the 4m–o series, with the introduction of a methoxy
group at the R2 position of the tetrazoloquinoline ring,
compound 4m, with an isonicotinohydrazide core, has an
enhanced antimycobacterial activity as compared to the
above-synthesized compound against MTB H37Ra, with an
−
1
of 30, 10, and 3 μg mL using an established XTT Reduction
Menadione assay (XRMA) antitubercular screening protocol
using the first-line antitubercular drug rifampicin as the ref-
erence standard, and the MIC values are presented in
Table 2. The representative IC50 values are given in the ESI‡
−
1
MIC value of 1.66 μmol mL . Compounds 4n and 4o,
with nicotinohydrazide and 4-nitrobenzohydrazide moieties,
have a moderately increased antitubercular activity, with
(Table S9).
The 4-thiazolidinone-incorporated tetrazoloquinoline de-
−
1
rivatives 4a, 4d, 4g, 4j, 4m, and 4p with an isoniazid skele-
MIC values greater than 64.75 μmol mL . For compounds
4p–r, with a change in the position of the methoxy group
−
1
ton with an MIC range of 0.99–13.55 μmol mL and 0.14–
−
1
2
0.11 μmol mL were found to be most active against
2 1
from R to R in the tetrazoloquinoline ring, compound
MTB H37Ra and M. bovis BCG strains, respectively. How-
ever, the rest of the derivatives 4b, 4c, 4e, 4f, 4h, 4i, 4k, 4l,
4p, with isonicotinohydrazide, shows excellent anti-
tubercular activity among all the synthesized compounds,
−
1
4
n, 4o, 4q, and 4r derived from nicotinic and 4-nitrobenzoic
with an MIC value of 0.99 μmol mL . Similarly, compounds
4q and 4r, with nicotinohydrazide and 4-nitrobenzohydrazide
cores, do not show any significant change in antitubercular
activity.
acid hydrazide were found to be less active against MTB
H37Ra and BCG strains with MIC values > 64.44 μmol
−
1
mL .
In compounds 4a–c, the unsubstituted tetrazoloquinoline
We also screened the antitubercular activity of the synthe-
sized compounds against M. bovis BCG, and the results are
summarized in Table 2. The isoniazid-based conjugates 4a,
4d, 4g, 4j, 4m, and 4p display better antitubercular activity
against BCG, with MIC values of 0.43, 0.51, 0.30, 8.43, 0.36,
ring is constant and modifications in the hydrazide unit dis-
play a variation in the antitubercular activity against the MTB
H37Ra strain. The compound 4a with an isonicotinic acid hy-
drazide moiety displays excellent antitubercular activity
−
1
−1
against MTB H37Ra, with an MIC value of 13.55 μmol mL .
However, the nicotinic acid hydrazide and 4-nitrobenzoic acid
hydrazide derived conjugates 4b and 4c showed a lower anti-
tubercular activity against MTB H37Ra, with MIC values
and 0.14 μmol mL , respectively. The remaining derivatives
are less potent against the M. bovis BCG strain.
Hence, from the above study, it can be concluded that, the
methyl and methoxy group on the tetrazoloquinoline ring
with an isoniazid skeleton in the thiazolidinone framework
shows excellent to moderate activity against both strains as
compared to the derivatives with nicotinic acid and
4-nitrobenzoic acid hydrazide in their skeleton.
2.2.2. Cytotoxicity. The highly active tetrazoloquinoline–
thiazolidinone conjugates 4a, 4d, 4g, 4j, 4m, and 4p were fur-
ther evaluated against three human cancer cell lines (MCF-7,
A549, and HCT 116) to evaluate the toxicity of these com-
−
1
greater than 68.90 μmol mL . The presence of a methyl
group at the R position of the tetrazoloquinoline ring in the
3
4
d–f series leads to an increase in antitubercular activity. The
compound 4d derived from isonicotinohydrazide, displayed
excellent antitubercular activity as compared to 4a against
−
1
MTB H37Ra with an MIC value of 1.77 μmol mL .
Compounds 4e and 4f with nicotinohydrazide and
-nitrobenzohydrazide moiety, respectively, showed an in-
crease in antitubercular activity as compared to 4b and 4c,
a
4
4
1
−1
pounds. The GI50/GI90 (>100 μg mL ) values of all the com-
pounds indicate that they are potent and specific inhibitors
against MTB H37Ra and M. bovis BCG strains (Table 3).
Thus, all the active compounds were relatively non-toxic
−
1
with MIC values greater than 66.75 μmol mL against MTB
H37Ra. With the change in position of the methyl group on
the tetrazoloquinoline ring from R to R in the 4g–i series,
3
2
compound 4g, with an isonicotinohydrazide core, has a
slightly decreased antitubercular activity as compared to 4d
but is more active than 4a, with an MIC value of 2.61 μmol
mL against MTB H37Ra. Compounds 4h and 4i, with
nicotinohydrazide and 4-nitrobenzohydrazide cores, respec-
tively, showed no change in antitubercular activity when com-
against MCF-7, A549, and HCT 116 cell lines with (GI50/GI90
of >100.
2.2.3. Selectivity index. The selectivity index reflects the
concentration of the compound at which it is active against
mycobacteria but is not toxic toward host cells. A higher selec-
tivity index indicates that the compound can be used as a
)
−
1
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Table 2 Antimycobacterial activity of the 4-thiazolidinone-incorporated tetrazoloquinolinesa
MTB H37Ra
M. bovis BCG
−1
−1
Entry
Structures
MIC (μmol mL
)
MIC (μmol mL
)
4a
13.55 ± 0.69
0.43 ± 0.059
4b
>76.69
>76.69
4c
>68.90
>68.90
4d
1.77 ± 0. 28
0.51 ± 0.34
4e
>73.99
>73.99
4f
>66.75
>66.75
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Table 2 (continued)
MTB H37Ra
M. bovis BCG
−1
−1
Entry
Structures
MIC (μmol mL
)
MIC (μmol mL
)
4g
2.61 ± 1.32
0.30 ± 0.07
4h
>73.99
>73.99
4i
>66.75
>66.75
4j
2.14 ± 1.15
8.43 ± 1.94
4k
>73.99
>73.99
4l
>66.75
>66.75
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Table 2 (continued)
MTB H37Ra
M. bovis BCG
−1
−1
Entry
Structures
MIC (μmol mL
)
MIC (μmol mL
)
4m
1.66 ± 0.5
0.36 ± 0.09
4n
>71.23
20.11 ± 1.04
4o
>64.45
>64.45
4p
0.99 ± 0.078
0.14 ± 0.035
4q
>71.23
>71.23
4r
>64.45
>64.45
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Table 2 (continued)
MTB H37Ra
M. bovis BCG
−1
−1
Entry
Structures
MIC (μmol mL
)
MIC (μmol mL
)
b
RP
0.024 ± 0.0021
0.021 ± 0.039
a
−1
b
MIC in μmol mL . Antitubercular activity of each agent was determined by serial dose-dependent dilutions. Standard antitubercular drug
rifampicin as a positive control. Data were expressed as the means of triplicates. SD (±): standard deviation.
Table 3 In vitro cytotoxicity of selected tetrazoloquinoline–thiazolidinone conjugates
MCF-7 (breast) cell line
A549 (lung) cell line
HCT 116 (colorectal) cell line
−1
−1
−1
Entry
GI50 (μmol mL
)
GI50 (μmol mL
)
GI50 (μmol mL
)
4
4
4
4
4
4
a
>255.48
>246.65
>246.65
>246.65
>237.45
>237.45
>121.51
0.087 ± 0.052
>255.48
>246.65
>246.65
>246.65
>237.45
>237.45
>121.51
0.08 ± 0.0039
>255.48
>246.65
>246.65
>246.65
>237.45
>237.45
>121.51
6.69 ± 1.18
d
g
j
m
p
Rifampicin
Paclitaxel
The GI50 (cytotoxicity) values were calculated as the concentration of compounds resulting in 50% reduction of absorbance compared to
untreated cells.
therapeutic agent. The derivatives 4d (SI: >138), 4g (SI: >94),
j (SI: >114), 4m (SI: >142), and 4p (SI: >238) showed very
high SI index values, which indicates they would be good in-
of this study with respect to the developing resistance among
microorganisms against available antibiotics. According to a
study on the drug susceptibility of TB, antimycobacterial ac-
tivity was considered to be specific when the selectivity index
was >10. In the present work, the improved in vitro efficacy
(Table 2) and relatively high selectivity profile (Table 4) of
compounds 4a, 4d, 4g, 4j, 4m, and 4p indicates that these
compounds may be useful as antitubercular agents and
should be investigated further.
4
hibitors of MTB (Table 4). Compounds 4a (SI: >588), 4d (SI:
4
2
>476.2), 4g (SI: >833.3), 4j (SI: >29.23), 4m (SI: >666), 4n
(SI: >1180), and 4p (SI: >1754) showed very high SI values,
which indicates they would be good inhibitors of the M. bovis
BCG strain (Table 4). Although the selectivity index of rifam-
picin is very high, it is important to consider the significance
Table 4 Selectivity index values of compounds against dormant MTB
H37Ra and M. bovis BCG strains
−1
Table 5 Minimum inhibitory concentration values MIC (μmol mL ) of
compounds against two Gram-positive and two Gram-negative bacteria
MCF-7
A549
HCT 116
Entry
E. coli
P. fluorescens S. aureus
B. subtilis
Entry
H37Ra BCG
H37Ra BCG
H37Ra BCG
4
4d
4g
4j
4m
4p
a
>255.48
>246.65
>246.65
>246.65
>237.45
>237.45
>255.48
>246.65
>246.65
>246.65
>237.45
>237.45
>255.48
>246.65
>246.65
>246.65
>237.45
>237.45
>255.48
>246.65
>246.65
>246.65
>237.45
>237.45
4
4
4
4
4
4
a
18.9
138.9
94.3
114.9
142.8
238.1
588.2
476.2
833.3
29.23
666.7
11.80
18.9
138.9
94.3
114.9
142.8
238.1
588.2
476.2
833.3
29.23
666.7
11.80
18.9
588.2
476.2
833.3
29.23
666.7
11.80
1754.4
d
g
j
m
p
138.9
94.3
114.9
142.8
238.1
Ampicillin
Kanamycin 3.34 ± 0.41 1.01 ± 0.09
4.17 ± 1.04 12.47 ± 1.28
2.86 ± 0.78 29.53 ± 1.88
> 61.92 2.78 ± 0.85
Rifampicin >5000
1754.4 >5000
1754.4 >5000
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Table 6 Docking score and binding energy
2
.2.4. Antibacterial activity. For investigating the specific-
ity of these compounds, 4a, 4d, 4g, 4j, 4m, 4n, and 4p were
screened for their antibacterial activity against four bacteria
strains (Gram-negative strains: E. coli, P. fluorescens, Gram-
positive strains: S. aureus, B. subtilis). All the compounds
showed higher specificity toward MTB and BCG, as these
compounds showed nil antibacterial activity up to 100 μmol
MTB H37Ra
MIC
M. Bovis BCG
Binding
Docking energy
MIC
(μmol mL
−1
−1
−1
Compound (μmol mL
)
)
score
(kcal mol )
4
4d
a
13.55
1.77
2.61
2.14
1.66
0.99
0.43
0.51
0.30
8.43
0.36
0.14
−6.953
−7.446
−7.137
−7.282
−7.511
−7.847
−34.913
−44.533
−38.262
−41.727
−49.957
−57.148
4g
−
1
4j
mL (Table 5).
4
4
m
p
2
.3 Molecular docking
With the aim of rationalizing the promising in vitro results
obtained for the tetrazoloquinoline–thiazolidinone conju-
gates 4a, 4d, 4g, 4j, 4m, and 4p to investigate the molecular
basis of their interactions, a molecular docking study was
carried out with mycobacterial enoyl reductase (InhA) as the
target receptor. The enoyl-ACP (CoA) reductase (FabI/ENR/
InhA) is a crucial enzyme in the mycobacterial type II fatty
acid biosynthesis pathway and its inhibition has been shown
illustrated these details only for the most active compound
4p.
The lowest energy docked conformation (Fig. 4) for 4p
showed that, it binds with an overall binding energy of
−
1
−57.148 kcal mol and makes various close contact with the
active site residues. The per-residue–ligand interaction energy
distribution revealed that the tetrazolo quinoline scaffold was
involved in strong van der Waals interactions with the
4
3
−1
−1
to inhibit mycolic acid synthesis and induce cell lysis.
Leu218 (−1.385 kcal mol ), Ile215 (−2.363 kcal mol ),
1
−
−1
From the ensuing docked structures, it was clear that, all
these most active 4-thiazolidinone derivatives could snugly fit
into the active site of InhA and adopt a very similar orienta-
tion and at coordinates very close to that of the native ligand
in the crystal structure. Their resulting complexes were stabi-
lized by several bonded and non-bonded interactions (Fig. 3).
The results of the molecular docking study are summarized
in Table 6, where we can observe a significant correlation be-
tween the docking scores and the obtained biological activity
Met199 (−4.467 kcal mol ), Met155 (−1.654 kcal mol ),
−
1
−1
Phe149 (−3.356 kcal mol ), and Met103 (−1.922 kcal mol )
residues. Furthermore, the 4-thiazolidinone nucleus formed
significant van der Waals interactions with Th196 (−1.081
−
1
−1
kcal mol ), Met161 (−2.124 kcal mol ), and Tyr158 (−3.551
−
1
kcal mol ), while the isonicotinamide side chain was in-
volved in similar interactions with the Ile194 (−2.310 kcal
−
1
−1
mol ), Pro193 (−1.809 kcal mol ), Gly192 (−1.375 kcal
−
1
−1
mol ), Lys165 (−1.331 kcal mol ), Met147 (−1.659 kcal
−
1
−1
−1
expressed as MIC (μmol mL ), with the active compounds
having higher scores, while those with relatively low activity
are also predicted to have a lower docking score. Their bind-
ing energies were also found to be negative, ranging from
mol ), and Ile21 (−1.866 kcal mol ) residues, thus optimally
stabilizing the molecule in the active site of InhA.
The enhanced binding affinity of 4p can also be attributed
to favorable electrostatic interactions observed between the
−
1
−1
−1
−
57.148209 to −34.913443 kcal mol , signifying that they
Glu219 (−3.628 kcal mol ) and Pro156 (−1.434 kcal mol )
residues and the tetrazolo quinoline scaffold, as well as be-
tween the isonicotinamide side chain and the Asp261 (−2.353
could serve as a pertinent starting point for the rational de-
sign of drugs targeting InhA. Furthermore, an analysis of the
per-residue interactions between the enzyme and these mole-
cules was carried out to investigate in detail the various ther-
modynamic elements governing the binding of these mole-
cules to InhA. However, for the sake of brevity, we have
−
1
−1
kcal mol ), Ile194 (−1.102 kcal mol ), Gly192 (−3.418 kcal
−
1
−1
mol ), Ala191 (−1.251 kcal mol ), Val189 (−2.079 kcal
−
1
−1
mol ), Asp150 (−2.153 kcal mol ), and Asp148 (−2.011 kcal
−
1
mol ) residues, and also though the 4-thiazolidinone nucleus
Fig. 3 Binding mode of active 4-thiazolidinone derivatives in the MTB InhA active site.
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Fig. 4 Binding mode of 4p into the active site of MTB InhA.
−
1
with His93 (−1.542 kcal mol ). Hydrogen bonding interac-
tions serve as “anchors”, guiding the 3D orientation of a li-
gand in its active site, thereby aiding the steric and electro-
static interactions. The complex of 4p with InhA was observed
to be stabilized by three crucial strong hydrogen bonding in-
teractions: first, between nitrogen (N) of the pyridine ring
and the Asp148 residue at a distance of 1.936 Å; the second
interaction was between oxygen (O) of the amide linker and
the Ile194 residue at a distance of 2.133 Å, while the third hy-
drogen bond was formed between a sulfur (S) atom of the
dex. The conjugates 4a, 4d, 4g, 4j, 4m, 4n, and 4p showed a
higher selectivity index than 10 against MCF-7, A549, and
HCT 116, which makes them promising antitubercular
agents. Additionally, a molecular docking study provided us
with invaluable data to understand the experimental results
and also allowed us to the estimate the binding affinity as
well as the binding mode of 4-thiazolidinone derivatives to-
ward MTB InhA, which could be promising handle for the
discovery of better and specific inhibitors. The above results
demonstrate the potential and importance of developing new
4-thiazolidinone derivatives to treat mycobacterial infections.
4
-thiazolidinone scaffold and the Tyr158 residue with a bond-
ing distance of 2.261 Å. These strong thermodynamic interac-
tions of 4p with InhA account for its good in silico binding
and provide a clue to the significant in vitro antitubercular
activity.
4
. Experimental section
4.1. Chemistry
Analysis of the molecular docking results for the com-
pounds 4a, 4d, 4g, 4j, and 4m also revealed a similar binding
profile, and the docking results are shown in (Table 6). The
primary driving force for mechanical interlocking was ob-
served to be the steric and electrostatic interactions
supported with a prominent hydrogen bonding network, with
residues lining the active site. Overall, it is evident from this
docking simulation and more specifically from the per-
residue interaction analysis that these molecules have an af-
finity for the InhA, thus making them pertinent starting
points for structure-based drug design.
All the chemicals and reagents used were of analytical grade.
The completion of the reactions was monitored by thin-layer
chromatography (TLC) on aluminum plates coated with silica
gel 60 F254, 0.25 mm thickness (Merck). The detection of the
components was made by exposure to iodine vapors or UV
light. Melting points were determined by open capillary
1
13
methods and are uncorrected. H-NMR and C NMR spectra
were recorded in DMSO-d on a Bruker DRX-400 MHz
6
spectrometer. High-resolution mass spectra (HRMS) were
recorded on an Agilent 6520 (QTOF) mass spectrometer.
4
.2. Typical procedure for the preparation of N-(4-oxo-2-
3
. Conclusions
(
(
tetrazoloij1,5-a]quinolin-4-yl)thiazolidin-3-yl)isonicotinamide
4a)
The present protocol reports a one-pot, convenient, and eco-
friendly approach for the synthesis of new 4-thiazolidinone
derivatives using [DBUH]ijOAc] ionic liquid in excellent yields.
The tetrazoloquinoline–thiazolidinone conjugates 4a, 4d, 4g,
A mixture of tetrazoloij1,5-a]quinoline-4-carbaldehyde 1a (1
mmol), isoniazid 2a (1 mmol), and thioglycolic acid 3 (2
mmol) in DBU acetate as catalyst (20 mol%) were charged in
a 100 mL round bottom flask equipped with a mechanical
stirrer and condenser. The reaction mixture was heated at 80
°C under solvent-free conditions for 1 h. The progress of the
reaction was monitored by TLC. Completion of the reaction
was confirmed by TLC using n-hexane : ethyl acetate (8 : 2) as
the solvent. Then, the reaction mixture was poured in to 100
4
j, 4m, and 4p showed promising activity against MTB
H37Ra, with MIC values ranging from 0.99 to 13.55 μmol
mL , and also for M. bovis BCG, with MIC values ranging
from 0.14 to 8.43 μmol mL . In addition, they displayed low
cytotoxicity against MCF-7, A549, and HCT 116 cell lines
using the MTT assay, thereby providing a high therapeutic in-
−
1
−
1
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mL ice water and the obtained solid was filtered, dried, and
recrystallized from ethanol to obtain a white solid product.
thioglycolic acid 3 in 1 h as a white solid with an 86% yield,
1
mp: 236 °C. H NMR (400 MHz, DMSO-d , δ ppm): 11.95 (s,
6
4
.2.1. N-(4-Oxo-2-(tetrazoloij1,5-a]quinolin-4-yl)thiazolidin-
-yl)isonicotinamide (4a). The compound 4a was obtained via
the cyclocondensation of tetrazoloij1,5-a]quinoline-4-
1H, –NH), 9.07 (s, 1H, Ar–H), 8.15 (s, 1H, Ar–H), 7.58–7.90
3
(m, 6H, Ar–H), 6.77 (s, 1H, –S–CH–N–), 4.16 (d, 1H, –CH , J =
2
16 Hz), 4.02 (d, 1H, –CH J = 16 Hz) and 2.26 (s, 3H, –CH ).
2
3
1
3
carbaldehyde 1a, isonicotinohydrazide 2a, and thioglycolic
C NMR (100 MHz, DMSO-d
6
, δ ppm): 169.2, 161.9, 150.8,
acid 3 in 1 h as a white solid with a 90% yield, mp: 232 °C.
149.3, 143.3, 141.0, 135.7, 132.2, 130.7, 129.4, 127.4, 125.4,
122, 58.1, 36.2 and 22.9.
1
H NMR (400 MHz, DMSO-d , δ ppm): 11.76 (s, 1H, –NH),
6
8
6
.58–8.59 (m, 2H, Ar–H), 8.13 (s, 1H, Ar–H), 7.38–7.63 (m,
4.2.6. N-(2-(9-Methyltetrazoloij1,5-a]quinolin-4-yl)-4-oxo-
thiazolidin-3-yl)-4-nitrobenzamide (4f). The compound 4f was
obtained via the cyclocondensation of 9-methyltetrazoloij1,5-
a]quinoline-4-carbaldehyde 1b, 4-nitrobenzohydrazide 2c, and
H, Ar–H), 6.73 (s, 1H, –S–CH–N), 4.10 (d, 1H, –CH , J = 16
2
1
3
Hz) and 3.99 (d, 1H, –CH , J = 16 Hz). C NMR (100 MHz,
DMSO-d
2
6
, δ ppm): 167.8, 162.6, 156.09, 147.7, 143.7, 142.9,
1
32.2, 130.02, 129.5, 129.05, 128.6, 126.0, 124.8, 124.4, 57.7
thioglycolic acid 3 in 1 h as a yellow solid with an 83% yield,
+
1
and 35.3. HRMS (ESI-qTOF): calcd for C H N O S [M + H] ,
mp: 248 °C. H NMR (400 MHz, DMSO-d , δ ppm): 12.01 (s,
1
8
14
7
2
6
3
92.0929, found: 392.0933.
.2.2. N-(4-Oxo-2-(tetrazoloij1,5-a]quinolin-4-yl)thiazolidin-
-yl)nicotinamide (4b). The compound 4b was obtained via
cyclocondensation of tetrazoloij1,5-a]quinoline-4-
carbaldehyde 1a, nicotinohydrazide 2b, and thioglycolic acid
1H, –NH), 8.53–8.56 (m, 2H, Ar–H), 7.60–8.07 (m, 6H, Ar–H),
4
6.74 (s, 1H, –S–CH–N–), 3.98 (d, 1H, −CH , J = 16 Hz), 3.87 (d,
2
13
3
the
1H, −CH , J = 16 Hz) and 2.39 (s, 3H, –CH ). C NMR (100
2
3
MHz, DMSO-d
6
, δ ppm): 167.4, 162.9, 157.8, 150.9, 137, 136.5,
132.3, 131.4, 130.8, 127.4, 126.6, 124.9, 124, 58.4, 35.7 and
21.1.
4.2.7. N-(2-(8-Methyltetrazoloij1,5-a]quinolin-4-yl)-4-oxo-
thiazolidin-3-yl)isonicotinamide (4g). The compound 4g was
obtained via the cyclocondensation of 8-methyltetrazoloij1,5-
a]quinoline-4-carbaldehyde 1c, isonicotinohydrazide 2a, and
1
3
in 1 h as a white solid with an 86% yield, mp: 242 °C. H
NMR (400 MHz, DMSO-d , δ ppm): 11.83 (s, 1H, –NH), 8.95
s, 1H, Ar–H), 8.75 (s, 1H, Ar–H), 7.86–8.07 (m, 7H, Ar–H),
6
(
6
4
.86 (s, 1H, –S–CH–N–), 4.12 (d, 1H, −CH
2
, J = 16 Hz) and
1
3
.02 (d, 1H, −CH
2
, J = 16 Hz). C NMR (100 MHz, DMSO-d ,
6
δ ppm): 168.9, 162, 157.6, 149.7, 149.4, 143.4, 139.9, 132.9,
1
thioglycolic acid 3 in 1 h as a white solid with an 86% yield,
1
31.0, 130.9, 129.8, 129.5, 128.0, 125.4, 124.3, 61.9 and 35.6.
.2.3. 4-Nitro-N-(4-oxo-2-(tetrazoloij1,5-a]quinolin-4-yl)thiazolidin-
-yl)benzamide (4c). The compound 4c was obtained via the
mp: 257 °C. H NMR (200 MHz, DMSO-d
6
, δ ppm): 11.76 (s,
4
1H, –NH), 8.74–8.76 (m, 2H, Ar–H), 7.90–7.92 (m, 3H, Ar–H),
7.33.7.57 (m, 4H, Ar–H), 6.74 (s, 1H, –S–CH–N–), 3.98 (d, 1H,
3
cyclocondensation of tetrazoloij1,5-a]quinoline-4-carbaldehyde
a, 4-nitrobenzohydrazide 2c, and thioglycolic acid 3 in 1 h
−CH
3H, –CH
2
, J = 16 Hz), 3.87 (d, 1H, –CH
2
, J = 16 Hz) and 2.33 (s,
1
3
1
3
). C NMR (75 MHz, DMSO-d , δ ppm): 168.6,
6
1
as a yellow solid with an 85% yield, mp: 255 °C. H NMR
400 MHz, DMSO-d , δ ppm): 11.77 (s, 1H, –NH), 8.59–8.65 (m,
H, Ar–H), 8.41–8.43 (m, 2H, Ar–H), 8.17 (s, 1H, Ar–H), 7.85–
.06 (m, 4H, Ar–H), 6.87 (s, 1H, –S–CH–N–), 4.16 (d, 1H,
162.4, 157.0, 143.9, 143.1, 137, 135.8, 132.2, 132.0, 130.7,
130.0, 129, 126.3, 123.0, 59.4, 34.5 and 20.2. HRMS (ESI-
qTOF): calcd for C19
406.1083.
4.2.8. N-(2-(8-Methyltetrazoloij1,5-a]quinolin-4-yl)-4-oxo-
thiazolidin-3-yl)nicotinamide (4h). The compound 4h was
obtained via the cyclocondensation of 8-methyltetrazoloij1,5-
a]quinoline-4-carbaldehyde 1c, nicotinohydrazide 2b, and
thioglycolic acid 3 in 1 h as a white solid with an 83% yield,
mp: 239 °C. H NMR (400 MHz, DMSO-d , δ ppm): 8.64–8.72
(
6
+
2
8
16 7 2
H N O S [M + H] , 406.1086, found:
13
–CH
2
, J = 16 Hz) and 4.09 (d, 1H, –CH
, δ ppm): 167.0, 160.8, 154.1, 150.0, 146.0,
43.8, 140.3, 137.8, 131.5, 129.4, 129.1, 128.0, 126.2, 58.8 and
5.1.
.2.4. N-(2-(9-Methyltetrazoloij1,5-a]quinolin-4-yl)-4-oxo-
2
, J = 16 Hz). C NMR
(100 MHz, DMSO-d
6
1
3
4
1
thiazolidin-3-yl)isonicotinamide (4d). The compound 4d was
obtained via the cyclocondensation of 9-methyltetrazoloij1,5-
a]quinoline-4-carbaldehyde 1b, isonicotinohydrazide 2a, and
6
(m, 2H, Ar–H), 8.19–8.24 (m, 3H, Ar–H), 8.08 (s, 1H, Ar–H),
7.78–7.85 (m, 2H, Ar–H), 6.83 (s, 1H, –S–CH–N–), 4.10 (d, 1H,
–CH , J = 16 Hz), 4.01 (d, 1H, –CH , J = 16 Hz) and 2.48 (s,
thioglycolic acid 3 in 1 h as a white solid with a 90% yield,
2
2
1
13
mp: 245 °C. H NMR (400 MHz, DMSO-d
6
, δ ppm): 12.20
3 6
3H, –CH ). C NMR (100 MHz, DMSO-d , δ ppm): 167.4,
(
s, 1H, –NH), 8.65–8.67 (m, 2H, Ar–H), 7.89 (s, 1H, Ar–H),
162.3, 152.1, 147.8, 146.7, 141.9, 136.4, 133.2, 133.1, 130.1,
129.3, 128.8, 128.6, 124.3, 121.3, 57.0, 37.2 and 21.
4.2.9. N-(2-(8-Methyltetrazoloij1,5-a]quinolin-4-yl)-4-oxo-
thiazolidin-3-yl)-4-nitrobenzamide (4i). The compound 4i was
obtained via the cyclocondensation of 8-methyltetrazoloij1,5-
a]quinoline-4-carbaldehyde 1c, 4-nitrobenzohydrazide 2c, and
7
1
2
1
1
.30–7.58 (m, 5H, Ar–H), 6.73 (s, 1H, –S–CH–N–), 4.08 (d,
H, –CH , J = 12 Hz) and
, J = 16 Hz), 3.9 (d, 1H, −CH
.43 (s, 3H, –CH ). C NMR (100 MHz, DMSO-d , δ ppm):
2
2
1
3
3
6
69.0, 162.6, 157.2, 147.8, 144.2, 143.9, 137.2, 132.2, 130.2,
29.7, 129.3, 126.8, 126.0, 124.5, 59.9, 34.6 and 20.0. HRMS
+
(
ESI-qTOF): calcd for C19
H
16
N
7
O
2
S [M + H] , 406.1086,
thioglycolic acid 3 in 1 h as a yellow solid with an 81% yield,
1
found: 406.1067.
mp: 254 °C. H NMR (400 MHz, DMSO-d , δ ppm): 12.20 (s,
6
4
.2.5. N-(2-(9-Methyltetrazoloij1,5-a]quinolin-4-yl)-4-oxo-
1H, –NH), 8.59–8.61 (m, 2H, Ar–H), 8.34 (s, 1H, Ar–H), 7.95
(s, 1H, Ar–H),7.69–7.75 (m, 2H, Ar–H), 7.09–7.14 (m, 2H, Ar–
thiazolidin-3-yl)nicotinamide (4e). The compound 4e was
obtained via the cyclocondensation of 9-methyltetrazoloij1,5-
a]quinoline-4-carbaldehyde 1b, nicotinohydrazide 2b, and
H), 6.56 (s, 1H, –S–CH–N), 4.09 (d, 1H, –CH , J = 16 Hz), 3.98
2
1
3
2 3
(d, 1H, CH , J = 16 Hz) and 2.40 (s, 3H, –CH ). C NMR (100
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MHz, DMSO-d , δ ppm): 170, 162.3, 153.3, 150.2, 141.0, 138.5,
obtained via the cyclocondensation of 8-methoxytetrazoloij1,5-
a]quinoline-4-carbaldehyde 1e, nicotinohydrazide 2b, and
6
1
5
36.1, 135.6, 129.7, 129.3, 127.8, 126.3, 126.0, 125.7, 122.5,
8.4, 34.6 and 22.5.
thioglycolic acid 3 in 1 h as a pale yellow solid with an 82%
1
4
.2.10. N-(2-(7-Methyltetrazoloij1,5-a]quinolin-4-yl)-4-oxo-
yield, mp: 247 °C. H NMR (400 MHz, DMSO-d , δ ppm):
6
thiazolidin-3-yl)isonicotinamide (4j). The compound 4j was
obtained via the cyclocondensation of 7-methyltetrazoloij1,5-
a]quinoline-4-carbaldehyde 1d, isonicotinohydrazide 2a, and
11.99 (s, 1H, –NH), 8.10–8.13 (m, 2H, Ar–H), 7.92 (s, 1H, Ar–
H), 7.60–7.67 (m, 5H, Ar–H), 6.79 (s, 1H, –S–CH–N–), 4.02 (d,
1H, –CH , J = 16 Hz), 3.91 (d, 1H, CH , J = 16 Hz) and 3.72 (s,
2
2
1
3
thioglycolic acid 3 in 1 h as a white solid with a 90% yield,
3H, –OCH3). C NMR (100 MHz, DMSO-d , δ ppm): 167.5,
6
1
mp: 262 °C. H NMR (400 MHz, DMSO-d
6
, δ ppm): 11.69 (s,
160.7, 153.8, 147.2, 141.9, 135.5, 133.9, 133.4, 131.2, 130.7,
130.2, 129.9, 129.3, 124.4, 121.7, 58.7, 52.5 and 37.2.
4.2.15. N-(2-(8-Methoxytetrazoloij1,5-a]quinolin-4-yl)-4-oxo-
thiazolidin-3-yl)-4-nitrobenzamide (4o). The compound 4o
was obtained via the cyclocondensation of 8-methoxytetrazolo-
ij1,5-a]quinoline-4-carbaldehyde 1e, 4-nitrobenzohydrazide 2c,
1
8
H, –NH), 8.80–8.83 (m, 2H, Ar–H), 8.18 (s, 1H, Ar–H), 7.02–
.04 (m, 2H, Ar–H), 7.49 (s, 1H, Ar–H), 7.32–7.34 (m, 2H, Ar–
, J = 16 Hz),
H), 6.91 (s, 1H, –S–CH–N–), 4.02 (d, 1H, –CH
.89 (d, 1H, –CH , J = 16 Hz) and 2.45 (s, 3H, –CH ).
2
1
3
3
C
2
3
NMR (100 MHz, DMSO-d , δ ppm): 166.9, 161.4, 155.8, 149.4,
6
1
1
37.5, 135.8, 132.3, 129, 127.2, 126.4, 125.8, 125.2, 124.4,
22.2, 57.0, 36.8 and 21.2.
and thioglycolic acid 3 in 1 h as a yellow solid with an 81%
1
yield, mp: 256 °C. H NMR (400 MHz, DMSO-d , δ ppm):
6
4
.2.11. N-(2-(7-Methyltetrazoloij1,5-a]quinolin-4-yl)-4-oxo-
12.00 (s, 1H, –NH), 8.49–8.59 (m, 4H, Ar–H), 8.04 (s, 1H, Ar–
H), 7.71 (s, 1H, Ar–H), 7.37–7.40 (m, 1H, Ar–H), 7.20–7.23 (m,
thiazolidin-3-yl)nicotinamide (4k). The compound 4k was
obtained via the cyclocondensation of 7-methyltetrazoloij1,5-
a]quinoline-4-carbaldehyde 1d, nicotinohydrazide 2b, and
thioglycolic acid 3 in 1 h as a white solid with an 84% yield,
mp: 249 °C. H NMR (400 MHz, DMSO-d , δ ppm ): 11.69 (s,
1H, Ar–H), 6.85 (s, 1H, –S–CH–N–), 4.02 (d, 1H, –CH , J = 16
2
Hz), 3.91 (d, 1H, –CH
C NMR (100 MHz, DMSO-d , δ ppm): 168.0, 161.0, 154.0,
2
, J = 16 Hz) and 2.24 (s, 3H, –OCH
3
),
1
3
6
1
150.0, 146.9, 141.0, 136.8, 132.9, 129.2, 127.8, 126.5, 125.9,
123.9, 122.4, 121.0, 58.6, 54.6 and 35.1.
6
1
H, –NH), 8.84 (s, 2H, Ar–H), 8.55 (s, 1H, Ar–H), 8.02–8.11
(
6
1
m, 2H, Ar–H), 7.49 (s, 1H, Ar–H), 7.32–7.34 (m, 2H, Ar–H),
4.2.16. N-(2-(7-Methoxytetrazoloij1,5-a]quinolin-4-yl)-4-oxo-
thiazolidin-3-yl)isonicotinamide (4p). The compound 4p was
obtained via the cyclocondensation of 7-methoxytetrazoloij1,5-
a]quinoline-4-carbaldehyde 1f, isonicotinohydrazide 2a, and
.91 (s, 1H, –S–CH–N–), 4.08 (d, 1H, –CH , J = 16 Hz), 3.98 (d,
2
1
3
H, –CH
2
, J = 16 Hz) and 2.45 (s, 3H, –CH
3
). C NMR (100
MHz, DMSO-d
6
, δ ppm): 166.4, 162.3, 152.9, 149.3, 147.6,
1
6
41.9, 135.8, 133.3, 133.2, 132.2, 130.8, 130.1, 124.4, 122.0,
0.0, 37.2 and 20.7.
thioglycolic acid 3 in 1 h as a pale yellow solid with an 84%
1
yield, mp: 260 °C. H NMR (400 MHz, DMSO-d
6
, δ ppm):
4
.2.12. N-(2-(7-Methyltetrazoloij1,5-a]quinolin-4-yl)-4-oxo-
8.68–8.70 (m, 2H, Ar–H), 7.96 (s, 1H, Ar–H), 7.77–7.79 (m,
2H, Ar–H), 7.38 (s, 1H, Ar–H), 7.08–7.10 (m, 2H, Ar–H), 6.73
thiazolidin-3-yl)-4-nitrobenzamide (4l). The compound 4l was
obtained via the cyclocondensation of 7-methyltetrazoloij1,5-
a]quinoline-4-carbaldehyde 1d, 4-nitrobenzohydrazide 2c, and
(s, 1H, –S–CH–N–), 4.10 (d, 1H, –CH
2
, J = 16 Hz), 4.00 (d, 1H,
1
3
CH , J = 16 Hz) and 3.72 (s, 3H, –OCH ). C NMR (100 MHz,
2
3
thioglycolic acid 3 in 1 h as a yellow solid with an 82% yield,
DMSO-d , δ ppm): 168.5, 162.0, 156.1, 148.4, 141.7, 137.2,
6
1
mp: 240 °C. H NMR (400 MHz, DMSO-d
6
, δ ppm): 8.90–8.96
132.9, 132.5, 132.0, 129.0, 131.8, 131.3, 126.8, 60.6, 54.9 and
+
(m, 3H, Ar–H), 8.47 (s, 1H, Ar–H), 8.12–8.24 (m, 2H, Ar–H),
34.9. HRMS (ESI-qTOF): calcd for C19
H
16
N
7
O
3
S [M + H] ,
8
.89 (m, 1H, Ar–H), 7.69 (s, 1H, Ar–H), 6.89 (s, 1H, –S–CH–
, J = 16 Hz), 4.10 (d, 1H, –CH , J = 16
). C NMR (100 MHz, DMSO-d , δ
ppm): 163.6, 160.2, 152.6, 149, 148.7, 143.2, 135.9, 132.7,
30.8, 130.8, 129.8, 129.3, 127.4, 125.2, 124.0, 115.6, 61.9,
5.6 and 20.9.
422.1035, found: 422.1044.
N–), 4.17 (d, 1H, –CH
Hz) and 3.00 (s, 3H, –CH
2
2
4.2.17. N-(2-(7-Methoxytetrazoloij1,5-a]quinolin-4-yl)-4-oxo-
thiazolidin-3-yl)nicotinamide (4q). The compound 4q was
obtained via the cyclocondensation of 7-methoxytetrazoloij1,5-
a]quinoline-4-carbaldehyde 1f, nicotinohydrazide 2b, and
1
3
3
6
1
3
thioglycolic acid 3 in 1 h as a pale yellow solid with an 82%
1
4
.2.13. N-(2-(8-Methoxytetrazolo[1,5-a]quinolin-4-yl)-4-oxo-
yield, mp: 261 °C. H NMR (400 MHz, DMSO-d , δ ppm):
6
thiazolidin-3-yl)isonicotinamide (4m). The compound 4m was
obtained via the cyclocondensation of 8-methoxytetrazoloij1,5-
a]quinoline-4-carbaldehyde 1e, isonicotinohydrazide 2a, and
12.10 (s, 1H, –NH), 8.77 (s, 1H, Ar–H), 8.49 (s, 1H, Ar–H),
8.25–8.27 (m, 2H, Ar–H), 7.74–7.90 (m, 3H, Ar–H), 7.24 (s,
1H, Ar–H), 6.59 (s, 1H, –S–CH–N–), 4.23 (d, 1H, –CH , J = 16
2
thioglycolic acid 3 in 1 h as a pale yellow solid with an 85%
Hz), 4.13 (d, 1H, –CH
C NMR (100 MHz, DMSO-d , δ ppm): 167.5, 161.3, 153.6,
2
, J = 16 Hz) and 3.78 (s, 3H, –OCH
3
).
1
13
yield, mp: 258 °C. H NMR (400 MHz, DMSO-d
6
, δ ppm): 11.99
6
(
7
s, 1H, –NH), 8.10–8.13 (m, 2H, Ar–H), 7.92 (s, 1H, Ar–H), 7.60–
149.2, 146.6, 141.9, 135.8, 133.9, 133.4, 132.2, 131.4, 130.8,
130.7, 129.9, 124.4, 121.6, 59.0, 52.6 and 37.2.
4.2.18. N-(2-(7-Methoxytetrazoloij1,5-a]quinolin-4-yl)-4-oxo-
thiazolidin-3-yl)-4-nitrobenzamide (4r). The compound 4r was
obtained via the cyclocondensation of 7-methoxytetrazoloij1,5-
a]quinoline-4-carbaldehyde 1f, 4-nitrobenzohydrazide 2c, and
.67 (m, 5H, Ar–H), 6.79 (s, 1H, –S–CH–N–), 4.02 (d, 1H, –CH
, J = 16 Hz) and 3.72 (s, 3H,
OCH3). C NMR (100 MHz, DMSO-d , δ ppm): 170.7, 162.9,
2
,
J = 16 Hz), 3.91 (d, 1H, –CH
–
2
1
3
6
1
1
58.9, 147.7, 143.2, 142.9, 135.4, 133.5, 131.6, 130.4, 129.7,
29.3, 125.6, 123.3, 60.4, 55.9 and 34.7.
4
.2.14. N-(2-(8-Methoxytetrazoloij1,5-a]quinolin-4-yl)-4-oxo-
thioglycolic acid 3 in 1 h as a yellow solid with an 80% yield,
1
thiazolidin-3-yl)nicotinamide (4n). The compound 4n was
mp: 253 °C. H NMR (400 MHz, DMSO-d
6
, δ ppm): 11.95 (s,
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1
7
H, –NH), 8.49–8.59 (m, 2H, Ar–H), 8.13 (s, 1H, Ar–H), 7.77–
.79 (m, 1H, Ar–H), 7.73 (s, 1H, Ar–H), 7.45–7.47 (m, 1H, Ar–
lated culture was added in to each well of a 96-well plate
containing the compounds to be tested. Optical density for
each plate was measured at 620 nm after 8 h for the Gram-
negative bacteria and after 12 h for the Gram-positive
bacteria.
H), 7.28–7.30 (m, 1H, Ar–H), 6.55 (s, 1H, –S–CH–N–), 4.07 (d,
H, –CH , J = 16 Hz), 3.98 (d, 1H, –CH , J = 16 Hz) and 3.72
1
2
2
1
3
(s, 3H, –OCH3), C NMR (100 MHz, DMSO-d , δ ppm): 166.5,
6
1
1
61.2, 153.9, 149.3, 145.4, 137.6, 136.6, 132.7, 129.0, 126.1,
24.8, 123.5, 122.4, 117.0, 60.8, 55.5 and 35.9.
4.3.5. Molecular docking. Experimental observations were
followed with the molecular docking studies, in which the
most active compounds 4a, 4d, 4g, 4j, 4m, 4n, and 4p were
docked against mycobacterial enoyl reductase (InhA) to gain
insight into the mode of binding and the degree of affinity.
The Glide (Grid-Based Ligand Docking with Energetics) pro-
4
.3. Pharmacology
4
.3.1. Antitubercular assay. All the synthetic compounds
4
8
were screened for their in vitro activity against M. tuberculosis
MTB H37Ra (ATCC 25177) and M. bovis BCG (ATCC 35743)
using a two-fold dilution technique, in order to determine
the actual minimum inhibitory concentration (MIC). Activity
against MTB was determined through the XTT reduction
menadione assay (XRMA), reading absorbance at 470 nm as
gram incorporated in the Schrödinger molecular modeling
package was used to dock these 4-thiazolidinone derivatives
into the active site of the mycobacterial InhA enzyme. Glide is
an interactive molecular graphics program for performing
molecular docking calculations, visualizing ligand–receptor
interactions, and for identification of the probable binding
site for the molecules.
The enzyme structure (InhA) was prepared for docking
using the Protein Preparation Wizard in Glide, which involved
deleting all the crystallographically observed water (as no
interaction between the protein and any water molecules was
observed to be conserved), assigning the correct bond orders,
adding missing hydrogen atoms corresponding to pH 7.0
(considering the appropriate ionization states for the acidic
as well as the basic amino acid residues), and assigning the
appropriate charge and protonation state to the structure. Fi-
nally, the enzyme structure was subjected to energy minimi-
zation (to relieve the steric clashes among the residues due
to the addition of hydrogen atoms) using the OPLS-2005
force-field until the average root-mean-square deviation
(RMSD) of the non-hydrogen atoms reached 0.3 Å.
4
0
per the protocol developed earlier. The nitrate reductase
NR) assay was performed to estimate the inhibition of M.
(
4
4
bovis BCG by the compounds. Absorbance for the NR assay
was measured at 540 nm. In vitro activity against MTB and
M. bovis BCG at active (8 days) and dormant (12 days) stages
was performed using the XRMA and NR assay, respectively,
as described above. Percentage inhibition was calculated
using the following formula:
%
inhibition = [(control − CMP)/(control − blank)] × 100
where ‘control’ is the activity of the mycobacteria without the
compounds, ‘CMP’ is the activity of mycobacteria in the pres-
ence of the compounds, and ‘blank’ is the activity of the cul-
ture medium without mycobacteria.
4
.3.2. Cytotoxicity assay. To check the selectivity, active
The 3D structures of the 4-thiazolidinone derivatives were
sketched with the build panel in Maestro and optimized
using the ligprep module, which performs the addition of hy-
drogens, adjusts the realistic bond lengths and angles, cor-
rects the chiralities, and generates a number of low energy
3D structures, with various ionization states, tautomers,
stereochemistries, and ring conformations, from each input
molecule. The partial charges were ascribed using the OPLS-
2005 force-field, and finally, each of these structures was
subjected to energy minimization until their average RMSD
reached 0.001 Å.
After ensuring that the protein and ligands were in the
correct form, the shape and properties of the active site of
the InhA enzyme were characterized and setup for the
docking study using the receptor grid generation panel in
Glide, which uses two cubical boxes with a common centroid
to organize the calculations: a larger enclosing and a smaller
binding box. The receptor grid was generated by defining a
10 × 10 × 10 Å box that was centered on the geometric cen-
troid of the native ligand in the crystal complex to allow the
ligands to explore a sufficiently large region of the enzyme
structure. The native ligand was used as the reference as it
signifies the binding sites of a molecule with respect to the
target.
derivatives 4a, 4d, 4g, 4j, 4m, and 4p were assayed for their
cytotoxic effects in three different cell lines MCF-7, A549,
and HCT 116 using the MTT assay (Table 3). The cell
lines were maintained under standard cell culture condi-
tions under 5% CO at 37 °C in a 95% air humidified envi-
4
5
2
ronment. Each concentration was tested in duplicate in a
single experiment. GI /GI values were calculated using
50
90
OriginPro Software.
.3.3. Selectivity index. The selectivity index (SI) was calcu-
lated by dividing the 50% growth inhibition concentration
GI ) for the cell lines (MCF-7, A549, and HCT 116) by the
4
(
5
0
4
6
MIC for in vitro activity against dormant MTB and BCG.
.3.4. Antibacterial activity. All bacterial cultures were first
4
grown in Lysogeny Broth (LB) media at 37 °C at 180 RPM.
Once the culture reached 1 OD, it was used for the anti-
bacterial assay. Bacterial strains E. coli (NCIM 2688) and P.
fluorescens (NCIM 2036) as Gram-negative and B. subtilis
(
NCIM 2079) and S. aureus (NCIM 2010) as Gram-positive
were obtained from NCIM (NCL, Pune) and were grown in
Luria Burtony medium from Hi-media, India. The assay was
performed in 96-well plates after 8 h and 12 h for the Gram-
negative and Gram-positive bacteria, respectively. 0.1% of 1
4
7
OD culture at 620 nm was used for screening. 0.1% inocu-
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The optimized ligands were docked flexibly into the en-
zyme structures using the extra precision (i.e., GlideXP) scor-
ing function to estimate the protein–ligand binding affinities.
The Glide Extra-Precision (XP) scoring function is equipped
with force-field-based parameters accounting for contribu-
tions from the electrostatic and steric interactions energies
as well as solvation and repulsive interactions along with hy-
drophobic, hydrogen bonding, and metal–ligand interactions
all incorporated in the empirical energy functions. The out-
put files generated in the form of the docking poses of the li-
gands were visualized and analyzed for the key elements of
interaction with the enzyme using the Maestro's Pose Viewer
utility.
Secci, Eur. J. Med. Chem., 2016, 107, 82; (d) D. Secci, S.
Carradori, B. Bizzarri, P. Chimenti, C. D. Monte, A. Mollica,
D. Rivanera, A. Zicari, E. Mari, G. Zengin and A. Aktumsek,
Eur. J. Med. Chem., 2016, 117, 144.
11 D. P. Gouvea, F. A. Vasconcellos, G. A. Berwaldt, A. C. P. S.
Neto, G. Fischer, R. P. Sakata, W. P. Almeida and W. Cunico,
Eur. J. Med. Chem., 2016, 118, 259.
12 O. Unsal-Tan, K. Ozadali, K. Piskin and A. Balkan, Eur. J.
Med. Chem., 2012, 57, 59.
13 A. Srinivas, A. Nagaraj and C. S. Reddy, Eur. J. Med. Chem.,
2010, 45, 2353.
14 V. Murugesan, V. S. Tiwari, R. Saxena, R. Tripathi, R.
Paranjape, S. Kulkarni, N. Makwana, R. Suryawanshi and
S. B. Katti, Bioorg. Med. Chem., 2011, 19, 6919.
1
1
1
5 C. M. Bhalgat, P. V. Darda, K. G. Bothara, S. V. Bhandari,
Acknowledgements
J. Gandhi and B. Ramesh, Eur. J. Med. Chem., 2014, 76,
5
80.
The authors D. D. S. and M. H. S. are very much grateful to
the Council of Scientific and Industrial Research (CSIR), New
Delhi for the award of senior research fellowship. Authors are
also thankful to the Head, Department of Chemistry, Dr.
Babasaheb Ambedkar Marathwada University, for providing
laboratory facility. We also thank Schrödinger Inc. for provid-
ing the Demo license of Schrödinger Suite and especially
Craig Coel for delivering the valuable support that has tre-
mendously helped in this study.
6 A. P. G. Nikalje, A. N. Shaikh, S. I. Shaikh, F. A. K. Khan,
J. N. Sangshetti and D. B. Shinde, Bioorg. Med. Chem. Lett.,
2
014, 24, 5558.
7 (a) K. S. S. Kumar, A. Hanumappa, M. Vetrivel, M. Hegde,
Y. R. Girish, T. R. Byregowda, S. Rao, S. C. Raghavan and
K. S. Rangappa, Bioorg. Med. Chem. Lett., 2015, 25, 3616; (b)
F. E. Onen-Bayram, K. Buran, I. Durmaz, B. Berk and R.
Cetin-Atalay, Med. Chem. Commun., 2015, 6, 90.
1
8 P. Joshi, C. Anderson, H. Binch, S. Hadida, S. Yoo, D.
Bergeron, C. Decker, E. terHaar, J. Moore, M. Garcia-
Guzman and A. Termin, Bioorg. Med. Chem. Lett., 2014, 24,
Notes and references
8
45.
1
2
C. Dye and B. G. Williams, Science, 2010, 328, 856.
WHO Global Tuberculosis Report 2014; World Health
Organization: Geneva, 2014; http://www.who.int/tb/
publications/global report/en/.
19 X. Zhang, X. Li, D. Li, G. Qua, J. Wang, P. M. Loiseau and X.
Fan, Bioorg. Med. Chem. Lett., 2009, 19, 6280.
20 G. Caklr, I. Kucukguzel, R. Guhamazumder, E. Tatar, D.
Manvar, A. Basu, B. A. Patel, J. Zia, T. T. Talele and N.
Kaushik-Basu, Arch. Pharm., 2015, 348, 10.
21 S. Raza, S. P. Srivastava, D. S. Srivastava, A. K. Srivastava, W.
Haq and S. B. Katti, Eur. J. Med. Chem., 2013, 63, 611.
22 R. A. Rane, N. U. Sahu and C. P. Shah, Bioorg. Med. Chem.
Lett., 2012, 22, 7131.
23 O. M. Abdelhafez, K. M. Amin, H. I. Ali, M. M. Abdalla and
R. Z. Batran, J. Med. Chem., 2012, 55, 10424.
24 (a) A. B. Patel, K. H. Chikhalia and P. Kumari, Eur. J. Med.
Chem., 2014, 79, 57; (b) T. S. Chitre, K. D. Asgaonkar, P. B.
Miniyar, A. B. Dharme, M. A. Arkile, A. Yeware, D. Sarkar,
V. M. Khedkar and P. C. Jha, Bioorg. Med. Chem. Lett.,
2016, 26, 2224; (c) N. B. Patel, H. R. Patel, F. M. Shaikh and
D. Rajani, Med. Chem. Res., 2014, 23, 1360; (d) A. C.
Tripathi, S. Gupta, G. N. Fatima, P. K. Sonar, A. Verma and
S. K. Saraf, Eur. J. Med. Chem., 2014, 72, 52 and references
cited therein; (e) A. K. Jain, A. Vaidya, V. Ravichandran, S. K.
Kashaw and R. K. Agrawal, Bioorg. Med. Chem. Lett.,
2012, 20, 3378 and references cited therein; ( f ) S. A. E.
Bialy, M. M. Nagy and H. M. Abdel-Rahman, Arch. Pharm.,
2011, 344, 821.
3
4
S. Loewenberg, Lancet, 2012, 379, 205.
World Health Organization, Treatment of tuberculosis:
Guidelines for national programmes, WHO Press, Geneva,
Switzerland, 4th edn, 2009.
5
6
A. Zumla, P. Nahid and S. T. Cole, Nat. Rev. Drug Discovery,
2
013, 5, 388.
A. I. Zumla, S. H. Gillespie, M. Hoelscher, P. P. Philips, S. T.
Cole, I. Abubakar, T. D. McHugh, M. Schito, M. Maeurer and
A. J. Nunn, Lancet Infect. Dis., 2014, 4, 327.
CDC. Global routine vaccination coverage, 2011, MMWR
Morb Mortal Wkly Rep., 2012, vol. 61, p. 883.
7
8
9
R. J. Rees, Br. Med. Bull., 1969, 25, 183.
World Health Organization. Meeting of the strategic advisory
group of expertson immunization, April 2014-conclusions
and recommendations. Wkly Epi-demiol Rec., 2014, vol. 89,
p. 221.
1
0 (a) D. N. Pansare, N. A. Mulla, C. D. Pawar, V. R. Shende and
D. B. Shinde, Bioorg. Med. Chem. Lett., 2014, 24, 3569; (b) E.
Pitta, E. Tsolaki, A. Geronikaki, J. Petrovi, J. Glamoclija, M.
Sokovi, E. Crespan, G. Maga, S. S. Bhuniade and A. K.
Saxenade, Med. Chem. Commun., 2015, 6, 319; (c) C. D.
Monte, S. Carradori, B. Bizzarri, A. Bolasco, F. Caprara, A.
Mollica, D. Rivanera, E. Mari, A. Zicari, A. Akdemir and D.
25 A. Quemard, J. C. Sacchettini, A. Dessen, C. Vilcheze, R.
Bittman, W. R. Jacobs and J. S. Blanchard, Biochemistry,
1995, 34, 8235.
This journal is © The Royal Society of Chemistry 2016
Med. Chem. Commun.

View Article Online
Research Article
MedChemComm
2
6 (a) D. Kumar, G. Khare, Beena, S. Kidwai, A. K. Tyagi, R.
Singh and D. S. Rawat, Med. Chem. Commun., 2015, 6, 131;
2076; (h) R. Bhupathi, B. Madhu, B. R. Devi, Ch. V. R.
Reddy and P. K. Dubey, J. Heterocycl. Chem., DOI: 10.1002/
jhet.2506.
(
b) N. Nayak, J. Ramprasad and U. Dalimba, Bioorg. Med.
Chem. Lett., 2015, 25, 5540; (c) D. Kumar, Beena, G. Khare, S.
Kidwai, A. K. Tyagi, R. Singh and D. S. Rawat, Eur. J. Med.
Chem., 2014, 81, 301.
39 (a) D. D. Subhedar, M. H. Shaikh, M. Arkile, A. Yeware, D.
Sarkar and B. B. Shingate, Bioorg. Med. Chem. Lett.,
2016, 26, 1704; (b) D. D. Subhedar, M. H. Shaikh,
F. A. K. Khan, J. N. Sangshetti, V. M. Khedkar and B. B.
Shingate, New J. Chem., 2016, 40, 3047; (c) M. H. Shaikh,
D. D. Subhedar, M. Arkile, V. M. Khedkar, N. Jadhav, D.
Sarkar and B. B. Shingate, Bioorg. Med. Chem. Lett.,
2016, 26, 561; (d) M. H. Shaikh, D. D. Subhedar, L.
Nawale, D. Sarkar, F. A. K. Khan, J. N. Sangshetti and
B. B. Shingate, Med. Chem. Commun., 2015, 6, 1104; (e)
D. D. Subhedar, M. H. Shaikh, L. Nawale, A. Yeware, D.
Sarkar and B. B. Shingate, Res. Chem. Intermed., DOI:
10.1007/s11164-016-2484-0; ( f ) M. H. Shaikh, D. D.
Subhedar, F. A. K. Khan, J. N. Sangshetti and B. B.
Shingate, Res. Chem. Intermed., 2016, 42, 5115; (g) M. H.
Shaikh, D. D. Subhedar, F. A. K. Khan, J. N. Sangshetti,
L. Nawale, M. Arkile, D. Sarkar and B. B. Shingate,
J. Heterocycl. Chem., DOI: 10.1002/jhet.2598; (h) M. H.
Shaikh, D. D. Subhedar, F. A. K. Khan, J. N. Sangshetti
and B. B. Shingate, Chin. Chem. Lett., 2016, 27, 295; (i)
M. H. Shaikh, D. D. Subhedar, B. B. Shingate, F. A. K.
Khan, J. N. Sangshetti, V. M. Khedkar, L. Nawale, D.
Sarkar, G. R. Navale and S. S. Shinde, Med. Chem. Res.,
2016, 25, 790.
2
2
7 S. Jaju, M. Palkar, V. Maddi, P. Ronad, S. Mamledesai, D.
Satyanarayana and M. Ghatole, Arch. Pharm., 2009, 342,
7
23.
8 (a) C. B. Sangani, J. A. Makawana, Y. T. Duan, Y. Yin, S. B.
Teraiya, N. J. Thumar and H. L. Zhu, Bioorg. Med. Chem.
Lett., 2014, 24, 4472; (b) A. R. Ellanki, A. Islam, V. S. Rama,
R. P. Pulipati, D. Rambabu, G. R. Krishna, C. M. Reddy, K.
Mukkanti, G. R. Vanaja, A. M. Kalle, K. S. Kumar and M. Pal,
Bioorg. Med. Chem. Lett., 2012, 22, 3455; (c) A. A. Bekhit,
O. A. El-Sayed, T. A. K. Al-Allaf, H. Y. Aboul-Enein, M. Kunhi,
S. M. Pulicat, K. Al-Hussain, F. Al-Khodairy and J. Arif, Eur. J.
Med. Chem., 2004, 39, 499.
9 (a) A. A. Bekhit, O. A. El-Sayed, E. Aboulmagd and J. Y. Park,
Eur. J. Med. Chem., 2004, 39, 249; (b) S. S. Sonar, S. A.
Sadaphal, R. U. Pokalwar, B. B. Shingate and M. S. Shingare,
J. Heterocycl. Chem., 2010, 47, 441.
2
3
0 A. H. Kategaonkar, R. U. Pokalwar, S. S. Sonar, V. U. Gawali,
B. B. Shingate and M. S. Shingare, Eur. J. Med. Chem.,
2
010, 45, 1128.
3
1 (a) A. H. Kategaonkar, V. B. Labade, P. V. Shinde, A. H.
Kategaonkar, B. B. Shingate and M. S. Shingare, Monatsh.
Chem., 2010, 141, 787; (b) D. C. Mungra, M. P. Patel and
R. G. Patel, ARKIVOC, 2009, 14, 64.
40 (a) A. Khan, S. Sarkar and D. Sarkar, Int. J. Antimicrob.
Agents, 2008, 32, 40; (b) U. Singh, S. Akhtar, A. Mishra and
D. Sarkar, J. Microbiol. Methods, 2011, 84, 202; (c) S. Sarkar
and D. Sarkar, J. Biomol. Screening, 2012, 17, 966.
3
3
3
3
2 M. Shekarchi, M. B. Marvasti, M. Sharifzadeh and A. Shafiee,
Iran. J. Pharm. Res., 2005, 1, 33.
3 A. Adhikari, B. Kalluraya, K. V. Sujith, K. Gouthamchandra
and R. Mahmood, J. Adv. Res., 2012, 3, 325.
4 D. C. Mungra, H. G. Kathrotiya, N. K. Ladani, M. P. Patel
and R. G. Patel, Chin. Chem. Lett., 2012, 23, 1367.
5 N. Isambert, M. M. S. Duque, J. C. Plaquevent, Y. Genisson,
J. Rodriguez and T. Constantieux, Chem. Soc. Rev., 2011, 40,
41 (a) A. A. van de Loosdrecht, R. H. Beelen, G. J.
Ossenkoppele, M. G. Broekhoven and M. M. Langenhuijsen,
J. Immunol. Methods, 1994, 174, 311; (b) M. C. Alley, D. A.
Scudiere, A. Monks, M. L. Hursey, M. J. Czerwinski, D. L.
Fine, B. J. Abbott, J. G. Mayo, R. H. Shoemaker and M. R.
Boyd, Cancer Res., 1988, 48, 589.
1
347.
42 (a) R. C. Hartkoorn, B. Chandler, A. Owen, S. A. Ward,
S. B. Squire, D. J. Back and S. H. Khoo, Tuberculosis,
2007, 87, 248; (b) V. P. Bagla, L. J. McGaw, E. E.
Elgorashi and J. N. Eloff, BMC Complementary Altern.
Med., 2014, 14, 383; (c) M. Protopopova, C. Hanrahan, B.
Nikonenko, R. Samala, P. Chen, J. Gearhart, L. Einck and
C. A. Nacy, J. Antimicrob. Chemother., 2005, 56, 968; (d) I.
Orme, J. Secrist, S. Anathan, C. Kwong, J. Maddry and R.
Reynolds, Antimicrob. Agents Chemother., 2001, 7, 1943; (e)
M. Poggi, R. Barroso, A. J. Costa-Filho, H. B. Barros, F.
Pavan, C. Q. Leite, D. Gambino and M. H. Torre, J. Mex.
Chem. Soc., 2013, 57, 198.
3
6 M. A. P. Martins, C. P. Frizzo, A. Z. Tier, D. N. Moreira, N.
Zanatta and H. G. Bonacorso, Chem. Rev., 2014, 114, PR1
and references cited therein.
7 A. G. Ying, L. Liu, G. F. Wu, G. Chen, X. Z. Chen and W. D.
Ye, Tetrahedron Lett., 2009, 50, 1653.
8 DBUH][OAc] catalyzed organic transformations, see: (a) S. H.
Jayaprakash, B. S. Krishna, S. S. Sudha, N. B. Reddy, P.
Sreelakshmi, K. M. K. Reddy and C. S. Reddy, Synth.
Commun., 2015, 45, 2083; (b) X. T. Cao, P. F. Zhang and
H. Zheng, New J. Chem., DOI: 10.1039/c6nj00322b; (c)
H. R. Shaterian and M. Mohammadnia, J. Mol. Liq.,
3
3
2
013, 177, 353; (d) H. R. Shaterian and M.
43 C. Vilcheze, H. R. Morbidoni, T. R. Weisbrod, H. Iwamoto,
M. Kuo, J. C. Sacchettini and W. R. Jacobs Jr., J. Bacteriol.,
2000, 182, 4059.
44 A. Khan and D. Sarkar, J. Microbiol. Methods, 2008, 73, 62.
45 (a) T. Mosmann, J. Immunol. Methods, 1983, 65, 55; (b)
G. Ciapetti, E. Cenni, L. Pratelli and A. Pizzoferrato,
Biomaterials, 1993, 14, 359.
Mohammadnia, J. Mol. Liq., 2012, 173, 55; (e) H. Singh,
J. Sindhu, J. M. Khurana, C. Sharma and K. R. Aneja,
Eur. J. Med. Chem., 2014, 77, 145; ( f ) J. Hu, J. Ma, Z.
Zhang, Q. Zhu, H. Zhou, W. Lu and B. Han, Green
Chem., 2015, 17, 1219; (g) B. Yu, H. Zhang, Y. Zhao, S.
Chen, J. Xu, L. Hao and Z. Liu, ACS Catal., 2013, 3,
Med. Chem. Commun.
This journal is © The Royal Society of Chemistry 2016

View Article Online
MedChemComm
Research Article
4
6 (a) V. Kuete, Planta Med., 2010, 76, 1479; (b) X. Luo, D. Pires,
J. A. Ainsa, B. Gracia, N. Duarte, S. Mulhovo, E. Anes and
M. J. U. Ferreira, J. Ethnopharmacol., 2013, 146, 417; (c) L. L.
Gundersen, J. Nissen-Meyer and B. Spilsberg, J. Med. Chem.,
47 R. Singh, L. U. Nawale, M. Arkile, U. U. Shedbalkar, S. A.
Wadhwani, D. Sarkar and B. A. Chopade, Int. J. Antimicrob.
Agents, 2015, 46, 183.
48 R. A. Friesner, R. B. Murphy, M. P. Repasky, L. L. Frye, J. R.
Greenwood, T. A. Halgren, P. C. Sanschagrin and D. T. Mainz,
J. Med. Chem., 2006, 49, 6177 and references cited therein.
2
002, 45, 1383; (d) K. K. Sivakumar and A. Rajasekaran, Int.
J. Drug Des. Discovery, 2013, 4, 1065.
This journal is © The Royal Society of Chemistry 2016
Med. Chem. Commun.