A green synthesis of quinoline-4-carboxylic derivatives using p-toluenesulfonic acid as an efficient organocatalyst under microwave irradiation and their docking, molecular dynamics, ADME-Tox and biological evaluation

Article abstract of DOI:10.1002/jhet.3848

P-Toluenesulfonic acid, being an efficient, nonhazardous, and fast accessible organocatalyst, was used for the preparation of quinoline-4-carboxylic acid derivatives via a one-pot three-component reaction of aromatic benzaldehyde, substituted aniline, and pyruvic acid under microwave irradiation. After completion of the reaction, the pure products were isolated by column chromatography. Here, to achieve the desired synthesis, various catalytic and solvent conditions were applied to perform a comparison study. We are using higher yield, simple work-up process, avoiding the use of hazardous organic solvents, short reaction time and higher advantages of the present protocol in the study. Biological activities of synthesized compounds were tested against various antibacterial, antifungal, antimalarial, and antituberculosis strains. Compounds 4a and 4c (MIC 50 μg/mL) and compounds 4d and 4n (MIC 62.5 μg/mL) were found active against the Escherichia coli strain, compounds 4c and 4p (MIC 25 μg/mL) were found active against the Staphylococcus aureus strain, and compounds 4c and 4d were found active against the Plasmodium falciparum strain. Molecular docking revealed that ligands and proteins fitted exactly in the binding pocket and had significant correlation with the biological activity. We have also tested molecular dynamics and ADME-Tox parameters for the synthesized compounds.

Full text of DOI:10.1002/jhet.3848

Received: 29 July 2019
DOI: 10.1002/jhet.3848
Revised: 12 October 2019
Accepted: 19 November 2019
A R T I C L E
A green synthesis of quinoline-4-carboxylic derivatives
using p-toluenesulfonic acid as an efficient organocatalyst
under microwave irradiation and their docking, molecular
dynamics, ADME-Tox and biological evaluation
Dhaval B. Patel1 | Dhanji P. Rajani2 | Smita D. Rajani2 | Hitesh D. Patel1
1Department of Chemistry, School of
Abstract
Sciences, Gujarat University, Ahmedabad,
India
P-Toluenesulfonic acid, being an efficient, nonhazardous, and fast accessible
organocatalyst, was used for the preparation of quinoline-4-carboxylic acid
derivatives via a one-pot three-component reaction of aromatic benzaldehyde,
substituted aniline, and pyruvic acid under microwave irradiation. After com-
pletion of the reaction, the pure products were isolated by column chromatog-
raphy. Here, to achieve the desired synthesis, various catalytic and solvent
conditions were applied to perform a comparison study. We are using higher
yield, simple work-up process, avoiding the use of hazardous organic solvents,
short reaction time and higher advantages of the present protocol in the study.
Biological activities of synthesized compounds were tested against various
antibacterial, antifungal, antimalarial, and antituberculosis strains. Com-
pounds 4a and 4c (MIC 50 μg/mL) and compounds 4d and 4n (MIC 62.5 μg/
mL) were found active against the Escherichia coli strain, compounds 4c and
4p (MIC 25 μg/mL) were found active against the Staphylococcus aureus strain,
and compounds 4c and 4d were found active against the Plasmodium
falciparum strain. Molecular docking revealed that ligands and proteins fitted
exactly in the binding pocket and had significant correlation with the biologi-
cal activity. We have also tested molecular dynamics and ADME-Tox parame-
ters for the synthesized compounds.
2Microcare Laboratory and Tuberculosis
Research Centre, Surat, India
Correspondence
Hitesh D. Patel, Department of Chemistry,
School of Sciences, Gujarat University,
Ahmedabad, Gujarat, India.
Email: drhiteshpatel1@gmail.com
Funding information
GUJCOST, Grant/Award Number:
MRP/2015-16/2599
1 | INTRODUCTION
high yield and other advantages over conventional syn-
thesis methods.[1]Therefore, synthesis of designed reac-
Recently, the expansion of green protocols, which aid in the
synthesis of products that are environmentally benign and
pollution free, has received substantial levels of consideration
because the chemical industry is increasingly moving toward
greener unit processes. Method development is a very impor-
tant step for the synthesis, and it may reduced time and cost
of the synthesized products. At this time, multicomponent
reactions (MCRs) have received more focus in the field of
organic synthesis and medicinal chemistry because they offer
tion is very difficult in the green chemistry. Synthesis of
biologically active molecules as well as other important
intermediate molecules through an MCR approach
delivers a number of merits over conventional methods,
such as shorter reaction time, higher yield, lower cost,
and the use of green protocol.[2–4] Quinoline nucleus
has been found as an active antimalarial,[5–8]
antituberculosis,[9–11] anticancer,[12] antibacterial,[13] anti-
HIV,[14,15]
antihypertensive,[16]
anticonvulsant,[17,18]
J Heterocyclic Chem. 2020;1–21.
wileyonlinelibrary.com/journal/jhet
© 2020 Wiley Periodicals, Inc.
1

2
PATEL ET AL.
anti-infective,[19] antiplatelet,[20] antagonists,[21] and anal-
gesic agents.[22] It is used in inhibition of serotonin (5-HT3)
receptor antagonists,[23] tachykinin receptor 3 (NK-3),[24]
and immunodeficiency virus.[24] Quinoline was introduced
for the treatment of urinary tract infections in 1963.[25]
Drugs based on quinoline nucleus include oxolinic acid and
ciprofloxacin.[25] Owing to their highly potent biological
activities, quinoline derivatives are much attractive in the
synthesis chemistry. Development of efficient methods and
green synthetic protocols is necessary for the investigation
of the quinoline derivatives. In the literature, quinoline-
4-carboxylic derivatives have been synthesized through
multicomponent condensation of aromatic aldehyde,
substituted aniline, and pyruvic acid using various catalysts,
such as H2SO4,[26] hydroxylamine,[27] C33H46NO4PPdSi,[28]
MPA 100) melting point apparatus. Fourier transform
infrared spectroscopy (FT-IR) spectra were recorded on a
Perkin Elmer (FTIR 377) spectrometer using KBr in
cm−1. Proton nuclear magnetic resonance spectra were
recorded on a Bruker (AV 400 MHz) spectrometer using
DMSO as solvent and TMS as the internal reference. 13C
was recorded on the Bruker (AV 100 MHz). Mass spectra
were recorded at Advion expression CMS. Acetone is
used as the mobile phase, and electron spray ionization
(ESI) is used as the ion source. Elemental analysis was
performed on a CHN elemental analyzer. The develop-
ment of reactions was monitored by thin layer chroma-
tography (TLC) analysis on Merck precoated (silica gel
60 F254) aluminum sheets, visualized by UV light.
ytterbium
perfluorooctanoate,[29]
C26H26Cl2P2Pd,[30]
trifluoroacetic acid,[31] and InCl3.[32] Many of these
methods have some limitation and drawback, such as
strong acid or basic condition, toxic reagent, expensive
reagent and catalyst, longer reaction time, low yield, and
extreme work-up process. Several protocols have also been
developed for the quinoline-4-carboxylic acid derivatives
through a one-pot green synthesis approach that is of great
attention.
Green chemistry point of view, microwave irradiation
reaction (MWI) in organic synthesis has encouraged sci-
entists to explore for the organic synthesis. MWI has
emerged a great energy source for the wide range of
organic transformation with short reaction time and high
yield of the products with high purity.[33–44] However, a
study has been undertaken using MWI for the synthesis
of the quinoline-4-carboxylic acid (Scheme 1).
2.2 | General conventional method for
synthesis of quinoline-4-carboxylic acid
derivatives (4a-4p)
A
solution of aromatic aldehyde (1) (1.0 mmol),
substituted aniline (2) (1.2 mmol), and pyruvic acid
(3) (1.0 mmol) in ethanol (25 mL) was taken in a flask.
Stir and mix it well for 10 minutes, when the mixture
was homogeneous, then add p-toluenesulfonic acid (p-
TSA 10%) as a catalyst, after the addition of the catalyst
reaction mixture was reflux at 80ꢀC for the 3 hours and
stand by the mixture overnight at room temperature. The
reaction mixture was monitored by the TLC hexane:
ethyl acetate (1:1). After the completion of the reaction
mixture was poured into the ice-cold water, collect the
crude products and all derivatives were purified by col-
umn chromatography.
2 | EXPERIMENTAL
2.3 | General microwave irradiation
method for the synthesis of quinoline-
4-carboxylic acid derivatives (4a-4p)
2.1 | Apparatus and analysis
All chemicals were purchased from commercial sources
and of analytical grade; the products were determined by
a comparison of their physical parameter and melting
points with those of known samples or by their spectral
data. CEM Discover microwave (Model No. 908010; CEM
Matthews, Inc.) was used for the synthesis system. Melt-
ing points of the compounds were measured by (Optimelt
The route adopted for the synthesis of quinoline-
4-carboxylic acids is given in Scheme 1. A mixture of aro-
matic aldehyde (1) (1.0 mmol), substituted aniline (2)
(1.2 mmol), and pyruvic acid (3) (1.0 mmol) in 5 mL of
ethanol. Stir and mix it well for 10 minutes, when the
mixture was homogeneous, then add p-Toluenesulfonic
SCHEME 1 Synthetic
strategy for quinoline-4-carboxylic
acid derivatives (4a-4p) [Color
figure can be viewed at
wileyonlinelibrary.com]

PATEL ET AL.
3
acid (p-TSA 10%) as a catalyst. The flask was put under
microwave irradiation at 300 W for 3-4 minutes. Reaction
progress was monitored using a TLC plate every
30 seconds using hexane:ethyl acetate (1:1) as the solvent
system. After completion of the reaction, the reaction
mixture was diluted with a minimum amount of ice-cold
water, collect the crude products were purified by column
chromatography. The yield of the product was around
50% to 80%. The reaction products were confirmed by
comparing their physical data (ie, M.P., FT-IR, ESI-MS)
with those reported in the literature. New compounds
were confirmed by their spectral data (ie, FT-IR, ESI-MS,
1H NMR, 13C NMR).
clavatus MTCC 1323, Candida albicans MTCC 227 and
Aspergillus niger MTCC 282). Ampicillin, ciprofloxacin,
and chloramphenicol were used as standard control
drugs for antibacterial activity, whereas nystatin and
greseofulvin were used as standard drugs for antifungal
activity.
2.5 | In vitro antimalarial assay
The antimalarial activity was performed on Plasmodium
falciparum strain by reported method.[46] in vitro antima-
larial activity was carried out by using with modification
methods of microassay protocol. P. falciparum strain was
supplemented with 1% D-glucose, 25 mM HEPES, 0.23%
bicarbonate, and inactivated human serum. The culture
was stored at 37ꢀC for 24 hours. After the 5% D-sorbitol
treatment, the asynchronous P. falciparum was synchro-
nized. Primary-stage of parasitaemia of 0.9% to 1.4% at 4%
hematocrit in total volume of 200 μL of 25 mM HEPES.
The slides were observed of ring stage plasmodium into
schizonts and trophozoites in the presence of various con-
centrations of ring stage agents. The results of mean inhib-
itory concentration (IC50) record with the quinine and
chloroquine have been used as the standard drugs.
2.4 | In vitro biological assay
2.4.1 | Antimicrobial assay
The antimicrobial activities were performed on various
strains by the reported method,[45] and the results are
described. This work has been carried out in Microcare
Laboratory and TRC, Surat, India, as per reported
method. Mueller-Hinton broth and Sabouraud broth
were used as nutrient medium to grow bacteria and
fungi, respectively. Inoculum size for the test strain was
adjusted to 106 colony-forming units (CFU) per milliliter
by comparing turbidity. Serial dilutions were prepared
for primary and secondary screening. Control tube con-
taining no antibiotics was immediately subcultured
(before inoculation) by spreading a loopful evenly over a
quarter plate of medium suitable for growth of the test
organism and incubated at 37ꢀC for bacteria or 22ꢀC for
fungi overnight. The MIC of the control organism was
read to check the accuracy of the drug concentrations.
The lowest concentration inhibiting growth of the organ-
ism was recorded as the MIC. Each test compound was
diluted, and 2000 μg/mL concentration was achieved as
stock solution. In primary screening, 1000, 500, 250, and
125 μg/mL concentrations of the test compounds were
taken. The active synthesized compounds found in this
primary screening were further tested in a second dilu-
tion set against all organisms. The drugs found active in
primary screening were similarly diluted to obtain
100, 50, 62.5, 25, 12.5, and 6.25 μg/mL concentrations.
The highest dilution showing at least 99% inhibition was
taken as the MIC. The synthesized quinoline hybrid
thiosemicarbazides (4a-4p) were examined for antimicro-
bial activity against two Gram-positive bacterial strains
(Staphylococcus aureus MTCC 96, Streptococcus pyogenes
MTCC 442), two Gram-negative bacterial strains
(Escherichia coli MTCC 443, Pseudomonas aeruginosa
MTCC 8) as well as three fungal strains (Aspergillus
2.6 | In vitro antituberculosis assay
The antituberculosis activity was performed on the
H37Rv strain using an already known method, and
results are described. The MIC of the test compounds
against Mycobacterium tuberculosis H37Rv was deter-
mined by Lowenstein-Jensen (L-J) agar (MIC)
method.[47] Primary 1000, 500, and 250 μg/mL and sec-
ondary 200, 100, 50, 25, 12.5, 6.250, and 3.125 μg/mL
dilutions of each test compound were added to liquid L-J
medium, which was then sterilized by inspissation
method. Culture of M. tuberculosis H37Rv growing on L-J
medium was harvested in 0.85% saline in bijou bottles.
For all test compounds, stock solution of 2000 μg/mL
concentration was first prepared in DMSO. These tubes
were then incubated at 37ꢀC for 24 hours, followed by
streaking of M. tuberculosis H37Rv (5 9104 bacilli per mil-
liliter). These tubes were then incubated at 37 1ꢀC.
Growth of bacilli was observed after 12, 22, and finally
28 days of incubation. Tubes containing compounds were
compared with control tubes in which medium alone
was incubated with M. tuberculosis H37Rv. The concen-
tration at which no development of (or fewer than 20)
colonies occurred was taken as the MIC of the test com-
pound. The standard strain M. tuberculosis H37Rv was
tested with a known drug rifampicin.

4
PATEL ET AL.
2.7 | Molecular docking method
Desmond.[50] The best docked ligand was selected for the
MD simulation. First, the 4c ligand receptor complex
aqueous solvation system was built by system builder
with the aid of OPLS 2005 force field by predefined TIP3P
solvation of orthorhombic solvation boundary with box
volume (8924) A3 that is later followed by ions neutrali-
zation with addition of sodium. This system was later
minimized with 2000 iterations with convergence criteria
of 1 kcal/mol/Å. The minimized explicit solvation com-
plex of ligand receptor complex is simulated for 10 ns
using NPT ensemble at 300 K and 1.01325 bar with
default set of relaxation before simulation.
Molecular docking study was performed on Schrodinger
suite, Glide version 4.5.[48] This software was operated
under the Linux operating system on Intel 2.8 MHz proces-
sor with 8 GB RAM. Grid-based method was used for ligand
preparation with energy minimization on LigPrep-v2.1
(Maestro-v11.4, Schrodinger). In these studies, the X-ray
crystallographic structure of the protein complex with
ligand was taken from the protein data bank (www.rsc.org).
The protein was prepared under protein preparation wizard
(Maestro-v11.4, Schrodinger) for docking studies as follows:
removal of ligand molecule from the protein active site,
optimization of hydrogen bonding, and removal of cofactors
and water molecules from the protein. All the ligands were
docked into active site of protein by using default setting of
the Glide, and Glide-score were collected in terms of multi-
ligand scoring function.
2.10 | Selected spectral data of
representative compounds
2.10.1 | 2-Phenylquinoline-4-carboxylic
acid (4a)
2.8 | Automated docking setup
Cream crystalline powder; M.P. 212-214ꢀC; Yield: (89%);
FT-IR (KBr): (cm−1) 3290 (OH), 1700 (C O), 1675, 1521,
1335, 1220, 1175, 1120, 755; H NMR (400 MHz, DMSO-
1
Docking studies were performed by using the maestro
v11.4 software using the all default settings. Proteins
PDB: 4DUH, 4CJN, 1J3J were downloaded from protein
data bank, and this proteins were employed[49] as follows.
Default setting and flexible space of quinoline-
4-carboxylic acid derivatives were validated by docking
parameters and biological activity, which docked exactly
in the cavities present in the PDB with an affinity of
lower energetic compounds. Subsequently, small-
molecule compounds with respect to low energetic mole-
cules were docked using same docking parameters. Dock-
ing studies were performed on a single machine
equipped on Linux system using Glide with PDB protein
being prepaid on protein preparation wizard. Glide
searches for favorable interactions between the ligand
molecules and protein receptor using a grid based
method. PDB were downloaded from protein data bank,
and a few steps were performed before going for docking:
the protein preparation, removing the water molecule
having less than three hydrogen bonds and cofactors
from the protein, hydrogen bonding optimization, delet-
ing the ligand present in PDB protein, and adjusting the
bond order for ligand-protein. Then, the ligand was pre-
pared using the LigPrep tool in Maestro version 10.4.
d6): δ = 13.95 (1H, s, COOH), 8.67-8.65 (1H, d, J = 8),
8.47 (1H, s), 8.32-8.29 (2H, d, J = 12), 8.19-8.17 (1H, t,
J = 8), 7.88-7.84 (2H, m), 7.73-7.69 (1H, t, J = 16),
7.61-7.55 (3H, m); 13C NMR (100 MHz, DMSO-d6): 165.5,
156.2, 151.3, 140.6, 137.6, 135.8, 133.2, 132.7, 130.7, 129.5,
128.9, 128.2, 125.7, 123.1; Anal. Calcd. for C16H11NO2
(249.26): C 77.10, H 4.45, N 5.62; Found: C 77.80, H 4.49,
N 5.32; ESI-MS: m/z 251.52.
2.10.2 | 6-Nitro-2-phenyl quinoline-
4-carboxylic acid (4b)
Yellowish solid; M.P.165-167ꢀC; Yield: (67%); FT-IR
(KBr): (cm−1) 3241 (OH), 1770 (C O), 1676, 1530, 1340,
1
1230, 1170, 1122, 759; H NMR (400 MHz, DMSO-d6):
δ = 13.94 (1H, s, COOH), 8.68 (1H, d, J = 8.2), 8.45 (1H,
s), 8.41 (1H, d, J = 8.2), 8.21 (1H, t, J = 7.5), 7.89-7.93
(2H, m), 7.43-7.50 (3H, m); 13C NMR (100 MHz, DMSO-
d6): 170.4, 155.6, 148.7, 140.4, 136.8, 136.6, 133.2, 132.7,
130.7, 129.6, 128.9, 121.7, 116.5; Anal. Calcd. for
C16H10N2O4 (294.06): C 65.31, H 3.43, N 9.52; Found: C
65.31, H 3.49, N 9.32; ESI-MS: m/z 295.45.
2.9 | Molecular dynamics
2.10.3 | 6-Methoxy-2-phenylquinoline-
4-carboxylic acid (4c)
The explicit molecular dynamics (MD) study of the
ligand-receptor compounds of the identified lead against
the native ligand in the receptor was carried out using
Cream crystalline powder; M.P. 211-213ꢀC; Yield: (70%);
FT-IR (KBr): (cm−1) 3291 (OH), 1712 (C O), 1645, 1522,

PATEL ET AL.
5
1
1338, 1230, 1180, 1130, 775; H NMR (400 MHz, DMSO-
d6); δ = 13.95 (1H, s, COOH), 8.66 (1H, d, J = 8.2), 8.58
(1H, s), 8.52 (1H, d, J = 8.2), 8.20 (1H, t, J = 7.5),
7.90-7.93 (2H, m), 7.43-7.46 (3H, m), 3.8 (3H, s); 13C
NMR (100 MHz, DMSO-d6): 163.1, 156.1, 152.1, 140.1,
136.2, 134.7, 133.2, 132.4, 130.1, 129.5, 128.8, 128.2, 125.7,
122.9; Anal. Calcd. for C17H13NO3 (279.09): C 73.11, H
4.69, N 5.02; Found: C 73.14, H 4.65, N 5.03; ESI-MS: m/
z 280.
2.10.7 | 2-(2-Chlorophenyl)quinoline-
4-carboxylic acid (4h)
Cream crystalline powder; M.P. 233-235ꢀC; Yield: (50%);
FT-IR (KBr): (cm−1) 3247 (OH), 1715 (C O), 1645, 1530,
1
1343, 1232, 1165, 1130, 747; H NMR (400 MHz, DMSO-
d6): δ = 13.51 (1H, s, COOH), 8.70 (1H, d J = 8.9), 8.58
(1H, s), 8.00-8.10 (2H, m), 7.40-7.70 (5H, m); 13C NMR
(100 MHz, DMSO-d6): 166.4, 156.1, 150.1, 141.7, 137.6,
135.7, 133.2, 133.0, 130.1, 129.5, 128.9, 126.4, 125.7, 122.9;
Anal. Calcd. for C16H10ClNO2 (283.01): C 67.74, H 3.55,
N 4.94; Found: C 67.75, H 3.56, N 5.01; ESI-MS: m/z
284.10.
2.10.4 | 6-Chloro-2-phenylquinoline-
4-carboxylic acid (4d)
Cream crystalline powder; M.P. 202-203ꢀC; Yield: (75%);
FT-IR (KBr): (cm−1) 3256 (OH), 1716 (C O), 1645, 1530,
1340, 1214, 1145, 1120, 758; H NMR (400 MHz, DMSO-
2.10.8 | 6-Chloro-2-phenylquinoline-
4-carboxylic acid (4i)
1
d6): δ = 13.91 (1H, s, COOH), 8.46 (1H, s), 8.25-8.24 (2H,
d, J = 4), 8.15-8.14 (1H, d, J = 4), 8.09-8.07 (1H, d, J = 8),
7.58-7.53 (2H, m), 7.52-7.48 (2H, m); 13C NMR (100 MHz,
DMSO-d6): 170.2, 157.5, 153.2, 140.7, 137.4, 135.8, 135.2,
132.7, 130.7, 129.5, 129.1, 128.3, 124.7, 120.1; Anal. Calcd.
for C16H10ClNO2 (283.04): C 67.74, H 3.55, N 4.94;
Found: C 67.75, H 3.61, N 5.51; ESI-MS: m/z 284.02.
White powder; M.P. 210-211ꢀC; Yield: (72%); FT-IR
(KBr): (cm−1) 3280 (OH), 1692 (C O), 1640, 1532,
1324, 1215, 1170, 1110, 748; 1H NMR (400 MHz,
DMSO-d6): δ = 13.79 (1H, s, COOH), 8.77-8.74 (1H, d,
J = 12), 8.18-8.15 (2H, d), 7.91-7.88 (1H, t, J = 6),
7.87-7.73 (3H, m), 7.67-7.56 (2H, m), 3.45 (3H, s); 13C
NMR (100 MHz, DMSO-d6): 166.8, 154.6, 152.7, 141.1,
134.1, 134.2, 132.9, 132.1, 130.8, 129.1, 128.7, 128.1,
125.7, 121.4; Anal. Calcd. for C17H12ClNO3 (313.05): C
65.08, H 3.86, N 4.46; Found: C 65.64, H 3.85, N 4.50;
ESI-MS: m/z 313.32.
2.10.5 | 6-Methyl-2-phenylquinoline-
4-carboxylic acid (4e)
White solid; M.P. 190-192ꢀC; Yield: (70%); FT-IR (KBr):
(cm−1) 3445 (OH), 1710 (C O), 1665, 1530, 1344, 1245,
1170, 1130, 890, 724; 1H NMR (400 MHz, DMSO-d6):
δ = 13.92 (1H, s, COOH), 8.44-8.42 (2H, d, J = 8), 8.40
(1H, s), 8.29-8.27 (2H, d, J = 12), 8.08-8.06 (1H, d, J = 8),
7.71-7.68 (1H, m), 7.60-7.51 (3H, m), 3.47 (3H, s); 13C
NMR (100 MHz, DMSO-d6): 168.3, 156.2, 156.3, 149.3,
140.3, 138.6, 130.5, 130.4, 129.5, 129.2, 127.7, 125.6, 122.1;
Anal. Calcd. for C17H13NO2 (263.04): C 77.55, H 4.98, N
5.32; Found: C 77.62, H 4.44, N 5.33; ESI-MS: m/z 263.44.
2.10.9 | 2-(4-Chlorophenyl)quinoline-
4-carboxylic acid (4j)
Cream crystalline powder; M.P. 230-232ꢀC; Yield: (70%);
FT-IR (KBr): (cm−1) 3289 (OH), 1695 (C O), 1645, 1529,
1
1328, 1246, 1178, 1120, 745; H NMR (400 MHz, DMSO-
d6): δ = 13.47 (1H, s, COOH), 8.78-8.76 (1H, d, J = 8),
8.25-8.23 (3H, d, J = 8), 8.05-8.03 (1H, d, J = 8), 7.74-7.71
(1H, t, J = 6), 7.55-7.53 (3H, m), 7.70 (1H, m); 13C NMR
(100 MHz, DMSO-d6): 167.8, 155.6, 152.7, 141.1, 136.1,
135.2, 133.9, 132.1, 130.1, 129.1, 128.9, 128.2, 125.7, 122.6;
Anal. Calcd. for C16H10ClNO2 (283.04): C 67.74, H 3.55,
N 4.94; Found: C 67.71, H 3.56, N 5.01; ESI-MS: m/z
282.25.
2.10.6 | 6-Fluoro-2-phenylquinoline-
4-carboxylic acid (4g)
Light yellow solid; M.P. 135-136ꢀC; Yield: (57%); FT-IR
(KBr): (cm−1) 3030 (OH), 2611, 1696 (C O), 1593, 1548,
1236, 930, 873, 689; 1H NMR (400 MHz, DMSO-d6):
δ = 14.13 (1H, s), 8.55 (1H, s), 8.48 (1H, d, J = 2.9), 8.26
(3H, m), 7.78 (1H, t), 7.58 (3H, m); 13C NMR (100 MHz,
DMSO-d6): 170.2, 160.2, 151.2, 143.4, 137.1, 135.1, 133.9,
132.5, 131.7, 123.5, 129.8, 128.2, 125.4, 122.2; Anal. Calcd.
for C16H10FNO2 (267.10): C 71.91, H 3.77, N 5.24; Found:
C 71.95, H 3.70, N 5.32; ESI-MS: m/z 268.41.
2.10.10 | 2-(4-Chlorophenyl)-
6-nitroquinoline-4-carboxylic acid (4k)
Cream crystalline powder; M.P. 214-215ꢀC; Yield: (68%);
FT-IR (KBr): (cm−1) 3292 (OH), 1765 (C O), 1668, 1535,
1
1345, 1231, 1178, 1124, 748; H NMR (400 MHz, DMSO-

6
PATEL ET AL.
d6): δ = 14.00 (1H, s, COOH), 8.66 (1H, d, J = 8.2), 8.58
(1H, s), 8.52 (1H, d, J = 8.2), 8.20 (1H, t, J = 7.5),
7.90-7.93 (2H, m), 7.86 (1H, t, J = 7.5), 7.43-7.46 (3H, m);
13C NMR (100 MHz, DMSO-d6): 167.1, 155.6, 152.1,
141.7, 136.4, 135.8, 132.1, 132.4, 130.1, 129.5, 128.9, 128.2,
124.8, 121.2; Anal. Calcd. for C16H9ClN2O4 (228.03): C
58.46, H 2.76, N 8.52; Found: C 56.02, H 2.78, N 8.53;
ESI-MS: m/z 329.36.
68.58, H 4.06, N 4.70; Found: C 68.65, H 4.20, N 4.72;
ESI-MS: m/z 297.44.
2.10.14 | 2-(4-Chlorophenyl)-
6-hydroxyquinoline-4-carboxylic acid (4o)
Cream crystalline powder; M.P. 198-200ꢀC; Yield: (69%);
FT-IR (KBr): (cm−1) 3230 (OH), 1745 (C O), 1685, 1564,
1
1394, 1220, 1114, 1136, 775; H NMR (400 MHz, DMSO-
2.10.11 | 2-(4-Chlorophenyl)-
6-methoxyquinoline-4-carboxylic acid (4l)
d6): δ = 13.98 (1H, s, COOH), 10.54 (1H, s, OH), 8.67 (1H,
d, J = 8.2), 8.58 (1H, s), 8.56 (1H, d, J = 8.2), 8.30 (1H, t,
J = 7.5), 7.91-7.94 (2H, m), 7.88 (1H, t, J = 7.5), 7.35-7.32
(3H, m); 13C NMR (100 MHz, DMSO-d6): 168.0, 166.2,
160.1, 154.6, 144.6, 140.7, 139.5, 133.7, 131.8, 129.5, 129.1,
128.3, 125.7, 121.5; Anal. Calcd. for C16H10ClNO3
(299.08): C 64.12, H 3.36, N 4.67; Found: C 64.17, H 3.35,
N 4.71; ESI-MS: m/z 299.13.
Cream crystalline powder; M.P. 264-266ꢀC; Yield: (65%);
FT-IR (KBr): (cm−1) 3323 (OH), 3064, 2968, 2837, 1689
(C O), 1618 (C N), 1587, 780; 1H NMR (400 MHz,
DMSO-d6): δ = 13.98 (1H, s, COOH), 8.70 (1H, d,
J = 8.2), 8.58 (1H, s), 8.22 (1H, t, J = 7.5), 8.10-7.91 (2H,
m), 7.47-7.41 (3H, m), 3.97 (3H, s, OCH3); 13C NMR
(100 MHz, DMSO-d6): 166.2, 157.2, 150.1, 141.4, 137.1,
134.4, 132.1, 132.7, 130.7, 130.1, 129.0, 128.7, 125.7, 122.8;
Anal. Calcd. For C17H12ClNO3 (313.5): C 65.08, H 3.86, N
4.46; Found: C 65.19, H 4.07, N, 4.15; ESI-MS: m/z
314.25.
2.10.15 | 2-(4-Chlorophenyl)-
6-fluoroquinoline-4-carboxylic acid (4p)
Cream crystalline powder; M.P. 200-20ꢀC; Yield: (76%);
FT-IR (KBr): (cm−1) 3245 (OH), 1765 (C O), 1642, 1535,
1
1348, 1242, 1196, 1152, 748; H NMR (400 MHz, DMSO-
2.10.12 | 6-Chloro-2-(4-chlorophenyl)
quinoline-4-carboxylic acid (4m)
d6): δ = 13.91 (1H, s, COOH), 8.29-8.28 (1H, d, J = 4),
8.02-7.99 (1H, d, J = 12), 7.69-7.68 (1H, m), 7.63-7.61 (1H,
m), 7.52-7.45 (3H, m); 13C NMR (100 MHz, DMSO-d6):
170.1, 156.4, 150.4, 141.6, 137.1, 135.1, 132.2, 132.7, 130.7,
129.5, 128.9, 128.2, 125.7, 122.7; Anal. Calcd. for
C16H9ClFNO2 (301.18): C 63.70, H 3.01, N, 4.64; Found:
C 63.84, H 3.04, N 4.59; ESI-MS: m/z 302.03.
Cream crystalline powder; M.P. 256-258ꢀC; Yield: (50%);
FT-IR (KBr): (cm−1) 3250 (OH), 1642 (C O), 1645, 1520,
1
1340, 1230, 1180, 1120, 886, 830 760; H NMR (400 MHz,
DMSO-d6): δ = 13.56 (1H, s, COOH), 7.58-7.70 (2H, m),
7.84-7.96 (1H, m), 8.14-8.23 (2H, m), 8.34-8.45 (2H, d),
8.84-8.96 (1H, d); 13C NMR (100 MHz, DMSO-d6): 167.2,
157.1, 152.7, 141.1, 140.9, 134.7, 132.6, 132.1, 130.7, 128.5,
127.8, 127.1, 125.4, 121.2; Anal. Calcd for C16H9Cl2NO2
(317.00): C 60.40, H 2.85, N 4.40; Found: C 59.00; H 2.96,
N 4.54; ESI-MS: m/z 318.32.
3 | RESULTS AND DISCUSSION
A green, efficient route for the synthesis of the various
quinoline-4-carboxylic acid derivative was achieved using
conventional as well as microwave irradiation. However,
the Pfitzinger reaction occurred when MWI was used for
the synthesis of quinoline-4-carboxylic acids have been
reported yet. Synthesis of quinoline-4-carboxylic acid in a
nontoxic solvent like water, methanol, and ethanol has
been reported. However, it did not give higher amounts
of the products when trifluoroacetic acid was used in the
reaction. Moreover, employing all types of conditions
required heating in an oil bath for 3 to 5 hours. Compara-
tive study of model reaction carried out in the conven-
tional method.
2.10.13 | 2-(4-Chlorophenyl)-
6-methylquinoline-4-carboxylic acid (4n)
Cream crystalline powder; M.P. 212-213ꢀC; Yield: (63%);
FT-IR (KBr): (cm−1) 3329 (OH), 3025, 1670 (C O), 1689,
1523, 1365, 1245, 1178, 1122, 813, 759; 1H NMR
(400 MHz, DMSO-d6): δ = 10.52 (1H, s, COOH), 8.71
(1H, d, J = 8.2), 8.61 (1H, s), 8.18 (1H, t, J = 7.5),
7.91-7.95 (2H, m), 7.49-7.44 (3H, m), 2.3 (3H, d, CH3);
13C NMR (100 MHz, DMSO-d6): 164.2, 155.7, 154.8,
144.2, 138.3, 136.1, 134.2, 133.8, 132.7, 130.4, 128.9, 126.8,
125.7, 124.5; Anal. Calcd. for C17H12ClNO2 (297.46): C
The main aim of these work was to develop an effi-
cient and green protocol for the synthesis of quinoline-4-
carboxylic acids in the beginning. The reaction of

PATEL ET AL.
7
equimolar quantities of aromatic aldehyde (1) (1.0 mmol),
substituted aniline (2) (1.2 mmol), and pyruvic acid
(3) (1.0 mmol) was used as a model reaction to optimize
the reaction conditions and to evaluate the catalytic activ-
ity of p-toluenesulfonic acid (p-TSA) compared with men-
tion catalyst for the formation of quinoline-4-carboxylic
acid derivatives comparative experiments were performed,
and the data are shown in Table 2. Two catalysts were
tested: TFA and p-TSA. However, p-TSA was found to be
the most efficient in terms of reaction time and the yield
of the product and as well as green chemistry protocols
(Table 1). We have tested this reaction in different sol-
vents, including methanol, ethanol, acetic acid, water, and
some combination of the solvents in Table 3. But ethanol
was found as a most benefited solvent.
However, we have found that MWI has successfully
accelerated the condensation of aromatic aldehydes,
substituted anilines and pyruvic such as in alcoholic con-
dition, whereby the corresponding quinoline-4-carboxylic
acids (4a-4p) were obtained in 3 to 4 minutes; the reac-
tions were carried out in open vessel and the yield of
products ranged between 50% and80%. The highest yields
observed in the cases of benzaldehyde, aniline, and
pyruvic acid, under the conventional conditions the reac-
tion required heating under reflux for 3 hours give a
lower yield as compared to MWI.
catalyst loadings in the range of 10% were tested. From
the result table, we concluded that the lower yield of
the product was observed in the absence of the catalyst
(Table 2). In addition, it was discovered that the reac-
tion was rather slow and resulted in average yield
(50%) in the absence of the catalyst when the reaction
was carried out in refluxing water for 3 minutes
(Table 2), the product was found in good yield. Instead
of all applied condition when we are applying
ethanolic condition at 300 W MWI, product was found
in excellent in terms of yield.
We have also proposed a possible mechanism for the
final product (4a-4p) (Scheme 2). As we have described
in the mechanism, Schiff bases (g) are formed in the first
step by the reaction of aldehyde and aniline. Pyruvic acid
formed a scaffold (e) when p-TSA was added into the
reaction mixture and nucleophiles attacked on the Schiff
base carbon. After some intermediate steps (h, i, j) the
final step occurs by the oxidation of intermediate (k) and
forms carboxylic-4-acids (4a-4p).
3.1 | Biological activity
3.1.1 | Antibacterial and antifungal
activity
The model reaction was used to identify suitable
conditions, including solvents and catalyst. The results
are summarized in Tables 2 and 3. In this reaction,
The in vitro antibacterial study of synthesized quinoline-
4-carboxylic acid (4a-4p) was determined by the agar
TABLE 1 Quinoline-4-carboxylic acid derivatives catalyzed by p-TSA using MWI
Entry
1
Compound code
R1
R2
Time (min)
Yielda (%)
M.P. (ꢀC)
212-214
165-167
211-213
202-203
190-192
200-202
135-136
233-235
208-210
230-232
214-215
264-266
256-258
212-213
198-200
200-202
References
[50]
4a
4b
4c
4d
4e
4f
H
H
3
3
3
3
3
3
3
4
3
4
3
3
3
3
3
3
80
67
70
75
70
65
57
50
65
70
68
65
50
63
69
76
[52]
[51]
2
H
4-NO2
4-OCH3
4-Cl
3
H
4
H
-
[53]
5
H
4-CH3
4-OH
4-F
6
H
-
7
4g
4h
4i
H
-
[54]
8
2-Cl
2-Cl
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
H
9
4-OCH3
H
-
[55]
10
11
12
13
14
15
16
4j
4k
4l
4-NO2
4-OCH3
4-Cl
-
[56]
[57]
[50]
4m
4n
4o
4p
4-CH3
4-OH
4-F
-
-
Abbreviation: M.P., melting point.
aPurified product.

8
PATEL ET AL.
TABLE 2 Evaluation of catalytic
activity of different catalysts for the
condensation of benzaldehyde, aniline,
and pyruvic acid in ethanol at 300 W
microwave irradiation
Entry
Catalyst
TFA
Catalyst loading (mol%)
Time (min)
Yielda (%)
1
2
3
10
10
-
3
3
3
75
80
50
P-TSA
-
aPurified product.
TABLE 3 Evaluation of different
solvent activity in (10 mmol%) catalysts
for the condensation of benzaldehyde,
aniline, and pyruvic acid in ethanol at
300 W microwave irradiation
Entry
Solvent
Catalyst loading (mol%)
P-TSA (10%)
Time (min)
Yielda (%)
1
Methanol
Ethanol
AcOH
3
3
3
3
3
3
3
3
3
3
3
30
2
P-TSA (10%)
80
3
P-TSA (10%)
Trace
20
4
Methanol:H2O (50%)
Ethanol:H2O (50%)
Methanol
P-TSA (10%)
P-TSA (10%)
TFA (10%)
TFA (10%)
TFA (10%)
TFA (10%)
TFA (10%)
-
5
20
6
50
7
Ethanol
75
8
AcOH
Trace
30
9
Methanol:H2O (50%)
Ethanol:H2O (50%)
Ethanol
10
11
45
50
aPurified product.
SCHEME 2 Proposed mechanism
for derivative of quinoline-4-carboxylic
acid (4a-4p)
dilution method. As shown in Table 4, all synthesized
compounds were tested in various antibacterial and anti-
fungal strains such as E. coli MTCC 443 and
P. aeruginosa MTCC 441 Gram-negative strains, S. aureus
MTCC 96 and S. pyogenes MTCC 442 Gram-positive
strains, C. albicans MTCC 227, A. niger MTCC 282 and
A. clavatus MTCC 1323 strains, respectively. Their biolog-
ical activities compared with standard drugs such as
ampicillin, chloramphenicol, ciprofloxacin, nystatin, and
greseofulvin.

PATEL ET AL.
9
TABLE 4 Biological activity of synthesized compounds 4a-4p
Antibacterial
Gram-negative
organismd
Gram-positive
organisme
Antifungala
Ca An
500
Antimalarialb
Pf
AntiTBc
H37Rv
Entry
1
Code
4a
Ec
50
Pa
250
100
250
100
100
500
100
125
100
250
250
100
250
100
100
125
-
Sa
125
125
25
Sp
Ac
1000
MDR TBf
1000
>1000
250
1000
>1000
>1000
500
250
125
1000
500
>1000
1000
200
125
500
-
100
125
250
500
250
100
250
250
500
500
0.26
0.54
0.12
0.14
0.94
1.02
1.07
1.67
1.03
0.73
0.57
0.59
1.65
0.69
0.75
1.06
-
250
500
125
500
1000
1000
250
125
100
500
250
500
500
125
100
250
-
2
4b
125
50
250
250
>1000
>1000
1000
1000
500
500
500
>1000
1000
1000
500
500
500
-
250
250
>1000
>1000
1000
1000
500
1000
1000
>1000
1000
1000
500
1000
500
-
3
4c
1000
1000
>1000
500
500
250
1000
1000
>1000
500
500
250
1000
1000
-
4
4d
62.5
500
250
100
250
250
250
125
500
500
250
250
500
25
5
4e
125
500
250
100
125
250
250
50
6
4f
7
4g
8
4h
9
4i
62.5
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
4j
100
500
500
250
250
500
50
100
50
50
-
4k
4L
4m
4n
250
62.5
4o
125
4p
100
Ampf
Camf
Ciprof
Nyf
Grisf
INHf
RMPf
Quinf
CQf
KANf
100
250
50
50
50
-
-
-
-
-
-
25
25
50
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
100
500
-
100
100
-
100
100
-
-
-
-
-
-
-
-
-
-
-
-
-
-
0.20
1.00
-
100
50
-
-
-
-
-
-
-
-
-
-
-
-
-
0.26
0.02
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
50
aValues represented in μg/mL, Candida albicans (Ca), Aspergillus niger (An), Aspergillus clavatus (Ac).
bValues represented in IC50 μg/mL, antimalarial screening using Plasmodium falciparum strain.
cValues represented in μg/mL, antituberculosis screening via H37Rv strain.
dValues represented in μg/mL, Escherichia coli (Ec), Pseudomonas aeruginosa (Pa).
eValues represented in μg/mL, Staphylococcus aureus (Sa), streptococcus pyrogenes (Sp).
fReference drug, ampicillin, chloramphenicol, ciprofloxacin, nystatin, griseofulvin, isoniazid, rifampicin, quinine, chloroquine.
We have noted that all molecules exhibited excellent
activity against E. coli Gram-negative strain, significant
active against S. aureus strain and moderate active
against P. aeruginosa and S. pyrogenes strains. As per
Table 4 conclusion, four synthesized compounds, 4a
(MIC 50 μg/mL), 4c (MIC 50 μg/mL), 4d (62.5 μg/mL),
and 4n (MIC 62.5 μg/mL), were found be most active
against the Gram-negative strain E. coli as compared to
standard drugs ampicillin (MIC 100 μg/mL), 4a and 4c
found to be similarly active against chloramphenicol
(MIC 50 μg/mL) in the E. coli strain. Two compounds 4c
(MIC 25 μg/mL) and 4p (MIC 25 μg/mL) were shown
most potent against the S. aureus strains as compared to
chloramphenicol (MIC 50 μg/mL) and ciprofloxacin
(MIC 50 μg/mL), Four compounds 4a (MIC 125 μg/mL),
4b (MIC 125 μg/mL), 4f (MIC 100 μg/mL), and 4j (MIC
125 μg/mL) showed good activity against the Gram-
positive strain S. aureus as compared to ampicillin (MIC
250 μg/mL). Compound 4i (MIC 62.5 μg/mL) was found
to be active against the S. pyrogenes strain as compared to

10
PATEL ET AL.
FIGURE 1 Graphical representation of biological activity [Color figure can be viewed at wileyonlinelibrary.com]
TABLE 5 Molecular docking score of synthesized compound 4a-4p
PDB: 4DUH
PDB: 4CJN
PDB: 1J3J
Entry
1
Code
4a
XP GScore
−5.463
−6.022
−4.62
XP HBond
0
XP GScore
−2.495
−4.07
XP HBond
−0.287
−1.8
XP GScore
−7.064
−6.054
−6.157
−7.059
−7.329
−7.216
−6.934
−6.407
−5.666
−7.239
−6.042
−6.158
−7.174
−6.75
−7.333
−7.273
-
XP HBond
−1.94
−1.065
−1.22
−1.433
−1.356
−1.864
−1.229
−0.338
−1.194
−1.9
2
4b
−0.566
−0.05
−0.568
−0.567
−0.822
0
3
4c
−2.41
−0.223
−1.723
−1.693
−1.226
−0.285
−1.752
−0.232
0
4
4d
−6.17
−4.241
−4.238
−4.418
−2.477
−4.56
5
4e
−6.179
−6.511
−5.349
−6.104
−6.691
−5.475
−5.952
−5.354
−6.294
−6.267
−5.141
−6.249
−3.65
6
4f
7
4g
8
4h
−0.568
−0.735
0
9
4i
−2.567
−2.242
−4.182
−3.178
−4.402
−2.758
−4.348
−4.535
−4.051
−3.973
−3.024
-
10
11
12
13
14
15
16
17
18
19
20
21
4j
4k
−0.472
−0.35
−0.564
−0.566
−1.07
−0.564
−0.957
−2.085
−0.48
-
−1.675
−0.7
−1.435
−1.243
−1.088
−1.175
−1.244
−1.701
-
4l
4m
4n
−1.781
0
4o
−1.239
−1.747
−2.033
−1.92
−0.885
-
4p
Ampa
Cama
Ciproa
Quina
CQa
−6.721
−6.472
-
-
-
-
-
−4.878
−4.915
−0.336
0
-
-
-
-
aStandard drugs.

PATEL ET AL.
11
ampicillin. Compound 4p (MIC 50 μg/mL) shows a simi-
lar activity against S. pyrogenes compared with chloram-
phenicol and ciprofloxacin, while other remaining
compounds were moderately active against antibacterial
strains. Compounds 4h (MIC 250 μg/mL) and 4n (MIC
250 μg/mL) showed higher activity against the antifungal
strain C. albicans as compared to greseofulvin (MIC
500 μg/mL), but not active against the nystatin (MIC
100 μg/mL) as a standard drug. Compounds 4a, 4b, 4f,
4 g, 4l, and 4 m (MIC 500 μg/mL) showed a similar activ-
ity against C. albicans when compared to greseofulvin
(Table 4 and Figure 1). Many of the compounds were not
active against antifungal strains such as A. niger and
A. clavatus when compared to standard drugs.
FIGURE 2 3D and 2D interaction of PDB: 4UDH: A, pose with compound 4a and B, pose with compound 4c [Color figure can be
viewed at wileyonlinelibrary.com]

12
PATEL ET AL.
FIGURE 2 (Continued)
3.2 | Antimalarial and antituberculosis
activity
respectively. Moreover, all synthesized compounds
were tested for their multidrug resistance tuberculosis
study. As per Table 4, we have stated that compounds
4c (IC50 0.12 μg/mL) and 4d (IC50 0.14 μg/mL) were
found to be the most potent candidate among the all
synthesized compounds against the P. falciparum
All synthesized compounds (4a-4p) were evaluated
for their antimalarial activity and antituberculosis
activity against P. falciparum and H37Rv strain,

PATEL ET AL.
13
strain as compared to the standard drug quinine
(IC50 0.26 μg/mL). Compound 4a (IC50 0.26 μg/mL)
showed a similar activity against the P. falciparum
strain when compared to quinine. Compounds 4b
(IC50 0.54 μg/mL), 4k (IC50 0.57 μg/mL), and 4l
(IC50 0.59 μg/mL) were shown moderate active
against quinine, while all compounds were shown
moderate activity against chloroquine. The in vitro
tuberculosis activity of the synthesized compounds
(4a-4p) was performed against M. tuberculosis H37Rv
strain and MDR-TB. As per Table 4, none of the syn-
thesized compounds was active against both TB
strains as compared to the standard drugs isoniazid
and rifampicin.
3.3 | Structure-activity relationship
In the quest for finding the hit molecule of biological
activity, we have investigated the existing series of
FIGURE 3 3D and 2D interaction of PDB: 4CJN: A, pose with compound 4c and B, pose with compound 4p [Color figure can be
viewed at wileyonlinelibrary.com]

14
PATEL ET AL.
FIGURE 3 (Continued)
quinoline hybrid thiosemicarbazide derivatives. For
this study, we have tested synthesized compounds
against various biological activities. Based on these
studies, we noted that electronic configuration of func-
tional group effecting on biological activity. Com-
pounds comprising methoxy electron donating group
(EDG) on quinoline ring led to potent biological activ-
ity. Compounds having substation at the sixth position
of quinoline with EDG such as methoxy (4c, 4i),
methyl (4n), and hydroxy (4f), and having substituted
on quinoline ring with EWG such as chlorine (4d),
fluorine (4p), and nitro (4b) increased bioactivity in
Gram-negative (E. coli) and Gram-positive (S. aureus,
S. pyrogenes) bacteria. Moreover, phenyl ring substitu-
tion with chlorine group also effected antibacterial
activity. EDG or EWG at the sixth substituted position
on quinoline having excellent bioactivity against anti-
fungal activity is compared to standard drug such as
nitro (4b), hydroxy (4f, 4l), fluorine (4g), chlorine
(4m), and methyl (4n). Compounds having a fused
combination of EDG and EWG in derivative also
increased potency of molecules in antifungal activity.
In P. falciparum, we observed no substitution at any
position having similar potency. While, compounds

PATEL ET AL.
15
having quinoline substitution at six position with
strong EDG like methoxy (compound 4c) and weak
EWG like chlorine (compound 4d) having highest
potency against P. falciparum when compared with
quinine. But quinoline substitution with strong EWG
like nitro (compound 4b) and substituted on phenyl
ring at any position like ortho or para (compounds 4k,
4l) decreased potency against the P. falciparum.
FIGURE 4 3D and 2D interaction of PDB: 1J3J: A, pose with compound 4c and B, pose with compound 4d [Color figure can be viewed
at wileyonlinelibrary.com]

16
PATEL ET AL.
FIGURE 4 (Continued)
3.4 | Docking study
structures were downloaded from the protein data bank
(PDB), and docking study was performed using Glide
tools on Maestro 11.0 (Schrodinger, LLC, New York, NY,
2015) program. The summarized results are concluded in
Table 5, and we have selected the best binding 2D and
3D poses of compounds 4a and 4c with PDB: 4UDH are
Docking study was performed to find out the plausible
binding mechanism of all synthesized compounds; these
studies were performed on selected 4UDH (E. coli), 4CJN
(S. aureus), and 1J3J (P. falciparum) target. Protein 3D

PATEL ET AL.
17
TABLE 6 Molecular docking interaction with amino acid
H-bond
Halogen bond
Code Protein
Atoma
Amino acidb BLc π-π interaction
Amino acidb
BLc
4a
4UDH (E. coli)
C of Phenyl ring
O of ─CO
ASP 73
2.33 Quinoline
-
-
LYS 103
VAL 167
ASP 73
4.94
4c
C- of phenyl ring
2.36 Quinoline-LYS 103
-
-
-
2.21
ASP 73
2.86
C of ─CO
ARG 76
GLY 101
VAL 120
ARG 136
2.37
4l
C of phenyl ring
2.11 Quinoline-LYS 103
-
2.68
2.70
2.58
O of ─OCH3
C atom of phenyl-quinoline ARG 136
H of ─CH3
ARG 136
ARG 136
LYS 273
LYS 316
LYS 316
ASN 104
LYS 273
LYS 316
LYS 273
ARG 106
ARG 106
ARG 106
ARG 129
ARG 129
ARG 128
ASN 144
ARG 129
SER 128
ARG 106
ARG 129
ARG 106
ARG 106
ARG 106
O of ─OCH3
1.75
4c
4p
4CJN (S. aureus)
C of phenyl-quinoline
O of ─OCH3
2.53
2.02
2.57
2.34
1.85
1.58
4.25
2.69
1.76
2.13
2.69
2.07
2.37
-
-
-
-
-
-
H of ─OCH3
C of phenyl-quinoline
O of ─CO
C of ─CO
4a
1J3J (P. falciparum) O of ─CO
-
-
-
O of ─CO
4c
4d
C of ─CH3
C of ─CO
O of ─CO
2.55 Quinoline-ARG 129
-
-
1.85
2.69
1.85
C of ─CO
O of ─CO
1.85 Quinoline-ARG 129
─Cl with ASN 144 3.37
3.11
1.90
2.32
aLigand atom.
bProtein amino acid.
cBond-length between interaction.
shown in Figure 2, compounds 4c and 4p with PDB:
4CJN are shown in Figure 3, compounds 4c and 4d with
1J3J are shown in Figure 4. Each of the ligands has indi-
cated good docking score between −6.691 and −4.62 in
4UDH, −4.56 and −4.41 in 4CNJ, and −7.329 and −6.042
in 1J3J protein. LYS 103 and ARG 129 were found as
common π-π interaction in the compounds 4a, 4c, and 4l
in 4UDH and 4c and 4d in 1J3J, respectively. Plausible
binding mechanisms of selected compounds are
described in Table 5. From Table 6, it is clear that com-
pound 4a (XP GScore −5.463) generates two strong H-
bonds between phenyl-ASP 73 (2.33 Å) and ─CO-LYS
103 (4.94 Å); compound 4c (XP GScore −4.62) generates
five H-bonds between phenyl-VAL 167 (2.36 Å); and

18
PATEL ET AL.
TABLE 7 ADME-Tox parameters
Code
4a
PHOAa
QPPCacob
262.911
31.083
QPlogBBc
−0.48
QPlogKhsad
0.024
QPlogHERGe
−3.77
QPlogSf
−3.808
−4.027
−4.033
−4.544
−4.377
−3.53
PSAg
3
2
3
3
3
3
3
3
3
3
2
3
3
3
3
3
1
3
3
57.623
102.536
65.809
57.603
57.604
80.151
57.61
4b
−1.484
−0.547
−0.328
−0.51
−0.011
0.043
−3.754
−3.684
−3.721
−3.727
−3.663
−3.661
−3.711
−3.615
−3.72
4c
273.104
263.167
263.073
80.014
4d
0.139
4e
0.181
4f
−1.046
−0.375
−0.37
−0.145
0.066
4g
263.201
253.455
268.848
263.168
31.218
−4.169
−4.443
−4.656
−4.544
−4.726
−4.769
−5.283
−5.12
4h
0.139
58.508
66.655
57.607
102.553
65.812
57.592
57.61
4i
−0.427
−0.328
−1.35
0.156
4j
0.139
4k
0.102
−3.683
−3.63
4l
273.033
263.264
262.929
80.252
−0.395
−0.176
−0.359
−0.906
−0.223
−1.3
0.157
4m
4n
0.256
−3.663
−3.67
0.299
4o
−0.038
0.181
−3.61
−4.248
−4.907
−1.512
−3.306
−4.758
80.104
57.613
139.52
46.551
26.686
4p
263.137
1.298
−3.608
−0.709
−5.518
−6.484
Amph
Quinh
CQh
−0.929
0.26
633.127
1486.183
0.1
0.411
0.631
aPercentage human oral absorption (>80% high to <25% poor).
bcaco-2 cell permeability (<25 poor to >500 great).
cBlood brain partition coefficient (−3.0 to 1.2).
dPrediction of binding to human serum albumin (−1.5 to 1.5).
ePredicted IC50 value for blockage of HERG K+ channels (below −5.0).
fWater solubility parameter (−6.5 to 0.5).
gvan der Walls surface area of polar nitrogen and oxygen atoms (7.0-200.0).
hStandard drugs.
phenyl interacts with ASP 73 (2.21 Å), ASP 73 (2.86 Å),
─CO-ARG 76 (2.37 Å), and ─OCH3-GLY 101 (2.31 Å) in
4UDH protein. Compound 4c (XP GScore −2.41) has
three strong H-bonds between quinoline-C-LYS
273 (2.53 Å), ─OCH3 interact with LYS 316 (2.02 Å) and
LYS 316 (2.57 Å), compound 4p (XP GScore −4.535)
found four H-bonds between quinoline-C-ASN
104 (2.34 Å), ─CO interact with LYS 273 (1.85 Å), LYS
273 (4.25 Å), and LYS 316 (1.58 Å) in 4CJN protein. Com-
pound 4c (XP GScore −6.157) generates four H-bonds
between ─CH3-ASN 144 (2.55 Å), ─CO interact with
ARG 129 (1.85 Å), SER 128 (2.69 Å), and ARG
106 (1.85 Å); compound 4d (XP GScore −7.059) generates
one halogen bond and four H-bonds between ─Cl-ASN
144 (3.37 Å), ─CO interact with ARG 129 (1.85 Å), ARG
106 (3.11 Å), ARG 106 (1.90 Å), and ARG 106 (2.32) in
1J3J protein. Moreover, compounds 4c, 4d, and 4p hav-
ing good binding score as compared to standard drugs
ampicillin (4DUH: −3.65, 4CJN: −6.721), ciprofloxacin
(4DUH: −4.051, 4CJN: −3.973), quinine (1J3J: −4.878),
and chloroquine (1J3J: −4.915). Furthermore, com-
pounds 4o (XP GScore −5.141), 4j (XP GScore −2.242),
and 4i XP GScore (−5.666) having very low binding score
with proteins 4DUH, 4CJN, and 1J3J, respectively. Dock-
ing score and binding mechanism of all compounds
suggested that highlighted compounds would be a potent
active in the respective protein as described in Table 6.
3.5 | ADME-Tox prediction
ADME-Tox properties were evaluated for all synthe-
sized compounds for their in silico pharmacophore and
drug likeness properties via QikPro tool (Schrodinger,
LLC, New York, NY, 2015). Drug likeness properties of
all evaluated molecules results were described with
their acceptable range in Table 7. The predicted results
were compared with the acceptable range between
>80% high to <25% poor for percentage human oral
absorption (PHOA), <25 poor to >500 great for caco-2

PATEL ET AL.
19
FIGURE 5 Molecular dynamics simulation diagram of compound 4c with PDB: 1J3J. A, Ligand protein contact. B, Ligand protein
RMSF. C, Ligand protein contact histogram. D, Protein ligand RMSD [Color figure can be viewed at wileyonlinelibrary.com]
cell permeability (QPPCaco), −3.0 to 1.2 for blood-
brain partition coefficient (QPlogBB), −1.5 to 1.5 for
prediction of binding to human serum albumin
(QPlogKhsa), below −5.0 for predicted IC50 value for
blockage of HERG K+ channels (QPlogHERG), −6.5 to
0.5 for water solubility parameter (QPlogS), 7.0 to 200.0
for van der Walls surface area of polar nitrogen and
oxygen atoms (PSA). All synthesized compounds were
found to be satisfactory results for pharmacophore
properties. Among all the compounds, the selected
compounds 4a, 4c, 4d, 4l, and 4p have a higher biologi-
cal activity and an acceptable range of ADME-Tox. We
stated that the selected compounds should be promis-
ing considering the future scope.
nanosecond (10 000 ps) simulation running time was
selected for ligand complex study. The simulation trajec-
tory was analyzed every 1 ns with the best binding pose
from calculated RMSD (Å) value. MD suggested that pro-
tein residues LYS 43, ARG 106, SER 128, ARG 129, THR
130, and SER 167 interact with hydrogen during the sim-
ulation. Various energies, ligand properties, and ligand
interactions were noted in the study. According to the
study, we have found that compound 4c was fluctuated
at 2.8 Å with carboxylic group and the ligand was stabi-
lized in the fluctuation range 1.3 to 2.8 Å. Here, ligand-
protein showed their inhibitor bound and open catalytic
activity side with ARG 106. MD and other descriptions
are described in Figure 5.
3.6 | Molecular dynamics
4 | CONCLUSION
In the MD study, best-docked compound 4c was selected
with PDB: 1J3J for their simulation study. Ten-
In summary, we have established a green and highly effi-
cient one-pot three-component microwave irradiation

20
PATEL ET AL.
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ACKNOWLEDGMENTS
The authors are thankful to the Department of Chemis-
try, Gujarat University, Ahmedabad, for providing the
necessary facilities. UGC-Info net and INFLIBNET Guja-
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CONFLICT OF INTEREST
The authors declare no potential conflict of interest.
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How to cite this article: Patel DB, Rajani DP,
Rajani SD, Patel HD. A green synthesis of
quinoline-4-carboxylic derivatives using p-
toluenesulfonic acid as an efficient organocatalyst
under microwave irradiation and their docking,
molecular dynamics, ADME-Tox and biological
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