Synthesis of Some 4-Quinolinyl Pyridines and their Antimicrobial and Docking Studies

Article abstract of DOI:10.1002/jhet.2876

A series of some substituted diethyl 4-(2-chloroquinolin-3-yl)-2,6-dimethylpyridine-3,5-dicarboxylates has been synthesized from substituted diethyl4-(2-chloroquinolin-3-yl)-1,4-dihydro-2,6-dimethylpyridine-3,5-dicarboxylates (1,4-DHPs) by treating the latter with SiO₂–HNO₃ which proved to be a better oxidant in terms of product yield, reaction time, and cost. Further, these compounds were screened for their antimicrobial activity. All the diethyl 4-(2-chloroquinolin-3-yl)-2,6-dimethylpyridine-3,5-dicarboxylates exhibited more potent activities than the corresponding 1,4-DHPs. Further, docking simulation of the most active and least active compounds 3e and 2e into Escherichia coli topoisomerase II DNA Gyrase B was also performed.

Full text of DOI:10.1002/jhet.2876

Month 2017
Synthesis of Some 4-Quinolinyl Pyridines and their Antimicrobial and
Docking Studies
a
Ramesh Kumar,
Radhika Khanna,a Parvin Kumar,a Vikas Kumar,b and Ramesh C. Kamboja
*
aDepartment of Chemistry, Kurukshetra University, Kurukshetra 136119, India
bDepartment of Microbiology, Kurukshetra University, Kurukshetra 136119, India
*
E-mail: rameshkumarkuk@gmail.com
Received August 22, 2016
DOI 10.1002/jhet.2876
Published online 00 Month 2017 in Wiley Online Library (wileyonlinelibrary.com).
A series of some substituted diethyl 4-(2-chloroquinolin-3-yl)-2,6-dimethylpyridine-3,5-dicarboxylates
has been synthesized from substituted diethyl4-(2-chloroquinolin-3-yl)-1,4-dihydro-2,6-dimethylpyridine-
3,5-dicarboxylates (1,4-DHPs) by treating the latter with SiO2–HNO3 which proved to be a better oxidant
in terms of product yield, reaction time, and cost. Further, these compounds were screened for their antimi-
crobial activity. All the diethyl 4-(2-chloroquinolin-3-yl)-2,6-dimethylpyridine-3,5-dicarboxylates exhibited
more potent activities than the corresponding 1,4-DHPs. Further, docking simulation of the most active and
least active compounds 3e and 2e into Escherichia coli topoisomerase II DNA Gyrase B was also performed.
J. Heterocyclic Chem., 00, 00 (2017).
INTRODUCTION
and herbicide [31]. Antimicrobial activity of quinoline
derivative bearing pyrazoline and pyridine analogues
have been reported [32]. Prompted by these biological
properties of quinoline and pyridine derivatives [33], in
the present study, we report the synthesis of substituted
Quinoline nucleus is of substantial significance as this
ring is the key component in a variety of synthetic and
naturally occurring biologically active compounds [1,2].
Quinoline alkaloids such as quinine, chloroquine,
mefloquine, and amodiaquine are the drugs of choice
for the cure of malaria [3]. The quinoline ring containing
compounds exhibit various activities, such as
antitubercular [4,5], antimalarial [6], anti-inflammatory
[7], anticancer [8–10], antibiotic [11], antiprotozoic [12],
antifungal [13], anti-trypanosomal [14], anti-herps [15],
antihypertensive [16], anticonvulsant [17], tyrokinase
PDGF-RTK inhibiting agents [18], and anti-HIV [19,20].
The pyridines, especially the polysubstituted pyridines,
and their intermediate 1,4-dihydropyridines (1,4-DHPs)
have gained great importance in the field of medicinal
chemistry because they display a fascinating array of
pharmacological properties such as antimalarial [21],
antitumor [22,23], antihypertensive [24], antiproliferative
[25], antitubercular [26], anti-inflammatory [27], and
agrochemicals such as fungicide [28,29], pesticide [30],
diethyl
4-(2-chloroquinolin-3-yl)-2,6-dimethylpyridine-
3,5-dicarboxylates, a hybrid organic scaffold in which
both pyridine and quinoline units are linked together.
The substituted quinoline ring has been taken to study
the effect of substituents on antimicrobial activity.
Herein, we use SiO2–HNO3 for oxidation, and it is a
powerful oxidant for the aromatization of 1,4-DHPs and
has earlier been established as a cost-effective, milder,
and high yielding oxidant for obtaining the substituted
benzothiazoles in our laboratory [34].
RESULT AND DISCUSSION
The synthetic protocol used for the synthesis
of substituted diethyl-4-(2-chloroquinolin-3-yl)-1,4-
dihydro-2,6-dimethylpyridine-3,5-dicarboxylates(2a–2f)
© 2017 Wiley Periodicals, Inc.

R. Kumar, R. Khanna, P. Kumar, V. Kumar, and R. C. Kamboj
Vol 000
and
dimethylpyridine-3,5-dicarboxylates (3a–3f) is described
in Scheme 1. One pot condensation of
substituted
diethyl-4-(2-chloroquinolin-3-yl)-2,6-
in dichloromethane which afforded (Table 2) the
corresponding pyridine derivatives (3a–3f) whose
formation was supported by the absence of two singlet
between δ 5.0 and 6.0 for N―H and C4―H protons in
1H-NMR spectra and disappearance of N―H stretching
at 3100–3300 cmꢀ1 in the IR spectra. The pattern of Rf
values (TLC) and melting point of compounds 2a–2f and
3a–3f shows that the intermolecular hydrogen bonding
exists in compounds 2a–2f, resulting in higher melting
points and lower Rf values of 1,4-DHPs (2a–2f) as
compared to their respective oxidized pyridine derivatives
(3a–3f) (Tables 1 and 2).
quinolinecarbaldehydes (1 mol), ethylacetoacetate (2 mol),
and ammonium acetate (2 mol) in ethanol gave the desired
1,4-DHP products (2a–2f) in good yield (Table 1) which
were structurally in full agreement with the spectral data
IR, 1H NMR and 13C NMR. The 1,4-DHPs were identified
by the presence of characteristic N―H and C4―H
protons which resonate between δ 5.0 and 6.0 as a singlet
1
in H NMR. In the IR spectra, ester peak was observed
between 1680 and 1690 cmꢀ1, and N―H peak appeared
between 3100 and 3300 cmꢀ1. The aromatization of
these 1,4-DHPs (2a–2f) was carried out with SiO2–HNO3
In an initial attempt, the oxidation of diethyl 4-(-2-
chloroquinolin-3-yl)-1,4-dihydro-2,6-dimethylpyridine-3,5-
Scheme 1. Synthetic protocol of 1,4-DHPs and their oxidation.
Table 1
Synthesis of 1,4-DHPs.
S. no.
R
Product
Time
Yield
M.p.
Rf value (1:4 ethyl acetate:pet ether)
Color of crystal
1
2
3
4
5
6
H
p-CH3
m-CH3
o-CH3
p-OCH3
o-OCH3
2a
2b
2c
2d
2e
2f
60 min
80 min
60 min
65 min
70 min
65 min
75%
70%
72%
70%
70%
75%
228–230°C
226–228°C
205–207°C
244–246°C
238–240°C
240–243°C
0.15
0.18
0.21
0.21
0.09
0.11
Cream yellow
Cream yellow
Cream yellow
Cream yellow
Cream yellow
Cream yellow
Table 2
Oxidative aromatization of 1,4-DHPs with SiO2–HNO3.
Oxidation with SiO2–HNO3
Rf value (1:4 ethyl
acetate: pet ether)
S. no.
R
Product
Time
2 min
Yield
m.p.
Color
1
2
3
4
5
6
H
3a
3b
3c
3d
3e
3f
85%
87%
84%
88%
87%
81%
128–130°C
105–108°C
97–99°C
113–115°C
100–102°C
104–106°C
0.30
0.45
0.48
0.51
0.30
0.32
Yellow
Yellow
Yellow
Yellow
Yellow
Yellow
60-CH3
70-CH3
80-CH3
60-OCH3
80-OCH3
2 min
2 min
2 min
2 min
2 min
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2017
Synthesis of Some 4-Quinolinyl Pyridines
dicarboxylate 2a (1 mol) was carried out with
SiO2–HNO3 (2 wt %) in dichloromethane at room
temp which yielded diethyl 4-(-2-chloroquinolin-3-yl)-2,6-
dimethylpyridine-3,5-dicarboxylate 3a (85%) in 1 min.
When loading of SiO2–HNO3 was increased, then neither
the rate of reaction nor the yield of the product was
enhanced. But with decreasing amount of SiO2–HNO3 the
yield of oxidized product was reduced. So, we have found
that SiO2–HNO3 can serve as a mild and efficient oxidant
for the aromatization of quinolinyl substituted 1,4-DHPs to
their corresponding pyridine derivatives.
Docking studies.
To understand the reasonable
mechanism of action of most potent compound 3e and
least active compound 2e, docking simulation was
executed against E. coli. Compound 3e and 2e were
docked into active sites of E. coli topoisomerase II DNA
Gyrase
B
complexed with the natural inhibitor
clorobiocin (1KZN) [35]. Literature survey revealed that
the E. coli topoisomerase II DNA Gyrase B [36,37] was a
good target to study biological activity against this
bacterium. The minimum energy binding mode of
compound 3e and 2e was considered. The binding
affinity for 3e and 2e was found ꢀ7.3 and ꢀ6.8,
respectively. It was observed from in silico studies of
compound 2e (Fig. 1) that oxygen atom on ester linkage
forms hydrogen bond with the asparagine (Asn46) and
quinoline ring forms pi-alkyl (hydrophobic interaction)
with the Isoleucine (Ile78). It was observed from in silico
studies of compound 3e that the sp2 hybridized oxygen of
ester group forms carbon hydrogen bond with proline
(Pro79) and isoleucine (Ile78). The pyridine ring of
compound 3e forms pi-anion interaction with glutamic
acid (Glu50). The quinoline ring forms pi-alkyl interaction
with the isoleucine (Ile78) and pi-donor hydrogen bond
with asparagine (Asn46). The chlorine of quinoline
ring shows alkyl interaction with isoleucine (Ile90). From
the docking analysis, it can be seen that the higher
antimicrobial activity of compound 3e than compound 2e
may be due to the pi-anion interaction with glutamic
acid. Compounds 2e and 3e are shown along with co-
crystallized ligand clorobiocin in the active site of E. coli
topoisomerase II DNA Gyrase B (Fig. 2).
Biological discussion. All the synthesized compounds
(2a–2f) and (3a–3f) were assessed in vitro for their
antimicrobial activity against two Gram-positive
bacterium
strains,
i.e.
Bacillus
subtilis
and
Staphylococcus aureus, two Gram-negative bacterium
strains, i.e. Escherichia coli and Pseudomonas
aeruginosa and antifungal activity against two yeasts
named Candida albicans and Saccharomyces cerevisiae
by agar well diffusion method. Their activities were
compared with well-known commercially available
standard drugs, i.e. ciprofloxacin and amphotericin-B.
The widest antimicrobial activity was shown by diethyl
4-(2-chloro-6-methoxyquinolin-3-yl)-2,6-dimethylpyridine-
3,5-dicarboxylates (3e), which was found to be effective
against Gram-positive and Gram-negative bacteria, and
against the yeast as well. Among the whole series under
test (Table 3), substituted diethyl 4-(2-chloroquinolin-3-
yl)-2,6-dimethylpyridine-3,5-dicarboxylates exhibited more
potential activities than the corresponding 1,4-DHPs
(Table 4).
Table 3
In vitro antimicrobial activity of synthetic 1,4-DHPs and4-quinolinyl pyridines through agar well diffusion method.
Diameter of growth of inhibition zone (mm)a
Gram-positive bacteria
Gram-negative bacteria
E. coli P. aeruginosa
Yeast
Compounds
B. subtilis
11
S. aureus
11
C. albicans
S. cerevisiae
2a
2b
2c
2d
2e
2f
3a
3b
3c
3d
3e
3f
11
10
14
10
10
10
12
14
14
14
16
14
22.0
—
10
11
14
10
10
10
10
10
10
12
14
14
25.0
—
11
11
12
11
10
10
12
10
14
12
14
14
—
16.6
11
10
10
10
11
11
10
10
14
14
16
14
—
19.3
10
16
10
11
10
16
10
16
10
16
14
24
—
11
12
11
09
11
10
12
14
12
18
12
25.0
—
Ciprofloxin
Amphotericin-B
— = no activity.
aValues, including diameter of the well (8 mm), are means of three replicates.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

R. Kumar, R. Khanna, P. Kumar, V. Kumar, and R. C. Kamboj
Vol 000
Table 4
MIC (in μg/mL) of synthetic 1,4-DHPs and 4-quinolinyl pyridines obtained using macro dilution method.
Gram-positive bacteria
B. subtilis S. aureus
Gram-negative bacteria
E. coli P. aeruginosa
Yeast
Compounds
C. albicans
S. cerevisiae
2a
2b
2c
2d
2e
2f
3a
3b
3c
3d
3e
3f
200
200
50
200
200
200
50
200
50
200
50
200
200
100
200
200
200
200
100
100
100
50
200
200
50
200
200
100
200
200
200
200
200
200
100
100
100
200
200
50
200
200
200
200
200
200
200
200
100
100
50
200
200
200
100
100
100
100
50
200
200
200
100
200
100
100
100
100
—
100
6.25
—
100
6.25
—
100
6.25
—
100
—
12.5
Ciprofloxin
Amphotericin-B
12.5
—
12.5
Figure 1. 2D schematic of compound 2e and 3e docked in active site of DNA Gyrase B. [Color figure can be viewed at wileyonlinelibrary.com]
Figure 2. Surface diagram showing docked molecules 2e and 3e along with co-crystallized ligand clorobiocin in the active site of E. coli topoisomerase II
DNA Gyrase (2e in green, 3e in yellow and clorobiocin in magenta color). [Color figure can be viewed at wileyonlinelibrary.com]
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2017
Synthesis of Some 4-Quinolinyl Pyridines
(2 mol), and ammonium acetate (2 mol) was taken in
CONCLUSION
a 250-mL round bottom flask separately and dissolved in
ethanol. The reaction mixture was refluxed for about
60 min on water bath. Progress of the reaction was
monitored by TLC (ethylacetate:pet ether). After the
completion of reaction, the reaction mixture was cooled
to room temperature to give solid diethyl 1,4-dihydro-2,
6-dimethyl-4-(2-chloroquinolin-3-carbaldehyde)pyridine-
3,5-dicarboxylates (2a–2f) which was filtered and further
purified by recrystallization from aqueous ethanol.
A series of 4-quinolinyl pyridine based compounds
has been synthesized with the hope of new lead
molecules. The oxidation of 1,4-DHPs was carried out
with SiO2–HNO3 which proved to be efficient oxidant
in terms of yield, reaction time, easy workup, and
cost. Within this study, the diethyl 4-(2-chloroquinolin-
3-yl)-2,6-dimethylpyridine-3,5-dicarboxylates exhibited
more promising antimicrobial activities compared to 1,4-
DHPs against all the microbial strains. And among all the
derivatives, diethyl 4-(2-chloro-6-methoxyquinolin-3-yl)-
2,6-dimethylpyridine-3,5-dicarboxylates derivative 3e was
found to be the most biologically active compound.
Further, docking studies showed that compounds 3e
(minimum inhibitory concentration (MIC), 50 μg/mL)
inhibits E. coli topoisomerase II DNA GyraseB,
respectively, through carbon hydrogen bond, pi-anion,
pi-donor hydrogen bond, alkyl, and pi-alkyl interactions.
These findings can be exploited toward the development
and testing of pyridine and quinoline-based hybrid novel
molecules for better antimicrobial activities.
Diethyl
4-(2-chloroquinolin-3-yl)-1,4-dihydro-2,6-
dimethylpyridine-3,5-dicarboxylate [38] (2a, C22H23ClN2O4). IR
(νmax, cmꢀ1, KBr): 3271 (N―H stretch), 1697 (―COOEt);
1
0
H NMR[CDCl3, δ (ppm), 400 MHz]: 8.134 (s, 1H, C4 ―H),
0
7.973–7.952 (d, J = 8.4 Hz, 1H, C8 ―H), 7.746–7.726 (d,
J = 8.0 Hz, 1H, C5 ―H), 7.675–7.633 (m, J = 6.8 and
8.0 Hz, 1H, C7 ―H), 7.511–7.471 (m, J = 6.8 and 8.0 Hz,
1H, C6 ―H), 5.593 (s, 1H, N―H), 5.513 (s, 1H, C4―H),
0
0
0
4.117-4.021 (q, J = 7.2 Hz, 4H, ―OCH2―CH3), 2.357 (s,
6H, C2 and C6―CH3), 1.203-1.167 (t, J = 7.2 Hz, 6H,
―CH2―CH3); 13C NMR [CDCl3, δ (ppm), 75.4 MHz]:
167.2, 150.3, 146.3, 144.3, 140.3, 139.9, 129.8, 128.0, 127.7,
127.1, 126.5, 103.5, 59.9, 38.3, 19.6, 14.3; DART MS: m/z
414.23/416.14 (3:1), Anal. Calcd. C = 63.69, H = 5.59,
Cl = 8.55, N = 6.75, O = 15.43; Found C = 63.66, H = 5.58,
Cl = 8.59, N = 6.72, O = 15.45.
EXPERIMENTAL
Diethyl 4-(2-chloro-60-methylquinolin-3-yl)-1,4-dihydro-2,6-
Melting points recorded are uncorrected and taken in
open capillaries. IR spectra were recorded on a Perkin-
Elmer IR spectrophotometer. 1H and 13C spectra were
recorded in CDCl3 on a 300 MHz/400 MHz and
75.4 MHz/100.6 MHz Bruker spectrometer using TMS as
an internal standard, respectively. Mass spectra (DART-
MS) were recorded on a JMS-T100LC Mass spectrometer
having a DART (Direct Analysis in Real Time) source in
ES+ mode.
dimethylpyridine-3,5-dicarboxylate [39] (2b, C23H25ClN2O4). IR
(νmax, cmꢀ1, KBr): 3269 (N―H stretch), 1690 (―COOEt);
1
0
H NMR[CDCl3, δ (ppm), 300 MHz]: 8.052 (s, 1H, C4 ―H),
0
7.880–7.852 (d, 0J = 8.4 Hz, 1H, C8 ―H), 7.510–7.479 (m,
0
2H, C5 and C7 ―H), 5.829 (s, 1H, N―H), 5.505 (s, 1H,
C4―H), 4.489–4.164 (q, 4H, ―OCH2―CH3), 2.508 (s,
0
3H, C6 ―CH3), 2.364 (s, 6H, C2 and C6―CH3), 1.219–
1.172 (t, J = 7.2 Hz, 6H, ―CH2―CH3); 13C NMR
[CDCl3, δ (ppm), 75.4 MHz]: 166.1, 148.2, 143.7, 143.1,
139.0, 138.1, 135.3, 130.9, 126.5, 124.8, 102.4, 58.7, 37.0,
20.3, 18.4, 13.1; DART MS: m/z 429.26/431.26 (3:1), Anal.
Calcd. C = 64.41, H = 5.88, Cl = 8.27, N = 6.53,
O = 14.92; Found C = 64.43, H = 5.84, Cl = 8.29,
N = 6.51, O = 14.91.
Synthesis of substituted 2-chloroquinolin-3-carbaldehyde
(1a–1f): a general procedure.
N,N-Dimethylformamide
(2.2 mol) was cooled to 0°C in a flask equipped with a
CaCl2 guard tube, and phosphoryl chloride (4.0 mol) was
added in to it dropwise with stirring. To this reaction
mixture, acetanilide (1.0 mol) was added and kept the
whole reaction mixture at 80°C for 6–8 h. The reaction
mixture was cooled and poured into ice water (300 mL)
and stirred for 1 h at 0–10°C. The precipitated 2-chloro-
3-quinolincarbaldehyde 1a was filtered, washed with
water (100 mL), dried, and recrystallized from ethanol
to give the title product as yellow needles with M.p.
150°C. Likewise, other carbaldehydes were obtained with
M.p.: 1b—110°C, 1c—145°C, 1d—140°C, 1e—130°C,
and 1f—117°C.
Diethyl4-(2-chloro-70-methylquinolin-3-yl)-1,4-dihydro-2,6-
dimethylpyridine-3,5-dicarboxylate [40] (2c, C23H25ClN2O4). IR
(νmax
,
cmꢀ1
,
KBr): 3294 (N―H stretch), 1690
1
(―COOEt); H NMR[CDCl3, δ (ppm), 300 MHz]: 8.080
(s, 1H, C4 ―H), 7.747 (s, 1H, C8 ―H), 7.643–7.615 (d,
J = 8.4 Hz, 1H, C5 ―H), 7.345–7.317 (d, J = 8.4 Hz,
1H, C6 ―H), 5.888 (s, 1H, N―H), 5.505 (s, 1H, C4―H),
0
0
0
0
4.159–4.0240 (q, J = 7.2 Hz, 4H, ―OCH2―CH3), 2.575
(s, 3H, C7 ―CH3), 2.363 (s, 6H, C2 and C6―CH3),
1.280–1.167 (t, J = 7.2 Hz, 6H, ―CH2―CH3); 13C NMR
[CDCl3, δ (ppm), 75.4 MHz]: 167.3, 150.2, 146.6, 144.2,
139.6, 139.2, 128.8, 127.0, 126.8, 125.8, 103.5, 59.8, 38.2,
21.8, 19.6, 14.3; DART MS: m/z 428.12/430.14 (3:1),
Synthesis of substituted diethyl 4-(2-chloroquinolin-3-yl)-
1,4-dihydro-2,6-dimethylpyridine-3,5-dicarboxylate (2a–2f):
a general procedure. A mixture of 2-chloroquinolin-3-
carbaldehyde (1a–1e) (1 mol), ethylacetoacetate
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

R. Kumar, R. Khanna, P. Kumar, V. Kumar, and R. C. Kamboj
Vol 000
Anal. Calcd. C = 64.41, H = 5.88, Cl = 8.27, N = 6.53,
O = 14.92; Found C = 63.38, H = 5.81, Cl = 8.25,
N = 6.57, O = 14.93.
dichloromethane at room temperature for 1–2 min
separately. After the completion of reaction, indicated by
TLC, reaction mixture was filtered and neutralized with
saturated solution of sodium bicarbonate followed by the
extraction of organic layer and dried it over anhydrous
magnesium sulphate. Evaporation of the solvent afforded
the pure final product diethyl-2,6-dimethyl-4-(2-
chloroquinolin-3-carbaldehyde)pyridine-3,5-
Diethyl
4-(2-chloro-80-methylquinolin-3-yl)-1,4-dihydro-2,6-
dimethylpyridine-3,5-dicarboxylate [41] (2d, C23H25ClN2O4). IR
(νmax, cmꢀ1, KBr): 3294 (N―H stretch), 1690 (―COOEt);
1
0
H NMR[CDCl3, δ (ppm), 300 MHz]: 8.091 (s, 1H, C4 ―H),
0
7.591–7.565 (d, J 0= 7.8 Hz, 1H, C5 ―H), 7.512–7.489 (d,
J = 7.2 Hz, 1H, C7 ―H), 7.405–7.355 (t, J = 7.2, 7.8 Hz, 1H,
dicarboxylates (3a–3e).
0
C6 ―H), 5.806 (s, 1H, N―H), 5.533 (s, 1H, C4―H),
Diethyl 4-(2-chloroquinolin-3-yl)-2,6-dimethylpyridine-3,5-
4.167–4.0230 (q, J = 7.2 Hz, 4H, ―OCH2―CH3), 2.759
(s, 3H, C8 ―CH3), 2.361 (s, 6H, C2 and C6―CH3),
1.283–1.177 (t, J = 7.2 Hz, 6H, ―CH2―CH3); 13C
NMR [CDCl3, δ (ppm), 75.4 MHz]: 167.3, 149.2, 145.6,
144.2, 140.2, 139.5, 136.2, 129.8, 127.7, 126.2, 125.1,
103.4, 59.8, 38.4, 19.6, 17.8, 14.3; DART MS: m/z
428.23/430.14 (3:1), Anal. Calcd. C = 63.41, H = 5.88,
Cl = 8.27, N = 6.53, O = 14.92; Found C = 63.44,
H = 5.85, Cl = 8.28, N = 6.56, O = 14.94.
dicarboxylate (3a, C22H21ClN2O4). IR (νmax, cmꢀ1, KBr):
1
1720 (―COOEt); H NMR (CDCl3, δppm, 400 MHz):
0
0
8.084 (s, 1H, C4 ―H), 7.979 (s, 1H, C8 ―H), 7.841–
0
0
7.798 (m, 1H, C5 and C7 ―H), 7.652–7.614
(t, J = 5.7 Hz, 1H, C6 ―H), 4.064–3.931 (q, J = 7.2 Hz,
0
4H, ―OCH2―CH3), 2.796 (s, 6H, C2and C6―CH3),
0.839–0.804 (t, J = 7.2 Hz, 6H, ―CH2―CH3); 13C
NMR[CDCl3, δppm, 75.4 MHz]:165.4, 156.4, 148.2,
147.2, 137.8, 131.4, 129.3, 128.4, 128, 127.8, 127.7,
125.8, 62.0, 22.0, 13.4; DART MS: m/z 413.23/415.23
(3:1), Anal. Calcd. C = 64.00, H = 5.13, Cl = 8.59,
N = 6.79, O = 15.50; Found C = 64.02, H = 5.09,
Cl = 8.59, N = 6.81, O = 15.48
Diethyl
4-(2-chloro-60-methoxyquinolin-3-yl)-1,4-dihydro-2,6-
dimethylpyridine-3,5-dicarboxylate (2e, C23H25ClN2O5).
IR
(νmax, cmꢀ1, KBr): 3202 (N―H stretch), 1682 (―COOEt);
1
0
H NMR[CDCl3, δ (ppm), 300 MHz]: 8.034 (s, 1H, C4 ―H),
0
0
Diethyl
4-(2-chloro-60-methylquinolin-3-yl)-2,6-
7.882–7.852 (d, 1H, C8 ―H), 7.416–7.330 (d, 2H, C5 and
0
C7 ―H), 5.850 (s, 1H, N―H), 5.504 (s, 1H, C4―H),
dimethylpyridine-3,5-dicarboxylate (3b, C23H23ClN2O4).
IR
1
(νmax, cmꢀ1, KBr): 1728 (―COOEt); H NMR (CDCl3, δ
ppm, 300 MHz): 7.990–7.636 (m, 4H, quinolinyl-H),
4.235-3.895 (q, 4H, ―OCH2―CH3), 2.905 (s, 6H, C2 and
4.110–4.069 (q, J = 5.4 Hz, 4H, ―OCH2―CH3), 3.917 (s,
0
3H, C6 ―OCH3), 2.551 (s, 6H, C2 and C6―CH3),
1.309–1.206 (t, J = 5.1 Hz, 6H, ―CH2―CH3); 13C NMR
[CDCl3, δ (ppm), 100.6 MHz]: 167.4, 157.7, 147.7, 144.4,
142.3, 140.5, 138.8, 129.3, 128.8, 122.5, 104.7, 103.5, 59.9,
55.5, 38.1, 19.5, 14.3; DART MS: m/z 445.26/447.26 (3:1),
Anal. Calcd. C = 62.09, H = 5.66, Cl = 7.97, N = 6.30,
O = 17.98; Found C = 62.11, H = 5.63, Cl = 7.98, N = 6.26,
0
C6―CH3), 2.580 (s, 3H, C6 ―CH3), 1.978–1.813 (t, 6H,
―CH2―CH3); 13C NMR[CDCl3, δppm, 75.4 MHz]:
163.4, 154.6, 145.1, 136.3, 133.2, 128.5, 127.1, 125.7,
61.5, 20.7, 19.8, 12.5; DART MS: m/z 426.20/428.14
(3:1), Anal. Calcd. C = 64.71, H = 5.43, Cl = 8.30,
N = 6.56, O = 14.99; Found C = 64.73, H = 5.41,
Cl = 8.27, N = 6.59, O = 14.98.
O = 17.94.
Diethyl 4-(2-chloro-80-methoxyquinolin-3-yl)-1,4-dihydro-2,
6-dimethylpyridine-3,5-dicarboxylate (2f, C23H25ClN2O5). IR
Diethyl
4-(2-chloro-70-methylquinolin-3-yl)-2,6-
(νmax
,
cmꢀ1
,
KBr): 3282 (N―H stretch), 1685
dimethylpyridine-3,5-dicarboxylate (3c, C23H23ClN2O4). IR
1
1
(νmax, cmꢀ1, KBr): 1720 (―COOEt); H [CDCl3, δ ppm,
(―COOEt);0 H NMR[CDCl3, δ (ppm), 300 MHz]: 8.052
0
0
(s,0 1H, C4 ―H), 7.880–7.776 (t, J = 6.3 Hz, 1H,
300 MHz]: 7.917 (s, 1H, C4 ―H), 7.841 (s, 1H, C8 ―H),
0
0
C6 ―H), 7.510–7.479 (d, J = 6.3 Hz, 1H, C5 ―H),
7.717–7.690 (d, J = 8.1 Hz, 1H, C5 ―H), 7.453–7.427
(d, J = 8.1 Hz, 1H, C6 ―H), 4.162–3.932 (q, J = 6.9 Hz,
0
0
6.854–6.795 (d, 2H, C7 ―H), 5.829 (s, 1H, N―H),
5.505 (s, 1H, C4―H), 4.324–4.164 (m, 4H,
4H, ―OCH2―CH3), 2.718 (s, 6H, C2 and C6―CH3),
0
0
―OCH2―CH3), 3.506 (s, 3H, C8 ―OCH3), 2.364
2.613 (s, 1H, C7 ―CH3), 0.890–0.790 (t, J = 8.4 Hz,
6H, ―CH2―CH3); 13C NMR[CDCl3,
δ
ppm,
(s, 6H, C2 and C6―CH3), 1.467–1.381 (t, J = 7.2 Hz,
6H, ―CH2―CH3); 13C NMR [CDCl3,
δ (ppm),
75.4 MHz]:166.7, 157.1, 148.8, 147.4, 143.0, 141.7,
137.5, 129.8, 129.1, 127.4, 127.2, 126.6, 124.1, 61.5,
23.5, 21.9, 13.5; DART MS: m/z 427.25/429.25 (3:1),
Anal. Calcd. C = 64.71, H = 5.43, Cl = 8.30, N = 6.56,
O = 14.99; Found C = 64.68, H = 5.45, Cl = 8.26,
N = 6.54, O = 14.99.
75.4 MHz]: 167.3, 150.2, 145.6, 144.2, 139.5, 137.7,
128.8, 122.5, 104.7, 103.4, 59.8, 55.5, 38.1, 19.6, 14.3;
DART MS: m/z 445.20/447.14 (3:1), Anal. Calcd.
C = 62.09, H = 5.66, Cl = 7.97, N = 6.30, O = 17.98;
Found C = 62.09, H = 5.64, Cl = 7.99, N = 6.28,
O = 17.95.
Diethyl
4-(2-chloro-80-methylquinolin-3-yl)-2,6-
dimethylpyridine-3,5-dicarboxylate (3d, C23H23ClN2O4).
IR
Synthesis of substituted diethyl 4-(2-chloroquinolin-3-yl)-2,
1
6-dimethylpyridine-3,5-dicarboxylate
(3a–3e).
SiO2–
(νmax, cmꢀ1, KBr): 1720 (―COOEt); H NMR[CDCl3, δ
0
HNO3 (2 wt % of 1,4-DHP) was added to a magnetically
stirred solution of each 1,4-DHP (2a–2e) in
ppm, 300 MHz]: 7.936 (s, 1H, C4 ―H), 7.654–7.628 (m,
0
0
2H, C5 and C7 ―H), 7.513–7.463 (t, J = 7.8 Hz, 1H,
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2017
Synthesis of Some 4-Quinolinyl Pyridines
0
C6 ―H), 4.121–3.905 (q, J = 7.2 Hz, 4H, ―OCH2―CH3),
compounds were evaluated by the agar well
diffusion assay. The inoculum suspensions of the
test microorganisms were prepared by using 16-h-old
cultures adjusted to 108cfu/mL by referring the 0.5
McFarland standards. Twenty milliliters of agar medium
(Nutrient Agar and Malt Extract Agar) was poured into
each Petri plate, and plates were swabbed with 100-μL
inocula of the test microorganisms and kept for 15 min
for adsorption. Using sterile cork borer of 8-mm
diameter, wells were bored into the seeded agar plates,
and these were loaded with a 100-μL volume with
concentration of 4.0 mg/mL of each compound
reconstituted in the dimethylsulphoxide (DMSO).
All the plates were incubated at 37°C for 24 h.
Antimicrobial activity of each compound was evaluated
by measuring the zone of growth inhibition against the
test organisms with zone reader (HiAntibiotic zone
scale). Dimethylsulphoxide was used as a negative
control, whereas Ciprofloxacin was used as positive
control for bacteria and Amphotericin-B for yeast. This
procedure was performed in three replicate plates for
each organism [42].
0
2.930 (s, 3H, C8 ―CH3), 2.805 (s, 6H, C2and C6―CH3),
0.891–0.812 (t, J = 6.6 Hz 6H, ―CH2―CH3);
NMR [CDCl3, δ ppm, 100.6 MHz]: 166.2, 156.7,
147.4, 146.4, 144.2, 138.1, 136.6, 131.3, 129.4, 127.4,
127.2, 127.2, 126.0, 125.5, 61.7, 29.7, 22.9, 17.7, 13.4;
DART MS: m/z 426.25/428.25 (3:1), Anal. Calcd.
13
C
C
= 64.71, H = 5.43, Cl = 8.30, N = 6.56,
O = 14.99; Found C = 64.71, H = 5.46, Cl = 8.27,
N = 6.56, O = 14.98
Diethyl
dimethylpyridine-3,5-dicarboxylate (3e, C23H23ClN2O5).
(νmax, cmꢀ1, KBr): 1725 (―COOEt); H NMR[CDCl3, δ
4-(2-chloro-60-methoxyquinolin-3-yl)-2,6-
IR
1
ppm, 400 MHz]: 7.958–7.935 (d, J = 6.9 Hz, 1H,
0
C8 ―H), 7.849 (s, 1H, H-40), 7.434–7.406 (d, J = 6.9 Hz,
0
0
1H, C7 ―H), 7.046 (s, 1H, C5 ―H), 4.074–3.985 (q, 4H,
―OCH2―CH3), 3.960 (s, 6H, C6 ―H―OCH3), 2.714 (s,
0
6H, C4 and C6―CH3), 0.882–0.820 (t, J = 7.2 Hz, 6H,
―CH2―CH3); 13C NMR [CDCl3, δ ppm, 100.6 MHz]:
166.6, 158.5, 157.1, 146.1, 143.1, 136.6, 130.2, 129.7,
127.2, 126.6, 123.8, 105.1, 61.6, 55.6, 23.4, 13.5; DART
MS: m/z 444.25/446.25 (3:1), Anal. Calcd. C = 62.37,
H = 5.23, Cl = 8.00, N = 6.33, O = 18.06; Found
C = 62.39, H = 5.26, Cl = 7.98, N = 6.32, O = 18.03
Diethyl4-(2-chloro-80-methoxyquinolin-3-yl)-2,6-dimethylpyr-
Determination of minimum inhibitory concentration
(MIC) of chemical compounds.
Minimum inhibitory
concentration is the lowest concentration of an
antimicrobial compound that will inhibit the visible
growth of a microorganism after incubation. Minimum
inhibitory concentration of the 4-quinolinyl pyridines
against bacterial and yeast strains was tested through a
modified agar well diffusion method. In this method, a
twofold serial dilution of each chemically synthesized
compound was prepared by first reconstituting the
compound in DMSO followed by dilution in sterile
distilled water to achieve a decreasing concentration
range of 4 to 0.0625 mg/mL. A 100-μL volume of each
dilution was introduced into wells (in triplicate) in the
agar plates already seeded with 100 μL of standardized
inoculum (108 cfu/mL) of the test microbial strain. All
test plates were incubated aerobically at 37°C for 24 h
and observed for the inhibition zones. Minimum
inhibitory concentration, taken as the lowest
concentration of the chemical compound that inhibited
the growth of the microbe, shown by a clear zone of
inhibition, was recorded for each test organism.
Ciprofloxacin and Amphotericin-B were used as positive
control while DMSO as negative control.
idine-3,5-dicarboxylate (3f, C23H23ClN2O5). IR (νmax, cmꢀ1
,
KBr): 1710 (―COOEt); 1H NMR[CDCl3, δ(ppm),
0
300 MHz]: 8.0730 (s, C4 ―H), 7.774–7.751 (d,
J = 6.9 Hz, 1H, C5 ―H), 7.643–7.592 (t, J = 6.9 and
0
8.4 Hz, 1H, C6 ―H), 7.346–7.318 (d, J = 8.4 Hz, 1H,
0
C7 ―H), 4.164–4.003 (q,
J
=
8.4 Hz, 4H,
0
―OCH2―CH3), 3.941 (s, 6H, C8 ―CH3), 2.774 (s,
6H, C2 and C6―CH3), 1.271–1.171 (t, J = 6.9 Hz,
6H, ―CH2―CH3); 13C NMR [CDCl3, δ(ppm),
75.4 MHz]:166.7, 157.1, 148.8, 147.4, 146.1, 143.2,
141.5, 137.5, 129.6, 129.0, 127.2, 126.8, 124.0, 61.5,
55.7, 23.5, 13.5; DART MS: m/z 444.15/446.15 (3:1),
Anal. Calcd. C = 62.37, H = 5.23, Cl = 8.00,
N = 6.33, O = 18.06; Found C = 63.37, H = 5.21,
Cl = 8.02, N = 6.31, O = 18.05.
Pharmacology. Test microorganisms.
Total six
microbial strains, i.e. two Gram-positive bacteria
(S. aureus MTCC 96 and B. subtilis MTCC 121), two
Gram-negative bacteria (E. coli MTCC 1652 and
P. aeruginosa MTCC 741), and two yeasts (C. albicans
MTCC 227 and S. cerevisiae MTCC 170) were screened
for evaluation of antibacterial and antifungal activity of
the chemical compounds. All the microbial cultures were
procured from Microbial Type Culture Collection
(MTCC), Institute of Microbial Technology, Chandigarh.
The bacteria were subcultured on Nutrient Agar whereas
yeast on Malt Extract Agar plates.
Computational details.
The crystal structure of
topoisomerase II DNA Gyrase B was taken from
Protein Data Bank (PDB entry: 1KZN) [35]. To
execute docking studies, the 2D structure of most
active ligand (3e) was drawn, converted to 3D, and its
energy was minimized [43]. Ligand, 3e, was prepared
in pdb format with explicit hydrogen addition.
Co-crystallized ligand was removed from pdb file,
Antimicrobial assay (bacteria and yeasts).
antimicrobial activity and MIC value of 12 chemical
The
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

R. Kumar, R. Khanna, P. Kumar, V. Kumar, and R. C. Kamboj
Vol 000
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1KZN, and protein molecule was prepared by deleting
solvent molecules and non-complex ions using Chimera
[44]. Incomplete side chains were replaced using Dun
BrackRotamer library [45]. Hydrogens were added, and
gasteiger charges were calculated using Antechamber
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studies were executed by using Auto Dock Vina 1.1.2.
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Acknowledgment. One of the authors (Radhika Khanna) wishes
to express her gratitude to the Department of Science and
Technology (SRF-DST INSPIRE), New Delhi for the financial
assistance for the accomplishment of this work.
[30] Wang, P.; Yang, X.; Huang, W. W.; Zhang, M.; Lu, W. H.;
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Journal of Heterocyclic Chemistry
DOI 10.1002/jhet