Design, synthesis, spectral characterization and molecular docking studies of novel pyranoquinolinyl dihydropyridine carboxylates as potential antibacterial agents including Vibrio cholerae with minimal cytotoxity towards fibroblast cell line (L-929)

Article abstract of DOI:10.1016/j.bioorg.2020.104582

Novel pyranoquinolinyl dihydropyridine carboxylate (PDC) derivatives were designed by incorporating the multi-drug resistance modulating effects of 1,4 dihydropyridines along with potential antibacterial activity of quinolines in the molecular design. The

Full text of DOI:10.1016/j.bioorg.2020.104582

Bioorganic Chemistry 107 (2021) 104582
Contents lists available at ScienceDirect
Bioorganic Chemistry
journal homepage: www.elsevier.com/locate/bioorg
Design, synthesis, spectral characterization and molecular docking studies
of novel pyranoquinolinyl dihydropyridine carboxylates as potential
antibacterial agents including Vibrio cholerae with minimal cytotoxity
towards fibroblast cell line (L-929)
a
a,
*
a
b
a
G. Lavanya , C.J. Magesh , K. Venkatapathy , P.T. Perumal , S. Prema
a
PG & Research Department of Chemistry, Arignar Anna Govt. Arts and Science College Cheyyar, Tamilnadu, India
b
Department of Chemistry, B.S Abdur Rahman Crescent Institute of Science and Technology, Vandalur, Chennai, India
A R T I C L E I N F O
A B S T R A C T
Keywords:
Novel pyranoquinolinyl dihydropyridine carboxylate (PDC) derivatives were designed by incorporating the
multi-drug resistance modulating effects of 1,4 dihydropyridines along with potential antibacterial activity of
quinolines in the molecular design. The designed PDC derivatives were synthesized by multi-step synthesis
involving Michael addition, reduction followed by inverse electro demand Diels-Alder reaction to produce
pyranoquinolinyl dihydropyridine carboxylates in good yields. All the PDC derivatives were characterized by 1H
NMR, 13C NMR, FT-IR, Mass spectral and CHN analysis. The Quinolinyl dihydropyridine carboxylate derivatives
were evaluated for in vitro antibacterial activity by agar well diffusion method. Molecular docking studies
revealed that the exo diethyl 4-(4aR,5S,10bR)-5-(4-chlorophenyl)-3,4,4a,5,6,10b-hexahydro-2H-pyrano[3,2-c]
quinolin-8-yl)-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate diastereomer (5c) forms four hydrogen bonds
with the cell wall protein of vibrio cholerae in comparison to the endo diethyl 4-((4aR,5R,10bR)-5-(4-chlor-
ophenyl)-3,4,4a,5,6,10b-hexahydro-2H-pyrano[3,2-c]quinolin-8-yl)-2,6-dimethyl-1,4-dihydropyridine-3,5-
dicarboxylate diastereomer (4c) which forms two hydrogen bonds with the cell wall protein of vibrio cholerae
and hence leading to better anchorage, enhanced gold score and relatively good antibacterial activity for the exo
PDC derivatives. Minimum inhibitory concentration (MIC) of the active compounds was evaluated by macro
dilution method. The mechanism of antibacterial action of the PDC derivatives was investigated by SEM studies.
The cytotoxicity of PDC derivatives were evaluated against fibroblast cells (L-929).
Aryl aldehyde
DHP Amine
Lewis acid catalyst
Quinoline
Antibacterial activity
MIC
Cytotoxicity
Molecular docking and spectral
characterization
1
. Introduction
Research and development for finding new drugs and improved
cholera on infants and children [6], failure to develop new antibiotics,
lack of treatment options for drug resistant strains, the development of
new antibiotics to treat and mitigate cholera is highly desirable [7,8].
1,4–dihydropyridines exhibit wide spectrum of biological activities such
as vasodilator, bronchodilator, hepatoprotective, antitumor, ger-
oprotoctive, antidiabetic agents [9–11] and calcium chennal blockers
[12–14]. 1,4 dihyropyridines have been identified to bring about the
reversal of multidrug resistance and are known to be multi-drug resis-
tant modulators [15]. Pyrano and furano quinoline derivatives exhibit
wide spectrum of biological activies such as anti-inflamatory [16],
psychotropic [17], anti-allergic [18], antibacterial activity [19] and
estrogenic activities [20]. Hence in an attempt to counter the problem of
drug resistant bacteria, we have combined the multi-drug resistant
modulating effect of 1,4 dihydropyridines along with strong
chemical entities for treatment and mitigation of various diseases
associated with viruses such as Ebola virus, Corona virus, Avian influ-
enza virus and carbapenem resistant strains of bacteria’s such as Aci-
netobacter
baumannii,
Pseudomonas
aeruginosa
and
Enterobacteriaceae is of utmost priority for chemists & scientists
worldwide to ensure the very existence and survival of human beings
[
1–3]. According to WHO report (1995) [4], the major cause for children
mortality in developing and under developed countries is cholera,
contracted by ingesting food contaminated with vibrio cholerae. Drug
resistant strains of Vibrio cholera [5] have further worsened the scenario
posing a major challenge to medicinal practitioners. Due to the impact of
*
Corresponding author.
E-mail address: cjmageshchemistry@gmail.com (C.J. Magesh).
https://doi.org/10.1016/j.bioorg.2020.104582
Received 9 October 2020; Received in revised form 20 November 2020; Accepted 19 December 2020
Available online 12 January 2021
0
045-2068/© 2020 Elsevier Inc. All rights reserved.

G. Lavanya et al.
Bioorganic Chemistry 107 (2021) 104582
antibacterial activity of quinolines to find a promising class of new
chemical entities as potential antibacterial agents with minimal
cytotoxicity.
2.2.1.2. Diethyl 4-(4-aminophenyl)-2,6-dimethyl-1,4-dihydropyridine-3,5-
ꢀ
1
dicarboxylate (2). FT- IR (KBr) Vmax cm : 3340, 1670, 1230, 1109,
1
652; H NMR (CDCl
3
, 400 MHz) δ: 10.17 (brs, 2H, NH ), 8.09–8.07 (d,
2
Recently we have reported the novel pyranoquinolinyl acrylic acid
2H, J = 8 Hz), 7.47–7.45 (d, 2H, J = 8 MHz), 6.18 (brs, 1H, NH), 5.10 (s,
1
3
diasteromers as potential
α
-Glucosidase inhibitors [21] and carbazolyl
1H), 4.11–4.08 (q, 4H), 2.35 (s, 6H), 1.24–1.20 (t, 6H); C NMR (100
dihydropyrimidinones with good oral bioavailability [22]. In our search
for finding new antibacterial agents we have recently reported design,
synthesis, molecular docking and spectral studies of new class of Car-
bazolyl polyhydroquinolines derivatives as promising antibacterial
agents with non-cytotoxicity towards human mononuclear cells (HMNC-
PB) [23]. In continuation of our search for finding new chemical entities
with potential antibacterial activity and minimal cytotoxicity, we now
report the design, synthesis, spectral characterization, molecular dock-
ing and antibacterial studies of novel pyranoquinolinyl dihydropyridine
carboxylates as potential antibacterial agents including vibrio cholerae.
MHz, CDCl
3
) δ: 166.8, 155.1, 146.1, 144.9, 128.5, 123.0, 103.0, 59.8,
+
39.9, 19.4, 14.1; MS: m/z: 344 (M ); Anal. Calcd. for C19
H
24
N
2
O
4
: C,
66.26; H, 7.02; N, 8.13; Found: C, 66.31; H, 7.03; N, 8.09.
2.2.1.3. Diethyl
2,6-dimethyl-4-((4aR,5R,10bR)-5-phenyl-
3,4,4a,5,6,10b-hexahydro-2H-pyrano[3,2-c]quinolin-8-yl)-1,4-dihy-
dropyridine-3,5-dicarboxylate (4a). FT- IR (KBr) V
max
cm 1: 3385, 2943,
ꢀ
1655, 1272, 1121, 625; 1H NMR (CDCl , 400 MHz) δ: 9.72 (brs, 1H,
3
NH), 7.38–7.27 (m, 5H), 6.98–6.96 (d, 1H, J = 8 MHz), 6.47–6.45 (d,
2H, J = 8 MHz), 5.28–5.27 (d, 1H, J = 4.00 MHz), 5.19 (s, 1H), 4.90 (s,
1
H), 4.63 (brs, 1H, NH), 4.11–4.05 (q, 4H), 3.37–3.30 (t, 2H), 2.35–2.31
13
2
. Experimental section
(d, 1H), 2.17 (s, 6H), 1.54–1.48 (m, 4H), 1.26–1.22 (t, 6H); C NMR
100 MHz, CDCl
(
3
) δ: 167.66, 143.39, 141.26, 138.42, 128.22, 127.73,
2
.1. Materials & methods
127.41, 126.83, 118.98, 114.15, 104.36, 72.91, 61.84, 59.33, 39.90,
+
3
8.68, 30.94, 29.01, 25.44, 19.48, 14.33; MS: m/z: 516 (M ); Anal.
The AR grade solvents and chemicals were purchased from sigma
2 5
Calcd. for C31H36N O : C, 72.07; H, 7.02; N, 5.42; Found: C, 72.01; H,
Aldrich. The FT-IR spectrum of synthesized compounds were recorded
by using Nicolet impact 400 FT-IR spectrometer using KBr pellets
technique. 1H NMR spectra were recorded on Bruker (400 MHz) in
6.99; N, 5.31.
2
.2.1.4. Diethyl 2,6-dimethyl-4-((4aR,5S,10bR)-5-phenyl-3,4,4a,5,6,10b-
DMSO‑d
relative to the internal standard TMS and C NMR spectra were
recorded on 100 MHz in DMSO‑d or CDCl solvent. Elemental analysis
6 3
or CDCl solvent and chemical shifts are reported in δ values
hexahydro-2H-pyrano [3,2-c]quinolin-8-yl)-1,4-dihydropyridine-3,5-dicar-
13
ꢀ 1
boxylate (5a). FT- IR (KBr) Vmax cm : 3365, 2946, 1660, 1253, 1118,
1
6
3
6
5
30; H NMR (CDCl
H), 7.02–7.00 (d, 2H, J = 8 MHz), 6.61–6.59 (d, 1H, J = 8 MHz), 5.85
, 400 MHz) δ: 9.65 (brs, 1H, NH), 7.39–7.27 (m,
3
was determined by Yanagimoto MT3CHN recorder. Mass spectrum of all
products were recorded by VG 70-70H mass spectrometer. Thin layer
chromatography was performed on silica gel sheets (0.25 mm thickness
with UV indicator PF-254, Merck, Darmstadt). Column chromatography
was used with silica gel (100–200 mesh; SD Fine). SEM images of bac-
teria treated with quinolinyl dihydropyrine carboxylate derivatives
were determined with VEGA/TESCAN electron microscope.
(
brs, 1H, NH), 5.19 (s, 1H), 4.88 (s, 1H), 4.65–4.62 (d, 1H, J = 12 Hz),
4
1
1
1
2
.10–4.05 (q, 4H), 3.46–3.41 (t, 2H), 2.36–2.30 (d, 1H), 2.17 (s, 6H),
13
.48–1.41 (m, 4H), 1.29–1.23 (t, 6H); C NMR (100 MHz, CDCl ) δ:
3
68.06, 143.58, 141.93, 135.77, 130.01, 128.48, 127.40, 126.78,
20.09, 115.83, 104.33, 68.11, 59.72, 54.73, 38.56, 31.49, 29.36,
+
5.91, 22.69, 19.62, 14.26; MS: m/z: 516 (M ); Anal. Calcd. for
31 36 2 5
C H N O : C, 72.07; H, 7.02; N, 5.42; Found: C, 72.09; H, 7.01; N,
2
2
.2. Synthetic procedure
5
.39.
.2.1. General procedure for synthesis of pyranoquinolinyl dihydropyridine
2
3
.2.1.5. Diethyl
2,6-dimethyl-4-((4aR,5R,10bR)-5-(4-nitrophenyl)-
dicarboxylates derivatives
mixture of
dihydropyridine-3,5-dicarboxylate (2) (0.01 mol), benzaldehyde (6a)
0.01 mol) and 3,4 dihydro-2H-pyran (7) (0.01 mol) were added into a
,4,4a,5,6,10b-hexahydro-2H-pyrano[3,2-c]quinolin-8-yl)-1,4-dihy-
A
diethyl-4-(4-aminophenyl)-2,6-dimethyl-1,4-
ꢀ 1
dropyridine-3,5-dicarboxylate (4b). FT- IR (KBr) Vmax cm : 3345, 2987,
676, 1239, 1109, 689; 1H NMR (CDCl
1
3
, 400 MHz) δ: 9.74 (brs, 1H,
(
NH), 7.44–7.22 (m, 5H), 7.00 (s, 1H), 6.46 (d, 1H, J = 8 MHz), 5.80 (brs,
round bottom flask containing acetonitrile as solvent (10.0 ml) in the
presence of indiumtriflate (20.0 mol%) as catalyst and stirred at
1
4
1
1
1
1
6
H, NH), 5.22 (s, 1H), 4.88 (s, 1H), 4.10–4.07 (q, 4H), 3.76 (d, 1H, J =
.00 Hz), 3.68 (t, 2H), 2.73 (d, 1H), 2.17 (s, 6H), 1.69–1.67 (d, 4H),
2
5.0–27.0 ◦C for an appropriate time. The reaction was monitored by
13
.26–1.23 (t, 6H); C NMR (100 MHz, CDCl ) δ: 167.78, 150.56,
3
TLC. After complete conversion, the reaction mixture was concentrated
under vacuum. Ethyl acetate [20 ml] and water [20 ml] was added to the
reaction mixture. The organic layer was separated, concentrated under
vacuum and the crude product was purified by column chromatography
on silica gel (ethyl acetate/petroleum ether, 1:4) to give the products
46.12, 145.31, 139.89, 128.41, 124.51, 123.45, 116.22, 113.46,
04.66, 72.81, 69.54, 62.54, 61.27, 46.28, 43.27, 25.05, 22.72, 19.12,
+
4.43; MS: m/z: 561 (M ); Anal. Calcd. for C31
H
35
N
3
O
7
: C, 66.30; H,
.28; N, 7.48; Found: C, 66.27; H, 6.29; N, 7.51.
(
diethyl-2,6-dimethyl-4-((4aR,5R,10bR)-5-phenyl-3,4,4a,5,6,10b-
2
3
.2.1.6. Diethyl
2,6-dimethyl-4-((4aR,5S,10bR)-5-(4-nitrophenyl)-
hexahydro–2H-pyrano[3,2-c]quinolin-8-yl)-1,4-dihydropyridine-3,5-
dicarboxylate (4a) & diethyl 2,6-dimethyl-4-((4aR,5S,10bR)-5-phenyl-
,4,4a,5,6,10b-hexahydro-2H-pyrano[3,2-c]quinolin-8-yl)-1,4-dihy-
ꢀ 1
dropyridine-3,5-dicarboxylate (5b). FT- IR (KBr) Vmax cm : 3339, 2975,
3
,4,4a,5,6,10b-hexahydro-2H-pyrano[3,2-c]quinolin-8-yl)-1,4-dihy-
685, 1242, 1122, 701; 1H NMR (CDCl
1
3
, 400 MHz) δ: 9.45 (brs, 1H,
dropyridine-3,5-dicarboxylate (5a) in 71.0% yield.
NH), 7.42–7.27 (m, 5H), 7.08 (d, 1H, J = 12 MHz), 6.48 (d, 1H, J = 8
MHz), 5.75 (brs, 1H, NH), 4.90 (s, 1H), 4.52 (s, 1H), 4.11–4.08 (q, 4H),
2
.2.1.1. Diethyl 2,6-dimethyl-4-(4-nitrophenyl)-1,4-dihydropyridine-3,5-
3
.75–3.73 (d, 1H, J = 8 Hz), 3.56–3.50 (t, 2H), 2.71–2.70 (d, 1H), 2.19
ꢀ 1
dicarboxylate (1). FT- IR (KBr) Vmax cm : 3338, 1686, 1645, 1247,
13
(
s, 6H), 1.58–1.56 (d, 4H), 1.25–1.23 (t, 6H); C NMR (100 MHz,
1
1
6
4
119, 634; H NMR (CDCl
3
, 400 MHz) δ: 7.06–7.04 (d, 2H, J = 8 MHz),
CDCl
3
) δ: 168.00, 150.05, 146.45, 145.66, 139.13, 128.24, 124.45,
.54–6.52 (d, 2H, J = 8 MHz), 5.70 (brs, 1H, NH), 4.86 (s, 1H),
1
4
23.20, 116.32, 113.80, 104.89, 75.80, 69.83, 62.77, 61.73, 46.35,
1
3
.10–4.06 (q, 4H), 2.30 (s, 6H), 1.24–1.20 (t, 6H); C NMR (100 MHz,
+
3.68, 25.44, 22.01, 19.70, 14.05; MS: m/z: 561 (M ); Anal. Calcd. for
CDCl
3
) δ: 167.8, 144.3, 143.4, 138.5, 128.9, 114.7, 104.4, 59.6, 38.6,
31 35 3 7
C H N O : C, 66.30; H, 6.28; N, 7.48; Found: C, 66.32; H, 6.21; N,
+
1
9.5, 14.2; MS: m/z: 374 (M ); Anal. Calcd. for C19
H
22
N
2
O
6
: C, 60.95; H,
7
.40.
5
.92; N, 7.48; Found: C, 60.91; H, 5.99; N, 7.52.
2

G. Lavanya et al.
Bioorganic Chemistry 107 (2021) 104582
2
.2.1.7. Diethyl
4-((4aR,5R,10bR)-5-(4-chlorophenyl)-3,4,4a,5,6,10b-
139.85, 132.49, 127.59, 126.57, 117.73, 116.66, 114.35, 113.80,
hexahydro-2H-pyrano[3,2-c]quinolin-8-yl)-2,6-dimethyl-1,4-dihydropyr-
104.00, 71.43, 69.13, 62.61, 61.67, 55.88, 44.93, 42.01, 25.44, 24.12,
ꢀ 1
+
idine-3,5-dicarboxylate (4c). FT- IR (KBr) Vmax cm : 3353, 2935, 1690,
19.39, 14.16; MS: m/z: 546 (M ); Anal. Calcd. for C32
H
38
2
N O
6
: C, 70.31;
1
7
6
4
2
342, 1118, 704; 1H NMR (CDCl
3
, 400 MHz) δ: 9.64 (brs, 1H, NH),
H, 7.01; N, 5.12; Found: C, 70.29; H, 6.99; N, 5.10.
.36–7.25 (m, 4H), 7.00 (d, 1H, J = 8 MHz), 6.47 (d, 1H, J = 8 MHz),
.20 (s, 1H), 5.25 (d, 1H, J = 4.00 Hz), 4.89 (s, 1H), 4.58 (brs, 1H, NH),
.12–4.05 (q, 4H), 3.54 (d, 1H), 3.38–3.33 (t, 2H), 2.31–2.30 (d, 1H),
2.2.1.12. Diethyl 2,6-dimethyl-4-((4aR,5S,10bR)-5-(4-methoxyphenyl)-
3,4,4a,5,6,10b-hexahydro-2H-pyrano[3,2-c]quinolin-8-yl)-1,4-dihy-
1
3
ꢀ 1
.17 (s, 6H), 1.49–1.42 (m, 4H), 1.28–1.20 (t, 6H); C NMR (100 MHz,
dropyridine-3,5-dicarboxylate (5e). FT- IR (KBr) V
cm : 3361, 2936,
max
1681, 1255, 1130, 668; 1H NMR (CDCl , 400 MHz) δ: 9.13 (brs, 1H,
CDCl
3
) δ: 167.95, 143.79, 143.13, 139.89, 138.71, 132.94, 128.41,
3
1
3
27.76, 126.80, 119.05, 114.29, 104.22, 72.75, 60.30, 59.64, 58.77,
NH), 7.43 (s, 1H), 7.31 (m, 1H), 7.09 (s, 1H), 7.00 (m, 1H), 6.40 (d, 2H,
J = 12 MHz), 6.12 (s, 1H), 5.19 (brs, 1H, NH), 4.87 (s, 1H), 4.64 (s, 1H),
4.10–4.02 (q, 4H), 3.80–3.76 (d, 1H, J = 16 Hz), 3.52 (s, 3H), 3.37–3.30
(t, 2H), 2.57 (s, 1H), 2.17 (s, 6H), 1.74–1.70 (m, 4H), 1.26–1.22 (t, 6H);
+
9.11, 38.71, 30.89, 25.38, 19.34, 14.43; MS: m/z: 550 (M ); Anal.
2 5
Calcd. for C31H35ClN O : C, 67.56; H, 6.40; N, 5.08; Found: 67.50; H,
6
.38; N, 5.10.
1
3
C NMR (100 MHz, CDCl
3
) δ: 167.93, 149.93, 146.56, 145.63, 139.07,
2
.2.1.8. Diethyl
4-((4aR,5S,10bR)-5-(4-chlorophenyl)-3,4,4a,5,6,10b-
128.29, 124.94, 123.56, 117.27, 113.85, 104.07, 70.79, 68.86, 61.86,
hexahydro-2H-pyrano[3,2-c]quinolin-8-yl)-2,6-dimethyl-1,4-dihydropyr-
61.27, 54.60, 49.29, 43.27, 28.07, 23.50, 19.72, 14.07; MS: m/z: 546
ꢀ 1
+
idine-3,5-dicarboxylate (5c). FT- IR (KBr) Vmax cm : 3351, 2938. 1691,
38 2 6
(M ); Anal. Calcd. for C32H N O : C, 70.31; H, 7.01; N, 5.12; Found: C,
1
7
6
342, 1115, 653; 1H NMR (CDCl
3
, 400 MHz) δ: 9.96 (brs, 1H, NH),
70.28; H, 6.99; N, 5.14.
.44–7.43 (m, 1H), 7.33 (m, 3H), 7.09 (s, 1H), 6.40 (d, 1H, J = 12 MHz),
.12 (s, 1H), 5.19 (brs, 1H, NH), 4.87 (s, 1H), 4.62–4.59 (d, 1H, J = 12
2.2.2. General procedure for synthesis of furoquinolinyl dihydropyridine
dicarboxylate derivatives
Hz), 4.30 (s, 1H) 4.10–4.05 (q, 4H), 3.54–3.50 (t, 2H), 2.34–2.29 (d,
1
3
1
H), 2.17 (s, 6H), 1.76–1.72 (m, 4H), 1.26–1.22 (t, 6H); C NMR (100
MHz, CDCl
) δ: 167.66, 143.77, 142.77, 141.12, 137.50, 133.42,
28.71, 119.84, 113.80, 104.22, 74.60, 68.33, 61.73, 59.63, 54.36,
A mixture of diethyl 4-(4-aminophenyl)-2, 6-dimethyl-1, 4-dihy-
dropyridine-3, 5-dicarboxylate (2) (0.01 mol), benzaldehyde (6a) (0.01
mol) and 2, 3 dihydro-furan (0.01 mol) (8) was added into the round
bottom flask containing acetonitrile as solvent (10.0 ml) in the presence
of indium triflate (20.0 mol %) as catalyst and stirred at room temper-
ature for an appropriate time (Table 2). After complete conversion the
reaction mixture was concentrated under vacuum. Ethyl acetate [20 ml]
and water [20 ml] was added to the reaction mixture. The ethylacetate
layer was separated, concentrated under vacuum and the crude product
was purified by column chromatography on silica gel (ethyl acetate/
petroleum ether, 1:4) to give the product diethyl 2,6-dimethyl-4-
((3aR,4R,9bR)-4-phenyl-2,3,3a,4,5,9b-hexahydrofuro[3,2-c]quinolin-
3
1
3
+
8.64, 30.90, 24.12, 19.39, 14.32; MS: m/z: 550 (M ); Anal. Calcd. for
35ClN : C, 67.56; H, 6.40; N, 5.08; Found: , 67.51; H, 6.43; N,
.05.
C
31
H
2 5
O
5
2
3
.2.1.9. Diethyl
2,6-dimethyl-4-((4aR,5R,10bR)-5-(p-tolylphenyl)-
,4,4a,5,6,10b-hexahydro-2H-pyrano[3,2-c]quinolin-8-yl)-1,4-dihy-
dropyridine-3,5-dicarboxylate (4d). FT- IR (KBr) Vmax cm 1: 3348, 2942,
ꢀ
1
656, 1207, 1116, 731; 1H NMR (CDCl
3
, 400 MHz) δ: 9.74 (brs, 1H,
NH), 7.28 (d, 2H, J = 8 MHz), 7.17 (d, 2H, J = 8 MHz), 7.08 (s, 1H), 7.00
(
d, 1H, J = 8 MHz) 6.37 (d, 1H, J = 8 MHz), 5.69 (brs, 1H, NH), 4.87 (s,
7-yl)-1,4-dihydropyridine-3,5-dicarboxylate (9a)
&
diethyl 2,6-
1
3
4
1
1
2
7
H), 4.65 (d, 1H, J = 4.00 Hz), 4.30 (s, 1H), 4.10–4.03 (q, 4H),
dimethyl-4-((3aR,4S,9bR)-4-phenyl-2,3, 3a,4,5,9b-hexahydrofuro[3,2-
c]quinolin-7-yl)-1,4-dihydropyridine-3,5-dicarboxylate (10a) in 69.0%
yield.
.70–3.64 (t, 2H), 2.59 (d, 1H), 2.35 (s, 3H), 2.32 (s, 6H) 1.62–1.48 (m,
1
3
H), 1.27–1.22 (t, 6H); C NMR (100 MHz, CDCl ) δ: 167.78, 143.43,
3
43.11, 139.51, 137.44 137.11, 130.05, 129.24, 127.73, 119.94,
13.59, 104.46, 74.84, 68.47, 59.61, 54.55, 38.91, 33.81, 24.27, 22.06,
2.2.2.1. Diethyl 2,6-dimethyl-4-((3aR,4R,9bR)-4-phenyl-2,3,3a,4,5,9b-
hexahydrofuro[3,2-c]quinolin-7-yl)-1,4-dihydropyridine-3,5-dicarboxylate
+
1.14, 19.56, 14.12; MS: m/z: 530 (M ); Anal. Calcd. for C32
H
38
N
2
O
5
: C,
ꢀ
1
1
2.43; H, 7.22; N, 5.28; Found: C, 72.46; H, 7.21; N, 5.19.
(9a). FT- IR (KBr) Vmax cm : 3358, 2945, 1672, 1231, 1124, 659; H
NMR (CDCl
3
, 400 MHz) δ: 9.76 (brs, 1H, NH), 7.43–7.27 (m, 6H), 7.02
2
3
.2.1.10. Diethyl
2,6-dimethyl-4-((4aR,5S,10bR)-5-(p-tolylphenyl)-
(d, 1H, J = 4 MHz), 6.46 (d, 1H, J = 8 MHz), 5.80 (brs, 1H, NH),
5.20–5.19 (d, 1H, J = 4.00 Hz), 4.88 (s, 1H), 4.64 (s, 1H), 4.11–4.08 (q,
,4,4a,5,6,10b-hexahydro-2H-pyrano[3,2-c]quinolin-8-yl)-1,4-dihy-
dropyridine-3,5-dicarboxylate (5d). FT- IR (KBr) Vmax cm 1: 3364, 2925,
ꢀ
4H), 3.70–3.67 (t, 2H), 2.32–2.31 (d, 1H), 2.15 (s, 6H), 1.91–1.88 (m,
686, 1232, 1132, 701; 1H NMR (CDCl
13
1
3
, 400 MHz) δ: 9.48 (brs, 1H,
2H), 1.26–1.23 (t, 6H); C NMR (100 MHz, CDCl ) δ: 167.74, 143.24,
3
NH), 7.31 (m, 2H), 7.17 (d, 2H, J = 8 MHz), 6.99 (d, 1H, J = 8 MHz),
142.57, 139.25, 129.62, 128.64, 127.66, 126.61, 121.64, 114.71,
6
4
2
1
1
1
2
7
.45 (d, 2H, J = 8 MHz), 5.85 (brs, 1H, NH), 5.26 (d, 1H, J = 12.00 Hz),
.90 (s, 1H), 4.59 (s, 1H), 4.12–4.05 (q, 4H), 3.53–3.46 (t, 2H),
.57–2.56 (d, 1H), 2.34 (s, 3H), 2.31 (s, 6H) 1.52–1.41 (m, 4H),
.28–1.22 (t, 6H); C NMR (100 MHz, CDCl ) δ: 167.64, 144.29,
43.37, 138.23, 137.05, 136.01, 128.89, 127.69, 126.73, 118.95,
104.40, 76.17, 66.53, 59.23, 57.27, 45.98, 38.68, 28.67, 19.44, 14.05;
+
MS: m/z: 502 (M ); Anal. Calcd. for C30
H
34
N
2
O
5
: C, 71.69; H, 6.82; N,
5.57; Found: C, 71.60; H, 6.89; N, 5.56.
1
3
3
2.2.2.2. Diethyl 2,6-dimethyl-4-((3aR,4S,9bR)-4-phenyl-2,3,3a,4,5,9b-
hexahydrofuro[3,2-c]quinolin-7-yl)-1,4-dihydropyridine-3,5-dicarboxylate
13.92, 104.34, 72.93, 60.28, 59.00, 39.18, 38.69, 33.41, 25.48, 22.13,
+
ꢀ 1
1
1.08, 19.52, 14.32; MS: m/z: 530 (M ); Anal. Calcd. for C32
H
38
N
2
O
5
: C,
(10a). FT- IR (KBr) Vmax cm : 3351, 2939, 1658, 1240, 1110, 672; H
NMR (CDCl
, 400 MHz) δ: 9.76 (brs, 1H, NH), 7.42–7.32 (m, 6H), 7.07
2.43; H, 7.22; N, 5.28; Found: C, 72.39; H, 7.19; N, 5.26.
3
(
d, 1H, J = 8 MHz), 6.48 (d, 1H, J = 8 MHz), 5.75 (s, 1H), 5.22 (brs, 1H,
2
3
.2.1.11. Diethyl 2,6-dimethyl-4-((4aR,5R,10bR)-5-(4-methoxyphenyl)-
NH), 4.90 (s, 1H), 4.53 (d, 1H, J = 12.0 Hz), 4.14–4.03 (q, 4H), 3.79 (t,
,4,4a,5,6,10b-hexahydro-2H-pyrano[3,2-c]quinolin-8-yl)-1,4-dihy-
2H), 2.33–2.30 (d, 1H), 2.19 (s, 6H), 1.69–1.64 (m, 2H), 1.28–1.26 (t,
dropyridine-3,5-dicarboxylate (4e). FT- IR (KBr) Vmax cm 1: 3342, 2941,
ꢀ
13
6H); C NMR (100 MHz, CDCl
3
) δ: 167.72, 143.51,141.94, 137.99,
1
686, 1267, 1121, 675; 1H NMR (CDCl
3
, 400 MHz) δ: 9.55 (brs, 1H,
130.65, 128.47, 126.28, 124.44, 123.60, 117.12, 114.01, 104.22, 64.94,
NH), 7.34–7.28 (m, 3H), 7.04–7.02 (d, 1H, J = 8 MHz), 6.47 (d, 2H, J =
59.44, 57.69, 49.95, 43.37, 38.76, 28.76, 19.59, 14.26; MS: m/z: 502
+
8
4
4
MHz), 6.20 (s, 1H), 5.24 (brs, 1H, NH), 4.91 (s, 1H), 4.58 (s, 1H),
.12–4.04 (q, 4H), 3.77 (s, 3H), 3.64–3.61(t, 2H), 3.25–3.24 (d, 1H, J =
.00 Hz), 2.17 (s, 6H), 2.06–2.01(d, 1H), 1.66–1.61 (m, 4H), 1.26–1.20
(M ); Anal. Calcd. for C30
34 2 5
H N O : C, 71.69; H, 6.82; N, 5.57; Found: C,
71.63; H, 6.79; N, 5.60
(
t, 6H); 13C NMR (100 MHz, CDCl
3
) δ: 168.10, 158.33, 150.42, 145.16,
3

G. Lavanya et al.
Bioorganic Chemistry 107 (2021) 104582
2
2
3
1
8
6
4
1
.2.2.3. Diethyl
,3,3a,4,5,9b-hexahydrofuro
,5-dicarboxylate (9b). FT- IR (KBr) Vmax cm : 3347, 2942, 1659,
256, 1125, 659; 1H NMR (CDCl
, 400 MHz) δ: 9.47 (brs, 1H, NH),
2,6-dimethyl-4-((3aR,4R,9bR)-4-(4-nitrophenyl)-
solvent was removed by under vaccum. Ehyl acetate [20 ml] and water
[20 ml] was added to the reaction mixture. The organic layer was
separated and concentrated by high vaccum. The product was purified
by column chromatography on silica gel (100–200 mesh, ethyl acetate/
petroleum ether, 1:4) to give the product diethyl-2,6-dimethyl-4-
((3aS,9bR)-4-phenyl-3a,4,5,9b-tetrahydro-3H-cyclopenta[c]quinolin-7-
yl)-1,4-dihydropyridine-3,5-dicarboxylate (12a) in 51.0% yield.
[3,2-c]quinolin-7-yl)-1,4-dihydropyridine-
ꢀ 1
3
.27–8.14 (m, 2H), 7.53 (d, 2H, J = 4 MHz), 7.08 (d, 2H, J = 8 MHz),
.58 (s, 1H), 5.32 (brs, 1H, NH), 4.83 (s, 1H), 4.60 (s, 1H), 4.13–4.06 (q,
H), 3.86–3.84 (d, 1H, J = 8.00 Hz), 3.73–3.70 (t, 2H), 2.78–2.77 (d,
1
3
H), 2.21 (s, 6H), 1.94–1.91 (t, 2H), 1.29–1.27 (t, 6H); C NMR (100
MHz, CDCl
3
) δ: 167.96, 149.93, 146.56, 145.63, 139.07, 128.29,
2.2.3.1. Diethyl-2,6-dimethyl-4-((3aS,4R,9bR)-4-phenyl-3a,4,5,9b-tetra-
1
4
24.94, 123.56, 117.27, 113.85, 104.07, 74.79, 68.86, 61.86, 61.27,
hydro-3H-cyclopenta [c]quinolin-7-yl)-1,4-dihydropyridine-3,5-dicarbox-
+
ꢀ 1
9.29, 43.27, 28.07, 19.72, 14.07, MS: m/z: 547 (M ); Anal. Calcd. for
: C, 65.80; H, 6.07; N, 7.67; Found: C, 65.90; H, 6.06; N,
ylate (12a). FT- IR (KBr) V
cm : 3343, 2989, 1675, 1472, 1225,
max
1
C
30
H
33
3
N O
7
1070; H NMR (CDCl , 400 MHz) δ: 9.61 (brs, 1H, NH), 8.10 (d, 1H, J =
3
7
.70.
8 MHz), 7.48–7.33 (m, 5H), 6.60 (d, 1H, J = 8 MHz), 6.49–6.42 (m, 1H),
5
.65–5.61 (d, 2H), 5.26 (brs, 1H, NH), 4.90–4.87 (d, 1H), 4.10–4.05 (q,
2
2
3
1
7
6
4
1
.2.2.4. Diethyl
2,6-dimethyl-4-((3aR,4S,9bR)-4-(4-nitrophenyl)-
furo[3,2-c]quinolin-7-yl)-1,4-dihydropyridine-
4H), 3.69–3.66 (d, 1H), 3.09–3.05 (d, 1H), 2.60–2.57 (m, 1H),
13
,3,3a,4,5,9b-hexahydro
2.48–2.45 (d, 2H), 2.26 (s, 6H), 1.29–1.25 (t, 6H); C NMR (100 MHz,
CDCl
ꢀ 1
,5-dicarboxylate (10b). FT- IR (KBr) Vmax cm : 3342, 2939, 1649,
233, 1110, 662; 1H NMR (CDCl
, 400 MHz) δ: 9.41 (brs, 1H, NH),
3
) δ: 167.78, 154.84, 145.58, 143.94, 138.58, 133.23, 129.91,
3
128.65, 127.29, 125.62, 115.69, 112.39, 104.40, 61.40, 59.48, 58.27,
+
.49–7.43 (m, 3H), 7.19 (s, 1H), 7.10 (m, 1H), 6.46 (d, 1H, J = 12 MHz),
.20 (s, 1H), 5.21 (brs, 1H, NH), 4.90 (s, 1H), 4.62 (s, 1H), 4.16–4.13 (q,
H), 3.81–3.78 (d, 1H, J = 12.00 Hz), 3.39–3.35 (t, 2H), 2.60–2.58 (d,
45.87, 42.97, 31.58, 19.41, 14.05 ; MS: m/z: 498 (M ); Anal. Calcd. for
31 34 2 4
C H N O : C, 74.67; H, 6.87; N, 5.62; Found: C, 74.63; H, 6.81; N,
5.55.
1
3
H), 2.20 (s, 6H), 1.79–1.74 (t, 2H), 1.25–1.22 (t, 6H); C NMR (100
MHz, CDCl
3
) δ: 167.77, 150.13, 146.75, 145.80, 139.34, 130.65,
2.2.3.2. Diethyl 2,6-dimethyl-4-((3aS,9bR)-4-(4-nitrophenyl)-3a,4,5,9b-
1
4
24.44, 123.60, 117.12, 114.01, 104.11, 70.72, 68.23, 62.01, 61.53,
tetrahydro-3H-cyclopenta [c]quinolin-7-yl)-1,4-dihydropyridine-3,5-dicar-
+
ꢀ 1
9.95, 43.37, 28.76, 19.59, 14.26; MS: m/z: 547 (M ); Anal. Calcd. for
: C, 65.80; H, 6.07; N, 7.67; Found: C, 65.85; H, 6.11; N,
boxylate (12b). FT- IR (KBr) V
cm : 3351, 2998, 1677, 1491, 1260,
max
1
C
30
H
33
3
N O
7
1012; H NMR (CDCl , 400 MHz) δ: 9.32 (brs, 1H, NH), 8.26–8.21 (m,
3
7
.71.
2H), 7.52–7.48 (m, 2H), 6.98 (m, 1H), 6.60–6.58 (d, 1H, J = 8 MHz),
6
.41 (s, 1H), 5.66–5.65 (m, 2H), 5.29 (brs, 1H, NH), 4.80–4.78 ((d, 1H),
2
.2.2.5. Diethyl 4-((3aR,4R,9bR)-4-(4-chlorophenyl)-2,3,3a,4,5,9b-hex-
4.26 (q, 4H), 3.88 (d, 1H), 3.54 (d, 1H), 2.89–2.87 (m, 1H), 2.34–2.31
13
ahydrofuro[3,2-c]quinolin-7-yl)-2,6-dimethyl-1,4-dihydropyridine-3,5-
(d, 2H), 2.22 (s, 6H), 1.34–1.29 (t, 6H); C NMR (100 MHz, CDCl ) δ:
3
ꢀ 1
dicarboxylate (9c). FT- IR (KBr) Vmax cm : 3360, 2921, 1686, 1251,
169.92, 155.06, 146.00, 143.63, 138.82, 133.85, 130.31, 129.55,
128.57, 127.82, 125.13, 115.43, 112.29, 104.05, 61.33, 59.87, 57.92,
1
1
176, 686; H NMR (CDCl
m, 4H), 7.26 (s, 1H), 7.08 (d, 1H, J = 12 MHz), 6.48–6.46 (d, 1H, J = 8
MHz), 5.66 (brs, 1H, NH), 5.20 (s, 1H), 4.90 (s, 1H), 4.53–4.52 (d, 1H, J
4.00 Hz), 4.12–4.03 (q, 4H), 3.79–3.75 (t, 2H), 2.37–2.31 (m, 1H),
3
, 400 MHz) δ: 9.75 (brs, 1H, NH), 7.42–7.32
+
(
46.02, 42.72, 30.86, 19.29, 14.13 ; MS: m/z: 543 (M ); Anal. Calcd. for
31 33 3 6
C H N O : C, 68.49; H, 6.12; N, 7.73; Found: C, 68.51; H, 6.11; N,
=
7.71.
1
3
2
.17 (s, 6H), 2.02–1.93 (m, 2H), 1.26–1.23 (t, 6H); C NMR (100 MHz,
CDCl
3
) δ: 167.80, 143.66, 143.36, 141.91,138.15, 130.60, 129.15,
2.2.3.3. Diethyl 4-((3aS,9bR)-4-(4-chlorophenyl)-3a,4,5,9b-tetrahydro-
1
4
28.59, 128.30, 128.06, 119.32, 114.00, 104.51, 65.12, 59.73, 57.81,
3H-cyclopenta [c] quinolin-7-yl)-2,6-dimethyl-1,4-dihydropyridine-3,5-
+
ꢀ 1
3.37, 38.75, 30.81, 28.50, 19.50, 14.10; MS: m/z: 536 (M ); Anal.
dicarboxylate (12c). FT- IR (KBr) V
cm : 3382, 2956, 1684, 1448,
max
1
Calcd. for C30
H33ClN
2
O
5
: C, 67.09; H, 6.19; N, 5.22; Found: C, 67.15; H,
1277, 1067; H NMR (CDCl , 400 MHz) δ: 9.53 (brs, 1H, NH), 8.01–7.83
3
6
.16; N, 5.20.
(m, 5H), 7.38–7.31 (m, 1H), 7.01 (m, 1H), 5.71–5.67 (d, 2H), 5.19 (brs,
1
H, NH), 4.91–4.89 (d, 1H), 4.16–4.07 (q, 4H), 3.71–3.68 (d, 1H),
2
.2.2.6. Diethyl 4-((3aR,4S,9bR)-4-(4-chlorophenyl)-2,3,3a,4,5,9b-hex-
3.42–3.38 (d, 1H), 2.97–2.86 (m, 1H), 2.57–2.52 (d, 2H), 2.31 (s, 6H),
13
ahydrofuro[3,2-c]quinolin ꢀ 7-yl)-2,6-dimethyl-1,4-dihydropyridine-3,5-
1.28–1.22 (t, 6H); C NMR (100 MHz, CDCl ) δ: 168.38, 155.10,
3
ꢀ 1
dicarboxylate (10c). FT- IR (KBr) Vmax cm : 3346, 2985, 1645, 1238,
145.96, 143.76, 138.90, 133.44, 130.11, 128.43, 127.00, 125.06,
1
1
121, 682; H NMR (CDCl
3
, 400 MHz) δ: 9.65 (brs, 1H, NH), 7.45–7.22
115.34, 112.68, 103.99, 61.72, 58.49, 58.16, 45.94, 43.09, 29.66,
+
(
m, 5H), 7.02 (d, 1H, J = 4 MHz), 6.46 (d, 1H, J = 8 MHz), 5.65 (brs, 1H,
19.53, 14.30 ; MS: m/z: 532 (M ); Anal. Calcd. for C31
2
H33ClN O
4
: C,
NH), 5.21–5.18 (d, 1H, J = 12.00 Hz), 4.88 (s, 1H), 4.62 (s, 1H),
69.85; H, 6.24; N, 5.26; Found: C, 69.82; H, 6.26; N, 5.25.
4
1
1
1
3
.11–4.01 (q, 4H), 3.89–3.85 (t, 2H), 2.37–2.27 (m, 1H), 2.14 (s, 6H),
.91–1.84 (m, 2H), 1.28–1.19 (t, 6H); C NMR (100 MHz, CDCl
13
3
) δ:
2.2.3.4. Diethyl 2,6-dimethyl-4-((3aS,9bR)-4-(p-tolyl)-3a,4,5,9b-tetrahy-
dro-3H-cyclopenta [c] quinolin-7-yl)-1,4-dihydropyridine-3,5-dicarbox-
67.86, 143.55, 142.89, 140.95, 139.30, 133.15, 129.54, 128.86,
28.20, 127.73, 121.67, 114.64, 104.45, 76.05, 66.49, 59.56, 45.73,
ꢀ
1
ylate (12d). FT- IR (KBr) V
max
cm : 3385, 2966, 1689, 1438, 1268,
+
1069; 1H NMR (CDCl , 400 MHz) δ: 9.60 (brs, 1H, NH), 8.11–8.09 (d,
8.82, 24.37, 19.57, 14.24; MS: m/z: 536 (M ); Anal. Calcd. for
3
C
30
H
2
33ClN O
5
: C, 67.09; H, 6.19; N, 5.22; Found: C, 67.15; H, 6.26; N,
2H, J = 8 MHz), 7.48–7.33 (m, 3H), 6.61–6.42 (m, 2H), 5.76 (brs, 1H,
5
.20.
NH), 5.66–5.60 (m, 2H), 4.91–4.88 (d, 1H), 4.12–4.05 (q, 4H),
3
.68–3.65 (d, 1H), 3.10 (d, 1H), (2.59–2.57 (d, 1H), 2.39 (s, 3H),
13
2
.2.3. General procedure for synthesis of tetrahydrocyclopentaquinolinyl
2.33–2.30 (m, 2H), 2.17 (s, 6H), 1.29–1.23 (t, 6H); C NMR (100 MHz,
dihydropyridine dicarboxylate
CDCl ) δ: 168.31, 155.10, 146.00, 143.07, 138.90, 129.00, 128.43,
3
Freshly cracked 1,3 cyclopentadiene was prepared by the procedure
reported in literature [24]. Amine-diethyl 4-(4-aminophenyl)-2, 6-
dimethyl-1, 4-dihydropyridine-3, 5-dicarboxylate (2) (0.01 mol), benz-
aldehyde (6a) (0.01 mol) and cyclopentadiene (0.01 mol) (11) was taken
in the RB flask, in the presence of indium triflate (20.0 mol%) as a
127.13, 125.78, 114.52, 112.39, 104.43, 65.25, 59.69, 58.16, 46.53,
+
43.13, 30.94, 22.62, 19.62, 14.39 ; MS: m/z: 512 (M ); Anal. Calcd. for
C32H36N O : C, 74.97; H, 7.08; N, 5.46; Found: C, 74.87; H, 7.06; N,
2 4
5.51.
◦
catalyst and acetonitrile as solvent and stirred at 25.0–27.0 C. The re-
action was monitored by TLC. After completion of the reaction, the
2
3
.2.3.5. Diethyl 4-((3aS,9bR)-4-(4-hydroxyphenyl)-3a,4,5,9b-tetrahydro-
H-cyclopenta[c] quinolin-7-yl)-2,6-dimethyl-1,4-dihydropyridine-3,5-
4

G. Lavanya et al.
Bioorganic Chemistry 107 (2021) 104582
dicarboxylate (12e). FT- IR (KBr) Vmax cm 1: 3372, 2950, 1679, 1467,
ꢀ
C, 72.35; H, 6.66; N, 5.44; Found: C, 72.37; H, 6.76; N, 5.39.
1
1
279, 1072; H NMR (CDCl
3
, 400 MHz) δ: 9.45 (brs, 1H, NH), 7.48–7.28
(
m, 3H), 6.60–6.58 (d, 2H, J = 8.0 MHz), 6.49–6.42 (m, 2H), 5.89 (s,
2
2
.3. Biological assay
1
4
2
H), 5.76 (brs, 1H, NH), 5.65–5.61 (d, 2H), 4.90–4.87 (d, 1H),
.14–4.04 (q, 4H), 3.67 (d, 1H), 3.10 (d,1H), 2.59–2.57 (d, 1H),
.3.1. In vitro antibacterial assay
1
3
.40–2.29 (m, 2H), 2.17 (s, 6H), 1.31–1.26 (t, 6H); C NMR (100 MHz,
All synthesized compounds were evaluated for their in vitro anti-
bacterial activity against pathogenic bacteria by well diffusion method
25,26]. The tested compounds were dissolved in acetic acid and DMSO
solvent mixture. Test pathogens were spread on Mueller-Hinton agar
CDCl
3
) δ: 167.92, 155.04, 146.63, 143.94, 129.55, 128.65, 127.90,
1
3
26.04, 115.39, 114.52, 103.95, 59.69, 58.49, 47.00, 46.11, 38.70,
[
+
1.51, 19.57, 13.76 ; MS: m/z: 514 (M ); Anal. Calcd. for C31
H
34
2
N O
5
:
Scheme 1.
5

G. Lavanya et al.
Bioorganic Chemistry 107 (2021) 104582
(
MHA) plates. A well of diameter (6.0 mm) was made by using sterile
ligand binding site was defined as the binding site. The co-crystallized
ligand and water molecules were deleted. Hydrogen bonds were
added and the protein was saved in pdb format. CCDC GOLD was
employed for calculating the docking modes of Pyrano[3,2-c]quinolin-8-
yl)-1,4-dihydro pyridine-3,5-dicarboxylates derivatives with protein
cork borer and loaded with required concentration. The test plates were
◦
incubated for 24 h at 37 C. Antimicrobial activity was evaluated by
recording the zone of inhibition in mm against test microorganism and
solvent. Acetic acid and DMSO solvent mixture was used as control.
Ciprofloxacin was used as reference drug. The tests were carried out in
triplicates.
˜
binding sites. CCDC GOLD was used for molecular docking. 20 A… units
were set as the interaction diameter to allow better analysis of in-
teractions with multiple chains and to allow free rotation of the ligands
in the interaction sphere. In the analysis, the interactions of ligands were
assessed according to the bonding interactions against active site of the
protein. The Pyrano[3,2-c]quinolin-8-yl)-1,4-dihydro pyridine-3,5-
dicarboxylates conformer and coordinates based on best fitness value
for ligand was introduced into the protein using Discovery Studio
Visualizer. The protein–ligand interactions were analyzed and the
bonding type was noted. The fitness values of the screened drugs were
noted.
2
.3.2. Determination of minimum inhibitory concentration (MIC)
The minimum inhibitory concentration (MIC) of all the products
were evaluated by using the broth micro dilution method using 96-well
microplates reported in literature [27–29]. The test compounds in
different concentrations of 500, 250, 125.25, 62.50, 31.25, 15.63, 7.81
7
µg/ml along with standardized microbial suspensions (1-2x10 cfu/ml)
were incubated for 18-24hrs at 37 C. Ciprofloxacin was used as stan-
◦
dard reference drugs. The lowest concentration of the test compounds
that inhibited the bacterial growth completely was recorded as MIC in
μ
g/mL. All experiments were performed in triplicate.
3. Results and discussion
2
.3.3. Molecular docking methodology.
3.1. Chemistry
The first step in molecular docking studies is the preparation of
Pyrano[3,2-c]quinolin-8-yl)-1,4-dihydro
pyridine-3,5-dicarboxylates
In the present investigation, we report the multistep synthesis of
pyrano[3,2-c] quinolin-8-yl)-1,4-dihydropyridine-3,5-dicarboxylate de-
rivatives. In the first step (scheme 1, step 1), nitro substituted Hantzsch
dihydropyridine carboxylates were synthesized by condensation reac-
tion of ethylacetoacetate, nitro benzaldehyde and ammonium acetate.
The second step involves the reduction of the corresponding nitro group
to amino group by sodium hydrosulfide in methanol (scheme 1, step 2).
The schiffs base is generated insitu by reacting the amine; diethyl 4-(4-
aminophenyl)-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate
with various substituted aromatic aldehydes (scheme 1, step 3). The last
step (scheme 1, step 4) between insitu generated schiffs base with 3,4-
dihydro-2H-pyran in acetonitrile solvent promoted by indium triflate
derivatives for docking with cell wall protein of vibrio cholera which
includes structure optimization of the Pyrano[3,2-c]quinolin-8-yl)-1,4-
dihydro pyridine-3,5-dicarboxylates derivatives. 3D conformer struc-
tures of the ligands were obtained using Chemsketch software after
structure optimization and adding hydrogen bonds. They were con-
verted to .mol2 format using BIOVIA Discovery Studio visualizer.
Hydrogen bonds were added to all the ligands. The 3d crystal structure
of vibrio cholerea was obtained from RSCB protein data bank (PDB code
5
CXK). The water molecules were removed from the protein and
hydrogen atoms were added to the protein by using discovery studio
.5.5software The active sites of the protein were determined. The
2
Table 1
Effect of temperature and solvent on synthesis pyrano[3,2-c]quinolin-8-yl)-1,4-dihydropyridine-3,5-dicarboxylates (4a & 5a) synthesis.
o
S. No
Solvent
Temperature ( C)
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
9
Benzene
25–27
100–110
25–27
60–70
25–27
25–27
78–80
25–27
80–82
10.0
10.0
10.0
8.0
No reaction
No reaction
No reaction
10.0
Toluene
Dichloromethane
Ethyl acetate
Methanol
8.0
28.0
Ethanol
8.0
30.0
Ethanol
8.0
40.0
Acetonitrile
Acetonitrile
6.0
71.0
6.0
58.0
4
a - Diethyl 2,6-dimethyl-4-((4aR,5R,10bR)-5-phenyl-3,4,4a,5,6,10b-hexahydro-2H-pyrano[3,2-c]quinolin-8-yl)-1,4-dihydropyridine-3,5-dicarboxylate
a - Diethyl 2,6-dimethyl-4-((4aR,5S,10bR)-5-phenyl-3,4,4a,5,6,10b-hexahydro-2H-pyrano[3,2-c]quinolin-8-yl)-1,4-dihydropyridine-3,5-dicarboxylate
5
a
All the reactions were carried out according to typical experimental procedure A.
b
1
All the products were characterized by HNMR, FT-IR & mass spectra.
c
Isolated yield after purification.
6

G. Lavanya et al.
Bioorganic Chemistry 107 (2021) 104582
as catalyst proceeds via inverse electron demand Diels Alder reaction
(2) and 3,4-dihydro-2H-pyran in the presence of indium triflate (20.0
mol%) as catalyst in acetonitrile as solvent at room temperature. The
reaction proceeds smoothly with both electron donating and electron
withdrawing substituents on the aromatic ring of the aldehydes afford-
ing the corresponding PDC derivatives in good to moderate yields. The
results of the reaction are summarized in table 2 given below.
(
IED) at ambient temperature to afford the corresponding Pyrano[3,2-c]
quinolin-8-yl)-1,4-dihydropyridine-3,5-dicarboxylate derivatives (4a-e,
5
a-e) in moderate to good yields. The reaction is illustrated in scheme 1.
3
1
.2. Effect of temperature and solvent on Pyrano[3,2-c]quinolin-8-yl)-
,4-dihydro pyridine-3,5 dicarboxylates synthesis
3
.4. Synthesis of furo[3,2-c]quinolin-7-yl)-1,4-dihydropyridine-3,5-
The reaction of diethyl-4-(4-aminophenyl)-2,6-dimethyl-1,4-
dicarboxylate(FDC) and tetrahydro-3H-cyclopenta[c]qunolin-7-yl-1,4-
dihydropyridine-3,5-dicarboxylate(CDC) derivatives
dihydropyridine-3,5-dicarboxylate (2) with benzaldehyde (6a) and
,4-dihydro-2H-pyran (7) in the presence of indium triflate catalyst was
3
chosen as a model reaction for studying the effect of temperature and
solvent on pyrano[3,2-c]quinolin-8-yl)-1,4-dihydropyridine-3,5-dicar-
boxylates synthesis; the results are shown in Table 1. We have observed
that in the less-polar solvents such as benzene, toluene etc the reaction
did not progress at room temperature or elevated temperatures. The
reaction afforded poor yields in solvents such as ethyl acetate, methanol
and ethanol. However optimal yields and short reaction times were
observed in acetonitrile solvent in the presence of indium triflate (20.0
mol%) as catalyst at room temperature. The results of the reaction are
illustrated in table.1.
After synthesizing a series of pyranoquinolinyl dihydropyridine
carboxylate derivatives we focused our attention on extending the
methodology for the synthesis of a series of furo[3, 2-c]quinolin-7-yl)-
1,4-dihydropyridine-3,5-dicarboxylate and cyclopentaquinoline-1,4-
dihydro pyridine-3,5-dicarboxylate derivatives. Furo[3,2-c]quinolin-7-
yl)-1,4-dihydropyridine-3,5-dicarboxylates (9a-c & 10a-c) were formed
in moderate yields when aromatic aldehydes (6a-c) were reacted with
diethyl-4-(4-aminophenyl)-2,6-dimethyl-1,4-dihydropyridine-3,5-
dicarboxylate (2) and 2,3-dihydro-furan (8) in the presence of indium
triflate (20.0 mol%) as catalyst in acetonitrile at room temperature to
afford the corresponding furo[3,2-c]quinolin-7-yl)-1,4-dihydropyridine-
3,5-dicarboxylates (9a-c & 10a-c). Cyclopentaquinoline dihydropyr-
idine carboxylate derivatives (CDC) were formed in moderate yields
when aromatic aldehydes (6a-e) were reacted with diethyl 4-(4-ami-
nophenyl)-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate (2) and
cyclopenta-1,3-diene (11) in acetonitrile as solvent and indium triflate
(20.0 mol%) as catalyst at room temperature to afford the corresponding
3
.3. The effect of substituents
The reactions conditions were further extended for the synthesis of a
series of pyrano[3,2-c]quinolin-8-yl)-1,4-dihydropyridine-3,5-dicar-
boxylates by reacting various other aromatic aldehydes with diethyl 4-
(
4-aminophenyl)-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate
Table 2
Effect of substituents on Pyrano[3,2-c]quinolin-8-yl)-1,4-dihydro pyridine-3,5-dicarboxylates synthesis.
a
b
S.No
1
Aldehyde
Time (h/min)
Yield (%)
Endo:Exo ratio
48:52
Pyrano[3,2-c]quinolin-8-yl)-1,4-dihydropyridine-3,5-dicarboxylates
6.0
71.0
6
a
(
(
(
4a)
4b)
4c)
(
5a)
2
13.5
65.0
42:58
6
b
(
5b)
3
12.0
67.0
37:63
6
c
(
5c)
4
11.0
68.0
44:56
6
d
(
4d)
(
5d)
5
10.0
70.0
35:65
6
e
(
5e)
(
4e)
7

G. Lavanya et al.
Bioorganic Chemistry 107 (2021) 104582
Scheme 2.
CDC derivatives (12a-e) in good yields (scheme 2). Table 3 illustrates the
scope of the reaction with respect to various substituted aldehydes and
dienophiles.
which leads to better anchorage for the PDC derivatives leading to
comparatively better activity of the PDC derivatives in comparison to
CDC derivatives. However a reversal in activity was observed with the
methoxy substituted PDC derivative wherein diethyl 4-((4aR,5R,10bR)-
5
-(4-methoxyphenyl)-3,4,4a,5,6,10b-hexahydro-2H-pyrano[3,2-c]qui-
3
3
.5. Biological evaluation
nolin-8-yl)-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate (4e)
exhibited relatively superior activity to diethyl 4-((4aR,5S,10bR)-5-(4-
.5.1. Antibacterial activity
methoxyphenyl)-3,4,4a,5,6,10b-hexahydro-2H-pyrano[3,2-c]quinolin-
The newly synthesized pyranoquinolinyl dihydropyridine carbox-
8
-yl)-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate (5e). Howev-
ylate (PDC), furanoquinolinyl dihydropyridine carboxylate (FDC) and
cyclopentaquinolinyl dihydropyridine carboxylate (CPDC) derivatives
were screened for antibacterial activity against seven strains of patho-
genic bacteria shown in the table 4. The antibacterial activities of the
quinolinyl dihydropyridine carboxylate derivatives were evaluated by
employing agar well diffusion method. Among all the synthesized
compounds screened for invitro antibacterial activity, the pyr-
anoquinolinyl dihydropyridine carboxylate derivatives exhibited high-
est antibacterial activity in comparison to furanoquinolinyl
dihydropyridine carboxylate derivatives or cyclopentaquinolinyl dihy-
dropyridine carboxylate derivatives. Among the diastereomeric endo
PDC derivatives (4a-e) and exo PDC derivatives (5a-e), it was found that
the exo pyranoquinolinyl dihydropyridine carboxylate derivatives (5a-
e) exhibited relatively superior antibacterial activity in comparison to
the relatively less active endo pyranoquinolinyl dihydropyridine
carboxylate derivatives (4a-e). However when the oxygen atoms on the
quinolinyl dihydropyridine carboxylate derivatives were replaced by
carbon atom as in cyclopentaquinolinyl dihydropyridine carboxylate
derivatives (12a-e), diminished antibacterial activity was observed.
Hence it is evident that the presence of oxygen heteroatom on the pyr-
ano/furano quinolinyl dihydropyridine carboxylates is essential for
binding with the cell wall protein of the pathogenic bacteria. Moreover
the results of antibacterial studies is also supported by molecular
docking studies which show that the oxygen atom on the both exo and
endo PDC derivatives form strong hydrogen bonds with the amino acid
residue CYS154:SG, CYS154:GSG and LEU155:N of vibrio cholerae
er all the compounds reported herein including PDC, FDC & CDC de-
rivatives exhibited antibacterial activity against vibrio cholerae (zone of
inhibition 8.0 mm-42 mm) at various concentrations in comparison to
the reference drug ciprofloxacin. Hence these new class of compounds
are promising candidates for treatment and mitigation of cholera after
necessary pharmacological studies.
3
.5.2. Mechanism of antibacterial action
The mode of action of the PDC derivatives diethyl 4-((4aR,5R,10bR)-
-(4-chlorophenyl)-3,4,4a,5,6,10b-hexahydro-2H-pyrano[3,2-c]quino-
5
lin-8-yl)-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate (4c)
&
diethyl 4-((4aR,5S,10bR)-5-(4-chlorophenyl)-3,4,4a,5,6,10b-hexahy-
dro-2H-pyrano[3,2-c]quinolin-8-yl)-2,6-dimethyl-1,4-dihydropyridine-
3
,5-dicarboxylate (5c) on pseudomonas aeruginosa and streptococcus
mutans was studied by analyzing the changes in the cell morphology of
pathogenic bacteria via scanning electron microscope analysis by
following the procedure reported in literature [30,31]. Untreated
pseudomonas aeruginosa and streptococcus mutans were used as control
for studying the effect of these compounds on bacterial morphology.
Pseudomonas aeruginosa exhibited rod shape (SEM image 1) before
treatment with PDC derivatives whereas untreated streptococcus
mutans exhibited round (spherical) shape (SEM image 4) as shown in the
Fig. 1 below. The PDC derivatives (0.2 mM) were added to 2.0 ml of the
◦
standardized inoculums, incubated at 37 C for 18.0 h. The bacterial
cells were fixed with 2% glutaraldehyde in NA-cacodylate buffer. The
8

G. Lavanya et al.
Bioorganic Chemistry 107 (2021) 104582
Table 3
Synthesis of furo [3, 2-c] quinolin-7-yl)-1, 4-dihydropyridine-3, 5-dicarboxylates and Tetrahydro-3H-cyclopenta[c]qunolin-7-yl-1,4-dihydropyridine-3,5-
dicarboxylate.
a
b
S.No
1
Aldehyde
Time (h/min)
Yield (%)
Endo:Exo ratio
47:53
Furo[3,2-c]quinolin-7-yl)-1,4-dihydropyridine-3,5-dicarboxylate & Tetrahydro-3H-cyclopenta[c]qunolin-7-
yl-1,4-dihydropyridine-3,5-dicarboxylate
6.5
69.0
6
a
(
9a)
(10a)
e2
14.0
59.0
38:62
65:35
–
6
b
(
9b)
(
10b)
3
12.0
17.0
20.0
21.0
19.0
20.0
65.0
51.0
45.0
47.0
52.0
54.0
6
6
c
(
10c)
(
(
(
(
(
(
9c)
4
a
12a)
12b)
12c)
12d)
12e)
5
6
7
8
–
–
–
–
6
b
6
c
6
d
6
e
9

G. Lavanya et al.
Bioorganic Chemistry 107 (2021) 104582
Table 4
In vitro antibacterial activity studies of PDC, FDC and CDC derivatives.
Compounds
Positive Bacteria
B.substilis
Negative bacteria
E.coli
S.aureus
S.mutans
P.aeruginosa
K.pneumoniae
V.cholerae
4
5
4
5
4
5
4
5
4
5
9
1
9
1
9
1
1
1
a
16
12
9
10
12
10
14
–
–
–
11
10
7
–
12
16
15
37
30
42
25
11
38
16
12
18
13
12
14
20
8
a
–
–
11
7
b
8
–
b
25
17
30
13
12
8
35
18
46
–
–
22
8
18
–
19
19
38
–
12
37
–
11
10
–
12
11
13
–
10
36
21
–
c
c
24
–
40
–
34
–
d
d
–
35
8
–
–
e
28
–
12
7
e
10
9
a
10
10
9
–
–
–
–
11
6
0a
b
12
7
–
10
14
–
–
0b
c
15
11
12
10
11
30
10
11
10
12
–
8
–
–
–
0c
2a
2c
11
–
–
–
9
–
–
–
42
–
14
36
Ciprofloxacin (Control)
35
45
30
*Diametre of zone of inhibition in mm
attached cells were fixed by immersion in 1% osmium tetroxide (OsO
4
),
activity than the endo substituted PDC derivatives. However a reversal
in activity was observed for diethyl 4-((4aR,5R,10bR)-5-(4-methox-
yphenyl)-3,4,4a,5,6,10b-hexahydro-2H-pyrano[3,2-c]quinolin-8-yl)-
2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate (4e) & diethyl 4-
((4aR,5S,10bR)-5-(4-methoxyphenyl)-3,4,4a,5,6,10b-hexahydro-2H-
pyrano[3,2-c]quinolin-8-yl)-2,6-dimethyl-1,4-dihydropyridine-3,5-
dicarboxylate (5e) wherein diethyl 4-((4aR,5R,10bR)-5-(4-methox-
yphenyl)-3,4,4a,5,6,10b-hexahydro-2H-pyrano[3,2-c]quinolin-8-yl)-
2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate (4e) exhibited
relatively better activity than diethyl 4-((4aR,5S,10bR)-5-(4-methox-
yphenyl)-3,4,4a,5,6,10b-hexahydro-2H-pyrano[3,2-c]quinolin-8-yl)-
dehydrated, viewed at 15 kV accelerating voltage in a scanning electron
microscope and images were recorded at different intervals of incuba-
tion time to observe the changes in morphology of the bacterial cell.
After 18.0 h of incubating the bacteria with PDC derivatives diethyl 4-
(
(4aR,5R,10bR)-5-(4-chlorophenyl)-3,4,4a,5,6,10b-hexahydro-2H-pyr-
ano[3,2-c]quinolin-8-yl)-2,6-dimethyl-1,4-dihydropyridine-3,5-dicar-
boxylate (4c) diethyl 4-((4aR,5S,10bR)-5-(4-chlorophenyl)-
,4,4a,5,6,10b-hexahydro-2H-pyrano[3,2-c]quinolin-8-yl)-2,6-
&
3
dimethyl-1,4-dihydropyridine-3,5-dicarboxylate (5c), the bacterial cell
wall undergoes blubbing, budding and ruptures due to accumulation of
cytoplasm leading cell death. The SEM inages (2, 3, 5 & 6) clearly show
the cell wall rupture of pseudomonas aeruginosa and streptococcus
mutans caused by PDC derivatives diethyl-4-((4aR,5R,10bR)-5-(4-
chlorophenyl)-3,4,4a,5,6,10b-hexahydro-2H-pyrano[3,2-c] quinolin-8-
yl)-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate (4c) & diethyl
2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate
(5e)
against
Staphylococcus aureus and Vibrio cholerae in comparison to the refer-
ence drug ciprofloxacin. The MIC values for the various synthesized
compounds against pathogenic strains of gram positive and gram
negative bacteria is shown in table 5 given below
4
-((4aR,5S, 10bR)-5-(4-chlorophenyl)-3,4,4a,5,6,10b-hexahydro-2H-
pyrano[3,2-c]quinolin-8-yl)-2,6-dimethyl-1,4-dihydropyridine-3,5-
dicarboxylate (5c) by blebbing, budding and cell wall lysis causing
bacterial apoptosis due to cytoplasmic accumulation.
3.5.4. Molecular docking studies
Inorder to understand the mode of binding between cell wall protein
of vibrio cholerae and the exo & endo pyrano[3,2-c]quinolin-8-yl)-1,4-
dihydropyridine-3,5-dicarboxylate derivatives, molecular docking
studies were carried out by using Gold suite software [32]. The 3d
crystal structure of vibrio cholerea was obtained from RSCB protein data
bank (PDB code 5CXK) [33]. The water molecules were removed from
the protein and hydrogen atoms were added to the protein by using
discovery studio 2.5.5software [34].The energy minimized three
dimensional structures of diethyl 4-((4aR,5R,10bR)-5-(4-chlorophenyl)-
3,4,4a,5,6,10b-hexahydro-2H-pyrano[3,2-c]quinolin-8-yl)-2,6-
dimethyl-1,4-dihydropyridine-3,5-dicarboxylate (4c) and diethyl 4-
((4aR,5S,10bR)-5-(4-chlorophenyl)-3,4,4a,5,6,10b-hexahydro-2H-pyr-
ano[3,2-c]quinolin-8-yl)-2,6-dimethyl-1,4-dihydropyridine-3,5-dicar-
boxylate (5c) was docked with the cell wall protein of the vibrio
cholerae. The docking results showed that both the endo and exo di-
astereomers (4c & 5c) docked well within the binding pockets of vibrio
cholerae. The major difference in the mode of binding of endo dia-
steromer diethyl 4-((4aR,5R,10bR)-5-(4-chlorophenyl)-3,4,4a,5,6,10b-
hexahydro-2H-pyrano[3,2-c]quinolin-8-yl)-2,6-dimethyl-1,4-dihy-
dropyridine-3,5-dicarboxylate (4c) and exo diastereomer diethyl 4-
((4aR,5S,10bR)-5-(4-chlorophenyl)-3,4,4a,5,6,10b-hexahydro-2H-pyr-
ano[3,2-c]quinolin-8-yl)-2,6-dimethyl-1,4-dihydropyridine-3,5-
3
.5.3. Minimum inhibitory concentration (MIC)
The minimum inhibitory concentration is the lowest concentration of
the target compound that is required for inhibiting the visible growth of
the microorganism under scrutiny. The MIC was determined by using
the broth macro dilution method and the results are summarized in table
5
given below. Among the PDC derivatives screened for antibacterial
activity, diethyl 4-((4aR,5S,10bR)-5-(4-chlorophenyl)-3,4,4a,5,6,10b-
hexahydro-2H-pyrano[3,2-c]quinolin-8-yl)-2,6-dimethyl-1,4-dihy-
dropyridine-3,5-dicarboxylate (5c) exhibited superior antibacterial ac-
tivity against E.Coli, Pseudomonas aeruginosa, Klebsiella pneumonia
and Vibrio cholerae in comparison to the reference drug Ciprofloxacin.
Similarly diethyl 2,6-dimethyl-4-((4aR,5S,10bR)-5-(4-nitrophenyl)-
3
,4,4a,5,6,10b-hexahydro-2H-pyrano[3,2-c]quinolin-8-yl)-1,4-dihy-
dropyridine-3,5-dicarboxylate (5b) exhibited potential antibacterial
activity against Vibrio cholerae in comparison to the reference drug
Ciprofloxacin with MIC value of 31.250
μ
g/mL. On comparing the
antibacterial activity, MIC and zone of inhibition exhibited by both the
exo and endo substituted PDC derivatives, it is evident from the table 5
that the exo substituted PDC derivatives exhibited relatively superior
1
0

G. Lavanya et al.
Bioorganic Chemistry 107 (2021) 104582
Fig. 1. SEM studies of the mode of action of PDC derivatives on pseudomonas aeruginosa and streptococcus mutans.
dicarboxylate (5c) is that the endo PDC diasteromer (4c) formed two
hydrogen bonds with the target cell wall protein of V.cholera with a
glide score of 12.68 whereas the exo PDC diastereomer (5c) formed four
hydrogen bonds with the cell wall protein of V.cholera with a Goldsuite
glide score of 19.74. The –NH group of endo diasteromer (4c) formed an
hydrogen bond with GLU156 amino acid residue (bond length ꢀ 2.746
A) while the oxygen atom present in the pyran ring of 4c formed another
hydrogen bond with CYS154SG amino acid residue (bond length ꢀ 2.368
A) where as one –NH group, one oxygen atom on pyran ring and the two
ester carbonyl oxygen atoms of exo PDC diasteromer (5c) formed four
hydrogen atom with the aminoacid residues GLU156 (bond length
ꢀ 2.746 A), CYS154 (bond length ꢀ 2.746 A), LEU155 (bond length
1
1

G. Lavanya et al.
Bioorganic Chemistry 107 (2021) 104582
Table 5
Minimum Inhibitory Concentration (MIC) evaluation of the PDC, FDC & CDC derivatives against different pathogenic strains of bacteria.
Compounds
Minimum inhibitory concentration (
Bacterial strains
μg/mL)
B.substilis
S.aureus
S.mutans
E.coli
P.aeruginosa
K.pneumoniae
V.cholerae
4
5
4
5
4
5
4
5
4
5
9
1
9
1
9
1
1
1
a
125.0
250.0
N.D
500.0
500.0
250.0
250.0
N.D
N.D
N.D
500
N.D
250.0
125.0
125.0
31.25
62.50
31.25
62.50
125.0
31.25
250.0
250.0
125.0
250.0
250.0
250.0
125.0
500.0
125.0
31.25
a
N.D
N.D
500
500
b
500.0
62.50
125.25
31.25
N.D
N.D
N.D
N.D
b
31.25
125.0
62.50
250.0
250.0
N.D
250.0
N.D
250.0
62.50
31.25
N.D
62.50
N.D
c
c
62.50
N.D
31.25
N.D
31.25
N.D
d
d
N.D
N.D
N.D
125.0
31.25
N.D
N.D
e
31.25
500.0
500.0
500.0
N.D
125.0
500.0
N.D
62.50
N.D
250.0
500.0
N.D
e
500.0
N.D
a
N.D
500.0
N.D
0a
b
500.0
N.D
N.D
N.D
500.0
N.D
N.D
N.D
N.D
0b
c
500.0
250.0
250.0
500.0
500.0
62.50
500.0
500.0
N.D
500.0
N.D
N.D
250.0
250.0
125.0
500
N.D
N.D
N.D
0c
2a
2c
500.0
N.D
N.D
N.D
250.0
N.D
500
N.D
N.D
N.D
125.0
31.25
250.0
62.50
Ciprofloxacin (Control)
31.25
31.25
31.25
ND: Not Determined
ꢀ
2.746 A) and LYS184 (bond length ꢀ 2.746 A). The formation of four
dihydropyridine carboxylate (FDC) and cyclopentaquinolinyl dihy-
dropyridine carboxylate (CPDC) derivatives were screened for antibac-
terial activity against pathogenic strains of gram positive and gram
negative bacteria. The antibacterial results revealed that pyr-
anoquinolinyl dihydropyridine carboxylate (PDC) derivatives exhibited
superior antibacterial activity in comparison to furanoquinolinyl dihy-
dropyridine carboxylate (FDC) and cyclopentaquinolinyl dihydropyr-
idine carboxylate (CDC) derivatives with ciprofloxacin as a reference
drug. Among the PDC derivatives, exo pyranoquinolinyl dihydropyr-
idine carboxylate diastereomers (5a-e) exhibited relatively superior
activity in comparison to the relatively less active endo pyr-
anoquinolinyl dihydropyridine carboxylate diastereomers (4a-e). The
molecular docking results showed that the diethyl 4-((4aR,5S,10bR)-5-
(4-chlorophenyl)-3,4,4a,5,6,10b-hexahydro-2H-pyrano[3,2-c]quinolin-
8-yl)-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate derivatives
against Vibrio cholera (5c)
hydrogen bonds with the cell wall protein of Vibrio cholerae by exo PDC
diasteromer (5c) results in relatively better anchorage for the diethyl 4-
(
(4aR,5S,10bR)-5-(4-chlorophenyl)-3,4,4a,5,6,10b-hexahydro-2H-pyr-
ano[3,2-c]quinolin-8-yl)-2,6-dimethyl-1,4-dihydropyridine-3,5-dicar-
boxylate (5c) and hence relatively better antibacterial activity in
comparison
the
less
active
diethyl-4-((4aR,5R,10bR)-5-(4-
chlorophenyl)-3,4,4a,5,6,10b-hexahydro-2H-pyrano[3,2-c] quinolin-8-
yl)-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate (4c) (Fig. 2).
3
.5.5. Cytotoxicity
Many of the organic lead compounds developed for potential appli-
cation as drugs fail because of toxicity, poor stability, difficult to scale up
synthetic procedures etc. Hence in an effort to find a potential lead
compound we further evaluated the pyrano[3,2-c]quinolin-8-yl)-1,4-
dihydropyridine-3,5-dicarboxylate derivatives for cytotoxicity. The
pyrano[3,2-c]quinolin-8-yl)-1,4-dihydropyridine-3,5-dicarboxylate de-
rivatives were evaluated for cytotoxocity by MTT colorimetric assay
against against L929 mouse fibroblasts cells. The L929 fibroblasts cells
were treated with different concentrations of compounds (4a, 5a, 4c, 5c,
formed four hydrogen bonds with the amino acid residues of the
bacterial cell wall of Vibrio cholerae while diethyl 4-((4aR,5R,10bR)-5-
(4-chlorophenyl)-3,4,4a,5,6,10b-hexahydro-2H-pyrano[3,2-c]quinolin-
8-yl)-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate (4c) formed
only two hydrogen bonds with amino acid residues of cell wall of the
target enzyme thereby leading to better anchorage and increased ac-
tivity for diethyl 4-((4aR,5S,10bR)-5-(4-chlorophenyl)-3,4,4a,5,6,10b-
hexahydro-2H-pyrano[3,2-c]quinolin-8-yl)-2,6-dimethyl-1,4-dihy-
dropyridine-3,5-dicarboxylate derivatives against Vibrio cholera (5c).
However all the compounds reported herein including PDC, FDC & CDC
derivatives exhibited antibacterial inhibitory activity against vibrio
cholerae (zone of inhibition 8.0 mm-42 mm) at various concentrations
in comparison to the reference drug ciprofloxacin, Hence these com-
pounds are a promising class of lead molecules for treatment and miti-
gation of cholera after necessary pharmacological evaluations. Based on
the SEM analysis it was found that the PDC derivatives cause bacterial
apoptosis by blebbing, budding and cell wall lysis. Moreover, the cyto-
toxic assay of the PDC derivatives revealed minimal cytotoxicity to-
4
e, 5e, 9a & 10a) in ethanol with a final maximum concentration of 100
M for test compounds. All the compounds evaluated for cytotoxicity
exhibited minimal cytotoxicity (<10%) at concentration of 25.0 M and
M towards L929
μ
μ
moderate cytotoxicity at concentrations of 50.0–100.0
mouse fibroblasts cells as shown in Table. 6.
μ
4
. Conclusion
In conclusion the present work reports the synthesis of new class of
pyrano[3,2-c]quinolin-8-yl)-1,4-dihydropyridine-3,5-dicarboxylate de-
rivatives which combines the antibacterial activity of quinolines along
with the multidrug resistance modulating effect of dihydropyrimidines.
The designed pyrano[3,2-c]quinolin-8-yl)-1,4-dihydropyridine-3,5-
dicarboxylate derivatives were synthesized by multi-step synthesis
involving Michael addition and inverse electro demand Alder reaction
wards L929 mouse fibroblasts cells at 25
% Cell viability was found to be greater than 90.0% and moderate
M. Hence in conclusion,
μ
M concentration wherein the
(
IED) to produce pyranoquinolinyl dihydropyridine carboxylates in
1
13
good yields. All the products were characterized by H NMR, C NMR,
FT-IR, Mass spectral and CHN analysis. All the synthesized pyr-
anoquinolinyl dihydropyridine carboxylate (PDC), furanoquinolinyl
cytotoxicity at concentrations of at 50.0–100.0 μ
this paper reports a new class of PDC derivatives with simple synthetic
procedures, superior antibacterial activity including vibrio cholerae and
1
2

G. Lavanya et al.
Bioorganic Chemistry 107 (2021) 104582
Fig. 2. Molecular docking of (diethyl 4-((4aR,5R,10bR)-5-(4-chlorophenyl)-3,4,4a,5,6,10b-hexahydro-2H-pyrano[3,2-c]quinolin-8-yl)-2,6-dimethyl-1,4-dihy-
dropyridine-3,5-dicarboxylate (4c) diethyl 4-((4aR,5S,10bR)-5-(4-chlorophenyl)-3,4,4a,5,6,10b-hexahydro-2H-pyrano[3,2-c]quinolin-8-yl)-2,6-dimethyl-1,4-
dihydropyridine-3,5-dicarboxylate derivatives against Vibrio cholera (5c).
&
1
3

G. Lavanya et al.
Bioorganic Chemistry 107 (2021) 104582
Table 6
Cytotoxicity of PDC, FDC and CDC derivatives against L929 mouse fibroblasts cells.
S.No
1
Compound
4a
Concentration (µM)
% of cell viability (triplicate values)
25
91.20 ± 0.12
92.08 ± 0.08
86.51 ± 1.02
90.62 ± 0.27
85.63 ± 0.08
70.67 ± 0.12
95.89 ± 0.30
76.25 ± 0.47
70.38 ± 0.37
96.77 ± 0.56
85.92 ± 0.21
71.55 ± 0.34
94.13 ± 0.24
87.39 ± 0.36
72.43 ± 0.25
90.73 ± 0.16
84.73 ± 0.14
73.16 ± 0.32
91.98 ± 0.45
79.51 ± 0.61
70.45 ± 0.32
96.77 ± 0.21
85.92 ± 0.11
71.55 ± 0.21
95.30 ± 0.45
85.90 ± 0.32
73.37 ± 0.41
5
1
0
82.11 ± 0.13
72.43 ± 0.46
87.98 ± 0.30
77.71 ± 0.27
68.33 ± 0.59
98.24 ± 0.08
85.04 ± 0.06
83.58 ± 0.76
98.24 ± 0.20
85.04 ± 0.27
75.07 ± 0.58
90.10 ± 1.01
81.71 ± 2.31
73.32 ± 0.48
88.79 ± 0.52
78.91 ± 0.32
69.11 ± 0.51
98.24 ± 0.32
85.04 ± 0.43
83.58 ± 0.38
96.43 ± 0.68
86.41 ± 0.71
74.42 ± 0.68
00
70.38 ± 0.55
91.50 ± 0.11
79.47 ± 0.97
65.98 ± 0.76
99.71 ± 0.65
88.27 ± 0.81
79.18 ± 0.32
98.53 ± 0.99
86.51 ± 0.23
73.61 ± 0.15
91.81 ± 0.29
85.82 ± 0.21
72.01 ± 0.19
92.05 ± 0.34
80.71 ± 0.26
68.18 ± 0.01
99.71 ± 0.29
88.27 ± 0.45
79.18 ± 0.21
97.31 ± 0.07
87.19 ± 0.12
75.11 ± 0.31
2
3
4
5
6
7
8
5a
4c
25
5
1
0
00
25
5
1
0
00
5c
25
5
1
0
00
4e
5e
9a
10a
25
5
1
0
00
25
5
1
0
00
25
5
1
0
00
25
5
1
0
00
moderate cytoyoxicity towards L929 mouse fibroblasts cells.
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