Synthesis of a novel class of some biquinoline pyridine hybrids via one-pot, three-component reaction and their antimicrobial activity

Article abstract of DOI:10.1007/s12039-012-0254-0

A small library of novel class of biquinoline containing pyridine moiety were synthesized by a one-pot cyclocondensation of 2-chloro-3-formyl quinoline, active methylene compounds and 3-(pyridine-3- ylamino)cyclohex-2-enone in the presence of catalytic am

Full text of DOI:10.1007/s12039-012-0254-0

J. Chem. Sci. Vol. 124, No. 3, May 2012, pp. 669–677. ꢀc Indian Academy of Sciences.
Synthesis of a novel class of some biquinoline pyridine hybrids via
one-pot, three-component reaction and their antimicrobial activity
∗
NIMESH M SHAH, MANISH P PATEL and RANJAN G PATEL
Department of Chemistry, Sardar Patel University, Vallabh Vidyanagar 388120, India
e-mail: patelranjanben@yahoo.com
MS received 14 November 2011; accepted 30 December 2011
Abstract. A small library of novel class of biquinoline containing pyridine moiety were synthesized by a
one-pot cyclocondensation of 2-chloro-3-formyl quinoline, active methylene compounds and 3-(pyridine-3-
ylamino)cyclohex-2-enone in the presence of catalytic amount of sodium hydroxide. The protocol offers rapid
synthesis of structurally diverse novel class of some biquinoline pyridine hybrids for antimicrobial screen-
ing. These compounds were screened for their antibacterial activity against Gram-positive bacteria (Bacillus
subtilis, Clostridium tetani, Streptococcus pneumoniae), Gram-negative bacteria (Escherichia coli, Salmonella
typhi, Vibrio cholerae) and antifungal activity against Aspergillus fumigatus, Candida albicans. Some of the
biquinoline compounds were found to be more potent or equipotent than the first line standard drugs. The
compounds were evaluated for their in vitro antitubercular activity against Mycobacterium tuberculosis H37Rv
strain using Lowenstein–Jensen medium. Compound 4g showed a compelling activity at 6.25 μg/mL with a
9
6% inhibition and could be ideally suited for further modifications to obtain more efficacious compounds in
the fight against tuberculosis.
Keywords. Quinoline; MIC; antimycobacterial; antimicrobial activity.
1
. Introduction
research for the discovery and synthesis of new classes
of antimicrobial agents is needed.
4,5
Green chemistry emphasizes the development of envi-
ronmentally benign chemical processes and technolo-
gies. Besides typical multi-step syntheses, an increasing
number of organic chemical compounds are formed by
multicomponent reactions (MCRs). MCRs often com-
ply with the principles of green chemistry in terms of
economy of steps as well as the many stringent crite-
ria of an ideal organic synthesis. Multicomponent reac-
tions offer greater possibilities for molecular diversity
per step with a minimum of synthetic time, labour, cost,
and waste production. The rapid assembly of mole-
cular diversity utilizing multicomponent reactions has
received a great deal of attention, most notably for
Among the important pharmacophores responsible
for antimicrobial activity, the quinoline scaffold is still
considered a viable lead structure for the synthesis
of more efficacious and broad spectrum antimicrobial
agents. In the recent time, quinoline nucleus has gath-
ered an immense attention among chemists as well as
biologists as it is one of the key building elements for
many naturally occurring compounds. The quinoline
ring is endowed with various activities, such as anti-
6
7
8
tuberculosis, antimalarial, anti-inflammatory, anti-
9
10
11
cancer, antimicrobial, antihypertensive, antioxi-
12
13
dant, tyrokinase PDGF-RTK inhibiting agents, and
14
antiHIV. Amongst the various activities of their
derivatives, antimicrobial activity is noteworthy.
The pyridine nucleus is prevalent in numerous natu-
ral products and is extremely important in chemistry of
biological systems. It plays a key role catalysing both
biological and chemical systems. In many enzymes of
living organisms it is the prosthetic pyridine nucleotide
1–3
the construction of heterocyclic ‘drug-like’ libraries.
These methods have significant utility, particularly,
when they lead to the formation of privileged medicinal
heterocyclic compounds.
Emerging infectious diseases and the increasing
number of multi-drug resistant microbial pathogens still
make the treatment of infectious diseases an important
and pressing global problem. Therefore, a substantial
15
(NADP) that is involved in various oxidation–reduction
processes. Other evidence of the potent activity of pyri-
dine in biological systems is its presence in the impor-
tant vitamins niacin and pyridoxine (vitamin B6) and
∗
16,17
For correspondence
also in highly toxic alkaloids such as nicotine.
The
669

670
Nimesh M Shah et al.
pyridine substructure is one of the most important hete- Thin-layer chromatography (TLC, on aluminium plates
rocycles found in natural products, pharmaceuticals and precoated with silica gel, 60 F , 0.25 mm thickness)
2
54
functional materials.1
8,19
(Merck, Darmstadt, Germany) was used for monitor-
A thorough literature review reveals that more effi- ing the progress of all reactions. UV radiation and/or
cacious antibacterial compounds can be designed by iodine were used as the visualizing agents. Elemental
joining two or more biologically active heterocyclic analysis (% C, H, N) was carried out by Perkin-Elmer
20
systems together in a single molecular framework.
2400 series-II elemental analyzer (Perkin-Elmer, USA).
In continuation of our efforts to develop new, green The IR spectra were recorded in KBr on a Perkin-Elmer
chemistry methods21 as well as in continuation of our Spectrum GX FT-IR Spectrophotometer (Perkin-Elmer,
recent interest in the construction of heterocyclic scaf- USA) and only the characteristic peaks are reported in
folds with antimicrobial activity2
2–25
we report here the cm . H NMR and C NMR spectra were recorded
−1
1
13
synthesis, antimicrobial evaluation of some novel struc- in DMSO-d on a Bruker Avance 400F (MHz) spectro-
6
ture hybrids incorporating both the quinoline moiety meter (Bruker Scientific Corporation Ltd., Switzerland)
with pyridine. This combination was suggested in an using solvent peak as internal standard at 400 MHz and
attempt to investigate the influence of such hybridiza- 100 MHz, respectively. Chemical shifts are reported in
tion and structure variation on the anticipated biologi- parts per million (ppm). Mass spectra were scanned
cal activities, hoping to add some synergistic biological on a Shimadzu LCMS 2010 spectrometer (Shimadzu,
significance to the target molecules.
Tokyo, Japan).
2
.2 General procedure for the synthesis
2. Experimental
of 2-chloro-3-formyl quinolines (2a–d)
2
.1 Materials and methods
The starting material, 2-chloro-3-formyl quinolines 2a–
The reagents used in this work were obtained from d were prepared, according to literature procedure26
Aldrich and were used without purification. All used by Vilsmeier–Haack reaction of acetanilide deriva-
solvents were of analytical grade. All melting points tives (1a–d) with phosphorus oxychloride in DMF
were taken in open capillaries and are uncorrected. (scheme 1).
Scheme 1. General synthetic route for the title compounds (4a–l). VHR: Vilsmeier-Haack Reaction.

Synthesis of a novel class of some biquinoline pyridine hybrids
671
−1
2.3 General procedure for the synthesis
(KBr, ν, cm ) 3435 and 3155 (asym. and sym. stretch-
of 3-(pyridine-3-ylamino)cyclohex-2-enone
ing of NH ), 2185 (C≡N stretching), 1660 (C=O
2
1
stretching); H-NMR (400 MHz, DMSO-d ) δ (ppm):
6
H
1,3-Cyclohexanedione (1 mmol), 3-amino pyridine
1
.74–2.27 (m, 6H, 3×CH ), 2.45 (s, 3H, Ar-CH ), 5.20
2
3
(1 mmol), methanol (15 mL) and 2 drops of acetic acid
(s, 1H, quinoline H4), 5.67 (s, 2H, NH ), 7.59–8.48 (m,
2
13
were charged in 100 mL round bottom flask equipped
with refluxing condenser. The reaction mixture was
slowly heated and refluxed for 1 h. On completion
of reaction, monitored by TLC using 30% EtOAc in
toluene as eluent, the reaction mixture was cooled to
room temperature and the solid separated was filtered
and washed with methanol to obtain the pure compound
8
2
3
1
1
H, Ar-H); C NMR (100 MHz, DMSO-d ) δ (ppm):
1.28 (CH ), 21.54 (Ar-CH ), 28.74 (CH ), 34.67 (C4),
6.36 (CH -CO), 59.62 (C-CN), 112.5, 120.7, 123.5,
24.8, 127.8, 128.3, 130.2, 131.2, 133.3, 136.4, 138.4,
6 C
2
3
2
2
40.0, 142.6, 148.21, 150.3, 152.6, 153.2, 155.5 (18C,
+
Ar-C), 195.5 (C=O); MS: m/z = 442.6 [M+H] ;
Anal. Calcd. for C H ClN O (441.91 g/mol): C,
25
20
5
(scheme 1).
6
1
7.95; H, 4.56; N, 15.85. Found: C, 67.67; H, 4.63; N,
5.92.
2.4 General procedure for the synthesis of
2-amino-4-(2-chloro-6-(un)substituted (3-quinolyl))-5-
oxo-1-pyridin-3-yl-1,4,6,7,8-pentahydro quinoline
4a–l)
(
2.4c 2-Amino-4-(2-chloro-6-methoxy(3-quinolyl))-5-
oxo-1-pyridin-3-yl-1,4,6,7,8-pentahydro quinoline-3-
◦
A mixture of 2-chloro-3-formyl quinoline (5 mmol) carbonitrile (4c): Yield 78%; mp.: 218–220 C IR
−1
(2a–d), malononitrile or ethyl cyanoacetate or methyl (KBr, ν, cm ) 3440 and 3150 (asym. and sym. stretch-
cyanoacetate (5 mmol) (3a–c) and 3-(pyridine-3- ing of NH ), 2200 (C≡N stretching), 1665 (C=O
2
1
ylamino)cyclohex-2-enone (5 mmol) in ethanol (10 mL) stretching); H-NMR (400 MHz, DMSO-d ) δ
6
H
containing NaOH (1 mmol) was heated under reflux for (ppm): 1.80–2.28 (m, 6H, 3×CH ), 3.89 (s, 3H,
2
2
–3 h. On completion of reaction, monitored by TLC Ar-OCH ), 5.11 (s, 1H, quinoline H4), 5.59 (s, 2H,
3
13
(ethyl acetate:hexane::3:7), the reaction mixture was NH ), 7.60–8.71 (m, 8H, Ar-H); C NMR (100 MHz,
2
cooled to room temperature and the solid separated DMSO-d ) δC (ppm): 21.3, 28.6 (2C, CH ), 34.6
6
2
was filtered, washed with ethanol, dried, and recrys- (C4), 36.2 (CH -CO), 55.8 (Ar-OCH ), 59.4 (C-CN),
2
3
tallized to give the desired product. Analytical and 105.3, 112.8, 120.8, 122.3, 124.6, 125.1, 128.6, 130.2,
spectroscopic characterization data of the synthesized 132.4, 134.8, 136.1, 138.9, 140.2, 146.5, 148.3, 150.0,
compounds (4a–l) are given below.
153.3, 155.2 (18C, Ar-C), 195.5 (C=O); Anal. Calcd.
for C H ClN O (457.91 g/mol): C, 65.57; H, 4.40;
25
20
5
2
N, 15.29. Found: C, 65.43; H, 4.52; N, 15.39.
2.4a 2-Amino-4-(2-chloro(3-quinolyl))-5-oxo-1-pyridin-
3
-yl-1,4,6,7,8-pentahydro quinoline-3-carbonitrile (4a):
◦
−1
Yield, 84%; mp.: 242–244 C IR (KBr, ν, cm ): 3440
and 3160 (asym. and sym. stretching of NH ), 2185
2
1
2
.4d 2-Amino-4-(2,6-dichloro(3-quinolyl))-5-oxo-1-
(
C≡N stretching), 1665 (C=O stretching); H NMR
pyridin-3-yl-1,4,6,7,8-pentahydro quinoline-3-carbonitrile
(400 MHz, DMSO-d ): δ (ppm): 1.76–2.29 (m, 6H,
6
H
◦
(
4d): Yield 86%; mp.: 272–274 C IR (KBr, ν,
3
×CH ), 5.22 (s, 1H, quinoline H4), 5.63 (s, 2H,
2
−1
13
cm ) 3435 and 3150 (asym. and sym. stretching of
NH ), 7.66–8.62 (m, 9H, Ar-H); C NMR (100 MHz,
2
NH ), 2180 (C≡N stretching), 1665 (C=O stretch-
DMSO-d ) δ (ppm) 21.2, 28.7 (2C, CH ), 34.6 (C4),
2
6
C
2
1
ing); H-NMR (400 MHz, DMSO-d ) δ (ppm):
3
1
1
6.2 (CH -CO), 59.5 (C-CN), 112.3, 120.8, 125.6,
27.4, 128.5, 130.1, 131.2, 132.0, 136.2, 138.5, 140.1,
42.2, 144.6, 148.7, 150.1, 151.3, 153.5, 155.4 (18C,
6
H
2
1
.83–2.27 (m, 6H, 3×CH ), 5.13 (s, 1H, quinoline
2
H4), 5.69 (s, 2H, NH ), 7.62–8.74 (m, 8H, Ar-H);
2
13
C NMR (100 MHz, DMSO-d ) δC (ppm): 21.2,
Ar-C), 195.4 (C=O); Anal. Calcd. for C H ClN O
6
24
18
5
28.6 (2C, CH ), 34.6 (C4), 36.2 (CH -CO), 59.5 (C-
(427.89 g/mol): C, 67.37; H, 4.24 ; N, 16.37. Found: C,
2
2
CN), 112.1, 121.2, 125.1, 127.2, 129.0, 129.9, 131.2,
67.49; H, 4.15; N, 16.21.
131.8, 133.5, 137.5, 138.8, 140.2, 144.6, 150.4, 150.9,
1
51.3, 151.8, 154.1 (18C, Ar-C), 195.4 (C=O); MS:
+
2
.4b 2-Amino-4-(2-chloro-6-methyl(3-quinolyl))-5- m/z = 462.1 [M+H] ; Anal. Calcd. for C H Cl N O
24
17
2
5
oxo-1-pyridin-3-yl-1,4,6,7,8-pentahydro quinoline-3- (462.33 g/mol): C, 62.35; H, 3.71; N, 15.15. Found: C,
◦
carbonitrile (4b): Yield 82%; mp.: 266–268 C IR 62.47; H, 3.61; N, 15.08.

672
Nimesh M Shah et al.
2.4e Ethyl 2-amino-4-(2-chloro(3-quinolyl))-5-oxo-1- (504.96 g/mol): C, 64.22; H, 4.99; N, 11.10. Found: C,
pyridin-3-yl-1,4,6,7,8-pentahydro quinoline-3-carboxylate 64.34; H, 5.23; N, 11.18.
◦
−1
(
4e): Yield 81%; mp.: 227–229 C IR (KBr, ν, cm )
3
1
370 and 3180 (asym. and sym. stretching of NH ),
2
1
660 (C=O stretching), 1635 (C=O stretching); H- 2.4h Ethyl 2-amino-4-(2,6-dichloro(3-quinolyl))-5-oxo-
NMR (400 MHz, DMSO-d ) δ (ppm): 0.98 (t, 3H, 1-pyridin-3-yl-1,4,6,7,8-pentahydro quinoline-3-carboxylate
6
H
◦
−1
CH ), 1.60–2.18 (m, 6H, 3×CH ), 3.93 (q, 2H, OCH ), (4h): Yield 82%; mp.: 273–275 C IR (KBr, ν, cm )
3
2
2
5
8
.34 (s, 1H, quinoline H4), 7.11 (s, 2H, NH ), 7.57– 3360 and 3185 (asym. and sym. stretching of NH ),
2
2
.78 (m, 9H, Ar-H); 13C NMR (100 MHz, DMSO- 1665 (C=O stretching), 1640 (C=O stretching); H-
1
d ) δ (ppm): 14.7 (CH ), 21.1, 28.7 (2C, CH ), 35.2 NMR (400 MHz, DMSO-d ) δ (ppm): 0.97 (t, 3H,
6
C
3
2
6
H
(
C4), 36.4 (CH -CO), 58.9 (OCH ), 78.0 (C-COOEt), CH ), 1.62–2.20 (m, 6H, 3×CH ), 3.91 (q, 2H, OCH ),
2
2
3
2
2
1
1
1
13.6, 125.3, 126.6, 127.1, 127.1, 128.2, 130.3, 133.5, 5.38 (s, 1H, quinoline H4), 7.08 (s, 2H, NH ), 7.60–
2
13
38.8, 139.7, 140.5, 145.8, 150.7, 151.0, 151.3, 153.0, 8.75 (m, 8H, Ar-H); C NMR (100 MHz, DMSO-
53.3 (17C, Ar-C), 169.3 (COO), 195.5 (C=O); Anal. d6) δC (ppm): 14.7 (CH ), 21.1, 28.7 (2C, CH ),
3
2
Calcd. for C H ClN O (474.94 g/mol): C, 65.75; H, 35.1 (C4), 36.5 (CH -CO), 58.9 (OCH ), 78.0 (C-
26
23
4
3
2
2
4.88; N, 11.80. Found: C, 65.84; H, 4.72; N, 12.05.
COOEt), 113.5, 122.2, 125.5, 126.8, 129.1, 129.8,
131.4, 132.0, 133.1, 137.1, 138.9, 142.3, 144.6, 151.0,
1
52.5, 152.8, 153.2 (17C, Ar-C), 169.5 (COO), 195.5
+
2
5
.4f Ethyl 2-amino-4-(2-chloro-6-methyl(3-quinolyl))- (C=O); MS: m/z = 508.6 [M+H] ; Anal. Calcd. for
-oxo-1-pyridin-3-yl-1,4,6,7,8-pentahydro quinoline-3-
C H22Cl N O (509.38 g/mol): C, 61.31; H, 4.35; N,
26 2 4 4
◦
carboxylate (4f): Yield 77%; mp.: 254–256 C IR (KBr, 11.00. Found: C, 61.11; H, 4.16; N, 11.21.
−1
ν, cm ) 3365 and 3185 (asym. and sym. stretching
of NH ), 1660 (C=O stretching), 1640 (C=O stretch-
2
1
ing); H-NMR (400 MHz, DMSO-d ) δ (ppm): 0.97 2.4i Methyl 2-amino-4-(2-chloro(3-quinolyl))-5-oxo-1-
6
H
(
t, 3H, CH ), 1.58–2.16 (m, 6H, 3×CH ), 2.47 (s, 3H, pyridin-3-yl-1,4,6,7,8-pentahydro quinoline-3-carboxylate
◦ −1
3 2
3
2
Ar-CH ), 3.95 (q, 2H, OCH ), 5.35 (s, 1H, quinoline (4i): Yield 75%; mp.: 222–224 C IR (KBr, ν, cm )
H4), 7.10 (s, 2H, NH ), 7.52–8.72 (m, 8H, Ar-H); C 3350 and 3180 (asym. and sym. stretching of NH ),
13
2
2
1
NMR (100 MHz, DMSO-d ) δ (ppm): 14.7 (CH ), 1660 (C=O stretching), 1640 (C=O stretching); H-
6
C
3
2
3
1
1
1.1 (CH ), 21.5 (Ar-CH ), 28.7 (CH ), 35.2 (C4), NMR (400 MHz, DMSO-d ) δ (ppm): 1.64–2.25
2 3 2
6 H
6.4 (CH -CO), 58.9 (OCH ), 78.0 (C-COOEt), 113.5, (m, 6H, 3×CH ), 3.82 (s, 3H, OCH ), 5.28 (s, 1H,
2
2
2
3
24.2, 125.8, 126.2, 127.3, 128.5, 130.1, 132.6, 138.5, quinoline H4), 7.14 (s, 2H, NH ), 7.51–8.71 (m, 9H,
2
13
39.2, 142.3, 145.8, 149.4, 150.6, 151.2, 153.0, 153.8 Ar-H); C NMR (100 MHz, DMSO-d ) δ (ppm):
6
C
(
17C, Ar-C), 169.3 (COO), 195.5 (C=O); Anal. Calcd. 21.2, 28.7 (2C, CH ), 35.3 (C4), 36.5 (CH -CO),
2
2
for C H ClN O (488.97 g/mol): C, 66.32; H, 5.15; N, 52.8 (OCH ), 78.4 (C-COOCH ), 113.7, 122.3, 125.6,
27 25 4 3
3 3
1
1.46. Found: C, 66.54; H, 5.27; N, 11.30.
126.1, 127.0, 128.2, 128.9, 130.1, 132.4, 136.5, 138.3,
42.7, 146.3, 150.2, 151.5, 153.1, 153.6 (17C, Ar-
C), 169.6 (COO), 195.5 (C=O); Anal. Calcd. for
(460.91 g/mol): C, 65.15; H, 4.59; N,
1
2
5
3
.4g Ethyl 2-amino-4-(2-chloro-6-methoxy(3-quinolyl))-
C H21ClN O
25 4 3
-oxo-1-pyridin-3-yl-1,4,6,7,8-pentahydro quinoline- 12.16. Found: C, 65.33; H, 4.40; N, 12.29.
◦
-carboxylate (4g): Yield 78%; mp.: 246–248 C IR
−1
(KBr, ν, cm ) 3370 and 3190 (asym. and sym. stretch-
ing of NH ), 1665 (C=O stretching), 1640 (C=O 2.4j Methyl 2-amino-4-(2-chloro-6-methyl(3-quinolyl))-
2
1
stretching); H-NMR (400 MHz, DMSO-d ) δ
5-oxo-1-pyridin-3-yl-1,4,6,7,8-pentahydro quinoline-
6
H
◦
(
ppm): 0.97 (t, 3H, CH ), 1.61–2.16 (m, 6H, 3×CH ), 3-carboxylate (4j): Yield 74%; mp.: 262–264 C IR
3
2
−1
3
.88 (s, 3H, Ar-OCH ), 3.93 (q, 2H, OCH ), 5.32 (KBr, ν, cm ) 3350 and 3190 (asym. and sym. stretch-
3 2
(
(
s, 1H, quinoline H4), 7.12 (s, 2H, NH ), 7.58–8.73 ing of NH ), 1670 (C=O stretching), 1640 (C=O
2
2
13
1
m, 8H, Ar-H); C NMR (100 MHz, DMSO-d ) δC stretching); H-NMR (400 MHz, DMSO-d ) δ
6
6
H
(
ppm): 14.7 (CH ), 21.2, 28.7 (2C, CH ), 35.2 (C4), (ppm): 1.65–2.22 (m, 6H, 3×CH ), 2.47 (s, 3H, Ar-
3
2
2
3
7
1
1
6.5 (CH -CO), 55.9 (Ar-OCH ), 59.0 (OCH ), CH ), 3.84 (s, 3H, OCH ), 5.28 (s, 1H, quinoline
2 3 2 3 3
13
7.9 (C-COOEt), 105.3, 113.1, 124.1, 125.3, 127.4, H4), 7.11 (s, 2H, NH ), 7.56–8.64 (m, 8H, Ar-H); C
2
28.8, 130.2, 132.5, 137.4, 138.1, 142.3, 144.5, NMR (100 MHz, DMSO-d ) δ (ppm): 21.2 (CH ),
6
C
2
48.7, 150.6, 151.4, 153.0, 153.8 (17C, Ar-C), 169.4 21.5 (Ar-CH ) 28.7 (CH ), 35.2 (C4), 36.5 (CH -
3
2
2
(
COO), 195.6 (C=O); Anal. Calcd. for C H ClN O
CO), 52.8 (OCH ), 78.5 (C-COOCH ), 113.6, 122.3,
27
25
4
4
3 3

Synthesis of a novel class of some biquinoline pyridine hybrids
673
1
1
24.3, 126.1, 127.0, 128.6, 130.3, 132.2, 136.5, 137.7, CFU [Colony Forming Unit] per milliliter by compar-
42.0, 144.3, 147.4, 150.2, 151.2, 151.7, 153.8 (17C, ing the turbidity. The strains used for the activity were
Ar-C), 169.5 (COO), 195.5 (C=O); Anal. Calcd. for procured from [MTCC – Microbial Type Culture Col-
C H ClN O (474.94 g/mol): C, 65.75; H, 4.88; N, lection] Institute of Microbial Technology, Chandigarh.
26
23
4
3
11.80. Found: C, 65.85; H, 4.98; N, 11.66.
Dimethyl sulfoxide (DMSO) was used as diluent to get
desired concentration of drugs to test on standard bac-
terial strains. Serial dilutions were prepared in primary
2
5
3
.4k Methyl 2-amino-4-(2-chloro-6-methoxy(3-quinolyl))- and secondary screening. The control tube containing
-oxo-1-pyridin-3-yl-1,4,6,7,8-pentahydro quinoline- no antibiotic was immediately subcultured (before inoc-
◦
-carboxylate (4k): Yield 76%; mp.: 232–234 C IR ulation) by spreading a loopful evenly over a quar-
−
1
(
KBr, ν, cm ) 3365 and 3180 (asym. and sym. stretch- ter of plate of medium suitable for the growth of the
◦
ing of NH ), 1660 (C=O stretching), 1635 (C=O test organism and put for incubation at 37 C overnight.
2
1
stretching); H-NMR (400 MHz, DMSO-d ) δ
The tubes were then incubated overnight. The MIC
6
H
(
ppm): 1.63–2.24 (m, 6H, 3×CH ), 3.83 (s, 3H, of the control organism was read to check the accu-
2
OCH ), 3.87 (s, 3H, Ar-OCH ), 5.24 (s, 1H, quinoline racy of the drug concentrations. The lowest concentra-
3
3
13
H4), 7.04 (s, 2H, NH ), 7.62–8.76 (m, 8H, Ar-H); C tion inhibiting growth of the organism was recorded
2
NMR (100 MHz, DMSO-d ) δ (ppm): 21.3, 28.7 as the MIC. All the tubes not showing visible growth
6
C
(
2C, CH ), 35.4 (C4), 36.5 (CH -CO), 52.8 (OCH ), (in the same manner as control tube described above)
2 2 3
◦
5
1
1
5.9 (Ar-OCH ), 78.2 (C-COOCH ), 105.2, 113.6, was subcultured and incubated overnight at 37 C. The
3
3
24.5, 125.3, 126.6, 127.5, 130.2, 132.4, 136.5, 138.1, amount of growth from the control tube before incu-
42.2, 144.8, 150.1, 151.4, 152.6, 153.4, 154.4 (17C, bation (which represents the original inoculum) was
Ar-C), 169.5 (COO), 195.6 (C=O); Anal. Calcd. for compared.
C H ClN O (490.94 g/mol): C, 63.61; H, 4.72; N,
Subcultures might show similar number of colonies
26
23
4
4
1
1.41. Found: C, 63.82; H, 4.81; N, 11.24.
indicating bacteriostatic; a reduced number of colonies
indicating a partial or slow bactericidal activity and
no growth if the whole inoculum has been killed. The
test must include a second set of the same dilutions
inoculated with an organism of known sensitivity. Each
synthesized drug was diluted to 2000 μg/mL concen-
tration, as a stock solution. In primary screening 500,
2
5
3
.4l Methyl
2-amino-4-(2,6-dichloro(3-quinolyl))-
-oxo-1-pyridin-3-yl-1,4,6,7,8-pentahydro quinoline-
◦
-carboxylate (4l): Yield 83%; mp.: 259–261 C IR
−1
(KBr, ν, cm ) 3360 and 3180 (asym. and sym. stretch-
250, 200 and 125 μg/mL concentrations of the synthe-
ing of NH ), 1665 (C=O stretching), 1645 (C=O
2
1
sized drugs were taken. The active synthesized drugs
found in this primary screening were further tested in a
second set of dilution against all microorganisms. The
drugs found active in primary screening were similarly
diluted to obtain 200, 100, 50, 25, 12.5, 6.250, 3.125,
and 1.5625 μg/mL concentrations. The highest dilution
showing at least 99% inhibition is taken as MIC. The
protocols were summarized in table 1.
stretching); H-NMR (400 MHz, DMSO-d ) δ
6
H
(
ppm): 1.64–2.26 (m, 6H, 3×CH ), 3.83 (s, 3H,
2
OCH ), 5.22 (s, 1H, quinoline H4), 7.05 (s, 2H, NH ),
3
2
13
7
.60–8.71 (m, 8H, Ar-H); C NMR (100 MHz, DMSO-
d ) δ (ppm): 21.3, 28.7 (2C, CH ), 35.2 (C4), 36.4
6
C
2
(
CH -CO), 52.8 (OCH ), 78.1 (C-COOCH ), 112.8,
2 3 3
1
1
22.5, 124.2, 126.4, 127.9, 130.7, 132.1, 134.4, 136.3,
38.5, 140.0, 142.2, 145.6, 150.1, 151.6, 152.2, 154.6
(
17C, Ar-C), 169.5 (COO), 195.6 (C=O); Anal. Calcd.
for C H Cl N O (495.36 g/mol): C, 60.62; H, 4.07;
25
20
2
4
3
N, 11.31. Found: C, 60.39; H, 4.25; N, 11.15.
2.6 Antimycobacterial activity
A primary screen was conducted at 6.25 μg/mL against
M. tuberculosis H37Rv by Lowenstein–Jensen (LJ)
2.5 Antimicrobial activity
28
All the glass apparatus used were sterilized before use. MIC method, where primary 6.25 μg/mL dilution of
The MICs of all the synthesized compounds was car- each test compound were added to liquid Lowenstein–
ried out by broth microdilution method.27 Mueller Hin- Jensen medium and then media were sterilized by
ton broth was used as nutrient medium to grow and inspissation method. A culture of M. tuberculosis
dilute the compound suspension for the test bacteria and H37Rv growing on Lowenstein–Jensen medium was
Sabouraud Dextrose broth was used for fungal nutri- harvested in 0.85% saline in bijou bottles. DMSO was
8
tion. Inoculum size for test strain was adjusted to 10
used as vehicle to get desired concentration. These

6
74
Table 1. Antimicrobial activity of the compounds (4a–l).
Minimum inhibitory concentration (MIC, μg/mL)
Nimesh M Shah et al.
Gram-positive bacteria Gram-negative bacteria
Fungi
Compds
S.P. MTCC C.T. MTCC B.S. MTCC S.T. MTCC V.C. MTCC E.C. MTCC A.F. MTCC C.A. MTCC
1
936
449
441
98
3906
443
250
3008
227
500
4
4
4
4
4
4
4
4
4
4
4
4
a
b
c
d
e
f
g
h
i
500
500
250
125
200
250
200
100
125
200
200
250
100
50
500
500
250
200
250
250
500
250
200
100
250
200
250
50
125
250
250
200
125
500
500
250
250
200
100
200
250
50
200
125
200
200
250
100
250
500
200
200
125
200
250
200
200
250
500
200
100
50
>1000
>1000
>1000
500
500
500
500
500
1000
>1000
>1000
500
–
62.5
1000
1000
250
250
1000
>1000
>1000
250
500
500
1000
–
125
200
100
250
250
250
62.5
250
200
100
100
250
100
50
62.5
j
k
l
100
125
200
100
50
Ampicillin
Chloramphencol
Ciprofloxacin
Norfloxacin
Griseofulvin
Nystatin
–
–
50
10
–
–
100
50
–
50
100
–
25
10
–
–
25
10
–
–
25
10
–
–
–
–
100
100
–
–
500
100
–
–
B.S., Bacillus subtilis; C.T., Clostridium tetani; S.P., Streptococcus pneumoniae; E.C., Escherichia coli; S.T., Salmonella
typhi; V.C., Vibrio cholerae; A.F., Aspergillus fumigatus; C.A., Candida albicans
Bold entries = the compounds are found equipotent or more potent compared to the standard drugs used
◦
tubes were then incubated at 37 C for 24 h followed by was incubated with M. tuberculosis H37Rv. The con-
streaking of M. tuberculosis H37Rv (5 × 104 bacilli centration at which complete inhibition of colonies
◦
per tube). These tubes were then incubated at 37 C. occurred was taken as active concentration of test com-
Growth of bacilli was seen after 12, 22, and finally pound. The standard strain M. tuberculosis H37Rv was
28 days of incubation. Tubes having the compounds tested with known drug Isoniazide and Rifampicin. The
were compared with control tubes where medium alone screening results are summarized as % inhibition rela-
tive to standard drug Isoniazide and Rifampicin. Com-
pounds effecting <90% inhibition in the primary screen
were not evaluated further. Compounds demonstrating
Table 2. Antimycobacterial activity of the compounds at least 90% inhibition in the primary screen were re-
(
4a–l).
tested at lower concentration (MIC) in a Lowenstein–
Jensen medium. The protocols were summarized in
tables 2 and 3.
Compd.
Primary screen (6.25 μg/mL) % inhibition
4
4
4
4
4
4
4
4
4
4
4
4
a
b
c
d
e
f
g
h
i
12
20
65
14
8
74
96
52
90
25
25
84
99
98
Table 3. MIC of compounds against M. tuberculosis
H37Rv.
Compound
MIC μg/mL
j
k
l
4g
4i
12.5
100
0.2
Isoniazide
Rifampicin
Isoniazide
Rifampicin
40

Synthesis of a novel class of some biquinoline pyridine hybrids
675
3
. Results and discussion
A possible mechanism for the reaction is outlined
in scheme 2. The reaction occurs via an in situ ini-
tial formation of the heterylidenenitrile, containing the
electron-poor C=C double bond, from the Knoeve-
nagel condensation between 2-chloro-3-formyl quino-
lines (2a–d) and active methylene compounds (3a–c)
by loss of water molecules. Michael addition of β-
enaminone to the ylidenic bond in forming an acyclic
intermediate which cyclizes by nucleophilic attack of
the NH group on the cyano carbon, followed by tau-
tomerisation to the final products (4a–l).
3.1 Chemistry
The synthesis of the target compounds is outlined in
scheme 1. The core intermediate 2-chloro-3-formyl
quinolines (2a–d) were prepared according to literature
26
procedure by Vilsmeier–Haack reaction. The required
β-enaminone i.e., 3-(pyridine-3-ylamino)cyclohex-2-
enone was prepared as described above by reaction
of 1,3-cyclohexanedione and 3-amino pyridine. Subse-
quently, the one-pot three component cyclocondensa-
tion of a series of 2-chloro-3-formyl quinolines (2a–d),
active methylene compounds (3a–c) and 3-(pyridine-3-
ylamino)cyclohex-2-enone in ethanol containing NaOH
3.2 Spectroscopic analysis
afforded the target compounds (4a–l) in good to excel- The structures of newly synthesized compounds
1
lent yields.
were elucidated by combined use of IR, H and
13
To choose the most appropriate medium in this
C NMR, mass spectral data and elemental ana-
heterocyclization reaction, the reaction of 2-chloro- lysis. The absorption bands for compounds (4a–d)
-formyl quinolines (2a–d), malononitrile or ethyl in IR-spectra were observed in the range of 2180–
3
−
1
cyanoacetate or methyl cyanoacetate (3a–c) and 3- 2200 cm corresponding to C≡N. The NH stretching
2
(
pyridine-3-ylamino)cyclohex-2-enone various reaction and C=O stretching vibrations for all the compounds
−
1
conditions were investigated. To search for the optimal were observed in range of 3150–3440 cm and 1635–
−1
1
reaction solvent, the reaction was examined in ethylene 1670 cm , respectively. The H NMR spectrum of
glycol, DMF, HOAc, THF, and ethanol as solvent under compounds (4a–l) indicated the presence of one singlet
reflux, respectively. The reaction in ethanol resulted in in the range δ 5.11–5.38 ppm of C4H proton. Moreover,
1
higher yields with shorter reaction time compared to the H NMR spectrum of all the compounds showed
others. So ethanol was chosen as the appropriate sol- broad singlet in the range of δ 5.59–7.14 ppm due to
13
vent. Moreover, to further improve the reaction yields, the NH protons. In the C NMR spectra of (4a–l), the
2
different bases like NaOH, K CO , DMAP, Et N, and signals assigned to C4 δ 34.61–35.42 ppm and to the
2
3
3
piperidine were examined in ethanol. The base NaOH carbonyl group δ 195.45–195.65 were the most rele-
afforded the target product 4a with 84% yield. There- vant features. The signal at around δ 59.48–59.62 ppm
fore, NaOH was chosen as the most suitable base for all is assigned to carbon attached with carbonitrile in com-
further reactions.
pounds (4a–d) while signals around δ 77.93–78.58 ppm
Scheme 2. Plausible mechanistic pathway for the synthesis of biquinoline derivatives (4a–l).

676
Nimesh M Shah et al.
is assigned to carbon attached with carboxylate in com- compounds was found sufficiently potent to inhibit V.
pounds (4e–l). The obtained elemental analysis val- cholerae. The remaining compounds showed mode-
ues are in good agreement with theoretical data. Mass rate activity against other bacteria when compared with
+
spectra of the title compounds gave [M+H] peaks in the remaining standard drugs. The data indicate that a
agreement with their exact mass or molecular weight.
change in the substituent might also affect the antibac-
terial activity of title compounds 4a–l. Comparison
of biological activities among 4a–l shows functional
groups as R = CH /OCH to be potentially more active
1
3
3
3.3 Antimicrobial activity
against S. typhi. Also antibacterial potency of com-
pounds among 4a–l shows functional groups as R =
Reviewing of the antibacterial activities of biquinoline
1
H/CH found more active against E. coli.
derivatives (table 1) indicate that compound 4b (R =
3
1
Antifungal study revealed that all the synthesized
biquinoline derivatives have poor activity against A.
fumigatus. In comparison with standard fungicidal
griseofulvin (MIC = 500 μg/mL), among biquinolines,
CH , R = CN), 4i (R = H, R = COOMe) and 4g
3
2
1
2
(
(
R = OCH , R = COOEt) showed highest activity
1
3
2
MIC = 62.5 μg/mL) against E. coli and S. typhi, respec-
tively. So these compounds were found more potent
than ampicillin (MIC = 100 μg/mL). Moreover, com-
pounds 4e (R = H, R = COOEt) and 4j (R = CH ,
compounds 4d (R = Cl, R = CN), 4e (R = H,
1
2
1
R
= COOEt) and 4i (R = H, R = COOMe)
2
1
2
1
2
1
3
(
MIC = 250 μg/mL) exhibited excellent activity against
C. albicans where as compounds 4a (R = H, R =
R = COOMe) (MIC = 100 μg/mL) were found
2
equipotent to ampicillin (MIC = 100 μg/mL) towards
E. coli. Towards the Gram-negative strain S. typhi, com-
pounds 4f (R = CH , R = COOEt), 4j (R = CH ,
1
2
CN), 4j (R = CH , R = COOMe) and 4k (R =
1
3
2
1
OCH , R = COOMe) showed comparable activity
3
2
1
3
2
1
3
(
MIC = 500 μg/mL). The data indicate that functional
R = COOMe), and 4k (R = OCH , R = COOMe)
2
1
3
2
groups as R = H interferes in the antifungal potency of
(
MIC = 100 μg/mL) were equally active when com-
1
title compounds (4a–l). Other compounds showed poor
activity against the rest of the fungal species compared
with the standard drugs nystatin and griseofulvin.
pared to ampicillin (MIC = 100 μg/mL). Against S.
pneumoniae, only one compound 4h (R = Cl, R =
1
2
COOEt) (MIC = 100 μg/mL) was found to have same
activity as ampicillin (MIC = 100 μg/mL). Towards the
Gram-positive strain B. subtilis, compounds 4a (R =
1
H, R = CN), 4d (R = Cl, R = CN), 4e (R =
2
1
2
1
3.4 Antimycobacterial activity
H, R = COOEt), 4j (R = CH , R = COOMe), 4k
2
1
3
2
(
R = OCH , R = COOMe) and 4l (R = Cl, R =
1
3
2
1
2
The encouraging results from the antimicrobial stu-
dies prompted us to go for the preliminary screening
of the title compounds for their in vitro antituberculosis
activity against M. tuberculosis H37Rv.
COOMe) (MIC < 250 μg/mL) possessed pronounced
activity compared to ampicillin (MIC = 250 μg/mL)
where as compounds 4b (R = CH , R = CN), 4c
1
3
2
(
R = OCH , R = CN), 4h (R = Cl, R = COOEt)
1
3
2
1
2
Of the entire biquinoline derivatives compound, 4g
and 4i (R = H, R = COOMe) were found to have
1 2
(
R = OCH , R = COOEt) was the most active com-
1
3
2
equal activity as ampicillin (MIC = 250 μg/mL). Com-
pound 4k (R = OCH , R = COOMe) (MIC =
pound, with 96% inhibition. Compound 4i (R = H,
1
1
3
2
R = COOMe) also exhibited good inhibition of 90%
2
1
00 μg/mL) was also found equipotent to norfloxacin
with MIC = 100 μg/mL. Compound 4l (R = Cl, R =
1
2
(
4
4
MIC = 100 μg/mL) towards B. subtilis. Compounds
COOMe) displayed moderate inhibition of 84%. Thus,
d (R = Cl, R = CN), 4i (R = H, R = COOMe),
1 3 2 1 2
1
2
1
2
the most potent compound of the series, compound 4g
j (R = CH , R = COOMe) and 4l (R = Cl, R =
(
MIC = 12.5 μg/mL) opens up new door to optimize
COOMe) (MIC < 250 μg/mL) displayed significant
activity towards C. tetani compared to the standard
this series for new class of antituberculars.
ampicillin (MIC = 250 μg/mL). Compound 4j (R =
1
CH , R = COOMe) (MIC = 100 μg/mL) was also
3
2
equally active as ciprofloxacin (MIC = 100 μg/mL)
4
. Conclusion
towards C. tetani. Against C. tetani, compounds 4c
(
4
R = OCH , R = CN), 4e (R = H, R = COOEt), For the first time, a series of novel biquinoline deriva-
1
3
2
1
2
f (R = CH , R = COOEt), 4h (R = Cl, R = tives containing a pyridine moiety have been synthe-
1
3
2
1
2
COOEt) and 4k (R = OCH , R = COOMe) (MIC = sized via one-pot, three-component reaction catalysed
1 3 2
2
50 μg/mL) exhibited comparable activity as the stan- by non-hazardous NaOH and determined their antimi-
dard ampicillin (MIC = 250 μg/mL). None of the crobial and antimycobacterial activities. The one-pot

Synthesis of a novel class of some biquinoline pyridine hybrids
677
nature, the use of an ecocompatible catalytic reaction
and the easy separation of products make it an interest-
ing alternative to the reported approaches for the syn-
thesis of such potent bio-active compounds. The use
of an inorganic catalyst NaOH, not only gave good
yields in shorter reaction time but also provided a proce-
dure that does not use corrosive and hazardous organic
bases like piperidine. The antimicrobial results revealed
that numbers of compounds were found to be the most
active against C. tetani and B. subtilis compared to rest
of the employed species. In all the biquinolines syn-
thesized and screened for antimicrobial activity com-
pounds, 4b and 4i showed better inhibitory effects for E.
3. Elguero J, Goya P, Jagerovic N and Silva A M S 2002
Targets Heterocycl. Syst. 6 52
. Zafer A K, Gulhan T Z, Ahmet O and Gilbert R 2008
Eur. J. Med. Chem. 43 155
. Tim Cushnie T P and Lamb A J 2005 Int. J. Antimicrob.
Agents 26 343
4
5
6
. Lilienkampf A, Mao J, Wan B, Wang Y, Franzblau S G
and Kozikowski A P 2009 J. Med. Chem. 52 2109
7. Charris J E, Domínguez J N, Gamboa N, Rodrigues J R
and Angel J E 2005 Eur. J. Med. Chem. 40 875
8
9
. Bava S and Kumar S 2009 Indian J. Chem. 48B 142
. Ghorab M M, Ragab F A, Heiba H I, Arafa R K and
El-Hossary E B 2010 Eur. J. Med. Chem. 45 3677
1
0. Eswaran S, Adhikari A S and Shetty N S 2009 Eur. J.
Med. Chem. 44 4637
coli and 4g showed better results for S. typhi. Antifun- 11. Muruganantham N, Sivakumar R, Anbalagan N,
Gunasekaran V and Leonard J T 2004 Biol. Pharm. Bull.
gal activity of the compounds shows that compounds
27 1683
4d, 4e and 4i are found to be potent against C. albicans.
1
2. Naik H R P, Naik H S B, Naik T R R, Naika H R,
Moreover, compound 4g have shown a great potential to
serve as promising candidate for further development of
Gouthamchandra K, Mahmood R and Ahamed B M K
2009 Eur. J. Med. Chem. 44 981
antimycobacterial agents with improved potency. This 13. Maguire M P, Sheets K R, McVety K, Spada A P and
suggests that hybrid compounds possessing biquinoline
and pyridine moiety may have presented greater antimi-
crobial and antimycobacterial properties. These results
suggested that further development of such compounds
may be of interest.
Zilberstein A 1994 J. Med. Chem. 37 2129
4. Strekowski L, Mokrosz J L, Honkan V A, Czarny A,
1
Cegla M T, Patterson S E, Wydra R L and Schinazi R F
1991 J. Med. Chem. 34 1739
1
1
1
5. Bringmann G, Reichert Y and Kane V V 2004 Tetrahe-
dron 60 3539
6. Zhou Y, Kijima T, Kuwahara S, Watanabe M and Izumi
T 2008 Tetrahedron Lett. 49 3757
7. Farhanullah, Agarwal N, Goel A and Ram V J 2003 J.
Org. Chem. 68 2983
Acknowledgements
The authors are thankful to the Department of Chem-
istry, Sardar Patel University for providing research 18. Teague S J 2008 J. Org. Chem. 73 9765
facilities. We are also thankful to Vaibhav Analytical 19. Movassaghi M, Hill M D and Ahmad O K 2007 J. Am.
Chem. Soc. 129 10096
Laboratory, Ahmedabad for the FT-IR and Sophisti-
2
2
0. Xie J and Seto C T 2007 Bioorg. Med. Chem. 15 458
1. Shah N M, Patel M P and Patel R G 2011 J. Het. Chem.
doi:10.1002/jhet.918 (in press)
cated Instrumentation Centre for Applied Research and
Training (SICART), Vallabh Vidyanagar for elemen-
tal analysis. Oxygen Healthcare Research Pvt. Ltd.,
Ahmadabad for providing mass spectrometry facilities
2
2. Mungra D C, Patel M P, Rajani D P and Patel R G 2011
Eur. J. Med. Chem. 46 4192
and Ms Dhanji P Rajani, Microcare Laboratory, Surat 23. Shah N K, Patel M P and Patel R G 2009 Phosphorus
Sulfur Silicon 184 2704
for antimicrobial and antituberculosis screening of the
2
4. Makawana J A, Patel M P and Patel R G Med. Che. Res.
doi:10.1007/s00044-011-9568-6 (in press)
5. Mungra D C, Patel M P, Rajani D P and Patel R G 2009
Arkivoc xiv 64
compounds reported here. NMS is grateful to the Uni-
versity Grants Commission (UGC), New Delhi, India
for a Research Fellowship in Sciences for Meritorious
Students.
2
26. Meth-Cohn O and Bramha N A 1978 Tetrahedron Lett.
3 2045
2
2
7. National Committee for Clinical Laboratory Standards
(NCCLS), 940, West Valley Road, Suite 1400, Wayne,
Pennsylvania 19087-1898. USA. Performance Stan-
dards for Antimicrobial Susceptibility Testing; Twelfth
Informational Supplement (ISBN 1-56238-454-6) 2002
M100-S12 (M7)
References
1. McDonald E, Jones K, Brough P A, Drysdale M J and
Workman P 2006 Curr. Top. Med. Chem. 6 1193
2. Elguero J 1996 In Comprehensive heterocyclic chem-
istry (eds) A R Katritzky, C W Rees, E F V Scriven 28. Rattan A 2000 Antimicrobials in laboratory medicine
Oxford: Pergamon) Vol. 5
(New Delhi: B. I. Churchill, Livingstone) 85
(