Quinoline-3-carboxylates as potential antibacterial agents

Article abstract of DOI:10.1007/s11164-012-0505-1

The ethyl-2-chloroquinoline-3-carboxylates, 4, were achieved fromo-aminobenzophenones in two steps. i.e. initially, the ethyl-2-oxoquinoline- 3-carboxylates, 3, were obtained by base-catalyzed Friedlander condensations of o-aminobenzophenones, 1, and diethylmalonate, 2. The 2-chloroquinoline-3- carboxylates, 4, were then obtained by the reaction with POCl₃ in good yields. The chemical structures were confirmed by FTIR, mass and ¹H-NMR spectroscopic techniques. All the synthesized compounds were tested for their in vitro antibacterial activity against Bacillus subtilis and Vibrio cholera and found to possess moderate activity. Springer Science+Business Media B.V. 2012.

Full text of DOI:10.1007/s11164-012-0505-1

Res Chem Intermed (2012) 38:1819–1826
DOI 10.1007/s11164-012-0505-1
Quinoline-3-carboxylates as potential antibacterial
agents
•
V. Krishnakumar Fazlur-Rahman Nawaz Khan
•
•
Badal Kumar Mandal Sukanya Mitta
•
•
Ramu Dhasamandha Vindhya Nanu Govindan
Received: 9 December 2011 / Accepted: 6 February 2012 / Published online: 29 February 2012
Ó Springer Science+Business Media B.V. 2012
Abstract The ethyl-2-chloroquinoline-3-carboxylates, 4, were achieved from o-am-
inobenzophenones in two steps. i.e. initially, the ethyl-2-oxoquinoline-3-carboxylates,
3, were obtained by base-catalyzed Friedlander condensations of o-aminobenzophe-
nones, 1, and diethylmalonate, 2. The 2-chloroquinoline-3-carboxylates, 4, were then
obtained by the reaction with POCl3 in good yields. The chemical structures were
confirmed by FTIR, mass and 1H-NMR spectroscopic techniques. All the synthesized
compounds were tested for their in vitro antibacterial activity against Bacillus subtilis
and Vibrio cholera and found to possess moderate activity.
Keywords Quinolines ꢀ Friedlander synthesis ꢀ Antibacterial activity
Introduction
Quinoline heterocycles occur widely among medicinally important natural products.
Several natural products possessing quinoline moiety exhibit interesting biological
and pharmacological properties, such as antimalarial [1, 2], antibacterial [3], anti-
asthmatic, antihypertensive, anti-inflammatory [4], immunosuppressive activity [5],
antileishmanial activity [6], and anticancer [7] properties. In addition, quinolines
have been employed in the study of bioorganic and bioorganometallic processes [8].
These properties turn quinolines into very interesting targets for organic chemists,
and several strategies for their synthesis have been developed including Skraup [9],
V. Krishnakumar ꢀ F.-R. N. Khan (&) ꢀ S. Mitta ꢀ R. Dhasamandha ꢀ V. N. Govindan
Organic and Medicinal Chemistry Research Laboratory, Organic Chemistry Division,
School of Advanced Sciences, VIT University, Vellore 632014, Tamil Nadu, India
e-mail: nawaz_f@yahoo.co.in
V. Krishnakumar ꢀ B. K. Mandal
Environmental and Analytical Chemistry Division, School of Advanced Sciences,
VIT University, Vellore 632014, Tamil Nadu, India
123

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V. Krishnakumar et al.
Doebner-Von Miller [10], Friedlander [11, 12], Pfitzinger [13], Conard–Limpach
[14] and Combes [15] methods. Among these methods, the Friedlander approach,
involving an aromatic o-aminoaldehyde or ketone and a carbonyl compound
containing reactive a-methylene functionality, is the most efficient one.
A number of methods involving metal salts, Lewis acids, and Brønsted acid
catalysts [16, 17] have been commonly employed for the quinolines following
Friedlander synthesis. However, the above procedures are unsatisfactory with regard
to cost of the reagent, drastic reaction conditions, operational simplicity, and very
¨
low yield. Friedlander reactions are generally carried out by refluxing an alcoholic
solution or an organic solvent. Therefore, a general and efficient method is still
needed for the preparation of these important quinolines and and the search
continues to find a better and improved methodology.
In recent decades, chemists have focused much attention on environmentally
friendly reactions. In continuation of our interest in carbon–carbon and carbon–
nitrogen bond formation reaction [18–24] and environmentally benign reactions, in
the present study the titled compounds were obtained in excellent yields by the
Friedlander approach and chlorination method. However, in this paper, solvent-free
neat reaction under catalytic amounts of piperidine as a base catalyst is reported.
The experimental results indicate the formation of the corresponding quinolines
with good to excellent yields.
Results and discussion
The 2-chloro-3-carboxylatequinolines were synthesized in two steps involving
different o-amino arylaldehydes or ketones. Initially, when o-amino arylaldehyde or
ketone reacted with diethylmalonate formed keto esters (3a–f) (Table 1) by
Friedlander annulations. Purified keto esters (1a–f) were then allowed to react with
phosphorous oxychloride to give the corresponding 2-chloro-3-carboxylatequino-
lines (4a–f) (Table 2). The 2-chloro-3-carboxylatequinolines has been achieved by a
simple and an efficient route in good yields. Products of the reaction have been
isolated, purified, and characterized by various spectral techniques such as IR,
HRMS, 1H NMR, and 13C NMR techniques. Antibacterial screening was carried out
for all the synthesized compounds. The screened compounds showed moderate
activity against the Bacillus subtilis and Vibrio cholera.
The HRMS of compounds 3 and 4 showed a molecular ion peak M? in the
positive mode. The molecular ion peak for 3a was observed at m/z = 326.8033.
This was evidenced from HRMS analysis of other compounds, 3b–f. In the IR
spectrum, the initially formed keto esters 3a–f gave the ester carbonyl frequencies,
1,743–1,715 cm-1 and carbonyl frequencies around 1,650 cm-1, the NH group of
keto esters appeared at 3,452–3,413 cm-1, whereas in chloroesters, 4a–f obtained
from 3a–f gave IR frequencies corresponding to ester carbonyls around 1,730 cm-1
confirming the reaction between the keto carbonyl group of 3a–f and POCl3 with the
formation of 2-chloroquinolines. In 1H NMR compound 3a–f, the NH peak appears
as singlet between 12.32 and 12.88 ppm which disappears in 4a–f, and in 13C NMR
123

Quinoline-3-carboxylates as potential antibacterial agents
1821
Table 1 Friedlander reaction of o-aminoarylcarbonyls and diethylmalonate in the formation of ethyl-2-
oxoquinoline-3-carboxylate, 3
R"
R"
R'
COOC2H5
O
R'
COOC2H5
COOC2H5
Piperidine
180 o
O
N
H
C
NH2
R
R
2
1
3
Compound
R
R0
R00
Yielda % 3
mp °C
1a/3a
1b/3b
1c/3c
1d/3d
1e/3e
1f/3f
H
H
H
H
Br
H
Cl
H
C6H5
CH3
90
70
80
80
85
88
215–218
228–230
195–198
178–180
229–232
203–206
Cl
Cl
Br
Cl
2-Cl-C6H4
2-F-C6H4
H
4-F-C6H4
1 (1 mmol), 2 (1.2 mmol), piperidine two drops, reflux at 180 °C
a
Isolated yield of 3
Table 2 Conversion of ethyl-2-oxoquinoline-3-carboxylate, 3 into ethyl-2-chloroquinoline-3-carbox-
ylate, 4
R"
R"
R'
COOC2H5
O
R'
COOC2H5
Cl
POCl 3
reflux
N
H
N
R
R
3
4
Product
Yielda %
mp °C
4a
4b
4c
4d
4e
4f
85
50
60
70
80
80
98–100
78–80
98–101
108–110
[300
108–111
3 (1 mmol), POCl3, reflux in water bath
b
Isolated yield of 4
spectra, compound 3a–f, the cyclic amide carbonyl peaks appeared between d at
158.2–158.6 ppm which was shifted upfield region d at 147.9–148.6 ppm after
chorination which is confirmed the formation of the products.
Almost all the compounds showed moderate activity against both B. subtilis and
V. cholera. The activity data generated are tabulated in Table 3.
123

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V. Krishnakumar et al.
Table 3 Antibacterial
activity of 3a–f and 4a–f
Titled compounds organisms Microorganisms zone of inhibition
(mm)
Bacillus subtilis
Vibrio cholera
3a
15
7
15
13
7
3b
3c
11
15
17
13
16
9
3d
8
3e
11
10
16
12
12
14
15
13
26
3f
4a
4b
4c
12
8
4d
4e
12
10
31
4f
Streptomycin
Experimental section
Materials and methods
Chemicals were purchased from Aldrich Chemical (India) and used as such
without further purification. Completion of the reaction was performed by thin layer
chromatography. Melting points were taken in open capillary tubes and corrected with
benzoic acid as reference. IR spectra of compounds (KBr pellets) were recorded on
Nucon Infrared spectrophotometer. 1H NMR (300, 400, and 500 MHz) and 13C NMR
(75,100,and125 MHz)spectrawererecordedonadifferentBrukerNMRspectrometer,
respectively, in CDCl3.
Synthesis of 2-oxo-3-carboxylatequinoline derivatives (3a–f)
A mixture of 2-amino-5-chlorobenzophenone 1a (231 mg, 1 mmol) and diethyl-
malonate 2 (192 mg, 1.2 mmol) and catalytic amount of piperidine were taken into
the RB-flask. The mixture was heated under reflux at 180 °C and the reaction was
monitored by TLC. After completion, the reaction mixture was poured into the
water, and extracted with ethyl acetate, concentrated under reduced pressure. The
crude product was then purified by silica gel column (using petroleum ether and
ethyl acetate) as eluant. The desired product, 3a, obtained was characterized by IR,
1
HRMS, H and 13C NMR techniques. The reaction of substituted 2-aminoarylk-
etones 1a–f with diethylmalonate 2 gave the product of 2-chloro-3-carboxylatequi-
nolines, 3a–f (Table 1).
The spectral data of compounds, 3a–f, is given below
123

Quinoline-3-carboxylates as potential antibacterial agents
1823
Ethyl 6-chloro-1,2 -dihydro-2-oxo-4-phenylquinoline-3-carboxylate 3a). Pale
yellow, mp 215–218 °C; IR (film) 3,445 (NH), 1,743 (COOEt), 1,650 (CO),
1
756 cm-1; H NMR (400 MHz, CDCl3) d 1.42 (t, 3H, J = 7 Hz), 4.51 (q, 2H,
J = 7 Hz), 7.10–8.00 (m, 8H), 12.35 (s, 1H) ppm. 13C NMR (100 MHz, CDCl3) d
165.1, 158.7, 147.8, 137.9, 133.8, 131.9, 129.6, 129.5, 129.1, 129.0, 128.8, 128.1,
126.7, 126.2, 120.1, 118.3, 61.2, 13.97. HRMS [EI, M?] calcd for C18H14ClNO3 m/
z 327.7617 found 326.8033.
Ethyl 1,2-dihydro-4-methyl-2-oxoquinoline-3-carboxylate (3b). Pale brown, mp
1
225–230 °C; IR (film) 3,452 (NH), 1,732 (COOEt), 1,651 (CO), cm-1; H NMR
(400 MHz, CDCl3) d 1.24 (t, 3H, J = 7 Hz), 1.7 (s, 3H), 4.39 (q, 2H, J = 7 Hz),
7.2–7.6 (m, 4H), 12.32 (s, 1H) ppm. 13C NMR (100 MHz, CDCl3) d 164.9, 158.2,
146.9, 129.2, 128.4, 127.8, 126.3, 125.6, 120.7, 117.8, 61.7, 14.1, 13.94. HRMS [EI,
M?], calcd for C13H13NO3 m/z 231.0895 found 231.0892.
Ethyl
6-chloro-4-(2-chlorophenyl)-1,2-dihydro-2-oxoquinoline-3-carboxylate
(3c). Pale yellow, mp 193–198 °C, IR (film) 3,439 (NH), 1,715 (COOEt), 1,653,
757, 605 cm-1; 1H NMR (500 MHz, CDCl3) d 1.43 (t, 3H, J = 7 Hz), 4.32 (q, 2H,
J = 7 Hz), 7.05–7.81 (m, 7H), 12.88 (s, 1H); 13C NMR (125 MHz, CDCl3) d 165.4,
158.2, 147.3, 137.5, 132.9, 132.1, 129.9, 129.3, 128.7, 128.6, 128.1, 127.6, 126.9,
126.3, 120.5, 117.9, 61.6, 14.0 ppm. HRMS [EI, M?] calcd for C18H13Cl2NO3 m/
z.361.0272 found 361.0268.
Ethyl
6-chloro-4-(2-fluorophenyl)-1,2-dihydro-2-oxoquinoline-3-carboxylate
(3d). Pale yellow, mp 174–180 °C; IR (film) 3,413 (NH), 1,715 (COOEt), 1,652,
1
1,092, 758 cm-1; H NMR (500 MHz, CDCl3) d 1.12 (t, 3H, J = 7 Hz), 4.28 (q,
2H, J = 7 Hz), 6.92–7.80 (m, 7H), 12.45 (s, 1H) ppm; 13C NMR (125 MHz,
CDCl3) d 165.1, 158.6, 147.8, 137.9, 133.1, 132.7, 130.1, 129.8, 128.9, 128.4,
128.1, 127.4, 126.6, 126.2, 120.3, 118.3, 61.1, 14.0 ppm. HRMS [EI, M?] calcd for
C18H13ClFNO3 m/z 345.0568 found 345. 0498.
Ethyl 6,8-dibromo-1,2-dihydro-2-oxoquinoline-3-carboxylate (3e). Pale yellow,
1
mp 228–232 °C, IR (film) 3413 (NH), 1715 (COOEt), 1652, 1092, 758 cm-1; H
NMR (300 MHz, CDCl3) d 1.08 (t, 3H, J = 7 Hz), 4.21 (q, 2H, J = 7 Hz), 7.28 (s,
1H), 7.46 (s, 1H), 8.12 (s, 1H), 12.80 (s, 1H); 13C NMR (75 MHz, CDCl3) d 165.7,
158.6, 147.2, 137.9, 132.3, 132.6, 129.7, 129.2, 120.7, 117.6, 61.2, 13.89 ppm.
HRMS [EI, M?] calcd. for C12H9Br2NO3 m/z 374.8949 found 374.8929.
Ethyl 6-chloro-4-(4-fluorophenyl)-1,2-dihydro-2-oxoquinoline-3-carboxylate (3f).
White solid, mp 204–206 °C, IR (film) 3,413 (NH), 1,715 (COOEt), 1,652, 1,092,
1
758 cm-1; H NMR (300 MHz, CDCl3) d 1.02 (t, 3H, J = 7 Hz), 4.12 (q, 2H,
J = 7 Hz), 7.10–7.60 (m, 7H), 12.80 (s, 1H) 13C NMR (75 MHz, CDCl3) d 165.3,
158.4, 147.5, 137.5, 133.3, 132.9, 130.4, 129.4, 128.7, 128.7, 128.2, 127.8, 126.8, 126.3,
120.6, 117.9, 61.3, 13.96 ppm. HRMS [EI, M ?] calcd for C18H13ClFNO3 m/z,
calculated 345.0568 found 345.0632.
Synthesis of ethyl-2-chloroquinoline-3-carboxylate derivatives (4a–f)
A mixture of ethyl-6-chloro-1,2-dihydro-2-oxo-4-phenylquinoline-3-carboxylate 3a
(327 mg, 1 mmol) and POCl3 (93 ll, 1 mmol) was taken in a RB flash and refluxed
in water bath for 5–7 h. The reaction complection was monitored by TLC using
123

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V. Krishnakumar et al.
petroleum ether and ethylacetate mixture as eluent. The reaction mixture was
allowed to cool, poured into a crushed ice taken in a beaker stirred well for 15 min
and then filtered to get the products 4a–f (Table 2).
Ethyl 2, 6-dichloro-4-phenylquinoline-3-carboxylate (4a). White solid, mp
1
98–100 °C; IR (film) 1,736, 1,556, 1,483, 1,386, 1,214, 1,145, 761, 713 cm-1; H
NMR (400 MHz, CDCl3) d 0.94 (t, 3H, J = 7 Hz), 4.10 (q, 2H, J = 7 Hz), 7.42–7.45
(m, 3H), 7.59–7.61 (m, 2H), 7.95–7.98 (m, 2H), 8.1 (d, 1H) ppm; 13C NMR (100 MHz,
CDCl3) d 165.8 (C=O), 148.1 (C–Cl), 147.3, 138.6, 136.6, 131.8 9 2, 129.4 9 2,
125.5 9 2, 124.3 9 2, 123.8, 122.9 9 2, 62.1 (CH2), 13.6 (CH3) ppm.;. HRMS [EI,
M?] calcd for C18H13Cl2NO2 m/z 345.0323, found 346.1923.
Ethyl 2-chloro-4-methylquinoline-3-carboxylate (4b). Brown solid, mp
1
78–80 °C; IR (film) 1,723, 1,619, 1,573, 1,453, 1,390, 1,243, 755 cm-1; H NMR
(300 MHz, CDCl3) d 1.14 (t, 3H, J = 7 Hz), 2.3 (s, 3H), 4.24 (q, 2H, J = 7 Hz),
7.5–7.8 (m, 3H), 8.09 (d, 1H) ppm; 13C NMR (75 MHz, CDCl3) d 165.1 (C=O),
147.9 (C–Cl), 147.5, 136.4, 130.8, 125.8, 124.7, 123.4, 122.7, 62.4 (CH2), 16.4
(CH3), 13.2 (CH3) ppm.; HRMS [EI, M?] calcd for C13H12ClNO2 m/z 249.6929,
found 248.8972.
Ethyl 2,6-dichloro-4-(2-chlorophenyl)quinoline-3-carboxylate (4c). White solid,
mp 98–101 °C; 1H NMR (300 MHz, CDCl3) d 1.09 (t, 3H, J = 7 Hz), 4.17 (q, 2H,
J = 7 Hz), 7.2–7.3 (m, 2H), 7.5–7.6 (m, 2H), 7.8 (m, 2H), 8.1 (d, 1H) ppm; 13C
NMR (75 MHz, CDCl3)) d 164.9 (C=O), 148.6 (C–Cl), 147.9, 138.4, 136.7,
131.6 9 2, 129.7 9 2, 125.6 9 2, 124.6 9 2, 123.7, 122.5 9 2, 62.4 (CH2), 13.9
(CH3) ppm; HRMS [EI, M?] calcd for C18H12Cl3NO2 m/z 378.9934, found
378.6372.
Ethyl 2,6-dichloro-4-(2-fluorophenyl)quinoline-3-carboxylate (4d). White solid, mp
1
108–110 °C; H NMR (300 MHz, CDCl3) d 1.14 (t, 3H, J = 7 Hz), 4.26 (q, 2H,
J = 7 Hz), 7.2–7.6 (m, 6H); 8.1 (m, 1H) ppm; 13C NMR (75 MHz, CDCl3) d 164.4
(C=O), 148.2 (C–Cl), 147.4, 138.7, 136.3, 131.5 9 2, 129.3 9 2, 125.9 9 2,
124.3 9 2, 123.9, 122.2 9 2, 62.7 (CH2), 13.6 (CH3) ppm; HRMS [EI, M?] calcd
for C18H12Cl2FNO2 m/z 363.0229, found 362.0724.
Ethyl 6,8-dibromo-2-chloroquinoline-3-carboxylate (4e). White solid,
mp [ 300 °C; IR (film) 1,711, 1,634, 1,573, 1,487, 1,408, 1,242, 1,031,
1
748 cm-1; H NMR (300 MHz, CDCl3) d 1.11 (t, 3H, J = 7 Hz), 4.21 (q, 2H,
J = 7 Hz), 8.1 (s, 1H), 8.7 (s. 1H), 9.2 (s, 1H) ppm; 13C NMR (75 MHz, CDCl3) d
165.1 (C=O), 147.9 (C–Cl), 147.5, 138.4, 136.4, 130.8, 125.8, 124.7, 123.4, 122.7,
62.4 (CH2), 13.2 (CH3) ppm.; HRMS [EI, M?] calcd for C12H8Br2ClNO2 m/
z 390.8610, found 390.8112.
Ethyl 2-chloro-4-(4-fluorophenyl)-3-quinolinecarboxylate (4f). White solid, mp
108–111 °C; IR (film) 1,722, 1,605, 1,557, 1,492, 1,400, 1,227, 1,024, 768 cm-1
;
1H NMR (300 MHz, CDCl3) d 1.09 (t, 3H, J = 7 Hz), 4.17 (q, 2H, J = 7 Hz),
7.2–7.3 (m, 2H), 7.3–7.4 (m, 2H), 7.5–7.6 (m, 2H), 7.8 (m, 1H), 8.1 (m, 1H) ppm;
13C NMR (75 MHz, CDCl3) d 165.5 (C=O), 163.1 (C–F), 147.9 (C–Cl), 147.5,
145.8, 131.4, 131.2, 130.3, 128.9 9 2, 127.8, 127.7, 126.4, 125.7, 115.6 9 2, 62.0
(CH2), 13.7 (CH3) ppm. HRMS [EI, M?] calcd for C18H13ClFNO2 m/z 329.0619,
found 329.0612.
123

Quinoline-3-carboxylates as potential antibacterial agents
1825
Antibacterial activity
Antibacterial activity of all these compounds was determined by agar well diffusion
method, as recommended by the National Committee for Clinical Laboratory
Standards against B. subtilis (Gram-positive) and V. cholera (Gram-negative) micro
organisms at 100 lg/mL concentration, using dimethyl sulfoxide (DMSO) as
solvent. The bacterial were sub-cultured on Mueller–Hinton agar medium. Standard
Streptomycin was also screened under similar conditions at a concentration of
100 lg/mL for comparison. Solvent condition also maintained under similar
conditions.
Conclusions
In conclusion, a simple and efficient procedure for the synthesis of 2-chloro-3-
carboxylatequinoline derivatives (4a–f), using piperidine as a base catalyst via
Friedlander annulations is reported. The advantage of this method includes the use
of inexpensive reagents and catalyst, and operational simplicity. All the synthesized
compounds were tested for their in vitro antibacterial activity. These compounds
showed moderate activity against some bacteria such as B. subtilis and V. cholera.
Acknowledgments Authors are grateful to VIT University, Vellore, for providing research facilities.
The authors wish to express their gratitude to SAIF, Indian Institute of Technology, Chennai, for their
support of NMR and HRMS.
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