Microwave solvent-free condition synthesis and pharmacological evaluation of pyrano[3,2-c]quinolines

Article abstract of DOI:10.1007/s00044-011-9810-2

The microwave-induced three-component onepot synthesis of 2-amino-3-carbethoxy-4-phenylpyrano[3,2-c] quinolin-5(6H)-ones (4a-l) from 4-hydroxyquinolin-2(1H)- ones, aromatic aldehydes and ethyl cyanoacetate was described. The detailed synthesis, structure

Full text of DOI:10.1007/s00044-011-9810-2

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res (2012) 21:2902–2910
DOI 10.1007/s00044-011-9810-2
ORIGINAL RESEARCH
Microwave solvent-free condition synthesis and pharmacological
evaluation of pyrano[3,2-c]quinolines
•
Vetrivel Nadaraj Senniappan Thamarai Selvi
•
•
Helen Pricilla Bai Sellappan Mohan
•
Thangaian Daniel Thangadurai
Received: 23 March 2011 / Accepted: 6 October 2011 / Published online: 3 November 2011
Ó Springer Science+Business Media, LLC 2011
Abstract The microwave-induced three-component one-
pot synthesis of 2-amino-3-carbethoxy-4-phenylpyrano[3,2-c]
quinolin-5(6H)-ones (4a–l) from 4-hydroxyquinolin-2(1H)-
ones, aromatic aldehydes and ethyl cyanoacetate was
described. The detailed synthesis, structure analysis, and
antimicrobial screening for the title compounds were also
reported. Pharmacological screen studies like anti-inflam-
matory and antibacterial activities of newly synthesized
quinoline derivatives were evaluated against carrageenan-
induced rat paw edema model and Gram-positive and Gram-
negative bacteria, respectively.
Introduction
One-pot multicomponent reactions (Tietze and Lieb, 1998)
(MCRs) represent nearly ideal cases of syntheses which
can be used to construct compound libraries (Armstrong
et al., 1996; Li, 2005) because of their high degree of atom
economy, convergence and productivity, ease of extraction,
and excellent yield (Khurana and Kumar, 2009). The var-
iation of two or more components of the reaction can make
available a large number of compounds and increase the
chemical diversity. Moreover, the possibility of performing
multicomponent reactions under solventless conditions
with heterogeneous catalysts could enhance their efficiency
from an economic as well as an ecological point of view.
Naturally occurring compounds such as flindersine,
simulenoline, melicobisquinolone A, melicobisquinolone
B, zanthodioline, khaplofoline, huajiaosimulime, etc., were
found to possess the pyranoquinoline ring system (Ulubelen
et al., 1994; Shwu Jen and Ih Sheng, 1993; Barr et al.,
1995). Structures incorporating this moiety show marked
psychotropic, antiallergenic, anti-inflammatory, antihista-
minic, and estrogenic activities and are thus of prime
interest for biological applications (Chen et al., 1994).
Further, these compounds are also used as synthetic pre-
cursors for the preparation of other dimeric quinoline
alkaloids and polyheterocylces (Ramesh et al., 1984).
Hence, the novel and efficient synthesis of such compounds
still represents a highly pursued target (Huffman and Hsu,
1972; Ye et al., 1999; de Groot and Jansen, 1975).
Keywords Multicomponent ꢀ Pyranoquinolines ꢀ
4-Hydroxy-quinolin-2(1H)-ones ꢀ Microwaves ꢀ
Triethylamine
V. Nadaraj ꢀ S. Thamarai Selvi ꢀ H. Pricilla Bai
Department of Chemistry, Kongunadu Arts and Science College,
Coimbatore 641029, Tamilnadu, India
S. Thamarai Selvi (&)
Department of Chemistry, LRG Government Arts College for
Women, Tirupur 641604, Tamilnadu, India
e-mail: thamaraimohan@yahoo.co.in
S. Mohan
Department of Pharmaceutics, Saraswati Institute of
Pharmaceutical Sciences, Gandhinagar 382355, Gujarat, India
4-Hydroxyquinolin-2(1H)-ones, occur in Rutaceae
plants (Lee et al., 2001; Majumdar and Mukhopadhyay
2003, are attractive reactive intermediates that could be
readily converted to several quinoline alkaloids. In recent
years, the application of microwave irradiation in organic
synthesis has attracted much interest, due to the resulting
T. Daniel Thangadurai (&)
Department of Bio and Nano Chemistry, College of Natural
Science, Kookmin University, 861-1 Jeongneung-dong,
Seongbuk-gu, Seoul 136702, Republic of Korea
e-mail: danielt@kookmin.ac.kr
123

Med Chem Res (2012) 21:2902–2910
2903
shorter reaction time and operational simplicity with higher
conversion and high degree of selectivity (Caddick, 1995;
Varma, 1999). As part of our continued interest (Thamarai
Selvi et al., 2006; Nadaraj and Thamarai Selvi, 2007;
Nadaraj et al., 2006, 2009) in developing solvent-free
methodologies for the synthesis of quinoline derivatives,
we herein describe a simple and facile MCR synthesis of
pyrano[3,2-c]quinoline derivatives.
ring carbonyl, strong), 1660 ([C=O, carbethoxy carbonyl,
strong); 1H-NMR (500 MHz, DMSO-d6, d, ppm): 11.49 (s,
1H, NH), 7.81 (d, 1H, C10–H), 7.78 (s, 2H, NH2), 7.39–
7.11 (m, 6H, Ar–H), 5.12 (s, 1H, C4–H), 3.96–3.94 (q, 2H,
COOCH2CH3,
J1 = 4.15 Hz,
J2 = 2.90 Hz,
J3 =
4.00 Hz), 2.40 (s, 3H, C9–CH3), 1.09–1.06 (t, 3H,
COOCH2CH3, Jortho = 7.10 Hz, Jortho = 7.00 Hz); 13C-
NMR (125 MHz, DMSO-d6, d, ppm): 168.9, 161.3, 160.4,
151.9, 143.3, 136.7, 133.7, 133.4, 133.1, 131.8, 130.2,
128.4, 127.3, 122.2, 116.0, 112.7, 111.4, 76.8, 59.6, 34.6,
21.5, 15.1; EI-MS (70 eV, m/e, M?.): 410; Anal. Calcd.
For C22H19N2O4Cl: C, 64.31; H, 4.66; N, 6.82. Found: C,
64.37; H, 4.64; N, 6.80.
Materials and methods
All chemicals purchased were of analytic grade and used
without further purification unless mentioned otherwise.
The melting points (Mps) were determined using a Boeti-
eus micro heating table and are uncorrected. The infrared
spectra were recorded on a Shimadzu-8201 spectropho-
Ethyl 2-amino-4-(3-chlorophenyl)-5,6-dihydro-9-methyl-5-
oxo-4H-pyrano[3,2-c]quinoline-3-carboxylate (4b)
1
tometer as pellets on KBr disks. The H- and 13C-NMR
spectrum was recorded on a Bruker AMX-400 spectrom-
eter in DMSO-d6 using TMS as an internal reference unless
otherwise stated. The elemental analyses were performed
on a Perkin Elmer CHN-analyzer. The mass spectra (MS)
were recorded on a Shimadzu GCMS-QP5050A (70 eV)
mass spectrometer. The reactions were monitored by thin
layer chromatography (TLC) using glass plates coated with
Silica gel-G containing 13% calcium sulfate as a binder.
Column chromatography was performed on silica gel (60–
120 mesh). All reactions were performed in a microwave
reactor modified for synthesis (RG 31L, India).
IR (KBr, cm-1): 3310 (NH2, stretching, broad), 3220 (NH,
asym, medium), 3060 (NH, sym, medium), 1688 ([C=O,
ring carbonyl, strong), 1660 ([C=O, carbethoxy carbonyl,
strong); 1H-NMR (500 MHz, DMSO-d6, d, ppm): 11.54 (s,
1H, NH), 7.78 (d, 1H, C10–H), 7.75 (s, 2H, NH2), 7.39–7.12
(m, 6H, Ar–H), 5.14 (s, 1H, C4–H), 3.92–3.96 (q, 2H,
COOCH2CH3,
J1 = 4.14 Hz,
J2 = 2.91 Hz,
J3 =
4.04 Hz), 2.39 (s, 3H, C9–CH3), 1.08–1.06 (t, 3H,
COOCH2CH3, Jortho = 7.11 Hz, Jortho = 7.00 Hz); 13C-
NMR (125 MHz, DMSO-d6, d, ppm): 168.7, 161.2, 160.2,
152.0, 143.5, 136.6, 133.8, 133.3, 133.0, 131.5, 130.6,
128.5, 127.2, 122.1, 116.5, 112.4, 111.2, 76.7, 59.7, 34.6,
21.5, 15.2; EI-MS (70 eV, m/e, M?.): 410; Anal. Calcd. For
C22H19N2O4Cl: C, 64.31; H, 4.66; N, 6.82. Found: C, 64.36;
H, 4.69; N, 6.81.
General procedure for the synthesis of 2-amino-3-
carbethoxy-4-phenylpyrano-[3,2-c]quinolin-5(6H)-ones
(4a–l)
A mixture of 4-hydroxyquinolin-2(1H)-one (0.6 mmol,
0.100 g)
Ethyl 2-amino-4-(4-chlorophenyl)-5,6-dihydro-9-methyl-5-
oxo-4H-pyrano[3,2-c]quinoline-3-carboxylate (4c)
or
6-methyl-4-hydroxyquinolin-2(1H)-one
(0.6 mmol, 0.105 g), substituted aryl aldehyde (0.6 mmol)
and ethyl cyanoacetate (0.6 mmol, 0.03 ml) was placed in
a 100 ml beaker. Then, a ca. two drop of triethylamine was
added and the reaction mixture was irradiated with
microwaves at a power of 250 W at 120°C for the specified
time (5–12 min.). The reaction was monitored at intervals
of 30 s by TLC and the mixture was poured into ice. The
solid obtained was filtered, dried and purified by column
chromatography using a mixture of petroleum ether and
ethyl acetate (3:1) as the eluant.
IR (KBr, cm-1): 3305 (NH2, stretching, broad), 3215 (NH,
asym, medium), 3030 (NH, sym, medium), 1687 ([C=O,
ring carbonyl, strong), 1661 ([C=O, carbethoxy carbonyl,
strong); 1H-NMR (500 MHz, DMSO-d6, d, ppm): 11.50 (s,
1H, NH), 7.77 (d, 1H, C10–H), 7.74 (s, 2H, NH2), 7.38–
7.10 (m, 6H, Ar–H), 5.08 (s, 1H, C4–H), 3.93–3.90 (q, 2H,
COOCH2CH3,
J1 = 4.14 Hz,
J2 = 2.91 Hz,
J3 =
4.02 Hz), 2.38 (s, 3H, C9–CH3), 1.22–1.15 (t, 3H,
COOCH2CH3, Jortho = 7.20 Hz, Jortho = 7.05 Hz); 13C-
NMR (125 MHz, DMSO-d6, d, ppm): 168.8, 161.4, 160.5,
151.9, 143.2, 136.6, 133.5, 133.3, 133.0, 131.9, 130.3,
128.3, 127.2, 122.1, 116.3, 112.6, 111.3, 76.7, 59.7, 34.7,
21.6, 15.2; EI-MS (70 eV, m/e, M?.): 410; Anal. Calcd.
For C22H19N2O4Cl: C, 64.31; H, 4.66; N, 6.82. Found: C,
64.34; H, 4.67; N, 6.84.
Ethyl 2-amino-4-(2-chlorophenyl)-5,6-dihydro-9-methyl-5-
oxo-4H-pyrano[3,2-c]quinoline-3-carboxylate (4a)
IR (KBr, cm-1): 3325 (NH2, stretching, broad), 3215 (NH,
asym, medium), 3050 (NH, sym, medium), 1685 ([C=O,
123

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Med Chem Res (2012) 21:2902–2910
Ethyl 2-amino-5,6-dihydro-4-(4-hydroxyphenyl)-9-methyl-
5-oxo-4H-pyrano[3,2-c]quinoline-3-carboxylate (4d)
133.7, 133.3, 133.0, 131.6, 130.1, 128.2, 127.1, 122.2,
116.1, 112.7, 111.3, 76.6, 59.6, 34.5, 21.5, 15.2; EI-MS
(70 eV, m/e, M?.): 376; Anal. Calcd. For C22H20N2O4: C,
70.20; H, 5.36; N, 7.44. Found: C, 70.18; H, 5.32; N, 7.47.
IR (KBr, cm-1): 3300 (NH2, stretching, broad), 3225 (NH,
asym, medium), 3100 (NH, sym, medium), 2980 (OH,
sharp), 1688 ([C=O, ring carbonyl, strong), 1663 ([C=O,
carbethoxy carbonyl, strong); 1H-NMR (500 MHz,
DMSO-d6, d, ppm): 11.63 (s, 1H, NH), 10.72 (S, 1H, OH),
7.87 (d, 1H, C10–H), 7.74 (s, 2H, NH2), 7.37–7.22 (m,
6H, Ar–H), 4.90 (s, 1H, C4–H), 3.94–3.90 (q, 2H,
Ethyl 2-amino-4-(2-chlorophenyl)-5,6-dihydro-5-oxo-4H-
pyrano[3,2-c]quinoline-3-carboxylate (4g)
IR (KBr, cm-1): 3300 (NH2, stretching, broad), 3205 (NH,
asym, medium), 2995 (NH, sym, medium), 1685 ([C=O,
ring carbonyl, strong), 1660 ([C=O, carbethoxy carbonyl,
strong); 1H-NMR (500 MHz, DMSO-d6, d, ppm): 11.70 (s,
1H, NH), 7.97–7.95 (d, 1H, C10–H, Jortho = 7.50 Hz), 7.79
(s, 2H, NH2), 7.58–7.22 (m, 7H, Ar–H), 5.03 (s, 1H,
C4–H), 3.96–3.90 (q, 2H, COOCH2CH3), 1.12–1.08 (t,
3H, COOCH2CH3, Jortho = 7.10 Hz, Jortho = 7.06 Hz);
13C-NMR (125 MHz, DMSO-d6, d, ppm): 168.1, 163.3,
161.5, 156.6, 143.1, 137.9, 130.4, 130.1, 129.9, 129.4,
128.2, 127.5, 126.8, 125.2, 122.7, 116.8, 99.5, 76.5, 60.8,
39.2, 15.0; EI-MS (70 eV, m/e, M?.): 396; Anal. Calcd.
For C21H17N2O4Cl: C, 63.56; H, 4.32; N, 7.06. Found: C,
63.57; H, 4.30; N, 7.05.
COOCH2CH3,
4.01 Hz), 2.40 (s, 3H, C9–CH3), 1.10–1.06 (t, 3H,
COOCH2CH3, Jortho = 7.08 Hz, Jortho = 7.01 Hz);
J1 = 4.14 Hz,
J2 = 2.90 Hz,
J3 =
13C-NMR (125 MHz, DMSO-d6, d, ppm): 168.4, 161.2,
160.3, 151.6, 143.2, 136.5, 133.8, 133.3, 133.0, 131.1,
130.4, 128.6, 127.2, 122.1, 116.4, 112.6, 111.7, 76.7, 59.5,
34.7, 21.4, 15.0; EI-MS (70 eV, m/e, M?.): 392; Anal.
Calcd. For C22H20N2O5: C, 67.34; H, 5.14; N, 7.14. Found:
C, 67.30; H, 5.11; N, 7.10.
Ethyl 2-amino-5,6-dihydro-9-methyl-4-(3-nitrophenyl)-5-
oxo-4H-pyrano[3,2-c]quinoline-3-carboxylate (4e)
IR (KBr, cm-1): 3320 (NH2, stretching, broad), 3205 (NH,
asym, medium), 3050 (NH, sym, medium), 1688 ([C=O,
ring carbonyl, strong), 1662 ([C=O, carbethoxy carbonyl,
strong); 1H-NMR (500 MHz, DMSO-d6, d, ppm): 1H-NMR
(500 MHz, DMSO-d6, d, ppm): 11.42 (s, 1H, NH), 7.95 (s,
1H, C10–H), 7.79 (s, 2H, NH2), 7.37–7.10 (m, 6H, Ar–H),
5.04 (s, 1H, C4–H), 3.99–3.93 (q, 2H, COOCH2CH3,
J1 = 4.10 Hz, J2 = 2.92 Hz, J3 = 4.01 Hz), 2.35 (s, 3H,
Ethyl 2-amino-4-(3-chlorophenyl)-5,6-dihydro-5-oxo-4H-
pyrano[3,2-c]quinoline-3-carboxylate (4h)
IR (KBr, cm-1): 3299 (NH2, stretching, broad), 3150 (NH,
asym, medium), 3015 (NH, sym, medium), 1685 ([C=O,
ring carbonyl, strong), 1663 ([C=O, carbethoxy carbonyl,
strong); 1H-NMR (500 MHz, DMSO-d6, d, ppm): 11.72 (s,
1H, NH), 7.94–7.90 (d, 1H, C10–H, Jortho = 7.48 Hz), 7.82
(s, 2H, NH2), 7.36–7.10 (m, 7H, Ar–H), 4.98 (s, 1H, C4–
H), 3.94–3.90 (q, 2H, COOCH2CH3), 1.15–1.11 (t, 3H,
COOCH2CH3, Jortho = 7.08 Hz, Jortho = 7.06 Hz); 13C-
NMR (125 MHz, DMSO-d6, d, ppm): 168.1, 162.8, 161.5,
156.7, 143.1, 137.9, 130.3, 130.1, 129.5, 129.0, 128.2,
127.6, 126.5, 125.1, 122.4, 116.4, 99.6, 76.5, 60.6, 39.4,
15.1; EI-MS (70 eV, m/e, M?.): 396; Anal. Calcd. For
C21H17N2O4Cl: C, 63.56; H, 4.32; N, 7.06. Found: C,
63.59; H, 4.34; N, 7.04.
C9–CH3), 1.14–1.12 (t, 3H, COOCH2CH3, Jortho
=
7.10 Hz, Jortho = 7.00 Hz); 13C-NMR (125 MHz, DMSO-
d6, d, ppm): 168.4, 161.3, 160.6, 151.8, 143.3, 136.8,
133.8, 133.4, 133.0, 131.8, 130.1, 128.3, 127.3, 122.0,
116.1, 112.4, 111.2, 76.7, 59.6, 34.7, 21.5, 15.2; EI-MS
(70 eV, m/e, M?.): 421; Anal. Calcd. For C22H19N3O6: C,
62.70; H, 4.54; N, 9.97. Found: C, 62.68; H, 4.51; N, 9.92.
Ethyl 2-amino-5,6-dihydro-9-methyl-5-oxo-4-phenyl-4H-
pyrano[3,2-c]quinoline-3-carboxylate (4f)
Ethyl 2-amino-4-(4-chlorophenyl)-5,6-dihydro-5-oxo-4H-
pyrano[3,2-c]quinoline-3-carboxylate (4i)
IR (KBr, cm-1): 3305 (NH2, stretching, broad), 3115 (NH,
asym, medium), 3005 (NH, sym, medium), 1685 ([C=O,
ring carbonyl, strong), 1662 ([C=O, carbethoxy carbonyl,
strong); 1H-NMR (500 MHz, DMSO-d6, d, ppm): 1H-NMR
(500 MHz, DMSO-d6, d, ppm): 11.62 (s, 1H, NH), 7.81 (d,
1H, C10–H), 7.78 (s, 2H, NH2), 7.35–7.10 (m, 7H, Ar–H),
4.82 (s, 1H, C4–H), 4.00–3.96 (q, 2H, COOCH2CH3,
J1 = 4.13 Hz, J2 = 2.90 Hz, J3 = 4.01 Hz), 2.40 (s, 3H,
IR (KBr, cm-1): 3315 (NH2, stretching, broad), 3205 (NH,
asym, medium), 3070 (NH, sym, medium), 1688 ([C=O,
ring carbonyl, strong), 1662 ([C=O, carbethoxy carbonyl,
strong); 1H-NMR (500 MHz, DMSO-d6, d, ppm): 11.52 (s,
1H, NH), 7.97–7.96 (d, 1H, C10–H, Jortho = 7.5 Hz), 7.82
(s, 2H, NH2), 7.57–7.12 (m, 7H, Ar–H), 5.13 (s, 1H, C4–
H), 3.97–3.93 (q, 2H, COOCH2CH3), 1.09–1.06 (t, 3H,
COOCH2CH3, Jortho = 7.07 Hz, Jortho = 7.00 Hz); 13C-
NMR (125 MHz, DMSO-d6, d, ppm): 168.2, 163.0, 161.3,
C9–CH3), 1.12–1.00 (t, 3H, COOCH2CH3, Jortho
=
7.11 Hz, Jortho = 7.09 Hz); 13C-NMR (125 MHz, DMSO-
d6, d, ppm): 168.1, 161.2, 160.4, 151.8, 143.4, 136.8,
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Med Chem Res (2012) 21:2902–2910
2905
156.6, 143.1, 137.6, 130.5, 130.0, 129.7, 129.1, 128.0,
127.4, 126.3, 125.2, 122.1, 116.4, 99.6, 76.5, 60.7, 39.7,
14.9; EI-MS (70 eV, m/e, M?.): 396; Anal. Calcd. For
C21H17N2O4Cl: C, 63.56; H, 4.32; N, 7.06. Found: C,
63.61; H, 4.29; N, 7.01.
COOCH2CH3, Jortho = 7.10 Hz, Jortho = 7.05 Hz); 13C-
NMR (125 MHz, DMSO-d6, d, ppm): 168.0, 163.2, 161.4,
156.7, 143.0, 137.8, 130.5, 130.1, 129.8, 129.2, 128.2,
127.6, 126.6, 125.3, 122.4, 116.6, 99.8, 76.6, 60.7, 39.6,
15.2; EI-MS (70 eV, m/e, M?.): 362; Anal. Calcd. For
C21H18N2O4: C, 69.60; H, 5.01; N, 7.73. Found: C, 69.62;
H, 4.97; N, 7.71.
Ethyl 2-amino-5,6-dihydro-4-(4-hydroxyphenyl)-5-oxo-
4H-pyrano[3,2-c]quinoline-3-carboxylate (4j)
Antibacterial activity studies
IR (KBr, cm-1): 3295 (NH2, stretching, broad), 3175 (NH,
asym, medium), 3065 (NH, sym, medium), 3000 (OH,
sharp), 1687 ([C=O, ring carbonyl, strong), 1665 ([C=O,
carbethoxy carbonyl, strong); 1H-NMR (500 MHz,
DMSO-d6, d, ppm): 11.60 (s, 1H, NH), 10.56 (s, 1H, OH),
7.92–7.88 (d, 1H, C10–H, Jortho = 7.48 Hz), 7.72 (s, 2H,
NH2), 7.38–7.11 (m, 7H, Ar–H), 4.88 (s, 1H, C4–H), 3.99–
3.92 (q, 2H, COOCH2CH3), 1.16–1.11 (t, 3H, CO-
OCH2CH3, Jortho = 7.11 Hz, Jortho = 7.06 Hz); 13C-NMR
(125 MHz, DMSO-d6, d, ppm): 168.1, 163.2, 161.3, 156.4,
143.1, 137.4, 130.5, 130.0, 129.2, 129.0, 128.1, 127.4,
126.2, 125.0, 122.2, 116.7, 99.4, 76.2, 60.6, 39.4, 15.0; EI-
MS (70 eV, m/e, M?.): 378; Anal. Calcd. For C21H18N2O5:
C, 66.66; H, 4.79; N, 7.40. Found: C, 66.61; H, 4.77; N,
7.43.
Antibacterial activity screening studies of the pyrano[3,2-
c]quinoline derivatives were carried out by the paper disk
method (Collins and Lyne, 1970). 5 ml of nutrient agar
(NA) medium (pH 6.8) was poured into sterilized plates
and allowed to solidify. The plates were inoculated with
spore suspensions of gram-positive (Staphylococcus aur-
eus) and gram-negative (Escherichia coli) bacteria and, by
using a sterilized cork borer, paper disks (6 mm in diam-
eter) were inserted into the culture plates. 50 ll of bacteria
was used for the test. Different concentrations (50 and
100 lg/ml) of the test pyrano[3,2-c]quinoline derivatives
solution were prepared in DMSO and 10 ll of the test
solution was added to the disks. The plates were incubated
at 27°C for 24 h. The inhibition zone that appeared around
the disk was measured and recorded as the antibacterial
effect of the title compound. DMSO was used as a solvent
control. The antibacterial test was repeated three times to
determine the reproducibility. To calculate the antibacterial
activity of these newly prepared pyrano[3,2-c]quinoline
derivatives statistically, we used the standard Eq. 1 to
measure the inhibition zone.
Ethyl 2-amino-5,6-dihydro-4-(3-nitrophenyl)-5-oxo-4H-
pyrano[3,2-c]quinoline-3-carboxylate (4k)
IR (KBr, cm-1): 3295 (NH2, stretching, broad), 3155 (NH,
asym, medium), 3025 (NH, sym, medium), 1685 ([C=O,
ring carbonyl, strong), 1660 ([C=O, carbethoxy carbonyl,
strong); 1H-NMR (500 MHz, DMSO-d6, d, ppm): 11.68 (s,
1H, NH), 7.87–7.84 (d, 1H, C10–H, Jortho = 7.48 Hz), 7.72
(s, 2H, NH2), 7.48–7.12 (m, 7H, Ar–H), 4.87 (s, 1H, C4–
H), 3.93–3.89 (q, 2H, COOCH2CH3), 1.26–1.20 (t, 3H,
p
ꢀ
x ꢁ ts=ð nÞ
ð1Þ
where, n is the number of observations, s is the measured
standard deviation, x is the measured mean value of the
inhibition zone, and t is the student’s t value (t = 2.775 at
95% confidence level).
COOCH2CH3,
Jortho = 7.04 Hz,
Jortho = 7.00 Hz);
13C-NMR (125 MHz, DMSO-d6, d, ppm): 168.3, 163.0,
161.4, 156.4, 143.2, 137.5, 130.2, 130.0, 129.6, 129.0,
128.2, 127.4, 126.2, 125.1, 122.2, 116.3, 99.2, 76.2, 60.6,
39.4, 15.0; EI-MS (70 eV, m/e, M?.): 407; Anal. Calcd.
For C21H17N3O6: C, 61.91; H, 4.21; N, 10.31. Found: C,
61.87; H, 4.22; N, 10.30.
Anti-inflammatory activity
All the title compounds were tested for anti-inflammatory
activity by carrageenan induced rat paw edema model
employing Plethysmometer to measure the paw thickness.
Albino rats of either sex, weighing between 200 and 250 g
were divided into fourteen groups of six animals each. All
groups were fasted for overnight and allowed water ad
libitium. Inflammation was induced by injecting 0.05 ml of
1% carrageenan suspension subcutaneously into subplantar
region of the right hind paw and 0.05 ml of saline was
injected into subplantar region of left hind paw for all the
ten groups. One hour prior to carrageenan injection, the
groups III to XI treated with title compounds 4a–l
(100 mg/kg). 1% Sodium carboxy methyl cellulose (CMC)
Ethyl 2-amino-5,6-dihydro-5-oxo-4H-pyrano[3,2-
c]quinoline-3-carboxylate (4l)
IR (KBr, cm-1): 3295 (NH2, stretching, broad), 3205 (NH,
asym, medium), 3085 (NH, sym, medium), 1685 ([C=O,
ring carbonyl, strong), 1662 ([C=O, carbethoxy carbonyl,
strong); 1H-NMR (500 MHz, DMSO-d6, d, ppm): 11.73 (s,
1H, NH), 7.98–7.96 (d, 1H, C10–H, Jortho = 7.85 Hz), 7.78
(s, 2H, NH2), 7.58–7.22 (m, 8H, Ar–H), 4.81 (s, 1H, C4–
H), 4.03–3.99 (q, 2H, COOCH2CH3), 1.15–1.12 (t, 3H,
123

2906
Med Chem Res (2012) 21:2902–2910
gel (1 ml/kg) was given to group-I used as carrageenan
treated control and the standard drug saline (2 mg/kg) was
administered to group-II. The paw volume of each rat was
measured before 1 and 3 h of carrageenan treatment with
the help of a plethysmometer. The percent anti-inflamma-
tory activity was calculated according to the formula given
below:
Table 2 Effect of temperature on the synthesis of pyranoquinoline
under microwave irradiation in the presence of TEA
Entry
T (°C)
Time (min)
Yield (%)
1
2
3
4
80
100
120
140
11
8
74
76
80
79
5
5
Percentage of inhibition of edema ¼ ð1 ꢂ Vt=VcÞ ꢃ 100
where Vt and Vc are paw volume of rats of the treated and
control group, respectively. Results obtained were statisti-
cally analyzed.
product in 80% yield. Since this reaction can lead to the
formation of more than one product, viz. 4 or 5 and/or 6 or
7, the structure of the product was carefully examined
(Scheme 1).
The infrared spectrum of the product (4a) showed
absorption at 1685 cm-1 for the ester functional group. The
NMR spectral data also confirmed the presence of the
Results and discussion
In the search for an inexpensive and easily available cat-
alyst, triethylamine (TEA), piperidine, p-toluenesulfonic
acid (PTSA), and cetrimide were examined separately in
the microwave assisted reaction of 4-hydroxyquinolin-
2(1H)-one (1), o-chlorobenzaldehyde (2) and ethyl cya-
noacetate (3) at 120°C. All of the reactions were carried out
in a microwave reactor at a power of 250 W, interestingly,
in all of the reactions, a single product was obtained in high
yield and the shortest reaction time was observed in the
case of TEA (Table 1, entry 1). Therefore, TEA was cho-
sen as the catalyst to synthesize a library of pyrano[3,2-
c]quinolines.
1
–COOCH2CH3 group, as the H-NMR spectrum showed a
two proton quartet at d 3.94–3.96 and a three proton triplet
at d 1.06–1.09 and the 13C-NMR spectrum showed peaks at
d 21.5 & 34.6 for the –CH3 & –CH2 groups, respectively.
This evidence eliminates the possibility of the formation of
6 and 7. The characteristic upfield signal of C10–H (d 7.81)
1
in the H-NMR spectrum (Nadaraj et al., 2011) and quin-
olinone carbonyl carbon peak at d 161.3 in the 13C-NMR
spectrum (Manikandan et al., 2002) also favored the for-
mation of an angular product rather than a linear one.
Furthermore, the IR spectrum showed absorption at
1660 cm-1 corresponding to the 2-quinolinone group.
Conclusive evidence came from mass spectrum which
showed a molecular ion peak at m/z 410 (M?.). The frag-
mentation pattern of the mass spectrum showed a peak at
m/z 256 (100%) (Scheme 2), which is formed by the
removal of the –CONH group. This is only possible if the
2-quinolinone moiety is present in the compound. Hence,
the formed product is confirmed to be 4 rather than 5.
To explore this reaction in a synthetically useful context,
we further examined the reactions of 1a,b with various
aldehydes (2a–l) and 3, which afforded the products 4a–l
exclusively (Scheme 3; Table 3). This reaction may occur
via a Michael addition, elimination and cyclization mech-
anism. The structures of the products (4a–l) were com-
pletely characterized by their spectral (IR, 1H- & 13C-NMR
and Mass) and analytical data.
To optimize the reaction temperature, the reaction of 1,
2, and 3 was carried out using TEA at temperatures ranging
from 80 to 140°C with an increase of 20°C each time. It
was found that the yield of the product was high when the
temperature of the reaction was maintained at 120°C
(Table 2, entry 3). Since there was little difference in the
reaction time, we chose a reaction temperature of 120°C
and a microwave power of 250 W as the optimum
conditions.
Hence, in a typical experimental procedure, equimolar
amounts of 1, 2, and 3 were mixed thoroughly with a
catalytic amount of TEA and the reaction mixture was
irradiated with microwave irradiation at a power of 250 W
at 120°C for 6 min, which afforded exclusively a single
Table 1 Effect of catalyst on the synthesis of pyranoquinoline under
microwave irradiation at 120°C
Entry
Catalyst
Time (min)
Yield (%)
Antimicrobial studies
1
2
3
4
5
TEA
5
80
76
60
63
–
The in vitro antibacterial screening of the pyrano[3,2-c]
quinoline derivatives was carried out against one gram-
positive (Staphylococcus aureus) and one gram-negative
(Escherichia coli) bacteriocide using the paper disk method
(Collins and Lyne, 1970). Ofloxacin and Streptomycin were
Piperidine
PTSA
12
16
Cetrimide
None
17
No reaction
123

Med Chem Res (2012) 21:2902–2910
2907
NH2
COOCH2CH3
O
Cl
H
O
Cl
H
R
R
COOCH2CH3
and/or
N
H
4
O
OH
CHO
N
H
O
NH2
R
Cl
5
CN
TEA
MWI
+
+
COOCH2CH3
O
N
H
1
O
3
CN
H
2
O
Cl
O
Cl
H
R
R
CN
and/or
N
H
6
O
N
H
7
O
O
Scheme 1 Synthetic scheme of the expected products 4 or 5 and/or 6 or 7
NH2
NH2
.
NH2
COOCH2CH3
COOCH2CH3
COOCH2CH3
Cl
O
O
O
H3C
H3C
H3C
.
-C6H4
-Cl
N
H
O
N
H
O
N
H
O
m/z 299
C16H15N2O4
m/z 410
m/z 375
C22H19N2O4
C22H19N2O4Cl
-CONH
.
.
O
O
NH2
H3C
O
NH2
.
-NH2
-CH3
COOCH2CH3
COOCH2CH3
COOCH2CH3
m/z 225
C14H9O3
m/z 241
C14H11NO3
m/z 256
C15H14NO3
-COOCH2CH3
.
O
m/z 152
C11H4O
Scheme 2 Mass fragmentation pathways of 4a
NH2
COOCH2CH3
R1
OH
O
CHO
R
R
R2
R1
R2
TEA/MWI
°C,
CN
H2C
+
+
120 250 W
COOCH2CH3
N
H
O
N
H
4a-l
O
R3
3
1
R = CH3, H
R1 = H, Cl
R3
2
R2 = H, Cl, NO2
R3 = H, Cl, OH
Scheme 3 General synthetic scheme for the preparation of 2-amino-3-carbethoxy-4-(substituted phenyl)pyrano[3,2-c]quinolin-5(6H)-ones
(4a–l)
123

2908
Med Chem Res (2012) 21:2902–2910
concentration, and it is thought that the variation in the
effectiveness of the different compounds against different
organisms depends either on the impermeability of the cells
of the microbes or the differences in the ribosomes of
the microbial cells (Daniel Thangadurai et al., 2010).
Normally, the inhibition activity of compounds increases
with increasing concentration of the solution. However,
even though the newly prepared derivative compounds
possessed antibacterial activity, their effectiveness did
not match that of the standard drugs, Ofloxacin and
Streptomycin.
Table 3 Microwave promoted preparation of 2-amino-3-carb-eth-
oxy-4-(substituted phenyl) pyrano[3,2-c]quinolin-5(6H)-ones (4a–l)
Compound
R
R1 R2
R3 Time (min) Yield (%) Mp (°C)
4a
4b
4c
4d
4e
4f
CH3 Cl
H
H
6
5
80
75
80
81
81
81
82
81
83
80
80
84
248–250
220–222
210–211
196–197
160–161
192–193
200–201
185–186
240–242
228–229
165–166
206–207
CH3
CH3
CH3
CH3
CH3
H
H
H
H
H
H
Cl
H
H
H
H
H
Cl
H
H
Cl
OH
H
5
H
5
NO2
H
12
10
7
H
4g
4h
4i
H
H
H
Cl
H
H
7
H
Cl
OH
H
8
4j
H
H
5
Anti-inflammatory studies
4k
4l
H
NO2
H
8
H
H
5
The anti-inflammatory activity of title compounds have
been evaluated by using carrageenan-induced rat paw
edema method (Winter et al., 1962). The results of eval-
uation have been viewed by taking saline as the standard
drug (Table 5). The results of anti-inflammatory activity
revealed that the synthesized compounds exhibited mod-
erate to considerable activity when compared with refer-
ence standard saline, but at a higher dose level as the
standard drug was tested at 25 mg/kg, whereas the com-
pounds were tested at a dose of 100 mg/kg. Compounds 4g,
4i, and 4k possessed maximum activity. Other compounds
tested in this present study also showed some degree of
anti-inflammatory activity.
employed as reference standards. Table 4 shows the anti-
bacterial activity data of the title compounds and revealed
that almost all of the derivatives in this series were
effective against both bacteria at dose levels of 50 and
100 lg/ml. Compounds 4a, 4d, 4e, and 4k possessed the
maximum activity, which is probably due to the electronic
effects of the substituents at the various positions of the
aryl rings. This reveals the importance of such groups for
favorable antibacterial activity. A few of the compounds
were inactive against these two organisms at particular
Table 4 Antibacterial activity of the title compounds (4a–l)
Compound
Inhibition zone (mm)a ? Paper disk width (mm)b
Staphylococcus aureus (Gram positive)
Escherichia coli (Gram negative)
50 lg
100 lg
50 lg
100 lg
Ofloxacin
21.2 0.1
–
24.3 0.3
–
–
–
Streptomycin
20.1 0.1
–
25.2 0.2
–
Control
4a
4b
4c
–
–
16.1 0.1
14.6 0.2
15.8 0.1
17.6 0.3
18.1 0.1
14.7 0.4
15.2 0.1
15.4 0.5
16.3 0.4
16.9 0.3
17.3 0.5
15.6 0.2
17.3 0.3
15.7 0.4
18.5 0.3
19.7 0.5
19.2 0.3
–
15.4 0.2
14.1 0.5
15.4 0.4
16.2 0.1
16.5 0.3
15.7 0.1
13.7 0.2
14.1 0.4
15.2 0.3
15.7 0.4
16.1 0.2
15.2 0.4
17.3 0.4
15.2 0.1
–
4d
4e
18.2 0.2
17.4 0.4
16.2 0.3
15.0 0.2
–
4f
4g
4h
4i
16.3 0.3
15.7 0.5
16.7 0.5
17.6 0.3
–
16.2 0.4
17.0 0.5
17.0 0.3
16.2 0.2
4j
4k
4l
16.7 0.3
a
b
x
ts/(Hn), n = 5 at 95% confidence level, paper disk width of 6 mm
123

Med Chem Res (2012) 21:2902–2910
2909
Table 5 Anti-inflammatory
activity of the title compounds
(4a–l)
Compound
Dose (mg/kg)
Circumference of the hind paws Mean value
After 1 h
%ROV
After 2 h
%ROV
After 3 h
%ROV
Control
Saline
4a
0.5 ml
25
–
–
–
66.24 0.15
58.12 0.21
56.35 0.24
59.44 0.19
57.13 0.11
54.27 0.13
56.23 0.22
55.61 0.26
57.56 0.21
56.21 0.17
58.43 0.19
53.51 0.22
54.17 0.16
79.34 0.10
68.11 0.14
69.72 0.21
70.31 0.12
70.43 0.13
70.34 0.15
71.14 0.16
69.36 0.19
68.52 0.20
66.12 0.18
63.35 0.22
69.01 0.17
61.93 0.14
95.65 0.01
74.16 0.02
75.51 0.14
77.65 0.16
69.15 0.13
75. 45 0.15
75.24 0.18
80.61 0.17
75.87 0.30
80.65 0.22
75.17 0.20
79.32 0.23
75.17 0.26
100
100
100
100
100
100
100
100
100
100
100
100
4b
4c
4d
4e
4f
4g
4h
4i
4j
4k
4l
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Conclusion
In conclusion, we demonstrated a simple and convenient
synthesis of novel pyrano[3,2-c]quinoline derivatives in
good yield under microwave irradiation. The advantages of
the present protocol are its one-pot reaction conditions and
shorter reaction times, as well as the fact that the reactive
components used in the above reaction including the cat-
alyst are commercially available. Noteworthy is the com-
plete selectivity in the angular cyclization, which makes
this method a highly practical way to produce pharma-
ceutically important heterocycles. The present pharmaco-
logical studies showed that all of the derivative compounds
exhibited significant antibacterial and anti-inflammatory
activity. However, further studies are required to establish
the mechanism of action of the title compounds. The
physico-chemical properties leading to their antimicrobial
activity need to be established by detailed QSAR studies,
which may provide insight into the structural requirements
of this class of molecules. Currently, we are investigating
the mechanisms of various in vitro cytotoxic activities of
these newly prepared pyrano[3,2-c]quinoline derivatives
and the results will be published in due course.
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Acknowledgments The financial support provided by the Govern-
ment of Tamilnadu, India (to the author V. N.) is gratefully
acknowledged. The authors thank Professor Yong-Ill Lee, Changwon
National University, Changwon, Republic of Korea, and the Indian
Institute of Science, Bangalore, India, for the spectral analyses.
Manikandan S, Shanmugasundaram M, Raghunathan R (2002)
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