Microwave-assisted solid acid-catalyzed synthesis of quinolinyl quinolinones and evaluation of their antibacterial, antioxidant activities

Article abstract of DOI:10.1007/s11164-014-1575-z

Microwave-assisted montmorillonite K-10-catalyzed Friedlander synthesis of quinolinylquinolinones has been developed. The efficient and eco-friendly catalyst along with the convenience of the product isolation make this process an attractive alternative f

Full text of DOI:10.1007/s11164-014-1575-z

Res Chem Intermed
DOI 10.1007/s11164-014-1575-z
Microwave-assisted solid acid-catalyzed synthesis
of quinolinyl quinolinones and evaluation of their
antibacterial, antioxidant activities
•
R. Subashini Gangadhara Angajala
•
•
Kadirappa Aggile F. Nawaz Khan
Received: 15 November 2013 / Accepted: 23 February 2014
Ó Springer Science+Business Media Dordrecht 2014
Abstract Microwave-assisted montmorillonite K-10-catalyzed Friedlander syn-
thesis of quinolinylquinolinones has been developed. The efficient and eco-friendly
catalyst along with the convenience of the product isolation make this process an
attractive alternative for the synthesis of target heterocycles. The synthesized pro-
ducts were confirmed by FTIR, 1H NMR, 13C NMR, and mass spectroscopic
techniques. All the synthesized compounds showed good antibacterial property
similar to standard Ampicillin and enhanced antioxidant activity.
Keywords Quinolinone ꢀ 2-Aminobenzophenone ꢀ Montmorillonite
K-10 ꢀ Solvent-free conditions ꢀ Antibacterial ꢀ Antioxidant properties
Introduction
The quinoline structural motif occurs in several natural products (cinchona
alkaloids) and are pharmacologically active substances displaying a broad range
of biological activity [1–5]. Because of their importance as substructures in a broad
range of natural and designed products, significant efforts have been directed in the
development of new quinoline-based structures (Fig. 1) [6].
The quinolines has been found to possess antihelmintic [7], antibacterial [8],
antifungal [9], antimalarial [10], anticonvulsant, cardiotonic, anti-inflammatory
[11], and analgesic [12], antiprotozoal [13], antiviral [14], hypoglycemic [15],
cardiovascular [16], and antineoplastic [17] activities. Similarly, the quinolinones
R. Subashini ꢀ G. Angajala ꢀ K. Aggile ꢀ F. Nawaz Khan (&)
Organic Chemistry Division, School of Advanced Sciences, VIT University, Vellore 632 014,
Tamil Nadu, India
e-mail: nawaz_f@yahoo.co.in
R. Subashini
e-mail: dr.subashini.r@gmail.com
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R. Subashini et al.
Fig. 1 New quinoline based structures
have been of considerable scientific and clinical interest since their discovery in the
early 1960s [18–22]. The structural core of quinolinone is employed in medicinal
chemistry and present in various medicinally valuable compounds [23, 24].
Quinolinones and quinolones are important constituents of pharmacologically active
agents [25]. The first generation quinolinone, nalidixic acid, was introduced in 1962.
Since then, structural modifications have resulted in second, third, and fourth
generation fluoroquinolones, which have improved coverage of Gram-positive
organisms [26]. Quinoline has frequently been recognized in the structure of
numerous naturally occurring alkaloids [27, 28]. The functionalized quinolinones
are attractive compounds for drug discovery since many of them have been shown
to exhibit excellent biological activities. Therefore, the development of facile
methodologies for the synthesis of highly functionalized quinolinone derivatives
represents a challenge in medicinal chemistry [29, 30].
New developments in the chemistry of quinoline derivatives have been reviewed
[31]. The structural core of quinoline and related poly heterocycles has been
synthesized through Friedlander quinoline synthesis [32]. Amberlyst-15 is consid-
ered as a most effective catalyst in terms of the reaction times, yields, and
reusability as reported by Das et al. [33]. Simple and environmentally benign
operationally simple route for quinoline derivatives were efficiently prepared
through acid-catalyzed Friedlander reaction in ionic liquid ([bmim][BF4]) by Zhang
et al. [34]. A molecular iodine-mediated mild and efficient route for the synthesis of
quinolines, via Friedlander annulations, has been reported by Wu et al. [35]. This
method is not only a complement to quinoline synthesis via Friedlander annulations
but also avoids the use of hazardous acids or bases and harsh reaction conditions.
Dabiri and Bashiribod [36] have reported an efficient and recyclable catalyst
phosphotungstic acid (H3PW12O40) in the synthesis of polysubstituted quinolines,
through the Friedlander condensation, under solvent-free conditions. Zolfigol et al.
[37] have reported a green chemical route involving Lewis acids catalyst in
Friedlander annulation to quinolines where Zr(NO3)4 and Zr(HSO4)4 were found to
be more efficient than other investigated Lewis acids in the catalyzed condensation
of o-amino aryl ketones or o-amino benzonitrile with ketones or b-diketones in
water under reflux conditions.
Habibi and Marvi [38] have reported microwave-irradiated montmorillonite KSF
and montmorillonite K-10 clays catalysis under the solvent-free conditions for the
synthesis of different bismaleimides and bisphthalimides, in a simple and
environmentally benign method from the condensation reaction of maleic and
phthalic anhydrides, with different diamines in good yields and short reaction times.
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Synthesis of quinolinyl quinolinones
Fig. 2 Antibacterial efficacy of quinolones structure
The various structural features of the quinolinones that govern the antibacterial
efficacy and influence the side-effect profile have been delineated and summarized
at the molecular level (Fig. 2).
Based on the literature survey and the importance of quinolinones, in this paper
Friedlander synthesis of quinolinones, 4, and quinolines, 3, in the presence of
amberlite Na sr1L and MK-10, respectively, has been explored and the results
obtained are discussed in detail in continuation of our studies [39–48]. The catalyst
amberlite Na sr1L was also efficiently used for the regioselective N-alkylation of the
quinolinones. A variety of substituted quinolinones have also been prepared using
the microwave technique in high yield and purity.
Experimental
Chemistry
Solvents and reagents were commercially sourced and used without further purifica-
tion. Thin layered chromatography (TLC) was performed on preparative platesof silica
gel. Visualization was made with an iodine chamber. Column chromatography was
performed by using silica gel (100–200 mesh). Melting points were measured on
Elchem Microprocessor-based DT apparatus using an open capillary tube and are
corrected with standard benzoic acid. The NMR spectra were recorded on a Bruker
Advance III-400 MHz spectrometer using TMS as internal standard (chemical shifts d
in ppm). Mass was recorded on Finnigan Mat 8230 Mass Spectrometer.
General procedure
Ethyl-6-chloro-2-methyl-4-phenylquinoline-3-carboxylates, 3a–e A mixture of o-
amino ketones, 1 (1 mmol), ethyl -3-oxobutanoate, 2 (1.5 mmol), and MK-10
(100 mg) was taken in a vessel, mixed thoroughly and then irradiated in a
microwave oven at power of 65 W and at a temperature of 115 °C for 10 min. The
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R. Subashini et al.
completion of the reaction was monitored by TLC. Ethanol was added to the
reaction mixture and the catalyst was filtered off. The excess solvent was removed
under reduce pressure to gave the crystals of ethyl-2-methyl-4-phenylquinoline-3-
carboxylates, 3a–e in good yield.
Quinolin-2-yl-quinolin-2(1H)-ones, 5a–h A mixture of o-amino ketone, 1
(1 mmol), quinoline-2-[1H]-ones, 4 (1 mmol), and MK-10 (100 mg) was taken in
a reaction vessel, mixed thoroughly and then irradiated in a microwave oven at
500 W each time for 30 s up to 4–5 min. The completion of the reaction was
monitored by TLC. The reaction mixture was treated with ethanol and filtered off to
remove the catalyst. Then the ethanol was removed under reduced pressure and
poured onto crushed ice. The solid obtained was collected and further purified by
column chromatography (85:15- Pet.ether: EtOAc).
Analytical data
Ethyl-6-chloro-2-methyl-4-phenylquinoline-3-carboxylate, 3a Pale yellow solid,
95.1 % yield, mp 106–108 °C (Lit. 110 °C) (Dabiri and Bashiribod 2009). IR (KBr
1
pellets, cm-1) t: 796, 1,558, 1,603, 1,720, 2,927, 3,077. H NMR (CDCl3, ppm,
300 MHz) d: 0.95 (3H, t, J = 6 Hz, CH2CH3), 2.77 (3H, s, CH3), 4.03 (2H, q,
CH2CH3), 7.33 (2H, m, CH), 7.51 (4H, m, CH), 7.64 (1H, d, J = 9 Hz, CH), 8.01
(1H, d, J = 9 Hz, CH). 13C NMR (CDCl3, ppm, 75 MHz) d: 13.3, 23.1, 59.9, 95.6,
2 9 124.9, 125.7, 125.9, 2 9 126.8, 128.1, 2 9 128.9, 129.3, 134.8, 145.1, 147.0,
153.1, 168.2. Mol. formula: C19H16ClNO2 requires 325.0870; HRMS m/z 325.0816
(M?).
Ethyl-2-methyl-4-phenylquinoline-3-carboxylate, 3b Pale yellow solid, 96 %
yield, mp 96–98 °C (Lit. 99 °C) (Dabiri and Bashiribod 2009). IR (KBr pellets,
cm-1) t: 1,561, 1,611, 1,712, 2,928, 2,972, 3,056. 1H NMR (CDCl3, ppm,
500 MHz) d: 0.92 (3H, t, J = 10 Hz, CH2CH3), 2.69 (3H, s, CH3), 3.91 (2H, q,
CH2CH3), 7.35 (8H, m, CH), 8.03 (1H, d, J = 10 Hz, CH). 13C NMR (CDCl3, ppm,
125 MHz) d: 14.1, 21.2, 62.3, 118.9, 2 9 123.4, 124.7, 2 9 126.1, 126.9,
2 9 128.2, 132.8, 133.7, 139.1, 140.3, 148.2, 155.5, 168.8. Mol. formula:
C19H17NO2 requires 291.1259; EI-MS m/z 292 (M?1).
Ethyl-2,4-dimethylquinoline-3-carboxylate, 3c Pale yellow solid, 85 % yield, mp
1
Liquid. IR (KBr pellets, cm-1) t: 1,543, 1,604, 1,718, 2,921, 3,033. H NMR
(CDCl3, ppm, 500 MHz) d: 1.66 (3H, t, J = 10 Hz, CH2CH3), 2.51 (3H, s, CH3),
2.63 (3H, s, CH3), 4.31 (2H, q, CH2CH3), 7.39 (1H, t, J = 10 Hz, CH), 7.61 (1H, t,
J = 10 Hz, CH), 7.87 (1H, d, J = 10 Hz, CH), 7.93 (1H, d, J = 10 Hz, CH). 13C
NMR (CDCl3, ppm, 125 MHz) d: 14.5, 15.9, 23.8, 59.8, 2 9 122.9, 124.8, 125.8,
126.7, 129.1, 140.8, 146.5, 153.7, 167.3. Mol. formula: C14H15NO2 requires
229.1103; LC–MS m/z 230 (M?1).
1-(6-Chloro-2-methyl-4-phenylquinolin-3-yl)ethanone, 3d Pale yellow solid,
91 % yield, mp 150–152 °C (Lit.150 °C). IR (KBr pellets, cm-1) t: 711, 1,561,
1
1,720, 2,976, 3,071. H NMR (CDCl3, ppm, 500 MHz) d: 2.00 (3H, s, CH3), 2.68
(3H, s, CH3), 7.35 (4H, m, CH), 7.95 (4H, m, CH). 13C NMR (CDCl3, ppm,
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Synthesis of quinolinyl quinolinones
125 MHz) d: 16.9, 25.7, 122.1, 2 9 123.7,2 9 124.0, 125.4, 2 9 126.3, 127.8,
3 9 129.0, 134.1, 138.2, 156.3, 199.6 (–COCH3). Mol. formula: C18H14ClNO
requires 295.0764; LC–MS m/z 296 (M?1).
1-(2-Methyl-4-phenylquinolin-3-yl)ethanone, 3e Pale yellow solid, 89 % yield,
mp 112–114 °C (Lit. 115 °C). IR (KBr pellets, cm-1) t: 1,548, 1,609, 1,713, 2,934,
1
3,013. H NMR (CDCl3, 400 MHz, ppm) d: 2.05 (3H, s, CH3), 2.69 (3H, s, CH3),
7.36–8.09 (9H, m, CH). 13C NMR (CDCl3, 100 MHz) d: 15.7, 26.1, 121.7, 122.4,
2 9 124.9, 125.7, 125.9, 126.8, 2 9 128.1, 128.9, 129.3, 134.8, 136.1, 137.0, 157.4,
198.2 (–COCH3). Mol. formula: C18H15NO requires 261.1154; GC–MS m/z 262
(M?1).
6-Chloro-3-(6-chloro-4-phenylquinolin-2-yl)-4-phenylquinolin-2(1H)-one,
5a
Colorless solid, 91 % yield, mp 160–162 °C. IR (KBr, cm-1) t: 3,421, 2,917,
1
1,647. H NMR (DMSO-d6, ppm, 500 MHz): d 7.25–7.27 (2H, m, CH), 7.29–7.30
(2H, m, CH), 7.34–7.36 (2H, dd, CH), 7.39 (1H, s, CH), 7.00 (1H, d, J = 5 Hz,
CH), 7.48–7.49 (1H, d, J = 8.5 Hz, CH), 7.53–7.58 (4H, m, CH), 7.63–7.65 (1H,
dd, CH), 7.68 (1H, d, J = 5 Hz, CH), 7.72–7.74 (1H, dd, CH), 7.91–7.93 (1H, d,
J = 10 Hz, CH), 12.40 (1H, s, NH). 13C NMR (DMSO-d6, ppm, 125 MHz): d
117.9, 121.3, 2 9 124.0, 125.1, 125.6, 2 9 126.1, 126.3, 128.5, 3 9 129.3,
2 9 129.6, 2 9 129.7, 130.3, 131.2, 132.0, 2 9 132.6, 135.1, 136.9, 137.9,
146.2, 146.4, 148.9, 156.0, 161.1 (NH–C=O). Mol. formula: C30H18Cl2N2O
requires 492.0796; HRMS: m/z 492.0366 (M?).
3-(6-Chloro-4-phenylquinolin-2-yl)-4-methylquinolin-2(1H)-one, 5b Color less
1
solid, 87 % yield, m.p. 143–145 °C. IR (KBr, cm-1) t: 3,407, 2,886, 1,639. H
NMR (DMSO-d6, ppm, 400 MHz): d 2.41 (3H, s, CH3), 7.24 (2H, m, CH), 7.29
(2H, m, CH), 7.34–7.39 (2H, m, CH), 7.56 (1H, s, CH), 7.62–7.66 (1H, d, J = 8 Hz,
CH), 7.72–7.76 (1H, d, J = 8 Hz, CH), 7.88–8.05 (3H, m, CH), 8.10–8.21 (1H, dd,
CH), 12.1 (1H, s, NH). 13C NMR (DMSO-d6, ppm, 100 MHz): d 13.4, 116.7, 121.3,
123.1, 124.6, 125.5, 126.2, 2 9 127.6, 2 9 128.2, 3 9 129.3, 130.1, 131.4,
2 9 132.5, 135.8, 137.6, 144.6, 145.1, 148.3, 159.2, 160.1 (NH–C=O). Mol.
formula: C25H17ClN2O requires 396.1029; HRMS: m/z 396.1000 (M?).
3-(6-Chloro-4-phenylquinolin-2-yl)-4-phenylquinolin-2(1H)-one, 5c Color less
1
solid, 89.3 % yield, mp 195–197 °C. IR (KBr, cm-1) t: 3,414, 2,916, 1,641. H
NMR (500 MHz, DMSO-d6, ppm): d 7.10–7.14 (2H, m,CH), 7.23–7.30 (5H, m,
CH), 7.35–7.38 (3H, m, CH), 7.45–7.47 (1H, d, J = 10 Hz, CH), 7.53–7.57 (4H, m,
CH), 7.68 (1H, s, CH), 7.71–7.74 (1H, dd, CH), 7.91–7.93 (1H, d, J = 10 Hz, CH),
12.20 (1H, s, NH). 13C NMR (125 MHz, DMSO-d6): d 115.9, 120.0, 2 9 122.5,
124.0, 125.3, 2 9 127.5, 2 9 128.2, 128.3, 2 9 129.2, 129.4, 129.6, 129.8,
2 9 130.2, 131.3, 131.5, 2 x 131.8, 132.0, 135.7, 136.9, 146.1, 146.4, 150.0,
156.4, 161.3 (NH–C=O). Mol. formula: C30H19ClN2O requires 458.1186; HRMS:
m/z 458.1201 (M?).
6-Chloro-3-(4-methylquinolin-2-yl)-4-phenylquinolin-2(1H)-one, 5d Color less
1
solid, 87.2 % yield, mp 174–176 °C. IR (KBr, cm-1) t: 3,371, 2,827, 1,641. H
NMR (DMSO-d6, ppm, 400 MHz): d 2.23 (3H, s, CH3), 6.91 (2H, m, CH),
7.06–7.08 (1H, d, J = 8 Hz, CH), 7.21 (3H, m, CH), 7.42 (3H, m, CH), 7.59–7.61
(1H, d, J = 8 Hz, CH), 7.79 (2H, m, CH), 8.02 (1H, d, J = 8 Hz, CH), 12.31 (1H, s,
NH). 13C NMR (DMSO-d6, ppm, 100 MHz): d 22.3, 117.1, 121.9, 2 9 122.3,
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R. Subashini et al.
124.6, 3 9 126.3, 2 9 128.1, 128.4, 2 9 129.2, 3 9 129.7, 2 9 133.6, 139.2,
143.3, 145.8, 151.8, 157.9, 161.1 (NH–C=O). Mol. formula: C25H17ClN2O requires
396.1029; HRMS: m/z 396.5001 (M?).
4-Methyl-3-(4-methylquinolin-2-yl)quinolin-2(1H)-one, 5e Colorless solid,
1
83.7 % yield, mp 118–120 °C. IR (KBr, cm-1) t: 3,372, 2,917, 1,642. H NMR
(DMSO-d6, ppm, 400 MHz): d 2.32 (3H, s, CH3), 2.41 (3H, s, CH3), 6.89 (1H, t,
CH), 7.09 (2H, m, CH), 7.16–7.18 (1H, d, J = 8 Hz, CH), 7.59 (3H, m, CH), 7.71
(2H, m, CH), 12.19 (1H, s, NH). 13C NMR (DMSO-d6, ppm, 100 MHz): d 14.8,
26.0, 117.8, 121.7, 2 9 122.3, 124.6, 2 9 126.2, 126.8, 128.2, 2 9 128.6, 129.3,
134.4, 136.7, 144.3, 150.3, 156.8, 160.7 (NH–C=O). Mol. formula: C20H16N2O
requires 300.1263; LC–MS: m/z 301 (M?1).
3-(4-Methylquinolin-2-yl)-4-phenylquinolin-2(1H)-one, 5f Colorless solid,
1
88.6 % yield, mp 196–198 °C. IR (KBr, cm-1) t: 3,341, 2,891, 1,646. H NMR
(400 MHz, DMSO-d6, ppm): d 2.23 (3H, s, CH3), 6.89 (1H, t, J = 8 Hz, CH),
7.12–7.16 (3H, m, CH), 7.26 (4H, m, CH), 7.61–7.63 (1H, d, J = 8 Hz, CH), 7.79
(4H, m, CH), 8.00 (1H, d, J = 8 Hz, CH), 12.21 (1H, s, NH). 13C NMR (DMSO-d6,
ppm, 100 MHz): d 22.9, 118.3, 121.6, 2 9 122.7, 2 9 124.1, 124.8, 3 9 126.3,
127.1, 2 9 128.1, 2 9 129.2, 132.8, 134.1, 136.2, 141.1, 143.4, 146.2, 151.8, 156.2,
161.1 (NH–C=O). Mol. formula: C25H18N2O requires 362.1419; HRMS: m/
z 362.6311 (M?).
6-Chloro-4-phenyl-3-(4-phenylquinolin-2-yl)quinolin-2(1H)-one, 5g Color less
solid, 87 % yield, mp 265–267 °C. IR (KBr, cm-1) t: 3,427, 2,923, 1,644. 1H NMR
(DMSO-d6, ppm, 500 MHz): d 6.99 (1H, d, J = 5 Hz, CH), 7.34–7.36 (2H, m, CH),
7.48–7.57 (5H, m, CH), 7.65 (3H, m, CH), 7.63 (4H, m, CH), 7.69 (1H, t,
J = 10 Hz, CH), 7.76–7.78 (1H, d, J = 10 Hz, CH), 7.90–7.92 (1H, d, J = 10 Hz,
CH), 12.30 (1H, s, NH). 13C NMR (DMSO-d6, ppm, 125 MHz): d 117.9, 121.3,
2 9 124.2, 124.8, 125.4, 2 9 126.1, 126.3, 127.4, 128.5, 3 9 129.0, 2 9 129.2,
2 9 129.7, 129.8, 131.0, 133.2, 2 9 135.1, 137.6, 137.9, 146.2, 148.1, 148.6, 155.1,
161.4 (NH–C=O). Mol. formula: C30H19ClN2O requires 458.1186; HRMS: m/
z 458.1199 (M?).
4-Phenyl-3-(4-phenylquinolin-2-yl)quinolin-2(1H)-one, 5h Colorless solid, 89 %
yield, mp 232–234 °C. IR (KBr, cm-1) t: 3,414, 2,923, 1,641. 1H NMR (DMSO-d6,
ppm, 400 MHz): d 7.09 (4H, m, CH), 7.17–7.19 (1H, d, J = 8 Hz, CH), 7.32 (5H,
m, CH), 7.48 (2H, m, CH), 7.59 (3H, m, CH), 7.68 (1H, d, J = 8 Hz, CH), 7.79 (2H,
m, CH), 8.01 (1H, d, J = 8 Hz, CH), 12.20 (1H, s, NH). 13C NMR (DMSO-d6, ppm,
100 MHz): d 119.2, 2 9 121.4, 122.6, 123.4, 2 9 124.6, 3 9 126.2, 126.8,
2 9 128.1, 128.9, 2 9 129.4, 131.1, 132.4, 2 9 136.3, 2 9 138.1, 140.1,
2 9 142.4, 146.5, 149.7, 151.2, 156.0, 161.6 (NH–C=O). Mol. formula:
C30H20N2O requires 424.1576; HRMS: m/z 424.1602 (M?).
Anti-oxidant property
Radical scavenging activity of compounds against stable DPPH (2,2-diphenyl-2-
picrylhydrayl hydrate) was determined spetrophotometrically. When DPPH reacts
with an antioxidant compound, which can donate hydrogen, it is reduced. The
changes in color (from deep violet to light yellow) were measured at 517 nm on a
123

Synthesis of quinolinyl quinolinones
UV–Vis light spectrophotometer. A solution of DPPH is mixed with that of a
substance that can donate a hydrogen atom and then give rise to the reduced form
with the loss of violet color. The reaction is:
DPPH ꢀ þRH ¼ DPPH þ Rꢀ
Stock solutions were prepared by dissolving 1 mg of compound in 1 ml of
ethanol. Then, different concentrations of the sample, 10, 50, and 100 lg, were
dissolved in 3 ml ethanol. The solution of DPPH in ethanol was prepared just before
UV measurements. Next, 3 ml of the sample and 1 ml of the DPPH solution were
mixed and kept in the dark for 30 min at room temperature, when the decrease in
absorption was measured. For the control absorption, a blank sample containing the
same amount of ethanol and DPPH solution was measured. Ascorbic acid was used
as standard. The experiment was carried out in triplicate. The IC50 value were
calculated for each compound as well as ascorbic acid as standard is represented in
Table 3 (below) and graphically represented in Fig. 1. The scavenging activity
increased with increasing concentrations of the test samples. The IC50 values for
compounds 5a, 5b, 5c, and 5d were 43.22, 48.62, 55.85, and 72.18, respectively,
which were comparatively higher than the IC50 value (39.81) of standard ascorbic
acid. From the results of the DPPH, it demonstrated that all four compounds are
equally effective as antioxidants compared to ascorbic acid. The radical scavenging
activity was calculated by the following formula:
I%ðpercentage inhibitionÞ ¼ ½AB ꢁ AA/ABꢂ ꢃ 100;
where AB is the absorption of the blank sample and AA is the absorption of the
sample
In vitro antibacterial studies
In vitro antibacterial activity was studied by thr agar disc diffusion method. In this
method, a Petri plate containing an agar growth medium was inoculated uniformly
over its entire surface. Paper discs impregnated with various chemotherapeutic agents
are placed on the surface of the agar. During incubation, the chemotherapeutic agent
diffuses from the disc, i.e. from the area of high concentration to the area of lower
concentration. An effective chemotherapeutic agent can inhibit the bacterial growth,
and measurements can be made of the size of the zone of inhibition around the disc.
The concentration of the chemotherapeutic agent at the edge of the zone of
inhibition represents its minimum inhibitory concentration (MIC). In the agar disc
diffusion method, Mueller–Hinton agar was used since it allows chemotherapeutic
agents to diffuse freely.
Pure cultures of the organisms were inoculated onto nutrient broth (Himedia,
India), incubated for 24 h at 37 °C and maintained on respective agar slants at 4 °C.
The cultures used for screening the antibacterial activities were Gram-positive S.
aureus ATCC 700699 and B. subtilis MTCC 430, and Gram-negative E. coli ATCC
11105, Klebsiella ATCC 10273, and P. aeruginosa ATCC 27853 by the agar well
technique. All the compounds were dissolved in 100 % DMSO to obtain
concentrations of 15.6, 31.2, 62.5, 125, 250, 500, 1,000, 5,000, and 10,000 lg/ml.
123

R. Subashini et al.
Standard antibacterial ampicillin was also tested under similar conditions for
comparison. The MIC of all the compounds was determined by the modified agar
well diffusion method. The concentration of test cultures was adjusted to 0.5
McFarland standards by using a spectrophotometer. Test organisms were lawn
cultured on the MHA plates. The agar surface was bored by using a sterilize cork
borer. Then, 100 ll of each dilution was poured into the wells. All test plates were
incubated at 37 °C for 24 h. MIC was noted as the minimum concentration of each
compound which showed a clear zone of inhibition. Experiments were repeated
thrice (Table 4, below).
Results and discussion
The product formation 3a–e (Scheme 1) was confirmed by comparing the literature
melting points. Single crystal for compound ethyl-6-chloro-2-methyl-4-phenylqui-
noline-3-carboxylate, 3a was grown and published [49] (Fig. 3). When the same
reaction was carried out with other catalysts, such as amberlite and acidic alumina,
the reaction did not proceed to the expected product. Optimization of the catalyst,
MK-10, offered maximum yield of 95 % at 100 mg. Reusability of the catalyst was
found to be effective with comparable yield.
Quinolin-2[1H]-ones, 4 [50], readily underwent Friedlander condensation with o-
amino ketones, 1, in the presence of MK-10 under solvent-free condition in
microwave (MW) at a power level of 500 W for the appropriate time (Table 1) to
yield 4-phenyl-3-(4-phenyl quinolin-2-yl)quinolin-2(1H)- ones, 5 (Scheme 2).
Earlier, the reaction was effected with glacial acetic acid and a few drops of conc.
H2SO4 for 8 h on a water bath, but the conversion of the desired product was less.
When 100 mg of the catalyst, MK-10, was used, it led to complete conversion of the
compound, 5, with high yield and purity. After an initial amino-ketone conden-
sation, the intermediate undergoes MK-10 catalyzed cyclocondensation to produce a
quinoline derivative, 5. Selection of the catalyst was carried out using various
catalysts, such as amberlite Na sr1L, bentonite, montmorillonite KSF, amberlite,
acidic alumina, montmorillonite K-10, among which MK-10 gave a very high yield
(Table 2; Fig. 4). The amount of catalyst used was optimized starting from 20, 40,
60, 80, 100, and 140 mg and found to be effective at 100 mg.
1
All the synthesized compounds were confirmed by FTIR, H NMR, 13C NMR,
and mass spectral studies. Compound 5a showed FTIR absorption bands at 3,427,
1,644, and 1,484 cm-1 corresponding to –NH, NH–C = O, and –C = N groups,
respectively, the disappearance of –C = O at 1,707 cm-1 of 4a at C-3, indicates
that the Friedlander annulations have occurred at the acetyl moiety of the
quinolinones, 4.
1H NMR spectrum of 5a revealed a signal at d 12.4 (–NH) as singlet for one
proton.
The aromatic proton appears at d 7.39, 7.91, 7.68, 7.48, and 7.00 gave various
doublets for four aromatic protons, doublet of doublet appears at d 7.72, 7.63, and
7.34 accounts for four aromatic protons, at d 7.53, 7.29, and 7.25 gave multiplet
which accounts for eight aromatic protons of the quinolinylquinolinones compound,
123

Synthesis of quinolinyl quinolinones
Scheme 1 Synthesis of ethyl-6-chloro-2-methyl-4-phenylquinoline-3-carboxylates and 1-(6-Chloro-2-
methyl-4-phenylquinolin-3-yl)ethanone analogues, 3a–e
Fig. 3 Single crystal structure of ethyl-6-chloro-2-methyl-4-phenylquinoline-3 carboxylate, 3a
5a. 13C NMR spectrum showed the signals at d 117.0–156 for 29 aromatic carbons
and at d 161 for the NHC = O. HRMS of the compound, 5a, gave a peak at
492.3667 which matches with the molecular formula C30H18Cl2N2O.
Pharmacology
Anti-oxidant activity
Oxidative stress occurs when the production of free radicals in the body goes
beyond the protective defences, which initiates early stages of cancer and heart
disease. The free radicals are also suspected in the development of arthritis,
Alzheimer’s disease, arthritis, cataracts, diabetes, kidney disease, and age-related
123

R. Subashini et al.
Table 1 Synthesis of quinolin-2-yl-quinolin-2(1H)-ones, 5a–h
Entry
R
R0
R00
R000
Product
Time/yieldb
Conventional
heating h/(%)
MW Irradiation
min/(%)
1
2
3
4
5
6
7
8
a
-Cl
-H
-H
-Cl
-H
-H
-Cl
-H
-C6H5
-CH3
-Cl
-Cl
-Cl
-H
-H
-H
-H
-H
-C6H5
-C6H5
-C6H5
-CH3
-CH3
-CH3
-C6H5
-C6H5
5a
5b
5c
5d
5e
5f
8/66
4/91
8.5/65
9/62
5/87
-C6H5
-C6H5
-CH3
5/89.3
6/87.2
6/83.7
4/88.6
5/87
7/61
8/59
-C6H5
-C6H5
-C6H5
8.5/60
7.5/61
8/58
5g
5h
5.5/89
4 (1 mmol); 1 (1 mmol); MK-10 (100 mg); MW irradiation 500 W, Conventional heating: Gl. AcOH,
Conc. H2SO4
b
Isolated yield
Scheme 2 Synthesis of 4-phenyl-3-(4-phenyl quinolin-2-yl)quinolin-2(1H)-ones, 5
blindness. Antioxidants terminate these chain reactions by removing free radical
intermediates, and inhibit cell death and other oxidation reactions.
In the present study, quinazolinone derivatives were evaluated for their free
radical scavenging activity using the DPPH radical assay. Reduction of DPPH
radicals can be observed by a decrease in absorbance at 517 nm. Different
derivatives of quinazolinone significantly reduced DPPH radicals. Activity of
quinazolinone derivatives was compared with commercial antioxidant ascorbic acid.
2-Thioxo-2, 3-dihydro-1H-quinazolin-4-one had relatively high DPPH radical
scavenging activity. The IC50 value were calculated for each compound as well as
ascorbic acid as standard represented in Table 3 and graphically represented in
Fig. 5. The scavenging activity increased with increasing concentrations of the test
samples. The IC50 values for compounds 5a–h were 48.62, 43.22, 89.25, 93.49,
91.60, 95.52, 55.85, and 72.18, respectively, which were comparatively higher than
the IC50 value (39.81) of standard Ascorbic acid. From the results of DPPH, it
showed that out of eight compounds four compounds namely 5a, 5b, 5g, and 5h are
equally effective as antioxidant compared to standard ascorbic acid.
123

Synthesis of quinolinyl quinolinones
Table 2 Catalyst effect and its amount for the synthesis of quinolin-2-yl-quinolin-2(1H)-onesa, 5
S. no Catalyzed used
Amount
(mg)
Time/min
Yieldb/ %
S. no. MK-10 Time/min Yieldb/ %
(mg)
1
2
3
4
5
6
7
8
a
No catalyst
–
10 h Nil
1
2
3
4
5
6
7
20
40
8
8
8
8
8
4
4
59
64
72
81
93
91
92
AcOH/Conc. H2SO4
Amberlite Na sr1L
Bentonite
Few drops 8 h
66
100
100
100
100
100
30
30
30
20
20
4
Nil
Nil
Nil
40
60
80
Montmorillonite KSF
Amberlite
100
100
120
Acidic alumina
48
Montmorillonite K-10 100
91
1a (1.2 mol), 4a (1 mol), MK-10 (100 mg), MW irradiation 500 W
b
Isolated yield
Fig. 4 Mechanistic pathways for the synthesis of quinolin-2-yl-quinolin-2(1H)-ones, 5
123

R. Subashini et al.
Table 3 Percentage inhibition, IC50 values of standard and 5a–h
S. Conc I %
no lg/ml (Std)
IC50
I %
I %
I %
(5c)
IC50
89.25
I %
I %
(5e)
IC50
91.60
I %
(5f)
IC50
95.52
I %
I %
(5a)
IC50
48.62
(5b)
IC50
43.22
(5d)
IC50
93.49
(5g)
IC50
55.85
(5h)
IC50
72.18
39.81
1.
2.
10
50
26.20
62.78
93.30
15.77
52.40
86.23
18.01
57.84
86.41
10.25
28.01
63.12
9.23
26.74
61.08
10.12
27.29
60.85
8.33
26.17
59.24
13.44
44.76
85.27
10.74
33.05
72.93
3. 100
Fig. 5 Antioxidant activity of Ccompounds 5a–h and standard (ascorbic acid)
Table 4 Determination of minimum inhibition concentration of 5a–h and standard
Test organisms
MIC (lg/mL)
5a
5b
5c
5d
5e
5f
5g
5h
S*
S. aureus
15.62
125
31.25
15.62
31.25
31.25
[200
15.62
31.25
62.5
125
31.62
62.5
125
125
125
[200
31.25
125
31.25
15.62
B. subtilis
E. coli
125
125
[200
15.62
31.25
31.25
15.62
31.25
31.25
15.62
125
15.62
31.25
15.62
[200
[200
15.62
K.pneumonia
P.aeruginosa
62.5
125
15.62
62.5
62.5
125
[200
S* ampicillin
The quinalinone derivatives were also screened successfully for their in vitro
antibacterial studies using agar well diffusion method. All the derivatives were
screened for MIC and data reveals that all the compounds showed antibacterial
activity in good to moderate range in comparison to the standard drug. Compound
5a possess good antibacterial activity and comparable that of standard ampicillin
against S.aureus. Compound 5e shows better MIC than the standard against E.Coli
123

Synthesis of quinolinyl quinolinones
and compound 5b possess comparable activity with that of standard against B.
subtilis. Compound 5h possess good antibacterial activity when compared to all
other derivatives in comparison with that of ampicilin represented in Table 4.
Conclusion
In conclusion, we have reported a facile synthesis of quinolin-2-yl-quinolin-2(1H)-
one derivatives under solvent-free conditions under microwave irradiation, dem-
onstrating the use of montmorillonite K10 as an efficient, rapid, mild, and
inexpensive catalyst. The present procedure has advantages of a simple experi-
mental and product isolation procedure coupled with high purity and yields. The
synthesized compounds were evaluated for in vitro antibacterial and antioxidant
studies. The results showed that all compounds possess antibacterial activity in good
to moderate range when compared to that of standard ampicillin. The quinolinone
derivatives were also screened for antioxidant studies and, from the IC50 values, it
can be concluded that all the four compounds are equally potent as antioxidant and
comparable to that of standard ascorbic acid.
Acknowledgments The authors sincerely thank the management of VIT University, Vellore, Tamil
Nadu, India, for their constant encouragement and support and providing all the necessary facilities for
carrying out this study. The authors wish to express their gratitude to Syngene international limited for
their support of NMR, GCMS facilities to carry this research work.
References
1. P.M.S. Chauhan, S.K. Srivastava, Curr. Med. Chem. 8, 1535–1542 (2001)
2. P.M. Dewick, Medicinal natural products: a biosynthetic approach, 3rd edn. (Wiley, New York,
2009)
3. Peters, W.; Richards, W.H.G. Antimalarial Drugs II; Eds.; Springer: Berlin . Phys. 1984, 8, 311-314
4. Chikhalia, K.H.; Patel, M.J.; Vashi, D.B. Arkivoc. 2008, xiii, 189-197
5. V. Kumar, A. Mahajan, K. Chibale, Bioorg. Med. Chem. 17, 5433–5441 (2009)
6. M.Z. Hoemann, G. Kumaravel, R.L. Xie, R.F. Rossi, S. Meyer, A. Sidhu, G.D. Cuny, J.R. Hauske,
Bioorg. Med. Chem. Lett. 10, 2675–2678 (2000)
7. S. Rossiter, J.M. Peron, P.J. Whitfield, K. Jones, Bioorg. Med. Chem. Lett. 15, 4806–4808 (2005)
8. J.P. Sanchez, J.M. Domagala, S.E. Hagen, C.L. Heifetz, M.P. Hutt, J.B. Nichols, A.K. Trehan, J.
Med. Chem. 31, 983–991 (1988)
9. A.R. Gholap, K.S. Toti, F. Shirazi, R. Kumari, M.K. Bhat, M.V. Deshpande, K.V. Srinivasan, Bioorg.
Med. Chem. 15, 6705–6715 (2007)
10. K. Raynes, M. Foley, L. Tilley, L.W. Deady, Biochem. Pharmacol. 52, 551–559 (1996)
11. Y. Chen, Y. Zhao, C. Lu, C. Tzeng, J.P. Wang, Bioorg. Med. Chem. 14, 4373–4378 (2006)
12. A.H. Abadi, G.H. Hegazy, A.A.E. Zaher, Bioorg. Med. Chem. 13, 5759–5765 (2005)
13. A. Fournet, A.A. Barrios, V. Munoz, R. Hocquemiller, A. Cave, J. Bruneton, Antimicrob. Agents
Chemother. 37, 859–863 (1993)
14. J. Ghosh, V. Swarup, A. Saxena, S. Das, A. Hazra, P. Paira, S. Banerjee, N.B. Mondal, A. Basu, Int.
J. Antimicrob. Agents 32, 349–354 (2008)
15. D. Edmont, R. Rocher, C. Plisson, J. Chenault, Synthesis and evaluation of quinoline carboxygua-
nidines as antidiabetic agents. Bioorg. Med. Chem. Lett. 10, 1831–1834 (2000)
16. R.C. Bernotas, R.R. Singhaus, D.H. Kaufman, J. Ullrich, H. Fletcher, E. Quinet, P. Nambi, R.
Unwalla, A. Wilhelmsson, A.G. Nilsson, M. Farnegardh, Wrobel, J. Bioorg. Med. Chem. 17,
1663–1670 (2009)
123

R. Subashini et al.
17. D.A. Scott, C.L. Balliet, D.J. Cook, A.M. Davies, T.W. Gero, C.A. Omer, S. Poondru, M.E. The-
oclitou, B. Tyurin, M.J. Zinda, Bioorg. Med. Chem. Lett. 19, 697–700 (2009)
18. M.I. Anderson, A.P.J. MacGowan, Antimicrob. Chemoth. 51(S1), 1–11 (2003)
19. H.I. Abd-Alla, M. Shaaban, K.A. Shaaban, N.S. Abu-Gabal, N.M. Shalaby, H. Laatsch, Nat. Pro.
Res. 23, 1035–1049 (2009)
20. K. Goto, K. Yabe, T. Suzuki, T. Jindo, A. Sanbuissho, Toxicology 276, 122–127 (2010)
21. P.M.J. Hawkey, Antimicrob. Chemoth. 51(S1), 29–35 (2003)
22. M. Malik, G. Hoatam, K. Chavda, R.J. Kerns, K. Drlica, Antimicrob. Agents Chemother. 54(1),
149–156 (2010)
23. J. Minville, J. Poulin, C. Dufresne, C.F. Sturino, Tetrahedron. Lett. 49, 3677–3681 (2008)
24. X. Guo, Y.L. Li, Y.F. Liu, H.Y. Gou, Y.C. Wang, Chin. Chem. Lett. 21, 1141–1144 (2010)
25. M. Sachin, A. Choudhary, S. Kumar, G. Avasthi, J. Pharm. Res. 3, 1519–1523 (2010)
26. C.M. Oliphant, G.M. Green, Am. Fam. Phys. 65, 455–464 (2002)
27. M.F. Grundon, Nat. Pro. Rep. 7, 131–138 (1990)
28. J.P. Michael, Nat. Prod. Rep. 25, 166–187 (2007)
29. Jones, G. In comprehensive heterocyclic chemistry II; Katritzky AR, Rees CW, Scriven EFV.Eds.
Pergamon Press: Oxford. 1996, 5, 167-243
30. V.V. Kouznetsov, L.Y.V. Mendez, C.M.M. Gomez, Curr. Org. Chem. 9, 141–161 (2005)
31. A. Kouznetsov, Essentials of medicinal chemistry, 2nd edn. (Wiley, New York, 2008)
32. Cheng, C.C.; Yan, S.J. Inorganic reactions, Dauben WG. Ed. John Wiley & Sons: New York, 1982,
Vol.28, Chapter 2
33. B. Das, K. Damodar, N. Chowdhury, R.A. Kumar, J. Mol. Catal. A 274, 148–152 (2007)
34. X.Y. Zhang, X.S. Fan, J.J. Wang, Y.Z. Li, Chin. Chem. Lett. 15, 1170–1172 (2007)
35. J. Wu, H.G. Xia, K. Gao, Org. Biomol. Chem. 4, 126–129 (2006)
36. M. Dabiri, S. Bashiribod, Molecules 14, 1126–1133 (2009)
37. M.A. Zolfigol, P. Salehi, A. Ghaderi, M. Shiri, Catal. Commun. 8, 1214–1218 (2007)
38. Habibi, D.; Marvi, O.; Arkivoc. 2006, (xiii), 8-15
39. Prabakaran K., Nawaz Khan F., Jin JS (2011). Tetrahedron Lett. 52 (20): 2566-2570
40. K. Prabakaran, P. Manivel, F. Nawaz Khan, Tetrahedron. Lett. 51(33), 4340–4343 (2010)
41. S.M. Roopan, F.R.N. Khan, B.K. Mandal, Tetrahedron. Lett. 51(17), 2309–2311 (2009)
42. S.M. Roopan, F.R.N. Khan, Med. Chem. Res. 20(6), 732–737 (2011)
43. S.M. Roopan, B.R. Reddy, A.S. Kumar, F.N. Khan, Indian J. Heterocy. Ch. 19(1), 81–82 (2009)
44. Y. Isogai, F. Nawaz Khan, N. Asao, Tetrahedron 65(46), 9575–9582 (2009)
45. F.N. Khan, R. Jayakumar, C.N. Pillai, Tetrahedron. Lett. 43(38), 6807–6809 (2002)
46. F.N. Khan, P. Manivel, K. Prabakaran, V.R. Hathwar, S.W. Ng, Acta. Cryst. E. 66(2), o488 (2010)
47. S.M. Roopan, F.R.N. Khan, Chem. Pap. 64(6), 812–817 (2010)
48. Khan FN, Mohana Roopan S, Hathwar V, Ng SW (2009) Acta Cryst E 66(1):o201–o201
49. R. Subashini, F.N. Khan, S. Mittal, V.R. Hathwar, S.W. Ng, Acta. Crys. E65, o2986 (2009)
50. R. Subashini, F.R.N. Khan, Monatsh. Chem. 143, 485–489 (2012)
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