CC BY-NC-ND
0Arabian Journal of Chemistry (2011) xxx, xxx-xxx
King Saud University Arabian Journal of Chemistry
www.ksu.edu.sa www.sciencedirect.com
ORIGINAL ARTICLE
Synthesis, characterization and antimicrobial screening of quinoline based quinazolinone-4-thiazolidinone heterocycles
N.C. Desai *, Amit M. Dodiya
Medicinal Chemistry Laboratory, Department of Chemistry, Mahatma Gandhi Campus, Bhavnagar University, Bhavnagar 364 002, India
Received 10 May 2011; accepted 20 August 2011
KEYWORDS
Antimicrobial activity; 4-(3H)-Quinazolinone; Thiazolidinone; Quinoline derivatives
Abstract In an attempt to find new pharmacologically active molecules, we report here the synthesis and in vitro antimicrobial activity of various 2-(2-chloro-6-methyl(3-quinolyl))-3-[2-(4-chlorophenyl)-4-oxo(3-hydroquinazolin-3-yl)]-5-[(aryl)methylene]-1,3-thiazolidin-4-ones. In vitro antimicrobial activity of the title compounds are screened against two Gram positive bacteria (Staphylococcus aureus, Streptococcus pyogenes), two Gram negative bacteria ( Escherichia coli, Pseudomonas aeruginosa) and three strains of fungi (Candida albicans, Aspergillus niger, Aspergillus clavatus) using broth micro dilution method. Some derivatives bearing chloro or hydroxy group exhibited very good antimicrobial activity.
© 2011 King Saud University. Production and hosting by Elsevier B.V. All rights reserved.
1. Introduction
Quinazoline derivatives represent one of the most active classes of compounds possessing a wide spectrum of biological activity (Apfel et al., 2001). They are widely used in pharmaceuticals and agrochemicals (Tobe et al., 2003); e.g. fluquinco-
* Corresponding author. Tel.: +91 02782439852. E-mail address: dnisheeth@rediffmail.com (N.C. Desai).
1878-5352 © 2011 King Saud University. Production and hosting by Elsevier B.V. All rights reserved.
Peer review under responsibility of King Saud University. doi:10.1016/j.arabjc.2011.08.007
nazole fungicide for the control of agriculture diseases (Guang-Fang et al., 2007). Many reports have been published on the biological activity of quinazoline derivatives, including their bactericidal, herbal and antitumor activity (Raffa et al., 1999; Chenard et al., 2001). Thus, their synthesis has been of great interest in the elaboration of biologically active heterocyclic compounds. Recently, it was reported that some quinazolines exhibited very good antimicrobial activity (Alafeefy, 2008; Desai and Dodiya, 2010). Prompted by these findings, the present paper describes the synthesis of an extension series of 3-substituted-2-phenylquinazolin-4(3H)-one derivatives and testing of their antimicrobial activity.
Quinolines are known to inhibit DNA synthesis by promoting cleavage of bacterial DNA gyrase and type-IV topoisomer-ase, resulting in rapid bacterial death (Hooper and Wolfson, 1989; Hooper, 1995; Hardman et al., 2002). Certain drugs based on quinoline moiety such as doxorubicin and mitoxan-trone have been established as one of the most effective classes
Production and hosting by Elsevier
of anticancer agents in clinical use today with broad application in the treatment of several leukemia and lymphomas as well as in combination chemotherapy of solid tumors (Wakelin and Waring, 1990). The potent anticancer activity as well as toxic effects described for these compounds are normally ascribed, at least, to two main mechanisms: one, which is associated with protein, involves trapping of a protein enzyme-DNA cleavable intermediate, whereas the other, a non-protein-associated mechanism, is related to redox cycling of the quinoline moiety, which produces damaging free-radical species (Murray, 2000).
Similarly, various 4-thiazolidinones (Pan et al., 2010; Youssef et al., 2010) have attracted considerable attention as they are also endowed with a wide range of pharmaceutical activities including anesthetic (Surrey, 1949), anticonvulsant (Troutman and Long, 1948), antibacterial (Sayyed and Mokle, 2006) and antiviral (Rao and Zappala, 2004). Furthermore, drug research and development have led to the discovery of new pharmacologically active agents, including imidoxy compounds such as succinimidoxy (Farror et al., 1993). They also possess a strong anti-convulsant activity (Edafiogho et al., 1991). 4-Thiazolidinones may be considered as phosphate bioisosteres and therefore inhibit the bacterial enzyme MurB which is involved in the biosynthesis of peptidoglycan layer of the cell wall (Gursoy et al., 2005). In
addition, some thiazolidinones were recently reported as novel inhibitors of mycobacterial rhamnose synthetic enzymes (Gursoy et al., 2005). This new approach is believed to be selective, as rhamnose is not found in humans, but is essential for mycobacterial cell wall synthesis in animals (Andres et al., 2000).
Looking to the medicinal importance of 4(3H)-quinazoli-none, 4-thiazolidinone and quinoline, we report here the synthesis of a new class of heterocyclic molecules in which all of these moieties are present and try to develop potential bioactive molecules. The structures of compounds synthesized are assigned on the basis of IR, NMR, 13C NMR and Mass spectral data. These compounds are evaluated for their antimicrobial screening on different strains of bacteria and fungi Scheme 1.
2. Experimental
2.1. Materials and methods
All chemicals are of analytical grade and used directly. Melting points are determined in PMP-DM scientific melting point apparatus and are uncorrected. IR spectra are recorded on a Perkin-Elmer RX 1 FTIR spectrophotometer, using potassium bromide pellets and the frequencies are expressed in cm-1. The 1H NMR and 13C NMR spectra are recorded with a Bruker
N R cr (3)
Sr. No. R' Sr. No. R'
5a -2-C1 5g -2-OH
5b -3-C1 5h -3-OH
5c -4-C1 5i -4-OH
5d -2-NO2 5j -4-CH3
5e -3-NO2 5k -4-OCH3
5f -4-NO2 51 -3,4,5-(OCH3)2
(5a-l)
R = C6H4-C1
R' = Different substituents
Reagents : (a) Pyridine, 0-5°C, (b) Pyridine, NH2NH2.H2O, (c) Ethanol, acetic acid, (d) 1,4-dioxane, thioglycolic acid, anhydrous ZnCl2, (e) Ethanol, sodium ethoxide
Scheme 1 Preparation of compounds 5a-l.
Avance II 400 MHz NMR spectrometer, using tetramethylsil-ane as the internal reference, with dimethylsulfoxide DMSO-d6 as solvent. The chemical shifts are reported in parts per million (ppm). Elemental analysis is performed on a Heraeus Carlo Erba 1180 CHN analyzer. The purity of compounds is confirmed by TLC using Merck silica gel 60 F254 plates using n-hexane/ethyl acetate (7:3) as a mobile phase and spots are visualized under UV radiation. Compound 2-chloro-6-methyl-quinoline-3-carbaldehyde is synthesized by the literature method (Bawa and Suresh, 2009).
2.2. Chemistry
2-(4-Chlorophenyl)-4H-benzo[d][1,3]oxazin-4-one (1) (Eissa, 2007) and 3-amino-2-(4-chlorophenyl)quinazolin-4(3H)-one (2) were synthesized by the literature method (Gao et al., 2007). Reaction conditions were non-homogeneous and the use of an excess amount of hydrazine hydrate did not afford the desired results for procuring the products. When intermediate compound (2) reacted with 2-chloro-6-methylquinoline-
3-carbaldehyde by using catalytic amount of acetic acid in eth-anol, it furnished intermediate (3). Compound (3) reacted with thioglycolic acid by using anhydrous ZnCl2 as a catalyst and 1,4-dioxan as solvent. Due to the chemical transformation of compound (3) it produced compound (4), which possessed
4-thiazolidinone nucleus. When compound (4) reacted with different aromatic aldehydes by using catalytic amount of sodium ethoxide and ethanol as a solvent, it produced final het-erocyclic scaffolds (5a-l).
2.2.1. General procedure for 3-(1Z)-1-aza-[2-(2-chloro-6-methyl(3-quinolyl))vinyl]-2-(4-chlorophenyl)-3-hydroquinaz-olin-4-one (3)
To a solution of intermediate compound-(2) (0.01 mol) in eth-anol (20 ml) and 2-chloro-6-methylquinoline-3-carbaldehyde (0.01 mol) was slowly added to it, in this reaction mixture glacial acetic acid was slowly added as a catalyst. Then reaction mixture was refluxed for 4-5 h, when the Schiff base came out, the excess solvent was distilled off and the separated solid mass filtered and washed with ice-cold methanol, dried and recrystallized in ethanol. Yield 65%, mp 228 0C; IR(KBr, cm-1) v: 3051, 3063 (quinazolinone ring, quinoline ring Ar-H), 3072 (=CH stretching), 2959 (-CH3 stretching), 1467 (-CH3 bending), 1671 (C=O stretching), 1605, 1580 (C=N stretching), 1562-1439 (C=C, quinazolinone ring, quinoline ring, benzene ring), 838 (C-Cl stretching); *H NMR (DMSO): d (ppm): 2.38 (s, 3H, -CH3 group), 8.60 (s, 1H, =CH group), 7.51-9.22 (m, 8H, quinoline & quinazolinone-H), 7.29-7.83 (m, 4H, Ar-H); 13C NMR (DMSO): 21.7, 121.9, 124.1, 126.4, 126.6, 126.7, 126.9, 127.3, 128.1, 129.1, 128.9, 132.5, 133.4, 135.7, 136.6, 137.2, 143.3, 147.7, 148.7, 151.6, 153.6,
165.1, 166.7; GCMS: m/z: 458.07 (M+). Anal. calcd. for C25H16Cl2N4O: C, 65.37; H, 3.51; N, 12.19. Found: C, 65.24; H, 3.55; N, 12.23.
2.2.2. General procedure for 2-(2-chloro-6-methyl(3-quinolyl))-3-[2-(4-chlorophenyl)-4-oxo(3-hydroquinazolin-3-yl))-1,3-thiazolidin-4-one (4)
To a solution of compound (3) (0.01 mol) in 1,4 dioxane (50 ml) was added mercapto acetic acid (0.015mole) with stirring and a little amount of anhydrous ZnCl2 was added. The mixture was refluxed for 10-12 h, after the completion of
reaction, it was cooled and the excess solvent distilled and poured into sodium bicarbonate solution to neutralize it. The solid product was filtered and washed with cold water. The resulting solid was recrystallized in ethanol (99%). Yield 59%, mp 217 0C; IR (KBr, cm-1) v: 3052, 3068 (quinazolinone ring, quinoline ring Ar-H), 2959 (-CH3 stretching), 1467 (-CH3 bending), 1677, 1686 (>C=O stretching), 1609, 1582 (>C=N stretching), 1564-1448 (C=C, quinazolinone ring, quinoline ring, benzene ring), 849 (C-Cl stretching); 1H NMR (DMSO): d (ppm): 2.37 (s, 3H, -CH3 group), 3.853.95 (bs, 2H, CH2 group), 5.92 (s, 1H, S-CH-N), 7.47-8.26 (m, 8H, quinoline & quinazolinone-H), 7.38-7.53 (m, 4H, Ar-H); 13C NMR (DMSO): 21.7, 35.6, 57.4, 120.8, 125.8, 126.2, 126.5, 126.6, 126.7, 127.5, 127.3, 129.2, 128.6, 128.9, 130.8, 131.4, 133.4, 135.2, 135.7, 136.4, 143.4, 148.7, 150.8,
156.2, 160.8, 168.8; GCMS: m/z: 532.08 (M+). Anal. calcd. for C27H18Cl2N4O2S: C, 60.79; H, 3.40; N, 10.50. Found: C, 60.85; H, 3.44; N, 10.52.
2.2.3. General procedure for 2-(2-chloro-6-methyl(3-quinolyl))-3-[2-(4-chlorophenyl)-4-oxo(3-hydroquinazolin-3-yl)]-5-[(aryl)methylene]-1 ,3-thiazolidine-4-ones (5a-l)
A solution of intermediate compound-(4) (0.01 mol) was taken in ethanol (25 ml) and different aromatic aldehydes (0.01 mol) were slowly added to it with constant stirring and catalytic amount of sodium ethoxide (0.01 mol) was added along with it. The reaction mixture was refluxed for 6-7 h, after the completion of the reaction, the final products (5a-l) were obtained and excess amount of solvent was distilled out. The crude product was filtered off and washed with ethanol, dried and recrystallized in ethanol.
2.2.3.1. 2-(2-Chloro-6-methyl(3-quinolyl))-3-[2-(4-chloro-phenyl)-4-oxo-(3-hydroquinazolin-3-yl)]-5-[(2-chlorophenyl)-methylene]-1,3-thiazolidin-4-one (5a). Yield, 70%, yellow crystalline solid, mp 292-293 oc. IR (KBr, cm-1) v: 3057, 3065 (C-H stret., quinazolinone ring, quinoline ring, Ar-H), 3080 (=CH stretching), 2957 (-CH3 stretching), 1675, 1681 (>C=O stretching), 1605, 1589 (C=N stretching), 1568, 1445 (C=C, quinazolinone ring, quinoline ring, aromatic ring), 1464 (-CH3 bending), 845, 832 (C-Cl stretching), 768 (=CH bending), 692 (mono substituted benzene ring); *H NMR (DMSO) d (ppm): 2.34 (s, 3H, -CH3), 5.92 (s, 1H, S-CH-N), 7.47-8.24 (m, 8H, quinoline & quinazolinone-H), 7.35-7.92 (m, 8H, Ar-H), 8.03 (s, 1H, =CH group); 13C NMR (DMSO) d (ppm): 21.7, 63.6, 120.8, 125.2, 125.8, 126.5, 126.6, 126.7, 126.9, 127.3, 127.5, 127.8, 128.9, 129.1,
129.3, 129.9, 130.7, 131.4, 133.0, 133.4, 134.0, 135.6, 135.7,
136.4, 138.3, 143.3, 148.7, 150.8, 156.2, 160.6, 164.4; GCMS: m/z: 654.08 (M+). Anal. calcd. for C34H21Cl3N4O2S: C, 62.25; H, 3.22; N, 8.54. Found: C, 62.28; H, 3.27; N, 8.60.
2.2.3.2. 2-(2-Chloro-6-methyl(3-quinolyl))-3-[2-(4-chloro-phenyl)-4-oxo-(3-hydroquinazolin-3-yl)]-5-[(3-chlorophenyl)-methylene]-1 ,3-thiazolidin-4-one (5b). Yield, 66%, light brown crystalline solid, mp 148-150 oc. IR (KBr, cm-1) v: 3053, 3064 (C-H stret., quinazolinone ring, quinoline ring, Ar-H), 3083 (=CH stretching), 2952 (-CH3 stretching), 1673, 1684 (>C=O stretching), 1607, 1582 (C=N stretching), 1569, 1440 (C=C, quinazolinone ring, quinoline ring, aromatic ring), 1462 (-CH3 bending), 848, 833 (C-Cl stretching), 769 (=CH bending), 688 (mono substituted benzene ring); *H
NMR (DMSO) d (ppm): 2.36 (s, 3H, -CH3), 5.97 (s, 1H, S-CH-N), 7.42-8.24 (m, 8H, quinoline & quinazolinone-H), 7.32-7.82 (m, 8H, Ar-H), 8.08 (s, 1H, =CH group); 13C NMR (DMSO) d (ppm): 21.5, 63.7, 120.7, 125.2, 125.8,
126.4, 126.5, 126.6, 126.7, 127.3, 127.5, 128.0, 128.9, 129.1, 130.3, 130.7, 131.4, 133.4, 134.2, 135.7, 135.6, 136.4, 136.6, 138.3, 143.3, 148.7, 150.7, 156.4, 160.3, 164.6; GCMS: m/z: 654.08 (M+). Anal. calcd. for C34H21Cl3N4O2S: C, 62.25; H, 3.22; N, 8.54. Found: C, 62.29; H, 3.28; N, 8.58.
2.2.3.3. 2-(2-Chloro-6-methyl(3-quinolyl))-3-[2-(4-chloro-phenyl)-4-oxo-(3-hydroquinazolin-3-yl)]-5-[(4-chlorophenyl)-methylene]-1,3-thiazolidin-4-one (5c). Yield, 79%, yellow crystalline solid, mp 244-246 0C. IR (KBr, cm-1) v: 3057, 3065 (C-H stret., quinazolinone ring, quinoline ring. Ar-H), 3085 (=CH stretching), 2957 (-CH3 stretching), 1679, 1686 (>C=O stretching), 1609, 1594 (C=N stretching), 1572, 1450 (C=C, quinazolinone ring, quinoline ring, aromatic ring), 1454 (-CH3 bending), 840, 831 (C-Cl stretching), 761 (=CH bending), 698 (mono substituted benzene ring); *H NMR (DMSO) d (ppm): 2.32 (s, 3H, -CH3), 5.94 (s, 1H, S-CH-N), 7.47-8.21 (m, 8H, quinoline & quinazolinone-H), 7.34-7.88 (m, 8H, Ar-H), 8.05 (s, 1H, =CH group); 13C NMR (DMSO) d (ppm): 21.5, 63.6, 120.6, 125.2, 125.8,
126.5, 126.6, 126.7, 127.3, 127.5, 128.7, 128.9, 129.0, 129.1, 130.7, 131.4, 132.5, 133.3, 133.4, 135.7, 135.6, 136.4, 138.3,
143.3, 148.7, 150.8, 156.1, 160.5, 164.3; GCMS: m/z: 654.08 (M+). Anal. calcd. for C34H21Cl3N4O2S: C, 62.25; H, 3.22; N, 8.54. Found: C, 62.27; H, 3.31; N, 8.61.
2.2.3.4. 2-(2-Chloro-6-methyl(3-quinolyl))-3-[2-(4-chloro-phenyl)-4-oxo-(3-hydroquinazolin-3-yl)]-5-[(2-nitro-phenyl)methylene]-1,3-thiazolidin-4-one (5d). Yield, 63%, light brown crystalline solid, mp 145-147 0C. IR (KBr, cm -1) v: 3054, 3063 (C-H stret., quinazolinone ring, quinoline ring, Ar-H), 3089 (=CH stretching), 2957 (-CH3 stretching), 1674, 1680 (>C=O stretching), 1611, 1583 (C=N stretching), 1555, 1440 (C=C, quinazolinone ring, quinoline ring, aromatic ring), 1456 (-CH3 bending), 848, 836 (C-Cl stretching), 772 (=CH bending), 690 (mono substituted benzene ring); *H NMR (DMSO) d (ppm): 2.35 (s, 3H, -CH3), 5.90 (s, 1H, S-CH-N), 7.40-8.26 (m, 8H, quinoline & quinazolinone-H), 7.28-8.21 (m, 8H, Ar-H), 8.32 (s, 1H, =CH group); 13C NMR (DMSO) d (ppm): 21.8, 63.4, 120.6, 123.7, 125.2, 126.5, 126.6, 127.3, 127.4, 127.5, 128.8, 128.9, 129.1, 130.5,
131.4, 134.7, 135.6, 136.4, 147.7, 126.7, 125.8, 133.4, 135.7, 138.3, 143.3, 148.7, 150.8, 156.4, 160.5, 164.5; GCMS: m/z: 665.07(M+). Anal. calcd. for C34H21Cl2N5O4S: C, 61.26; H, 3.17; N, 10.50. Found: C, 61.29; H, 3.22; N, 10.55.
2.2.3.5. 2-(2-Chloro-6-methyl(3-quinolyl))-3-[2-(4-chloro-phenyl)-4-oxo-(3-hydroquinazolin-3-yl)]-5-[(3-nitrophenyl)-methylene]-1,3-thiazolidin-4-one (5e). Yield, 67%, dark yellow crystalline solid, mp 235-237 oc. IR (KBr, cm-1) v: 3050, 3067 (C-H stret., quinazolinone ring, quinoline ring, Ar-H), 3080 (=CH stretching), 2956 (-CH3 stretching), 1671, 1685 (>C=O stretching), 1604, 1583 (C=N stretching), 1562, 1452 (C=C, quinazolinone ring, quinoline ring, aromatic ring), 1462 (-CH3 bending), 852, 840 (C-Cl stretching), 762 (=CH bending), 690 (mono substituted benzene ring); *H NMR (DMSO) d (ppm): 2.38 (s, 3H, -CH3), 5.95 (s, 1H, S-CH-N), 7.52-8.24 (m, 8H, quinoline & quinazolinone-H),
7.32-8.31 (m, 8H, Ar-H), 8.35 (s, 1H, =CH group); 13C NMR (DMSO) d (ppm): 21.4, 63.8, 120.4, 122.6, 123.1,
125.2, 125.8, 126.5, 126.6, 126.7, 127.3, 127.5, 128.9, 129.1, 129.5, 130.7, 131.4, 133.4, 135.7, 135.6, 134.6, 136.1, 136.4,
138.3, 143.3, 147.8, 148.7, 150.3, 156.0, 160.3, 164.7; GCMS: m/z: 665.07 (M+). Anal. calcd. for C34H21Cl2N5O4S: C, 61.26; H, 3.17; N, 10.50. Found: C, 61.32; H, 3.23; N, 10.56.
2.2.3.6. 2-(2-Chloro-6-methyl(3-quinolyl))-3-[2-(4-chloro-phenyl)-4-oxo-(3-hydroquinazolin-3-yl)]-5-[(4-nitrophenyl)-methylene]-1,3-thiazolidin-4-one (5f). Yield, 70%, light orange crystalline solid, mp 292-293 oc. IR (KBr, cm-1) v: 3056, 3069 (C-H stret., quinazolinone ring, quinoline ring, Ar-H), 3080 (=CH stretching), 2957 (-CH3 stretching), 1671, 1688 (>C=O stretching), 1612, 1592 (C=N stretching), 1562, 1451 (C=C, quinazolinone ring, quinoline ring, aromatic ring), 1458 (-CH3 bending), 844, 832 (C-Cl stretching), 764 (=CH bending), 690 (mono substituted benzene ring); *H NMR (DMSO) d (ppm): 2.32 (s, 3H, -CH3), 5.98 (s, 1H, S-CH-N), 7.55-8.23 (m, 8H, quinoline & quinazolinone-H), 7.37-8.22 (m, 8H, Ar-H), 8.38 (s, 1H, =CH group); 13C NMR (DMSO) d (ppm): 21.4, 63.4, 120.5, 123.6, 125.2, 125.8, 126.5, 126.6, 126.7, 127.3, 127.5, 128.9, 129.0, 129.1, 130.7, 131.4, 133.4, 135.6, 135.7, 136.4, 138.3, 141.3, 143.3,
147.1, 148.7, 150.5, 156.2, 160.8, 164.4; GCMS: m/z: 665.07 (M+). Anal. calcd. for C34H21Cl2N5O4S: C, 61.26; H, 3.17; N, 10.50. Found: C, 61.33; H, 3.24; N, 10.57.
2.2.3.7. 2-(2-Chloro-6-methyl(3-quinolyl) )-3-[2-(4-chloro-phenyl)-4-oxo-(3-hydroquinazolin-3-yl)]-5-[(2-hydroxyphenyl)-methylene]-1,3-thiazolidin-4-one (5g). Yield, 85%, light brown crystalline solid, mp 201-203 oc. IR (KBr, cm-1) v: 3438 (-OH group stretching), 3053, 3069 (C-H stret., quinazolinone ring, quinoline ring, Ar-H), 3086 (=CH stretching), 2957 (-CH3 stretching), 1668, 1684 (>C=O stretching), 1609, 1583 (C=N stretching), 1568, 1445 (C=C, quinazolinone ring, quinoline ring, aromatic ring), 1464 (-CH3 bending), 841, 837 (C-Cl stretching), 769 (=CH bending), 692 (mono substituted benzene ring); 1H NMR (DMSO) d (ppm): 2.37 (s, 3H, -CH3), 5.35 (s, 1H, -OH group), 5.92 (s, 1H, S-CH-N), 6.72-7.60 (m, 8H, Ar-H), 7.51-8.29 (m, 8H, quinoline & quinazolinone-H), 8.08 (s, 1H, =CH group); 13C NMR (DMSO) d (ppm): 21.9, 63.4, 116.2, 117.6, 120.8, 121.2,
125.2, 125.8, 126.5, 126.6, 126.7, 127.3, 127.5, 128.9, 129.1,
129.3, 130.7, 131.4, 133.4, 135.6, 135.7, 136.4, 138.3, 143.3, 148.7, 150.8, 157.5, 156.1, 160.4, 164.0; GCMS: m/z: 636.08 (M+). Anal. calcd. for C34H22Cl2N4O3S: C, 64.05; H, 3.47; N, 8.78. Found: C, 64.09; H, 3.55; N, 8.85.
2.2.3.8. 2-(2-Chloro-6-methyl(3-quinolyl) )-3-[2-(4-chloro-phenyl)-4-oxo-(3-hydroquinazolin-3-yl)]-5-[(3-hydroxyphenyl)-methylene]-1,3-thiazolidin-4-one (5h). Yield, 70%, off yellow crystalline solid, mp 252-253 oc. IR (KBr, cm-1) v: 3432 (-OH group stretching), 3062, 3069 (C-H stret., quinazolinone ring, quinoline ring, Ar-H), 3080 (=CH stretching), 2951 (-CH3 stretching), 1671, 1689 (>C=O stretching), 1608, 1580 (C=N stretching), 1563, 1442 (C=C, quinazolinone ring, quinoline ring, aromatic ring), 1463 (-CH3 bending), 851, 842 (C-Cl stretching), 762 (=CH bending), 699 (mono substituted benzene ring); 1H NMR (DMSO) d (ppm): 2.34 (s, 3H, -CH3), 5.38 (s, 1H, -OH group), 5.95 (s, 1H, S-CH-N), 7.68-8.26 (m, 8H, quinoline&quinazolinone-H),
7.36-8.31 (m, 8H, Ar-H), 8.09 (s, 1H, =CH group); 13C NMR (DMSO) d (ppm): 21.7, 63.6, 112.1, 115.1, 120.8, 121.1, 125.2, 125.8, 126.5, 126.6, 126.7, 127.3, 127.5, 128.9, 129.1, 130.0, 130.7, 131.4, 133.4, 135.6, 135.7, 136.4, 136.6, 138.3, 143.3, 148.7, 150.8, 156.2, 158.4, 160.6, 164.4; GCMS: m/z: 636.08 (M+). Anal. calcd. for C34H22Cl2N4O3S: C, 64.05; H, 3.47; N, 8.78. Found: C, 64.11; H, 3.53; N, 8.84.
quinazolinone-H); 13C NMR (DMSO) d (ppm): 21.6, 55.8, 63.6, 114.2, 120.8, 125.2, 125.8, 126.5, 126.6, 126.7, 127.3, 127.4, 127.5, 128.9, 129.1, 130.0, 130.7, 131.4, 133.4, 135.6, 135.7, 136.4, 138.3, 114.2, 143.3, 148.7, 150.8, 156.2, 159.6, 160.2, 164.2; GCMS: m/z: 650.12 (M+). Anal. calcd. for C35H24Cl2N4O3S: C, 64.51; H, 3.71; N, 8.59. Found: C, 64.56; H, 3.77; N, 8.64.
2.2.3.9. 2-(2-Chloro-6-methyl(3-quinolyl) )-3-[2-( 4-chloro-phenyl)-4-oxo-(3-hydroquinazolin-3-yl) ]-5-[(4-hydroxyphenyl) -methylene]-1,3-thiazolidin-4-one (5i). Yield, 53%, dark brown crystalline solid, mp 263-265 oc. IR (KBr, cm-1) v: 3436 (-OH group stretching), 3056, 3069 (C-H stret., quinazolinone ring, quinoline ring, Ar-H), 3080 (=CH stretching), 1670, 1683 (>C=O stretching), 2956 (-CH3 stretching), 1614, 1590 (C=N stretching), 1560, 1441 (C=C, quinazolinone ring, quinoline ring, aromatic ring), 1462 (-CH3 bending), 846, 835 (C-Cl stretching), 769 (=CH bending), 691 (mono substituted benzene ring); *H NMR (DMSO) d (ppm): 2.36 (s, 3H, -CH3), 5.39 (s, 1H, -OH group), 5.96 (s, 1H, S-CH-N), 7.63-8.27 (m, 9H, quinoline & quinazolinone-H), 7.287.88 (m, 9H, Ar-H), 8.05 (s, 1H, =CH group); 13C NMR (DMSO) d (ppm): 21.4, 63.8, 115.2, 115.9, 120.9, 125.2, 125.8, 126.5, 126.6, 126.7, 127.3, 127.5, 127.8, 130.6, 130.7, 131.4, 133.4, 135.6, 135.7, 136.4, 138.3, 129.1, 128.9, 143.3, 148.7, 150.8, 156.0, 157.3, 160.9, 164.1; GCMS: m/z: 636.08 (M+). Anal. calcd. for C34H22Cl2N4O3S: C, 64.05; H, 3.47; N, 8.78. Found: C, 64.12; H, 3.53; N, 8.83.
2.2.3.12. 2-(2-Chloro-6-methyl(3-quinolyl))-3-[2-(4-chloro-phenyl)-4-oxo-(3-hydroquinazolin-3-yl)]-5-[(3 ,4,5-methoxy-phenyl)methylene]-1,3-thiazolidin-4-one (5l). Yield, 69%, dark brown crystalline solid, mp 189-191 oc. IR (KBr, cm-1) v: 3051, 3062 (quinazolinone ring, quinoline ring, Ar-H), 3080 (=CH stretching), 2942 (-OCH3 stretching), 1671, 1682 (>C=O stretching), 1605, 1585 (C=N stretching), 1566, 1450 (C=C, quinazolinone ring, quinoline ring, aromatic ring), 1461 (-OCH3 bending), 842 (C-Cl stretching), 763 (=CH bending), 694 (mono substituted benzene ring); 1H NMR (DMSO) d (ppm): 2.38 (s, 3H, -CH3), 3.83 (s, 9H, -OCH3 group), 5.96 (s, 1H, S-CH-N), 6.78-7.52 (m, 6H, Ar-H), 7.72 (s, 1H, =CH group), 7.49-8.29 (m, 8H, quinoline & quinazolinone-H); 13C NMR (DMSO) d (ppm): 21.2, 56.2, 60.8, 63.6, 103.8, 120.8, 125.2, 125.8, 126.5, 126.6, 126.7, 127.3, 127.5, 128.9, 129.1, 129.5, 130.7, 131.4, 133.4, 136.4, 135.7, 135.6, 138.3, 138.4, 143.3, 148.7, 150.8, 153.0, 153.4, 156.2, 160.4, 164.7; GCMS: m/z: 710.55 (M+). Anal. calcd. for C37H28Cl2N4O5S: C, 62.45; H, 3.96; N, 7.87. Found: C, 62.51; H, 3.99; N, 7.93.
2.2.3.10. 2-(2-Chloro-6-methyl(3-quinolyl))-3-[2-(4-chloro-phenyl)-4-oxo-(3-hydroquinazolin-3-yl)]-5-[(4-methylphenyl)-methylene]-1 ,3-thiazolidin-4-one (5j). Yield, 74%, off brown crystalline solid, mp 201-203 oc. IR (KBr, cm-1) v: 3054, 3068 (C-H stret., quinazolinone ring, quinoline ring, Ar-H), 3082 (=CH stretching), 1675, 1681 (>C=O stretching), 2950 (-CH3 stretching), 1605, 1589 (C=N stretching), 1567, 1442 (C=C, quinazolinone ring, quinoline ring, aromatic ring), 1460 (-CH3 bending), 846, 839 (C-Cl stretching), 762 (=CH bending), 696 (mono substituted benzene ring); *H NMR (DMSO) d (ppm): 2.34 (s, 6H, -CH3), 2.39 (s, 3H, -CH3 group), 5.91 (s, 1H, S-CH-N), 7.76 (s, 1H, =CH group), 7.47-8.24 (m, 8H, quinoline & quinazolinone-H), 7.18-7.60 (m, 8H, Ar-H); 13C NMR (DMSO) d (ppm): 21.3, 21.7, 63.6,
120.8, 125.2, 125.8, 126.5, 126.6, 126.7, 127.3, 127.5, 128.5,
128.9, 129.1, 130.7, 131.4, 132.2, 133.4, 135.6, 135.7, 136.4, 138.3, 143.3, 148.7, 150.8, 156.2, 157.6, 160.6, 164.4. Anal. calcd. for C35H24Cl2N4O2S: C, 66.14; H, 3.80; N, 8.81; GCMS: m/z: 634.11 (M + ). Found: C, 66.20; H, 3.86; N, 8.87.
2.2.3.11. 2-(2-Chloro-6-methyl(3-quinolyl) )-3-[2-(4-chloro-phenyl)-4-oxo-(3-hydroquinazolin-3-yl)]-5-[(4-methoxyphenyl)-methylene]-1,3-thiazolidin-4-one (5k). Yield, 72%, dark yellow crystalline solid, mp 224-226 oc. IR (KBr, cm-1) v: 3057, 3062 (quinazolinone ring, quinoline ring Ar-H), 3075 (=CH stretching), 2945 (-OCH3 stretching), 1672, 1684 (>C=O stretching), 1605, 1589 (C=N stretching), 1568, 1445 (C=C, quinazolinone ring, quinoline ring, aromatic ring), 1465 (-OCH3 bending), 845, 838 (C-Cl stretching), 763 (=CH bending), 694 (mono substituted benzene ring); *H NMR (DMSO) d (ppm): 2.33 (s, 3H, -CH3), 3.83 (s, 3H, -OCH3 group), 5.94 (s, 1H, S-CH-N), 6.94-7.62 (m, 8H, Ar-H), 7.76 (s, 1H, =CH group), 7.41-8.25 (m, 8H, quinoline &
3. Results and discussion
Characterization of newly synthesized compounds of the series is carried out by IR, NMR and Mass spectra and the data is discussed in the experimental section.
3.1. IR-DATA
IR spectrum of the final compound-5h (molecular formula C34H22Cl2N4O3S, m.w. 636.08, structure and carbon numbering is given in Fig. 1) over the 3062 and 3069 cm-1 ranges showed multiple weak absorption peaks corresponding to Qu-H and Ar-H stretching vibration absorption peaks. The absorption peak at 3080 cm-1 is due to the stretching vibration of the methylene group. The absorption at 2851 cm-1 is due to stretching vibration of the methyl group. The strong absorption at 1689 cm-1 is due to >C=O stretching vibration, which
Figure 1 Carbon numbering of the final compound-5h.
is present in thiazolidine ring at position C-15, while another absorption peak at 1671 cm-1 is due to >C=O stretching vibration in quinazolinone ring, which is present at position C-2. Moderate intensity absorptions at 1608 and 1580 cm-1 correspond to a > C=N- stretching vibration. Absorptions at 1563 and 1442 cm-1 are due to the C=C and skeleton vibrations of aryl and heterocyclic rings. The absorption peak at 1463 cm-1 is due to bending vibration of the methyl group. The broad absorption peak at 3432 cm-1 is observed due to -OH stretching vibration. The absorption peaks at 851 and 842 cm-1 are due to chlorine atoms, which are attached to carbon atom at C-2 and C-15 in thiazolidine and quinazolinone rings. The vibration at 762 cm-1 is due to bending vibration of methylene group. The absorption peaks 699 cm-1 arise due to phenyl-substituted at position-3.
3.2. 1H NMR-DATA
It can be seen from the chemical structure of compound-5h that different pairs of carbons e.g. C-10 and C-14, C-11 and C-13 are attached to chemically equivalent protons. The protons which are attached to C-10 and C-14 appeared at 7.39, while protons which are attached to C-11 and C-13 appeared at 7.52 ppm. The proton attached to C-5 position appeared as a multiplet at d = 7.63 ppm due to mutual coupling with protons attached to C-4 and C-6, while the proton attached to C-6 appeared as a multiplet at d = 7.70 ppm due to mutual coupling with the protons attached to C-5 and C-7. The proton attached to C-4 position appeared as a doublet at d = 8.03 ppm. A single peak that appeared at d = 5.92 ppm must be for the proton attached at C-17 which is present in the thiazolidine ring. A single peak appeared at d = 5.35 ppm of-OH group which is attached to C-31. The proton of the methylene group appeared as a singlet at d = 7.76 ppm. Protons of the phenyl ring (C-30, C-32, C-33 and C-34) appeared between d = 6.70-7.53 ppm, respectively. The protons of the methyl group appeared as a singlet at d = 2.43 ppm. The proton of the C-30 appeared as a singlet at d = 6.70 ppm due to the presence of a hydroxyl group at C-31, while the proton of the C-32 appeared as a doublet at d = 6.83 ppm due to the presence of a hydroxyl group at C-31. The proton attached to C-33 position appeared as a multiplet at d = 7.53 ppm due to mutual coupling with protons attached to C-32 and C-34. Proton of C-25 appeared as a singlet at d = 7.63 ppm due to the presence of methyl group at C-23, while proton of C-22 appeared as a doublet at d = 7.47 ppm due to the presence of methyl group at C-23.
3.3. 13C NMR-DATA
The final compound-5h has quinazolinone ring, quinoline ring and thiazolidine ring. Chemical shifts of final compound carbons vary from d = 164.4 to 21.7 ppm. The carbon nuclei under the influence of a strong electronegative environment appeared downfield, e.g. C-2 and C-15 carbonyl, which are directly linked to the ring nitrogen, have a chemical shift value of d = 160.8 and 164.4 ppm, respectively, whereas C-19 linked to a chlorine atom appeared at d = 150.8 ppm. Carbon C-1 which is attached on both sides to nitrogen atoms appeared at d = 156.2. Carbon of methylene group C-28 appeared at d = 125.2 ppm. Carbon of the methyl group C-24 appeared at d = 21.7 ppm, while carbon C-23, where the methyl group is attached appeared at d = 136.4 ppm. Chemical shift of the
ring carbons at C-3 and C-16 which are affected by the presence of the nearest carbonyl group appeared at d = 120.8 and 138.3 ppm, respectively. Carbons of benzene ring which are attached to quinazolinone ring having equivalent carbons C-10 and C-14 appeared at d = 129.1 ppm, C-11 and C-13 appeared at d = 128.9 ppm respectively, while carbon C-12, which is directly attached with highly electro negative chlorine atom appeared at d = 135.7 ppm. While the carbon atom C-17, which is present in the thiazolidine ring between the nitrogen atom and sulfur atom appeared at d = 63.6 ppm. The carbon C-31 which is directly attached to hydroxyl group appeared at d = 158.4 ppm, the other carbons of this ring (C-29, C-30, C-32, C-33 and C-34) appeared between d = 112.1-136.6 ppm, respectively. The carbons of the quinoline ring (C-18, C-20, C-21, C-22, C-25, C-26 and C-27) appeared between d = 125.8 and 143.4 ppm, respectively. Structure and carbon numbering of compound-5h is described in Fig. 1.
3.4. Antimicrobial activity
Many of the newly synthesized compounds are found to exhibit good to excellent antimicrobial activity. From antimicrobial activity data (Table 1), it is observed that compounds 5c(-4-Cl), 5g(-2-OH) and 5h(-3-OH) are the most active compounds. Data of antibacterial activity reveals that, compounds 5a (-2-Cl), 5d (-2-NO2), 5g (-2-OH) and 5j (-4-CH3) are considered to be good active against Escherichia coli, while compounds 5c (-4-Cl) and 5l (-3,4,5-(OCH3)2) are considered as very good active against E. coli. Similarly when we have taken the -3-OH group as substitution in compound 5h, it shows excellent activity against E. coli. Compounds 5b (-3-Cl), 5c (-4-Cl) and 5i (-4-OH) are considered as good active against Pseudomonas aeruginosa. When we change the substitution in compounds 5h and 5k by 3-hydroxy and 4-methoxy groups, they exhibit very good activity against P. aeruginosa. Compounds 5d (-2-NO2) is considered as good active against Staphylococcus aureus, while compounds 5b (-3-Cl), 5c (-3-Cl), 5f (-4-NO2), 5h (-3-OH), 5i (-4-OH) and 5l (-3,4,5-(OCH3)2) are considered as very good active against S. aureus. When we have replaced -2-OH group as a substitution in compound 5g, it is an excellent active compound against S. aureus. Compounds 5b (-3-Cl), 5h (-3-OH) and 5k (-4-OCH3) are considered as good active against Streptococcus pyogenes, while compound 5i (-4-OH) is considered as very good active against S. pyogenes. For the antifungal activity, we have screened the same compounds which are used for antibacterial activity. Compounds 5a (-2-Cl), 5c (-3-Cl), 5e (-3-NO2), 5g (-2-OH), 5i (-4-OH) and 5k (-4-OCH3) are considered as good active against Candida albicans, while compounds 5b (-3-Cl), 5d (-2-NO2), 5f (-4-NO2) and 5h (-3-OH) are considered as excellent active against C. albicans. Compounds 5c (-3-Cl), 5g (-2-OH), 5i (-4-OH) and 5l (-3,4,5-(OCH3)2) are considered as good active against Aspergillus niger. Compounds 5a (-2-Cl), 5e (-3-NO2) and 5g (-2-OH) are considered as good active against Aspergillus clavatus. Thus we have discussed and compared antibacterial and antifungal activities based on standard drugs ampicillin and griseofulvin, respectively.
3.4.1. Antibacterial activity
For the antibacterial activity, the newly synthesized compounds are screened for their antibacterial activity against Gram positive bacteria S. aureus (MTCC-96) and S. pyogenes
Table 1 Results of antibacterial and antifungal screening of the compounds (5a-l).
Sr. No. -Ar Minimum inhibitory concentration (MIC) lg/ml ± SD Minimum inhibitory concentration (MIC) in lg/ml ± SD
E. coli P. aeruginosa S. aureus S. pyogenes C. albicans A. niger A. clavatus
MTCC 443 MTCC 1688 MTCC 96 MTCC 442 MTCC 227 MTCC 282 MTCC 1323
5a -2-Cl 100 ± 3.56* 250 ± 4.04* 500 ± 4.93* 200 ± 3.46* 500 ± 3.15* 500 ± 3.60* 100 ± 3.05*
5b -3-Cl 250 ± 3.05* 100 ± 3.51* 100 ± 4.72* 100 ± 3.15* 100 ± 4.04* 1000 ± 3.51* 1000 ± 4*
5c -4-Cl 50 ± 4.04* 100 ± 4.50* 100 ± 4.93* 500 ± 4.04* 500 ± 3.21* 100 ± 4.35* 500 ± 3.78*
5d -2-NO2 100 ± 3.78* 125 ± 4* 250 ± 34.04* 500 ± 4.58* 100 ± 4.58* 500 ± 3.78* 500 ± 3.05*
5e -3-NO2 500 ± 3.05* 500 ± 1* 500 ± 3.78* 250 ± 4.08* 500 ± 4.04* 200 ± 4.50* 100 ± 3.60*
5f -4-NO2 250 ± 2.51* 500 ± 3.51* 100 ± 4.04* 500 ± 3.46* 100 ± 4.50* 1000 ± 4.58* 500 ± 4.04*
5g -2-OH 100 ± 3.51* 500 ± 1* 50 ± 4.93* 500 ± 4.58* 500 ± 3.51* 100 ± 4.04* 100 ± 4.04*
5h -3-OH 25 ± 4.04* 50 ± 1.32* 100 ± 4* 100 ± 3.60* 100 ± 3.21* 500 ± 3.05* 200 ±4.16*
5i -4-OH 250 ± 3* 100 ± 4.04* 100 ± 3.78* 50 ± 4.04* 500 ± 3.51* 100 ± 3.51* 500 ± 3*
5j -4-CH3 100 ± 3.21* 500 ±4.16* 500 ± 3.21* 500 ± 3.51* 1000 ± 3.05* 1000 ± 3.05* 1000 ± 4.04*
5k -4-OCH3 500 ± 3.51* 50 ± 2.08* 500 ± 3.21* 100 ± 3.05* 500 ± 3.78* 500 ±4.16* 200 ± 3.05*
51 -3,4,5-(OCH3)3 62.5 ± 3.05* 500 ± 3.60* 100 ± 4.58* 500 ± 3.51* 1000 ± 3.05* 100 ± 4.04* 500 ± 2.51*
Ampicillin 100 ± 1.52* 100 ± 2.08* 250 ± 2.0* 100 ± 1.0* - - -
Griseofulvin - - - - 500 ± 0.57* 100 ± 1* 100 ± 1.15*
SD = Standard deviation.
* p 6 0.0001.
(MTCC-442) and Gram negative E. coli (MTCC-443) and P. aeruginosa (MTCC-1688)]. Antibacterial activity is carried out by serial broth dilution method (Ghalem and Mohamed, 2009; Desai and Trivedi, 1993). The standard strains used for antimicrobial activity were procured from Institute of Microbial Technology, Chandigarh. Compounds (5a-l) are screened for their antibacterial activity in triplicate against E. coli, S. aureus, P. aeruginosa and S. pyogenes at different concentrations of 1000, 500, 200, 100, 50, 25 ig/ml as shown in (Table 1). The drugs which are found to be active in primary screening are similarly diluted to obtain 100, 50, 25, 12.5 ig/ml concentrations. 10 ig/ml suspensions are further inoculated on appropriate media and growth is noted after 24 and 48 h. The lowest concentration, which showed no growth after spot subculture is considered as MIC for each drug. The highest dilution showing at least 99% inhibition is taken as (MIC). The test mixture should contain 108 cells/ml. The standard drug used in the present study is 'ampicillin' for evaluating antibacterial activity which shows (100, 100, 250 and 100 ig/mL) MIC against E. coli, P. aeruginosa, S. aureus and S. pyogenes, respectively. For bacterial growth, in the present protocol, we have used Muller Hinton broth at 37 0C in aerobic condition for 24 h to 48 h.
3.4.2. Antifungal activity
While for the antifungal activity, same compounds are tested for antifungal activity in triplicate against C. albicans, A niger and A. clavatus at various concentrations of 1000, 500, 200 and 100 ig/ml as shown in (Table 1). The results are recorded in the form of primary and secondary screening. Synthesized compounds are diluted at 1000 ig/ml concentration, as a stock solution. Synthesized compounds which are found to be active in this primary screening are further tested in a second set of dilution against all microorganisms. The lowest concentration, which shows no growth after spot subculture is considered as (MIC) for each drug. The highest dilution showing at least 99% inhibition is taken as MIC. The test mixture should contain 108 spores/ml MIC. 'Griseofulvin' is used as a standard drug for antifungal activity, which shows (500, 100 and 100 ig/mL) MIC against C. albicans, A. niger and A. clavatus,
respectively. In the present protocol for fungal growth, we have used Sabourauds dextrose broth at 22 0C in aerobic condition for 72 h. The results of antimicrobial evaluation of derivatives (5a-l) are collected in (Table 1).
3.4.3. Statistical analysis
The standard deviation value is expressed in terms of ±SD. On basis of the calculated value by using ANOVA method, it has been observed that the differences below 0.0001 level (p 6 0.0001) are considered as statistically significant.
4. Conclusion
Some of the newly synthesized compounds exhibited promising antibacterial activity against E. coli, P. aeruginosa, S. aureus and S. pyogenes strains, while antifungal activity against C. albicans, A. niger and A. clavatus strains. Compounds 5g and 5h possess excellent activity against both bacterial and fungal species. It seems that the hydroxy group at ortho and meta position are very significant for enhancing activity against both bacterial and fungal species. Results biological activities of novel quinoline based quinazolinone,4-thiazolidine derivatives are interesting for optimization of lead molecules for further generation of antimicrobial agents.
Acknowledgments
The authors are thankful to the Department of Chemistry, Bhavnagar University, Bhavnagar for providing research facilities. One of authors A.M.D. is thankful to the University Grants Commission, New Delhi for providing UGC-meritori-ous scholarship.
References
Alafeefy, A.M., 2008. Pharm. Biol. 46, 751.
Andres, C.J., Bronson, J.J., D'Andrea, S.V., Deshpande, M.S., Falk, P.J., Grant-Young, K.A., Harte, W.E., 2000. Bioorg. Med. Chem. Lett. 10, 715-717.
Apfel, C., Banner, D.W., Bur, D., Dietz, M., Hubschwerlen, C., Locher, H., Marlin, F., Masciadri, R., 2001. J. Med. Chem. 44, 1847.
Bawa, S., Suresh, K., 2009. Indian J. Chem. 48, 142. Chenard, B.L., Welch, W.M., Blake, J.F., Butler, T.W., Reinhold, A., Ewing, F.E., Menniti, F.S., Pagnozzi, M.J., 2001. J. Med. Chem. 44, 1710.
Desai, N.C., Dodiya, A.M., 2010 (Accepted paper). Med. Chem. Res.
Doi. 10.1007/s00044-011-9621-5. Desai, N.C., Trivedi, P.B., 1993. Indian J. Chem. 33B, 497. Edafiogho, I, O., Scott, K.R., Moore, J.A., Farrar, Y.A., Nicholson,
J.M., 1991. J. Med. Chem. 34, 387. Eissa, A.M.F., 2007. Grasas Y. Aceites 58, 379. Farror, Y.A., Rutkowaka, M.C., Grochowski, J., Serda, P., Pilati, T., Cory, M., Nicholson, J.M., Scott, K.R., 1993. J. Med. Chem. 36, 3517.
Gao, X., Cai, X., Zhuo, Chen., 2007. Molecules 12, 2621. Ghalem, B.R., Mohamed, B., 2009. Afr. J. Pharm. Pharmacol. 3, 92. Guang-Fang, X., Bao-An, S., Pinaki, S.B., Song, Y., Pei-Quan, Z., Lin-Hong, J., Wei, X., De-Yu, H., Ping, L., 2007. Bioorg. Med. Chem. 15, 3768.
Gursoy, A., Otuk, G., Terzioglu, N., 2005. Turk. J. Pharm. Sci. 2, 110.
Hardman, J.G., Limbird, E.L., Molinoff, P.B., Ruddon, R.W., Gilman, A.G., 2002. Goodman & Gilman's The Pharmacological Basis of Therapeutics, ninth ed. McGraw-Hill Publication, p.1065. Hooper, D.C., 1995. Quinolones. In: Mandell, Douglas (Ed.), Bennett's Principles and Practice of Infectious Diseases, forth ed. Churchill Livingstone Inc., New York, p. 364. Hooper, D C., Wolfson, J.S., 1989. Clin. Microbiol. Rev. 2, 378. Murray, V.A., 2000. Academic Press, New York, p. 367. Pan, B., Huang, R.Z., Ying, H.J., 2010. Bioorg. Med. Chem. Lett. 20, 2461.
Raffa, D., Daidone, G., Schillaci, D., Maggio, B., Plescia, F., 1999.
Pharmazie 54, 251. Rao, A., Zappala, M., 2004. Arkivoc v, 147. Sayyed, M., Mokle, S., 2006. Arkivoc ii, 187. Surrey, A.R., 1949. J. Am. Chem. Soc. 71, 3354. Tobe, M., Isobe, Y., Tomizawa, H., Nagasaki, T., Obara, F., Hayashi,
H., 2003. Bioorg. Med. Chem. 11, 609. Troutman, H.D., Long, L.M., 1948. J. Am. Chem. Soc. 70, 3436. Wakelin, I., Waring, M.J., 1990. DNA Intercalating Agents. In: Sammes, P.G. (Ed.), . In: Comprehensive Medicinal Chemistry, vol. 2. Pergamon, Oxford, UK, p. 725. Youssef, A.M., White, M.S., Klegeris, A., 2010. Bioorg. Med. Chem. 20, 2019.
