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Abstract: Solvent-free syntheses of quinazolin-4(3H)-ones were performed by reaction ... Published on the NRC Research Press Web site at canjchem.nrc.ca on.
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Solvent-free syntheses of some quinazolin-4(3H)ones derivatives S. Mohana Roopan, T. Maiyalagan, and F. Nawaz Khan

Abstract: Solvent-free syntheses of quinazolin-4(3H)-ones were performed by reaction of anthranillic acid with different amides, such as nicotinamide, benzamide, formamide, etc., on montmorillonite K-10. Products were confirmed by FTIR, 1HNMR, and 13CNMR spectroscopic techniques. All synthesized compounds exhibited antioxidant properties and have been compared with standard antioxidant BHT. Key words: quinazolinone, montmorillonite K-10, solvent-free conditions, antioxidant properties. Résumé : On a réalisé des synthèses sans solvant de quinazolin-4(3H)-ones par réaction de l’acide anthranillique avec divers amides, tel le nicotinamide, le benzamide et le formamide sur de la montmorillonite K-10. Les produits ont été caractérisés par la spectroscopie infrarouge avec transformée de Fourier (IR-TF), et par les méthodes spectroscopiques de RMN du 1H et du 13C. Tous les produits synthétisés présentent une propriété antioxydante et ils ont été comparés avec l’antioxydant standard, BHT. Mots-clés : quinazolinone, montmorrillonite K-10, conditions sans solvant, propriétés antioxydante [Traduit par la Rédaction]

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Introduction The quinazoline ring skeleton is widely found in alkaloids and many biologically active compounds. In general, quinazolones were considered important compounds in the fields of pharmacology and biology (1) because of their wide range of strong biological activities (2–6). Some of these compounds are identified as drugs (7) and as diuretics. Among this class of molecules, quinazolin-4-ones and their derivatives are well-known to possess an array of physiological activities, e.g., antitubercular (8), antifungal (9), antibacterial (10), anti-inflammatory, anticancer (11), and anti-proliferative (5) activities. Quinazolin-4(3H)-one was prepared by many methods (5, 8, 10–13). However, quinazoline derivatives were synthesized mainly by a common approach involving amidation, starting from anthranilic acid, 2-aminobenzonitrile, and 2aminobenzamide. Other methods included the condensation of anthranilic acid, ammonium acetate, and the orthoesters (14), reaction of imidates and anthranilic acid (15), reaction of polymer-bound isothioureas with isatoic anhydride derivatives (16), and were associated with drawbacks such as multistep procedures (17), costly reagents, harse reaction conditions, complex experimental procedures, and low yields (18). Previous methods have been excluded from practical applications because of environmental and economic considerations. Finding an efficient method for the synthesis of quinazolin-4(3H)-one is still a challenge. Nowadays, solvent-free organic reactions have led to experimen-

tally and industrially important organic syntheses that are more effective and eco-friendly than conventional reactions (19, 20). In continuation of our interest in C–C bond-forming reactions (21–25), we have explored a one-pot synthesis of quinazolin-4(3H)-ones (Schemes 1 and 2, Tables 1 and 2) from anthranillic acid and amides, such as formamide, acetamide, benzamide, nicotinamide, etc., in the presence of montmorillonite K-10 catalyst and other inorganic catalysts such as acidic alumina, bentonite, etc., (Table 3), under solvent-free conditions. The above reactions, carried out over montmorillonite K-10 clay, give good yields because of the ditopic nature (26, 27) of montmorillonite K-10 clay. However, the reaction takes less time to complete. The optimization of catalyst amount was also done (Table 4). Thus, we have developed a simple, economical, and environmentally benign synthesis of classical procedures, by avoiding volatile and toxic organic solvents. The reusability of the catalyst in synthesis has also been explored (Table 5). Scope of the reaction (Tables 1 and 2) and antioxidant properties of the reaction products have also been discussed.

Experimental Anthranillic acid and amides used for the reaction were from Sigma-Aldrich Co., and montmorillonite K-10 was obtained from Fluka. The substances were used as provided with no other purification. Melting points were taken in open capillary tubes and are corrected with reference to ben-

Received 17 March 2008. Accepted 29 August 2008. Published on the NRC Research Press Web site at canjchem.nrc.ca on 8 October 2008. S.M. Roopan, T. Maiyalagan,1 and F.N. Khan.1 School of Science and Humanities, Organic Chemistry Division, VIT University, Vellore 632 014, Tamil Nadu, India. 1

Corresponding authors (e-mail: [email protected], [email protected]).

Can. J. Chem. 86: 1019–1025 (2008)

doi:10.1139/V08-149

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Can. J. Chem. Vol. 86, 2008 Table 1. Synthesis of 2-substituted quinazolinone by solvent-free montmorillonite K-10 catalysis.

Scheme 1. Montmorillonite K-10 catalysed reaction of anthranillic acid and different amides.

Scheme 2. Montmorillonite K-10 catalysed reaction of anthranillic acid with urea and thiourea.

zoic acid. IR spectra in KBr pellets were recorded on Nucon infrared spectrophotometer. Nuclear Magnetic Resonance (1H and 13C) spectra were recorded on a Bruker Spectrospin Avance DPX400 Ultrashield (400 MHz) spectrometer. Chemical shifts are reported in parts per million (δ) downfield from an internal tetramethylsilane reference.

General procedure for the synthesis of 2-substituted3H-quinazolin-4-ones and 1H,3H-quinazolin-2,4-diones A mixture of anthranillic acid, 1 amide, 2 or 4a or 4b, and montmorillonite K-10 clay when heated under reflux conditions gave 2-substituted-3H-quinazolin-4-one 3 or 1H,3H-quinazolin-2,4-dione 5 (Scheme 1). After completion © 2008 NRC Canada

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1021 Table 1 (concluded).

Note: 1 = 10 mmol, 2 = 10 mmol, catalyst = 0.1 g. a 3 in isolated yields after column chromatography. b All products were characterized by 1H NMR and IR spectroscopic data and their melting points were compared with literature values (31–32).

of the reaction, ethyl acetate was added to the reaction mixture, and the catalyst was recovered by filtration. Filtrate was washed with a 10% NaHCO3 solution to remove any unreacted acid and further washed with water to remove any inorganic materials. The organic layer was dried, solvent evaporated to obtain the products. FT-IR and NMR spectral techniques were used for product analysis.

Synthesis of 2-pyridin-3-yl-3H-quinazolin-4-one (3a) Anthranillic acid 1 (10 mmol), nicotinamide 2a (10 mmol), and montmorillonite K-10 (0.1 g) were placed in a mortar and mixed well, transferred to a 50 mL roundbottomed flask, and refluxed at 150 °C for 30 min. The reaction was monitored by TLC, and after completion of the reaction, work-up was performed as above to give crude © 2008 NRC Canada

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Can. J. Chem. Vol. 86, 2008 Table 2. Synthesis of quinazolidione by solvent-free montmorillonite K-10 catalysis.

Note: 1 = 10 mmol, 4 = 10 mmol, catalyst = 0.1g. a 5 in isolated yields.

Table 3. Selection of catalyst. Refluxing at 150 °C solvent-free conditions Sl. No.

Catalyst used

Catalyst amount (mg)

Time (h)

Product 3a

1 2 3 4 5

Silica gel Bentonite Montmorillonite KSF Acidic alumina Montmorillonite K10

10 10 10 10 10

4 4 4 4 0.5

Nil Nil Nil Low yield High yield

Note: Anthranilic acid 1 (1 mmol) and nicotinamide 2a (1 mmol).

Table 4. Optimization of catalyst concentration. Refluxing at 150 °C solvent-free conditions Sl. No.

Amide, R RCONH2

Montmorillonite K-10 (g)

Time (h)

Product 3a (R)

Yielda (%)

1 2 3 4 5 6 7 8

-C5H4N -C5H4N -C5H4N -C5H4N -C5H4N -C5H4N -C5H4N -C5H4N

None 0.02 0.04 0.06 0.08 0.1 0.12 0.14

2 1 1 1 0.5 0.5 0.5 0.5

-C5H4N -C5H4N -C5H4N -C5H4N -C5H4N -C5H4N -C5H4N -C5H4N

40 59 67 65 71 85 86 86

Note: 1 = 10 mmol, 2a = 10mmol, refluxed at 150 °C. a 3a in isolated yields.

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Table 5. Life cycle of catalyst. Entry

Cycle No.

Catalyst amount (g)

Yield (%)

1 2 3

Cycle I Cycle II Cycle III

0.1 0.096 0.091

85 82 81

Fig. 1. Time vs. absorbance graph for antioxidant property of quinazolinone derivatives.

product. Pure 2-pyridin-3-yl-3H-quinazolin-4-one 3a was obtained by performing column chromatography using silica gel and petroleum ether/ethyl acetate as eluent. Yield was determined (Table 1, compound 3a). The quinazolinone 3a was recrystallized from petroleum ether and ethyl acetate. The melting point was found to be 114 °C. A similar procedure was followed to obtain other quinazolinone derivatives 3 from different amides 2 (Scheme 1 and Table 1). Products were characterized by FTIR, 1HNMR, 13CNMR, and GCMS spectral techniques, and known compounds were compared with literature reports. The recrystallization of products was effected using petroleum ether and ethyl acetate. Synthesis of 1H,3H-quinazolin-2,4-dione (5a) A mixture of anthranillic acid 1 (10 mmol), urea 4a (10 mmol), and 0.1 g of montmorillonite K-10 was heated under reflux conditions (150 °C) for 2 h. After completion of the reaction, the catalyst was removed by filtration; the mixture was poured into ice-cooled water and extracted with ethyl acetate. The product 5a, obtained after solvent removal, was purified by performing column chromatography using silica gel and petroleum ether/ethyl acetate as eluent (Scheme 2, Table 2). The quinazolindione 5a was recrystallized from petroleum ether and ethyl acetate. The melting point was found to be >300 °C. Synthesis of 2-thioxo-2,3-dihydro-1H-quinazolin-4-one (5b) A mixture of anthranillic acid 1 (10 mmol), thiourea 4b (10 mmol), and 0.1 g of montmorillonite K-10 was heated under reflux conditions (150 °C) for 2 h. After completion of the reaction, the catalyst was removed; the mixture was poured into ice-cooled water and extracted with ethyl acetate. The product 5b, obtained after solvent removal, was purified by column chromatography (Scheme 2, Table 2). The dihydroquinazolinone 5b was recrystallized from ethyl acetate. The melting point was found to be >300 °C. Life cycle of the catalyst The reusability of catalyst was explored by checking the successive runs of the reactions on recycled catalyst; i.e., after first run of the reaction, the catalyst was recovered by a simple filtration from reaction mixture, washed with ethyl acetate, and dried. Then it was utilized in the second run of the reaction. It was noticed that use of recycled catalyst in subsequent experiments gave similar yields (Table 5). Thus, the catalyst is not leached. Free-radical scavenging activity of quinazolinone derivatives Radical scavenging activities are very important due to the deleterious role of free radicals in foods and biological sys-

tems. In this study, the free-radical scavenging activity of quinazolin-4(3H)-ones derivative was measured by a 1,1diphenyl-2-picryl-hydrazyl (DPPH) method. This activity was measured by the following Blos methodology as assessed by Ansari et al. (28). The absorbance of DPPH is monitored at a characteristic wavelength in the presence of a synthesized sample. In its radical form, DPPH absorbs at 517 nm, but upon reduction by an antioxidant or a radical species its absorption decreases. Briefly, a 1.5 × 10–4 mmol/L solution of DPPH in ethanol was prepared and 1 mL of this solution was added to 3 mL of 1.5 × 10–4 mmol/L of quinazolinone in ethanol. At each 5 min interval, absorbance was measured at 517 nm until 30 min. The standard used was butylated hydroxyl toluene (BHT), (1.5 × 10– 4 mmol/L) in ethanol solution. Lower absorbance of reaction mixture indicates higher free-radical scavenging activity. Absorbance of the DPPH (control) is 1.544. The capability to scavenge DPPH radical (28, 29) was calculated using the following equation, DPPH Scavenging effect (%) = [(Acontrol – Asample / Acontrol) * 100] where Acontrol is the absorbance of the DPPH solution and Asample is the absorbance in the presence of quinazolinone. Two different graphs (Figs. 1 and 2) are plotted with time vs. absorbance and time vs. % inhibition.

Results and discussion Solvent-free syntheses of quinazolinone 3a from anthranillic acid 1 and nicotinamide 2a have been explored by using inorganic catalysts such as montmorillonite K-10, silica gel, acidic alumina, etc. (Table 3). Preliminary results indicated the formation of quinazolinone in high yield only in the case of montmorillonite K-10. The optimization of catalyst amount was done to improve the yield (Table 4). Montmorillonite K-10 has had a great impact in organic synthesis and has offered major breakthroughs for the manufacture of fine chemicals. This reagent has advantages over the © 2008 NRC Canada

1024 Fig. 2. Time vs. % inhibition graph for antioxidant property of quinazolinone derivatives.

Can. J. Chem. Vol. 86, 2008

compared with commercial antioxidant butylated hydroxyl toluene (BHT). 2-Thioxo-2,3-dihydro-1H-quinazolin-4-one had relatively high DPPH radical-scavenging activity. As shown in Figs. 1 and 2, all quinazolinone derivatives were found to have the ability to scavenge hydroxyl radical at a concentration of 1.5 × 10–4 mmol/L. Analytical data Data of the new compound 3a and that of a few known compounds, 3b–3d, 5a–5b, which have not been reported earlier are given below. The data of a few compounds that have been found to be identical to those reported (30–32) are given as Supplementary Data available with this paper.2

conventional homogeneous solution techniques: easy set-up and work-up, mild experimental conditions, and high yield. As part of our research, quinazolin-4(3H)-ones were synthesized using K-10 as catalyst (Schemes 1 and 2). The results of the quinazolinones synthesis are summarized (Tables 1– 5). The essence of the catalyst can be understood from the following facts: when anthranillic acid 1 was treated with montmorillonite K-10 under conventional heating in the presence of nicotinamide 2a, the product 3a was obtained in quantitative yield (Table 3, entry 5). When the same reaction was performed without montmorillonite catalyst, 3a was obtained in much lower yield in 2 h (Table 4, entry 1). The reaction optimization with different amounts of montmorillonite K-10 was carried out, and at 0.1 g, the yield was good (Table 4). In the IR spectra of all 4-quinazolinones 3, absorption bands are observed in the region of 1690–1730 (Ar C=O), 1600–1635, 1510–1570, 1460–1500 cm –1 (the quinazolone ring). Assignments of 1H NMR signals of quinazolinones 3 were derived from splitting patterns and characteristic chemical shift values. The data consistently show that the homocyclic proton signal with the lowest field shift in series of compounds is a doublet with additional fine structure due to further meta and para couplings. This signal is assigned to H-5 on the basis of the proximity to the carbonyl group. The assignment of H-5 led to the assignment of H-8 by default. In the same spectral region, the signal for H-2 is found as a singlet. The signals for protons H-6 and H-7 show two ortho couplings. We have assigned the H-7 signal to the lower field. 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 quinazolinones reduced DPPH radicals significantly. The activity of quinazolinone derivatives was 2

2-Pyridin-3-yl-3H-quinazolin-4-one (3a) Colourless solid, mp 114 °C. IR (KBr pellets, cm–1) ν: 3351.67, 1655.03, 1601.16, 1585.32, 1535.27, 1491.45. 1H NMR (300MHz, CDCl3) δ: 9.1 (s, 1H), 8.76–8.75 (d, J = 4.56Hz, 1H), 8.23–8.20 (d, J = 7.77Hz, 1H), 8.13 (s, 1H), 7.66–7.64 (d, 1H), 7.46–7.41 (m, 1H), 7.39–7.36 (d, J = 7.56, 2H), 7.21–7.16 (m, 1H). 13C NMR (100 MHz, CDCl3) δ: 163.92 (C=O), 152.37, 147.82, 137.49, 135.49, 130.86, 129.17, 125.08, 123.73, 120.51. EI-Mass: 223. GC-MS m/z 223 (M+) C13H9N3O (mol. wt. 223.23) calcd.: C 69.95, H 4.06, N 18.82, O 7.17; found: C 69.83, H 4.14, N 18.75, O 7.01. 2-Phenyl-3H-quinazolin-4-one (3b) Mp 242–246 °C (lit. value (32), 242–246 °C). IR (KBr pellets, cm–1) ν: 3342.55, 1654.76, 1437.47. 13C NMR (100MHz, CDCl3) δ: 165.70 (C=O), 137.85, 134.93, 131.78, 129.03, 128.72, 126.95, 124.51, 120.14. C14H10N2O (mol. wt. 222.24) calcd.: C 75.66, H 4.54, N 12.60, O 7.20; found: C 75.54, H 4.46, N 12.52, O 7.11. 2-Methyl-3H-quinazolin-4-one (3c) Mp 240–248 °C (lit. value (32), 238–240 °C). IR (KBr pellets, cm–1) ν: 3295.81, 1666.07, 1434.67. C9H8N2O (mol. wt. 160.17) calcd.: C 67.49, H 5.03, N 17.49, O 9.99; found: C 67.31, H 5.13, N 17.51. 3H-Quinazolin-4-one (3d) White solid, mp 216 °C (lit. value (32), 215–216 °C). IR (KBr pellets, cm–1) ν: 3428.88, 1704.98, 1665.87. 13C NMR (75MHz, CDCl3) δ: 143.34, 134.89, 127.76, 127.42, 126.35. C8H6N2O (mol. wt. 146.15) calcd.: C 65.75, H 4.14, N 19.17, O 10.95; found: C 65.80, H 4.03, N 19.04, O 10.86. (4-Oxo-quinazolin-2yl)-acetonitrile (3e) Colourless solid, mp 240 °C (lit. value (32), 242 °C. C10H7N3O (mol. wt. 185.18) calcd.: C 64.86, H 3.81, N 22.69, O 8.64; found: C 64.74, H 3.91, N 22.57, O, 8.58. 2-(4-Methylphenyl)quinazolin-4(3H)-one (3g) Colourless solid, mp 240 °C (lit. value (31), 239 °C). 13C NMR (75MHz, CDCl3) δ: 159.9, 147.34, 146.20, 134.31, 133.20, 131.58, 128.15, 127.12, 126.35, 125.14, 124.81, 124.13, 122.11, 19.30. GC-MS m/z 236 (M+).

Supplementary data for this article are available on the journal Web site (canjchem.nrc.ca) or may be purchased from the Depository of Unpublished Data, Document Delivery, CISTI, National Research Council Canada, Ottawa, ON K1A 0R6, Canada. DUD 3833. For more information on obtaining material refer to cisti-icist.nrc-cnrc.gc.ca/cms/unpub_e.shtml. © 2008 NRC Canada

Roopan et al.

2-(4-Methoxyphenyl)quinazolin-4(3H)-one (3h) Pale yellow, mp 245–247 °C (lit. value (31), 244 °C). 13C NMR (75MHz, CDCl3) δ: 161.22, 148.33, 146.20, 134.32, 133.20, 131.56, 128.11, 127.10, 126.22, 125.14, 124.81, 124.21, 122.13, 19.31. GC-MS m/z 252 (M+). 2-(4-Chlorophenyl)quinazolin-4(3H)-one (3j) Colourless solid, mp 306–308 °C (lit. value (31), 312 °C). 13 C NMR (75MHz, CDCl3) δ: 160.12, 147.73, 146.64, 136.45, 135.26, 134.66, 132.62, 130.55, 128.33, 127.91, 126.84, 124.14, 122.43, 19.31. GC-MS m/z 240 (M+). 1H,3H-Quinazolin-2,4-dione (5a) Pale yellow solid, mp >300 °C (lit. value (32) >280 °C). IR (KBr pellets, cm–1) ν: 3367.88 (br), 1673.92, 1609.99. C8H6N2O2 (mol. wt. 162.15) calcd.: C 59.26, H 3.73, N 17.28, O 19.73; found: C 59.14, H 3.67, N 17.16, O 19.82. 2-Thioxo-2,3-dihydro-1H-quinazolin-4-one (5b) Colourless solid, mp >300 °C. IR (KBr pellets, cm–1) ν: 3406.32, 3203.67, 3008.42, 1696.52, 1263.87. 1H NMR (400MHz, CDCl3) δ: 7.89 (s, 1H, NH), 7.45–7.44 (d, 1H), 7.43–7.42 (d, 1H), 7.41–7.37(m, 2H) 7.34 (s, 1H, NH). 13C NMR (100MHz, CDCl3) δ: 179.94 (C=S), 137.05, 129.62, 127.15, 125.30. C8H6N2OS (mol. wt. 178.21) calcd.: C 53.92, H 3.39, N 15.72, O 8.98, S 17.99; found: C 53.84, H 3.48, N 15.81, O 8.87, S 17.87.

Conclusion In conclusion, we have reported a facile synthesis of quinazolin-4(3H)-ones under solvent-free conditions and conventional heating, demonstrating the use of montmorillonite K-10 as an efficient, rapid, mild, and inexpensive catalyst. The procedure has the advantages of simplicity and easy product isolation, coupled with high purity and yields.

Acknowledgement The authors wish to express their gratitude to Syngene International Limited for their support of their NMR and GCMS facilities to carry this research work.

References 1. D.J. Brown. In Comprehensive heterocyclic chemistry. Vol. 3. Edited by A.R. Katritzky and C.W Rees. Pergamon Press, Oxford, UK. 1984. p. 57. 2. H. Wamhoff and J. Dzenis. Adv. Heterocyclic. Chem. 55, 129 (1992). 3. S. Sinha and M. Srivastava. Prog. Drug Res. 43, 143 (1994). 4. X. Gao, X. Cai, K. Yan, B. Song, L. Gao, and Z. Chen. Molecules, 12, 2621 (2007).

1025 5. S. Yang, Z. Li, L. Jin, B. Song, G. Liu, J. Chen, Z. Chen, D. Hu, W. Xue, and R. Xu. Bioorg. Med. Chem. Lett. 17, 2193 (2007). 6. J. Bartroli, E. Turmo, M. Alguero, E. Boncompte, M.L. Vericat, L.Conte, J. Ramis, M. Merlos, J.G. Rafanell, and J. Forn. J.Med.Chem. 41, 1869 (1998). 7. B.A. Keay and P.W. Dibble. In Comprehensive Heterocyclic Chemistry. Vol. II. Edited by A.R. Katritzky, C.W. Rees, and E.F.V. Scriven. Pergamon Press, Oxford, UK. 1996. pp. 395– 436. 8. J. Kunes, J. Bazant, M. Pour, K. Waisser, M. Slosarek, and J. Janota. Il Farmaco, 55, 725 (2000). 9. G. Grover and S.G. Kini. Eur. J. Med. Chem. 41, 256 (2006). 10. A.K. Tiwari, V.K. Singh, A. Bajpai, G. Shukla, S. Singh, and A.K. Mishra. Eur. J. Med. Chem. 42, 1234 (2007). 11. P.M. Chandrika, T. Yakaiah, A.R.R. Rao, B. Narsaiah, N.C. Reddy, V. Sridhar, and J.V. Rao. Eur. J. Med. Chem. 43, 846 (2008). 12. D.J. Connolly, D.Cusack, T.P.O. Sullivan, and P.J. Guiry. Tetrahedron, 61, 10153 (2005). 13. G.M. Buckley, N. Davies, H.J. Dyke, P.J. Gilbert, D.R. Hannah, A.F. Haughan, C.A. Hunt, W.R. Pitt, R.H. Profit, N.C. Ray, M.D. Richard, A. Sharpe, A.J. Taylor, J.M. Whitworth, and S.C. Williams. Bioorg. Med. Chem. Lett. 15, 751 (2005). 14. K. Rad-Moghadam and M. Mohseni. J. Chem. Res. Synop. 487 (2003). 15. W. Ried and W. Stephan. Chem. Ber. 96, 1218 (1963). 16. R.Y. Yang and A. Kaplan. Tetrahedron Lett. 41, 7005 (2000). 17. V. Alagarsamy, S. Murugesan, K. Dhanabal, M. Murugan, and E. De Clercq. Indian J. Pharm. Sci. 69, 304 (2007). 18. P. Pannerselvam, R.V. Pradeepchandran, and S.K. Sridhar. Indian J. Pharm. Sci. 65, 268 (2003). 19. R.S. Varma. Green Chem. 1, 43 (1999). 20. R.S. Varma. Clean Prod. Pros. 1, 132 (1999). 21. F. Nawaz Khan, R. Jayakumar, and C. N. Pillai. J. Mol. Catal. A: Chem. 195, 139 (2003). 22. F. Nawaz Khan, R. Jayakumar, and C.N. Pillai. Tetrahedron Lett. 43, 6807 (2002). 23. V.R. Hathwar, P. Manivel, F. Nawaz Khan, and T.N. Guru Row. Acta Crystallogr. Sect. E, 63, o3707 (2007). 24. V.R. Hathwar, P. Manivel, F. Nawaz Khan, and T.N. Guru Row. Acta Crystallogr. Sect. E, 63, o3708 (2007). 25. S. Syed Tajudeen and F. Nawaz Khan. Synth. Commun. 37, 3649 (2007). 26. M.D. Bhor, N.S. Nandurkar, M.J. Bhanushali, and B.M. Bhanage. Ulrasonics Sonochemistry, 15, 195 (2008). 27. M. Kidwai and R. Mohan. J. Chin. Chem. Soc. 47, 1205 (2006). 28. N.M. Ansari, L. Houlihan, B. Hussain, and A. Pieroni. Phytother. Res. 19, 907 (2005). 29. H. Chen, M. Zhang, and B. Xie. J. Agric. Food Chem. 52, 11 (2004). 30. C.A. Jaleel, P. Manivannan, B. Sankar, A. Kishorekumar, R. Gopi, R. Somasundaram, and R. Panneerselvam. Colloids Surf. B Biointerfaces, 60, 201 (2007). 31. T.Mc.C. Paterson, R.K. Smalley, and H. Suschitzky. Synthesis, 187 (1975). 32. F. Li, Y. Feng, Q. Meng, W. Li, Z. Li, Q. Wang, and F. Tao. ARKIVOC, i, 40 (2007).

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