Table of Contents Author Guidelines Submit a Manuscript
Journal of Chemistry
Volume 2013, Article ID 741953, 9 pages
http://dx.doi.org/10.1155/2013/741953
Research Article

Ultrasonication-Induced Synthesis and Antimicrobial Evaluation of Some Multifluorinated Pyrazolone Derivatives

1P. G. Department of Chemistry and Research Centre, Padmashri Vikhe Patil College, Pravaranagar, Ahmednagar 413713, India
2Department of Chemistry, Radhabai Kale Mahila Mahavidyalaya, Ahmednagar 414001, India

Received 6 June 2012; Revised 6 August 2012; Accepted 28 August 2012

Academic Editor: Qing Li

Copyright © 2013 Anil Gadhave et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

A series of novel fluorine containing pyrazole-pyrazolone (4a–j) and chromone-pyrazolone (5a–i) was synthesized from multifluorinated pyrazolone by the Knoevenagel condensation reaction. All compounds were synthesized by conventional heating as well as ultrasound irradiation technique. It was found that ultrasonication method was more efficient than conventional heating method. The newly synthesized compounds were subjected for in vitro antimicrobial screening against four bacterial pathogens, namely, Staphylococcus aureus, Streptococcus pyogenes, Escherichia coli, and Pseudomonas aeruginosa and three fungal pathogens Candida albicans, Aspergillus niger, and Aspergillus clavatus, using broth microdilution (MIC) method (CLSI guidelines). Among them, some compounds exhibited promising antibacterial activity against the tested strains. All synthesized compounds were characterized by IR, 1H-NMR, mass, and elemental analysis.

1. Introduction

An alarming increment in pathogenic resistance to existing drugs is a serious problem with antimicrobial therapy, and therefore it is very important to search for new class of antimicrobial agents [1]. The introduction of fluorine in organic molecules may lead to significant influence on the biological and physical properties of compounds due to increase of membrane permeability, hydrophobic binding, and stability against metabolic oxidation [2]. As a consequence of key role of fluorine in medicinal chemistry, the interest to incorporate fluorine to prepare biologically active compounds is increased during the past decades. The compounds containing fluorine or trifluoromethyl substituents such as fluoxetine and Prozac are well-known antidepressant drugs (Figure 1). Fluoxetine as well as the related antidepressants functions as selective serotonin reuptake inhibitors (SSRIs).

741953.fig.001
Figure 1

Pyrazolone is a key heterocyclic moiety present in numerous organic compounds because they possess antifungal [3], antibacterial [4, 5], antimycobacterial [6, 7], anti-inflammatory [8, 9], antitumor [10], gastric secretion stimulatory [11], antidepressant [12], and antifilarial [13] activities. They inhibit the production of TNF-α and decrease levels of proinflammatory cytokines and thereby reduce inflammation and prevent further tissue destruction in disease as rheumatoid arthritis, osteoarthritis, and crohns’ disease [1416]. Pyrazolone-containing drugs such as phenazone, propyphenazone, ampyrone, and metamizole are useful antipyretic and analgesic drugs [17], while edaravone (MCI-186) has been used for treating brain [18, 19] and myocardial ischemia [20] (Figure 1).

Pyrazole derivatives are known to possess wide spectrum of biological activities such as antibacterial [2123], antifungal [24, 25], antidiabetic [26], herbicidal [27, 28], and antianxiety [29], and it is present as an active pharmacophore in celecoxib which is a COX-2 inhibitor [30] and sildenafil citrate as cGMP-specific phosphodiesterase type-5 inhibitors [31]. The chromone is an important oxygen containing heterocycle present in numerous naturally occurring compounds exhibiting interesting biological activities such as antiviral [32], anticancer [33], anti-inflammatory [34, 35], and antioxidant [36, 37] activities.

Knoevenagel condensation reaction [38] is an important tool for construction of new carbon-carbon bonds. It is used for synthesis of different pharmaceutical products [39, 40] by using acidic and basic condition. Ultrasonication has increasingly been used for organic synthesis in the last three decades. It has been demonstrated as an alternative energy source for organic reactions ordinarily accomplished by heating. A large number of organic reactions have been carried out in higher yields, shorter reaction time, and milder conditions under ultrasound [4144].

In view of broad spectrum of biological activities associated with pyrazolone, pyrazole, chromone nucleus, high potential of fluorine-containing compounds, and advantageous use of ultrasonication technique and in continuation to our ongoing efforts for search of biologically important heterocycles [4547], it was envisaged to construct a system which combines all these pharmacophores in a single molecular framework to explore the additive effects towards their biological activities. Herein we wish to report green synthesis and antimicrobial evaluation of some multifluorinated pyrazolone derivatives containing pyrazole and chromone nucleus. The general route for synthesis of multifluorinated pyrazolone derivatives is outlined in Scheme 1.

741953.sch.001
Scheme 1: Synthesis of multifluorinated pyrazolone containing pyrazole and chromone.

2. Experimental

2.1. Chemistry

Melting points were taken in open capillaries and are uncorrected. The IR spectra were recorded in KBr on a Shimadzu FTIR 8400 spectrophotometer, and only characteristic peaks are reported in cm−1. The 1H-NMR spectra were recorded in DMSO- on a Bruker Avance spectrometer using TMS as an internal standard at 400 MHz, and chemical shifts are reported in parts per million (ppm). Mass spectra were scanned on a Finnigan mass spectrometer. Elemental analysis was performed on a Perkin-Elmer analyzer. Thin-layer chromatography (TLC, on aluminium plates coated with silica gel 60F254, 0.25 mm thickness, Merck) was used for monitoring the progress of reactions, purity, and homogeneity of the synthesized compounds. UV radiation and iodine were used as the visualizing agents. Experiment under ultrasound irradiation was carried out in ultrasonic cleaner model EN-20U-S manufactured by Enertech Electronics Pvt. Ltd., Mumbai, India, has maximum output of 100 W and 33 KHz operating frequency.

2.2. General Procedure for Synthesis of Pyrazole-Pyrazolone (4a–j) and Chromone-Pyrazolone (5a–i)
2.2.1. Method (A) Conventional Method

Fluorinated pyrazolone 3 (0.001 mole) and 4-formyl pyrazole or 3-formyl chromone (0.001 mole) were taken in 10 mL glacial acetic acid in 50 mL single neck round bottom flask equipped with condensor. The reaction mixture was heated in an oil bath at 100°C till completion of reaction (checked by TLC). After completion of reaction, contents were allowed to cool and then poured into crushed ice. Solid obtained was separated by filtration and purified by recrystallization from acetic acid to get pure compounds. The formation of compounds was confirmed by spectral techniques. The data of synthesized compounds is given in Tables 1 and 2.

tab1
Table 1: Physical data of synthesized pyrazole-pyrazolone (4a–j).
tab2
Table 2: Physical data of synthesized chromone-pyrazolone (5a–i).

2.2.2. Method (B) Ultrasound Method

Fluorinated pyrazolone 3 (0.001 mole) and 4-formyl pyrazole or 3-formyl chromone (0.001 mole) were taken in 10 mL glacial acetic acid in 50 mL round bottom flask. Contents of flask were subjected for ultrasound irradiation for time as shown in Tables 1 and 2, till completion of reaction (checked by TLC). After completion of reaction, contents were poured into crushed ice. Solid obtained was separated by filtration and purified by recrystallization from acetic acid to get pure compounds. The formation of compounds was confirmed by mp, mixed mp, and spectral techniques. The physical data of synthesized compounds is given in Tables 1 and 2.

(4Z)-4-[(1,3-Diphenyl-1H-pyrazol-4-yl)methylene]-5-propyl-2-(2,3,5,6-tetrafluorophenyl)-2,4-dihydro-3H-pyrazol-3-one (4a). Yellow solid; IR ( , cm−1): 1688 (C=O lactum), 1595 (C=C), 1515 (C=N), 1121 (Ar–F); 1H-NMR δ (400 MHz, DMSO- ): 1.01–1.04 (t, 3H, J = 12 Hz), 1.71–1.79 (m, 2H), 2.56–2.60 (t, 2H, J = 16 Hz), 7.13–7.18 (m, 1H, Ar–H), 7.35–7.39 (m, 1H, Ar–H), 7.46–7.51 (m, 2H, Ar–H), 7.54–7.60 (m, 4H, Ar–H), 7.66–7.69 (m, 2H, Ar–H), 7.87–7.90 (m, 2H, one proton Ar–H & one pyrazole proton), 10.16 (s, 1H, olefinic proton); MS: m/z 504 (M+); Anal. Calcd for C28H20F4N4O: C, 66.66; H, 4.00; N, 11.11. Found: C, 66.71; H, 3.92; N, 11.04.

(4Z)-4-{[3-(4-Fluorophenyl)-1-phenyl-1H-pyrazol-4-yl]methylene}-5-propyl-2-(2,3,5,6-tetrafluorophenyl)-2,4-dihydro-3H-pyrazol-3-one (4b). Yellow solid; IR ( , cm−1): 1697 (C=O lactum), 1580 (C=C), 1521 (C=N), 1133 (Ar–F); 1H-NMR δ (400 MHz, DMSO- ): 1.01–1.05 (t, 3H, J = 16 Hz), 1.73–1.79 (m, 2H), 2.56–2.60 (t, 2H, J = 16 Hz), 7.13–7.18 (m, 1H, Ar–H), 7.25–7.29 (m, 2H, Ar–H), 7.36–7.40 (m, 1H, Ar–H), 7.47–7.52 (m, 3H, Ar–H), 7.64–7.68 (m, 2H, Ar–H), 7.86–7.89 (m, 2H, one proton Ar–H & one pyrazole proton), 10.15 (s, 1H, olefinic proton); MS: m/z 522 (M+); Anal. Calcd for C28H19F5N4O: C, 64.37; H, 3.67; N, 10.72. Found: C, 64.50; H, 3.61; N, 10.65.

(4Z)-4-{[3-(4-Methylphenyl)-1-phenyl-1H-pyrazol-4-yl]methylene}-5-propyl-2-(2,3,5,6-tetrafluorophenyl)-2,4-dihydro-3H-pyrazol-3-one (4c). Yellow solid;  IR ( , cm−1): 1693 (C=O lactum), 1597 (C=C), 1505 (C=N), 1114 (Ar–F); 1H-NMR δ (400 MHz, DMSO- ): 0.99–1.03 (t, 3H, J = 16 Hz), 1.72–1.77 (m, 2H), 2.46 (s, 3H, Ar–CH3), 2.56–2.58 (t, 2H, J = 8 Hz), 7.09–7.17 (m, 1H, Ar–H), 7.35–7.38 (m, 3H, Ar–H), 7.44–7.48 (m, 2H, Ar–H), 7.54–7.56 (d, 2H, J = 8 Hz, Ar–H), 7.59 (s, 1H, pyrazole proton), 7.85–7.87 (d, 2H, J = 8 Hz, Ar–H), 10.13 (s, 1H, olefinic proton); MS: m/z 518 (M+); Anal. Calcd for C29H22F4N4O: C, 67.18; H, 4.28; N, 10.81. Found: C, 67.11; H, 4.37; N, 10.89.

(4Z)-4-{[3-(4-Chlorophenyl)-1-phenyl-1H-pyrazol-4-yl]methylene}-5-propyl-2-(2,3,5,6-tetrafluorophenyl)-2,4-dihydro-3H-pyrazol-3-one (4d). Yellow solid; IR ( , cm−1): 1681 (C=O lactum), 1583 (C=C), 1526 (C=N), 1125 (Ar–F); 1H-NMR δ (400 MHz, DMSO- ): 1.02–1.06 (t, 3H, J = 16 Hz), 1.74–1.79 (m, 2H), 2.57–2.60 (t, 2H, J = 12 Hz), 7.13–7.18 (m, 1H, Ar–H), 7.36–7.40 (m, 1H, Ar–H), 7.47–7.52 (m, 3H, Ar–H), 7.54–7.56 (m, 2H, Ar–H), 7.62–7.63 (m, 2H, one proton Ar–H & one pyrazole proton), 7.86–7.88 (m, 2H, Ar–H), 10.16 (s, 1H, olefinic proton); MS: m/z 538 (M+); Anal. Calcd for C28H19ClF4N4O: C, 62.40; H, 3.55; N, 10.40. Found: C, 62.30; H, 3.61; N, 10.35.

(4Z)-4-{[1-Phenyl-3-(2-thienyl)-1H-pyrazol-4-yl]methylene}-5-propyl-2-(2,3,5,6-tetrafluorophenyl)-2,4-dihydro-3H-pyrazol-3-one (4e). Yellow solid; IR ( , cm−1): 1688 (C=O lactum), 1603 (C=C), 1509 (C=N), 1101 (Ar–F); 1H-NMR δ (400 MHz, DMSO- ): 1.05–1.08 (t, 3H, J = 12 Hz), 1.79–1.85 (m, 2H), 2.65–2.68 (t, 2H, J = 12 Hz), 7.13–7.18 (m, 1H, Ar–H), 7.24–7.26 (m, 1H, Ar–H), 7.35–7.38 (m, 1H, Ar–H), 7.45–7.51 (m, 3H, Ar–H), 7.54–7.55 (m, 1H, Ar–H), 7.83 (s, 1H, pyrazole proton), 7.86–7.88 (m, 2H, Ar–H), 10.16 (s, 1H, olefinic proton); MS: m/z 510 (M+); Anal. Calcd for C26H18F4N4OS: C, 61.17; H, 3.55; N, 10.97. Found: C, 61.29; H, 3.49; N, 10.85.

(4Z)-4-[(1,3-Diphenyl-1H-pyrazol-4-yl)methylene]-2-(2,3,5,6-tetrafluorophenyl)-5-(trifluoromethyl)-2,4-dihydro-3H-pyrazol-3-one (4f). Yellow solid; IR ( , cm−1): 1701 (C=O lactum), 1591 (C=C), 1515 (C=N), 1112 (Ar–F); 1H-NMR δ (400 MHz, DMSO- ): 7.20 (s, 1H, Ar–H), 7.41–7.44 (m, 1H, Ar–H), 7.46–7.57 (m, 5H, Ar–H), 7.76 (s, 2H, Ar–H), 7.81–7.92 (m, 2H, Ar–H), 7.99 (s, 1H, pyrazole proton), 10.23 (s, 1H, olefinic proton); MS: 530 (M+); Anal. Calcd for C26H13F7N4O: C, 58.88; H, 2.47; N, 10.56. Found: C, 58.80; H, 2.51; N, 10.50.

(4Z)-4-{[3-(4-Fluorophenyl)-1-phenyl-1H-pyrazol-4-yl]methylene}-2-(2,3,5,6-tetrafluorophenyl)-5-(trifluoromethyl)-2,4-dihydro-3H-pyrazol-3-one (4g). Yellow solid; IR ( , cm−1): 1691 (C=O lactum), 1609 (C=C), 1522 (C=N), 1130 (Ar–F); 1H-NMR δ (400 MHz, DMSO- ): 7.27–7.31 (m, 3H, Ar–H), 7.42–7.52 (m, 3H, Ar–H), 7.66 (s, 2H, Ar–H), 7.88–7.91 (m, 3H, two proton Ar–H & one pyrazole proton), 10.22 (s, 1H, olefinic proton); MS: 548 (M+); Anal. Calcd for C26H12F8N4O: C, 56.94; H, 2.21; N, 10.22. Found: C, 56.90; H, 2.30; N, 10.28.

(4Z)-4-{[3-(4-Methylphenyl)-1-phenyl-1H-pyrazol-4-yl]methylene}-2-(2,3,5,6-tetrafluorophenyl)-5-(trifluoromethyl)-2,4-dihydro-3H-pyrazol-3-one (4h). Yellow solid; IR ( , cm−1): 1708 (C=O lactum), 1600 (C=C), 1510 (C=N), 1122 (Ar–F); 1H-NMR δ (400 MHz, DMSO- ): 2.46 (s, 3H, Ar–CH3), 7.19–7.21 (m, 1H, Ar–H), 7.35–7.40 (m, 3H, Ar–H), 7.47–7.50 (m, 2H, Ar–H), 7.54–7.56 (d, 2H, J = 8 Hz, Ar–H), 7.87–7.89 (d, 2H, J = 8 Hz, Ar–H), 7.99 (s, 1H, pyrazole proton), 10.20 (s, 1H, olefinic proton); MS: m/z 544 (M+); Anal. Calcd for C27H15F7N4O: C, 59.57; H, 2.78; N, 10.29. Found: C, 59.65; H, 2.70; N, 10.20.

(4Z)-4-{[3-(4-Chlorophenyl)-1-phenyl-1H-pyrazol-4-yl]methylene}-2-(2,3,5,6-tetrafluorophenyl)-5-(trifluoromethyl)-2,4-dihydro-3H-pyrazol-3-one (4i). Yellow solid; IR ( , cm−1): 1711 (C=O lactum), 1599 (C=C), 1501 (C=N), 1109 (Ar–F); 1H-NMR δ (400 MHz, DMSO- ): 7.26 (s, 1H, Ar–H), 7.42–7.61 (m, 7H, Ar–H), 7.87–7.91 (m, 3H, two proton Ar–H & one pyrazole proton), 10.23 (s, 1H, olefinic proton); MS: m/z 564 (M+), Anal. Calcd for C26H12ClF7N4O: C, 55.29; H, 2.14; N, 9.92. Found: C, 55.21; H, 2.20; N, 9.81.

(4Z)-4-{[1-Phenyl-3-(2-thienyl)-1H-pyrazol-4-yl]methylene}-2-(2,3,5,6-tetrafluorophenyl)-5-(trifluoromethyl)-2,4-dihydro-3H-pyrazol-3-one (4j). Yellow solid; IR ( , cm−1): 1701 (C=O lactum), 1605 (C=C), 1505 (C=N), 1116 (Ar–F); 1H-NMR δ (400 MHz, DMSO- ): 7.22 (s, 1H, Ar–H), 7.41–7.56 (m, 6H, Ar–H), 7.85–7.89 (m, 2H, Ar–H), 8.22 (s, 1H, pyrazole proton), 10.20 (s, 1H, olefinic proton); MS: m/z 536 (M+); Anal. Calcd for C24H11F7N4OS: C, 53.74; H, 2.07; N, 10.44. Found: C, 53.69; H, 2.10; N, 10.55.

(4Z)-4-[(4-Oxo-4H-chromen-3-yl)methylene]-5-propyl-2-(2,3,5,6-tetrafluorophenyl)-2,4-dihydro-3H-pyrazol-3-one (5a). Yellow solid; IR ( , cm−1): 1700 (C=O lactum), 1659 (C=O chromone), 1623 (C=C), 1599 (C=N), 1129 (Ar–F); 1H-NMR δ (400 MHz, DMSO- ): 0.99–1.02 (t, 3H, J = 12 Hz), 1.69–1.75 (m, 2H), 2.71–2.74 (t, 2H, J = 12 Hz), 7.59–7.63 (m, 1H, Ar–H), 7.79–7.81 (d, 1H, J = 8 Hz, Ar–H), 7.90–7.94 (m, 1H, Ar–H), 8.05 (s, 1H, Ar–H), 8.11–8.19 (m, 2H, Ar–H), 10.35 (s, 1H, olefinic proton); MS: m/z 430 (M+); Anal. Calcd for C22H14F4N2O3: C, 61.40; H, 3.28; N, 6.51. Found: C, 61.31; H, 3.22; N, 6.61.

(4Z)-4-[(6-Methyl-4-oxo-4H-chromen-3-yl)methylene]-5-propyl-2-(2,3,5,6-tetrafluorophenyl)-2,4-dihydro-3H-pyrazol-3-one (5b). Yellow solid; IR ( , cm−1): 1694 (C=O lactum), 1669 (C=O chromone), 1627 (C=C), 1588 (C=N), 1140 (Ar–F); 1H-NMR δ (400 MHz, DMSO- ): 0.97–1.01 (t, 3H, J = 16 Hz), 1.68–1.73 (m, 2H), 2.45 (s, 3H, Ar–CH3), 2.69–2.72 (t, 2H, J = 12 Hz), 7.66–7.72 (m, 2H, Ar–H), 7.95 (s, 1H, Ar–H), 8.03 (s, 1H, Ar–H), 8.07–8.11 (m, 1H, Ar–H), 10.35 (s, 1H, olefinic proton); MS: m/z 444 (M+); Anal. Calcd for C23H16F4N2O3: C, 62.16; H, 3.63; N, 6.30. Found: C, 62.24; H, 3.59; N, 6.23.

(4Z)-4-[(6,8-Dichloro-4-oxo-4H-chromen-3-yl)methylene]-5-propyl-2-(2,3,5,6-tetrafluorophenyl)-2,4-dihydro-3H-pyrazol-3-one (5c). Yellow solid; IR ( , cm−1): 1707 (C=O lactum), 1659 (C=O chromone), 1624 (C=C), 1577 (C=N), 1126 (Ar–F); 1H-NMR δ (400 MHz, DMSO- ): 1.03–1.07 (t, 3H, J = 12 Hz), 1.77–1.82 (m, 2H), 2.68–2.71 (t, 2H, J = 12 Hz), 7.10–7.16 (m, 1H, Ar–H), 7.77 (s, 1H, Ar–H), 7.99 (s, 1H, Ar–H), 8.13 (s, 1H, Ar–H), 10.66 (s, 1H, olefinic proton); MS: m/z 449 (M+); Anal. Calcd for C22H12Cl2F4N2O3: C, 52.93; H, 2.42; N, 5.61. Found: C, 52.86; H, 2.47; N, 5.70.

(4Z)-4-[(6-Chloro-4-oxo-4H-chromen-3-yl)methylene]-5-propyl-2-(2,3,5,6-tetrafluorophenyl)-2,4-dihydro-3H-pyrazol-3-one (5d). Yellow solid; IR ( , cm−1): 1695 (C=O lactum), 1655 (C=O chromone), 1605 (C=C), 1580 (C=N), 1119 (Ar–F); 1H-NMR δ (400 MHz, DMSO- ): 1.06–1.09 (t, 3H, J = 12 Hz), 1.79–1.85 (m, 2H), 2.71–2.74 (t, 2H, J = 12 Hz), 7.14–7.19 (m, 1H, Ar–H), 7.52–7.54 (d, 1H, J = 8 Hz, Ar–H), 7.69–7.72 (m, 1H, Ar–H), 8.08 (s, 1H, Ar–H), 8.25–8.26 (d, 1H, J = 4 Hz, Ar–H), 10.65 (s, 1H, olefinic proton); MS: m/z 464 (M+); Anal. Calcd for C22H13ClF4N2O3: C, 56.85; H, 2.82; N, 6.03. Found: C, 56.78; H, 2.87; N, 6.11.

(4Z)-4-[(6-Chloro-7-methyl-4-oxo-4H-chromen-3-yl)methylene]-5-propyl-2-(2,3,5,6-tetrafluorophenyl)-2,4-dihydro-3H-pyrazol-3-one (5e). Yellow solid; IR ( , cm−1): 1711 (C=O lactum), 1649 (C=O chromone), 1630 (C=C), 1588 (C=N), 1135 (Ar–F); 1H-NMR δ (400 MHz, DMSO- ): 1.05–1.09 (t, 3H, J = 16 Hz), 1.79–1.84 (m, 2H), 2.53 (s, 3H, Ar–CH3), 2.70–2.74 (t, 2H, J = 16 Hz), 7.14–7.18 (m, 1H, Ar–H), 7.45 (s, 1H, Ar–H), 8.09 (s, 1H, Ar–H), 8.24 (s, 1H, Ar–H), 10.63 (s, 1H, olefinic proton); MS: m/z 478 (M+); Anal. Calcd for C23H15ClF4N2O3: C, 57.69; H, 3.16; N, 5.85. Found: C, 57.60; H, 3.29; N, 5.89.

(4Z)-4-[(4-Oxo-4H-chromen-3-yl)methylene]-2-(2,3,5,6-tetrafluorophenyl)-5-(trifluoromethyl)-2,4-dihydro-3H-pyrazol-3-one (5f). Yellow solid; IR ( , cm−1): 1699 (C=O lactum), 1655 (C=O chromone), 1625 (C=C), 1596 (C=N), 1133 (Ar–F); 1H-NMR δ (400 MHz, DMSO- ): 7.52–7.60 (m, 3H, Ar–H), 7.77–7.82 (m, 1H, Ar–H), 8.30–8.33 (d, 1H, J = 8 Hz, Ar–H), 8.53 (s, 1H, Ar–H), 10.69 (s, 1H, olefinic proton); MS: m/z 456 (M+); Anal. Calcd for C20H7F7N2O3: C, 52.65; H, 1.55; N, 6.14. Found: C, 52.53; H, 1.46; N, 6.08.

(4Z)-4-[(6-Methyl-4-oxo-4H-chromen-3-yl)methylene]-2-(2,3,5,6-tetrafluorophenyl)-5-(trifluoromethyl)-2,4-dihydro-3H-pyrazol-3-one (5g). Yellow solid; IR ( , cm−1): 1705 (C=O lactum), 1662 (C=O chromone), 1620 (C=C), 1593 (C=N), 1141 (Ar–F); 1H-NMR δ (400 MHz, DMSO- ): 2.48 (s, 3H, Ar–CH3), 7.20–7.23 (m, 2H, Ar–H), 7.44–7.46 (d, 1H, J = 8 Hz, Ar–H), 8.06 (s, 1H, Ar–H), 8.51 (s, 1H, Ar–H), 10.64 (s, 1H, olefinic proton); MS: m/z 470 (M+); Anal. Calcd for C21H9F7N2O3: C, 53.63; H, 1.93; N, 5.96. Found: C, 53.53; H, 1.89; N, 5.90.

(4Z)-4-[(6,8-Dichloro-4-oxo-4H-chromen-3-yl)methylene]-2-(2,3,5,6-tetrafluorophenyl)-5-(trifluoromethyl)-2,4-dihydro-3H-pyrazol-3-one (5h). Yellow solid; IR ( , cm−1): 1711 (C=O lactum), 1677 (C=O chromone), 1622 (C=C), 1599 (C=N), 1135 (Ar–F); 1H-NMR δ (400 MHz, DMSO- ): 7.52–7.57 (m, 1H, Ar–H), 7.69–7.71 (m, 1H, Ar–H), 8.01 (s, 1H, Ar–H), 8.40 (s, 1H, Ar–H), 10.59 (s, 1H, olefinic proton); MS: m/z 525 (M+); Anal. Calcd for C20H5Cl2F7N2O3: C, 45.74; H, 0.96; N, 5.33. Found: C, 45.61; H, 0.88; N, 5.41.

(4Z)-4-[(6-Chloro-4-oxo-4H-chromen-3-yl)methylene]-2-(2,3,5,6-tetrafluorophenyl)-5-(trifluoromethyl)-2,4-dihydro-3H-pyrazol-3-one (5i). Yellow solid;IR ( , cm−1): 1695 (C=O lactum), 1671 (C=O chromone), 1611 (C=C), 1580 (C=N), 1109 (Ar–F); 1H-NMR δ (400 MHz, DMSO-d6): 7.54–7.56 (m, 2H, Ar–H), 7.72–7.74 (d, 1H, J = 8 Hz, Ar–H), 8.26 (s, 1H, Ar–H), 8.46 (s, 1H, Ar–H), 10.66 (s, 1H, olefinic proton); MS: m/z 490 (M+); Anal. Calcd for C20H6ClF7N2O3: C, 48.95; H, 1.23; N, 5.71. Found: C, 48.90; H, 1.12; N, 5.64.

2.3. Antimicrobial Activity

The antimicrobial activity of all newly synthesized compounds was evaluated by broth microdilution method according to Clinical and Laboratory Standards Institute (CLSI 2005, formerly known as NCCLS) [48]. The results were determined using minimum inhibitory concentration (MIC) values in μg/mL. Antibacterial activity was screened against two Gram-positive (Staphylococcus aureus MTCC 96 and Streptococcus pyogenes MTCC 443) and two Gram-negative (Escherichia coli MTCC 442 and Pseudomonas aeruginosa MTCC 441) bacterial strains using ampicillin as a standard antibacterial agent. Antifungal activity was screened against three fungal species (Candida albicans MTCC 227, Aspergillus niger MTCC 282, and Aspergillus clavatus MTCC 1323) where griseofulvin was used as a standard antifungal agent. All MTCC cultures were collected from Institute of Microbial Technology, Chandigarh.

Sterile 96-well microtiter plates were used in this assay. All tests were performed in Mueller Hinton broth for bacterial strains and Sabouraud’s dextrose broth for fungal strains. Overnight broth cultures of each strain were prepared, and the final inoculum concentration in each well was adjusted to 2 × 106 CFU mL−1 for the bacterial strains and 2 × 107 CFU mL−1 for fungal strains. The inoculum concentration was adjusted by diluting broth culture supernatant in sterile distilled water to a density of 0.5 McFarland standards using a nephelometer. Stock solutions of all compounds at 2000 μg/mL were prepared by dissolving them in DMSO. Serial dilutions were prepared in primary and secondary screening. In primary screening, 500, 250, and 200 μg/mL concentrations of the synthesized compounds were taken. The compounds found active in primary screening were further tested in a second set of dilutions against all microorganisms. The compounds found active in primary screening were similarly diluted to obtain 100, 62.5, 50, and 25 μg/mL concentrations. In the tests, triphenyltetrazolium chloride (TTC) was also added to culture medium as growth indicator. The final concentration of TTC after inoculation was 0.05%. The microbial growth was determined after 24 h incubation at 37°C for the bacteria and at 25°C after 48 h for the fungi. The MIC is defined as the lowest concentration of a compound at which the microorganism does not demonstrate visible growth. All determinations were performed in duplicate to check the accuracy of results. The antimicrobial activity results (MIC) are presented in Table 3.

tab3
Table 3: Antibacterial and antifungal data of newly synthesized pyrazole-pyrazolone (4a–j) and chromone-pyrazolone (5a–i) indicated by MIC values ( g/mL).

3. Result and Discussion

3.1. Chemistry

In the present investigation, our aim was to do the synthesis of multifluorinated pyrazole-pyrazolone (4) and chromone-pyrazolone (5) by using green technique such as ultrasonication and investigate their antibacterial and antifungal activities (Scheme 1). The starting material multifluorinated pyrazolone (3) was prepared by literature known procedure [49] using β-ketoester (1) and 2,3,5,6-tetra-fluoro phenyl hydrazine (2). The pyrazolone (3) was treated with 3-formyl chromone or 4-formyl pyrazole in acetic acid under conventional heating as well as ultrasound irradiation to give pyrazole-pyrazolone (4) and chromone-pyrazolone (5). The structures of all compounds were confirmed on the basis of spectral analysis. The IR spectra of compounds 4 and 5 showed a peak in the range 1680–1711 cm−1 for C=O stretching of five membered lactum ring. They also exhibited a peak in the range 1500–1600 cm−1 for C=N stretching. The 1H-NMR spectra of compounds 4ae and 5ae clearly showed peaks for CH3–CH2–CH2–(propyl group) protons, while such peaks were absent in compounds 4fj and 5fi as they have no propyl group. The exocyclic methylene group proton appeared as a singlet in the range of 10.11–10.66 δ. The aromatic protons present in all compounds were also confirmed by 1H-NMR spectra. Further the structures of all compounds were also confirmed by molecular ion peak in their mass spectra. For all the synthesized compounds, elemental analysis values are in good agreement with theoretical data.

It was observed that ultrasound irradiation method was practically more superior than conventional heating method in terms of higher yields, rapid, and environmentally benign process which makes this protocol more useful.

3.2. Antimicrobial Activity

Antibacterial activity was screened against Staphylococcus aureus, Streptococcus pyogenes, Escherichia coli, and Pseudomonas aeruginosa bacterial strains using ampicillin as a standard antibacterial agent. Antifungal activity was screened against fungal species Candida albicans, Aspergillus niger, and Aspergillus clavatus where griseofulvin was used as a standard antifungal agent.

Reviewing the antibacterial activity data (Table 1) of all newly synthesized pyrazole-pyrazolone (4aj) and chromone-pyrazolone (5ai), it was revealed that the compounds (4b, 4d), (5i), (5f), and (4e, 5b) showed highest activity, that is, 62.5 μg/mL against E. coli, P. aeruginosa, S. aureus, and S. pyogenes, respectively. Among pyrazole-pyrazolone, the compounds 4b, 4c, 4d, 4e containing propyl group and compound 4f containing trifluoromethyl group, similarly among chromone-pyrazolone, the compounds 5a, 5b, 5c, 5d, 5e containing propyl group and compounds 5f, 5g containing trifluoromethyl group are found to possess high potency against Gram-Positive S. aureus bacterial strain as compared with standard bactericidal ampicillin. So it is concluded that compounds with propyl group rather than CF3 group exhibited high potency against gram positive S. aureus bacterial strain. It is also observed that compounds (4c, 4g, 5h), (4a, 4b, 5b), (4a, 4g, 4j, 5h, 5i), and (4b, 4d, 5c, 5e) showed promising activity against E. coli, P. aeruginosa, S. aureus, and S. pyogenes, respectively, as compared with standard ampicillin drug.

Antifungal activity study of synthesized compounds reveals that compounds 5e and 5f exhibited more potency while compounds 4b, 4i, 4j, 5a, and 5g showed good antifungal activity against C. albicans as compared with standard fungicidal griseofulvin. All the synthesized compounds showed moderate-to-poor antifungal activity profile against A. niger and A. clavatus fungal strains.

4. Conclusion

Present study describes synthesis of a series of novel multifluorinated pyrazolone containing pyrazole and chromone nucleus by conventional heating as well as ultrasonication technique. The ultrasonication method was more efficient in terms of short reaction time, high yields, and clean reaction process. The antimicrobial activity result reveals that some of the synthesized compounds exhibited promising activity against the tested bacterial and fungal strains. The insights gained in this study will be useful for further studies on potential anti-infective agents. A study regarding structure activity relationship is in progress.

Acknowledgments

The authors are thankful to Dr. S. R. Walunj (Principal, PVP, College), Dr. T. N. Gholap (Principal, RKMM, Ahmednagar), and Management, PRES, for providing necessary facilities and constant encouragement. The authors also thank SAIF, Chandigarh, for spectral analysis.

References

  1. N. Woodford, “Novel agents for the treatment of resistant Gram-positive infections,” Expert Opinion on Investigational Drugs, vol. 12, no. 2, pp. 117–137, 2003. View at Publisher · View at Google Scholar · View at Scopus
  2. L. Kuznetsova, M. I. Ungureau, and A. Pepe, “Trifluoromethyl- and difluoromethyl-β-lactams as useful building blocks for the synthesis of fluorinated amino acids, dipeptides, and fluoro-taxoids,” Journal of Fluorine Chemistry, vol. 125, no. 4, pp. 415–500, 2004. View at Publisher · View at Google Scholar
  3. M. A. Al-Haiza, S. A. El-Assiery, and G. H. Sayed, “Synthesis and potential antimicrobial activity of some new compounds containing the pyrazol-3-one moiety,” Acta Pharmaceutica, vol. 51, no. 4, pp. 251–261, 2001. View at Google Scholar · View at Scopus
  4. F. Moreau, N. Desroy, J. M. Genevard et al., “Discovery of new Gram-negative antivirulence drugs: structure and properties of novel E. coli WaaC inhibitors,” Bioorganic and Medicinal Chemistry Letters, vol. 18, no. 14, pp. 4022–4026, 2008. View at Publisher · View at Google Scholar · View at Scopus
  5. R. N. Mahajan, F. H. Havaldar, and P. S. Fernandes, “Syntheses and biological activity of heterocycles derived from 3-methoxy-1-phenyl-1H-pyrazole-5-carboxylate,” Journal of the Indian Chemical Society, vol. 68, no. 4, pp. 245–246, 1991. View at Google Scholar · View at Scopus
  6. D. Castagnolo, F. Manetti, M. Radi et al., “Synthesis, biological evaluation, and SAR study of novel pyrazole analogues as inhibitors of Mycobacterium tuberculosis: part 2. Synthesis of rigid pyrazolones,” Bioorganic and Medicinal Chemistry, vol. 17, no. 15, pp. 5716–5721, 2009. View at Publisher · View at Google Scholar · View at Scopus
  7. M. Radi, V. Bernardo, B. Bechi, D. Castagnolo, M. Pagano, and M. Botta, “Microwave-assisted organocatalytic multicomponent Knoevenagel/hetero Diels-Alder reaction for the synthesis of 2,3-dihydropyran[2,3-c]pyrazoles,” Tetrahedron Letters, vol. 50, no. 47, pp. 6572–6575, 2009. View at Publisher · View at Google Scholar · View at Scopus
  8. E. A. M. Badawey and I. M. El-Ashmawey, “Nonsteroidal antiinflammatory agents—part 1: antiinflammatory, analgesic and antipyretic activity of some new 1-(pyrimidin-2-yl)-3-pyrazolin-5-ones and 2-(pyrimidin-2-yl)-1,2,4,5,6,7-hexahydro-3H-indazol-3-ones,” European Journal of Medicinal Chemistry, vol. 33, no. 5, pp. 349–361, 1998. View at Publisher · View at Google Scholar
  9. A. Tantawy, H. Eisa, A. Ismail, and M. E. Alexandria, “Synthesis of 1-(substituted) 4-arylhydrazono-3-methyl-2-pyrazolin-5-ones as potential antiinflammatory agents,” Journal of Pharmaceutical Sciences, vol. 2, p. 133, 1988. View at Google Scholar
  10. F. A. Pasha, M. Muddassar, M. M. Neaz, and S. J. Cho, “Pharmacophore and docking-based combined in-silico study of KDR inhibitors,” Journal of Molecular Graphics and Modelling, vol. 28, no. 1, pp. 54–61, 2009. View at Publisher · View at Google Scholar · View at Scopus
  11. C. E. Rosiere and M. I. Grossman, “An analog of histamine that stimulates gastric acid secretion without other actions of histamine,” Science, vol. 113, no. 2945, p. 651, 1951. View at Google Scholar · View at Scopus
  12. D. M. Bailey, P. E. Hansen, A. G. Hlavac et al., “3,4-Diphenyl-1H-pyrazole-1-propanamine antidepressants,” Journal of Medicinal Chemistry, vol. 28, no. 2, pp. 256–260, 1985. View at Google Scholar · View at Scopus
  13. P. M. S. Chauhan, S. Singh, and R. K. Chatterjee, “Antifilarial profile of substituted pyrazoles: a new class of antifilarial agents,” Indian Journal of Chemistry B, vol. 32, pp. 858–861, 1993. View at Google Scholar
  14. X. Zhang, Y. Kluger, Y. Nakayama et al., “Gene expression in mature neutrophils: early responses to inflammatory stimuli,” Journal of Leukocyte Biology, vol. 75, no. 2, pp. 358–372, 2004. View at Publisher · View at Google Scholar · View at Scopus
  15. M. T. Quinn and K. A. Gauss, “Structure and regulation of the neutrophil respiratory burst oxidase: comparison with nonphagocyte oxidases,” Journal of Leukocyte Biology, vol. 76, pp. 760–781, 2004. View at Publisher · View at Google Scholar
  16. S. J. Weiss, “Tissue destruction by neutrophils,” The New England Journal of Medicine, vol. 320, pp. 365–376, 1989. View at Publisher · View at Google Scholar
  17. M. Himly, B. Jahn-Schmid, K. Pittertschatscher et al., “Ig E-mediated immediate-type hypersensitivity to the pyrazolone drug propyphenazone,” Journal of Allergy and Clinical Immunology, vol. 111, no. 4, pp. 882–888, 2003. View at Publisher · View at Google Scholar · View at Scopus
  18. T. Watanabe, S. Yuki, M. Egawa, and H. Nishi, “Protective effects of MCI-186 on cerebral ischemia: possible involvement of free radical scavenging and antioxidant actions,” Journal of Pharmacology and Experimental Therapeutics, vol. 268, pp. 1597–1604, 1994. View at Google Scholar
  19. H. Kawai, H. Nakai, M. Suga, S. Yuki, T. Watanabe, and K. I. Saito, “Effects of a novel free radical scavenger, MCI-186, on ischemic brain damage in the rat distal middle cerebral artery occlusion model,” Journal of Pharmacology and Experimental Therapeutics, vol. 281, no. 2, pp. 921–927, 1997. View at Google Scholar · View at Scopus
  20. T. W. Wu, L. H. Zeng, J. Wu, and K. P. Fung, “Myocardial protection of MCI-186 in rabbit ischemia-reperfusion,” Life Sciences, vol. 71, no. 19, pp. 2249–2255, 2002. View at Publisher · View at Google Scholar · View at Scopus
  21. R. Aggarwal, V. Kumar, P. Tyagi, and S. P. Singh, “Synthesis and antibacterial activity of some new 1-heteroaryl-5-amino-3H/ methyl-4-phenylpyrazoles,” Bioorganic and Medicinal Chemistry, vol. 14, no. 6, pp. 1785–1791, 2006. View at Publisher · View at Google Scholar · View at Scopus
  22. V. Kumar, R. Aggarwal, P. Tyagi, and S. P. Singh, “Synthesis and antibacterial activity of some new 1-heteroaryl-5-amino-4-phenyl-3-trifluoromethylpyrazoles,” European Journal of Medicinal Chemistry, vol. 40, no. 9, pp. 922–927, 2005. View at Publisher · View at Google Scholar
  23. J. L. Kane, B. H. Hirth, B. Liang, B. B. Gourlie, S. Nahill, and G. Barsomian, “Ureas of 5-aminopyrazole and 2-aminothiazole inhibit growth of gram-positive bacteria,” Bioorganic and Medicinal Chemistry Letters, vol. 13, no. 24, pp. 4463–4466, 2003. View at Publisher · View at Google Scholar · View at Scopus
  24. P. P. Deohate, J. P. Deohate, and B. N. Berad, “Synthesis of some novel 1,2,4-dithiazolidines and their antibacterial and antifungal activity,” Asian Journal of Chemistry, vol. 16, no. 1, pp. 255–260, 2004. View at Google Scholar · View at Scopus
  25. O. Prakash, R. Kumar, and V. Prakash, “Synthesis and antifungal activity of some new 3-hydroxy-2-(1-phenyl-3-aryl-4-pyrazolyl) chromones,” European Journal of Medicinal Chemistry, vol. 43, pp. 435–440, 2008. View at Publisher · View at Google Scholar
  26. K. L. Kees, J. J. Fitzgerald, K. E. Steiner et al., “New potent antihyperglycemic agents in db/db mice: synthesis and structure-activity relationship studies of (4-substituted benzyl)(trifluoromethyl)pyrazoles and -pyrazolones,” Journal of Medicinal Chemistry, vol. 39, no. 20, pp. 3920–3928, 1996. View at Publisher · View at Google Scholar · View at Scopus
  27. G. Meazza, F. Bettarini, P. La Porta et al., “Synthesis and herbicidal activity of novel heterocyclic protoporphyrinogen oxidase inhibitors,” Pest Management Science, vol. 60, no. 12, pp. 1178–1188, 2004. View at Publisher · View at Google Scholar · View at Scopus
  28. T. W. Waldrep, J. R. Beck, M. P. Lynch, and F. L. Wright, “Synthesis and herbicidal activity of 1-aryl-5-halo- and 1-aryl-5-(trifluoromethyl)-1H-pyrazole-4-carboxamides,” Journal of Agricultural and Food Chemistry, vol. 38, no. 2, pp. 541–544, 1990. View at Google Scholar · View at Scopus
  29. D. J. Wustrow, T. Capiris, R. Rubin et al., “Pyrazolo[1,5-a]pyrimidine CRF-1 receptor antagonists,” Bioorganic and Medicinal Chemistry Letters, vol. 8, no. 16, pp. 2067–2070, 1998. View at Publisher · View at Google Scholar · View at Scopus
  30. A. G. Habeeb, P. N. Praveen Rao, and E. E. Knaus, “Design and synthesis of celecoxib and rofecoxib analogues as selective cyclooxygenase-2 (COX-2) inhibitors: replacement of sulfonamide and methylsulfonyl pharmacophores by an azido bioisostere,” Journal of Medicinal Chemistry, vol. 44, no. 18, pp. 3039–3042, 2001. View at Publisher · View at Google Scholar · View at Scopus
  31. A. M. Martel, A. Graul, X. Rabasseda, and R. Castañer, “Sildenafil,” Drugs of the Future, vol. 22, no. 2, pp. 138–143, 1997. View at Google Scholar · View at Scopus
  32. A. S. Bhat, J. L. Whetstone, and R. W. Brueggemeier, “Novel synthetic routes suitable for constructing benzopyrone combinatorial libraries,” Tetrahedron Letters, vol. 40, no. 13, pp. 2469–2472, 1999. View at Publisher · View at Google Scholar · View at Scopus
  33. B. Bauvois, M. L. Puiffe, J. B. Bongui, S. Paillat, C. Monneret, and D. Dauzonne, “Synthesis and biological evaluation of novel flavone-8-acetic acid derivatives as reversible inhibitors of aminopeptidase N/CD13,” Journal of Medicinal Chemistry, vol. 46, no. 18, pp. 3900–3913, 2003. View at Publisher · View at Google Scholar · View at Scopus
  34. H. P. Kim, K. H. Son, H. W. Chang, and S. S. Kang, “Anti-inflammatory plant flavonoids and cellular action mechanisms,” Journal of Pharmacological Sciences, vol. 96, no. 3, pp. 229–245, 2004. View at Publisher · View at Google Scholar
  35. E. Middleton, C. Kandaswami, and T. C. Theoharides, “The effects of plant flavonoids on mammalian cells: implications for inflammation, heart disease, and cancer,” Pharmacological Reviews, vol. 52, no. 4, pp. 673–751, 2000. View at Google Scholar · View at Scopus
  36. C. J. Bennett, S. T. Caldwell, D. B. McPhail, P. C. Morrice, G. G. Duthie, and R. C. Hartley, “Potential therapeutic antioxidants that combine the radical scavenging ability of myricetin and the lipophilic chain of vitamin E to effectively inhibit microsomal lipid peroxidation,” Bioorganic and Medicinal Chemistry, vol. 12, no. 9, pp. 2079–2098, 2004. View at Publisher · View at Google Scholar · View at Scopus
  37. V. Krishnamachari, L. H. Levine, C. Zhou, and P. W. Pare, “In vitro flavon-3-ol oxidation mediated by a B ring hydroxylation pattern,” Chemical Research in Toxicology, vol. 17, no. 6, pp. 795–804, 2004. View at Publisher · View at Google Scholar
  38. E. Knoevenagel, “Condensation von Malonsure mit aromatischen Aldehyden durch Ammoniak und Amine,” Berichte der deutschen chemischen Gesellschaft, vol. 31, no. 3, pp. 2596–2619, 1898. View at Publisher · View at Google Scholar
  39. E. Castelli, G. Cascio, and E. Manghisi, WO, 9807698, 1988.
  40. A. J. Kesel and W. Oberthur, WO, 9820013, 1998.
  41. A. Gaplovsky, M. Gaplovsky, S. Toma, and J. L. Luche, “Ultrasound effects on the photopinacolization of benzophenone,” Journal of Organic Chemistry, vol. 65, no. 25, pp. 8444–8447, 2000. View at Publisher · View at Google Scholar · View at Scopus
  42. R. Rajgopal, D. V. Jarikote, and K. V. Srinivasan, “Ultrasound prompted Suzuki cross-coupling reactions in ionic liquids at ambient conditions,” Chemical Communications, no. 6, pp. 616–617, 2002. View at Publisher · View at Google Scholar
  43. B. A. Song, G. P. Zhang, S. Yang, D. Y. Hu, and L. H. Jin, “Synthesis of N-(4-bromo-2-trifluoromethylphenyl)-1-(2-fluorophenyl)-O,O-dialkyl-α-aminophosphonates under ultrasonic irradiation,” UltraChem, vol. 13, p. 1544, 2001. View at Google Scholar
  44. S. S. Shindalkar, B. R. Madje, and M. S. Shingare, “A simple procedure for the preparation of acylals from 4-oxo-(4H)-1- benzopyran-3-carboxaldehyde using envirocat EPZ10R catalyst under ultrasonic irradiation,” Indian Journal of Heterocyclic Chemistry, vol. 15, no. 1, pp. 81–82, 2005. View at Google Scholar · View at Scopus
  45. B. K. Karale and A. G. Gadhave, “Synthesis and antibacterial activity of some spiroisoxazolines,” Indian Journal of Heterocyclic Chemistry, vol. 19, no. 4, pp. 389–392, 2010. View at Google Scholar · View at Scopus
  46. R. B. Gaikar, A. G. Gadhave, and B. K. Karale, “Synthesis of some biologically active pyrazolones,” Indian Journal of Heterocyclic Chemistry, vol. 19, no. 4, pp. 325–328, 2010. View at Google Scholar · View at Scopus
  47. A. V. Gadakh, C. Pandit, S. S. Rindhe, and B. K. Karale, “Synthesis and antimicrobial activity of novel fluorine containing 4-(substituted-2-hydroxybenzoyl)-1H-pyrazoles and pyrazolyl benzo[d]oxazoles,” Bioorganic and Medicinal Chemistry Letters, vol. 20, no. 18, pp. 5572–5576, 2010. View at Publisher · View at Google Scholar · View at Scopus
  48. Clinical and Laboratory Standards Institute (CLSI), “Performance standards for antimicrobial susceptibility testing: 15th informational supplement,” CLSI Document M100-S15, Wayne, Pa, USA, 2005. View at Google Scholar
  49. B. S. Furniss, A. J. Hannaford, P. W. G. Smith, and A. R. Patchel, Vogels Text Book of Practical Organic Chemistry, Pearson Education, 5th edition, 2007.