CC BY-NC-ND
0Journal of Saudi Chemical Society (2013) xxx, xxx-xxx
ORIGINAL ARTICLE
Synthesis of 2-pyrazolines from pyridine based chalcone by conventional and microwave techniques: Their comparison and antimicrobial studies
Navin B. Patel a *, Faiyazalam M. Shaikh a, Hemant R. Patel a, Dhanji Rajani b
a Research Laboratory, Department of Chemistry, Veer Narmad South Gujarat University, Surat 395 007, Gujarat, India b Microcare Laboratory, Surat 395 001, Gujarat, India
Received 10 December 2012; accepted 30 January 2013
KEYWORDS
Pyridine; 2-Pyrazoline; Microwave irradiation; Antimicrobial activity
Abstract 2-Pyrazolines from pyridine based chalcones by conventional and microwave techniques have been synthesized and their antimicrobial activity as well as a comparison study between conventional and microwave techniques has been done. Antimicrobial activity was carried out according to the broth micro dilution method and it was observed that compound 2d was found to be most active against gram negative bacteria and fungus Candida albicans. Microwave technique has been found superior over the conventional method in view of reaction time and energy requirement. Compounds have been characterized by 1H NMR, 13C NMR, IR and Mass spectral analyses.
© 2013 Production and hosting by Elsevier B.V. on behalf of King Saud University.
1. Introduction
Synthesis from microwave irradiation was first carried out in 1986 (Gedye et al., 1986). This pioneer work ignited the scope of microwave assisted synthesis. A number of articles were published on the microwave assisted synthesis and its comparison with conventional methods. This revealed that the microwave irradiated synthesis proved to be superior to that of
Corresponding author. Address: Department of Chemistry, Veer Narmad South Gujarat University, Surat 395 007, Gujarat, India. Tel.: + 91 9825350484; fax: +91 0261 2256012.
E-mail addresses: drnavin@satyam.net.in (N.B. Patel), faiyaz_online 007@yahoo.co.in (F.M. Shaikh).
Peer review under responsibility of King Saud University.
conventional ones in terms of time and energy consumption. Microwave synthesis has been important in the medicinal chemistry which is useful for the rapid synthesis of a library of large number of compounds.
Chalcones act as precursor for biologically important hetero-cyclic compounds. It can be prepared by easy synthetic approaches and can be readily cyclized to a variety of compounds including 2-pyrazolines. 2-Pyrazolines are biologically active scaffolds with a variety of biological activities like antimicrobial (Patel et al., 2012), antitubercular (Taj et al., 2011), antiinflammatory (Bano et al., 2011), anticancer (Lee et al., 2011), antitumor (Bai et al., 2012), anticonvulsant (Aboul-Enein et al., 2012), and anti-HIV (Ali et al., 2007). 2-Pyrazolines have been synthesized from cyclization of chalcones using conventional heating (Sridhar and Rajendraprasad, 2012; Koduru et al., 2012; Santos et al., 2012) as well as from microwave irradiation (Chawla et al., 2010; Azarifar and Ghasemnejad, 2003).
In this regard, we have also reported the cyclization of chal-cones from conventional methods (Patel and Patel, 2010,
1319-6103 © 2013 Production and hosting by Elsevier B.V. on behalf of King Saud University. http://dx.doi.org/10.1016/jjscs.2013.0L008
2012). Considering the above facts, here in this study, we are reporting the synthesis of 2-pyrazolines from chalcones by conventional and microwave techniques and a study of their comparison in terms of reaction time and yield as well as antimicrobial activity.
2. Experimental
2.1. General
Laboratory Chemicals were supplied by Rankem India Ltd. and Ficher Scientific Ltd. Melting points were determined by the open tube capillary method and are uncorrected. IR absorption spectra were recorded on a Thermo scientific Nicolet iS10 FT-IR spectrometer using KBr pellet, 1H NMR spectra were recorded in a CDCl3/DMSO-d6 Bruker Avance II 400 NMR (400 MHz FT NMR) instrument (chemical shifts in d ppm), 13C NMR spectra were recorded in a Bruker Avance II 400 NMR (100 MHz FT NMR) instrument (chemical shifts in d ppm) and Mass spectra recorded on a micromass Q-T of micro (TOF MS ES+). Elemental analyses were performed on a Heraeus Carlo Erba 1180 CHN analyzer. The purity of products was routinely checked by TLC using silica gel in toluene:methanol solvents. The microwave assisted reactions were conducted in a ''QPro-M Microwave Synthesis System'' manufactured by Questron Technologies Corporation, Ontario L4Z 2E9 Canada, whereby microwaves are generated by magnetron at a frequency of 2450 MHz having an output energy range of 100-500 Wand with an individual sensor for temperature control (fiber optic is used as a individual sensor for temperature control) with attachment of reflux condenser with constant stirring (thus avoiding the risk of high pressure development) and synthesis on preparative scales.
3-(4-(2-(5-Ethylpyridin-2-yl)ethoxy)phenyl)-1-phenylprop-2-en-1-ones 1a-j have been synthesized from reported methods (Patel and Patel, 2009).
2.2. Synthesis of 5-Ethyl-2-{2-[4-(3-phenyl-4,5-dihydro-1H-pyrazol-5-yl)phenoxy]ethyl} pyridine(2a)
Conventional method:
A mixture of 3-(4-(2-(5-Ethylpyridin-2-yl)ethoxy)phenyl)-1-phenylprop-2-en-1-ones 1a-j (0.003 mol) and hydrazine hydrate (0.0045 mol) was refluxed for 5-6 h in acetic acid (50 mL). Progress of the reaction was checked by TLC using toluene:methanol (7.5:2.5) as mobile phase. After completion of reaction, the mixture was cooled and poured into crushed ice with continuous stirring. The resulting solid thus obtained was collected by filtration, washed well with cold water, dried and recrystallized from methanol. Microwave method:
A mixture of 3-(4-(2-(5-Ethylpyridin-2-yl)ethoxy)phenyl)-1-phenylprop-2-en-1-ones 1a-j (0.003 mol) and hydrazine hydrate (0.0045 mol) was irradiated under microwave in solvent-free conditions. All these reactions were carried out by microwave irradiation for 3-7 min at the power level 700 W and at the temperature of 80-85 0C which was recorded by the temperature probe of the microwave. Progress of the reaction was checked after a regular interval of one minute till the completion of reaction by TLC using toluene:methanol
Fig. 1 2-Pyrazolines 2a-j.
(7.5:2.5) as mobile. Product was collected by the same way as in conventional methods.
Compounds 2(b-j) have also been synthesized by using the similar method. (Fig. 1)
2.2.1. 5-Ethyl-2-{2-[4-(3-phenyl-4,5-dihydro-1H-pyrazol-5-yl)phenoxy]ethyl}pyridine (2a)
m.p. 127-129 0C; IR spectrum (cm"1): 3268 (N-H), 2923, 2815 (C-H, asym, sym), 1617 (>C=N), 1220, 1034 (C-O-C). *H NMR spectrum (400 MHz, CDCl3, TMS), d: 1.13 (t, 3H, -CH3), 2.54 (q, 2H, -CH2-), 3.17 (t, 2H, -CH2-), 3.29-3.34 (dd, 1H, pyrazoline), 3.65-3.72 (dd, 1H, pyrazoline), 4.33 (t, 2H, -CH2-O), 5.87-5.91 (dd, 1H, pyrazoline), 6.98-7.70 (m, 9H, Ar-H), 8.23 (s, 1H, -NH), 7.18-8.32 (m, 3H, Pyridine-H). 13C NMR spectrum (100 MHz, CDCl3, TMS), d: 18.72 (C-1), 25.90 (C-2), 35.61 (C-8), 46.76 (C-17), 55.20 (C-16), 69.20 (C-9), 114.80 (C-11,15), 123.92 (C-6), 125.61 (C-12,14), 127.93 (C-20,24), 128.71 (C-21,23), 131.97 (C-22), 134.71 (C-7), 135.94 (C-3), 136.73 (C-13), 137.86 (C-19), 148.22 (C-4), 153.40 (C-18), 159.23 (C-5), 161.28 (C-10). MS: mjz 371.18 (M+). Elemental analyses data of C24H25N3O: calculated, %: C, 77.60; H, 6.68; N, 11.31; found, %: C, 77.62; H, 6.66; N, 11.29.
2.2.2. 5-Ethyl-2-{2-[4-(3-(4-methoxyphenyl)-4,5-dihydro-1H-pyrazol-5-yl)phenoxy]ethyl} pyridine (2b)
m.p. 133-135 0C; IR spectrum (cm"1): 3273 (N-H), 2927, 2832 (C-H, asym, sym), 1624 (>C=N), 1218, 1041 (C-O-C). *H NMR spectrum (400 MHz, CDCl3, TMS), d: 1.15 (t, 3H, -CH3), 2.57 (q, 2H, -CH2-), 3.12 (t, 2H, -CH2-), 3.27-3.31 (dd, 1H, pyrazoline), 3.67-3.74 (dd, 1H, pyrazoline), 3.80 (s, 3H, -OCH3), 4.37 (t, 2H, -CH2-O), 5.89-5.93 (dd, 1H, pyrazoline), 7.16-8.27 (m, 3H, Pyridine-H), 7.05-7.82 (m, 8H, Ar-H), 8.21 (s, 1H, -NH). 13C NMR spectrum (100 MHz, CDCl3, TMS), d: 18.68 (C-1), 25.79 (C-2), 35.56 (C-8), 46.71 (C-17), 52.55 (-OCH3), 55.23 (C-16), 69.23 (C-9), 114.83 (C-11,15), 115.72 (C-21,23), 123.92 (C-6), 125.67 (C-12,14), 128.12 (C-20,24), 129.76 (C-19), 134.76 (C-7), 135.82 (C-3), 136.65 (c-13), 147.25 (C-4), 153.42 (C-18), 159.18 (C-5), 161.18 (C-10), 164.93 (C-22). MS: m/z 401.15 (M+). Elemental analyses data of C25H27N3O2; calculated, %: C, 74.79; H, 6.78; N, 10.47; found, %: C, 74.77; H, 6.75; N, 10.45.
2.2.3. 5-Ethyl-2-{2-[4-(3-(4-fluorophenyl)-4,5-dihydro-1H-pyrazol-5-yl)phenoxy]ethyl} pyridine (2c)
m.p. 112-114 0C; IR spectrum (cm"1): 3265 (N-H), 2930, 2835 (C-H, asym, sym), 1618 (>C=N), 1221, 1035 (C-O-C), 1212 (c-F). *H NMR spectrum (400 MHz, CDCl3, TMS), d: 1.16 (t, 3H, -CH3), 2.54 (q, 2H, -CH2-), 3.10 (t, 2H, -CH2-), 3.25-3.29 (dd, 1H, pyrazoline), 3.69-3.76 (dd, 1H, pyrazoline), 4.35 (t, 2H, -CH2-O), 5.87-5.91 (dd, 1H, pyrazoline), 7.057.79 (m, 8H, Ar-H), 7.19-8.31 (m, 3H, Pyridine-H), 8.27 (s,
1H, -NH). 13C NMR spectrum (100 MHz, CDCl3, TMS), d: 18.68 (C-1), 25.79 (C-2), 35.56 (C-8), 46.71 (C-17), 55.23 (C-16), 69.23 (C-9), 114.83 (C-11,15), 116.43 (C-21,23), 123.92 (C-6), 125.67 (C-12,14), 130.32 (C-20,24), 132.16 (C-19), 134.76 (C-7), 135.82 (C-3), 136.65 (C-13), 147.25 (C-4), 153.42 (C-18), 159.18 (C-5), 161.18 (C-10), 167.91 (C-22). MS: mjz 389.19 (M+). Elemental analyses data of C24H24FN3O: calculated, %: C, 74.01; H, 6.21; N, 10.79; found, %: C, 74.03; H, 6.19; N, 10.81.
2.2.4. 5-Ethyl-2-{2-[4-(3-(2,4-dichlorophenyl)-4,5-dihydro-1H-pyrazol-5-yl)phenoxy]ethyl} pyridine (2d)
m.p. 145-147 0C; IR spectrum (cm"1): 3264 (N-H), 2927, 2836 (C-H, asym, sym), 1621 (>C=N), 1215, 1030 (C-O-C), 760 (C-Cl). *H NMR spectrum (400 MHz, CDCl3, TMS), d: 1.12 (t, 3H, -CH3), 2.57 (q, 2H, -CH2-), 3.12 (t, 2H, -CH2-), 3.29-3.33 (dd, 1H, pyrazoline), 3.61-3.70 (dd, 1H, pyrazoline), 4.31 (t, 2H, -CH2-O), 5.82-5.87 (dd, 1H, pyrazoline), 7.007.76 (m, 7H, Ar-H), 7.21-8.21 (m, 3H, Pyridine-H), 8.29 (s, 1H, -NH). 13C NMR spectrum (100 MHz, CDCl3, TMS), d: 18.62 (C-1), 25.76 (C-2), 35.45 (C-8), 46.69 (C-17), 55.22 (C-16), 69.24 (C-9), 114.72 (C-11,15), 123.88 (C-6), 125.58 (C-12,14), 126.68 (C-20), 128.91 (C-21), 131.98 (C-22), 133.35 (C-23), 134.71 (C-7), 135.18 (C-24), 135.76 (C-3), 136.62 (C-13), 137.74 (C-19), 147.21 (C-4), 153.34 (C-18), 159.11 (C-5), 161.10 (C-10). MS: mjz 439.12 (M+), 441.15 (M++2), 443.17 (M++4). Elemental analyses data of C24H23Cl2N3O: calculated, %: C, 65.46; H, 5.26; N, 9.54; found, %: C, 65.44; H, 5.28; N, 9.56.
2.2.5. 5-Ethyl-2-{2-[4-(3-(4-hydroxyphenyl)-4,5-dihydro-lH-pyrazol-5-yl)phenoxy]ethyl} pyridine (2e)
m.p. 137-139 0C; IR spectrum (cm"1): 3325 (O-H), 3261 (N-H), 2921, 2841 (C-H, asym, sym), 1612 (>C=N), 1204, 1018 (C-O-C). NMR spectrum (400 MHz, CDCl3, TMS), d: 1.12 (t, 3H, -CH3), 2.59 (q, 2H, -CH2-), 3.15 (t, 2H, -CH2-), 3.25-3.29 (dd, 1H, pyrazoline), 3.65-3.74 (dd, 1H, pyrazoline), 4.28 (t, 2H, -CH2-O), 5.76-5.81 (dd, 1H, pyrazoline), 7.04-7.69 (m, 8H, Ar-H), 7.15-8.24 (m, 3H, Pyridine-H), 8.71 (s, 1H, -NH), 9.01 (s, 1H, -OH). 13C NMR spectrum (100 MHz, CDCl3, TMS), d: 18.58 (C-1), 25.71 (C-2), 35.43 (C-8), 46.62 (C-17), 55.18 (C-16), 69.21 (C-9), 114.65 (C-11,15), 118.65 (C-21,23), 123.82 (C-6), 125.48 (C-12,14), 128.65 (C-19), 129.62 (C-20,24), 134.65 (C-7), 135.71 (C-3), 136.68 (C-13), 147.12 (C-4), 153.38 (C-18), 159.21 (C-5), 161.28 (C-10), 163.85 (C-22). MS: mjz 387.19 (M + ). Elemental analyses data of C24H25N3O2: calculated, %: C, 74.39; H, 6.50; N, 10.84; found, %: C, 74.36; H, 6.47; N, 10.83.
2.2.6. 5-Ethyl-2-{2-[4-(3-(3,4-dichlorophenyl)-4,5-dihydro-1H-pyrazol-5-yl)phenoxy]ethyl} pyridine (2f)
m.p. 156-158 0C; IR spectrum (cm"1): 3272 (N-H), 2928, 2832 (C-H, asym, sym), 1622 (>C=N), 1212, 1021 (C-O-C), 765 (C-Cl). NMR spectrum (400 MHz, CDCl3, TMS), d: 1.11 (t, 3H, -CH3), 2.61 (q, 2H, -CH2-), 3.12 (t, 2H, -CH2-), 3.27-3.31 (dd, 1H, pyrazoline), 3.61-3.70 (dd, 1H, pyrazoline), 4.31 (t, 2H, -CH2-O), 5.78-5.83 (dd, 1H, pyrazoline), 6.967.71 (m, 7H, Ar-H), 7.18-8.25 (m, 3H, Pyridine-H), 8.67 (s, 1H, -NH). 13C NMR spectrum (100 MHz, CDCl3, TMS), d: 18.62 (C-1), 25.65 (C-2), 35.53 (C-8), 46.61 (C-17), 55.23 (C-16), 69.25 (C-9), 114.69 (C-11,15), 123.85 (C-6), 125.52
(C-12,14), 126.18 (C-24), 130.63 (C-20), 130.85 (C-23), 132.92 (C-21), 133.71 (C-19), 134.58 (C-7), 135.67 (C-3), 136.12 (C-22), 136.78 (C-13), 147.18 (C-4), 153.45 (C-18), 159.31 (C-5), 161.29 (C-10). MS: mjz 439.15 (M+), 441.17 (M++2),
444.16 (M++4). Elemental analyses data of C24H23Cl2N3O: calculated, %: C, 65.46; H, 5.26; N, 9.54; found, %: C, 65.48; H, 5.26; N, 9.52.
2.2.7. 5-Ethyl-2-{2-[4-(3-(3-methoxyphenyl)-4,5-dihydro-1H-pyrazol-5-yl) phenoxy]ethyl} pyridine (2g)
m.p. 161-163 0C; IR spectrum (cm"1): 3262 (N-H), 2927, 2821 (C-H, asym, sym), 1618 (>C=N), 1212, 1028 (C-O-C). 1H NMR spectrum (400 MHz, CDCl3, TMS), d: 1.18 (t, 3H, -CH3), 2.58 (q, 2H, -CH2-), 3.18 (t, 2H, -CH2-), 3.26-3.30 (dd, 1H, pyrazoline), 3.63-3.73 (dd, 1H, pyrazoline), 3.82 (s, 3H, -OCH3), 4.26 (t, 2H, -CH2-O), 5.76-5.81 (dd, 1H, pyrazoline), 7.04-7.72 (m, 8H, Ar-H), 7.12-8.29 (m, 3H, Pyridine-H), 8.56 (s, 1H, -NH). 13C NMR spectrum (100 MHz, CDCl3, TMS), d: 18.67 (C-1), 25.69 (C-2), 35.51 (C-8), 46.58 (C-17), 55.21 (C-16), 69.28 (C-9), 112.59 (C-20), 114.62 (C-11,15), 116.78 (C-22), 120.59 (C-24), 123.81 (C-6), 125.48 (C-12,14),
130.17 (C-23), 134.51 (C-7), 135.62 (C-3), 136.71 (C-13), 137.79 (C-19), 147.25 (C-4), 153.48 (C-18), 159.21 (C-5), 161.35 (C-10), 162.86 (C-21). MS: mjz 401.17 (M+). Elemental analyses data of C25H27N3O2: calculated, %: C, 74.79; H, 6.78; N, 10.47; found, %: C, 74.75; H, 6.81; N, 10.50.
2.2.8. 5-Ethyl-2-{2-[4-(3-(3-fluorophenyl)-4,5-dihydro-1H-pyrazol-5-yl)phenoxy]ethyl} pyridine (2h)
m.p. 168-169 0C; IR spectrum (cm"1): 3238 (N-H), 2931, 2829 (C-H, asym, sym), 1618 (>C=N), 1212, 1022 (C-O-C), 1225 (c-F). 1H NMR spectrum (400 MHz, CDCl3, TMS), d: 1.11 (t, 3H, -CH3), 2.61 (q, 2H, -CH2-), 3.23 (t, 2H, -CH2-), 3.22-3.26 (dd, 1H, pyrazoline), 3.68-3.77 (dd, 1H, pyrazoline), 4.31 (t, 2H, -CH2-O), 5.72-5.77 (dd, 1H, pyrazoline), 7.027.65 (m, 8H, Ar-H), 7.08-8.30 (m, 3H, Pyridine-H), 8.51 (s, 1H, -NH). 13C NMR spectrum (100 MHz, CDCl3, TMS), d: 18.57 (C-1), 25.64 (C-2), 35.45 (C-8), 46.52 (C-17), 55.27 (C-16), 69.21 (C-9), 113.56 (C-20), 114.68 (C-11,15), 117.72 (c-22), 123.78 (C-6), 124.12 (C-24), 125.42 (C-12,14), 129.92 (c-23), 134.45 (C-7), 135.58 (C-3), 136.67 (C-13), 137.74 (C-19), 147.21 (C-4), 153.43 (C-18), 159.17 (C-5), 161.28 (C-10), 163.69 (C-21). MS: mjz 389.15 (M+). Elemental analyses data of C24H24FN3O: calculated, %: C, 74.01; H, 6.21; N, 10.79; found, %: C, 74.05; H, 6.24; N, 10.76.
2.2.9. 5-Ethyl-2-{2-[4-(3-(4-chlorophenyl)-4,5-dihydro-1H-pyrazol-5-yl)phenoxy]ethyl} pyridine (2i)
m.p. 118-119 0C; IR spectrum (cm"1): 3242 (N-H), 2928, 2834 (C-H, asym, sym), 1612 (>C=N), 1202, 1018 (C-O-C), 766 (C-Cl). 1H NMR spectrum (400 MHz, CDCl3, TMS), d: 1.15 (t, 3H, -CH3), 2.57 (q, 2H, -CH2-), 3.27 (t, 2H, -CH2-), 3.21-3.25 (dd, 1H, pyrazoline), 3.70-3.78 (dd, 1H, pyrazoline), 4.25 (t, 2H, -CH2-O), 5.68-5.73 (dd, 1H, pyrazoline), 6.947.64 (m, 8H, Ar-H), 7.12-8.20 (m, 3H, Pyridine-H), 8.49 (s, 1H, -NH). 13C NMR spectrum (100 MHz, CDCl3, TMS), d: 18.62 (C-1), 25.61 (C-2), 35.42 (C-8), 46.48 (C-17), 55.31 (C-16), 69.27 (C-9), 114.65 (C-11,15), 123.74 (C-6), 125.35 (C-12,14), 127.45 (C-20,24), 128.61 (C-21,23), 134.32 (C-7), 135.48 (C-3), 136.57 (C-13), 137.72 (C-19), 138.65 (C-22),
147.18 (C-4), 153.46 (C-18), 159.21 (C-5), 161.31 (C-10). MS:
la-j O
153.36 (C-18), 159.11 (C-5), 161.23 (C-10), 162.34 (C-20), 165.15 (C-22), MS: mjz 407.18 (M + ). Elemental analyses data of C24H23F2N3O: calculated, %: C, 70.75; H, 5.69; N, 10.31; found, %: C, 70.73; H, 5.71; N, 10.33.
3. Result and discussion
Acetic acid (microwave) Irradiated 300 watt 4-6 min
NHjNH^O Refluxed (conventional) 3-4 h
Scheme 1 Synthesis of 2-pyrazolines from chalcones via conventional and microwave irradiated techniques.
mjz 405.16 (M + ), 407.18 (M + +2). Elemental analyses data of C24H24ClN3O: calculated, %: C, 71.01; H, 5.96; N, 10.35; found, %: C, 71.03; H, 5.94; N, 10.37.
2.2.10. 5-Ethyl-2-{2-[4-(3-(2,4-difluorophenyl)-4,5-dihydro-1H-pyrazol-5-yl)phenoxy] ethyl} pyridine (2j) m.p. 149-151 0C; IR spectrum (cm"1): 3232 (N-H), 2912, 2831 (C-H, asym, sym), 1622 (>C=N), 1201, 1023 (C-O-C), 1212 (c-F). *H NMR spectrum (400 MHz, CDCl3, TMS), d: 1.18 (t, 3H, -CH3), 2.48 (q, 2H, -CH2-), 3.29 (t, 2H, -CH2-), 3.23-3.27 (dd, 1H, pyrazoline), 3.67-3.75 (dd, 1H, pyrazoline), 4.28 (t, 2H, -CH2-O), 5.66-5.71 (dd, 1H, pyrazoline), 6.987.79 (m, 7H, Ar-H), 7.10-8.20 (m, 3H, Pyridine-H), 8.32 (s, 1H, -NH). 13C NMR spectrum (100 MHz, CDCl3, TMS), d: 18.54 (C-1), 25.52 (C-2), 35.37 (C-8), 46.41 (C-17), 55.28 (C-16), 69.25 (C-9), 111.51 (C-23), 112.68 (C-21), 113.68 (C-19), 114.71 (C-11,15), 123.72 (C-6), 125.21 (C-12,14), 132.34 (C-24), 134.26 (C-7), 135.38 (C-3), 136.47 (C-13), 147.21 (C-4),
3.1. Chemistry
Cyclization of chalcone with hydrazine hydrate in conventional and microwave methods has been described in Scheme 1. Comparison of conventional and microwave techniques, in terms of time and yields has been described in Table 1. Spectral and elemental analyses data conformed the structure of compounds 2a-j. In IR spectra an absorption band at 3232 cm"1 was observed for N-H stretching. Absorption band at 2928, 2812 cm"1 was observed for the methylene group. Absorption bands for functional groups like 1552, 1330 cm"1 (-NO2 asym, sym), 1220 cm"1 (C-F), 1215, 1028 cm"1 (C-O-C), 767 cm"1 (C-Cl) were observed. In 1H NMR spectra of 2a-j three double doublets observed at d 3.23-3.27, 3.67-3.75 and 5.66-5.71 conformed the cyclization of chalcones to 2-pyrazolines. Singlets at d 3.78 for methoxy and 9.1 for hydroxy group were also observed. 13C NMR spectra for compounds 2a-j were in accordance with expected shifts. Mass spectra of compounds 2a-j were collected and the molecular ion peak was found correct according to the molecular formula.
3.2. Antibacterial and antifungal activities
Antimicrobial activity of synthesized compounds is reported in Table 2. Compounds were screened for in vitro against two Gram positive (Staphylococcus aureus MTCC 96, Streptococcus pyogenes MTCC 442) and two Gram negative (Escherichia coli MTCC 443, Pseudomonas aeruginosa MTCC 741) bacteria for antibacterial and three fungal species (Candida albicans MTCC 227, Aspergillus niger MTCC 282 and Aspergillus clavatus MTCC 1323) for antifungal activity respectively using the broth microdilution method (Rattan, 2005). Minimum inhibitory concentration (MIC) was determined and compared with standard drugs ampicillin for antibacterial activity while gre-seofulvin and nystatin for antifungal activity.
Compounds 2b (R = 4-OCH3), 2d (R = 2,4-di-Cl) and 2j (R = 2,4-di-F) showed good to comparable activity
Table 1 Comparison of conventional and microwave techniques.
Comp. No. R Irradiation in Microwave Conventional Refluxed
Time (min) Yield % Time (hour) Yield %
2a -H 4.2 87 4.4 76
2b 4-OCH3 4.8 84 3.8 78
2c 4-F 6.5 89 5.1 75
2d 2,4-di-Cl 6.2 86 5.8 72
2e 4-OH 3.8 85 5.2 79
2f 3,4-di-Cl 4.5 84 4.6 73
2g 3-OCH3 5.6 83 4.9 74
2h 3-F 4.0 82 4.2 76
2i 4-Cl 5.2 89 5.1 73
2j 2,4-di-F 5.7 85 5.5 76
Table 2 Antimicrobial data of compounds 2a-j.
Compd. No. R Minimum Inhibition Concentration in lg/ml
Gram negative Gram negative Fungal species
E. coli P. aeruginosa S. aureus S. pyogenes C. albicans A. niger A. clavatus
2a -H 500 500 200 200 >1000 >1000 >1000
2b 4-OCH3 100 200 250 250 >1000 200 200
2c 4-F 200 200 500 500 >1000 500 500
2d 2,4-di-Cl 100 62.5 500 500 250 1000 1000
2e 4-OH 200 100 250 250 500 1000 1000
2f 3,4-di-Cl 200 200 250 250 100 500 500
2g 3-OCH3 250 250 500 500 250 500 500
2h 3-F 250 250 200 200 200 500 500
2i 4-Cl 200 200 200 200 500 500 500
2j 2,4-di-F 125 250 100 100 500 1000 1000
Ampicillin 100 100 250 100 - - -
Griseofulvin - - - 500 100 100
Nystatin - - - 100 100 100
(MIC = 100-125 ig/ml) whereas 2c (R = 4-F), 2e (R = 4-OH), 2f (R = 3,4-di-Cl) and 2i (R = 4-Cl) showed a moderate activity (MIC = 200 ig/ml) against E. coli. Compounds 2d (R = 2,4-di-Cl) and 2e (R = 4-OH) exhibited good activity (MIC = 62.5-100 ig/ml) whereas 2b (R = 4-OCH3), 2c (r = 4-F), 2f (R = 3,4-di-Cl) and 2i (R = 4-Cl) showed a moderate activity (MIC = 200 ig/ml) against P. aeruginosa. Compounds 2a (R = -H), 2b (R = 4-OCH3), 2e (R = 4-OH), 2f (R = 3,4-di-Cl), 2h (R = 3-F), 2i (R = 4-Cl) and 2j (R = 2,4-di-F) showed good to very good activity (MIC = 100-250 ig/ml) against S. aureus. None of the compounds except 2j(R = 2,4-di-F) showed good activity (MIC = 100 ig/ml) against S. pyogenes.
Compounds 2d (r = 2,4-di-Cl), 2e (4-OH), 2f (R = 3,4-di-Cl), 2g (3-OCH3), 2h (R = 3-F), 2i (R = 4-Cl) and 2j (R = 2,4-di-F) displayed very good to good activity (MIC = 100-500 ig/ml) against C. albicans, when compared with standard drug griseofulvin. Compound 2f (3,4-di-Cl) showed good to comparable activity (MIC = 100-125 ig/ml) against C. albicans when compared with nystatin. None of the synthesized compounds showed good activity against other two fungal species A. niger and A. clavatus.
4. Conclusion
A series of 2-pyrazolines have been synthesized from cycliza-tion of chalcones by a conventional heating approach as well as non-conventional microwave irradiated solvent free conditions and evaluated as antibacterial and antifungal agents. Most of the compounds were found active against S. aureus as antibacterial while against C. albicans as antifungal agents. The non-conventional protocol offers several advantages such as simple procedure, fast reaction rate, mild reaction conditions and improved yields compared to conventional methods.
Acknowledgments
The authors thank Professor and Head, Department of Chemistry, VNSGU, Surat, for providing laboratory facilities. The
authors also thank S.A.I.F., Chandigarh for 1H NMR, 13C NMR, and Mass spectral analysis. Prof. Navin B. Patel is grateful to University Grants Commission, New Delhi for providing funding for Major Research Project. F.NO-37-475/ 2009(SR).
References
Aboul-Enein, M.N., El-Azzouny, A.A., Attia, M.I., Maklad, Y.A., Amin, K.M., Abdel-Rehim, M., El-Behairy, M.F., 2012. Design and synthesis of novel stiripentol analogues as potential anticon-vulsants. Eur. J. Med. Chem. 47, 360-369. Ali, M.A., Yar, M.S., Siddiqui, A.A., Sriram, D., Yogeeswari, P., de Clercq, E., 2007. Synthesis and anti-HIV activity of N1-nicotinoyl-3-(4'-hydroxy-3'-methylphenyl)-5-substituted phenyl]-2-pyrazo-lines. Acta Pol. Pharm. Drug Res. 63, 423-428. Azarifar, D., Ghasemnejad, H., 2003. Microwave-assisted synthesis of
some 3,5-arylated 2-pyrazolines. Molecules 8, 642-648. Bai, X., Shi, W.Q., Chen, H.F., Zhang, P., Li, Y., Yin, S.F., 2012. Synthesis and antitumor activity of 1-acetyl-3-(4-phenyl)4,5-dihy-dro-2-pyrazoline-5-phenylursolate and 4-chalcone ursolate derivatives. Chem. Nat. Compd. 48, 60-65. Bano, S., Javed, K., Ahmad, S., Rathish, L.G., Singh, S., Alam, M.S., 2011. Synthesis and biological evaluation of some new 2-pyrazo-lines bearing benzene sulfonamide moiety as potential anti-inflammatory and anti-cancer agents. Eur. J. Med. Chem. 46, 5763-5768. Chawla, R., Sahoo, U., Arora, A., Sharma, P.C., Radhakrishnan, V.,
2010. Microwave assisted synthesis of some novel 2-pyrazoline derivatives as possible antimicrobial agents. Acta Pol. Pharm. Drug Res. 67, 55-61.
Gedye, R., Smith, F., Westaway, K., Ali, H., Baldisera, L., Laberge, L., Rousell, J., 1986. The use of microwave ovens for rapid organic synthesis. Tetrahedron Lett. 27, 279-282. Koduru, B.S., Shinde, A.R., Preeti, P.J., Kumar, K.P., Rajavel, R., Sivakumar, T., 2012. Synthesis, Characterization, anti-tubercular, analgesic and antiinflammatory activities of new 2-pyrazoline derivatives. Asian J. Pharm. Tech. 2 (2), 47-50. Lee, M., Brockway, O., Dandavati, A., Tzou, S., Sjoholm, R., Satam, V., Westbrook, C., Mooberry, S.L., Zeller, M., Babu, B., Lee, M.,
2011. A novel class of trans-methylpyrazoline analogs of combre-tastatins: synthesis and in-vitro biological testing. Eur. J. Med. Chem. 46, 3099-3104.
Patel, N.B., Patel, H.R., 2009. Synthesis and pharmacological studies of 5-ethyl pyridin-2-ethanol analogs derivatives. Arkivoc 12, 302321.
Patel, N.B., Patel, H.R., 2010. Synthesis and antibacterial and antifungal studies of novel nitrogen containing heterocycles from 5-ethylpyridin-2-ethanol. Indian J. Pharm. Sci. 72, 613-620.
Patel, N.B., Patel, H.R., 2012. Characterization and pharmacological evaluation of new pyridine analogs. Arabian J. Chem. 5, 81-91.
Patel, N.B., Patel, J.C., Barat, G.G., 2012. In vitro evaluation of the antibacterial and antifungal activity of some new pyrazolyl-quinazolin-4(3H)-one derivatives. Med. Chem. Res. 21, 229-238.
Rattan, A., 2005. Antimicrob. Lab. Med. B. Churchill Livingstone, New Delhi, pp. 85-90, Chapter 5.
Santos, C.M.M., Silva, A.M.S., Jeko, J., Levai, A., 2012. Synthesis and structure elucidation of novel pyrazolyl-2-pyrazolines obtained by
the reaction of 3-(3-aryl-3-oxopropenyl)chromen-4-ones with phen-ylhydrazine. Arkivoc 5, 265-281.
Sridhar, S., Rajendraprasad, Y., 2012. Synthesis and analgesic studies of some new 2-pyrazolines. E-J. Chem. 9, 1810-1815.
Taj, T., Kamble, R.R., Gireesh, T.M., Hunnur, R.K., Margankop, S.B., 2011. One-pot synthesis of pyrazoline derivatised carbazoles as antitubercular, anticancer agents, their DNA cleavage and antioxidant activities. Eur. J. Med. Chem. 46, 4366-4373.
