Int J Pharm Pharm Sci, Vol 7, Issue 10, 69-73Original Article


STEREO SELECTIVE SYNTHESIS OF NOVEL PYRAZOLE AND COUMARIN APPENDED BRIDGED PYRANS AS ANTIMICROBIAL AGENTS

N. RENUKA,K. AJAY KUMAR*

Post Graduate Department of Chemistry, Yuvaraja’s College, University of Mysore, Mysore 570005, India
Email: ajaykumar@ycm.uni-mysore.ac.in 

 Received: 19 Jun 2015 Revised and Accepted: 08 Aug 2015

ABSTRACT

Objectives:The aim of the present study was to synthesize a series of novel bridged pyrans as antimicrobial agents.

Methods:An isomeric mixture of 3-(4-ethoxy-10-methyl-8-oxo-2-phenyl-4,8-dihydro-2H-pyrano[3',2':6,7]chromeno[4,3-c]pyrazol-6-yl)-1-phenyl-1H-pyrazole-4-carbaldehydes,2(a-f) and 3-(4-ethoxy-8-methyl-10-oxo-2-phenyl-4,10-dihydro-2H-pyrano[2',3':5,6]chromeno[4,3-c]pyrazol-6-yl)-1-phenyl-1H-pyrazole-4-carbaldehydes,3(a-f) were synthesized by the reaction of 3,3'-(7-hydroxy-4-methyl-2-oxo-2H-chromene-6,8-diyl)bis(1-phenyl-1H-pyrazole-4-carbaldehyde) 1(a-f) and ethyl alcohol in the presence of conc. H2SO4. The synthesized compounds were evaluated for their antimicrobial activity.

Results:The structures of the new bridged pyran analogues 3-(4-ethoxy-10-methyl-8-oxo-2-phenyl-4,8-dihydro-2H-pyrano [3',2':6,7] chromeno [4,3-c]pyrazol-6-yl)-1-phenyl-1H-pyrazole-4-carbaldehydes,2(a-f) and 3-(4-ethoxy-8-methyl-10-oxo-2-phenyl-4,10-dihydro-2H-pyrano [2',3':5,6] chromeno[4,3-c]pyrazol-6-yl)-1-phenyl-1H-pyrazole-4-carbaldehydes,3(a-f) were confirmed by spectral studies and elemental analysis. The compounds 2e and 3e were having-CONH2 substitution and 2f and 3f were having-CSNH2 substitutions in the pyrazole rings showed antibacterial at minimum concentrations against all the tested organisms.

Conclusions:Results of the antimicrobial activity reveal that some of the synthesized compounds act as potential antimicrobial agents against different fungal and bacterial organisms.

Keywords:Antibacterial, Antifungal, Cyclisation, Formyl pyrazoles, Inhibitory.

© 2016 The Authors. Published by Innovare Academic Sciences Pvt Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)

INTRODUCTION

The construction of complex molecular architectures that exhibit greater biological potency in a facile and efficient manner remains an overarching goal for the chemists. In recent years coumarin libraries have attracted great attention because of their synthetic utility as building blocks for the construction of bioactive molecules. Coumarin derivatives are known to a wide range of activities; such as an antioxidant, antimicrobial, anti-HIV, antibiotic, anticancer, muscle relaxant, anti-inflammatory and anticoagulant properties [1]. An efficient synthesis of poly functionalized 4H-pyrans is carried out in one pot synthesis from an aldehyde, malononitrile and an active methylene diketo compound using a heterogeneous Mg/la mixed oxide catalyst [2]. A facile one-pot expeditious synthesis of 2-amino-4H-pyrans and 2-amino-5-oxo-5, 6, 7, 8-tetrahydro-4H-chromenes under solvent-free conditions using magnesium oxide as a catalyst is reported [3].

Pyrazole scaffolds drew a great deal of attention due to its contribution in biological and pharmacological fields [4]. The pyrazole nucleus has pronounced pharmacological applications such as anti-inflammatory [5], antimicrobial [6], antioxidant [7] and analgesic activity [8]. They have a long history of applications in agrochemicals and pharmaceutical industry as herbicides and active pharmaceuticals.

In search of new antimicrobial agents and in continuation of our work on coumarin analogues we herein report the synthesis of a series of isomeric bridged pyrans tagged to pyrazole and coumarin skeleton and their antimicrobial activities.

Experimental

In a typical procedure, a series of isomeric bridged pyrans tagged to pyrazole and coumarin moiety 2(a-f) and 3(a-f) were synthesized by the condensation reaction of 3,3'-(7-hydroxy-4-methyl-2-oxo-2H-chromene-6,8-diyl)bis(1-aryl-1H-pyrazole-4-carbaldehyde), 1(a-f) in ethyl alcohol (10 ml) in the presence of conc. H2SO4 (5 ml) under reflux conditions (Scheme-1).

Minimum inhibitory concentrations (MICs) were determined by broth dilution technique [9]. The nutrient broth, which contains logarithmic serially two-fold diluted amount of test compound and controls was inoculated with approximately 5 x 105 c. f. u of actively dividing bacteria cells. The bacterial cultures were incubated for 24 h at 37 °C and fungi cultures were incubated for 72 h at 37 °C; the growth was monitored visually and spectrophotometrically. The lowest concentration required to arrest the growth of bacteria and fungi was regarded as minimum inhibitory concentration (MIC). The synthesized compounds were screened for their antibacterial activity against Escherichia coli, Bacillus substilis, Staphylococus aureus and antifungal activity against Aspergillus niger, Aspergillus flavus, C. albicans. The antibiotics streptomycin and nystatin were used as standard drugs against bacteria and fungi species respectively. The experiments were carried out in triplicate; the results were taken as a mean of three determinations.

Melting points were determined by open capillary method and are uncorrected. IR spectra were recorded on a Nujol mull on Shimadzu 8300 spectrometer. 1H NMR and 13C NMR spectra were recorded on Agilent-NMR 400 MHz and 125 MHz spectrophotometer respectively in CDCl3 with TMS as an internal standard. The chemical shifts are expressed in δ ppm. Mass spectra were obtained on Mass Lynx SCN781 spectrophotometer TOF mode. Elemental analysis was performed on a Thermo Finnigan Flash EA 1112 CHN analyzer. Chromatographic separations were carried out on silica gel (70-230 mesh, Merck) column using hexane: ethyl acetate (9:2) as eluent.

Typical procedure for synthesis of 3-(4-ethoxy-10-methyl-8-oxo-2-phenyl-4,8-dihydro-2H-pyrano[3',2':6,7]chromeno[4,3-c]pyrazol-6-yl)-1-phenyl-1H-pyrazole-4-carbaldehyde, 2a

To a solution of 3,3'-(7-hydroxy-4-methyl-2-oxo-2H-chromene-6,8-diyl)bis(1-phenyl-1H-pyrazole-4-carbaldehyde), 1a (2.58g, 0.005 mol) in ethyl alcohol (10 ml), concentrated sulfuric acid (5 ml) was drop wise and the mixture was refluxed for 4 h at 80 °C. The progress of the reaction was monitored by TLC. After completion, the solvent was removed in vacuo. The resulting mass was extracted in to ether (30 ml), washed successively with NaOH and NaHCO3. The organic phase was dried over anhydrous sodium sulphate. The solvent was evaporated to dryness to get isomeric mixture of 3-(4-ethoxy-10-methyl-8-oxo-2-phenyl-4,8-dihydro-2H-pyrano [3',2':6,7] chromeno [4,3-c]pyrazol-6-yl)-1-phenyl-1H-pyrazole-4-carbaldehyde,2a and 3-(4-ethoxy-8-methyl-10-oxo-2-phenyl-4,10-dihydro-2H-pyrano [2',3': 5,6]chromeno[4,3-c]pyrazol -6-yl)-1-phenyl-1H-pyrazole-4-carbal-dehyde,3a (Scheme-1). The products were purified by column chromato-graphy using hexane and ethyl acetate (9:2 v/v) as eluent. The same procedure was used in all cases.

RESULTS AND DISCUSSION

3-(4-Ethoxy-10-methyl-8-oxo-2-phenyl-4,8-dihydro-2H-pyrano[3',2':6,7]chromeno[4,3-c]pyrazol-6-yl)-1-phenyl-1H-pyrazole-4-carbaldehyde, 2a

Solid in 59% (3.20g) yield; m. p. 192-194 °C. IR (Nujol, γ cm-1): 1772 (s) (lactone C=O str), 1733 (s) (aldehyde C=O str), 1219 (s) (C-O str). 1HNMR (CDCl3): δ 1.051 (t, 3H, CH3), 2.423 (s, 3H, CH3), 3.920 (q, 2H, OCH2), 6.026 (s, 1H, C9-H), 6.304 (s, 1H, C4-H), 7.423-7.728 (m, 12H, Ar-H), 8.320 (s, 1H, 5m ring-H), 9.782 (s, 1H, CHO). 13CNMR (CDCl3): δ 15.06 (1C, CH3), 20.13 (1C, CH3), 62.33 (1C, OCH2), 112.59 (1C), 113.64 (1C), 114.87 (1C), 115.30 (1C), 116.02 (1C), 116.86 (1C), 117.40 (1C), 119.72 (4C), 123.22 (1C), 126.16 (2C), 128.13 (1C), 128.90 (4C), 130.17 (1C), 138.46 (2C), 147.80 (1C), 148.63 (1C), 151.12 (1C), 152.94 (1C), 156.10 (1C), 161.18 (1C, C8), 181.32 (1C, CHO). MS (m/z): 545 (MH+), 544 (M+), 516, 488, 280 (100%, base peak), 236. Anal. Calcd. for C32H24N4O5: C, 70.58; H, 4.44; N, 10.29%; Found: C, 70.49; H, 4.26; N, 10.21%.

3-(4-Ethoxy-2-(4-methylphenyl)-10-methyl-8-oxo-4,8-dihydro-2H-pyrano[3',2':6,7]chromeno[4,3-c]pyrazol-6-yl)-1-(4-methylphenyl)-1H-pyrazole-4-carbaldehyde, 2b

Obtained from 3,3'-(7-hydroxy-4-methyl-2-oxo-2H-chromene-6,8-diyl)bis (1-(4-methyl phenyl)-1H-pyrazole-4-carbaldehyde), 1b (2.72g, 0.005 mol) as solid in 48% (2.75g) yield; m. p. 144-146 °C. IR (Nujol, γ cm-1): 1765 (s) (lactone C=O str), 1726 (s) (aldehyde C=O str), 1213 (s) (C-O str). 1HNMR (CDCl3): δ 1.089 (t, 3H, CH3), 2.314 (s, 6H, CH3), 2.453 (s, 3H, CH3), 3.984 (q, 2H, OCH2), 6.066 (s, 1H, C9-H), 6.202 (s, 1H, C4-H), 7.405-7.748 (m, 10H, Ar-H), 8.263 (s, 1H, 5m ring-H), 9.707 (s, 1H, CHO). 13CNMR (CDCl3): δ 15.62 (1C, CH3), 20.30 (1C, CH3), 21.40 (2C, CH3), 62.66 (1C, OCH2), 112.16 (1C), 113.04 (1C), 114.44 (1C), 115.33 (1C), 116.21 (1C), 119.42 (4C), 123.12 (1C), 128.76 (1C), 129.32 (4C), 130.37 (1C), 134.78 (2C), 135.14 (2C), 147.88 (1C), 148.66 (1C), 150.32 (1C), 151.64 (1C), 152.49 (2C), 156.11 (1C), 161.36 (1C, C8), 180.66 (1C, CHO). MS (m/z): 573 (MH+), 572 (M+), 544, 516, 280 (100%, base peak), 236. Anal. Calcd. for C34H28N4O5: C, 71.32; H, 4.93; N, 9.78%; Found: C, 71.20; H, 4.78; N, 9.73%.

3-(4-Ethoxy-2-(4-methoxyphenyl)-10-methyl-8-oxo-4,8-dihydro-2H-pyrano[3',2':6,7]chromeno[4,3-c]pyrazol-6-yl)-1-(4-methoxyphenyl)-1H-pyrazole-4-carbaldehyde, 2c

Obtainedfrom3,3'-(7-hydroxy-4-methyl-2-oxo-2H-chromene-6,8-diyl)bis(1-(4-methoxyphenyl)-1H-pyrazole-4-carbaldehyde), 1c (2.88g, 0.005 mol) as solid in 49% (2.95g) yield; m. p. 178-180 °C. IR (Nujol, γ cm-1): 1769 (s) (lactone C=O str), 1732 (s) (aldehyde C=O str), 1221 (s) (C-O str). 1HNMR (CDCl3): δ 1.126 (t, 3H, CH3), 2.394 (s, 3H, CH3), 3.813 (s, 6H, OCH3), 3.955 (q, 2H, OCH2), 6.148 (s, 1H, C9-H), 6.322 (s, 1H, C4-H), 7.361-7.707 (m, 10H, Ar-H), 8.123 (s, 1H, 5m ring-H), 9.869 (s, 1H, CHO). 13CNMR (CDCl3): δ 15.62 (1C, CH3), 20.30 (1C, CH3), 55.40 (2C, OCH3), 62.10 (1C, OCH2), 111.32 (1C, C9), 112.04 (4C), 113.20 (1C), 114.12 (4C), 114.93 (1C), 115.32 (1C), 116.00 (1C), 117.56 (1C), 123.22 (1C), 130.30 (1C), 131.18 (1C), 132.78 (2C), 145.06 (1C), 147.33 (2C), 151.44 (1C), 153.56 (1C), 154.86 (1C), 157.08 (2C), 162.10 (1C, C8), 179.86 (1C, CHO). MS (m/z): 605 (MH+), 604 (M+), 576, 548, 280 (100%, base peak), 236. Anal. Calcd. for C34H28N4O7: C, 67.54; H, 4.67; N, 9.27%; Found: C, 67.40; H, 4.57; N, 9.14%.

3-(4-Ethoxy-2-(4-fluorophenyl)-10-methyl-8-oxo-4,8-dihydro-2H-pyrano[3',2':6,7]chromeno[4,3-c]pyrazol-6-yl)-1-(4-fluorophenyl)-1H-pyrazole-4-carbaldehyde, 2d

Obtained from 3,3'-(7-hydroxy-4-methyl-2-oxo-2H-chromene-6,8-diyl) bis (1-(4-fluoro phenyl)-1H-pyrazole-4-carbaldehyde), 1d (2.76g, 0.005 mol) as solid in 54% (3.15g) yield; m. p. 182-185 °C. IR (Nujol, γ cm-1): 1763 (s) (lactone C=O str), 1724 (s) (aldehyde C=O str), 1213 (s) (C-O str). 1HNMR (CDCl3): δ 1.105 (t, 3H, CH3), 2.343 (s, 3H, CH3), 3.908 (q, 2H, OCH2), 6.244 (s, 1H, C9-H), 6.440 (s, 1H, C4-H), 7.224-7.682 (m, 10H, Ar-H), 8.189 (s, 1H, 5m ring-H), 9.804 (s, 1H, CHO). 13CNMR (CDCl3): δ 15.02 (1C, CH3), 20.14 (1C, CH3), 63.00 (1C, OCH2), 112.02 (1C, C9), 113.16 (1C), 113.53 (1C), 114.32 (1C), 115.14 (4C), 115.52 (1C), 116.32 (4C), 116.68 (1C), 117.26 (1C), 123.12 (1C), 128.18 (1C), 130.14 (1C), 134.18 (2C), 146.23 (1C), 148.13 (1C), 150.65 (1C), 152.36 (1C), 155.46 (1C), 159.28 (2C), 162.34 (1C, C8), 180.22 (1C, CHO). MS (m/z): 581 (MH+), 580 (M+), 552, 524, 280 (100%, base peak), 236. Anal. Calcd. for C32H22F2N4O5: C, 66.20; H, 3.82; N, 9.65%; Found: C, 66.07; H, 3.66; N, 9.49%.

6-(1-Carbamoyl-4-formyl-1H-pyrazol-3-yl)-4-ethoxy-10-methyl-8-oxo-4,8-dihydro-2H-pyrano[3',2':6,7]chromeno[4,3-c] pyrazole-2-carboxamide, 2e

Obtained from 3,3'-(7-hydroxy-4-methyl-2-oxo-2H-chromene-6,8-diyl)bis(4-formyl-1H-pyrazole-1-carboxamide), 1e (4) (2.25g, 0.005 mol) as solid in 50% (2.39g) yield; m. p. 200-203 °C. IR (Nujol, γ cm-1): 1771 (s) (lactone C=O str), 1730 (s) (aldehyde C=O str), 1217 (s) (C-O str). 1HNMR (CDCl3): δ 1.166 (t, 3H, CH3), 2.404 (s, 3H, CH3), 3.902 (q, 2H, OCH2), 6.215 (s, 1H, C9-H), 6.363 (s, 1H, C4-H), 7.636 (s, 1H, C11-H), 7.923 (s, 4H, NH2), 8.26 (s, 1H, 5m ring-H), 8.677 (s, 1H, 5m ring-H), 9.803 (s, 1H, CHO). 13CNMR (CDCl3): δ 15.56 (1C, CH3), 21.10 (1C, CH3), 62.24 (1C, OCH2), 110.72 (1C), 112.46 (1C), 112.82 (1C, C9), 114.02 (1C), 114.51 (1C), 115.66 (1C), 126.48 (1C), 128.88 (1C), 135.12 (1C), 136.28 (1C), 142.33 (1C), 144.63 (1C), 147.54 (1C), 152.10 (1C), 156.31 (1C), 157.30 (2C, CONH2), 161.14 (1C, C8), 167.22 (1C, CHO). MS (m/z): 479 (MH+), 478 (M+), 450, 422, 280 (100%, base peak), 236. Anal. Calcd. for C22H18N6O7: C, 55.23; H, 3.79; N, 17.57%; Found: C, 55.20; H, 3.64; N, 17.44%.

6-(1-Carbamoyl-4-formyl-1H-pyrazol-3-yl)-4-ethoxy-10-methyl-8-oxo-4,8-dihydro-2H-pyrano[3',2':6,7]chromeno[4,3-c]pyrazole-2-carbothioamide, 2f

Obtained from 3,3'-(7-hydroxy-4-methyl-2-oxo-2H-chromene-6,8-diyl)bis(4-formyl-1H-pyrazole-1-carbothioamide), 1f (4) (2.41g, 0.005 mol) as solid in 56% (2.85g) yield; m. p. 174-178 °C. IR (Nujol, γ cm-1): 1766 (s) (lactone C=O str), 1735 (s) (aldehyde C=O str), 1215 (s) (C-O str). 1HNMR (CDCl3): δ 1.101 (t, 3H, CH3), 2.414 (s, 3H, CH3), 3.882 (q, 2H, OCH2), 6.128 (s, 1H, C9-H), 6.343 (s, 1H, C4-H), 7.638 (s, 1H, C11-H), 7.864 (s, 1H, 5m ring-H), 8.076 (s, 1H, 5m ring-H), 8.622 (s, 4H, NH2), 9.844 (s, 1H, CHO). 13CNMR (CDCl3): δ 15.78 (1C, CH3), 20.86 (1C, CH3), 62.68 (1C, OCH2), 111.72 (1C), 112.54 (1C, C9), 112.96 (1C), 114.88 (1C), 115.24 (1C), 116.12 (1C), 126.72 (1C), 128.74 (1C), 135.27 (1C), 136.7 (1C), 142.21 (1C), 144.51 (1C), 147.33 (1C), 152.32 (1C), 155.44 (1C), 162.36 (1C, C8), 174.10 (2C, CSNH2), 180.26 (1C, CHO). MS (m/z): 511 (MH+), 510 (M+), 482, 454, 280 (100%, base peak), 236. Anal. Calcd. for C22H18N6O5S2: C, 51.76; H, 3.55; N, 16.46%; Found: C, 51.82; H, 3.45; N, 16.30%.

3-(4-Ethoxy-8-methyl-10-oxo-2-phenyl-4,10-dihydro-2H-pyrano[2',3':5,6]chromeno[4,3-c]pyrazol-6-yl)-1-phenyl-1H-pyrazole-4-carbaldehyde, 3a

Solid in 36% (1.95g) yield; m. p. 189-190 °C. IR (Nujol, γ cm-1): 1765 (s) (lactone C=O str), 1728 (s) (aldehyde C=O str), 1214 (s) (C-O str). 1HNMR (CDCl3): δ 1.052 (t, 3H, CH3), 2.422 (s, 3H, CH3), 3.940 (q, 2H, OCH2), 6.126 (s, 1H, C9-H), 6.316 (s, 1H, C4-H), 7.416-7.745 (m, 12H, Ar-H), 8.319 (s, 1H, 5m ring-H), 9.770 (s, 1H, CHO). 13CNMR (CDCl3): δ 15.22 (1C, CH3), 20.18 (1C, CH3), 62.21 (1C, OCH2), 112.50 (1C), 113.50 (1C), 114.66 (1C), 115.43 (1C), 116.32 (1C), 116.88 (1C), 117.68 (1C), 119.74 (4C), 123.98 (1C), 126.02 (2C), 128.10 (1C), 128.94 (4C), 130.16 (1C), 138.41 (2C), 147.36 (1C), 148.60 (1C), 151.06 (1C), 152.54 (1C), 152.10 (1C, C8), 156.15 (1C), 185.30 (1C, CHO). MS (m/z): 545 (MH+), 544 (M+), 516, 488, 442, 353, 249 (100%, base peak). Anal. Calcd. for C32H24N4O5: C, 70.58; H, 4.44; N, 10.29%; Found: C, 70.36; H, 4.28; N, 10.11%.

3-(4-Ethoxy-8-methyl-10-oxo-2-(4-methylphenyl))-4,10-dihydro-2H-pyrano[2',3':5,6]chromeno[4,3-c]pyrazol-6-yl)-1-(4-methylphenyl)-1H-pyrazole-4-carbaldehyde, 3b

Obtained from 3,3'-(7-hydroxy-4-methyl-2-oxo-2H-chromene-6,8-diyl)bis(1-(4-methylphenyl)-1H-pyrazole-4-carbaldehyde), 1b (2.72g, 0.005 mol) as solid in 38% (2.17g) yield; m. p. 147-149 °C. IR (Nujol, γ cm-1): 1772 (s) (lactone C=O str), 1731 (s) (aldehyde C=O str), 1216 (s) (C-O str). 1HNMR (CDCl3): δ 1.123 (t, 3H, CH3), 2.281 (s, 6H, CH3), 2.487 (s, 3H, CH3), 3.760 (q, 2H, OCH2), 6.112 (s, 1H, C9-H), 6.306 (s, 1H, C4-H), 7.452-7.790 (m, 10H, Ar-H), 8.436 (s, 1H, 5m ring-H), 9.780 (s, 1H, CHO). MS (m/z): 573 (MH+), 572 (M+), 516, 470, 249 (100%, base peak). Anal. Calcd. for C34H28N4O5: C, 71.32; H, 4.93; N, 9.78%; Found: C, 71.24; H, 4.77; N, 9.56%.

3-(4-Ethoxy-2-(4-methoxyphenyl)-8-methyl-10-oxo-4,10-dihydro-2H-pyrano[2',3':5,6]chromeno[4,3-c]pyrazol-6-yl)-1-(4-methoxyphenyl)-1H-pyrazole-4-carbaldehyde, 3c

Obtained from 3,3'-(7-hydroxy-4-methyl-2-oxo-2H-chromene-6,8-diyl)bis (1-(4-methoxy phenyl)-1H-pyrazole-4-carbaldehyde), 1c (2.88g, 0.005 mol) as solid in 37% (2.23g) yield; m. p. 172-174 °C. IR (Nujol, γ cm-1): 1770 (s) (lactone C=O str), 1730 (s) (aldehyde C=O str), 1222 (s) (C-O str). 1HNMR (CDCl3): δ 1.099 (t, 3H, CH3), 2.346 (s, 3H, CH3), 3.855 (s, 6H, OCH3), 3.980 (q, 2H, OCH2), 6.133 (s, 1H, C9-H), 6.338 (s, 1H, C4-H), 7.380-7.745 (m, 10H, Ar-H), 8.469 (s, 1H, 5m ring-H), 9.789 (s, 1H, CHO). 13CNMR (CDCl3): δ 15.66 (1C, CH3), 20.38 (1C, CH3), 55.56 (2C, OCH3), 62.19 (1C, OCH2), 112.08 (1C, C9), 112.22 (4C), 113.26 (1C), 114.56 (4C), 114.98 (1C), 115.74 (1C), 116.08 (1C), 117.88 (1C), 123.20 (1C), 130.34 (1C), 131.28 (1C), 132.26 (2C), 145.38 (1C), 147.40 (2C), 151.40 (1C), 152.10 (1C, C8), 153.55 (1C), 154.92 (1C), 157.18 (2C), 183.32 (1C, CHO). Anal. Calcd. for C34H28N4O7: C, 67.54; H, 4.67; N, 9.27%; Found: C, 67.42; H, 4.48; N, 9.36%.

3-(4-Ethoxy-2-(4-fluorophenyl)-8-methyl-10-oxo-4,10-dihydro-2H-pyrano[2',3':5,6]chromeno[4,3-c]pyrazol-6-yl)-1-(4-fluorophenyl)-1H-pyrazole-4-carbaldehyde, 3d

Obtained from 3,3'-(7-hydroxy-4-methyl-2-oxo-2H-chromene-6,8-diyl)bis (1-(4-fluoro phenyl)-1H-pyrazole-4-carbaldehyde), 1d (2.76g, 0.005 mol) as solid in 36% (2.08g) yield; m. p. 177-178 °C. IR (Nujol, γ cm-1): 1775 (s) (lactone C=O str), 1734 (s) (aldehyde C=O str), 1224 (s) (C-O str). 1HNMR (CDCl3): δ 1.219 (t, 3H, CH3), 2.338 (s, 3H, CH3), 3.914 (q, 2H, OCH2), 6.241 (s, 1H, C9-H), 6.466 (s, 1H, C4-H), 7.220-7.686 (m, 10H, Ar-H), 8.185 (s, 1H, 5m ring-H), 9.820 (s, 1H, CHO). Anal. Calcd. for C32H22F2N4O5: C, 66.20; H, 3.82; N, 9.65%; Found: C, 66.10; H, 3.64; N, 9.44%.

6-(1-Carbamoyl-4-formyl-1H-pyrazol-3-yl)-4-ethoxy-8-methyl-10-oxo-4,10-dihydro-2H-pyrano[2',3':5,6]chromeno[4,3-c]pyrazole-2-carboxamide, 3e

Obtained from 3,3'-(7-hydroxy-4-methyl-2-oxo-2H-chromene-6,8-diyl)bis(4-formyl-1H-pyrazole-1-carboxamide), 1e (2.25g, 0.005 mol) and ethyl alcohol (0.002 mol)as solid in 36% (1.72g) yield; m. p. 205-206 °C. IR (Nujol, γ cm-1): 1762 (s) (lactone C=O str), 1722 (s) (aldehyde C=O str), 1112 (s) (C-O str). 1HNMR (CDCl3): δ 1.162 (t, 3H, CH3), 2.404 (s, 3H, CH3), 3.923 (q, 2H, OCH2), 6.210 (s, 1H, C9-H), 6.362 (s, 1H, C4-H), 7.646 (s, 1H, C7-H), 7.923 (s, 4H, NH2), 8.262 (s, 1H, 5m ring-H), 8.672 (s, 1H, 5m ring-H), 9.834 (s, 1H, CHO). 13CNMR (CDCl3): δ 15.52 (1C, CH3), 21.48 (1C, CH3), 62.36 (1C, OCH2), 110.70 (1C), 112.38 (1C), 112.80 (1C, C9), 114.00 (1C), 114.50 (1C), 115.42 (1C), 126.43 (1C), 128.81 (1C), 135.10 (1C), 136.24 (1C), 142.30 (1C), 144.23 (1C), 147.30 (1C), 152.56 (1C), 156.26 (1C), 151.30 (2C, CONH2), 152.14 (1C, C8), 187.20 (1C, CHO). MS (m/z): 479 (MH+), 478 (M+), 450, 422, 249 (100%, base peak). Anal. Calcd. for C22H18N6O7: C, 55.23; H, 3.79; N, 17.57%; Found: C, 55.08; H, 3.60; N, 17.39%.

6-(1-Carbamothioyl-4-formyl-1H-pyrazol-3-yl)-4-ethoxy-8-methyl-10-oxo-4,10-dihydro-2H-pyrano[2',3':5,6]chromeno[4,3-c]pyrazole-2-carbothioamide, 3f

Obtained from 3,3'-(7-hydroxy-4-methyl-2-oxo-2H-chromene-6,8-diyl)bis(4-formyl-1H-pyrazole-1-carbothioamide), 1f (4) (2.41g, 0.005 mol) as solid in 38% (1.93g) yield; m. p. 170-171 °C. IR (Nujol, γ cm-1): 1778 (s) (lactone C=O str), 1738 (s) (aldehyde C=O str), 1226 (s) (C-O str). 1HNMR (CDCl3): δ 1.118 (t, 3H, CH3), 2.414 (s, 3H, CH3), 3.895 (q, 2H, OCH2), 6.129 (s, 1H, C9-H), 6.348 (s, 1H, C4-H), 7.684 (s, 1H, C11-H), 7.846(s, 1H, 5m ring-H), 8.022 (s, 1H, 5m ring-H), 8.560 (s, 4H, NH2), 9.789 (s, 1H, CHO). Anal. Calcd. for C22H18N6O5S2: C, 51.76; H, 3.55; N, 16.46%; Found: C, 51.88; H, 3.33; N, 16.26%.

The structures of the synthesized compounds were provided by IR, 1H NMR, 13C NMR, MS studies and elemental analysis. For instance, in IR spectra, the stretching frequencies of the compounds 2(a-f) and 3(b-e) showed a strong absorption bands in the region 1778-1762 cm-1and 1738-1722 cm-1 for lactone and aldehydic C=O bonds respectively. A strong and intense absorption band is absorbed in the region 1226-1112 cm-1was assigned to C-O bonds.

In 1H NMR spectra, the compounds2(a-f) and 3(a-f) showed the absorption signals due to aromatic and substituent protons in the expected region. The compounds 2(a-f) showed consistent pattern signals due to C9-H and C4-H appeared as singlet in the region d 6.000-6.100 ppm, and d 6.200-6.300 ppm. The–CHO proton appeared as singlet in the region d 9.700-9.900 ppm. While the compounds 3(a-f) showed consistent pattern signals due to C9-H and C4-H appeared as singlet in the region d 6.120-6.150 ppm, and d 6.300-6.400 ppm. The–CHO proton appeared as singlet in the region d 9.770-9.980 ppm.

In 13C NMR, all compounds showed the signals due to aromatic and substituent carbons at the expected region. The carbonyl carbons absorbed in the region d 179.00-185.00 ppm. The synthesized compounds 2(a-f) showed significantly stable molecular ion peaks with a relative abundance ranging up to 18-66% and the base peak at m/z 280; While 3(a-f) showed a base peak at m/z 249. Further, all compounds showed satisfactorily CHN analysis with a deviation of±0.20% from the theoretically calculated values, which strongly favor the formation of the products.

The results of MICs) of the synthesized compounds 2(a-f) and 3(a-f) tested against different bacterium were tabulated in table-1.

Table 1: MIC’s of the synthesized compounds 2(a-f) and 3(a-f) tested against bacteria species

Compound

Minimum inhibitory concentrations in µg/ml

S. aureus

B. substilis

E. coli

2a

50

**

200

2b

100

**

100

2c

50

**

150

2d

50

**

200

2e

25

150

50

2f

25

100

50

3a

150

200

150

3b

200

200

150

3c

150

150

200

3d

150

200

150

3e

25

50

25

3f

25

25

50

Streptomycin

25

50

25

Values are expressed as mean of the three determinations (n=3), **No inhibition observed even at a higher concentration of 200 µg/ml


The synthesized compounds exerted moderate to good antibacterial activity against the tested organisms. Compounds 2(a-d) failed to show antibacterial activity against B. substilis even at a concentration higher than 200 µg/ml, but showed moderate activity against the species S. aureus and E. coli. Compounds 3(a-d) showed moderate activities against all the bacterium tested. Compounds 2e and 3e were having-CONH2 substitution and 2f and 3f were having-CSNH2 substitutions in the pyrazole rings showed antibacterial at minimum concentrations against all the tested organisms.

The results of MICs) of the synthesized compounds 2(a-f) and 3(a-f) tested against different fungi species were tabulated in table-2.

Table 2: MIC’s of the synthesized compounds 2(a-f) and 3(a-f) tested against fungi species

Compound

Minimum inhibitory concentrations in µg/ml

A. niger

A. flavus

C. albicans

2a

100

200

100

2b

100

150

150

2c

200

150

150

2d

150

200

100

2e

50

50

25

2f

25

50

25

3a

100

150

150

3b

150

150

100

3c

200

150

200

3d

100

20

150

3e

25

50

25

3f

25

50

50

Nystatin

25

50

25

Values are expressed as mean of the three determinations (n=3).


The synthesized compounds showed promising antifungal activity against the tested organisms. Compounds 2(a-d) and 3(a-d) showed moderate activities against all the bacterium tested in comparison with that of the reference standard. Compounds 2e and 3e were having-CONH2 substitution and 2f and 3f were having-CSNH2 substitutions in the pyrazole rings showed antifungal activities at minimum concentrations against all the tested organisms.

CONCLUSION

The synthesized compounds showed promising in vitro antifungal activity against the tested organisms. The compounds 2e and 3e were having-CONH2 substitution and 2f and 3f were having-CSNH2 substitutions in the pyrazole rings showed antibacterial and antifungal activity at minimum concentrations against all the tested organisms. Their MIC values indicate that these compounds act as potential antimicrobial agents. The compounds 2(a-d) and 3(a-d) showed antimicrobial activity at a higher concentration comparison with those of standard antibiotics used as reference drugs.

ACKNOWLEDGEMENT

The authors are grateful to the University Grants Commission, New Delhi for financial assistance. IOE, University of Mysore and SAIF, Madras for spectral analysis of the compounds reported.

CONFLICT OF INTERESTS

Declared None

REFERENCES

  1. Murakami A, Gao G, Omura M, Yano M, Ito C, Furukawa H, et al. 1,1-Dimethylallylcoumarins potently suppress both lipopolysaccharide-and interferon-gamma-induced nitric oxide generation in mouse macrophage RAW 264.7 cells. Bioorg Med Chem Lett 2000;10:59-62.
  2. Seshu Babu N, Nayeem Pasha, Venkateswara Rao KT, Sai Prasad PS, Lingaiah N. A heterogeneous strong basic Mg/la mixed oxide catalyst for efficient synthesis of polyfunctionalized pyrans. Tetrahedron Lett 2008;49:2730-3.
  3. Dalip K, Buchi Reddy V, Shashwat S, Urvashi D, Suman K. A facile one-pot green synthesis and antibacterial activity of 2-amino-4H-pyrans and 2-amino-5-oxo-5,6,7,8-tetrahydro-4H-chromenes. Eur J Med Chem 2009;44:3805-9.
  4. Ajay Kumar K, Jayaroopa P, Pyrazoles: Synthetic strategies and their pharmaceutical applications-An overview, Int J Pharm Tech Res 2013;5:1473-86.
  5. Eid AI, Kira MA, Fahmy HH. Synthesis of new pyrazolones as potent anti-inflammatory agents. J Pharm Belg 1978;33:303-11.
  6. Jayaroopa P, Ajay Kumar K. Synthesis and antimicrobial activity of 4,5-dihydropyrazoline derivatives. Int J Pharm Pharm Sci2013;5:431-3.
  7. Renuka Nagamallu, Ajay Kumar Kariyappa. Synthesis and biological evaluation of novel formyl-pyrazoles bearing coumarin moiety as potent antimicrobial and antioxidant agents. Bioorg Med Chem Lett 2013;23:6406-9.
  8. Kuo SC, Huang LJ, Nakamura H. Studies on heterocyclic compounds. Synthesis and analgesic and anti-inflammatory activities of 3,4-dimethylpyrano[2,3-c]pyrazol-6-one derivatives. J Med Chem 1984;27:539-44.
  9. Jayaroopa P, Vasanth Kumar G, Renuka N, Harish Nayaka MA, Ajay Kumar K. Evaluation of new pyrazole derivatives for their biological activity: Structure-activity relationship. Int J PharmTech Res 2013;5:264-70.