Synthesis and evaluation of novel pyrazole-imidazole hybrids as antimicrobial candidates

Abstract

and 2D NMR spectrum of compounds 3(a-b) and 7(a-t) …………………………………………………[4] HRMS spectrum of compound 3(a-b) and (7a-7t)………………………. Experimental Material and MethodsIn present study, chemicals were procured from Alfa-Aesar /Sigma Aldrich and used as such without further purification. To detect the melting point of synthesized compounds, open capillary method was used. Standard literature procedures were used for drying the solvents. To perform thin layer chromatography (TLC), Pre-coated Merck silica gel (SIL G/UV254, ALUGRAM) plates were used in ethyl acetate: hexane mixture solvent system followed by observing spots under UV light (254 nm). The spectrum for 1 H NMR (400 MHz) and 13 C NMR (100 MHz) were taken in dimethylsulfoxide-d6 by Bruker Avance III. The chemical shifts of DMSO for 1 H (δ 2.50 ppm) and 13 C (δ 39.50 ppm) were used as reference. Coupling constant values are given in Hertz. Peaks splitting patterns in 1 H NMR are reported as follow: s, singlet; bs, broad singlet; d, doublet; bd, broad doublet; t, triplet; bt, broad triplet; m, multiplet. The IR spectra of synthesized compounds were recorded on Shimazdu IR Affinity-I using KBr powder as a standard in the region of 4000-400 cm -1 . The high resolution mass spectra (HRMS) were recorded by Mass spectrometer Esquire 3000 with ESI resource. General method for synthesis of 1-(4-phenyl-1H-imidazol-2-yl)-1H-pyrazole (3a) and 3,5- Dimethyl-1-(4-phenyl-1H-imidazol-2-yl)-1H-pyrazole (3b):1H-pyrazole-1-carboximidamide hydrochloride (1a, 1mmol) was dissolved in 10 ml of the mixture of tetrahydrofuran and water (5:1), clamped with the reflux condenser. Potassium carbonate (2.5 mmol) was added in small portions. Then a solution of 2-bromo-1-phenylethanone (2, 1.2 mmol) in tetrahydrofuran was constantly added drop wise via pressure equalizing funnel over a period of 20 min while refluxing. The progress of reaction was monitored by thin layer chromatography (TLC). After completion of reaction, crude product was filtered and purified with the help of column chromatography (60-120 mesh silica, hexane/ethylacetate 90/10). Compound 3b was prepared by the same procedure from 3,5-dimethyl-1H-pyrazole-1-carboximidamide nitrate.