Thermal solvent-free synthesis of novel pyrazolyl chalcones and pyrazolines as potential antimicrobial agents.

Abstract A novel approach was adopted for the synthesis of series of new pyrazolyl chalcones ( 3a – c ) by the reaction of 5-chloro-3-methyl-1-phenylpyrazole-4-carboxaldehyde ( 1 ) with different 5-acetylbarbituric acid derivatives ( 2a – c ) under thermal solvent-free condition. The chalcones were then converted to the corresponding pyrazolines ( 4a – c ) under the same condition in excellent yields. All the synthesized compounds were characterized using elemental analysis and spectral data (IR, 1 H NMR, and mass spectrometry). The synthesized compounds were tested for their antimicrobial activity by disk diffusion assay with slight modifications against Gram-positive, Gram-negative strains of bacteria as well as fungal strains. The investigation of antimicrobial screening revealed that compounds ( 3a – 4c ) showed good antibacterial and antifungal activities, respectively. Among the screened compounds, 3b showed more potent inhibitory activity (MIC = 12.5 μg/ml) nearly to that of standard antibiotics ciprofloxacin, griseofulvin and fluconazole.