Microwave assisted synthesis, characterization and investigation of antibacterial activity of 3-(5-(substituted-phenyl)-4,5-dihydro-1H-pyrazol-3-yl)-2H-chromen-2-one derivatives

Abstract

A variety of 3-(5-(substituted-phenyl)-4,5-dihydro-1H-pyrazol-3-yl)-2H-chromen-2-one derivatives 3a–j were synthesized through microwave assisted thermal annulation of corresponding α,β-unsaturated ketones (chalcones) 2a–j via hydrazinolysis. Chalcones 2a–j were prepared from 3-acetyl-coumarin 1 which was previously accessed by Pechmann condensation reaction of salicylaldehyde. The series of pyrazoline-based coumarin motifs 3a–j synthesized, were structurally confirmed by analytical and spectral data. They were then evaluated for their antimicrobial activities using agar diffusion method. The result showed that microwave assisted method (MAM) for the reaction was remarkably successful and gave the targeted products 3a–j in higher yields at shorter reaction times compared to conventional synthetic method (CSM). The results showed that these skeletal frameworks exhibited marked potency as antibacterial agents. The most active antibacterial agent was 3-(5-(4-(diethylamino) phenyl)-4,5-dihydro-1H-pyrazol-3-yl)-2H-chromen-2-one 3j with MIC and MBC values of 3.92 ± 0.22 µg/mL and 7.82 ± 0.43 µg/mL respectively.

Keywords

• microwave synthesis
• pyrazoline
• coumarin motifs
• antibacterial
• gentamicin