Synthesis, characterization, and antimicrobial studies of new rigid linker-based bispyrazolines

Abstract

The bispyrazolines 4a-4e were synthesized from the cyclization reaction of bischalcones 3a-3e with phenyl hydrazine by refluxing under alcoholic medium in the presence of glacial acetic acid. The bischalcones were obtained from the Claisen-Schmidt reaction of acetophenone with dibenzaldehydes 1a-1e and later were obtained in good yield from the O-alkylation of 4-hydroxybenzaldehyde with suitable alkylating agents. The structures of the prepared compounds were determined from the rigorous analysis of their spectral data (UV-vis, IR, 1H-NMR, 13C-NMR, and ESI-MS). The elemental analysis also confirmed the purity of these compounds. All the bischalcones 3a-3e and bispyrazolines 4a-4e were screened for their antimicrobial activity using the serial dilution method. Seven bacterial and five fungal species were used as the antimicrobial test strains, namely Klebsiella pneumoniae (MTCC 3384), Pseudomonas aeruginosa (MTCC 424), Escherichia coli (MTCC 443), Staphylococcus aureus (MTCC 443), Bacillus subtilis (MTCC 441), Pseudomonas fluorescens (MTCC 103), and Staphylococcus pyrogens (MTCC 442), and Aspergillus janus (MTCC 2751), Penicillium glabrum (MTCC 4951), Fusarium oxysporum (MTCC 2480), Aspergillus sclerotiorum (MTCC 1008), and Aspergillus niger (MTCC 281), respectively. The minimum inhibitory concentrations (MIC in μg/mL) were determined by using different dilutions.