Synthesis, characterization and anti-microbiological evaluation of 2-[(2,6-diaryl piperidin-4-yl)hydrazono]-2,3-dihydrothiazoles as a new class of antimicrobial agents

A series of 2-[(2,6-diarylpiperidin-4-yl)hydrazono]-2,3-dihydrothiazoles (25–40) were synthesized by the reaction of respective thiosemicarbazones (9–24) with phenacyl bromide in the presence of sodium acetate-acetic acid buffer and refluxing in ethanol for 12–16 h. The newly synthesized target compounds were characterized by elemental analysis, mass, FT-IR, ¹H and ¹³C NMR spectroscopic methods. A Structure activity relationship study was carried out for the title compounds against a panel of bacterial strains viz Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Salmonella typhi, Bacillus subtilis and Klebsiella pneumonia and the fungal strains Cryptococcus neoformans, Candida albicans, Rhizopus sp, Aspergillus niger and Aspergillus flavus, respectively, using ciprofloxacin and amphotericin-B as standard drugs. These studies proved that compounds 26 and 34 against Staphylococcus aureus, 35 against P. aeruginosa, 38 against B. subtilis, and 27 against K. pneumonia showed maximum inhibitory potency at the lowest concentration (6.25 µg/mL), whereas 26, 34 and 35 against C. neoformans and 26 and 27 against Candida albicans showed beneficial antifungal activity at a minimum concentration (MIC) of 6.25 µg/mL.