Design, synthesis and QSAR studies of 2-amino benzo[d]thiazolyl substituted pyrazol-5-ones: novel class of promising antibacterial agents

Novel analogs of 3-(4-substituted benzylideneamino)-N-(6-substituted-1,3-benzo[d]thiazol-2-yl)-4,5-dihydro-5-oxo-pyrazole-1-carboxamide (5a–s) were designed and synthesized by reacting 3-amino-N-(6-substituted-1,3-benzo[d]thiazol-2-yl)-4,5-dihydro-5-oxo-pyrazole-1-carboxamide (4a–d) with p-substituted benzaldehydes. The Infrared Spectroscopy, 1H-Nuclear Magnetic Resonance, 13C-Nuclear Magnetic Resonance, and High Resolution Mass Spectra spectral data confirmed the structures of all the novel synthesized compounds. Among the series tested, two compounds 5k and 5o displayed promising antibacterial activity especially against Staphylococcus aureus (MIC = 3.14 and 1.57 µg/mL) and Bacillus subtilis (MIC = 3.12 and 1.84 µg/mL) respectively. Further, these title compounds were also assessed for their cytotoxic activity (IC50) against mammalian Vero cell line using 3-(4,5-dimethylthiazo-2-yl)-2,5-diphenyl-tetrazolium bromide assay, indicating that the compounds exhibit antibacterial activity at non-cytotoxic concentrations. Field based three-dimensional quantitative structure–activity relationships were also discussed based on the antimicrobial screening data. Synthesis, spectral studies, antibacterial evaluation and QSAR studies of nineteen novel Schiff bases of pyrazol-5-one derivatives derived from 2-aminobenzothiazole nucleus are described.