Synthesis, antimicrobial and antitubercular activities of some novel pyrazoline derivatives

Abstract

In the present study, two new series of pyrazolines (3a–h &4a–h) were synthesized starting from p-acetamidophenol (paracetamol) and evaluated for their antibacterial, antifungal and antitubercular activities. Chalcones (2a–h) prepared by condensing 3-acetyl-4-hydroxyphenyl acetamide (1) with different aromatic aldehydes were reacted with phenyl hydrazine and isonicotinic acid hydrazide to obtain phenyl-pyrazolines (3a–h) and isoniazid-pyrazolines (4a–h), respectively. The structures of the synthesized compounds were confirmed by spectral and microanalysis studies. Newly prepared pyrazoline compounds exhibited significant antibacterial activity against the organisms Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa when compared with the standard antibiotic Ciprofloxacin. Compound 4g showed potent antibacterial activity against P. aeruginosa and S. aureus (MIC-3.12μg/mL), however, against E. coli compound 3d, 4c, 4d, 4f &4g were found to have an MIC of 6.25μg/mL. Antifungal activity of compound 4d against Candida albicans and Aspergillus niger (MIC-3.12μg/mL) was found to be better than the standard drug Ketoconazole. The results of antitubercular activity of the synthesized compounds against Mycobacterium tuberculosis H37Rv by the agar microdilution method are quite promising. The antitubercular activity of compounds 4c, 4d &4g (MIC-3.12μg/mL) was found to be superior than that of the reference drug Streptomycin which showed MIC equal to 6.25μg/mL. It was observed that pyrazolines with chloro, nitro or methoxy substituent showed better activity. Also, the pyrazolines derived from isoniazid (4a–h) were found to be better in their antibacterial, antifungal and antitubercular action than those derived from phenyl-hydrazine (3a–h).