Synthesis, SAR Study and Evaluation of Mannich and Schiff Bases of Pyrazol-5(4H)-one Moiety Containing 3-(Hydrazinyl)-2-phenylquinazolin-4(3H)-one

In the present investigation, a series of 12 Mannich bases (QP1-12) and 5 Schiff bases (QSP1-5) of pyrazol-5(4H)-one moiety containing 3-(hydrazinyl)-2-phenylquinazolin-4(3H)-one has been synthesized and characterized by physicochemical as well as spectral means. The synthesized Mannich and Schiff bases were screened for their preliminary antimicrobial activity against Gram-positive and Gram-negative bacterial as well as fungal strains by the determination of zone of inhibition. Mannich bases (QP1-12) were found to be more potent antibacterial agents against Gram-positive bacteria, whereas Schiff bases (QSP1-5) were more potent against Gram-negative bacteria and fungi. Minimum inhibitory concentration result demonstrated that Mannich base compound (QP7) having ortho -OH and para -COOH group showed some improvement in antibacterial activity (minimum inhibitory concentration of 48.88×10(−3) μM/ml) among the tested Gram-positive organisms and it also exhibit minimum inhibitory concentration of value of 12.22×10(−3) μM/ml for Klebsiella pneumoniae. The antitubercular activity of synthesized compounds against Mycobacterium tuberculosis (H(37)Rv) was determined using microplate alamar blue assay. Compound QP11 showed appreciable antitubercular activity (minimum inhibitory concentration of 6.49×10(−3) μM/ml) which was more active than the standard drugs, ethambutol (minimum inhibitory concentration of 7.60×10(−3) μM/ml) and ciprofloxacin (9.4×10(−3) μM/ml). Compounds QP11, QP9, QSP1, QSP2, and QSP5 have good selective index and may be selected as a lead compound for the development of novel antitubercular agents.