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 (H₃₇Rv) 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.

Synthesis, in-vitro antimicrobial and antitubercular screening of Schiff bases of 3-amino-1-phenyl-4- [2-(4-phenyl-1,3-thiazol-2-yl) hydrazin-1-ylidene]-4,5-dihydro-1H-pyrazol-5-one

PURPOSE:

Synthesis and antimicrobial activity of some Schiff bases of 3-amino-1-phenyl-4- [2-(4-phenyl-1,3-thiazol-2-yl) hydrazin-1-ylidene]-4,5-dihydro-1H-pyrazol-5-ones (TZP4a-l) are described.

MATERIALS AND METHODS:

Structures of the synthesized compounds were confirmed using infrared, ¹H nuclear magnetic resonance, and mass spectral data. Synthesized compounds were tested in-vitro against four Gram-positive and four Gram-negative bacterial strains, three fungal strains and two mycobacterial strains. Title compounds were screened its in-vitro cytotoxicity (IC₅₀) by 3-(4,5-dimethythiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay using mouse embryonic fibroblasts cell line (NIH 3T3).

RESULTS AND DISCUSSION:

Compounds TZP4 g and TZP4 h were found to be significant activity against Bacillus substilis (bacteria) and Aspergillus niger (fungi). In-vitro anti-tuberculosis (TB) activity of compound TZP4g showed appreciable antitubercular activity against Mycobacterium tuberculosis H37Rv strain (minimum inhibitory concentration [MIC] =0.6.48 × 10⁻³ μM/mL) which was 1.69 and 3.91 times more active than the standard drug, pyrazinamide (25.38 × 10⁻³ μM/mL) and streptomycin (MIC = 11.01 × 10⁻³ μM/mL), respectively. Their in-vitro cytotoxicity (IC₅₀) was determined to establish a selectivity index (SI) (SI = IC₅₀/MIC). Compounds TZP4 c, TZP4 g, and TZP4 h have SI 82.85, 168.88, and 199.07, respectively.

CONCLUSION:

All the title compounds had mild toxicity on the mouse embryonic fibroblasts NIH 3T3 cells (IC₅₀ ≥ 100 μM). In comparison to the results of toxicity and antimycobacterial activity tests, it was observed that the activity of the compounds is not due to general toxicity effect; however, their antimycobacterial activity can be possibly because of their selective antimycobacterial effect. We concluded from our investigations that TZP4 c, TZP4 g, and TZP4 h may be considered promising for the development of new anti-TB agents.