Antioxidant and antimicrobial studies on fused-ring pyrazolones and isoxazolones.

A series of 3-nitrochalcones have been synthesized enroute towards fused ring pyrazolones and isoxazolones. Base catalyzed condensation of the chalcones with ethylacetoacetate yielded cyclohexenones in good yields (74-76%). The treatment of cyclohexenones with hydrazine hydrate or hydroxylamine chloride in the presence of a base afforded the corresponding fused-ring pyrazolinones (70-78% yield) and isoxazolinones (58-66% yield). The newly synthesized compounds were characterized by IR, 1D and 2D NMR and HRMS spectral analysis. The compounds were screened for their antioxidant and antimicrobial activities. Pyrazolinones showed good DPPH radical scavenging and iron metal chelating properties. The para-hydroxy group was important for a compound to have enhanced antioxidant activity. Pyrazolinones and isoxazolinone exhibited a wider range of antimicrobial activities compared to cyclohexenones. Pyrazolinones and isoxazolinone bearing a thiophene ring were the most potent type of compounds against Bacillus subtilis and Candida albicans with MIC values of 0.313-1.25 μg/mL. Some of the synthesized compounds were found to have promising antioxidant, metal chelation and antimicrobial activities.