Synthesis and Evaluation of Novel Spiro[oxindole-isoxazolidine] Derivatives as Potent Antioxidants

The antioxidant activity of isatin derivatives can be described with the presence of enolic hydroxyl group at the second position of the ring because of the keto-enol tautomerism between NH and CO groups of indolone moiety. The reducing ability of the tested compounds was evaluated by their interaction with the stable free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH) at various concentrations. Novel spiro[oxindole-isoxazolidine] derivatives (4a, 4b, 4c, 4d, 4e, 4f, 4g, 4h, 4i) have been synthesized by 1,3-dipolar cycloaddition reactions of variously substituted maleimides (1) with isatin ketonitrone (3) and tested for their in vitro antioxidant potency in the DPPH assay. All the synthesized compounds have been identified as potent in vitro antioxidants.