Powering the antioxidant properties of tyrosol by selenylation: tyrosol selenide and diselenide as potent reactive oxygen species scavengers and glutathione peroxidase mimics

The remarkable enhancement of the antioxidant activity of tyrosol (Tyr), a natural phenolic compound with well-established health-promoting properties, through its selenylation is reported. Two novel selenylated derivatives, 3,3′-selenobistyrosol ( 1 ) and 3,3′-diselenobistyrosol ( 2 ), were obtained via the reaction of Tyr with SeCl₄ followed by preparative TLC purification. Both compounds displayed dramatically improved radical scavenging abilities and reducing properties, being up to 194-fold and 36-fold more active than parent Tyr in the 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing/antioxidant power (FRAP) assays, respectively. Kinetic studies of inhibited autoxidation in an apolar solvent revealed a relatively modest reactivity toward alkylperoxyl radicals, following the trend 1  > Tyr >  2 . This behavior, attributed to hydrogen atom donation, reflects a balance between the stabilization of the resulting phenoxyl radical via selenium introduction and the involvement of phenolic hydroxyl groups in intramolecular hydrogen bonding, as supported by DFT analysis. The superior efficacy of the selenylated compounds was clearly evident in radical-induced lipid peroxidation in micellar systems. Indeed, in these biologically relevant conditions both 1 and 2 outperformed Tyr and Trolox, especially in the presence of H₂O₂ and thiols. Notably, 2 also demonstrated significant glutathione peroxidase (GPx)-like activity, with catalytic performance markedly surpassing that of benchmark compounds such as selenocystine and diphenyldiselenide. Product analysis indicated the formation of Se O species, pointing to a complex selenium-centered redox chemistry. Overall, these findings highlight selenylation as a promising strategy to access multifunctional phenolic derivatives with enhanced antioxidant efficacy and selenium-based redox activity. Such compounds may hold potential for the prevention or treatment of oxidative stress-related disorders.