Radical Chain Breaking Bis(ortho-organoselenium) Substituted Phenolic Antioxidants.

Abstract

The presence of chalcogen atom at the ortho -position of phenols enhances their radical chain-breaking activity. Here, a copper(I)-catalyzed reaction of 2,6-dibromo- and 2,6-diiodophenols with diorganodiselendes has been studied for the introduction of two-organoselenium substituents at both ortho -positions of the phenolic radical chain-breaking antioxidants, which afforded 2,6-diorganoseleno-substituted phenols in 80-92% yields. Additionally, 2,6-diiodophenols with electron-withdrawing CHO and CN groups afforded novel 5,5 -selenobis(4-hydroxy-3-(phenylselanyl)benzaldehyde) and 5,5 -selenobis(4-hydroxy-3-(phenylselanyl)benzonitrile) consisting of three selenium and two phenolic moieties. The developed copper-catalyzed reaction conditions enable the installation of two-arylselenium group ortho to phenolic radical chain-breaking antioxidants, which may not be possible by the conventional organolithium-bromine exchange methods due to sluggish reactivity of trianions (dicarba and phenoxide anion), which is generated by the reaction of organolithium with 2,6-dibromophenols, with diorgano-diselenide. The antioxidant activities of the synthesized bis and tris selenophenols have been accessed by DPPH, thiol peroxides, and singlet oxygen quenching assays. The radical quenching antioxidant activity has been studied on the synthesized compounds by 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. The bis-selenophenols show comparable radical deactivating activity, while tris selenobisphenols shows higher radical deactivating activity than the α-tocopherol. Also, the tris phenylselenobisphenol shows comparable peroxide decomposing activity with ebselen molecule.