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Chain‐Breaking Phenolic 2,3‐Dihydrobenzo[ b ]selenophene Antioxidants: Proximity Effects and Regeneration Studies
Author(s) -
Singh Vijay P.,
Yan Jiajie,
Poon JiaFei,
Gates Paul J.,
Butcher Ray J.,
Engman Lars
Publication year - 2017
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201702350
Subject(s) - chemistry , antioxidant , trolox , ascorbic acid , lipid peroxidation , organic chemistry , medicinal chemistry , photochemistry , food science , dpph
Phenolic 2,3‐dihydrobenzo[ b ]selenophene antioxidants bearing an OH‐group ortho ( 9 ), meta ( 10 , 11 ) and para ( 8 ) to the Se were prepared by seleno‐Claisen rearrangement/intramolecular hydroselenation. meta ‐Isomer ( 11 ) was studied by X‐ray crystallography. The radical‐trapping activity and regenerability of compounds 8 – 11 were evaluated using a two‐phase system in which linoleic acid was undergoing peroxidation in the lipid phase while regeneration of the antioxidant by co‐antioxidants ( N ‐acetylcysteine, glutathione, dithiothreitol, ascorbic acid, tris(carboxyethyl)phosphine hydrochloride) was ongoing in the aqueous layer. Compound 9 quenched peroxyl radicals more efficiently than α‐tocopherol. It also provided the most long‐lasting antioxidant protection. With thiol co‐antioxidants it could inhibit peroxidation for more than five‐fold longer than the natural product. Regeneration was more efficient when the aqueous phase pH was slightly acidic. Since calculated O−H bond dissociation energies for 8 – 11 were substantially larger than for α‐tocopherol, an antioxidant mechanism involving O‐atom transfer from peroxyl to selenium was proposed. The resulting phenolic selenoxide/alkoxyl radical would then exchange a hydrogen atom in a solvent cage before antioxidant regeneration at the aqueous lipid interphase.