Dihydrochalcones are a family of bicyclic flavonoids, defined by the presence of two benzene rings joined by a saturated three carbon bridge. In the present study, we systematically examined the antioxidant activities of dihydrochalcones against the stable free radical (1,1-diphenyl-2-picrylhydrazyl) and lipid peroxidation in the erythrocyte membrane. All dihydrochalcones exhibited higher antioxidant activities than the corresponding flavanones. The (1)H NMR analysis indicated that the active dihydrochalcone has a time-averaged conformation in which the aromatic A ring is orthogonal to the carbonyl group, while the inactive dihydrochalcone such as 2'-O-methyl-phloretin has a strongly hydrogen-bonded phenolic hydroxyl group, suggestive of a coplanar conformation. A hydroxyl group at the 2'-position of the dihydrochalcone A ring, newly formed by reduction of the flavanone C ring, is an essential pharmacophore for its radical scavenging potential.
alpha-Tocopherol was reacted with alkyl and alkylperoxyl radicals at 37 degrees C in bulk phase. The lipid-free radicals were generated by the reaction of methyl linoleate with the free radical initiator, 2,2'-azobis(2,4-dimethylvaleronitrile) (AMVN) under air-insufficient conditions. The products were isolated by high-performance liquid chromatography. Their structures were identified as 2-(alpha-tocopheroxy)-2,4- dimethylvaleronitrile (1), a mixture of methyl 9-(8a-peroxy-alpha-tocppherone)-10(E),12(Z)-octadecadienoate and methyl 13-(8a-peroxy-alpha-tocopherone)-9(Z),11(E)-octadecadienoate (2), methyl 9-(alpha-tocopheroxy)-10(E),12(Z)-octadecadienoate (3a), methyl 13-(alpha-tocopheroxy)-9(Z),12(E)-octadecadienoate (3b), alpha-tocopherol spirodiene dimer (4) and alpha-tocopherol trimer (5). When methyl linoleate containing alpha-tocopherol was oxidized with AMVN under air-sufficient conditions, the main products were 8a-alkylperoxy-alpha-tocopherones (2). In addition to these compounds, 6-O-alkyl-alpha-tocopherols (1, 3a and 3b) were formed when the reaction was carried out under air-insufficient conditions. The results indicate that alpha-tocopherol can react with both alkyl and alkylperoxyl radicals during the autoxidation of polyunsaturated lipids.
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