Dihydrochalcones: evaluation as novel radical scavenging antioxidants.

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.