Singlet oxygen quenching- and chain-breaking antioxidant-properties of a quercetin dimer able to prevent age-related macular degeneration

A dimer of quercetin prepared through a Mannich reaction protects pyridinium bisretinoid A2E from photooxidationat 430 nm in aqueous medium at pH 7.4. In the presence of light and O2, A2E is quickly attacked by1O2 produced in situ (by excited A2E) to give nonaoxirane and other oxygenated compounds which can beinvolved in diseases of the macula. Peroxyl radicals might have only a marginal role on the photooxidation ofA2E. The dimer is actually a potent quencher of 1O2 with a rate constant kQ of 8.5×108M-1 s-1 in methanol atroom temperature. On the other hand, its antioxidant abilities against ROO· radicals are quite limited sincekROO·=7.3×105M-1 s-1 (in buffer solution at pH 7.4), the value being essentially identical to that of quercetin.The quenching of 1O2 by the dimer is therefore the main reason for the A2E protection and prevention ofage-related macular degeneration.[object Object]