Polyhydroxylated 2-styrylchromones as potent antioxidants

Abstract

Four polyhydroxylated 2-styrylchromones, structurally related to flavones and cinnamic acid, have been studied. An SC derivative with OH groups only at positions 3′ and 4′ on the styryl moiety and another SC bearing an additional OH group at position 5 on the benzopyrone ring were more potent inhibitors of the Cu2+-induced peroxidation of LDL than the flavonoid quercetin. Fluorescence and absorption spectroscopies suggested that one LDL particle may bind 40 SC molecules. A pulse radiolysis study in pH 7 buffered micellar solutions of neutral TX100 and positively charged CTAB demonstrated that one-electron oxidation by Br2−, O2− and tryptophan radicals (Trp) depends strongly on the micellar microenvironment. All SCs were readily oxidized by O2− in CTAB micelles (rate constants: 6–18×106 M−1 s−1). In TX100 micelles only the SC derivative with OH groups in position 3′ and 4′ reacted with O2− (rate constant: 1.1×106 M−1 s−1). In CTAB, electron transfer to Trp radicals was observed for all SCs with rate constants ≥3.2×107 M−1 s−1. In TX100 micelles, this reaction occurred solely with the derivative bearing OH groups only at positions 3′ and 4′.