Oxidative Transformation of Dihydroflavonols and Flavan-3-ols by Anthocyanidin Synthase from Vitis vinifera .

Twelve polyphenols from three distinct families (dihydroflavonols, flavan-3-ols, and flavanones) were studied as potential substrates of anthocyanidin synthase from Vitis vinifera ( Vv ANS). Only flavan-3-ols of (2 R ,3 S ) configuration having either a catechol or gallol group on ring B are accepted as substrates. Only dihydroflavonols of (2 R ,3 R ) configuration are accepted as substrates, but a catechol or gallol group is not mandatory. Flavanones are not substrates of Vv ANS. HPLC and MS/MS analyses of the enzymatic products showed that the Vv ANS-catalyzed oxidative transformation of (+)-dihydroflavonols, such as dihydroquercetin, dihydrokaempferol and dihydromyricetin, leads only to the corresponding flavonols. Among the flavan-3-ols recognized as substrates, (+)-gallocatechin was only transformed into delphinidin by Vv ANS, whereas (+)-catechin was transformed into three products, including two major products that were an ascorbate-cyanidin adduct and a dimer of oxidized catechin, and a minor product that was cyanidin. Data from real-time MS monitoring of the enzymatic transformation of (+)-catechin suggest that its products are all derived from the initial C 3 -hydroxylation intermediate, i.e., a 3,3-gem-diol, and their most likely formation mechanism is discussed.