Constituents with radical scavenging effect from Opuntia dillenii: structures of new alpha-pyrones and flavonol glycoside

The aqueous ethanolic extract from the fresh stems of Opuntia dillenii HAW. showed potent radical scanvenging activity. Three new compounds, opuntioside I, 4-ethoxyl-6-hydroxymethyl-alpha-pyrone, and kaempferol 7-O-beta-D-glucopyranosyl-(1-->4)-beta-D-glucopyranoside, were isolated from the extract. The structures of the new compounds were determined on the basis of chemical and physicochemical evidence and the radical scavenging effects of principal constituents were examined.