Identification of Novel Poly-Acylated Anthocyanins from Gynura bicolor Leaves and Their Antioxidative Activity

Abstract

Gynura bicolor DC. is a traditional vegetable in Japan and its leaves are characterized by the fact that their adaxial and abaxial sides are green and reddish purple, respectively. Two novel poly-acylated anthocyanins (bicolnin and bicolmalonin) and a known one (rubrocinerarin) were isolated from the leaves of G. bicolor as major anthocyanins. These anthocyanins were identified to be cyanidin 3-O-[β-D-glucopyranoside]-7-O-[6-O-(E)-(4-O-(6-O-(E)-caffeoyl-β-D-glucopyranosyl)-caffeoyl)-β-D-glucopyranoside]-3′-O-[6-O-(E)-caffeoyl-β-D-glucopyranoside] (bicolnin), cyanidin 3-O-[6-O-malonyl-β-D-glucopyranoside]-7-O-[6-O-(E)-(4-O-(6-O-(E)-caffeoyl-β-D-glucopyranosyl)-caffeoyl)-β-D-glucopyranoside]-3′-O-[6-O-(E)-caffeoyl-β-D-glucopyranoside] (rubrocinerarin), and cyanidin 3-O-[4, 6-di-O-malonyl-β-D-glucopyranoside]-7-O-[6-O-(E)-(4-O-(6-O-(E)-caffeoyl-β-D-glucopyranosyl)-caffeoyl)-β-D-glucopyranoside]-3′-O-[6-O-(E)-caffeoyl-β-D-glucopyranoside] (bicolmalonin) by MS and NMR analyses. These three anthocyanins exhibited higher antioxidative activities compared to cyanidin 3-glucoside as evaluated by 1, 1-diphenyl-2-picrylhydrazyl and oxygen radical absorbance capacity assays.