Triacylated Anthocyanidin 3-Arabinosylglucoside-7,3’-diglucosides Isolated from the Bluish Flowers of Tradescantia virginiana Cultivars and Their Distribution in the Tradescantieae

Abstract

Two triacylated anthocyanidin 3-arabinosylglucoside-7,3'-diglucosides were isolated from the purple-violet ― violet-blue flowers of Tradescantia virginiana cultivars. The structures were determined to be 3-O-[6-O-(2-O-(trans-caffeoyl)-α-arabinofuranosyl)-β-glucopyranoside]-7,3'-O-di-[6-O-(trans-caffeoyl)-β-glucopyranoside]s of delphinidin and cyanidin. The former is a new anthocyanin in plants, whereas the latter, a rare anthocyanin has been recognized to be present in Zebrina pendula. Both anthocyanins exhibited typical three λmax in the visible region at 537, 574 and 620 nm for the delphinidin glycoside and at 510, 545 and 580 nm for the cyanidin glycoside in a 5.6 pH solution. These spectroscopic characteristics might be responsible for forming the intramolecular co-pigmentation between anthocyanidin and caffeic acid residues in these pigments. By HPLC analysis of nine species of the tribe Tradescantieae it was revealed that polyacylated anthocyanidin 3-arabinosylglucoside-7,3'-diglucosides were commonly found in all these plants as their major anthocyanins.