Anthocyanins with 4'-glucosidation from red onion, Allium cepa

The anthocyanins, cyanidin 3-O-(3"-O-beta-glucopyranosyl-6"-O-malonyl-beta-glucopyranoside)-4'-O-beta-glucopyranoside, cyanidin 7-O-(3"-O-beta-glucopyranosyl-6"-O-malonyl-beta-glucopyranoside)-4'-O-beta-glucopyranoside, cyanidin 3,4'-di-O-beta-glucopyranoside, cyanidin 4'-O-beta-glucoside, peonidin 3-O-(6"-O-malonyl-beta-glucopyranoside)-5-O-beta-glucopyranoside and peonidin 3-O-(6"-O-malonyl-beta-glucopyranoside) have been isolated in minor amounts from pigmented scales of red onion, Allium cepa, in addition to six known anthocyanins. The structures were established mainly by extensive use of 2D NMR spectroscopy and electrospray LC-MS. With exception of cyanidin 4'-glucoside and cyanidin 3,4'-diglucoside reported from Hibiscus esculentus with inadequate documentation, this is the first identification of anthocyanins with 4'-glycosidation. Compared to cyanidin 3-glycosides the cyanidin 4'-glucoside derivatives showed hypsochromic shifts of visible lambda(max) and hyperchromic effects on wavelengths around 440 nm, similar to pelargonidin 3-glycosides.