Acylated cyanidin glycosides in the violet-blue flowers of Ipomoea purpurea.

Six acylated cyanidin glycosides were isolated from violet-blue flowers of Ipomoea purpurea. These anthocyanins were all based on cyanidin 3-sophoroside-5-glucoside, acylated with caffeic acid and/or p-coumaric acid. Three anthocyanin structures were elucidated to be cyanidin 3-O(-)[2-O-(6-O-(trans-3-O-(beta-D-glucopyranosyl)caffeyl)-beta -D-glucopyranosyl)-6-O-(trans-4-O-(6-O-(trans-caffeyl)-beta-D-glucopyran osyl) caffeyl)-beta-D-glucopyranoside]-5-O(-)[beta-D-glucopyranoside], cyanidin 3-O(-)[2-O-(trans-3-O-(beta-D-glucopyranosyl)caffeyl)-beta-D-glucopyrano syl)- 6-O-(trans-caffeyl)-beta-D-glucopyranoside]-5-O(-)[beta-D-glucopyranosid e d and cyanidin 3-O(-)[2-O-(6-O-(trans-caffeyl)-beta-D-glucopyranosyl)-6-O- (trans-caffeyl)-beta-D-glucopyranoside]-5-O(-)[beta-D-glucopyranoside]. These three anthocyanins were present in all 12 violet-blue flower strains as major pigments. The colours of these acylated antocyanins were stabler in neutral solution than their deacyl analogues.