Nasunin from eggplant consists of cis-trans isomers of delphinidin 3-[4-(p-coumaroyl)-L-rhamnosyl (1→6)glucopyranoside]-5-glucopyranoside

Two major anthocyanins were isolated from the acidified methanolic extract of eggplant (Solanum melongena L.) by column chromatography and preparative high-performance liquid chromatography. These anthocyanins were interconvertible under room light illumination condition. By means of tandem time-of-flight mass spectrometry and nuclear magnetic resonance spectroscopy, their structures were identified and elucidated as delphinidin 3-[4-(cis-p-coumaroyl)-L-rhamnosyl(1 -> 6)glucopyranoside]5-glucopyranoside (compound 1) and delphinidin 3-[4-(trans-p-coumaroyl)-L-rhamnosyl-(1 -> 6)glucopyranoside]-5-glucopyranoside (compound 2), respectively. The results indicated that nasunin comprised cis and trans isomers of the p-coumaric acid moiety in its structure.