Nasunin from Eggplant Consists of Cis<i>−</i>Trans Isomers of Delphinidin 3-[4-(<i>p-</i>Coumaroyl)-<scp>l</scp>-rhamnosyl (1→6)glucopyranoside]-5-glucopyranoside

Abstract

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.