Acylated peonidin glycosides from duskish mutant flowers of Ipomoea nil

Abstract

Five acylated peonidin glycosides were isolated from the pale gray-purple flowers of a duskish mutant in the Japanese morning glory ( Ipomoea nil or Pharbitis nil) as major pigments, along with a known anthocyanin, Heavenly Blue Anthocyanin (HBA). Three of these were based on peonidin 3-sophoroside and two on peonidin 3-sophoroside-5-glucoside as their deacylanthocyanins; both deacylanthocyanins were acylated with caffeic acid and/or glucosylcaffeic acids. By spectroscopic and chemical methods, the structures of the former three pigments were determined to be 3- O-[2- O-(6- O-( trans-caffeoyl)-β- D-glucopyranosyl)-β- D-glucopyranoside], 3- O-[2- O-(6- O-(3- O-(β- D-glucopyranosyl)- trans-caffeoyl)-β- D-glucopyranosyl)-6- O-(4- O-(6- O-(3- O-(β- D-glucopyranosyl)- trans-caffeoyl)-β- D-glucopyranosyl)- trans-caffeoyl)-β-glucopyranoside], and 3- O-[2- O-(6- O-( trans-caffeoyl)-β- D-glucopyranosyl)-6- O-(4- O-(6- O-(3- O-(β- D-glucopyranosyl)- trans-caffeoyl)-β- D-glucopyranosyl)- trans-caffeoyl)-β- D-glucopyranoside] of peonidin. The structures of the latter two pigments were also confirmed as 3- O-[2- O-(6- O-( trans-caffeoyl)-β- D-glucopyranosyl)-β- D-glucopyranoside]-5- O-β- D-glucopyranoside, and 3- O-[2- O-(6- O-( trans-caffeoyl)-β- D-glucopyranosyl)-6- O-(4- O-(6- O-(3- O-(β- D-glucopyranosyl)- trans-caffeoyl)-β- D-glucopyranosyl)- trans-caffeoyl)-β- D-glucopyranoside]-5- O-β- D-glucopyranoside of peonidin. The mutation affecting glycosylation and acylation in anthocyanin biosynthesis of Japanese morning glory was discussed.