Covalent anthocyanin–flavonol complexes from flowers of chive, Allium schoenoprasum

Abstract

The structures of eight anthocyanins have been determined in acidified methanolic extract of pale-purple flowers of chive, Allium schoenoprasum. Four of them have been identified as the anthocyanin–flavonol complexes (cyanidin 3- O-β-glucoside AII) (kaempferol 3- O-(2- O-β-glucosyl FIII-β-glucoside FII)-7- O-β-glucosiduronic acid FIV) malonate AIII (AII-6→AIII-1, FIV-2→AIII-3), 1, (cyanidin 3- O-(3- O-acetyl-β-glucoside AII) (kaempferol 3- O-(2- O-β-glucosyl FIII-β-glucoside FII)-7- O-β-glucosiduronic acid FIV) malonate AIII (AII-6→AIII-1, FIV-2→AIII-3), 2, and their 7- O-(methyl- O-β-glucosiduronate FIV) analogous, 3 and 4. Pigments 1 and 2 are the first final identification of covalent complexes between an anthocyanin and a flavonol, while 3 and 4 are formed during the isolation process. The other four anthocyanins ( 5– 8) were found to be the 3-acetylglucoside, 3-glucoside, 3-(6-malonylglucoside) and 3-(3,6-dimalonylglucoside) of cyanidin. The three latter pigments have earlier been identified as the major anthocyanins of the chive stem. The covalent anthocyanin–flavonol complexes show intramolecular association between the anthocyanidin (cyanidin) and flavonol (kaempferol) units, which influence the colour.