Identification of flavonoid diglycosides in yellow lupin (Lupinus luteus l.) with mass spectrometric techniques

Abstract

Various mass spectrometric techniques were used for the structural elucidation of flavonoid glycosides isolated from green parts of yellow lupin plants (Lupinus luteus). A methodological approach is proposed consisting of (1) extraction and purification of flavonoid glycosides from plant tissues, (2) registration of liquid secondary ion mass spectra of intact compounds and (3) gas chromatographic/mass spectrometric analyses of those compounds subjected to several types of chemical modification. On the basis of these data, it was possible to define the molecular mass of the glycosides, the structure of the aglycones, the configuration of sugar moieties and the position of glycosidic linkages between sugars in diglycosides or between aglycone and sugar moieties. Analysis of the mass spectrometric data permitted structural identification of four flavonoid diglycosides, where the aglycones had flavone, isoflavone and flavonol structures. They were recognized as: apigenin 7-O-(2″-O -rhamnopyranosyl)glucopyranoside (1), genistein 4′,7-O-diglucopyranoside (2), kaempferol 3-O -(6″-rhamnopyranosyl)glucopyranoside (3) and 3′- or 4′-methylquercetin 3-O-(6″-O -rhamnopyranosyl)glucopyranoside (4). Complete structural evaluation of flavonoid glycosides was possible with only submilligram quantities of samples needed to register various mass spectra. It was not possible, however, to define the anomeric configuration of the C-1 carbons in investigated glycosides. Copyright © 1999 John Wiley & Sons, Ltd.