Structural characterization of flavonol 3,7‐di‐ O ‐glycosides and determination of the glycosylation position by using negative ion electrospray ionization tandem mass spectrometry

Flavonol 3,7‐di‐ O ‐glycosides were investigated by negative ion electrospray ionization tandem mass spectrometry using a quadrupole linear ion trap (LIT) mass spectrometer. The results indicate that the fragmentation behavior of flavonol 3,7‐di‐ O ‐glycosides is substantially different from that of their isomeric mono‐ O ‐diglycosides. In order to characterize a flavonoid as a flavonol 3,7‐di‐ O ‐glycoside, both [Y 3 0 − H] −• and [Y 0 − 2H] − ions should be present in [M − H] − product ion spectrum. The MS 3 product ion spectra of Y 3 0 − , [Y 3 0 − H] −• and Y 7 0 − ions generated from the [M − H] − ion provide sufficient structural information for the determination of glycosylation position. Furthermore, the glycosylation positions are determined by comparing the relative abundances of Y 3 0 − and Y 7 0 − ions and their specific fragmentation patterns with those of flavonol mono‐ O ‐glycosides. In addition, a [Y 3 0 − H] −• ion formed by the homolytic cleavage of 3‐ O glycosidic bond with high abundance points to 3‐ O glycosylation, while a [Y 0 − 2H] − ion formed by the elimination of the two sugar residues is consistent with glycosylation at both the 3‐ O and 7‐ O positions. Investigation of negative ion ESI‐MS 2 and MS 3 spectra of flavonol O ‐glycosides allows their rapid characterization as flavonol 3,7‐di‐ O ‐glycoside and their differentiation from isomeric mono‐ O ‐diglycosides, and also enables their direct analysis in crude plant extracts. Copyright © 2006 John Wiley & Sons, Ltd.