Study of the collision-induced radical cleavage of flavonoid glycosides using negative electrospray ionization tandem quadrupole mass spectrometry.

Negative electrospray ionization tandem quadrupole mass spectrometry was used to study the collision-induced dissociation (CID) of the O-glycosidic bond from different commercially available flavonoid glycosides. Depending on the structure, flavonoid glycosides can undergo both a collision-induced homolytic and heterolytic cleavage of the O-glycosidic bond producing deprotonated radical aglycone ((Y(0) - H)(-*)) and aglycone (Y(0) (-)) product ions. The relative abundance of the radical aglycone to the aglycone fragment from flavonol-3-O-glycosides increased with increasing number of hydroxyl substituents in the B ring and in the order kaempferol - <quercetin - <myricetin-3-O-glycoside. The nature and position of the sugar substitution of the flavonol glycosides also affected the fragmentation to the radical aglycone. Obtained under similar conditions, the product ion spectrum of kaempferol-7-O-neohesperidoside showed only a minor radical aglycone product ion as opposed to kaempferol-3-O-rutinoside. The relative abundance of the radical aglycone to the aglycone fragment from flavone-7-O-glycosides was also dependent on the substitution in the B ring. CID of apigenin-7-O-glucoside produced relatively more of the radical aglycone fragment than luteolin-7-O-glucoside, while only the aglycone fragment was found from diosmetin-7-O-rutinoside. The position of the sugar substitution also affected the fragmentation of the flavone glycosides, such that the product ion spectrum of luteolin-4'-O-glucoside showed only the aglycone fragment as opposed to luteolin-7-O-glucoside. No radical aglycone fragments were found from the flavanone-7-O-glycosides and dihydrochalcone glycoside investigated in the study.