title: Determination of the glycosylation site in flavonoid mono-O-glycosides by collision-induced dissociation of electrospray-generated deprotonated and sodiated molecules.
abstract: The influence of the glycosylation site on the fragmentation behavior of 18 flavonoid glycoside standards was studied using positive and negative electrospray ionization mass spectrometry in combination with collision-induced dissociation and tandem mass spectrometry. The glycosylation position is shown to affect the relative abundance of the radical aglycone ions that can be observed in the [M-H]- collision-induced dissociation spectra. In particular, the radical aglycone ions are very abundant for deprotonated flavonol 3-O-glycosides. Collisional activation of the radical aglycone ions produced from positional isomers revealed minor differences: m,nB0- product ions are pronounced for 7-O-glycosides, whereas m,nA0- product ions are relatively more abundant for 4'-O-glycosides. In addition, the ratio between the radical aglycone and the regular aglycone ions in the [M+Na]+ high-energy collision-induced dissociation spectra gives an indication about the glycosylation site. This ion ratio allows the differentiation between flavonoid 3-O- and 7-O-glycosides or can be useful in the comparison of unknown compounds with standards. Unambiguous differentiation between O-glycosylation at the common positions of flavonoid O-glycosides, i.e. the 3-, 4'- and 7-positions, is achieved by collisional activation of sodiated molecules at high collision energy. The presence of a B-ring product ion containing the sugar residue indicates 4'-O-glycosylation, whereas the loss of the B-ring part from the aglycone product ion is characteristic of 3-O-glycosylation and the loss of the B-ring part from both the [M+Na]+ precursor ion and the aglycone product ion points to 7-O-glycosylation.
authors.affiliation: Department of Pharmaceutical Sciences, University of Antwerp (Campus Drie Eiken), Universiteitsplein 1, B-2610 Antwerp, Belgium.
authors.forename: Filip
authors.initials: F
authors.lastname: Cuyckens
authors.forename: Magda
authors.initials: M
authors.lastname: Claeys
mesh_terms: D005419:Flavonoids / Q000737:chemistry*; D006027:Glycosides / Q000737:chemistry*; D006031:Glycosylation; D015394:Molecular Structure; D011522:Protons; D012964:Sodium / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D013329:Structure-Activity Relationship
chemical_list: D005419:Flavonoids; D006027:Glycosides; D011522:Protons; D012964:Sodium