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Fifty three O-glycosyl-C-glycosyl flavones with O-glycosylation on phenolic hydroxyl or on the C-glycosyl residue or combination of both forms have been studied by liquid chromatography-UV diode array detection-electrospray ionisation mass spectrometry ion trap in the negative mode. The study of the relative abundance of the main ions from the MS preferential fragmentation on –MS2 and/or –MS3 events allows the differentiation of the position of the O-glycosylation, either on phenolic hydroxyl or on the sugar moiety of C-glycosylation. In addition, it is possible to discriminate between O-glycosylation at 2″ and at 6″ positions. The occurrence of an abundant ion Y₀⁻ ([(M−H)-132/-146/-162]⁻, mono-O-pentosyl/rhamnosyl/hexosyl-C-glycosyl derivatives) after –MS2 fragmentation characterizes the O-glycosylation on phenolic hydroxyls. The preferential fragmentation leading to a relevant Z₁⁻ ([Y₁-18]⁻) fragment is …