Biomimetic Reagents for Selective Free Radical and Acid-Base Chemistry of Glycans: Application to Glycan Structure Determination by Mass Spectrometry

摘要

Similar to enzymatic glycosidic bond cleavage, the PRAGS reagent derivatizes the reducing terminus of glycans with a pyridine moiety with moderate proton affinity and employs acid-base chemistry to selectively catalyze C1-O glycosidic bond cleavage (Y ions), with the charge retained on the reducing terminus. The FRAGS reagent combines a reactive free radical precursor with a pyridinium (FRAGS II) or a quaternary alkyl pyridinium moiety (FRAGS I). With both a labile proton and radical precursor, collisional activation of FRAGS II derivatized glycans yields abundant cross-ring as well as glycosidic bond cleavages, resulting from both free radical and acid-base chemistry, with charge retention at the reducing terminus. With the FRAGS I reagent, radical induced fragmentation pathways are dominant, inhibiting formation of misleading ions, Y+Y, Y+~(1,5)X, and Y+Z ions, significantly simplifying glycan structure determination.