Arguably, the most prominent glycan rearrangement is the intramolecular migration of fucose units. Although, fucose migration is generally associated with ion activation and fragmentation during tandem MS experiments, our group provided direct evidence for this reaction taking place in intact glycan ions (E. Mucha et. al, Angew. Chem. Int. Ed. 2018, 57, 7440). Building on these findings, we here report an in-depth spectroscopy study on the impact of varied mobility of protons in fucose migration in the prototypical fucosylated glycans Lewis x and blood group antigen H-2. The mobility of protons is increased or diminished using functional groups and adduct ions with competitive proton affinity. The results correlate well with the promotion or inhibition of fucose migration through the presence or absence of a mobile proton.

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