Mechanism of a gas-phase dissociation reaction of 4-aminobutyl glycosides under CID MS/MS conditions

The assembly of monosaccharides during the synthetic process of glycan structures is responsible for the diversity of this family of molecules. Because of the complexity of the glycan structure, synthesis of oligosaccharides and structural analysis have been difficult tasks. During efforts to develop glycosides carrying an aglycon that can be used in both functional and structural investigations, we found that 4-aminobutyl glycosides fulfill these criteria. We also observed that the glycosidic linkage underwent an interesting dissociation reaction under collision-induced MS/MS, and that the reaction product is very useful in structural investigation based on mass spectrometry, especially since it provides information regarding anomeric configurations. Despite its importance, the reaction mechanism of the dissociation is not fully understood. For this reason, we studied the mechanism by synthesizing possible products and used them in detailed analyses based on energy-resolved mass spectrometry where the energy dependence of the dissociation reaction was analyzed under collision-induced dissociation conditions. As a result of spectral match with one of synthesized reference compounds, it was suggested that the dissociation reaction to generate a C-ion species and a pyrrolidine took place through a five-membered transition state in two-step reaction sequence.