The glycosidic bond cleavage and desulfation investigation of fucosylated glycosaminoglycan during mild acid hydrolysis through structural analysis of the resulting oligosaccharides

Mild acid hydrolysis is a common method to study the chemical structure of fucosylated glycosaminoglycan (FG). It was generally considered that the fucose branches alpha-L-FucS-(1, of FG could be hydrolyzed selectively in mild acid. This report focused on the selectivity of glycosidic bond cleavage and extensive desulfation characteristics of the backbone during mild acid hydrolysis. The hydrolyzed product of native SvFG (dfSvFG) was prepared by mild acid hydrolysis in 0.1 M H2SO4 at 100 degrees C for 2 h. A series of oligosaccharides were purified by GPC and SAX-HPLC from dfSvFG, then they were analyzed by HPGPC, 1D/2D NMR and ESI-Q-TOF-MS. The precise structure of these oligosaccharides was elucidated to be trisaccharides, tetrasaccharides and pentasaccharides, indicating SvFG branches hydrolyzed basically and its' backbone composed of repeating beta-D-GlcA-(1,3)-D-GalNAc and beta-D-GalNAc-(1,4)-D-GlcA unit. The prevalent presence of the GlcA residues at the non-reducing terminal of these oligosaccharides, suggesting the glycosidic bond of beta-D-GalNAc-(1,4)-D-GlcA was more susceptible to acid than that of beta-D-GlcA-(1,3)-D-GalNAc during mild acid hydrolysis. Moreover, the sulfate ester groups in GalNAc(4S6S) unit could also be hydrolyzed by acid, and it at position C-4 was more susceptible to hydrolysis than that at C-6. This extensive degradation and desulfation of the backbone should be taken into consideration when mild acid hydrolysis was used in elucidating the exact structure or structure-activity relationship of native FG.