Oligosaccharide mapping analysis by HILIC-ESI-HCD-MS/MS for structural elucidation of fucoidan from sea cucumber Holothuria floridana

The elucidation of precise structure of fucoidan is essential for understanding their structure-function relationship and promoting the development of marine drugs. In this work, we firstly reported the oligosaccharide mapping of fucoidan from Holothuria floridana using a combination of hydrothermal depolymerization, hydrophilic interaction liquid chromatography (HILIC) coupled with electrospray mass spectrometry (ESI-FTMS) and high energy collision-induced dissociation (HCD-MS/MS) and 2D NMR analysis. With careful selection of fully deprotonated molecular ions of fucoidan oligosaccharides and their NaBD4 reduced alditols, HILIC-ESI-HCD-MS/MS provided structurally relevant glycosidic product ions with no sulfate loss for definitive assignment of sequence and sulfation pattern of all the oligosaccharides and their isomers from dp2 to dp7 from hydrothermal depolymerization. The oligosaccharide mapping clarified the structure of fucoidan with various oligosaccharide domains with 2,4-di-O-sulfated and 2-O sulfated fucose residues. [Display omitted] •HCD-MS/MS of fully deprotonated parent ions provides abundant glycosidic cleavages without sulfate loss.•Sequences of fucoidan oligosaccharides and their reduced alditols were achieved by HILIC-ESI-HCD-MS/MS.•HILIC-ESI-HCD-MS/MS with hydrothermal degradation was applicable for the oligosaccharide mapping analysis of fucoidan.•Fucoidan contains various oligosaccharide domains with 2-O and 2,4-O-sulfation in fucose.