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• Oligosaccharide fractions H1 – H4 from depolymerized HcFG was purified and characterized. • HcFG was deduced as -{→4)-[ l -FucS-α(1→3)]- d -GlcA-β(1→3)- d -GalNAc 4S6S - β(1}n-. • FG branched with Fuc 3S4S was susceptible to β -eliminative depolymerization. • Anticoagulant activities of native and depolymerized HcFG were assessed. A glycosaminoglycan was isolated from the sea cucumber Holothuria coluber (HcFG). A series of oligosaccharide fragments (dp range 3–11) were prepared from its β -eliminative depolymerized product (dHcFG). Extensive NMR characterization of the oligosaccharides indicated the d -GlcA- β 1,3- d -GalNAc 4S6S repeating disaccharide backbone was substituted by monosaccharide branches comprising of Fuc 2S4S , Fuc 3S4S and Fuc 4S , linked to O-3 of d -GlcA. For the prevailing Fuc 3S4S at nonreducing end of dHcFG, the β- eliminative depolymerization process of HcFG was compared with those of the FGs from Actinopyga miliaris (AmFG, branched with Fuc 3S4S) and Stichopus variegatus (SvFG, branched with Fuc 2S4S). The result suggested that d -GlcA substituted with Fuc 3S4S was more susceptible to depolymerization than that with Fuc 2S4S. It might be due to the larger steric hindrance effects from Fuc 2S4S on the esterification of GlcA. Biological assays confirmed that the minimum chain length (dp8), regardless of the Fuc branch types, was required for the potent anti-iXase and anticoagulant activities in FG fragments. [ABSTRACT FROM AUTHOR]

• A novel FG (AmFG) were extracted from sea cucumber Acaudina molpadioides. • The structures of eight oligosaccharides from depolymerized AmFG were determined. • AmFG branched with unusual disaccharide GalNAc-α1,2-Fuc, besides monosaccharides. • The anticoagulant and anti-iXase activities of AmFG and oligomers were discussed. A fucosylated glycosaminoglycan (AmFG) was extracted from the sea cucumber Acaudina molpadioides. And a series of oligosaccharides were purified from the size-homogeneous fractions, which were prepared from the β-eliminative depolymerized AmFG. According to "bottom-up" strategy, the precise structure of AmFG was elucidated by analyzing the structures of these purified oligosaccharides, combining with NMR analysis of its free-radical depolymerized product. It contained a CS-E-like backbone, and each GlcUA was branched with a mono- or di-sulfated fucose (Fuc) at O -3. Intriguingly, besides two types of monosaccharide branches, Fuc 2S4S (60 %) and Fuc 4S (25 %), that were common in FG, AmFG also contained an unusual disaccharide branch GalNAc-α1,2-Fuc 3S4S (15 %); this is the first report of such a structure in a glycosaminoglycan. Biological assays indicated that native AmFG and its oligosaccharides had potent anticoagulant and intrinsic tenase (iXase) inhibitory activities in a chain length-dependent manner. For these oligosaccharides, octasaccharide was the minimum structural fragment for potent anti-iXase activity, and the disaccharide branch might enhance this activity. [ABSTRACT FROM AUTHOR]