Structure of a sulfated xylofucan from the brown alga Punctaria plantaginea

•A sulfated xylofucan was isolated from the brown alga Punctaria plantaginea.•Polysaccharide structure was elucidated by chemical and spectral methods.•The polysaccharide backbone is built up of 3-linked α-l-Fucp.•Two of every three Fuc are sulfated at O-2 forming trisaccharide repeating units.•The backbone regularity is masked by random substitution by β-d-Xylp at Fuc O-4.

A polysaccharide composed of l-fucose, d-xylose, and sulfate in a molar proportion of about 5:2:3 was isolated from the brown alga Punctaria plantaginea. Polysaccharide structure was elucidated by methylation analysis, Smith degradation, as well as by 1D and 2D NMR spectroscopy. The polysaccharide was shown to contain a backbone of 3-linked α-l-fucopyranose residues, about two thirds of which are sulfated at O-2 forming trisaccharide repeating units →3)-α-l-Fucp2S-(1→3)-α-l-Fucp2S-(1→3)-α-l-Fucp-(1→. This structural regularity is masked by random distribution of non-sulfated β-d-Xylp residues attached to position 4 of the backbone. The polysaccharide is a new representative of a complex ‘fucoidan’ family of sulfated polysaccharides of brown seaweeds.

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