Further studies on structure of fucoidan from brown alga Saccharina gurjanovae

•Structure of galactofucan SgF from Saccharina gurjanovae was established.•SgF was depolymerized by autohydrolysis, and structure of products was studied.•Autohydrolysis of SgF at 25 °C leaded to a selective desulfation at C-2.•SgF and its derivative inhibited colony formation of colon cancer cell DLD-1.

A sulfated galactofucan SgF (MW 123 kDa) was purified from the brown alga Saccharina gurjanovae. Polysaccharide was depolymerized by autohydrolysis at 25 and 60 °C, and products were studied by mass spectrometry and 13C NMR spectroscopy. According to results of investigation, the main chain of this polysaccharide is built of a repeating units →3)-α-L-Fucp-(2,4-OSO3−)-(1→. Fucose chains could be sometimes terminated by (1 → 3)-linked galactose residues. Shorter (1 →4 )- and/or (1 → 6)-linked sulfated galactose chains are attached at positions C-2, C-3 of fucose residues. Sulfate groups can occupy positions C-2 and/or sometimes C-3 of Gal residues, but a sulfation at C-4 of the galactofucan could not be excluded. The SgF-AH25-H preparation (71 kDa) was obtained by autohydrolysis of SgF at 25 °C, which leaded to a selective desulfation at C-2 and, probably, to a cleavage of galactose chains, since structure of SgF-AH25-H represented a repeating unit →3)-α-l-Fucp-(4-OSO3−)-(1→, which was definitely established by 13C NMR spectroscopy. Galactofucan SgF and its derivative SgF-AH25-H exhibited no cytotoxic activity and leaded to about the same colony formation inhibition in colon cancer DLD-1 cells. Hence, structural simplification of SgF by lowering its molecular weight, desulfation at C-2 and removing of galactose residues by autohydrolysis at 25 °C did not decrease its anticancer activity. This procedure allows obtaining standardized products which can be used as medical.