Regioselective sulfation of alginate at 2-O-position of mannuronic acid unit with Py∙SO in DMSO.

Alginates are brown algal polysaccharides consisting of β-D-mannuronic (M) and α-l-guluronic acid (G) residues linked with 1→4 glycosidic bonds. To functionalize these natural resources for biomedical use, alginates can be chemically modified, including by sulfation. Here regioselective sulfation of alginates at M-2 in DMSO with Py∙SO is described, by either sulfating alginates directly or through using alginates with added protecting groups (PG-s), including TBDMS-ether, Piv-, Bz-esters and intramolecular 3,6-lactone. Highest regioselectivity was found by sulfating TBDMS- and Piv-protected alginates, with over 65 % of M-residues being 2-O-sulfated. However significant reduction in molecular weight was found when alginates were sulfated in DMSO. Results from this work will allow a degree of control over substitution patterns in sulfated alginates. This will allow to more accurately determine structure-property relationships in biomedical research.