1H and 15N NMR Characterization of the Amine Groups of Heparan Sulfate Related Glucosamine Monosaccharides in Aqueous Solution

Glucosamine is an important constituent of the heterogeneous glycosaminoglycans heparin and heparan sulfate occurring in N-acetylated and N-sulfated forms, and as the unmodified amine. Though the H-1 and N-15 NMR chemical shifts of N-acetyl- and N-sulfoglucosamine residues have been extensively characterized, this study provides the first direct NMR characterization of the amine groups of glucosamine and 3-O-sulfoglucosamine in aqueous solution. The solvent exchange properties of the amine protons are examined, and the possibility of a salt bridge between the sulfate and amine groups of 3-O-sulfoglucosamine is explored through H-1 NMR pK(a) measurements but is not supported by the experimental results.