Conformational study of synthetic Δ4-uronate monosaccharides and glycosaminoglycan-derived disaccharides

Sixteen Δ4-uronate monosaccharides were chemically synthesized. Their carboxy group was protected as a methyl or benzyl ester, the anomeric hydroxyl group as a benzyl glycoside and the 2 and 3 hydroxyl groups were protected with different substitution patterns as both ester and ether derivatives. Disaccharides containing Δ4-uronates were prepared from heparin using heparin lyases. Their carboxy group was unprotected or protected as a benzyl ester and the two hydroxyls in the uronate moiety were free, as O-sulfo derivatives or acylated. The conformation of these unsaturated uronate monosaccharide and disaccharide residues was studied using 1H NMR by examining interproton vicinal coupling constants. The Δ4-uronate residue adopted either the 2H1 or the 1H2 conformations. The equilibrium between these two conformers was shown to be controlled by substitution pattern.