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 vic inal 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.