Solution syntheses of protected type II Lewis blood group oligosaccharides: study for automated synthesis

Glycosyl phosphate and trichloroacetimidate monosaccharide building blocks were used in a stepwise solution-phase synthesis of three Lewis blood group oligosaccharides. The syntheses were conducted to establish general routes for the automated assembly of the oligosaccharide portion of biologically important glycolipids. The H-type II pentasaccharide, Le(x) pentasaccharide, and Le(y) hexasaccharide were prepared in high yield. These syntheses served to evaluate the utility and limitations of the 2-(azidomethyl)benzoate ester (AZMB) for the construction of complex carbohydrates. Development of a glucosamine building block containing a N-trichloroacetamide group to mask the C2 amine improved coupling yields and was key for completion of the Le(x) and Le(y) structures.