APPLICATION OF GLYCALS TO THE SYNTHESIS OF OLIGOSACCHARIDES - CONVERGENT TOTAL SYNTHESES OF THE LEWIS-X TRISACCHARIDE SIALYL-LEWIS-X ANTIGENIC DETERMINANT AND HIGHER CONGENERS

Exploiting the differences in reactivity of the hydroxyl groups of glucal allows for rapid access to the sLe(x) tetrasaccharide glycal. This compound is readily converted to the title compounds by azaglycosylation followed by deprotection. The use of stannyl alkoxides in the glycosylation-rearrangement step allows for the use of minimally protected glycosides as the glycosyl accepters. Employing a galactal epoxide as a glycosyl donor allows for a maximally convergent synthesis of the Le(x) glycal.