Total synthesis of the Glc3Man N-glycan tetrasaccharide

The total synthesis of the tetrasaccharide Glcα(1→2)Glcα(1→3)Glcα(1→3)ManαOMe, which corresponds to the terminal tetrasaccharide portion of the glucose terminated arm of the N-glycan tetradecasaccharide, was achieved by the use of differentially protected selenoglycosides and thioglycosides as glycosyl donors, all of which possessed non-participating protection of the 2-hydroxyl group. Favourable anomeric stereoselectivity was achieved for the glycosylation reactions by the use of ether as solvent, or co-solvent. Global deprotection by catalytic hydrogenation with palladium acetate in a mixture of ethanol and acetic acid yielded the target tetrasaccharide.