Synthesis of α-d-galactopyranosyl-linked oligosaccharides containing the α-Gal → β-Gal → GlcNAc sequence employing methyl-2,3,4,6-tetra-O-(4-methoxybenzyl)-1-thio- β-d-galactopyranoside as an efficient glycosyl donor

Synthesis of two trisaccharides and a tetrasaccharide, namely, α-Gal-(1 → 3)- β-Gal-(1 → 3)-GlcNAc-β-OBn (6), α-Gal-(1 → 3)-β-Gal-(1 → 4)-GlcNAc- β-OBn (9) and α-Gal-(1 → 3)-β-Gal-(1 → 4)-GlcNAc-β-(1 → 6)-GalNAc- α-OBn (19) was accomplished through development and utilization of a key α- galactosyl donor, methyl 2,3,4,6-tetra-O-(4-methoxybenzyl)-1-thio-β-d- galactopyranoside (1).