Synthesis of disaccharide glycosyl donors suitable for introduction of the β-d-Gal p-(1 → 3)-α- and -β-d-Gal pNAc groups

2-(Trimethylsilyl)ethyl 2-azido-4,6-O-benzylidene-2-deoxy-β-d-galactopyranoside (4) was glycosylated with phenyl 2,3,4,6-tetra-O-acetyl-1-thio-β-d-galactopyranoside to give 2-(trimethylsilyl)ethyl 2-azido-4,6-O-benzylidene-2-deoxy-3-O-(2,3,4,6-tetra-O-acetyl-β-d-galactopyranosyl)-β-d-galactopyranoside (6) in 99% yield. Removal of the benzylidene group and acetylation gave the key intermediate 2-(trimethylsilyl)ethyl 4,6-di-O-acetyl-2-azido-2-deoxy-3-O-(2,3,4,6-tetra-O-acetyl-β-d-galactopyranosyl)-β-d- galactopyranosyl) (7), which was transformed into methyl 4,6-di-O-acetyl-2-deoxy-2-phthalimido-3-O-(2,3,4,6-tetra-O-acetyl-β-d-galactopyranosyl)-1-thio-β-d- galactopyranoside (9) in two steps in an overall yield of 69%. Similarly, 7 was transformed in two steps into 4,6-di-O-acetyl-2-azido-2-deoxy-3-O-(2,3,4,6-tetra-O-acetyl-β-d-galactopyranosyl)-α-d-galactopyranosyl bromide (11) in an over-all yield of 86%. Compounds 9 and 11 are suitable glycosyl donors for introduction of the β-d-Gal p-(1 → 3)-β- and -α-d-Gal pNAc groups.