Synthesis of the saccharide moiety of galactosylgloboside (SSEA-3) and its conjugation to bovine serum albumin and sepharose

The pentasaccharide glycoside corresponding to galactosylgloboside (SSEA-3), β-d-Gal p-(1 → 3)-β-d-Gal pNAc-(1 → 3)-α-d-Gal p-(1 → 4)-β-d-Gal p-(1 → 4)-β-d-Glc p-1-OCH2CH2Si-(CH3)3 (4), was synthesized via glycosylation (87%) of 2-(trimethylsilyl)ethyl 2,3,6-tri-O-benzyl-4-O-[2,3,6-tri-O-benzyl-4-O-(2,4,6-tri-O-benzyl-α-d-galactopyranosyl)-β-d- galactopyranosyl]-β-d-glucopyranoside (2) with the glycosyl donor 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 (1), followed by removal of protecting groups. Compound 4 was transformed into the spacer glycoside β-d-Gal p-(1 → 3)-β-d-Gal pNAc-(1 → 3)-α-d-Gal p-(1 → 4)-β-d-Gal p-(1 → 4)-β-d-Glcp-1-SCH2CH2COOH (10), which was coupled to bovine serum albumin (BSA), and Sepharose beads, to give the corresponding neoglycoprotein (11, 6 mol of saccharide/mol of BSA) and glycosylated Sepharose (12, 2.7 μmol of saccharide/mL of sedimented beads), respectively. An improved synthesis of a protected globotetraoside β-d-Gal pNAc-(1 → 3)-α-d-Gal p-(1 → 4)-β-d-Gal p-(1 → 4)-β-d-Glc p-1-OCH2CH2SiMe3 is also reported.