Synthesis of a spacer-armed disulfated tetrasaccharide of SB1a, a carbohydrate hapten associated with human hepatocellular carcinoma

A disulfated tetrasaccharide fragment with a spacer arm of human hepatocellular carcinoma carbohydrate antigen SB(1a), namely, 2-aminoethyl 3-O-sulfo-beta-D-galactopyranosyl-(1 --3)-2-acetamido-2-deoxy-beta-D-galactopyranosyl-(1 --4)-3-O-sulfo-beta-D-galactopyranosyl-(1 --4)-beta-D-glucopyranoside was synthesized via a [2 + 1 + 1] block building mode. In the last coupling step toward the trisaccharide acceptor 8, benzoyl protected galactosyl bromide donor 14 was found to be much more reactive than the acetyl-protected donors.