Synthesis of oligosaccharides containing the X-antigenic trisaccharide (α-l-Fucp-(1→3)-[β-d-Galp-(1→4)]-β-d-GlcpNAc) at their nonreducing ends

The "armed" methyl 2,3,4-tri-O-benzyl-1-thio-β-l-fucopyranoside was reacted with "disarmed" phenyl O-(tetra-O-acetyl-β-d-galactopyranosyl)-(1→4)-6-O-benzyl-2-deoxy-2-phthalimido-1-thio-β-d-glucopyranoside in the presence of CuBr₂-Bu₄NBr complex to give phenyl O-(2,3,4,6-tetra-O-acetyl-β-d-galactopyranosyl)-(1→4)-O-[(2,3,4-tri -O-benzyl-α-l-fucopyranosyl)-(1→3])-6-O-benzyl-2-deoxy-2-phthalimido-1-thio-β-d-glucopyranoside (6) as a novel glycosyl donor. The glycosylating capability of 6 was further examined using N-iodosuccinimide-triflic acid as a reagent. This led to the synthesis of a tetrasaccharide and a pentasaccharide incorporating the X-antigenic structure represented by 6.