Chemical synthesis of a hexasaccharide comprising the Lewisx determinant linked β-(1 → 6) to a linear trimannosyl core and the precursor pentasaccharide lacking fucose

Phenyl 2,3,4-tri-O-acetyl-6-O-chloroacetyl-1-thio-α,β-mannopyranoside (5) was condensed with benzyl O-(2,3,4-tri-O-benzyl-β-d-mannopyranosyl)-(1 → 6)-2,3,4-tri-O-benzyl-α-d-manno-pyranoside (12) in the presence of NIS-triflic acid to give, after removal of the chloroacetyl group, the key intermediate, benzyl O-(2,3,4-tri-O-acetyl-α-d-mannopyranosyl)-(1 → 6)-O-(2,3,4-tri-O-benzyl-β-d-mannopyranosyl)-(1 → 6)-2,3,4-tri-O-benzyl-α-d-mannopyranoside (14). A similar condensation of 6 and 7 with acceptor 14, followed by the removal of protecting groups, afforded 16 and 18, respectively. These compounds are expected to be useful in specificity studies of an antibody raised against a related, synthetic antigen that we are currently investigating.