Synthesis of the beta-methyl glycoside of lacto-N-fucopentaose III

A total synthesis of the beta-methyl glycoside of lacto-N-fucopentaose III (1) is described. Phenyl 2,3,4,6-tetra-O-benzoyl-beta-D-galactopyranosyl-(1 -->4)-6-O-benzyl-2-deoxy-2-phthalimido-1-thio-beta-D-glucopyranoside (4), a key intermediate prepared by condensation of 2,3,4,6-tetra-O-benzoyl-alpha -D-galactopyranosyl bromide (2) and phenyl 6-O-benzyl-2-deoxy-2-phthalimido -1-thio-beta-D-glucopyranoside (3), was glycosylated with ethyl 2,3,4-tri-O -benzyl-1-thio-beta-L-fucopyranoside (5) to give the trisaccharide donor 6, which, on coupling with methyl 2,6-di-O-benzyl-beta-D-galactopyranosyl-(1- ->4)2,3,6-tri-O-benzyl-beta-D-glucopyranoside (7), afforded the pentasaccha ride 8. It was easily transformed into the target pentasaccharide 1 via hyd razinolysis, acetylation, O-deacetylation, and hydrogenolysis.