Synthesis of the pentasaccharide repeating unit of lactosillan [correction of latosillan

A pentasaccharide, beta-D-Man-(1-->2)-beta-D-GlcNAc-(1-->4)]-alpha-L-Rha-(1-->4)-alpha-L-Rha-(1-->4)-alpha-L-Rha-1-OC8H17, representing the repeating unit of latosillan, was convergently synthesized from the building blocks, ethyl 2,3-O-isopropylidene-1-thio-alpha-l-rhamnopyranoside, 2-O-acetyl-3,4,6-tri-O-benzyl-beta-d-glucopyranosyl trichloroacetimidate, and 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-beta-d-glucopyranosyl trichloroacetimidate under standard glycosylation conditions. The target pentasaccharide showed acceptable differentiation-inducing activity on HL-60 cell lines at the dosages of 10-50 microg/mL.