Promoter-Assisted Stereoselective Synthesis of the 6-Deoxy-β-d-manno-heptopyranose Oligosaccharides.

We report a promoter-assisted glycosidation approach for the stereoselective synthesis of the 6-deoxy-β-d-manno-heptopyranose oligosaccharides. SphosAuNTf2-promoted glycosidation of 6-deoxy-d-manno-heptopyranosyl o-hexynylbenzoate with common alcohols afforded a range of 6-deoxy-d-manno-heptosides with good to excellent β-selectivities. The counterion and the ligand of SPhosAuNTf2 were found to have a dramatic effect on the formation of the 1,2-cis-β-linked 6-deoxy-d-manno-heptosides. This approach was effectively applied to the stereocontrolled synthesis of the 6-deoxy-β-d-manno-heptopyranose oligosaccharides relevant to Burkholderia pseudomallei and Burkholderia mallei.