A Siloxane-Bridged Glycosyl Donor Enables Highly Stereoselective β‑Xylulofuranosylation

We
report a siloxane-protected donor (7) for the highly
stereoselective formation of β-(2,3-cis)-xylulofuranosyl
bonds. Glycosylation reactions with 7 gave >80% yields,
and only β-xylulofuranosides were isolated in all cases. The
utility of 7 for the synthesis of complex glycans was
shown by its successful application to the preparation of the repeating
unit from the lipopolysaccharide O-antigen of Yersinia enterocolitica serovars O:5/O:5,27. This structure is a pentasaccharide with two
β-xylulofuranose residues; using 7, both were introduced
simultaneously with excellent stereocontrol.