Synthesis of l-glycero- and d-glycero-d-manno-Heptose Building Blocks for Stereoselective Assembly of the Lipopolysaccharide Core Trisaccharide of Vibrio parahemolyticus O2.

Synthesis of bacterial cell surface l-glycero-d-manno-heptose (l,d-Hep)- and d-glycero-d-manno-heptose (d,d-Hep)-containing higher carbon sugars is a challenging task. Here, we report a convenient and efficient approach for the synthesis of the l,d-Hep and d,d-Hep building blocks. Using l-lyxose and d-ribose as starting materials, this approach features diastereoselective Mukaiyama-type aldol reactions as the key steps. On the basis of the synthetic l,d-Hep and d,d-Hep building blocks, we achieved the first stereoselective synthesis of the unique α-l,d-Hep-(1→3)-α-d,d-Hep-(1→5)-α-Kdo core trisaccharide of the lipopolysaccharide of Vibrio parahemolyticus O2.