PhPO-Modulated Kdo Glycosidation for Stereoselective Synthesis of β-Kdo-Containing Disaccharides.

A PhPO-modulated β-selective Kdo glycosidation approach is developed for the stereoselective synthesis of β-Kdo glycosides. With the readily available per--acetylated Kdo ynenoate as the donor, the glycosylation with a series of alcohols in the presence of PhPAuOTf and PhPO in toluene at low temperatures afforded the desired Kdo glycosides with good to excellent β-selectivities. Furthermore, the PhPO-modulated approach was effectively applied to the synthesis of β-(2→4)- and β-(2→8)-linked Kdo-Kdo disaccharides for further biological studies.