Stereoselective synthesis of α-3-deoxy-D-manno–oct-2-ulosonic acid(α-Kdo) derivatives using a C3-p-tolylthio-substituted Kdo fluoride donor

3-Deoxy-D-manno–oct-2-ulosonic acid(Kdo) is widely distributed in bacteria, and the synthesis of Kdocontaining oligosaccharides is important for the development of novel antibiotics and immunological agents. We have recently developed a strategy to achieve α-stereocontrolled glycosylation using a C3-p-tolylthio-substituted Kdo phosphite donor. The wide substrate scope and high reactivity of the donors enabled the efficient synthesis of a series of Kdo-containing glycosides with complete α-stereoselectivity and without the formation of 2,3-ene byproducts. In this study, we improved the method by replacing the leaving group diethyl phosphite with fluoride, which enhanced the stability of the donor and led to cleaner reaction. Furthermore, the substrate range was expanded by synthesizing a series of Kdo O/C/S/Nglycosides, which also opened up a new avenue for the synthesis of CMP-Kdo synthase inhibitors.