2-Deoxyoligosaccharides are structural units in many biological active natural products and play important roles in their biological activities. The synthesis of various deoxyoligosaccharides derivatives would be attractive and effective way for the synthesis of new biologically active small molecules. However, construction of 2-deoxyoligosaccharide is very difficult because the lack of electron-withdrawing substituent at C-2 makes the glycosidic linkage unstable under acidic condition. In this symposium, we describe effective α- and β-selective glycosylation for the synthesis of deoxyoligosaccharides and an application to the synthesis of a versipelostatin sugar-part. First, we describe β-selective glycosidation of 2-deoxyosugars via oxidative activation of glycosyl imidates with iodine and a catalytic amount of Et_3SiH. Using this method, β(1,4) tetraolivoside was prepared by a simple glycosidation and deprotection procedure. Next we report α-selective glycosylation based on the oxidative activation of the glycosyl imdiates. This method enables the direct and stereoselective synthesis of deoxyoligosaccharide involving both α- and β-glycosidic linkages. Finally, we describe the synthesis of 7-reduced-versipelostatin (VST) derivatives from a protected reduced aglycon. We also report the biological effect of the deoxusugar part on the biological activity, and structure revision of the deoxysugar part of VST.
