Complex Oligosaccharides Synthesis—Challenges and Tactics

Abstract

Abstract1,2-cis glycoside structures exist as constituents of biologically active natural products, pharmaceuticals, and functional materials. Therefore, there is a pressing need for the development of novel and efficient 1,2-cis-glycosylation methods to understand their specific roles and to create new lead compounds for pharmaceutical and functional materials by derivatization of these glycosides. In this context, we have developed a conceptually new glycosylation method called boron-mediated aglycon delivery (BMAD), which utilizes organoboron catalysis for simultaneously controlling the 1,2-cis stereoselectivity of the glycosidic bond formed and regioselectivity of the reaction site in the glycosyl acceptor. The method has been applied to synthesize useful glycosides including complex oligosaccharides found in pathogenic bacteria. We recently extended the BMAD method to the reaction of partially protected and unprotected glycosides for the late-stage modification of natural glycosides with interesting biological activities, and synthesized complex oligosaccharides using minimal protecting groups. Furthermore, we developed a diastereoselective desymmetric BMAD reaction of meso-diols as a new synthetic tactic for complex glycosides. Herein, we discuss the abovementioned BMAD methods and their use in the synthesis of useful glycosides.