New Methods in Glycoside Synthesis by Using Early Transition Metal-Derived Reagent

Abstract

Recent study in this laboratory is reviewed. Combination of group 4 metallocene dichloride (Cp₂MCl₂ : M= Zr, Hf) and silver salt (AgX : X = ClO₄, OTf etc.) is a particularly effective reagent for activating glycosyl fluoride, which offers a new and efficient method for O-glycoside synthesis, which made us to succeed in the first total synthesis of mycinamicin macrolide antibiotics. Mechanistic consideration of this activation led us to find that the reagent combination in 1 : 2-ratio, rather than the original 1 : 1-ratio, of Cp₂MCl₂ and AgX engendered further enhanced reactivity. Some of the recent application in oligosaccharide synthesis is listed to show the broad scope of this new glycosidation reaction in natural product synthesis. Furthermore, this combinational reagent offers a powerful basis for aryl C-glycoside synthesis and the total syntheses of three prototypical compounds of this class, vineomycinone B₂ methyl ester and gilvocarcin M and V, were successfully carried out by this glycoside activation method.