Regioselective and Stereospecific β‐Arabinofuranosylation by Boron‐Mediated Aglycon Delivery

Abstract

AbstractRegio‐ and stereoselective formation of the 1,2‐cis‐furanosidic linkage has been in great demand for efficient synthesis of biologically active natural glycosides. In this study, we developed a regioselective and β‐stereospecific d‐/l‐arabinofuranosylation promoted by a boronic acid catalyst under mild conditions. The glycosylations proceeded smoothly for a variety of diols, triols, and unprotected sugar acceptors to give the corresponding β‐arabinofuranosides (β‐Arbf) in high yields with complete β‐stereoselectivity and high regioselectivity. The regioselectivity was completely reversed depending on the optical isomerism of the donor used and was predictable a priori using predictive models. Mechanistic studies based on DFT calculations revealed that the present glycosylation occurs through a highly dissociative concerted SNi mechanism. The usefulness of the glycosylation method was demonstrated by the chemical synthesis of trisaccharide structures of arabinogalactan fragments.