De novo asymmetric synthesis of rhamno di- and tri-saccharides related to the anthrax tetrasaccharide

An asymmetric synthesis of the di- and tri-saccharide portion of the naturally occurring anthrax tetrasaccharide from acetylfuran has been developed. The construction of the di- and tri-saccharide subunits is based upon our previously disclosed route to anthrax tetrasaccharide. The approach uses iterative diastereoselective palladium-catalyzed glycosylations, Luche reductions, diastereoselective dihydroxylations, and regioselective protections for the assembly of the rhamno-di- and tri-saccharide. The route was also modified for the preparation of the mixed d-/l-di-saccharide analogue.