Synthetic oligorhamnans related to the most common O-chain backbone from phytopathogenic bacteria

Abstract The synthesis of the tetrasaccharide rhamnanic motif α- l -Rha-(1→3)-α- l -Rha-(1→2)-α- l -Rha-(1→2)-α- l -Rha and its dimerization to octasaccharide have been developed. Three different pathways toward the dimerization have been investigated; the best one was based on a [4+2]+2 stepwise condensation of a rhamnose tetrasaccharide with two rhamnosyl N -phenyl trifluoroacetimidates as glycosyl donors and on an orthogonal set of protecting groups consisting of benzoyl, levulinoyl, and allyl groups.