Synthesis of #beta#-D-Ribofuranosyl-(1->3)-#alpha#-L-rhamnopyranosyl-(1->3)-L-rhamnopyranose by in situ Activating Glycosylation Using 1-OH Sugar Derivative and Me_3SiBr-CoBr_2-Bu_4NBr-Molecular Sieves 4A System

摘要

#beta#-D-Ribofuranosyl-(1->3)-#alpha#-L-rhamnopyranosyl-(1->3)-L-rhamnopyranose, the trisaccharide repeating unit of the C. freundii O28, 1c O-specific polysaccharide, was synthesized using in situ activating glycosylation of the 1-OH sugar derivatives and a reagent mixture of trimethylsilyl bromide, cobalt(II) bromide, tetrabutylammonium bromide, and molecular sieves 4A. Regioselective tritylation was usfurl for synthesizing the 3-OH derivatives of methyl, allyl, and benzyl #alpha#-L-rhamnosides.