Total Synthesis of Trisaccharide Repeating Unit of Staphylococcus aureus Strain M.

An efficient total synthesis of a conjugation-ready trisaccharide repeating unit of strain M is reported here. The main challenges involved in this synthesis are the procurement of rare sugars (d-FucNAc and d-GalNAcA) and installation of consecutive 1,2--glycosidic linkages between them. Stereoselective 1,2- glycosylation with the linker acceptor was achieved with easily accessible benzylidene protected d-galactosamine thioglycoside by employing a DMF modulated preactivation glycosylation method. The consecutive 1,2- linkages were installed with the help of solvent participation. The carboxylic acid functionality was introduced via postglycosylation oxidation on the disaccharide moiety. The total synthesis of trisaccharide repeating unit was accomplished with the longest linear sequence of 24 steps in 4.5% overall yield.