Convergent synthesis of the pentasaccharide repeating unit of the O-antigen of Shigella boydii type 14

An efficient synthesis of the pentasaccharide repeating unit of the O-antigen of Shigella boydii type 14 is reported. A one-pot, two step iterative glycosylation and [3+2] block synthetic strategy have been adopted for the construction of the pentasaccharide derivative 11, which was then transformed into target compound 1 after a series of functional group transformations. The primary hydroxyl group has been selectively oxidized to a carboxylic acid functionality without affecting the secondary hydroxyl groups. HClO4-SiO2 has been used as a solid acid substitute in all glycosylation and functional group transformations. The yields were excellent in all glycosylation steps.