Synthetic routes toward pentasaccharide repeating unit corresponding to the O-antigen of Escherichia coli O181

An efficient synthetic strategy has been developed for the synthesis of the pentasaccharide repeating unit corresponding to the O-antigen of Escherichia coli O181. A one-pot, two step iterative glycosylation and 2?+?3] block glycosylation strategy have been adopted for the construction of the pentasaccharide derivative 2, which was then transformed into target compound 1 after a series of functional group transformations. Here H₂SO₄-silica has been used successfully as a promoter for all glycosylation reaction. The stereoselective outcomes of all glycosylation reactions were very good. The 2-acetamido-2,6-dideoxy-l-glucose (l-QuipNAc) building block was obtained from known carbohydrate l-rhamnose precursors.