Providencia alcalifaciens along with some of its other species proved to be pathogenic in humans causing variety of serious infections. Pentasaccharide 1 is a repeating unit of lipopolysaccharide (LPS) of Providencia alcalifaciens O60. In order to elucidate the molecular basis and use them as vaccine, synthesis of these kind of glycans is very important. An efficient synthesis of the pentasaccharidic repeating unit 1 of LPS of Providencia alcalifaciens O60 is presented. A convergent [2 + 3] glycosylation strategy was employed to construct a fully protected pentasaccharide 2. The L-serine was installed on glucuronic acid by HATU mediated coupling. Further, a disaccharidic trichloroacetimidate donor and a trisaccharide acceptor were furnished in a linear fashion from respective monosaccharide building blocks in excellent yields. The global deprotection by using Birch condition gave the desired pentasaccharide 1 in good yields. The reactive n-pentenyl group was preserved throught the synthesis to add desired functionalities later on for the bioconjugation, which is a prerequisite for immunological studies.
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