Synthesis of the Pentasaccharide Repeating Unit Corresponding to the Cell Wall <i>O</i> ‐Polysaccharide of <i>Salmonella riogrande</i> O:40 (Group R) Strain

Synthesis of a pentasaccharide corresponding to the repeating unit of the cell wall O ‐polysaccharide of Salmonella riogrande O:40 has been achieved in very good yield. During the process of synthesis, construction of the α ‐D‐galactosamine moiety was achieved by using 2‐azido‐2‐deoxy‐D‐galactosamine thioglycoside donor in ether‐based reaction solvent. Construction of the β ‐mannosidic linkage in the pentasaccharide was achieved using remotely placed picoloyl group influenced H ‐bond mediated aglycone delivery. All glycosylation steps were high yielding with satisfactory stereochemistry at the newly formed glycosidic linkages. Azido group was directly converted into acetamido group by the treatment with thioacetic acid and triethylsilane was used as the source of hydrogen in a catalytic transfer hydrogenation condition.