Convergent Synthesis of the Tetrasaccharide Repeating Unit of the O-Polysaccharide of Salmonella enterica O41

A convergent approach has been developed for the synthesis of the unique tetrasaccharide repeating unit corresponding to the O-polysaccharide of Salmonella enterica O41. The synthetic strategy involved generation of a beta-D-mannopyranosidic linkage and an alpha-L-quinovasaminyl glycosidic linkage, which require special tuning in the reaction conditions to avoid the formation of undesired products. A stereoselective [2 + 2] block glycosylation strategy has been adopted for the synthesis of the target tetrasaccharide derivative. All glycosylations were highly stereoselective with satisfactory yield.