Total Synthesis of D-Fucp3NAc Containing Conjugation-Ready Pentasaccharide Repeating Unit Related to Acinetobacter baumannii RCH51.

Herein, we report a concise synthetic strategy for the first total synthesis of the pentasaccharide repeating unit of the capsular polysaccharide of Acinetobacter baumannii RCH51. The structurally unique pentasaccharide possesses three successive1,2-cis-glycosidic linkages and ddD-Fucp3NAc as a rare-sugar. The protected pentasaccharide was synthesized using a highly stereoselective (4 + 1) block glycosylation strategy. The ddD-Fucp3N3 monosaccharide donor was synthesized efficiently on a gram scale from easily available d-glucose. The linker-appended pentasaccharide repeating unit offers a compelling opportunity for further preparation of glycoconjugates and for immunological investigations.