Synthesis of Conjugation-Ready Trisaccharide Repeating Units of Multidrug-Resistant Pathogen Acinetobacter baumannii MG1 and Strain 24

We report the first total synthesis of conjugation-ready trisaccharide repeating units from Acinetobacter baumannii clinical isolates MG1 and strain 24, both featuring the same trisaccharide framework. A key synthetic challenge addressed here is the stereoselective installation of a 1,2-cis glycosidic linkage with a poorly nucleophilic axially oriented C4-OH of the d-GalNAcA acceptor, which was efficiently achieved by conformational switching of the pyranose ring from ⁴C₁ to ¹C₄ leading to enhanced reactivity.