Construction of α‐ <scp>GlcN3</scp> Glycosidic Bonds to the Total Synthesis of <i>Acinetobacter baumannii</i> Capsular Polysaccharide <scp>K88</scp> Repeating Units

Comprehensive Summary The 1,2‐ cis ‐2‐amino‐2‐deoxyglycoside represents a critical structural motif in numerous bioactive natural products and pharmaceuticals, yet its stereoselective synthesis remains a long‐standing challenge. Building on our previous ZnI₂‐mediated methodology for constructing 1,2‐ cis ‐2‐azido‐2‐deoxy glycosidic linkages, we herein report systematic refinements that substantially enhance the versatility and efficiency of this approach. Key advancements include: (i) Substitution of zinc iodide with zinc triflate [Zn(OTf)₂], a superior Lewis acid catalyst that expands substrate scope to include sterically hindered and electronically deactivated glycosyl acceptors; (ii) Development of a novel glycosyl donor platform superseding the conventional 4,6‐O‐TIPDS/3‐O‐TIPS protection patterns, enabling streamlined post‐glycosylation deprotection sequences for iterative glycan assembly. These methodological improvements effectively address prior limitations in functional group compatibility and synthetic scalability. Leveraging this optimized protocol as the cornerstone synthetic strategy, we achieved the total synthesis of the Acinetobacter baumannii capsular polysaccharide (CPS) K88 pentasaccharide repeating unit, a structurally complex target containing two consecutive 1,2‐ cis glucosaminide linkages. This synthetic milestone demonstrates the robustness of our methodology and furnishes essential molecular tools for subsequent immunological investigations of this clinically significant pathogen.