Total Synthesis of the O-Antigen Repeating Unit of Pseudomonas aeruginosa Serotype O1

Herein, we report the total synthesis of the tetrasaccharide repeating unit of the Pseudomonas aeruginosa O1 O-antigen → 4)-α-d-GalpNAc-(1 → 4)-β-d-GlcpNAc3NAcA-(1 → 3)-α-d-FucpNAc-(1 → 3)-α-d-QuipNAc-(1 → using a convergent strategy. The approach highlights the orthogonal protection of rare deoxy sugars, the stereoselective introduction of multiple amino functionalities, and the construction of several challenging 1,2-cis glycosidic linkages involving 2-deoxyamino sugars. Four rare monosaccharides were synthesized with tailored protecting group schemes and assembled into two disaccharide intermediates. The convergent [2 + 2] β-trans-glycosylation provided the target tetrasaccharide 1.