Chemical synthesis of the Pseudomonas aeruginosa O11 O-antigen trisaccharide based on neighboring electron-donating effect

Pseudomonas aeruginosa O11 O-antigen is immunologically active but an exact protective epitope has not yet been identified. Synthesis of O11 O-antigen trisaccharide is of importance for identifying the epitopes. Here, neighboring electron-donating effects are keys to enhance the nucleophilicity of the C3 hydroxyl groups of D- and L-fucosamines, to facilitate the efficient synthesis of the trisaccharide. The disarmed peracetylated glycosyl donor with low glycosylation reactivity and glycosyl trifluoroacetimidate with good stability allowed for the glycosylation under mild conditions. The C6 nucleophilic tosylate substitution of D-galactose with iodine was found to be dependent on the steric effect of the axial C4.