Chemical synthesis elucidates the absolute configuration and key antigenic epitope of serotype O100 O-antigen.

The emergence of drug-resistant strains of , coupled with the current limitations of oral vaccines, underscores the urgent need for the development of new vaccines. The O-antigen of serotype O100 has emerged as a promising candidate for vaccine development. To investigate the absolute configuration of 3,5-dihydroxyhexanoyl (dHh) and to evaluate the structure-activity relationship of the O-antigen trisaccharide repeating unit, we completed total synthesis of four potential trisaccharide isomers, along with 11 additional oligosaccharide fragments of the O-antigen. Stereoselective reduction was used for the synthesis of dHh, and the efficient assembly of dHh and ()-3-hydroxybutanoyl (Hb) was achieved through a post-glycosylation modification strategy. Through NMR analysis, the absolute configuration of dHh was assigned 3,5. Glycan microarray screening indicated that Hb is essential for the antigenicity of O-antigen. The nonreducing end disaccharide may serve as the minimal antigenic epitope. These findings are an important step toward the design of semi-synthetic carbohydrate vaccines against .