Synthesis, Conformal Analysis, and Antibody Binding of <i>Staphylococcus aureus</i> Capsular Polysaccharide Type 5 Oligosaccharides

Staphylococcus aureus is one of the most prominent pathogens responsible for life-threatening hospital acquired infections. Most clinical isolates belong to serotype 5 or 8, which express unique capsular polysaccharides (CP), composed of the rare N-acetyl-β-d-mannosaminuronic acid (β-d-ManNAcA), N-acetyl-α-l-fucosamine (α-l-FucNAc) and N-acetyl-β-d-fucosamine (β-d-FucNAc) that can be used for the development of conjugate vaccines. Different acetylation patterns of CP5 create microheterogeneous polymers, carrying partial zwitterionic character, which may be important for immunological activity. We here report on the assembly of a set of conjugation-ready CP5 oligosaccharides, ranging in length from trisaccharides to nonasaccharides. The developed protecting group strategy has allowed the incorporation of N-acetyl, -NH₃ ⁺ and O-acetyl groups. The reported syntheses offer solutions for the construction of the challenging cis-glycosidic linkages, the incorporation of many different functional groups and the installation of an appropriate linker for future conjugation purposes. Conformational analysis of the O-acetylated oligomers has revealed a distinctive linear conformation with the repeating units (RUs) being flipped ∼180° with respect to the flanking RUs. Binding studies with CP5-antibodies revealed the trisaccharide to be too short for relevant binding, while the hexa- and nonasaccharides exhibited strong binding. The l-FucNAc acetyl esters and d-FucNAc acetamides were shown to be crucial for binding.