Linear and cyclic oligo-β-(1→6)-D-glucosamines: Synthesis, conformations, and applications for design of a vaccine and oligodentate glycoconjugates

Abstract

Poly-β-(1→6)-N-acetyl-D-glucosamine is an exopolysaccharide secreted by numerous pathogenic bacteria, includingStaphylococcus aureus,Escherichia coli,Yersinia pestis,Bordetella pertussis,Acinetobacter baumannii,Burkholderiaspp., and others. A convergent approach was developed for the synthesis of oligosaccharide fragments consisting of 5, 7, 9, and 11 glucosamine orN-acetylglucosamine units and for the preparation of five nona-β-(1→6)-D-glucosamines with variousN-acetylation patterns. Penta- and nona-β‑(1→6)-D-glucosamines conjugated to protein carriers through a specially developed sulfhydryl linker proved to be highly immunogenic in mice and rabbits and elicited antibodies that mediated opsonic killing of multiple strains ofS. aureus(including methicillin-resistantS. aureus, MRSA) andE. coli, and protected againstS. aureusskin abscesses and lethalE. coliandB. cenocepaciaperitonitis. These findings provide a basis for the construction of a unique semisynthetic vaccine against multiple bacterial targets. Conformational studies by means of special NMR experiments and computer modeling revealed that the oligo-β-(1→6)-D-glucosamine chain exists mostly in a helix-like conformation, where the terminal monosaccharides are arranged close to each other. Owing to this feature, oligoglucosamines consisting of 2 to 7 residues easily form products of cycloglycosylation. Cyclooligo-β-(1→6)-D-glucosamines represent a new family of functionalized cyclic oligosaccharides. Owing to their molecular architectonics, these compounds are convenient scaffolds for the design of conjugates with defined valency, symmetry, flexibility, and function.