Synthesis and Evaluation of 3-Deoxy-D-manno-oct-2-ulosonic Acid Derivatives to Perturb Escherichia coli Lipopolysaccharide Biosynthesis

Lipopolysaccharides (LPS) play important roles in the Gram-negative bacterial cell envelope. LPS are located in the outer leaflet of the outer membrane and generally serve as the first defense layer against environmental stress. 3-Deoxy-D-manno-oct-2-ulosonic acid (Kdo) is a highly conserved monosaccharide that resides in the inner core region of LPS and that connects the lipid A moiety to the extending polysaccharide chain through the hydroxyl group on its C-5 position. Due to its central function in LPS, we hypothesized that metabolically incorporated Kdo derivatives modified on the C-5 position may impair LPS synthesis and therefore lead to a reduced outer membrane integrity. To test this, we successfully synthesized four Kdo derivatives, 5-epi-Kdo, 5-deoxy-Kdo, 5-epi-Kdo-8-N₃, and 5-deoxy-Kdo-8-N₃, and incubated Escherichia coli (E. coli) strains in the presence of these derivatives to investigate their influence on LPS production and labeling. Interestingly, while the 5-deoxy derivatives were not incorporated, 5-epi-Kdo-8-N₃ was successfully incorporated in cell envelope-associated LPS and increased the sensitivity of the bacteria to vancomycin, indicating that 5-epi-Kdo-8-N₃ incorporation in LPS interferes with outer membrane integrity.