Exopolysaccharides (EPS) are present on the outside of bacteria, where they can be loosely attached to the cell wall or secreted in the environment. EPS of lactobacilli and bifidobacteria demonstrate several beneficial effects such as antitumor activity, and they serve as prebiotic or as immune modulators. The EPS structure of Bifidobacterium adolescentis, a beneficial strain commonly observed in the gut microbiome, contains 6-deoxy-L-talose (6dTal) residues linked in a 1,2 cis fashion. To understand the biological impact of the cis-linked 6dTal moieties, well-defined structures are needed. Because little is known about the glycosylation properties and preferences of 6dTal, this is the main challenge of this project.
To develop a robust method to attach multiple 6dTal residues through cis-linkages, an efficient protective group strategy, together with a study on the reactivity and selectivity of the resulting 6dTal donors, is essential. To orthogonally protect the C-3 position to allow subsequent elongation, various protective groups were introduced regioselectively. The resulting donors were glycosylated to a set of acceptors using different activation protocols. The best suitable donor was further applied in the oligosaccharide assembly.
This communication will demonstrate the unexpected properties of unusual 6dTal monosaccharides as building blocks and their properties and limitations when used in oligosaccharide synthesis.
- Castro-Bravo, N.; Wells, J. M.; Margolles, A.; Ruas-Madiedo, P. Front. Microbiol. 2018, 9, 2426.
- Nagaoka, M.; Muto, M.; Yokokura, T.; Mutai, M. J. Biochem. 1988, 103, 618–621.