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Structural Studies of the O-Acetyl-Containing O-Antigen from a Shigella flexneri Serotype 6 Strain and Synthesis of Oligosaccharide Fragments Thereof
Stockholm University, Faculty of Science, Department of Organic Chemistry.
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2013 (English)In: European Journal of Organic Chemistry, ISSN 1434-193X, E-ISSN 1099-0690, no 19, 4085-4106 p.Article in journal (Refereed) Published
Abstract [en]

Extensive analysis by NMR spectroscopy of the delipidated lipopolysaccharide of Shigella flexneri serotype 6 strain MDC 2924-71 confirmed the most recently reported structure of the O-antigen repeating unit as {4)--D-GalpA-(13)--D-GalpNAc-(12)--L-Rhap3Ac/4Ac-(12)--L-Rhap-(1}, and revealed the non-stoichiometric acetylation at O-3C/4C. Input from the CASPER program helped to ascertain the fine distribution of the three possible patterns of O-acetylation. The non-O-acetylated repeating unit (ABCD) corresponded to about 2/3 of the population, while 1/4 was acetylated at O-3C (3AcCDAB), and 1/10 at O-4C (4AcCDAB). Di- to tetrasaccharides with a GalpA residue (A) at their reducing end were synthesized as their propyl glycosides following a multistep linear strategy relying on late-stage acetylation at O-3C. Thus, the 3C-O-acetylated and non-O-acetylated targets were synthesized from common protected intermediates. Rhamnosylation was most efficiently achieved by using imidate donors, including at O-4 of a benzyl galacturonate acceptor. In contrast, a thiophenyl 2-deoxy-2-trichloroacetamido-D-galactopyranoside precursor was preferred for chain elongation involving residue B. Final Pd/C-mediated deprotection ensured O-acetyl stability. All of the target molecules represent parts of the O-antigen of S. flexneri 6, a prevalent serotype. Non-O-acetylated oligosaccharides are also fragments of the Escherichia coli O147 O-antigen.

Place, publisher, year, edition, pages
2013. no 19, 4085-4106 p.
Keyword [en]
Carbohydrates, Glycosylation, Oligosaccharides, NMR spectroscopy, Structure elucidation, Polysaccharides
National Category
Organic Chemistry
URN: urn:nbn:se:su:diva-92505DOI: 10.1002/ejoc.201300180ISI: 000320720100021OAI: diva2:639786
Swedish Research CouncilKnut and Alice Wallenberg FoundationEU, FP7, Seventh Framework Programme


Available from: 2013-08-09 Created: 2013-08-07 Last updated: 2013-08-26Bibliographically approved

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Fontana, CarolinaWidmalm, Göran
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