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Convergent synthesis, NMR and conformational analysis of tetra-and petasaccharide haptens of the Shigella flexneri serotype 5a O-specific polysaccharide

Abstract : Convergent syntheses of the methyl glycosides of the branched pentasaccharide -L-Rhap-(12)-[-D-Glcp(13)]--L-Rhap-(13)--L-Rhap-(13)--D-GlcNAcp [A(E)BCD], featuring the biological repeating unit of the O-specific polysaccharide of Shigella flexneri serotype 5a, and of a related linear tetrasaccharide (EBCD) are described. The strategy, based on the trichloroacetimidate methodology, relied on the use of a key EB disaccharide donor and appropriate CD acceptors. The use of an isopropylidene acetal to block OH-4 and OH-6 of residue D was found to be a suitable alternative to the employment of the more commonly used benzylidene acetal. Conformational analysis of EBCD-OMe and A(E)BCD-OMe was based on analysis of 1H and 13C chemical shifts and inter-proton distances data obtained by NMR spectroscopy. The data showed that residue A had no influence on the conformational behaviour of residue E, although these two residues were involved in a 2,3-cis vicinal glycosylation pattern in A(E)BCD-OMe. Comparison of 1H and 13C chemical shifts of the two oligosaccharides with those of their corresponding sequences in the O-specific polysaccharide of S. flexneri 5a showed that the two oligosaccharides presented a distribution of solution conformations similar to that in the O-specific polysaccharide. The conformation of A(E)BCD-OMe was investigated by two approaches: (i) energy minimisation based on ROE-derived distances with the DISCOVER program and (ii) a conformational searching method (the CICADA algorithm interfaced with MM3 force-field). The minimised conformation obtained by the former approach was in total agreement with the average of the two major families of conformations resulting from the CICADA calculations.
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Submitted on : Friday, March 27, 2009 - 3:19:13 PM
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Laurence A Mulard, Marie-Jeanne Clément, Anne Imberty, Muriel Delepierre. Convergent synthesis, NMR and conformational analysis of tetra-and petasaccharide haptens of the Shigella flexneri serotype 5a O-specific polysaccharide. European Journal of Organic Chemistry, Wiley-VCH Verlag, 2002, 15, pp.2486-2498. ⟨10.1002/1099-0690(200208)2002:15<2486::AID-EJOC2486>3.0.CO;2-E⟩. ⟨pasteur-00371353⟩

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