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  • 1.
    Ali, Tara
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Structural Studies of O-Polysaccharides from Diarrhoeal Escherichia coli2007Doctoral thesis, monograph (Other academic)
    Abstract [en]

    This thesis describes the structural analysis of O-polysaccharides from the Gram-negative bacterium Escherichia coli that is a diarrhoeal pathogen. The Escherichia coli serotypes investigated were O178, O171, O166 and O128. The methods used in these studies were nuclear magnetic resonance spectroscopy and component analysis.

    All analysed serotypes had pentasaccharide repeating units. E. coli strain O128 and O166 was shown to have the topology of four carbohydrate residues in the backbone while the 5-residue backbone is found in E. coli O178 and O171.

    The biological repeating units have been determined for the analysed polysaccharides and it was shown that all of the serotypes studied had a 3-substituted N-acetylgalactosamine residue at the reducing end. From this it was deduced that the terminal end of E. coli O171 and O128 have sialic acid and blood type antigens, respectively. This should make E. coli O171 and O128 less recognizable to the immune system as a foreign invader. This can result in that E. coli O171 and O128 may evade the immune system more easily.

  • 2.
    Sebelius, Sara
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Palladium-Catalyzed Synthesis and Transformation of Organoboranes2006Doctoral thesis, monograph (Other academic)
    Abstract [en]

    This thesis presents the development of new palladium-catalyzed transformations involving synthesis and application of allylborane reagents. In these reactions various palladium sources, including pincer complexes and commonly used catalysts were applied.

    A new transformation for allylation of aldehyde and imine substrates was devised using allyl acetates, diboronate reagents and catalytic amounts of Pd2(dba)3. By employment of commercially available chiral diboronates enantioenriched homoallyl alcohols could be obtained.

    We have also developed a palladium-catalyzed method for synthesis of functionalized allylboronic acids from vinyl cyclopropane, vinyl aziridine, allyl acetate and allyl alcohol substrates using diboronic acid as reagent. In this process a highly selective selenium based pincer-complex was used as catalyst. The resulting allylboronic acid products were converted to potassium trifluoro(allyl)borates or allylboronates.

    The functionalized allylboronic acids generated in the above procedure were employed as reagents in two synthetic transformations. One of these transformations involves a palladium(0)-catalyzed coupling reaction between allylboronic acids and aryl iodides. The reaction was regioselective for the branched allylic product, typically difficult to prepare in the absence of directing groups. We also developed another transformation for allylation of aldehydes with allyl alcohols via allylboronic acid intermediate. This procedure can be performed as a simple one-pot sequence affording homoallyl alcohols with excellent stereo- and regioselectivity.

  • 3.
    Staaf, Mikael
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Structural and conformational studies of bacterial polysaccharides employing NMR spectroscopy2000Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Methods and approaches for performing structural and conformational analysis of bacterial polysaccharides in solution are described. The structure of one exopolysaccharide from Lactobacillus helveticus and two O-antigens from Escherichia coli have been determined using NMR spectroscopy, chemical degradation and mass spectrometry. This thesis discusses different problems encountered in connection with these structural elucidations, namely, overlap of NMR signals, heterogeneity in the polysaccharide sequence and the configurations of a nonulosonic acid.

    A conformational analysis of the enterobacterial common antigen (ECA) in the form of a cyclic dodecamer is described. Nuclear Overhauser effects (NOEs) and heteronuclear three-bond coupling constants (3JCH) over the glycosidic linkages were determined and used to calculate proton-proton distances and torsion angles. Residual dipolar couplings were measured in a liquid crystalline medium. These couplings provide orientational information distinct from that contained in the local NOE and 3JCH data. The experimental data were compared to the averaged distances, three-bond proton-carbon coupling constants and C-H vector orientations in a model obtained by molecular dynamics simulations. From a fragment that were in agreement with experimental data, a three-dimensional structure was generated for the cyclic ECA in solution

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