Synthesis of inositolphosphoglycans found in Trypanosoma cruzi and development of novel carbohydrate monomolecular layers

Abstract: In this thesis, synthetic carbohydrate chemistry has been utilized to contribute to the fundamental understanding of three biological relevant areas. These include parasite cell-membrane glycoconjugates, protein-resistant surfaces and antifreeze glycoproteins.The synthesis of inositolphosphoglycans found in Trypanosoma cruzi, the pathogen of Chagas´ disease, is described. A protected derivative of 6-(2-aminoethyl phosphonic acid)-2-amino-2-deoxy-α-D-glucopyranosyl-(1→6)-D-myo-inositol-1-phosphate was identified as an appropriate acceptor to give a synthetic route to the core oligosaccharide of T. cruzi glycoinositolphospholipids. The assembly of three building blocks accomplished the synthesis of the heptasaccharyl myo-inositol Galf(β1→3)-Manp(α1→2)-[Galf(β1→3)]-Manp(α1→2)-Manp(α1→6)-Manp(α1→4)-6-(2 -aminoethyl phosphonic acid)-GlcNp-(α1→6)-myo-Ins-1-PO4, the glycan of the T. cruzi lipopeptidophosphoglycan.Carbohydrate self-assembled monolayers (SAMs) on gold were designed, synthesized and characterized to investigate their protein rejecting properties. Synthesis of methylated and non-methylated galactose-terminated alkanethiols provided mixed carbohydrate monomolecular layers. The physiochemical properties of the mixed SAMs were elucidated with ellipsometry, infrared reflection-absorption spectroscopy and contact angle goniometry. The irreversible adsorption of the model proteins fibrinogen and lysozyme was determined with ex-situ ellipsometry. Neither of the proteins adsorbed within a mixed regime corresponding to contact angles of water between 24° and 45°.A carbohydrate model system mimicking the properties of antifreeze glycoproteins was developed. A Gal(β1→3)-GalNAc terminated 16-mercapto-hexadecanoic acid derivative was synthesized and co-adsorbed with an ethyl-terminated thiol in various proportions to form mixed SAMs on gold. The monolayers were characterized and the antifreeze model system was evaluated by initial ice nucleation studies.Synthetic routes to protected ethyl 2-deoxy-2-phthalimido-1-β-D-thio-galactosamine derivatives via epimerization of corresponding glucosamine compounds were explored to provide methods in future synthesis of antifreeze glycoproteins and analogues.