Potent inhibitors of uropathogenic E. coli papG adhesins; Synthesis, conformational studies and biological evaluation of galabiose derivatives and synthesis of glycosphingolipid analogues

Abstract: The importance of carbohydrates in biological systems has become evident during the last fifty years. It is well known that pathogenic bacteria and viruses attach to glycoconjugates present at mammalian cell surfaces, and that this attachment is a prerequisite for the later stages of infection. Obviously, this interaction is interesting as a target for the development of novel ways to treat bacterial infections. In this thesis, the affinities of galabiose derivatives for PapG class I and II adhesins from uropathogenic E. coli have been investigated. The objective of this project was to further explore the binding event between galabiose and the adhesins, aiming at finding a high-affinity inhibitor. A high-affinity galabioside might have a future as an anti-adhesive therapeutic agent targeting urinary tract infections. A large-scale synthesis of galabiose was developed and seven collections of galabiosides, totally 66 different galabiosides were synthesised and evaluated. For the class I adhesin the best known inhibitor so far was identified, being 20-30 times more potent than the natural ligand globotetraose. For the class II adhesin, associated with pyelonephritis, galabiosides with about the same affinity as the natural tetrasaccharide ligand were found. For the class II adhesin the Kd-values of the best galabiosides are still about 0.1 mM. However, this Kd-value is in the same range as the more synthetically demanding tetrasaccharide. These inhibitors represent the best inhibitors known against the class I and II PapG adhesin and the results constitute an advancement towards anti-adhesion therapeutic agents targeting urinary tract infections. In the examination of glycolipid-lectin interactions, the lipid part has often been neglected. However, during the last years, evidence has accumulated that the mode of presentation influences the recognition event. In order to mimic the binding characteristics in Nature as close as possible, the lipid part should resemble its natural counterpart. In this thesis, synthetic routes to w-mercapto and w-carboxy analogues of glycosphingolipids are described. The lipids were designed to be suitable for functionalization of gold and aminofunctionalized surfaces and to be as similar the natural glycosphingolipids as possible.