Design, synthesis and evaluation of multivalent glycodendrimers as multivalent ligands

Abstract

Carbohydrates are more and more of interest in drug design as they are important mediators in a whole range of biological processes. Because of the low affinity of carbohydrates for their receptors, multivalent ligand presentation was introduced. Multivalent compounds were shown to improve the affinity towards lectins, AB5 toxins and bacteria. In this thesis both the design and synthesis of new glycodendrimers is described. A solid phase strategy was developed to speed up the synthesis of glycosides. Selective protection and deprotection steps were performed on-bead, followed by on-bead glycosylation. Simple glycosides were obtained however the yield was poor. As key step for the synthesis of a galabiose building block an enzymatic approach was applied. The product from an enzymatic cleavage was converted into the desired galabiose unit using simple synthetic chemistry. The obtained building block was used for the preparation of galabiose dendrimers which showed to be capable for inhibition of S. suis binding using a heamagglutination inhibition assay, a clear multivalency effect was observed. To inhibit Cholera Toxin binding, mono- to octavalent GM1- and galactose-dendrimers were synthesized. Both series of compounds showed a dramatic increase in inhibition potency to block CT binding in an inhibition assay. Especially the tetra- and octavalent compounds showed an increased affinity up to 47.500 per ligand. The tetra- and octavalent galactose-dendrimers showed an inhibition capacity which can compete with the natural ligand and thereby opens routes for medical applications. Finally flow-through microarray technology was introduced to study multivalent interactions. Amine terminated mannose-dendrimers were synthesized and covalently attached to a porous microarray chip surface. Protein binding to the chip surface was observed in time for the mannose binding lectins ConA and GNA, only GNA showed to benefit from a multivalent ligand display. Curve fitting was used to obtain Kd values for these binding events. The microarray technology was also successfully applied in an inhibition assay with soluble monovalent inhibitors.