SINTESI E PROPRIETA’ BIOLOGICHE DI LIGANDI GLICOSIDICI MULTIVALENTI

Protein-carbohydrate interactions are at the heart of many important biological processes as the adesion of bacteria and viruses to the cell surfaces. It is widely accepted that nature compensates for the low intrinsic affinity of carbohydrate for proteins through the cooperative binding between multiple copies of ligands and receptors so that a strong adhesion results. This important concept, termed cluster effect, has stimulated the search for the construction of highly glycosylated ligands to inhibit polyvalent processes as well as probe for cell-surfaces-binding events. The aim of this PhD research work was the synthesis of calix[4]arene-based glycoclusters via Cu(I)-catalyzed azide-alkyne coupling reaction (CuAAC), as well as the investigation of their biological proprieties. The first research conducted dealt with the synthesis of sialoside clusters as potential inhibitors of viruses infectivity. Tetra- and octavalent sialoside clusters were prepared exploiting the multiple copper-catalyzed cycloaddition of a propargyl thiosialoside with calix[4]arene polyazides. It was demonstrated that these unnatural motifs did not hamper the desired biological activity of the sialoclusters. In fact, they were able to inhibit, at submillimolar concentrations, the hemagglutination and the viral infectivity mediated both by BK and influenza A viruses. Then, this thesis focused on the possibility to support C-glycoside clusters on microarrays to study their affinity against lectins. To this aim C-glycosylated calix[4]arenes have been synthesized in which four galactose residues are linked through a triazole tether to the upper rim of the macrocycle cavity while an azido group is present on the opposite side. Next the calixsugars were grafted through CuAAC on mono or dipropargyloxymethyl-propanediol moieties allowing the synthesis of oligonucleotides bearing one or two calixarene glycoclusters, respectively. Finally, their affinity for lectins PA-IL and RCA 120, galactose specific lectins from Pseudomonas aeruginosa and Ricinus communis, respectively, were compared to that displayed by linear and antenna-type glycoclusters. During the last period of the PhD work it was performed the immobilization of calix[4]arenebased glycoclusters on TiO2 nanoparticles via Cu(I)-catalyzed azide-alkyne coupling reaction. The strategy that has been followed involved first the grafting of bis-functionalized calix[4]arenes (azido groups at upper rim and fenolic or carboxylic groups at the lower rim) onto TiO2 and then multiple click copper(I)-catalyzed cycloaddition to propargil glycosides. The glyconanoparticles obtained were characterized by thermogravimetric analysis (TGA) and infrared spectroscopy. This constitutes the first example of TiO2 nanoparticles coated by a monolayer of calix[4]arene-based glycoclusters.