CyClick

Conjugation of polymer scaffolds with multiple copies of a sugar ligand has become a popular approach for improving protein targeting. While multivalent linear polymer scaffolds allow an enhanced potency, also called “statistical binding”, where a nearby ligand quickly replaces the bound ligand due to its proximity, their selectivity can be limited. To overcome this, the CyClick project aims at designing new multivalent cyclic polymer ligands with dramatically enhanced potency and selectivity toward a protein target. For this purpose, the CyClick project consortium is composed of three complementary teams at Le Mans University, Nantes University, and GLYcoDiag SARL. The synthetic approach retained for the CyClick project consists in developing a versatile and robust method for the synthesis of well-defined multivalent cyclic polymer ligands in high purity and useful quantities. The cyclic polymer scaffold will be synthesized by ring-expansion metathesis polymerization (REMP) of cyclo-alkenes having a clickable moiety, and post-functionalized with biologically relevant carbohydrate ligands by click chemistry. Clickable azlactone functionalities have been chosen as they show high reactivity toward amine nucleophiles with full atom economy in a broad range of organic solvents as well as in aqueous solution at room temperature without generating by-products, and are compatible with ruthenium-based catalysts used for REMP. Ligands of carbohydrate-binding (lectins) or carbohydrate-processing proteins (glycosidases) involved in a host of biological events such as fertilization, cell-cell communication and the adhesion of pathogenic bacteria, fungi or viruses to human cells have been selected. Optimized carbohydrate and iminosugar ligands that proved particularly efficient for the multivalent inhibition of model or therapeutically relevant lectins and glycosidases will be clicked on the cyclic polymer scaffolds. This two-steps strategy has the particular advantage to allow the creation of diverse multivalent libraries from a single polymer platform and the large-scale production of multivalent ligands. The binding affinity of the so-obtained multivalent ligands for lectins and glycosidases will then be evaluated with the GLYcoPROFILE® technology developed by the industrial partner of this project: GLYcoDiag SARL. The motivation underlying this project is twofold: on one hand, the tuning of the rigidity of the scaffold and inter-binding site distances to allow an unprecedented match with the protein target through the use of different cyclo-alkenes with varying rigidity as well as the possibility to perform their alternating copolymerization; on the other hand, the synthesis of the linear equivalent counterparts by ring-opening metathesis polymerization (ROMP) will give the opportunity to study the impact of the scaffold topology on the strength and specificity of glycans recognition and the concomitant biological properties. This project will pave the way to a new class of cyclic polymer ligands with unprecedented biological activity. For the industrial partner, this project will bring new expertise in carbohydrate-binding proteins interaction analyses from cyclic polymer ligands. Last but not least, the Cyclick project will provide a chemical methodology to access a new type of (cyclic) polymers displaying specific physiochemical parameters with potentially high interest in polymer industry.