NONCOVALENT FLUOROUS INTERACTIONS: NEW APPROACHES FOR DRUG DISCOVERY AND DRUG DELIVERY

The unique chemical properties of fluorine atom (high electronegativity, high ionization potential, low polarizability and low van der Waals interactions) modify the chemical properties of organic compounds as well as their reactivity when hydrogen atoms are replaced by fluorines. Actually, fluorocarbons show low polarity, which is responsible for the high hydrophobicity of these molecules. Additionally, the low polarizability of fluorines leads to weaker van der Waals interactions, which makes fluorocarbons lipophobic. Therefore, fluorinated compounds show an amphiphilic character that leads to the formation of the fluorous phase, which is separated to both aqueous and organic layers. The aim of my project was applying the strong and noncovalent fluorous interactions to drug discovery and drug delivery. The first part of my thesis is focused on the development of a new strategy for target identification able to overcome the several limitations associated to classic chemical proteomics techniques. Indeed, traditional chemical proteomics methodology uses agarose beads covalently bound to streptavidin as stationary phase for affinity purification. This resin is able to retain biotin-tagged proteins as well as sticky components abundant in the lysate. These contaminants might be aspecifically eluted with the biological targets, complicating the mass analysis and therefore the target identification. In order to increase the selectivity of the proteomics approach, we designed an innovative fluorous proteomics methodology using the strong fluorous-fluorous interactions as recognition system for affinity purification. Indeed, perfluorinated stationary phase can anchor only fluorinated species, avoiding aspecific binding. To test the fluorous proteomics approach, papain was considered as biological target. Fluorinated inhibitors of papain with different fluorinated-chain length were synthesized. The number of fluorine atom of the inhibitor is crucial for the interaction with the fluorinated stationary phase in the purification step. Actually, only papain inhibitors with a long fluorous alkyl chain are able to bind the fluorinated resin and therefore immobilize papain. In contrast, inhibitors with a short fluorous alkyl chain cannot bind the fluorinated stationary phase by means of fluorous-fluorous interactions. Consequently, papain cannot be anchored to the resin. The second part of my thesis is focused on the application of fluorous interactions for drug delivery. This project was carried out in the School of Pharmacy, University of Wisconsin-Madison (Madison, WI, U.S.A.) under the supervision of Professor Sandro Mecozzi. The aim was designing and synthesizing semifluorinated dibranched polymers. The synthesis of fluorinated molecules is a challenge, due to their poor reactivity and low solubility in commonly-used organic solvents. To increase the final yield, each step of the synthesis of the semifluorinated dibranched polymers was optimized. The dibranched fluorinated polymers will be used to prepare oil-in-water nanoemulsions for controlled drug release of paclitaxel. We reasoned that semifluorinated polymers with different chemical structures might lead to nanoemulsions with different stability and drug release profile. Small diameter of the nanoemulsion droplets and long half-lives are desired to maximize the tumoritropic accumulation of these nanosystems by EPR effect before drug release. This allows the release of the drug within the tumor instead of in the bloodstream, avoiding side effects due to the interaction of the drug with off targets and consequently reducing the systemic toxicity.