Protein-protein interactions are central to most biological processes. Although in the field of drug discovery there is a great interest in targeting protein-protein interactions, the discovery and development of small-molecules, which effect these interactions has been challenging. The purpose of this project is to determine if in situ click chemistry is a practical approach towards testing whether Bcl-XL is capable of assembling it's own inhibitory compounds. Abbott laboratories developed compound ABT-737, which binds with high affinity (Ki < 1 nM) to the binding sites of Bcl-XL.³⁶ Based on ABT-737, two acetylene anchor molecules AM3 and AM4 have been synthesized. These anchor molecules are distinguished by the reactivity of the their carbon-carbon triple bond. Compound AM3 contains an electron withdrawing carbonyl in the alpha-position to the acetylene resulting in an activating effect towards the [1,3]-dipolar cycloaddition compared to compound AM4. To determine the reactivity of the activated system, ¹ H-NMR kinetic studies were performed to compare the relative rates of these two systems by reacting model alkynes 1,2,3, and 4 with azide AZ7. It was shown that the activated systems, 1 and 3, produce triazoles in an accelerated rate compared to the unactivated systems 2 and 3. To test for the self-assembly of inhibitory triazoles, the acetylenes AM3 and AM4 were incubated with Bcl-XL and 14 azide building blocks (AZ1-AZ12) for 12 hours at 37 degrees C. Subjecting these mixtures to LC/MS-SIM led to the discovery of two hit compounds, 35 and 36, of which 35 has been chemically synthesized confirming the hit. Future work includes the synthesis of all hit compounds. Since hit triazoles can be syn or anti, both need to be synthesized for each hit to investigate which regioisomer Bcl-XL generates. Tests to confirm if hit compounds are actually modulating Bcl-XL activity will be done using conventional bio-assays. This will validate that Bcl-XL is capable of assembling its own inhibitor via the in situ click chemistry approach to drug discovery.

La synthèse contrôlée par la cible sous contrôle cinétique (Kinetic Target-Guided Synthesis, KTGS) est une approche relativement peu explorée, alternative à la chimie combinatoire traditionnelle,dans laquelle la protéine cible participe à la synthèse du ou de ses propres ligands. Ainsi, les travaux présentés dans la première partie de cette thèse ont pour principal objectif d'élargir l'éventail des réactions actuellement disponibles en KTGS grâce à la réaction d'aldolisation voire d'amidation, et ce en utilisant la β-sécrétase (BACE-1) comme cible biologique, qui est une enzyme étroitement impliquée dans la maladie d'Alzheimer. La seconde partie de cette thèse a été consacrée à la synthèse de marqueurs de masse fluorescents bioconjugables basés sur l'association d'un noyau coumarinique et d'une fonction phosphonium. Les deux générations présentées dans ce manuscrit ont entre autre permis de synthétiser une sonde FRET permettant de détecter l'activité enzymatique de la BACE-1, qui pourrait par ailleurs être un outil intéressant pour l'analyse des bruts réactionnels des réactions de click in situ,et diminuer les quantités d'enzyme engagées dans ces expériences. Enfin dans la dernière partie de cette thèse nous décrivons la mise au point de nouvelles réactions de conjugaison bio-orthogonale pour le marquage de molécules comportant une fonction aldéhyde. Nous avons ainsi développé d'une part une réaction trois composants via une séquence de condensation/Mannich/lactamisation et d'autre part une réaction d'oléfination de Wittig. / The kinetic target-guided synthesis (KTGS), is an underexplored alternative approach to combinatorial chemistry, in which the biological target is able to assemble its own inhibitors from a pool of fragments. Thus, the first part of this thesis aimed at extending the scope of the reactions available for the KTGS, by investigating the aldolisation and amidation reaction, using the β-secretase (BACE-1) as biological target, which is an enzyme narrowly involved in the Alzheimer's disease. The second part of this thesis was dedicated to the synthesis of bioconjagatable fluorophores containing a phosphonium group as mass tag associated to a coumarin core. Both generations presented in this manuscript allowed us, among other things, to synthesize a FRET probe that proved suitable for the determination of BACE-1 enzymatic activity. The utility of such a fluorogenic tool could be leveraged to facilitate the analysis of crude mixtures obtained during KTGS experiments, and lessen the amount of enzyme required in these experiments. Finally, in the last part of this thesis, we describe the development of two new bioorthogonal reactions allowing the selective labeling of molecules containing an aldehyde moiety : 1) a three component reaction involving a condensation/Mannich/lactamisation procedure, between an amine, an aldehyde and an enol partner; 2) a Wittig ligation between an aldehyde and a phosphonium bearing an active methylene.