Malaria kills at least one million people each year, mostly children - a death every 30 seconds. Almost one half of the world population is at risk from malaria. Antimalarial drugs are the only means for the treatment of about 500 million annual global malaria cases. Because of prevalent drug-resistance it is extremely urgent to identify new drug targets. Many proteins involved in eukaryotic signal transduction and cell cycle progression undergo post-translational lipid modification by a prenyl group. Protein prenyltransferases, which catalyze the post-translational prenyl modification, have been established as a target for anticancer therapy. Research done in our laboratory has demonstrated recently that prenyl modification of proteins could be a novel target for the development of antimalarial drugs.The goal of this study is to understand the molecular mechanism of protein prenylation in Plasmodium. The key to use of prenyltransferase inhibitors for the pharmacological intervention is a thorough understanding of the in vivo prenylation pathways in the malaria parasite. Knowledge of the physiological functions of the cellular protein substrates of malarial prenyltransferases is an important first step in the elucidation of the mechanism of antimalarial action of inhibitors of protein prenylation. The research described in this thesis revealed the evidence for the existence of farnesylated and geranylgeranylated malaria parasite proteins. The study shows that the dynamics of protein prenylation changes with the intraerythrocytic development cycle of the parasite. We detected that prenylated proteins in the 50 kDa range were mostly farnesylated and that the proteins in the 22-25 kDa range were mostly geranylgeranylated. The prenylation of P. falciparum proteins is inhibited by prenyltransferase inhibitors. We have also demonstrated unique features of protein prenylation in P. falciparum compared to the human host such as farnesylation of proteins are sensitive to inhibition by geranylgeranyltransferase inhibitors.. In-silico search of the malarial genome sequence identified potential protein prenyltransferase substrates. One of these substrates is a SNARE protein Ykt6 homologue. The malarial Ykt6 was recombinantly expressed and subjected to an in-vitro prenylation assay. We showed that the recombinant Ykt6 was indeed a substrate for the malarial prenyltransferase.

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Binding to protein surfaces or shallow grooves with synthetic molecules poses a unique challenge, since this inherently requires large areas to facilitate interactions. Peptoids have been shown to interact with proteins, and combinatorial libraries of peptoids have been proven to be effective in discovering new ligands for protein binding. Unfortunately, most peptoids are flexible and lack the surface area required to compete with larger protein interactions. To combat these problems, we have created spiroligomers that have a rigid backbone, exhibit functionality comparable to proteins, and are resistant to proteases. To facilitate the rapid installment of spiroligomers into peptoid subunits, we required a more streamlined approach for functionalization of spiroligomers. To this end we applied a single-pot alkylation method, with which we installed over 25 unique functional groups onto different spiroligomer hydantoins. These spiroligomer hydantoins are spirocycles that possesses two stereocenters, of which we have complete control, as well as a protected proline amino acid. These new proline amino acids (enhanced prolines) have been incorporated into peptides via Fmoc-SPPS. Finally, we have functionalized these enhanced proline residues with another functional group and a protected primary amine, which allow for their use in peptoid synthesis. We developed methods to tether multiple spiroligomers together utilizing a peptoid backbone, as well as being able to incorporate spiroligomers into peptoid macrocycles. These spiroligomer-peptoid hybrids are large, diverse, and preorganized structures that have a large potential interacting surface area for binding to protein surfaces or shallow grooves. / Chemistry

La ghréline, une hormone peptidique principalement synthétisée au niveau de l'estomac, est le ligand endogène du récepteur des sécrétagogues de l'hormone de croissance appelé GHS-R1a. Elle est impliquée dans de nombreux processus biologiques dont principalement la sécrétion de l'hormone de croissance et la régulation de l'homéostasie énergétique. En raison de ses propriétés orexigènes et adipogènes, la ghréline est un outil puissant pour lutter contre les déséquilibres énergétiques. Développer des antagonistes de son récepteur représente ainsi une stratégie prometteuse pour la découverte de nouvelles pharmacothérapies contre l'obésité.Cette thèse est consacrée au développement d'antagonistes du récepteur de la ghréline dont la structure est basée sur une plateforme peptidomimétique : le 1,2,4-triazole 3,4,5-trisubstitué. Notre objectif est de concilier au mieux l'affinité et l'activité de nos ligands vis-à-vis du GHS-R1a avec des propriétés optimisées permettant de favoriser une bonne biodisponibilité orale. Nous nous sommes basés sur une synthèse rapide et efficace de ces composés pour réaliser des études approfondies de relations structure-activité et structure-propriété. En optimisant successivement les différentes positions autour du motif triazole, des compromis intéressants ont été obtenus. Nous avons ainsi identifié des antagonistes affins du récepteur qui présentent une stabilité microsomale suffisante et une perméabilité membranaire satisfaisante pour envisager des études in vivo. / Ghrelin, a peptidic hormone which is mainly synthesized in the stomach, is the endogenous ligand of the growth hormone secretagogue receptor named GHS-R1a. It is involved in numerous biological processes such as the growth hormone secretion and the control of energy homeostasis. Because of its orexigenic and adipogenic properties, ghrelin is a potent tool to control energy imbalance. Developing ghrelin receptor antagonists represents a promising strategy for the discovery of anti-obesity new drugs.This thesis is devoted to the development of ghrelin receptor antagonists based on a peptidomimetic scaffold: the 3,4,5-trisubstituted 1,2,4-triazole. Our aim is to combine ligand affinity and activity towards GHS-R1a with optimized properties which enable to promote a good oral bioavailability. We based our work on a rapid and efficient synthesis of our compounds to carry out detailed structure-activity and structure-property studies. By successively optimizing the different positions around the triazole scaffold, interesting compounds were obtained. We have thus identified receptor antagonists which exhibit sufficient microsomal stability and satisfactory membrane permeability to consider in vivo studies.

Peptidomimetics are synthetic foldamers that expected more resistant to proteolytic degradation and enormous chemodiversity when compared with peptides. To date, the functional peptidomimetics such as β-peptides, peptoids, oligoureas, etc have been developed in many science fields. In order to explore the unnatural foldameric architectures, it’s necessary to discover the novel frameworks and molecular scaffolds. γ-AApeptides were reported to be a new class of peptidomimetics that showed its potential applications in drug discovery and chemical biology. However, a wide function and property of γ-AApeptides need to be further explored. To expand the potential application of γ-AApeptides in biochemistry, I have been focusing on the development of bioactive peptidomimetics, such as exploring the antibacterial activity of helical 1:1 α-sulfono-γ-AA heterogeneous peptides, developing the helical peptidomimetic as the inhibitor of the protein Ras_Raf interaction, identifying the protein/peptide ligands by the novel one-bead-two compound macrocyclic γ-AApeptide screening library, and elucidating the de novo dragon-boat-shaped synthetic foldamers.

This thesis describes the synthesis and biological evaluation of highly substituted, ring-fused 2-pyridones. The utility of the bicyclic 2-pyridones to gain fundamental insights into the disease processes of bacterial infections and Alzheimer’s disease has been investigated. The 2-pyridones have mainly been studied as a new class of anti-infective agents termed pilicides. The function of the pilicides has been explored using uropathogenic E. coli (UPEC) as a prototype pathogen and urinary tract infection as a model disease. The pilicides target the infectious ability of UPEC by inhibiting key proteins (chaperones) in the so-called chaperone-usher pathway, thus preventing the assembly of bacterial surface organelles (pili/fimbriae). Synthetic pathways to aminomethylate the 2-pyridones have been developed in order to increase their aqueous solubility while retaining biological activity. Also, the importance of a carboxylic acid has been demonstrated in studies with various carboxylate derivatives and by bioisosteric replacement. Moreover, synthetic procedures to extend the backbone of the rigid, dipeptide-mimicking 2-pyridones have been established. This rendered peptidomimetic building blocks and structures that alongside their potential use as pilicides are of more general interest in peptidomimetic-related research. The potential pilicides have been screened for chaperone affinity using relaxation-edited 1H-NMR spectroscopy. In addition, their ability to inhibit pilus biogenesis in E. coli has been demonstrated by assays of hemagglutination, biofilm formation and attachment to bladder cells, as well as with electron and atomic force microscopy. Moreover, it has been confirmed that pilicides regulate the expression of pili without affecting the biofunctional properties of the pilus rod. This was verified by measurements of individual P pili, on living bacteria, using force measuring optical tweezers. The pilicide binding site was investigated using NMR spectroscopy and X-ray crystallography of a pilicide-chaperone complex. Based on the results obtained, a mechanism whereby the pilicides may inhibit pilus assembly was proposed, which was subsequently experimentally supported by surface plasmon resonance assays and genetic analysis. Finally, based on the generic 2-pyridone scaffold, a new collection of substituted compounds has been synthesized and validated as inhibitors of Amyloid β (Aβ)-peptide aggregation, which has been suggested to be involved in Alzheimer’s disease.

Ces travaux de thèse s’inscrivent dans un projet à long terme concernant le développement de nouveaux composés peptidomimétiques à motif oxaprolines et oxadiazine-3,6-diones présentant des activités biologiques ou des potentiels de structuration intéressants. En particulier, nous nous sommes attachés à synthétiser différents mimes du peptide Pro-Leu-Gly-NH2, un modulateur allostérique des récepteurs D2 de la dopamine. Ces dérivés ont présenté une activité sur des cellules du striatum supérieure en comparaison avec les valeurs obtenues avec le peptide de référence PLG. D’autre part, notre intérêt pour des structures de type oxadiazine-3,6-diones (Oxd), des motifs très peu décrits dans la littérature, nous a permis d’accéder à une librairie de 1,2,4- et d’1,2,5-Oxd, que nous avons par la suite insérée dans de courtes séquences peptidiques, valorisées comme mime potentiel de beta-turn. Enfin, au cours de ces travaux de doctorat, une nouvelle méthodologie de clivage chimiosélectif de groupements protecteurs a été développée. Cette stratégie originale, basée sur l’utilisation de MgI2 dans le THF sous irradiation micro-ondes, a permis de mettre en évidence de nouvelles orthogonalités telles que le maintien d’un groupement Fmoc lors d’un clivage d’un ester éthylique ou méthylique, ou encore de la résine de Merrifield. / This work is a part of a long-term project aiming to develop original oxaproline and oxadiazine-3,6-diones peptidomimetics with biological activities or potential folding properties. Especially, we proposed an access to various mimetics of the Pro-Leu-Gly-NH2 peptide (PLG), an allosteric modulator of the dopamine D2 receptor. The synthesized derivatives revealed to exhibit higher activity on striatum cells than the PLG initial reference.Moreover, our interest for the poorly described oxadiazine-3,6-diones (Oxd) scaffolds led us to access to a library of 1,2,4- and 1,2,5- Oxd, that we are able to efficiently insert into short peptide sequences with potential beta-turn inducing properties.Finally, during this Ph.D work, an unprecedented methodology for the chemoselective cleavage of protecting groups was developed. Using MgI2 in THF under microwave irradiations, this strategy highlighted novel orthogonalities such as the conservation of the Fmoc protecting group during ethyl or methyl ester deprotection, or even, during the Merrifield resin cleavage.

Over the past recent years, β-aminocarbonyls have been of great interest to medicinal chemists. As a practical method to obtain these moieties, alkene aminocarbonylation, accounting for the formation of a C-N and a C-C bond, has been the subject of limited research efforts (very specific intramolecular metal-catalyzed variants have been reported). Direct aminocarbonylation of alkenes constitutes a challenging and an important potential innovation in the synthesis of β-aminocarbonyls such as β-amino acids. The research efforts described in the present thesis have been primarily directed towards the development of concerted pathways for the amination of alkenes using hydrazine derivatives as bifunctional reagents. Building on our previous report on the reactivity of hydrazides, progress on the aminocarbonylation of alkenes along with the synthetic scope of this reactivity are herein provided. Therefore, the first part of the present thesis (Chapter 2) focuses primarily on the development of thermolytic conditions for the intramolecular aminocarbonylation of alkenes using amino-isocyanates. Alongside, development of imino-isocyanates have provided complementary synthetic tools for aminocarbonylation. The second part (Chapter 3) describes the work accomplished towards intermolecular aminocarbonylation of alkenes and the synthesis of complex azomethine imine products (Chapter 3). Finally, the last part of the discussion (Chapter 4) will be on the development of new hydrazide reagents for the intramolecular Cope-type hydroamination of alkenes. In doing so, description of the synthetic utility of amino-isocyanates as amphoteric reagents for cascade reactions and heterocyclic synthesis will be provided.

Deux sujets indépendants ont été traités dans ce manuscrit.Dans une première partie a été étudiée la possibilité d'obtenir des synthons chiraux à partir de la pyridine. Pour cela nous avons dans un premier temps développé une méthode originale de quaternisation des sels de pyridium et d'imidazoliums grâce à une réaction de Mitsonubu. Par la suite, des 2-aminopyridines ont été substituées puis engagées dans une réaction de quaternisation-réduction conduisant à des composants saturés. Malheureusement, des composés n'ont pu conduire aux synthons linéaires envisagés.Dans une seconde partie, nous nous sommes intéressés au développement d'un nouveau type de peptidomimétique dans lequel le lien amide est remplacé par un cycle imidazolique, ceci dans la continuité de travaux menés dans notre équipe. Dans un premier temps, nous nous sommes focalisés sur la mise au point de conditions efficaces menant au mime considéré. Cette méthodologie nous a permis la synthèse de plusieurs dipeptides. / Two different topics will be discussed in this work.In the first part has been studied the possibility to obtain chiral building-blocks from pyridine. For this purpose, we intially developed an original method for quartenization of pyridium and imidazolium salts through a Mitsonubu reaction. Then, 2-aminopyridines were substituted and then engaged in a quaternization-reduction reaction, leading to satured compounds. Unfortunately, these compounds have not leaded to targeted linear building-blocks.In a second part, we have been interested in the deveopment of a new peptidomimetic family in which the amide bond is replaced by an imidazole ring, extension of previous work in our research group. Initially we focused on the development of conditions leading to considered mimic. This methodology has allowed us the synthesis of several dipetides incorporating our mimic with good results. The determination of acido-basic properties of these structures has also been investigated.

Les fluoroalcènes sont employés pour préparer des mimes de peptides. Malgré de nombreuses études réalisées dans ce domaine, la préparation d'analogues de peptides comportant une proline modifiée en position C-terminale a été très peu explorée. Ce travail de thèse est consacré à la synthèse de pyrrolidine comportant un motif fluorovinylique. La préparation de sulfones fluorées comportant un cycle pyrrolidine a été réalisée, par réaction d'aza-Michael intramoléculaire. Ce réactif permet la formation de pyrrolines par réaction de Julia modifiée, là où la réaction de Horner-Wadworth-Emmons échoue. Cette étude a été étendue à la préparation de pipéridines fluorées. Cette méthode a été appliquée avec succès à la préparation de précurseurs de peptides Pro-Ψ[CF=CH]-Xaa, peu étudiés dans la littérature. / Fluoroalkenes are used to prepare peptide mimics. In spite of numerous studies carried out in this field, the preparation of peptide analogs comprising a modified proline in the C-terminal position has been very little explored. This thesis is devoted to the synthesis of pyrrolidine with a fluorovinyl unit. The preparation of fluorinated sulfones containing a pyrrolidine ring was carried out by reaction of intramolecular aza-Michael. This reagent allows the formation of pyrrolines by modified Julia reaction, where the Horner-Wadworth-Emmons reaction fails. This study was extended to the preparation of fluorinated piperidines. This method has been successfully applied to the preparation of pro-Ψ peptide precursors [CF = CH] -Xaa, which are poorly studied in the literature.