Diazonium salts are intermediates that are widely used in organic synthesis. They are typically obtained by in-situ generation of a nitrosonium ion from sodium nitrite and an acid, or by a nitrosyl transfer from an organic nitrite. Unlike extensively used aryl diazonium salts, alkyl diazonium intermediates are much less studied, due to their lower stability, and their general carcinogenicity. They usually decompose into the corresponding carbocation, affording the alcohol, halide and/or elimination product. Despite the large range of reactivity of these intermediates, diazonium salts are generally under-used, as they are potentially dangerous, especially on large scale. Solutions have been found to overcome this drawback, namely in situ formation of the diazonium species. Continuous flow is a powerful technology to handle hazardous compounds. Such a technology was recently used by our group to perform the continuous flow esterification of carboxylic acids via the diazotisation of alkylamines. The reaction proceeds in 20 minutes and is compatible with a large range of functional groups. The nitrite used in the reaction is propane-1,3-dinitrite. Notably, the reaction is compatible with hydroxy-substituted carboxylic acids. These substrates led us to study the synthesis of hydroxyesters from carboxylic acids and amino alcohols. The reaction was described in continuous flow in 30 to 60 min at 70 to 100 °C. In addition, a batch procedure in t-BuOH at 80 °C with reaction time varying from 6 h to overnight was developed. Alkyl diazonium intermediates were also used in the etherification of aryl alcohols. We developed a base-free etherification of electron-poor phenols. The reaction proceeded in batch with moderate to high yields within one hour. 2-, 3-, and 4-hydroxypyridines were also successfully reacted, as well as hydroxyquinoline and hydroxypyrimidine derivative, leading to the O-alkylated ether as the major product. Finally, N-alkylation of 5-substituted-1H-tetrazole was also achieved, and the 2N-alkylated tetrazole was obtained as a major product. A one-pot sequential 1,3-dipolar cycloaddition -diazotisation was optimized, enabling the synthesis of 2,5-disubstituted tetrazoles from nitriles, TMSN3, and alkylamine. Furthermore, different parameters governing the ratio of formation of the 1,5- and the 2,5- isomers were studied. / Les sels de diazonium sont des intermédiaires largement utilisés en synthèse organique. Ils sont généralement obtenus par génération in situ d'un ion nitrosonium à partir de nitrite de sodium et d'un acide, ou par transfert de nitrosyle à partir d'un nitrite organique. Contrairement aux sels de diazoniums d’aryle, largement utilisés, les intermédiaires diazoniums d’alkyle sont beaucoup moins étudiés, en raison de leur stabilité moindre et de leur caractère cancérigène. Ils se décomposent généralement pour former des produits résultant de la formation d’un carbocation en donnant l'alcool, l'halogénure et/ou le produit d'élimination. Malgré les différentes possibilités de réactivité de ces intermédiaires, les sels de diazonium sont généralement sous-utilisés, car ils sont potentiellement dangereux, surtout à grande échelle. Des solutions ont été trouvées pour surmonter cet inconvénient, à savoir la formation in situ des espèces de diazonium. Par ailleurs, la chimie en flux continu est une technologie puissante pour manipuler les composés dangereux. Cette technologie a récemment été utilisée par notre groupe pour réaliser l'estérification en flux continu d'acides carboxyliques via la diazotation d'amines aliphatiques. La réaction se déroule en 20 minutes et est compatible avec une large gamme de groupement fonctionnels. Le nitrite utilisé dans la réaction est le propane-1,3-dinitrite. Notamment, la réaction est compatible avec les acides carboxyliques substitués par des groupement alcool. Ces substrats nous ont conduit à étudier la synthèse d'hydroxyesters à partir d'acides carboxyliques et d'aminoalcools. La réaction a été décrite en flux continu en 30 à 60 min avec des températures allant de 70 à 100 °C. De plus, une procédure batch dans du t-BuOH à 80 °C avec un temps de réaction variant de 6 h à toute la nuit a été développée. Les intermédiaires diazoniums d’alkyle ont également été utilisés pour l'éthérification des alcools aromatiques. Nous avons développé une éthérification sans base de phénols pauvres en électrons. La réaction s'est déroulée en batch avec des rendements modérés à élevés en une heure. Les 2-, 3-, et 4-hydroxypyridines ont également été utilisées avec succès, ainsi que des dérivés d'hydroxyquinoléine d'hydroxypyrimidine, conduisant à l'éther O-alkylé comme produit majoritaire. Enfin, la N-alkylation du 1H-tétrazole 5-substitué a également été réalisée, et le tétrazole 2Nalkylé a été obtenu comme produit majoritaire. Une cycloaddition 1,3-dipolaire - diazotisation séquentielle à un pot a été optimisée, permettant la synthèse de tétrazoles 2,5-disubstitués à partir de nitriles, de TMSN3 et d'amine aliphatique. En outre, différents paramètres régissant le ratio de formation des isomères 1,5- et 2,5- ont été étudiés.

New methods have been developed for the synthesis of bicyclic β-lactams and 2-pyridinones by combining acyl Meldrum’s acids and Δ2-thiazolines. The 2-pyridinones were synthesised both in solution using conventional heating or microwave assisted heating as well as by solid supported chemistry. The compounds (pilicides) were designed to interfere with the assembly of pili in uropathogenic E. coli by inhibiting the periplasmic chaperones. The affinity of the pilicides to the chaperones was investigated with surface plasmon resonance technique (Biacore) and with relaxation-edited 1H NMR spectroscopy experiments. Finally, the pilicides were investigated for their ability to inhibit pili formation in uropathogenic E. coli in a hemagglutination assay, where members of the 2-pyridinone family proved to be able to cause depiliation.

This thesis describes studies directed towards development of novel antiadhesive agents, with particular emphasis on compounds that prevent attachment of bacteria to a host-cell. Three different proteins involved in the assembly or function of adhesive pili in uropathogenic Escherichia coli have been targeted either by rational structure based design or statistical molecular methods. A library of substituted galabiose (Galα1-4Gal) derivatives was screened for binding to the E. coli adhesin PapG in an assay based on surface plasmon resonance, and for inhibition of Streptococcus suis adhesins PN and PO in a hemagglutination assay. The results were used to generate QSAR models which had good predictive powers and provided further insight in the structural requirements needed for high affinity binding. 2-pyridones and amino acid derivatives were modelled into the binding site of chaperones involved in pilus assembly in E. coli and a heuristic method, VALIDATE, was used for affinity prediction. The affinity of the compounds for the chaperones PapD and FimC were assessed in assays based on surface plasmon resonance and relaxation-edited NMR spectroscopy. Their ability to disrupt chaperone/subunit complexes was investigated in vitro through a FPLC assay and their capacity to inhibit pilus formation in vivo was determined via hemagglutination and confirmed with atomic force microscopy. Statistical molecular design was used to design a diverse peptide library targeting pili subunits, and an ELISA was developed to investigate the ability of the peptides to inhibit chaperone/subunit complexation. The resulting QSAR model provided extensive information regarding binding of the peptides to the subunits. Because the peptides were suggested to bind in an extended β-strand formation, β-strand mimetics consisting of oligomeric enaminones were designed. Finally, new methods to synthesize enaminone building blocks were developed using microwave assisted chemistry. The projects described have generated compounds that besides their value as leads for developing novel antibacterial agents, also constitute new chemical tools to study the mechanisms underlying bacterial virulence.

No description available.

New strategies are needed to counter the growing problem of bacterial resistance to antibiotics. One such strategy is to design compounds that target bacterial virulence, which could work separately or in concert with conventional bacteriostatic or bactericidal antibiotics. Pilicides are a class of compounds based on a ring-fused 2-pyridone scaffold that target bacterial virulence by blocking the chaperone/usher pathway in E. coli and thereby inhibit the assembly of pili. This thesis describes the design, synthesis, and biological evaluation of compounds based on the pilicide scaffold with the goal of improving the pilicides and expanding their utility. Synthetic pathways have been developed to enable the introduction of substituents at the C-2 position of the pilicide scaffold. Biological evaluation of these compounds demonstrated that some C-2 substituents give rise to significant increases in potency. X-ray crystallography was used to elucidate the structural basis of this improved biological activity. Furthermore, improved methods for the preparation of oxygen-analogues and C-7 substituted derivatives of the pilicide scaffold have been developed. These new methods were used in combination with existing strategies to decorate the pilicide scaffold as part of a multivariate design approach to improve the pilicides and generate structure activity relationships (SARs). Fluorescent pilicides were prepared using a strategy where selected substituents were replaced with fluorophores having similar physicochemical properties as the original substituents. Many of the synthesized fluorescent compounds displayed potent pilicide activities and can thus be used to study the complex interactions between pilicide and bacteria. For example, when E. coli was treated with fluorescent pilicides, it was found that the compounds were not uniformly distributed throughout the bacterial population, suggesting that the compounds are primarily associated to bacteria with specific properties. Finally, by studying compounds designed to inhibit the aggregation of Aβ, it was found that some compounds based on the pilicide scaffold inhibit the formation of the functional bacterial amyloid fibers known as curli; these compounds are referred to as 'curlicides'. Some of the curlicides also prevent the formation of pili and thus exhibit dual pilicide-curlicide activity. The potential utility of such 'dual-action' compounds was highlighted by a study of one of the more potent dual pilicide-curlicides in a murine UTI model were the compound was found to significantly attenuate virulence in vivo.

No description available.