No description available.

No description available.

No description available.

No description available.

No description available.

Antibiotic resistance is a worldwide threat to human health yet fewer new antibiotics are being approved. New antimicrobial drugs are urgently required. 3 Deoxy-D-manno-2-octulosonate-8-phosphate synthase (KDO8PS) is a target for antimicrobial drug design. KDO8PS catalyzes the condensation of D-arabinose-5 phosphate (A5P) with phosphoenolpyruvate (PEP) to produce KDO8P. KDO8PS catalyzes the first committed step in the lipopolysaccharides (LPS) biosynthesis pathway in Gram-negative bacteria and is critical for bacterial pathogenicity/virulence. We have characterized KDO8PS from Campylobacter jejuni (cjKDO8PS), a new metal-dependent KDO8P synthase (KDO8PS). cjKDO8PS is a tetramer in solution and optimally active at pH 7.5 and 60 °C. We have kinetically established that cjKDO8PS follows a rapid equilibrium sequential ordered ter ter kinetic mechanism, where Mn2+ binds first, followed by PEP, then A5P. Pi dissociates first, before KDO8P, then Mn2+. cjKDO8PS was inhibited by KDO8P oxime, a novel slow tight-binding inhibitor. KDO8P oxime is a competitive inhibitor with respect to PEP and A5P, but uncompetitive with respect to Mn2+, with Ki = 10 ± 1 μM and an ultimate Ki* = 0.28 ± 0.10 μM. KDO8P oxime has a residence time (tR) of 5 days on the enzyme, a parameter that is highly correlated to in vivo efficacy. Crystallization conditions for the cjKDO8PS‧Mn2+‧KDO8P oxime complex have been found and can be optimized to obtain a crystal structure that shows how KDO8P oxime interacts with the active sites. / Thesis / Doctor of Science (PhD) / The relentless increase in global antibiotic resistance is, regrettably, not matched with an increase in new effective antibiotics. New antimicrobial drug discovery strategies are desperately needed. Enzymes are key targets for drug design because they catalyze the majority of biological processes. In this project we sought to study and inhibit the activity of KDO8P synthase (KDO8PS) from Campylobacter jejuni, a common cause of food poisoning. KDO8P synthase is a critical enzyme involved in the lipopolysaccharide (LPS) biosynthesis in Gram-negative bacteria. The LPS acts as a permeability barrier and is crucial for bacterial pathogenicity/virulence. We found that C. jejuni KDO8PS is potently inhibited by KDO8P oxime, a novel inhibitor of KDO8PS. This inhibitor presents a unique opportunity to study these enzymes and a platform from which antibiotics against Gram-negative bacteria can be developed.

Organophosphates are insecticides which result in acute adverse signs when exposed at toxic doses by animals and lead to death if left untreated. The current treatment for organophosphate toxicity includes atropine and the federally approved oxime 2-PAM. However, 2-PAM is not very effective at crossing the blood brain barrier which results in prolonged inactivation of acetylcholinesterase, which is the primary target of organophosphates, in the brain even after administration. The novel oximes, Oxime 15 and Oxime 20, are able to cross the blood brain barrier and reactivate the inhibited acetylcholinesterase. In this experiment with six animal species frequently used in toxicity studies, they were proven to be just as effective and sometimes better than 2-PAM at reactivating acetylcholinesterase or butyrylcholinesterase inhibited by paraoxon, chlorpyrifos-oxon, phorate-oxon, or dicrotophos. The detoxication enzymes butyrylcholinesterase, carboxylesterase, and paraoxonase were also studied as potential influences of the toxicity of the organophosphates in these different species.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Oximes are chemical compounds used to reactivate the inhibited acetylcholinesterase (AChE) enzyme by organophosphates (OPs). The OPs, besides classically recognized as AChE irreversible inhibitors, are also involved in the generation of oxidative stress conditions. However, researches focusing on the possible antioxidant properties of oximes are lacking in the literature. The aim of this study was to investigate the potential antioxidant and toxic properties of 3-(phenylhydrazono)butan-2-one oxime and butane-2,3-dionethiosemicarbazone oxime in mice, and to understand the mechanism(s) by which they act. Firstly, we investigated the existence and the mechanism(s) by which 3- (phenylhydrazono)butan-2-one oxime exert its antioxidant properties (Manuscript 1). The obtained results show that in vitro hydrogen peroxide (H2O2), malonate, or ferrous ions (Fe2+)-induced lipid peroxidation was decreased by low concentrations of the oxime. Oxime treatment did not modify the basal peroxidation level nor prevented the induced lipid peroxidation determined ex vivo. The obtained results suggest that 3-(phenylhydrazono)butan-2-one oxime could be employed as a satisfactory antioxidant compound. The absence of toxicity signs after in vivo administration of 3-(phenylhydrazono)butan-2-one oxime to mice may indicate that it could be a safe drug for further studies. The other objective of this study was to investigate the existence and the mechanism(s) by which butane-2,3-dionethiosemicarbazone oxime exert its antioxidant properties (Manuscript 2). The obtained results indicate a significant H2O2, nitric oxide (NO) and 1,1-diphenyl-2-picrylhydrazyl (DPPH●) scavenging activity at low oxime concentrations. Besides, the butane-2,3-dionethiosemicarbazone oxime significantly diminished the deoxyribose degradation induced by Fe2+ or Fe2+ + H2O2, and also the benzoate hydroxylation induced by ferric ions (Fe3+) + H2O2 reaction. Besides, the oxime showed a significant inhibitory effect on s-phenantroline reaction with Fe2+. A significant decrease in the basal and pro-oxidants induced lipid peroxidation in brain, liver, and kidney of mice was observed both in vitro and ex vivo. In addition, in our ex vivo experiments the butane-2,3- dionethiosemicarbazone oxime did not determine significant changes in thiol (-SH) levels of liver, kidney and brain, as well as did not modify the delta-aminolevulinate dehydratase (δ- ALA-D) activity in these tissues of mice. The obtained results indicate that the oximes tested depicted significant antioxidant properties, and that further studies are necessary to improve our knowledge regarding the exact antioxidant action mechanism of these oximes. / As oximas são compostos químicos utilizados para reativar a enzima actilcolinesterase (AChE) inibida por organofosforados (OPs). Os OPs, além de serem classicamente reconhecidos como inibidores da AChE, também estão envolvidos em situações que geram estresse oxidativo. Contudo, pesquisas enfocando as possíveis propriedades antioxidantes das oximas são escassas na literatura. O objetivo deste estudo foi investigar o potencial antioxidante e as propriedades tóxicas das oximas 3-(fenil hidrazona) butano-2-ona e butana- 2,3-dionatiosemicarbazona em camundongos, e entender o(s) possível(is) mecanismo(s) pelo(s) qual(is) elas atuam. Inicialmente investigamos a existência, e o(s) mecanismo(s) pelo(s) qual(is) a oxima 3-(fenil hidrazona) butano-2-ona exerce suas propriedades antioxidantes (Manuscrito 1). Os resultados obtidos mostram que a peroxidação lipídica induzida por peróxido de hidrogênio (H2O2), por malonato, e por íons ferrosos (Fe2+) foi diminuída em baixas concentrações da oxima. O tratamento dos camundongos com a oxima não alterou os níveis basais de peroxidação lipídica, nem preveniu a peroxidação lipídica induzida em experimentos ex vivo. Os resultados obtidos sugerem que a oxima 3-(fenil hidrazona) butano-2-ona pode ser empregada como um satisfatório composto antioxidante. A ausência de sinais de toxicidade após a administração in vivo da oxima 3-(fenil hidrazona) butano-2-ona em camundongos indica que esta pode ser uma droga segura para futuros estudos. O outro objetivo deste estudo foi investigar a existência e o(s) mecanismo(s) pelo(s) qual(is) a oxima butana-2,3-dionatiosemicarbazona exerce suas propriedades antioxidantes (Manuscrito 2). Os resultados obtidos indicam uma significativa atividade da oxima em neutralizar H2O2, o radical 1,1-difenil-2-picrilhidrazil (DPPH●), e a formação de óxido nítrico (NO), em baixas concentrações. Além disso, a oxima butana-2,3-dionatiosemicarbazona diminuiu significativamente a degradação da desoxirribose induzida por Fe2+ e pela reação Fe2+ + H2O2, e também a hidroxilação do benzoato induzida pela reação íons férricos (Fe3+) + H2O2. Além disso, a oxima apresentou um efeito inibitório significativo na reação da s- fenantrolina com Fe2+ Uma diminuição significativa na peroxidação lipídica basal e na peroxidação lipídica induzida por agentes pro-oxidantes no cérebro, fígado e rim de camundongos foi observada tanto in vitro quanto ex vivo. A oxima butana-2,3- dionatiosemicarbazona não determinou mudanças nos níveis de tióis (-SH) no fígado, rim e cérebro, bem como não modificou a atividade da enzima delta-aminolevulinato desidratase (δ-ALA-D) nestes tecidos de camundongos em experimentos ex vivo. Os resultados obtidos indicam que as oximas testadas apresentaram propriedades antioxidantes significativas, e que futuros estudos são necessários para aumentar o conhecimento a respeito do exato mecanismo de ação antioxidante destas oximas.

Récemment, de nombreux efforts ont été consacrés au développement d’oligonucléotides synthétiques pour des applications thérapeutiques et de diagnostique variées. Les oligonucléotides modifiés peuvent inhiber sélectivement l’expression des gènes en se liant spécifiquement à des séquences d’ADN et/ou d’ARN ciblées à travers les stratégies antigène, antisens ou d’ARN interférent. Les aminoxy peptides forment facilement des structures secondaires bien définies comme des alpha-, béta-, gamma-turns ou des hélices, ce qui nous a inspiré pour concevoir de nouveaux oligonucléotides modifiés dans le but d’étudier leurs propriétés physico-chimiques et biologiques. Au cours de ce travail, la synthèse de nucléosides aminoxy acides et de leurs oligomères a été entreprise en séries ribose et désoxyribose. Dans la première partie, les fonctions aminoxyle, acide carboxylique et aldéhyde ont été introduites sur la partie osidique de la thymidine. Différents nucléosides monofonctionnalisés ont été synthétisés à l’aide notamment des réactions de Mitsunobu, d’O-allylation et d’oxydation. Les nucléosides monomères ont ensuite été couplés entre eux conduisant aux nouveaux dinucléosides liés par liaison N-oxy amide, oxime et aminoxy. Dans la seconde partie, la synthèse de différentes uridines aminoxy acides a été étudiée à partir de l’uridine, des 2,2’-anhydro et 2,3’-anhydro uridines. Une uridine aminoxy ester a pu être obtenue en passant par la 3’-oxo uridine via une homologation (réaction de Wittig) et l’introduction de la fonction oxyamine en position 5’ par une substitution nucléophile du dérivé iodé. En parallèle, dans la continuité des travaux réalisés au laboratoire sur la synthèse des glycoamino acides, nous avons synthétisé des C-glycosyl aminoxy acides jamais décrits dans la littérature, dans le but de générer de nouveaux mimes de glycopeptides. A partir du C-allyl glucopyranoside perbenzylé, deux C-glucosyl aminoxy acides diastéréoisomères ont été préparés. / Much recent efforts have been devoted to the development of synthetic oligonucleotides for various therapeutic and diagnostic applications because of their capability to cause selective inhibition of gene expression by bonding to the target DNA/RNA sequences through antigen, antisense and RNA interference. The easy formation of well-defined structures like alpha-, béta-, gamma-turns or helical structures of N-oxy peptides promoted us to design new modified oligonucleotides so as to study their physico-chemical and biological properties. During this work, synthesis of different nucleosides aminoxy acids as well as their oligomers has been investigated. In the first part, aminoxy, carboxylic acid and aldehyde functions were introduced into the sugar ring of thymidine and different monofunctionalized nucleosides were obtained thanks to Mitsunobu, O-allylation and oxidation reactions. Different nucleoside monomers were then linked together, leading to novel dinucleosides with N-oxy amide, oxime or aminoxy linkage. In the second part, preparation of different uridines aminoxy acids was studied by using uridine, 2,2’-anhydro and 2,3’-anhydro uridines as starting materials. An uridine aminoxy ester was obtained from 3’-oxo uridine, through homologation with Wittig reaction and introduction of the oxyamine function by nucleophilic substitution of the 5’-iodo derivative. In parallel, as a continuing program in the laboratory on the glycoamino acids synthesis, we have synthesized novel C-glycosyl aminoxy acids in order to generate new mimes of glycopeptides. From perbenzylated C-allyl glucopyranoside, two diastereomeric C-glucosyl aminoxy acids have been successfully prepared.

Le motif spiroacétal constitue une partie du squelette de nombreux produits naturels possédant des activités biologiques variées. Récemment, de nouveaux spiroacétals de synthèse incorporant un hétéroatome supplémentaire en bêta du carbone spiranique et possédant des activités biologiques intéressantes, ont été décrits. Nous avons mis au point une synthèse efficace et modulable de spiroacétals originaux possédant des hétéroatomes (oxygène, soufre, azote) en position 4 et 10 du squelette 1,7-dioxaspiro[5.5]undécane. Elle repose sur une étape clé de déprotection-spirocyclisation d'une cétone masquée obtenue par substitution nucléophile du 1,3-dichloropropanone O-benzyloxime par des précurseurs issus du solkétal. Ainsi nous avons préparé les motifs 4,10-dioxa-, 4,10-dithia-, 4-thia-10-oxa-, 10-aza-4-thia- et 10-aza-4-oxa-1,7-dioxaspiro[5.5]undécanes, pour lesquels une étude structurale complète a été effectuée par RMN. Une première approche du motif 4,10-diaza- est également présentée