GÖÇ VE YAŞAM

Uluslararası Bakalorya Programı, A1 dersi Türk Dili ve Edebiyatı alanında ele alınan bu tezde, Orhan Kemal'in Gurbet Kuşları adlı yapıtında göç olgusu nedenleri ve sonuçlarıyla beraber incelenmiştir. Göç olgusuyla değişen toplumsal yapı, ekonomik ve kültürel farklılıklar çerçevesinde değerlendirilmiştir. Bu tezin amacı, göç olgusunun toplumsal yapıda alt sınıf ve üst sınıflardaki bireyler üzerindeki etkilerini ortaya koymaktır. Üç ana bölümden oluşan tezin ilk bölümünde yapıta adını veren Gurbet Kuşları kavramı üzerinde durulmuştur. Köylülerin aidiyetsizliği ve uyum sorunu bu bölümde aktarılmıştır. Tezin ikinci bölümünde ise köylülerin köyden kente göç sürecinde yaşadıkları kadın ve erkek figürler üzerinden neden ve sonuçlarıyla işlenmiştir. Tezin üçüncü bölümünde şehirliler başlığı altından genel olarak şehirde – İstanbul – yaşayan insanların göç sürecinde köylülerle yaşadıkları uyumsuzluk ve çatışmalara yer verilmektedir. Çalışmada göç sürecinde şehre yerleşen figürlerin şehirlilerle aralarındaki ekonomik ve kültürel farklılıkların sınıflar arasında geçişe olanak tanımadığı sonucuna varılmıştır

La biosynthèse des isoprénoïdes (Une cible pour la synthèse de nouveaux antibactériens)

Les isoprénoïdes (menthol, cholestérol, b-carotène) constituent une vaste famille de composés naturels présents chez tous les êtres vivants. Ils peuvent être biosynthétisés selon deux voies: la voie du mévalonate et la voie du 2-C-méthylérythritol 4-phosphate (MEP).La voie du MEP est présente chez de nombreux microorganismes pathogènes responsables de la tuberculose, de la lèpre ou du paludisme. Du fait de la résistance de plus en plus importante des microorganismes aux antibiotiques et antiparasitaires actuels, il devient nécessaire de trouver de nouvelles cibles thérapeutiques pour lutter contre les agents pathogènes.Comme l homme ne synthétise pas ses isoprénoïdes par la voie du MEP, toutes les enzymes de cette voie de biosynthèse deviennent des cibles potentielles pour de nouveaux inhibiteurs. Dans cette optique nous avons choisi comme cible la désoxyxylulose phosphate réducto-isomérase (DXR). Plusieurs structures cristallines de cette enzyme sont connues, dont une avec l un de ses inhibiteurs, la fosmidomycine, donne un aperçu de son mode d inhibition. La fosmidomycine est ancrée dans le site actif de l enzyme par l extrémité phosphonate mais aussi via sa fonction rétro-hydroxamate qui chélate un cation divalent par ses deux atomes d oxygène.Nous avons donc choisi de synthétiser des analogues de la fosmidomycine en modifiant soit la fonction chélatante, soit l extrémité phosphonate, soit la longueur de la chaîne carbonée. Notre choix s est porté sur les groupements hydroxamate, hydrazide et dithiocarbamate comme pince chélatante, et sur la fonction acide carboxylique pour remplacer le groupe phosphonate.Des études biochimiques ont été effectuées sur l ensemble des composés synthétisés pour déterminer leurs activités biologiques. Nous avons montré que l un des dérivés synthétisé de type hydroxamate possède une activité comparable à celle de la fosmidomycine, et que de plus il garde son activité sur une souche d E. coli résistante à la fosmidomycine.Isoprenoids (menthol, cholesterol, b-carotene) are natural compounds which are present in all living organisms. Isoprenoid biosynthesis proceeds via two biosynthetic pathways, depending on the organisms. The mevalonate pathway is found in animals, fungi, the cytoplasm of phototrophic organisms, some eubacteria and archaea, whereas the 2-C-methylerythritol 4-phosphate (MEP) pathway is present in most eubacteria, in unicellular green algae and in the chloroplasts of phototrophic organisms. As the MEP pathway occurs in a number of pathogens but not in humans, all enzymes of this pathway may represent interesting targets for the development of new drugs.Among the enzymes, we focused on the deoxyxylulose phosphate reducto-isomerase (DXR). Several three dimensional DXR structures were resolved, and especially a complex with fosmidomycine, a potent inhibitor of this enzyme. This revealed the chelation of the Mn2+ cation of the active site by the retro-hydroxamate group and the fixation of the phosphonate moiety in a specific positive-charged cavity.We present here the synthesis of analogues of fosmidomycine. We chose to modify either the retro-hydroxamate group by a hydroxamate with different length of the carbon backbone, a hydrazide and a dithiocarbamate group, or the phosphonate moiety by a carboxylic acid.Biochemical studies were performed on all compounds to determine their biological activities. One of our molecules with a hydroxamate group presents an activity comparable to that of fosmidomycine, and is even active on a fosmidomycin-resistant strain of E. coli.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

Biosynthèse des isoprénoïdes (Synthèses d'analogues du 1-désoxy-D-xylulose 5-phosphate,inhibiteurs potentiels de la voie du méthylérythritol phosphate)

Les isoprénoïdes sont des produits naturels présents chez tous les organismes vivants qui peuvent être synthétisés selon deux voies de biosynthèse différentes: la voie du mévalonate et la voie du méthylérythritol 4-phosphate (MEP). Les enzymes de la voie du MEP présentes chez de nombreux microorganismes mais absentes chez les animaux, représentent des cibles potentielles pour le développement de nouveaux médicaments contre les maladies causées par des bactéries pathogènes ou par des parasites. Dans cet objectif, l'élaboration d'inhibiteurs potentiels de cette voie a été envisagée. La désoxyxylulose réducto-isomèrase (DXR), une enzyme de la voie du MEP, a été choisie comme cible et des analogues de son substrat, le désoxyxylulose 5-phosphate, (DXP), ont été préparés puis leurs caractéristiques biochimiques (substrat, inhibiteur) ont été déterminées. La première partie de ce travail consiste en la mise au point d'une synthèse simple et efficace du DXP qui a été appliquée à la préparation de DXP marqué au deutérium, de son analogue non phosphorylé, le DX, et de DX marqué au deutérium. Ces composés ont été utilisés dans le cadre de collaborations. Dans une deuxième partie, la synthèse d'analogues phosphonates et fluorés du DXP est réalisée selon deux approches: une approche à partir de chirons et une approche par synthèse asymétrique. Les chirons utilisés sont des dérivés du L-tartrate. L'approche par synthèse asymétrique utilisée met en jeu une aldolisation asymétrique enzymatique. Au cours de ce travail une nouvelle méthode de synthèse d'un précurseur de la dihydroxyacétone phosphate (DHAP), substrat spécifique des aldolases, a été mise au point. L'activité biologique des analogues du DXP synthétisés a ensuite été évaluée in vitro sur la DXR et in vivo sur des souches d'E. coli. Nous avons pu montrer que l'analogue phosphonate du DXP est substrat de la DXR et que les autres composés synthétisés se comportent comme des inhibiteurs.Isoprenoids are natural compounds present in all living organism and can be synthesised via two different biosyntheses: the mevalonate pathway or the methylerytritol phosphate pathway (MEP). The enzymes involved in the MEP pathway are present in many microorganisms but absent in animal cells and therefore are potential targets for the design of new drugs acting on the diseases cause by pathogenic bacteria or parasites. In this purpose, the elaboration of potential inhibitors of this pathway has been considered. The deoxyxylulose 5-phosphate reducto-isomerase (DXR), one of the enzymes of the MEP pathway, has been chosen as a target. The synthesis of analogues of deoxuxylulose phosphate (DXP), the natural substrate of the DXR has been developed and their biochemical properties (substrate, inhibitor) have been determined. The first part of this work is the elaboration of a practical and efficient synthesis of DXP. This relevant synthesis allowed the preparation of deuterium labelled DXP, and its non phosphorylated analogue, DX, with a possible deuterium labelling at C-5. All these compounds were used for investigations on the MEP pathway. In a second part, phosphonate and fluorinated analogues of DXP have been synthesised via two different approaches: one from chirons and the other one from asymmetric synthesis. Compounds derived from the L-tartrate ester were used as chirons for the synthesis of the analogues of DXP. Such compounds were prepared by using biocatalysts: the aldolases, allowing an asymmetric aldolisation reaction. Due to the specific substrate of aldolases, the dihydroxyacetone phosphate (DHAP), a short and efficient synthesis of a precursor of DHAP, has been developed. The biological activity of the synthesised compounds was then determined in vitro on the DXR and in vivo on E. coli. We found that the phosphonate analogue of DXP is substrate of DXR and that the other analogues are inhibitors.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

Synthèse d'inhibiteurs potentiels non phosphorylés de la désoxyxylulose phosphate réductoisomérase et étude de la voie de biosynthèse des unités isopréniques chez Acanthamoeba polyphaga

Synthèse d inhibiteurs potentiels non phosphorylés de la désoxyxylulose phosphate réductoisomérase et étude de la voie de biosynthèse des unités isopréniques chez Acanthamoeba polyphaga. De nombreux microorganismes pathogènes utilisent la voie du méthylérythritol phosphate (MEP) pour la synthèse des unités isopréniques (IPP et DMAPP). Absente chez l homme, cette voie constitue une cible de choix pour lutter contre ces microorganismes. La fosmidomycine est un des meilleurs inhibiteurs connus à ce jour de la désoxyxylulose phosphate réductoisomérase (DXR), deuxième enzyme de cette voie. Afin d améliorer d une part la biodisponibilité de ce type d inhibiteur et d autre part de lutter contre le phénomène de résistance à cet antibiotique, nous avons synthétisé des analogues de la fosmidomycine où le groupement phosphonate est remplacé par un groupement tétrazole ou par un groupement squaryle. Les molécules synthétisées ont été testées sur la DXR d Escherichia coli et n ont pas révélé d activité inhibitrice significative.Par ailleurs, nous avons montré, par des expériences d incorporation de glucose marqué au 13C, que l amibe Acanthamoeba polyphaga, utilise la voie du mévalonate pour synthétiser les unités isopréniques nécessaires à la synthèse de ses stérolsSynthesis of potential non-phosphonate inhibitors of the deoxyxylulose phosphate reductoisomerase and study of the biosynthetic pathway for isoprenoids units synthesis using by Acanthamoeba polyphagaMany pathogenic microorganisms synthesize their isoprenoid units (IPP and DMAPP) via the methylerythritol phosphate pathway (MEP pathway). Absent in man, all enzymes of this metabolic route are potential targets for the design of new antimicrobials. This pathway is present in pathogenic bacteria, but absent in mammals. Hence, the development of small-molecule inhibitors for the MEP enzymes constitutes a novel approach for the design of new antimicrobials. Fosmidomycin is the most efficient inhibitor of the the deoxyxylulose phosphate reductoisomerase (DXR), the second enzyme of the MEP pathway. In an attempt to improve the pharmacological properties and the bioavailability of this antibiotic, we synthesized analogues of the fosmidomycin by replacing the phosphonate group by tetrazole or squaryl moieties. These synthesized compounds were tested on the DXR isolated from Escherichia coli.Otherwise, we showed by achieving incorporation experiments with 13C labeled glucose that the amoeba Acanthamoeba polyphaga utilize the mevalonate pathway to synthesize its sterols.STRASBOURG-Bib.electronique 063 (674829902) / SudocSudocFranceF

The Multifaceted MEP Pathway: Towards New Therapeutic Perspectives

Isoprenoids, a diverse class of natural products, are present in all living organisms. Their two universal building blocks are synthesized via two independent pathways: the mevalonate pathway and the 2-C-methyl-ᴅ-erythritol 4-phosphate (MEP) pathway. The presence of the latter in pathogenic bacteria and its absence in humans make all its enzymes suitable targets for the development of novel antibacterial drugs. (E)-4-Hydroxy-3-methyl-but-2-enyl diphosphate (HMBPP), the last intermediate of this pathway, is a natural ligand for the human Vγ9Vδ2 T cells and the most potent natural phosphoantigen known to date. Moreover, 5-hydroxypentane-2,3-dione, a metabolite produced by Escherichia coli 1-deoxy-ᴅ-xylulose 5-phosphate synthase (DXS), the first enzyme of the MEP pathway, structurally resembles (S)-4,5-dihydroxy-2,3-pentanedione, a signal molecule implied in bacterial cell communication. In this review, we shed light on the diversity of potential uses of the MEP pathway in antibacterial therapies, starting with an overview of the antibacterials developed for each of its enzymes. Then, we provide insight into HMBPP, its synthetic analogs, and their prodrugs. Finally, we discuss the potential contribution of the MEP pathway to quorum sensing mechanisms. The MEP pathway, providing simultaneously antibacterial drug targets and potent immunostimulants, coupled with its potential role in bacterial cell–cell communication, opens new therapeutic perspectives

The Multifaceted MEP Pathway: Towards New Therapeutic Perspectives

Isoprenoids, a diverse class of natural products, are present in all living organisms. Their two universal building blocks are synthesized via two independent pathways: the mevalonate pathway and the 2-C-methyl-ᴅ-erythritol 4-phosphate (MEP) pathway. The presence of the latter in pathogenic bacteria and its absence in humans make all its enzymes suitable targets for the development of novel antibacterial drugs. (E)-4-Hydroxy-3-methyl-but-2-enyl diphosphate (HMBPP), the last intermediate of this pathway, is a natural ligand for the human Vγ9Vδ2 T cells and the most potent natural phosphoantigen known to date. Moreover, 5-hydroxypentane-2,3-dione, a metabolite produced by Escherichia coli 1-deoxy-ᴅ-xylulose 5-phosphate synthase (DXS), the first enzyme of the MEP pathway, structurally resembles (S)-4,5-dihydroxy-2,3-pentanedione, a signal molecule implied in bacterial cell communication. In this review, we shed light on the diversity of potential uses of the MEP pathway in antibacterial therapies, starting with an overview of the antibacterials developed for each of its enzymes. Then, we provide insight into HMBPP, its synthetic analogs, and their prodrugs. Finally, we discuss the potential contribution of the MEP pathway to quorum sensing mechanisms. The MEP pathway, providing simultaneously antibacterial drug targets and potent immunostimulants, coupled with its potential role in bacterial cell–cell communication, opens new therapeutic perspectives

New Application of <i>cyclo</i>Saligenyl Prodrugs Approach for the Delivery of Fosfoxacin Derivatives in Mycobacteria

In this work, we implemented for the first time the cycloSaligenyl prodrug strategy to increase the bioavailability of fosmidomycin phosphate analogs in bacteria. Here, we report the synthesis of 34 cycloSaligenyl prodrugs of fosfoxacin and its derivatives. Among them, fifteen double prodrugs efficiently prevented the growth of the non-pathogenic, fast-growing Mycobacterium smegmatis

Isoprenoid biosynthesis in higher plants and in Escherichia coli: on the branching in the methylerythritol phosphate pathway and the independent biosynthesis of isopentenyl diphosphate and dimethylallyl diphosphate.

In the bacterium Escherichia coli, the mevalonic-acid (MVA)-independent 2-C-methyl-d-erythritol 4-phosphate (MEP) pathway is characterized by two branches leading separately to isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP). The signature of this branching is the retention of deuterium in DMAPP and the deuterium loss in IPP after incorporation of 1-[4-(2)H]deoxy-d-xylulose ([4-(2)H]DX). Feeding tobacco BY-2 cell-suspension cultures with [4-(2)H]DX resulted in deuterium retention in the isoprene units derived from DMAPP, as well as from IPP in the plastidial isoprenoids, phytoene and plastoquinone, synthesized via the MEP pathway. This labelling pattern represents direct evidence for the presence of the DMAPP branch of the MEP pathway in a higher plant, and shows that IPP can be synthesized from DMAPP in plant plastids, most probably via a plastidial IPP isomerase

Cutting Edge: Human γδ T Cells Are Activated by Intermediates of the 2- C

Activation of V gamma 9/V delta 2 T cells by small nonprotein Ags is frequently observed after infection with various viruses, bacteria, and eukaryotic parasites. We suggested earlier that compounds synthesized by the 2-C:-methyl-D-erythritol 4-phosphate (MEP) pathway of isopentenyl pyrophosphate synthesis are responsible for the V gamma 9/V delta 2 T cell reactivity of many pathogens. Using genetically engineered Escherichia coli knockout strains, we now demonstrate that the ability of E. coli extracts to stimulate gamma delta T cell proliferation is abrogated when genes coding for essential enzymes of the MEP pathway, dxr or gcpE, are disrupted or deleted from the bacterial genome