• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 132
  • 29
  • 20
  • 8
  • 7
  • 4
  • 2
  • 2
  • 1
  • 1
  • Tagged with
  • 265
  • 96
  • 72
  • 50
  • 40
  • 39
  • 36
  • 25
  • 24
  • 23
  • 23
  • 20
  • 19
  • 19
  • 19
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
201

Synthèse de la triphénylphosphine liée au polystyrène non réticulé et son utilisation lors de la réaction de Mitsunobu. Cyclopropanation catalytique énantiosélective d'alcènes utilisant le diazométhane

Janes, Marc K. January 2005 (has links)
Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal
202

Total Synthesis Of Palmerolide A, Dihydroconduritols And Lentiginosine

Pawar, Amit Balkrishna 03 1900 (has links) (PDF)
The thesis entitled “Total synthesis of palmerolide A, dihydroconduritols and lentiginosine” is divided into two chapters. First chapter of the thesis describes the formal total synthesis of bioactive marine macrolide palmerolide A. Palmerolide A was isolated by Baker and co-workers from an Antarctic tunicate Synoicum adareanum. Palmerolide A is a 20-membered macrolactone containing five chiral centers and seven unsaturations. Palmerolide A was found to be potent and selectively cytotoxic against human melanoma cancer cell lines and was also shown to inhibit vacuolar V-ATPase. In section A, enantioselective formal total synthesis of palmerolide A is described. key steps in the synthesis involve Jung non-aldol aldol reaction to construct the C16-C23 fragment 1 and oxidation of a chiral furyl carbinol to assemble the C1-C15 fragment 2. Scheme 1: Synthesis of C16-C23 fragment of palmerolide A. Scheme 2: Formal total synthesis of palmerolide A In section B, enantiospecific formal total synthesis of palmerolide A is presented from chiral pool tartaric acid. This approach is based on coupling of the three fragments viz. C1-C8 enoic acid fragment 3, C9-C15 vinyl stannane fragment 4 and the C16-C23 vinyl iodide fragment 1. The C1-C8 enoic acid fragment 3 is synthesized from L-threotol obtained from L-tartaric acid, while synthesis of the C9-C15 fragment 4 involved the elaboration of a γ-hydroxy amide derived from the bis-Weinreb amide of tartaric acid. Stille coupling of the vinyl iodide 1 obtained by Jung non-aldol aldol process with the vinyl stannane 4 delivered the C9-C23 unit. Esterification of this unit with the enoic acid 3 followed by zinc mediated Boord olefination and RCM furnished the macrolactone which is further elaborated to palmerolide A. Scheme 3: Synthesis of C1-C8 fragment of palmerolide A. Scheme 4: Enantiospecific formal total synthesis of palmerolide A. Section A of the second chapter deals with the enantiospecific synthesis of dihydroconduritols E and F from tartaric acid. Conduritols are 1,2,3,4-cyclohex-5-ene tetrols and are shown to be inhibitors of glycosidase. A number of derivatives of conduritols were found to possess various biological activities. Enantiospecific synthesis of dihydroconduritol E and F is accomplished from tartaric acid employing the Boord type fragmentation and ring closing metathesis as the key steps. Scheme 5: Enantiospecific synthesis of dihydroconduritols E and F Section B of the second chapter describes the enantiospecific total synthesis of ()lentiginosine. Lentiginosine is a dihydroxylated indolizidine alkaloid isolated from leaves of the plant Astragalus lentiginosus. Lentiginosine is the most powerful and competitive inhibitor (IC50 5µg/mL) of amyloglucosidase known so far. Key transformation in the synthesis include the in situ reduction and cyclization of a dihydroxyazide derived from the γ-hydroxy amide prepared from tartaric acid amide. (for structural formula pl see the abstract file.)
203

Optimisation of a stereoconvergent process catalysed by whole yeast cells / Charl Alan Yeates

Yeates, Charl Alan January 2008 (has links)
Thesis (Ph.D. (Pharmaceutical Chemistry)--North-West University, Potchefstroom Campus, 2009.
204

Optimisation of a stereoconvergent process catalysed by whole yeast cells / Charl Alan Yeates

Yeates, Charl Alan January 2008 (has links)
Thesis (Ph.D. (Pharmaceutical Chemistry)--North-West University, Potchefstroom Campus, 2009.
205

Intestinal Permeability and Presystemic Extraction of Fexofenadine and R/S-verapamil

Tannergren, Christer January 2004 (has links)
The main objective of this thesis was to investigate the in vivo relevance of membrane transporters and cytochrome P450 (CYP) 3A4-mediated metabolism in the intestine and liver for the bioavailability of drugs in humans after oral administration. In the first part of the thesis, the main transport mechanisms involved in the intestinal absorption and bioavailability were investigated for fexofenadine, a minimally metabolized drug, which is a substrate for P-glycoprotein (P-gp) and members of organic anion transporting polypeptide (OATP) family. Jejunal perfusion studies revealed that co-perfusion with verapamil increased the bioavailability of fexofenadine by decreasing the first-pass liver extraction as the low intestinal permeability was unchanged by the transport inhibitors studied. The mechanism behind the interaction probably involves inhibition of OATP-mediated sinusoidal uptake and/or P-gp-mediated canalicular secretion of fexofenadine. Results from the Caco-2 model supported that the intestinal absorption of fexofenadine is mainly determined by the low passive permeability of the drug, even though fexofenadine clearly is a P-gp substrate. In the second part of the thesis, the effect of repeated oral administration of the P-gp and CYP3A4 inducer St. John’s wort on the in vivo intestinal permeability and presystemic metabolism of the dual P-gp and CYP3A4 substrate verapamil was investigated in a jejunal perfusion study. St. John’s wort decreased the bioavailability of the enantiomers of verapamil by inducing the CYP3A4-mediated presystemic metabolism, probably mainly in the gut. It was also concluded that induction of efflux transporters, such as P-gp, does not affect the intestinal transport or the gut wall extraction of high permeability substrates like verapamil. Data from Caco-2 cells with induced CYP3A4-activity supported these findings. The plasma levels of the enantiomers of norverapamil also decreased despite an increased formation, which was attributed to induction of CYP3A4 and/or other metabolic routes.
206

Nitroxydes chiraux à squelette imidazolidin-4-one comme catalyseurs d'oxydation énantiosélective d'alcools par O2 / L'auteur n'a pas fourni de titre en anglais

Carbo Lopez, Marta 09 December 2014 (has links)
L'objectif de cette thèse était d'évaluer des nitroxydes chiraux à squelette imidazolidin-4-one comme catalyseurs d'oxydation énantiosélective d'alcools par le dioxygène. Pour cela, plusieurs nitroxydes avec différents substituants en position α ont été synthétisés afin de voir les effets possibles de chacun des groupements. Différents co-catalyseurs décrits dans la bibliographie ont été testés afin de faire ces réactions qui ont lieu à température ambiante et pression atmosphérique. Ces systèmes catalytiques peuvent se différencier selon s'ils utilisent ou pas de métal comme additif.La stratégie utilisée pour la synthèse des catalyseurs a été développée au laboratoire à partir de travaux sur des nitrones réalisés précédemment. Grâce à cette stratégie et à l'utilisation de différentes nitrones de départ, des analogues différemment substitués en position α peuvent être synthétisés rapidement en seulement deux étapes. En particulier, l'utilisation d'une nitrone chirale nous permettra l'obtention de catalyseurs énantiopurs qui pourront être utilisés pour les réactions d'oxydation énantiosélectives.Dans la première partie de notre étude, différents systèmes catalytiques ont été testés avec nos catalyseurs sur un substrat modèle : l'alcool benzylique. Les résultats obtenus nous ont aidé à déterminer : (1) la capacité des nitroxydes de type imidazolidin-4-one à agir en tant que catalyseurs pour les réactions d'oxydation aérobie ; (2) la différence de réactivité selon la substitution en position α ; (3) les systèmes catalytiques les plus efficaces avec nos catalyseurs ; (4) le type de substrats qui pourront être envisagés lors de l'oxydation énantiosélective.C'est ainsi la désymétrisation de diols conduisant à la formation d'atropoisomères qui a été envisagée. L'oxydation par le dioxygène de trois substrats a ainsi été testée avec plusieurs catalyseurs énantiopurs et un système catalytique à base de cuivre. Les résultats d'énantiosélectivité obtenus ont été variables selon le substrat et le catalyseur utilisés. Des résultats très encourageants ont été obtenus pour l'un des substrats, avec des excès enantiomériques d'environ 60 %.En parallèle avec les différentes réactions d'oxydation, des études de voltammétrie cyclique et de résonance paramagnétique électronique (RPE) ont aussi été réalisées. La voltammétrie cyclique nous a servi surtout pour expliquer la différence de réactivité de différents analogues selon leur substitution en position α. Avec la RPE, nous avons essayé de comprendre un peu plus l'organisation autour du cuivre des différents éléments qui font partie du système catalytique à base de cuivre utilisé pour les oxydations énantiosélectives.Grâce à tous ces travaux, nous avons démontré que les nitroxydes à squelette imidazolidin-4-one peuvent être utilisés en tant que catalyseurs pour l'oxydation aérobie d'alcools. Nous avons noté l'importance des substituants en position α qui jouent un rôle important sur la stabilité de l'espèce active, ce qui pourra faire varier l'efficacité de chaque composé. Les nitroxydes contenant le squelette imidazolidin-4-one ont aussi donné des bons résultats dans des réactions d'oxydation énantioséletive de diols benzyliques. / The aim of this thesis was to evaluate the use of chiral nitroxides containing an imidazolidin-4-one squeletton as enantioselective catalysts for the aerobic oxidation of alcohols. In this view, several nitroxides with different α substituents have been synthesized to investigate the influence of these groups. Several co-catalysts reported in the literature have been tested for the oxidation reactions that take place at room temperature and atmospheric pressure. These catalytic systems can be classified relatively to the presence or the absence of metal as additive.The strategy used for the catalyst synthesis has been developped in the laboratory from previous studies about nitrones. Using this strategy and different starting nitrones, several α-substituted analogues can be rapidly synthesized in only two steps. Particularly, the use of a chiral nitrone will permit the obtention of enantiopur catalysts that will be able used for the enantioselective oxidations.In the first part of our study, several catalytic systems have been tested with our catalysts with a reference substrate: benzylic alcohol. According to the results, we have been able to determine: (1) the capacity of imidazolidin-4-one nitroxides to behave as catalysts for the aerobic oxidations; (2) the difference of reactivity depending on the α substituents; (3) the more effective catalytic systems for our catalysts; (4) the scope of the reaction in order to determine the suitable substrates for enantioselective reactions.With all these results in hand, diol desymmetrization for the synthesis of atropoisomers has been considered. Dioxygen oxidation of three diols has been tested using different enantiopur catalysts with a copper-based catalytic system. The enantioselectivity obtained proved variable depending on the substrate and the catalyst used. Very encouraging results have been obtained for one of the substrate, with enantiomeric excess of about 60 %.At the same time as the oxidation reactions, cyclic voltammetry and electron paramagnetic resonance (EPR) studies have been carried out. Cyclic voltammetry has been useful to explain the difference of reactivity of the catalysts according the α substituents. Using the EPR, we have tried to understand the organisation around copper for the different species from the catalytic system used for the enantioselective oxidations.By means of this study, we have demonstrated that imidazolidin-4-one nitroxides can be used as catalysts for the aerobic oxidation of alcohols. The α substituents play an important role in the stability of the active species that can change the efficacity of each compound. Imidazolidin-4-one nitroxides have also given encouraging results in the enantioselective oxidation of benzylic diols.
207

Análise enantiosseletiva de venlafaxina e de seus principais metabólitos - aplicações em estudos de biotransformação in vitro e in vivo / Enantioselective analysis of venlafaxine and its major metabolites application to in vitro and in vivo biotransformation studies

Patricia da Fonseca 08 September 2011 (has links)
A microextração em fase líquida com membranas cilíndricas ocas (HF-LPME) é uma técnica bastante interessante de preparação de amostras, uma vez que com pequenas quantidades de solventes orgânicos é possível a extração dos analitos presentes em matrizes complexas. Sendo assim, essa técnica foi empregada para extração da venlafaxina (VEN) e seus metabólitos em fração microssomal de fígado de ratos e plasma, visando o desenvolvimento de métodos para análise enantiosseletiva desses analitos. Esses métodos foram então empregados em um estudo in vitro de biotransformação da VEN e em um estudo piloto de disposição cinética em ratos e humanos. A VEN é um fármaco quiral empregado no tratamento da depressão, cujas propriedades farmacocinéticas e farmacodinâmicas são estereosseletivas. Após a otimização das condições de extração por HF-LPME, foram obtidas recuperações de 12-60%. O método empregado no estudo in vitro de biotransformação da VEN foi desenvolvido usando a coluna ChiralpaK AD®, fase móvel composta por hexano : 2-propanol (95:5, v/v) + 0,025% de dietilamina (DEA) e detecção por absorção no UV. A coluna ChiralpaK AD-H® e a fase móvel composta por metanol : etanol (70:30, v/v) + 0,025% de DEA foram empregadas para análise da VEN e seus metabólitos em plasma. Para esse método, empregou-se a detecção por espectrometria de massas visando à obtenção de menores limites de quantificação. O método empregado para a determinação da VEN e de seus metabólitos em fração microssomal de fígado de ratos foi linear no intervalo de 200 a 5000 ng mL-1 e o método empregado para a determinação da VEN e de seus metabólitos em amostras de plasma foi linear no intervalo de 5 a 500 ng mL-1. Os métodos analíticos desenvolvidos para determinação da VEN e seus metabólitos nas matrizes biológicas foram aplicados em estudos de biotransformação in vitro e em estudos de disposição cinética em duas espécies (ratos e humanos). O objetivo destes estudos foi avaliar a correlação da biotransformação entre as diferentes espécies avaliadas e comparar os resultados obtidos nos estudos in vitro com os verificados nos estudos in vivo. Os resultados dos estudos empregando fração microssomal de fígado de ratos são semelhantes aos obtidos no estudo de disposição cinética em ratos, com formação mais pronunciada da Ndesmetilvenlafaxina (N-VEN) e com produção prioritária do enantiômero (-)-(R). Comparando-se os estudos de disposição cinética em ratos e humanos, observa-se enantiosseletividade na biotransformação da VEN com a (-)-(R)-VEN sendo preferencialmente biotransformada. Entretanto, em humanos observa-se que a (-)- (R)-O-desmetilvenlafaxina ((-)-(R)-O-VEN) é formada em maior proporção enquanto que, em ratos, a (-)-(R)-N-VEN é preferencialmente formada. / Hollow Fiber-Liquid Phase Microextraction (HF-LPME) is a very interesting technique for sample preparation, since it uses small amounts of organic solvents to extract drugs present in complex matrices. Thus, this technique was employed for the extraction of venlafaxine (VEN) and its metabolites from rat liver microsomal fraction and plasma, aiming the development of methods for the enantioselective analysis of these analytes. These methods were then applied to study the in vitro biotransformation and the kinetic disposition of VEN in rats and humans. VEN is a chiral drug used in the treatment of depression, whose pharmacokinetic and pharmacodynamic properties are stereoselective. After the optimization of the HFLPME conditions, recoveries of 12-60% were obtained. The method employed in the in vitro biotransformation study of VEN was developed using a ChiralpaK AD® column, mobile phase consisting of hexane : 2-propanol (95:5, v/v) + 0.025% of diethylamine (DEA) and UV detection. The ChiralpaK AD-H® column and the mobile phase consisting of methanol : ethanol (70:30, v/v) + 0.025% of DEA were employed for the analysis of VEN and its metabolites in plasma. In order to obtain lower quantification limits, mass spectrometry detection was used in this method. The method used for the determination of VEN and its metabolites in rat liver microsomal fraction was linear over the concentration range of 200 to 5000 ng mL-1 whereas the method used for the determination of VEN and its metabolites in plasma was linear in the range of 5 to 500 ng mL-1. The developed methods for the determination of VEN in biological matrices were applied to an in vitro biotransformation study and to kinetic disposition studies in two species (rats and humans). The objective of these studies was to evaluate the correlation of the biotransformation between different species and to compare the results of the in vitro and in vivo studies. The results obtained using rat liver microsomal fraction were similar to those obtained in the rat kinetic disposition study, with more pronounced formation of N-desmethylvenlafaxine (NVEN) and major production of the (-)-(R) enantiomer. Comparing the kinetic disposition studies in rats and humans, the enantioselectivity in the biotransformation of VEN with (-)-(R)-VEN being preferentially biotransformed was observed for both species. However, (-)-(R)-O-desmethylvenlafaxine ((-)-(R)-O-VEN) is preferentially formed in humans whereas the major metabolite in rat plasma is (-)-(R)-N-VEN.
208

Estudo da arilação enantiosseletiva de 3-pirrolinas N-protegidas via reação de Heck-Matsuda / Studies on the enantioselective Heck-Matsuda arylation of N-protected 3-pyrrolines

Lustosa, Danilo Machado, 1990- 12 January 2014 (has links)
Orientador: Carlos Roque Duarte Correia / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-26T20:32:55Z (GMT). No. of bitstreams: 1 Lustosa_DaniloMachado_M.pdf: 59336060 bytes, checksum: e1999d97ac1f1ad2f49b0e334514c4fa (MD5) Previous issue date: 2014 / Resumo: A reação de Heck convencional consiste em uma reação entre olefinas e haletos de arila ou vinila catalisada por paládio. A variante Heck-Matsuda (HM) utiliza sais de arenodiazônio, mais reativos do que os respectivos haletos de arila ou vinila.. Por muito tempo a HM apresentava como principal limitação metodológica a ausência de uma versão enantiosseletiva. Em 2012, o grupo do prof. Carlos Correia relatou a primeira reação de Heck-Matsuda enantiosseletiva. Com o intuito de tornar esta metodologia uma ferramenta sintética mais robusta e compreender melhor esta reação, esta dissertação relata novos estudos de complexos de paládio quirais, não racêmicos, como sistemas catalíticos na arilação de 3-pirrolinas N-protegidas em reações de Heck-Matsuda enantiosseletivas. Com a utilização de complexos Pd/piridinoxazolina obteve-se adutos de Heck contendo substituintes doadores de elétrons em rendimentos de bons a excelentes e razões enantiômericas de moderadas a boas. Ao se fazer uso de sais de arenodiazônio com substituintes retiradores de elétrons, obteve-se os adutos de Heck em rendimentos de baixos a bons e razões enantiômericas de boas a excelentes. Alguns dos adutos de Heck foram selecionados e aplicados na obtenção de análogos do baclofeno e suas respectivas butirolactamas, com o objetivo de demonstrar a aplicabilidade sintética da nova metodologia e determinar a estereoquímica absoluta dos adutos de Heck obtidos (via comparação dos valores de [a]D obtidos com aqueles relatados na literatura). Por fim, com a estereoquímica dos produtos determinadas, racionalizou-se a obtenção destes adutos de forma enantiosseletiva através da apresentação de ciclos catalíticos apropriados / Abstract: The conventional Heck reaction consists of a reaction between olefins and vinyl or aryl halides catalyzed by palladium. The variant Heck-Matsuda (HM) uses arenediazonium salts, more reactive than the corresponding aryl or vinyl halides. For a long time the HM was seeing as a limited synthetic method due to the absence of its enantioselective version. In 2012, the group of prof. Carlos Correia reported the first enantioselective Heck-Matsuda reaction. Aiming at making this methodology a powerful synthetic tool, as well as to get mechanistic insights, this dissertation describes our studies on the enantioselective HM employing chiral, non-racemic, palladium complexes for the arylation of 3-N-protected- pyrrolines. With the use of Pd/pyridine-oxazoline complexes chiral Heck adducts were obtained containing electron rich substituents in good to excellent yields in enantiomeric ratios from moderate to good. When making use of arenediazonium salts with electron withdrawing substituents, the Heck adducts were obtaining in low from good yields in enantiomeric ratios from good to excellent. Some of the Heck adducts were selected in order to synthesize baclofen analogues and butyrolactams to demonstrate not only the applicability of the new method but also to determine the absolute stereochemistry of the Heck adducts (comparison of our [a]D values with those reported in the literature). Finally, with the absolute stereochemistry of the products determined, a rationale for this new enantioselective Heck-Matsuda was provided / Mestrado / Quimica Organica / Mestre em Química
209

Synthese neuer Furo[3,2-a]- und Pyrano[3,2-a]carbazolalkaloide

Spindler, Benedikt 17 September 2020 (has links)
Für die Synthese neuer Furo[3,2-a]- und Pyrano[3,2-a]carbazolalkaloide wurde eine Sequenz aus oxidativer Cyclisierung verschiedener Diarylamine verwendet. Über diese Strategie konnten drei verschiedene Furo[3,2-a]carbazole dargestellt werden und aufgrund eines Vergleichs der analytischen Daten eine fehlerhafte Strukturzuweisung bei der Isolierung zweier dieser Verbindungen aus natürlichen Quellen festgestellt werden. Die Synthese von Furoclausin-B konnte durch diese Strategie erfolgreich durchgeführt werden und führte ferner zur Aufklärung der absoluten Konfiguration dieser Verbindung. Desweiteren konnte über eine ähnliche Synthesestrategie die racemische Synthese zweier Pyrano[3,2-a]carbazole erfolgen, namentlich Guillauminin-B und Clausin-T. Durch Studien zur enantioselektiven Epoxidierung konnte die Grundlage für eine zukünftige enantioselektive Synthese dieser Verbindungen gelegt werden.
210

Réaction d’aza-Piancatelli : nouvelles applications, version diastéréosélective et utilisation en synthèse totale / Aza-Piancatelli reaction : scope, diastereoselective version and application in total synthesis

Marin, Lucile 28 June 2018 (has links)
Grâce à leurs multiples sites de fonctionnalisation, les cyclopenténones sont des intermédiaires particulièrement utiles dans la synthèse de produits naturels d’intérêt thérapeutique. En particulier, les composés 4-aminocyclopenténones permettent l’accès au motif aminocyclopentitol présent dans des molécules bioactives telles que le peramivir, la pactamycine, ou encore la trehazoline. L’une des méthodes les plus efficaces pour accéder aux 4-aminocyclopenténones est la réaction de cyclisation d’aza-Piancatelli. Cette réaction est basée sur le réarrangement de 2-furylcarbinols en présence d’un nucléophile azoté suivant un mécanisme faisant intervenir une électrocyclisation 4π-conrotatoire. Au sein de notre laboratoire, un système catalytique simple, utilisant un complexe de calcium combiné à un sel d’ammonium, a été mis au point pour avoir accès à ces composés. Cette méthode présente de nombreux avantages : elle est efficace (rendements allant jusqu’à 98%), rapide (15 à 30 minutes), elle nécessite seulement 1 mol% de catalyseur dans des conditions commodes (solvants non distillés et réaction à l’air libre) sur une grande échelle (multi-grammes). Dans ce contexte, nous avons cherché à exploiter tout le potentiel de cette réaction en synthétisant des 2-furylcarbinols plus complexes dans le but de concevoir un accès direct à des squelettes de composés bioactifs. Nous nous sommes en particulier concentrés sur la synthèse totale de la jogyamycine. Par ailleurs, nous avons effectué la synthèse totale de la bruceolline D avec un rendement global de 16% sur 5 étapes. Nous avons également développé une nouvelle séquence réactionnelle impliquant une réaction d’aza-Piancatelli suivie d’une réaction d’hydroamination promue par des sels de cuivre qui fournit un large éventail de cyclopenta[b]pyrroles polyfonctionnels à partir de 2-furylcarbinols facilement accessibles incorporant un groupement alcyne. Par cette méthode, 42 cyclopenta[b]pyrroles ont été obtenus avec des rendements atteignant 98%. Une caractéristique originale de notre approche est liée à l'utilisation d'anilines ortho-substituées. En effet, dans ce cas, des atropisomères avec un excès diastéréomérique supérieur à 20:1 ont pu être obtenus, accompagnés par la création d'une chiralité axiale N-C lors de l'étape d'hydroamination. A ce jour, il n'existait aucun autre exemple de synthèse atropodiastéréosélective de cyclopenta[b]pyrroles. Au cours de nos recherches sur le champ d’application de la réaction, nous avons remarqué que les cyclopenta[b]pyrroles pouvaient se réarranger spontanément en cyclopenta[b]pyrrolines suivant une déaromatisation lorsque l’hexafluoroisopropanol était utilisé comme solvant, permettant d’obtenir 13 cyclopenta[b]pyrrolines avec des rendements variant de 44 à 73%. Nous nous sommes également intéressés à la fonctionnalisation du motif cyclopenta[b]pyrrole pour illustrer l'utilité de notre méthodologie, en combinant en particulier cette séquence réactionnelle avec des réactions de type Friedel-Crafts. L’un des objectifs du projet de thèse était le développement de la version énantiosélective de la réaction. Après la publication récente de trois articles utilisant des acides phosphoriques chiraux en tant que catalyseurs, nous avons envisagé une autre approche pour la synthèse asymétrique de 4-aminocyclopenténones, s’appuyant sur l’utilisation d’une copule chirale (sulfoxyde chiral) portée par l’aniline en collaboration, avec le Dr. Wencel-Delord et le Pr. Colobert (Université de Strasbourg). Ainsi nous avons pu générer les 4-aminocyclopenténones correspondantes avec d’excellents rendements et diastéréosélectivités. / Due to their various functionalizable sites, cyclopentenones are very useful intermediates for the synthesis of natural products of therapeutic value. In particular, 4-aminocyclopentenones enable the access to the aminocyclopentitol frameworks, which are present in a variety of bioactive molecules such as peramivir, pactamycin, or trehazolin. One of the most efficient methods to access 4-aminocyclopentenones is the aza-Piancatelli reaction. It is based on the rearrangement of 2-furylcarbinols in the presence of a nitrogen nucleophile following a mechanism involving a 4π-conrotatory electrocyclization. In our laboratory, a simple catalytic system using a calcium complex combined with an ammonium salt was developed to gain access to these compounds. This method has many advantages : it is effective (yields up to 98%), fast (15 to 30 minutes), it requires only 1 mol% of catalyst under pratical conditions (undistilled solvents without an inert atmosphere) on a large scale (multi-gram). In this context, we sought to extend the scope of this reaction by designing more complex 2-furylcarbinols in order to directly access skeletons of bioactive compounds. In particular, we focused on the total synthesis of jogyamycin. In addition, we achieved the total synthesis of bruceollin D with an overall yield of 16% over five steps. We also developed a new reaction sequence involving an aza-Piancatelli reaction followed by a hydroamination reaction promoted by a copper salt. This sequence provides a wide range of highly functionalized cyclopenta[b]pyrroles from readily-available 2-furylcarbinols substituted by an alkyne moiety. Following this method, 42 cyclopenta[b]pyrroles were obtained with yields up to 98%. An original feature of this transformation is related to the use of ortho-substituted anilines. Indeed, in this case, atropisomers with a diastereomeric excess superior to 20:1 could be obtained accompanied by the creation of an chiral N-C axis during the hydroamination step. To date, no other example of atropodiastereoselective synthesis of cyclopenta[b]pyrroles has been reported. During our investigations on the scope of the reaction, we noticed that cyclopenta[b]pyrroles underwent a rearrangement into cyclopenta[b]pyrrolines, following a dearomatization when hexafluoroisopropanol was used as solvent. This transformation led to 13 cyclopenta[b]pyrrolines with yields ranging from 44% to 73%. We also investigated the functionalization of the cyclopenta[b]pyrrole motif to illustrate the synthetic utility of our methodology, notably by combining this reaction sequence with a Friedel-Crafts reaction. One of the objectives of this Ph.D. was the development of an enantioselective version of the reaction. After the recent publication of three papers using chiral phosphoric acids as catalysts, we devised another approach for the asymmetric synthesis of 4-aminocyclopentenones, relying on the use of a chiral auxiliary (chiral sulfoxide) in collaboration with Dr. Wencel-Delord and Pr. Colobert (University of Strasbourg). Thus, we were able to provide the corresponding 4-aminocyclopentenones with excellent yields and diastereoselectivity.

Page generated in 0.0963 seconds