Дисертації з теми "Chemoenzymatic catalysis"

Du fait de la raréfaction des ressources fossiles, l’industrie chimique doit aujourd’hui évoluer pour se tourner vers de nouvelles sources de matière première. A cela s’ajoutent les pressions environnementales toujours croissantes qui imposent une réduction de l’impact écologique et énergétique des procédés. Répondre à ces enjeux technologiques majeurs implique la conception de nouveaux procédés chimiques rendant notamment possible la transformation massive des ressources chimiques d’origine naturelle (cellulose, lignine, algues...etc) en produits chimiques à haute valeur ajoutée et répondant aux critères dits de « chimie verte ». , Dans ce contexte, la catalyse hétérogène est un outil incontournable puisqu’elle permet d’accélérer les réactions chimiques, dans des conditions durables, en rendant possible le recyclage des phases actives. Le développement de procédés toujours plus adaptés aux enjeux industriels et environnementaux actuels nécessite cependant l’élaboration de nouveaux catalyseurs, notamment capables de réduire toujours davantage la consommation d’énergie, de faire des économie d’atomes et de réduire autant que possible les quantités de réactifs et de solvants utilisés ainsi que les déchets produits. Pour ce faire, les catalyseurs hétérogènes capables de catalyser plusieurs réactions chimiques en une seule étape « en cascade » sont particulièrement prometteurs. [...] L’objectif global de [ma] thèse était de fabriquer un système chimioenzymatique capable de réaliser une cascade de deux réactions permettant la transformation d’alcools en amines. Pour cela il était proposé d’immobiliser sur un matériau hybride organique-inorganique poreux cristallin appelé MOF (Metal-Organic Framework), un catalyseur chimique, responsable d’une première étape d'oxydation d'alcool en composé carbonylé, et une enzyme transaminase catalysant l’étape ultérieure de transfert d'amine. La mise en œuvre d'un tel système sophistiqué était un réel défi, notamment parce qu’il s’agissait de trouver des conditions de réaction (solvant, température, pH, et choix des réactifs chimiques) qui soient compatibles avec les conditions de travail des transaminases (températures de réaction douces ≤ 60 ° C, solvants au moins partiellement aqueux). Ceci était un pré-requis nécessaire à la réalisation des synthèses "one-pot", où les deux réactions visées devaient être catalysées consécutivement par le catalyseur chimique et l’enzyme dans le même milieu réactionnel sans isolement du carbonylé intermédiaire. Il fallait également s’assurer de la stabilité du MOF dans le milieu réactionnel, et notamment de l’intégrité de sa structure dans des solvants contenant les solutions tampons aqueuses nécessaires à la stabilité des enzymes. [...]
Due to the scarcity of fossil resources, the chemical industry must today evolve to turn to new sources of raw material. Added to this are the ever-increasing environmental pressures that impose a reduction in the ecological and energy impact of the processes. Responding to these major technological challenges involves the design of new chemical processes making it possible, in particular, for the massive transformation of natural chemical resources (cellulose, lignin, algae, etc.) into high value-added chemicals that meet the so-called "Green chemistry" i, ii. In this context, heterogeneous catalysis is an essential tool since it makes it possible to accelerate the chemical reactions under sustainable conditions by making it possible to recycle the active phases ii. The development of processes that are increasingly adapted to today's industrial and environmental challenges, however, requires the development of new catalysts, in particular capable of reducing energy consumption even more, of saving atoms and of reducing as much as possible the quantities of reagents and solvents used as well as the waste produced. To do this, heterogeneous catalysts capable of catalyzing several chemical reactions in one step "in cascade" are particularly promising. [...] The overall goal of this thesis was to build a chemoenzymatic system capable of carrying out a cascade of two reactions allowing the transformation of alcohols into amines. For that it was proposed to immobilize on a crystalline organic-inorganic hybrid material called MOF (Metal-Organic Framework), a chemical catalyst, responsible for a first step of oxidation of alcohol to carbonyl compound, and a transaminase enzyme catalyzing the subsequent amine transfer step. The implementation of such a sophisticated system was a real challenge, especially because it was a question of finding reaction conditions (solvent, temperature, pH, and choice of chemical reagents) that are compatible with the working conditions of transaminases (mild reaction temperatures ≤ 60 ° C, at least partially aqueous solvents). This was a prerequisite for carrying out "one-pot" syntheses, where the two targeted reactions were to be catalyzed consecutively by the chemical catalyst and the enzyme in the same reaction medium without isolation of the intermediate carbonyl. It was also necessary to ensure the stability of the MOF in the reaction medium, and in particular the integrity of its structure in solvents containing the aqueous buffer solutions necessary for the stability of the enzymes. [...]

The main focus of this thesis lies on transition metal-catalyzed hydrogen transfer reactions. In the first part of the thesis, the mechanism for racemization of sec-alcohols with a ruthenium complex, Ru(CO)2Cl(η5-C5Ph5) was studied. The reaction between 5-hexen-2-ol and Ru(CO)2(Ot-Bu)(η5-C5Ph5) was studied with the aim to elucidate the origin of the slow racemization observed for this sec-alcohol. Two diastereomers of an alkoxycarbonyl complex, which has the double bond coordinated to ruthenium, were characterized by NMR and in situ FT-IR spectroscopy. The observed inhibition of the rate of racemization for substrates with double bonds provided further confirmation of the importance of a free coordination site on ruthenium for β-hydride elimination. Furthermore, we observed that CO exchange, monitored by 13C NMR using 13CO, occurs with both the precatalyst, Ru(CO)2Cl(η5-C5Ph5), and the active catalytic intermediate, Ru(CO)2(Ot-Bu)(η5-C5Ph5). It was also found that added CO has an inhibitory effect on the rate of racemization of (S)-1-phenylethanol. Both these observations provide strong support for reversible CO dissociation as a key step in the racemization mechanism. In the second part of this thesis, Ru(CO)2Cl(η5-C5Ph5) was combined with an enzymatic resolution catalyzed by a lipase, leading to several efficient dynamic kinetic resolutions (DKR). DKR of exocyclic allylic alcohols afforded the corresponding acetates in high yields and with excellent enantiomeric excess (ee). The products were utilized as synthetic precursors for α-substituted ketones and lactones. DKR of a wide range of homoallylic alcohols afforded the products in good to high yields and with high ee. The homoallylic acetates were transformed into 5,6-dihydropyran-2-ones in a short reaction sequence. Furthermore, DKR of a wide range of aromatic β-chloroalcohols afforded the products in high yields and with excellent ee. The β-chloro acetates were further transformed into chiral epoxides.

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 5: Mansucript.

L'objectif de ce travail était de développer un catalyseur chimio-enzymatique hétérogène basé sur l'utilisation de polymères de coordination poreux (ou Metal-Organic Framework: MOF) comme supports pour l'amination durable d'alcools à travers un procédé en cascade réalisé en une seule étape. Le processus en cascade est composé de deux étapes: la reaction d’oxydation de l'alcool catalysée chimiquement et l'amination énantiosélective de l'intermédiaire carbonylé resultant, catalysée par une enzyme ω-transaminase (ω-TA). Le ZIF-8 a été choisi comme support pour sa stabilité dans l’eau et à hautes températures, ce qui en fait un support idéal pour l’immobilisation de catalyseurs chimiques et biologiques. Dans ce travail, l'un des principaux défis consistait à sélectionner un système catalytique chimique dédié à la réaction d'oxydation de l'alcool dans des conditions aqueuses douces, compatibles avec les conditions de travail des enzymes ω-TAs. Dans ce contexte, deux systèmes catalytiques à base de nanoparticules supportées ont été développés. Dans le premier système, des sites actifs Cu2+ ont été hétérogénéisés dans la structure du ZIF-8 en vue de l'oxydation de l'alcool benzylique en présence de 2,2,6,6-Tétraméthylpipéridine-1-oxyle (TEMPO). Le problème de la lixiviation du Cu2+ au cours du processus catalytique a été résolu en réduisant le Cu2+ in situ dans les pores du ZIF-8 pour former des nanoparticules de Cu0 supportées et bien dispersées au sein du support. Ce catalyseur présente une stabilité et une sélectivité élevées, mais n'est pas actif lorsque l'eau est utilisée comme solvant. Dans le second système, des nanoparticules d'alliage bimétallique PdAu dispersées au sein du ZIF-8 ont été formées (PdAu@ZIF-8) pour catalyser l'oxydation aérobie de l'alcool en milieu aqueux à pH neutre. Le catalyseur présente une excellente activité dans des conditions douces, la meilleure performance étant obtenue pour un rapport atomique Pd/Au de 9:1. Les deux catalyseurs ont été caractérisés par PXRD, physisorption d’azote, microscopie électronique à haute résolution et XPS. La deuxième étape du processus en cascade implique l'amination biocatalysée du composé carbonylé obtenu lors de la première étape. Deux ω-TA S-sélectives issues des bactéries Silicibacter pomeroyi (3HMU) et Chromobacterium violaceum ont été testées. Le rendement maximal en S-α-méthylbenzylamine obtenu par amination de l'acétophénone en présence de 3HMU en utilisant la L-alanine comme donneur d'amine était de 77%. Les efforts visant à combiner ensuite l'oxydation de l'alcool catalysée par les nanoparticules de PdAu supportées sur le ZIF-8 et la catalyse enzymatique utilisant la 3HMU dans un processus en une seule étape ont révélé des interférences entre les composants chimiques indispensables à la réalisation de chaque étape. En conséquence, un processus en cascade alternatif réalisé dans un même milieu réactionnel mais dans lequel les deux étapes sont découplées a été mis au point. Celui-ci a permis d'obtenir un rendement global de S-MBA de 49%. Des tentatives ont finalement été effectuées pour immobiliser la 3HMU sur le catalyseur PdAu@ZIF-8 afin d'obtenir le catalyseur entièrement hétérogène ciblé. L’immobilisation a tout d’abord été réalisée par adsorption physique, mais l'activité des ω-TAs ainsi immobilisées s’est avérée être limitée. La modification de PdAu@ZIF-8 par adsorption de Ni2+ a légèrement amélioré l'immobilisation de l'enzyme. Dans une autre approche, le ZIF-8 fonctionnalisé avec des fonctions carbonyles grâce à un échange partiel “post-synthèse” des ligands 2-méthylimidazole du ZIF-8 avec des dérivés carbonylés d’imidazole, a conduit à des résultats encourageants, avec une amélioration de l'activité de la 3HMU immobilisée sur le ZIF-8 ainsi préparé d'un facteur 4. Cette approche prometteuse sera exploitée plus avant prochainement afin de synthétiser le catalyseur entièrement hétérogène 3HMU@PdAu@ZIF-8 visé dans ce projet de doctorat
The aim of this work was to develop a heterogeneous chemoenzymatic catalyst based on the use of Metal-Organic Frameworks (MOFs) as support for the eco-friendly amination of alcohols in a one-pot cascade synthesis. The cascade process is divided into two steps: an alcohol oxidation chemically catalyzed and the subsequent enantioselective amination of the resulting carbonyl intermediate catalyzed by a ω-transaminase enzyme (ω-TA). ZIF-8 was selected as MOF for its hydro- and thermo- stability, making it an ideal support for both chemical and biological catalysts. One of the key challenges was to select a chemical catalytic system for alcohol oxidation under mild aqueous conditions that is compatible with the working conditions of ω-TAs. In this context, two supported nanoparticles catalytic systems were developed for the aerobic alcohol oxidation. In the first system, Cu2+ active sites were heterogenized on ZIF-8 for benzyl alcohol oxidation in the presence of 2,2,6,6-Tetramethylpiperidine 1-oxyl (TEMPO). The leaching issue of Cu2+ during the catalytic process was overcome by reducing Cu2+ into Cu0 within ZIF-8 pores to form supported well-dispersed Cu0 nanoparticles. This catalyst exhibits high stability and selectivity, but is not active when using water as a solvent. In the second system, well-dispersed PdAu bimetallic alloy nanoparticles were formed on ZIF-8 (PdAu@ZIF-8) to catalyze base-free aerobic alcohol oxidation in water. The catalyst shows excellent activity under mild conditions, with the best performance obtained fora Pd/Au atomic ratio 9:1. Both catalysts were characterized using PXRD, N2-adsorption, TEM, HRTEM, and XPS. The second step of the cascade process involves the biocatalytic amination of the ketone. Two S-selective ω-TAs from Silicibacter pomeroyi (3HMU) and Chromobacterium violaceum were tested. The maximum yield of S-α-methylbenzylamine obtained by amination of acetophenone in the presence of 3HMU using L-alanine as the amine donor was 77%. Efforts to combine alcohol oxidation catalyzed by the ZIF-8-supported PdAu nanoparticles and enzymatic catalysis with 3HMU in a one-pot/one-step process revealed interferences between components of the two steps. Instead, a one-pot/two-step cascade process was developed, achieving an overall S-MBA yield of 49%. Attempts were finally made to immobilize 3HMU on PdAu@ZIF-8 in order to obtain the targeted fully heterogenized catalyst by first using physical adsorption, but the activity of the hence-immobilized ω-TAs was limited. Ni2+ modification of PdAu@ZIF-8 slightly improved the enzyme immobilization. Carbonyl-functionalized ZIF-8, obtained by a partial post-synthesis exchange of the 2-methylimidazolate ligands with carbonyl-imidazolate derivatives produced encouraging results, with a 4-fold improvement in activity of 3HMU immobilized on ZIF-8-90. As outlooks, this promising approach will be further investigated in forthcoming attempts to synthesize the entirely heterogeneous 3HMU@PdAu@ZIF-8 targeted in this PhD project

This  thesis  is  divided  into  four  parts,  all  centered  around  Constitutional Dynamic  Chemistry  (CDC)  and  Dynamic  Kinetic  Resolution  (DKR)  using biocatalysts for selective transformations, and their applications in screening of bioactive compounds, organic synthesis, and enzyme classification.    In  part  one,  an  introduction  to  CDC  and  DKR  is  presented,  illustrating  the basic  concepts,  practical  considerations  and  potential  applications  of  such dynamic systems, thus providing the background information for the studies in the following chapters.   In part two, Dynamic Systemic Resolution (DSR), a concept based on CDC is exemplified.  With  enzyme-catalyzed  transformations  as  external  selection pressure,  optimal  structures  can  be  selected  and  amplified  from  the  system. This  concept  is  expanded  to  various  types  of  dynamic  systems  containing single, double cascade/parallel, and multiple reversible reactions. In addition, the  substrate  selectivity  and  catalytic  promiscuity  of  target  enzymes  are  also investigated.   In   part   three,   DKR   protocols   using   reversible   reactions   for   substrate racemizations  are  illustrated.  Biocatalysts  are  here  employed  for  asymmetric transformations,  resulting  in  efficient  synthetic  pathways  for  enantioenriched organic compounds.   Part  four  demonstrates  two  unique  applications  of  CDC:  one  resulting  in enzyme  classification  by  use  of  pattern  recognition  methodology;  the  other involving  enzyme  self-inhibition  through  in  situ  transformation  of  stealth inhibitors employing the catalytic activity of the target enzyme.

QC 20130614

Directing groups (DGs) are moieties installed onto organic molecules to confer regioselectivity in subsequent reactions. DGs have found utility in selective CH activations catalyzed by transition metal (TM) catalysis on starting materials with multiple CH bonds. Despite their utility, DGs are scarcely used in industrial applications due to the generally wasteful nature of conventional DG strategies and their associated increase in step-count. Transient directing groups (TDGs) have been developed to overcome these limitations, with additives reversibly forming adducts with compounds of interest prior to the DG-mediated CH activation, in one-pot processes. However, the use of TDGs still requires harsh conditions to achieve significant yields, hindering broad applications. Chemoenzymatic catalytic cascades have attracted attention due to the mild and environmentally friendly nature of biocatalysis, with the greatest challenge being compatibility issues between biocatalytic and traditional chemical transformations. Here we propose a concurrent chemoenzymatic catalytic cascade that would enable TM-catalyzed DG chemistry via flanking biocatalytic reductive amination to install, and oxidative deamination to remove, a TDG. Preliminary efforts have identified some incompatibilities arising from the biocatalytic portion of the cascade, namely substrate specificity and organic co-solvent tolerance, that need to be addressed to achieve the proposed chemoenzymatic cascade in a one-pot concurrent protocol.

Section 1 (Introduction) is a comprehensive review of the subjects discussed in this thesis: biocatalysis, aldolases and iminocyclitols. It contains a description of the application of dihydroxyacetone phosphate (DHAP) and dihydroxyacetone (DHA) utilizing aldolases to the chemoenzymatic synthesis of bioactive compounds and an introduction to the structure, biological activities and synthesis of iminocyclitols. Recent bibliographic references are included at the end of the section. Section 2 (Objectives) outlines the aims of this thesis. Section 3 (Results and discussion) describes the studies carried out in this thesis. Bibliographic references are included as an overview of previous results and to support our statements at the end of each chapter. - Section 3.1 deals with the application of D-fructose-6-phosphate aldolase in organic chemistry. It describes the chemoenzymatic preparation of polyhydroxylated compounds, sugars 1-deoxy-D-xylulose and 1-deoxy-D-ido-hept-2-ulose and iminocyclitols 1-deoxynojirimycin, 1-deoxymannojirimycin and N-alkylated derivatives, 1,4-dideoxy-1,4-imino-D-arabinitol and 1,4,5-trideoxy-1,4-imino-D-arabinitol. An unprecedented methodology, having as a key step a novel enzymatic aldol addition reactions catalyzed by D-fructose-6-phosphate aldolase, is presented. - Section 3.2 presents the cascade chemical-enzymatic synthesis of a collection of novel 1,4-dideoxy-1,4-imino-D- and -L-arabinitol (DAB and LAB) 2-aminomethyl derivatives including 2-oxopiperazine conjugates which have an interest as potential glycosidase inhibitors. - Section 3.3 describes the chemoenzymatic synthesis of novel polyhydroxylated pyrrolizidines of the family of casuarines by means of an asymmetric strategy based on cascade aldol additions catalyzed by dihydroxyacetone phosphate (DHAP) and dihydroxyacetone (DHA) aldolases. - Section 3.4 describes the methodology and results of the preliminary in vitro assays for glycosidases inhibition activity of some of the compounds synthetized during the course of this thesis. Section 4 (Experimental) describes the procedure for the experimental work carried out in this project. 1H and 13C NMR spectra can be found in the attached CD.
La reacción aldólica es uno de los métodos más útiles y potentes para la formación de enlaces carbono carbono que permite, simultáneamente, la funcionalización y generación de nuevos centros estereogénicos adyacentes. Las aldolasas dependientes del fosfato de dihidroxiacetona (DHAP) catalizan estereoselectivamente la adición aldólica de DHAP a una gran variedad de aldehídos aceptores y han sido objeto de numerosos estudios que demuestran su utilidad como catalizadores en síntesis orgánica asimétrica. La principal limitación de esta clase de aldolasa es su estricta especificidad por el sustrato dador, la DHAP, que es un reactivo costoso y químicamente inestable. Por ello, los estudios dirigidos a la eliminación de la necesidad de la utilización de DHAP mediante estrategias de ingeniería de reacción, evolución dirigida, o a través del descubrimiento de nuevas enzimas naturales, son de gran interés. En este contexto el descubrimiento de la D-fructosa 6-fosfato aldolasa (FSA), una enzima natural que acepta dihidroxiacetona (DHA) como dador, ha sido de enorme importancia. El objeto de esta tesis es la aplicación de aldolasas dependientes de DHA y DHAP a la síntesis de compuestos quirales bioactivos. Los iminociclitoles son una clase de glicomiméticos muy atractivos en química médica ya que poseen actividad inhibidora de glicosidasas y glicosiltransferasas y, por tanto, con un vasto potencial terapéutico para el tratamiento de enfermedades como diabetes, infecciones virales y cáncer, entre otras. En este trabajo se describe una metodología quimioenzimática para la preparación de desoxiazúcares e iminociclitoles cuyas etapas clave son nuevas adiciones aldólicas estereoselectivas de dihidroxiacetona (DHA) e hidroxiacetona (HA) a diferentes aldehídos catalizadas por FSA. Mediante esta estrategia se han obtenido los iminociclitoles 1-deoxinojirimicina, 1-deoximannojirimicina y sus derivados N-alquilados, 1,4-dideoxi-1,4-imino-D-arabinitol y 1,4,5 trideoxi-1,4-imino-D-arabinitol y los desoxiazúcares 1-deoxi-D-xilulosa y 1 deoxi-D-ido-hept-2-ulosa. El 1,4-dideoxi-1,4-imino-D-arabinitol (DAB) y su enantiómero (LAB) son pirrolidinas polihidroxiladas con una amplia actividad inhibidora de varias glicosidasas. Las pirrolizidinas polihidroxilados son una clase de iminociclitoles bicíclicos que también poseen una importante actividad biológica. En este trabajo se presenta una estrategia quimioenzimática que emplea aldolasas dependientes de DHA y DHAP, para la síntesis de DAB y LAB, de una colección de sus derivados 2-aminometílicos y conjugados 2 oxo-piperazinicos y de nuevas pirrolizidinas polihidroxiladas de la familia de las casuarinas, todos con potencial actividad inhibidora de glicosidasas.

2008/2009
Aim of this thesis is the synthesis of enantiomerically pure ligands for their application in asymmetric catalysis. In particular, the work is focused on the synthesis of three different classes of ligands. Chapters 2 and 3 deal with the synthesis of CNN-pincer and N-Nˈ(bipyridine) ligands respectively, obtained in both enantiomeric forms by stereocomplementary chemoenzymatic methods, while Chapter 4 presents the synthesis of P-N type ligands obtained from L-proline. The activity of the complexes that containing the optically pure synthesized ligands was also investigated.
XXII Ciclo
1980

The major subject of this thesis is the synthesis of enantiomerically enriched gamma and delta lactones via Ring Closing Metathesis (RCM). Furan and thiophene substituted aldehydes were transformed to the corresponding heteroaryl substituted allylic and homoallylic alcohols by using vinyl and allylmagnesium bromide, respectively and then resultant racemic alcohols were resolved by hydrolase type enzymes (PSC-II, Lipozyme, CAL-B) with high enantiomeric excess values. Since the absolute configuration of alcohols were known, it was possible to determine the configuration of the synthesized compounds. After the enantiomeric enrichment of the alcohols, subsequent acylation with acryloyl and methacryloyl chloride afforded feasible diene system that was subjected to ring closing metathesis reaction 1st and 2nd generation Grubbs&rsquo
catalysts were used. These lactones were used to test their biological activities.

Modular total syntheses of the biologically active resorcylic acid lactones (RALs) L-783.277 (1) and L-783.290 (128) are reported. The three key buildings blocks employed for this purpose were the aromatic 133, the enantiopure alcohol (R)-25 or (R)-166 and the protected diol 127. The building blocks (R)-25, (R)-166 and 127 were prepared by chemoenzymatic methods with the last of these being derived from the cis-1,2-dihydrocatechol 82 (X = Cl) which is itself obtained through the whole-cell biotransformation of chlorobenzene. These building blocks have been linked to one another using Heck and Mitsunobu chemistries and the fourteen-membered macrolide rings formed using either a RCM reaction (as applied to compound 132) or through intramolecular addition of an acetylide anion to a tethered Weinreb amide (as applied to compound 165). Attempts to extend the RCM-based route to the RAL aigialomycin C (131) are also described. -- provided by Candidate.

Chapter One of this Thesis briefly describes the history and production of cis-1,2-dihydrocatechol chiral starting materials and summarises their synthetic attributes as well as providing several examples of their use in natural product synthesis. Chapter Two begins with a succinct review of the structural characteristics and biological properties of the Amaryllidaceae alkaloid ({uF02D})-lycorine and describes several established synthetic approaches to compounds of this type. Thereafter, experimentally-based research leading to the development of a rapid and enantioselective synthesis of the lycorine framework, starting from the cis-1,2-dihydrocatechol and culminating in the syntheses of two lycorine derivatives is described. Additionally, the true structure of the Amaryllidaceae alkaloid nobilisitine A is disclosed. Chapter Three provides a short review of the classic Ullmann bi-aryl synthesis and introduces the Pd[0]-catalysed variant. The synthesis of indoles and quinolones via a Pd[0]-catalysed Ullmann cross-coupling/reductive cyclisation approach is then described. Thereafter, research leading to the efficient synthesis of C-3 monoalkylated oxindoles by such means is presented. Chapter Three also presents the results of methodological studies directed towards improving the efficiency of the Pd[0]-catalysed Ullmann cross-coupling reaction by using highly activated copper powders. This theme is developed further in Chapter Four.