Dissertations / Theses on the topic 'Multicatalysis'

Les travaux de cette thèse ont porté sur la production d’énantiomères optiquement enrichis avec une consommation complète du substrat racémiques grâce à un nouveau système compartimenté de double réaction comportant une membrane polydimethylsiloxane (PDMS) à perméabilité sélective.D'abord, la perméabilitéde la membrane PDMS a été étudiée montrant une sélectivité de transfert des espèces en fonction de leur polarité. Par la suite, les réactions opposées d'estérification et de transestérification isolées par une membrane PDMS ont été réalisées pour produire des alcools énantioenrichis séparés à partir d'alcool racémique. Cependant, nous n’avons pas réussi à mettre en œuvre ce système en raison de l'incompatibilité du PDMS avec les conditions de transestérification. Deuxièmement, le dédoublement cinétique parallèle compartimentée combinant deux systèmes catalytiques d’énantiosélectivité opposées isolés par une membrane PDMS a été réalisée pour produire les deux produits énantio-enrichis image l’un de l’autre isolé dans chacun des compartiments à partir d'un substrat racémique. Ce concept a été établi avec succès avec le dédoublement cinétique hydrolytique de Jacobsen de l'époxyde terminal. Chacun des diols énantioenrichis peut être ainsi obtenu jusqu'à 100% de conversion à partir d'époxyde racémique. Troisièmement, le processus de résolution cinétique dynamique compartimenté combinant une résolution cinétique et une réaction de racémisation isolée par membrane PDMS a été réalisé pour produire un seul produit énantioenrichi à partir d'un substrat racémique. Ce processus énantioconvergent permet d’obtenir un seul ester allylique énantioenrichi jusqu'à 100% de conversion à partir d'alcool secondaire allylique racémique contournant les inconvénients de l'incompatibilité
The goal of this thesis was focused on the production of optically enriched enantiomers with complete consumption of racemic starting materials through newly designed double reactions system compartmentalized by a polydimethylsiloxane (PDMS) membrane with selective permeability. Firstly, the permeability of the PDMS membrane was studied showing a transfer selectivity of species depending on their polarity. Subsequently, the esterification and transesterification opposite reactions isolated by a PDMS membrane were performed to produce separated enantioenriched alcohols starting from racemic alcohols. However, we failed to set up such system due to the incompatibility of PDMS with the conditions of transesterification. Secondly, the compartmentalized parallel kinetic resolution combining two catalytic systems with opposite enantioselectivity isolated by a PDMS membrane was performed to produce both enantioenriched enantiomers, mirror image each other, isolated in each compartment starting from a racemic substrate. This concept was successfully established using the Jacobsen’s hydrolytic kinetic resolution of terminal epoxide. Each enantioenriched diol can be obtained up to 100% conversion from racemic epoxides. Thirdly, the compartmentalized dynamic kinetic resolution process combining a kinetic resolution and a racemization reaction isolated by PDMS membrane was performed to produce one single enantioenriched product starting from a racemic substrate. This enantioconvergent process allows to obtain an enantioenriched allylic ester up to 100% conversion from racemic allylic secondary alcohol circumventing the drawbacks of the incompatibility of the two catalytic system

Les groupements alcooliques sont présents dans une grande diversité de produits chimiques fins précieux issus de la nature et de la synthèse, c'est pourquoi les méthodes permettant leur diversification structurelle sont recherchées. Cependant, la modification de la structure des alcools à certaines positions non réactives, même avec l'aide de la catalyse, reste un défi ou nécessite des procédures multi-étapes fastidieuses et souvent coûteuses. Récemment, une attention accrue a été accordée à la multicatalyse, qui combine plusieurs catalyseurs au sein d'un même système, ce qui permet de découvrir des réactivités auparavant inaccessibles ou d'accroître l'efficacité globale des transformations en plusieurs étapes. Les méthodes décrites ici permettent l'α- et la β-arylation diastéréo- et énantiosélective d'alcools. En combinant des catalyseurs à base de Ru et de Pd, il est possible de réaliser une β-arylation énantiosélective (et diastéréodivergente dans le cas d'alcools portant déjà des stéréocentres) sans précédent d'alcools primaires. En outre, dans le cadre d'une catalyse relais séquentielle, il est possible d'obtenir des alcools benzyliques secondaires enrichis enantioénergie à partir de divers produits de départ disponibles, tels que des alcools primaires ou des alcools portant une double liaison. Dans l'ensemble, ces protocoles démontrent le potentiel de la multicatalyse en tant qu'outil synthétique pour diversifier les alcools. Dans un contexte plus large, cette thèse ouvre la voie à la conception de nouvelles stratégies et méthodes multicatalytiques pour une synthèse efficace
Alcohol moieties are present in a great diversity of valuable fine chemicals from nature and synthesis, therefore methods enabling their structural diversification are sought after. However, modifying the structure of alcohols at certain unreactive positions, even with the aid of catalysis, remains a challenge or requires tedious often wasteful multistep procedures. Recently, increased attention has been paid to multicatalysis, which combines multiple catalysts within one system, enabling the discovery of previously inaccessible reactivities or increasing the overall efficiency of multistep transformations. Described within are methods which enable the diastereo-, and enantioselective α-, and β-arylation of alcohols. By combining Ru- and Pd-based catalysts the unprecedented, enantioselective (and diastereodivergent in the case of alcohols already bearing stereocenters) β-arylation of primary alcohols can be carried out. Also, under sequential relay catalysis enantioenriched secondary benzylic alcohols can be obtained from a variety of available starting materials, such as primary alcohols, or alcohols bearing a double bond. Overall, these protocols demonstrate the potential of multicatalysis as a synthetic tool for diversifying alcohols. In a broader context, this thesis sets the stage for devising novel, multicatalytic strategies and methods for efficient synthesis

This Doctoral Thesis is framed in the area of Sustainable Chemistry and more specifically in the field of continuous flow chemistry. The main objective has been the design and development of new continuous multicatalytic systems based on the use of supported ionic liquids, materials with very interesting catalytic properties. This objective has been applied to C-C bond forming reactions such as cyanosilylation, Strecker reaction or Negishi cross-couplings; whose products mean key synthetic intermediates in several processes in organic synthesis, specially in Fine and Pharmaceutical Chemistry. Telescopic processes and divergent syntheses have been succesfully achieved under continuous flow conditions. In addition, the novel additive manufacturing 3D printing technology has been introduced for the potential obtaining of continuous flow catalytic reactors.
La presente Tesis Doctoral se engloba dentro del área de la Química Sostenible y más concretamente en el campo de la química en flujo continuo. El principal objetivo es el diseño y desarrollo de nuevos sistemas multicatalíticos en continuo basados en el uso de líquidos iónicos soportados, cuyas propiedades catalíticas son muy interesantes. Este objetivo se ha aplicado a reacciones de formacion de enlaces C-C como la cianosililación, la reacción de Strecker y el acoplamiento de Negishi; cuyos productos resultan intermedios sintéticos clave en muchos procesos de síntesis orgánica, sobre todo en Química Fina y Farmacéutica. Procesos telescópicos y síntesis divergentes han sido desarrolados con éxito en continuo. Además, también se ha introducido la nueva tecnología de impresion 3D para la potencial obtención de reactores catalíticos de flujo continuo.

The multicatalytic proteinase (MCP) is a 700 kDa multisubunit complex which is found in eukaryotic cells. MCP is involved in ubiquitin-dependent non-lysosomal protein degradation and has been implicated in the processing of antigens by the major histocompatability complex class 1 pathway. The MCP purified from rat liver is composed of at least 16 distinct subunits of molecular masses between 22 and 34 kDa. MCP is known to possess at least three distinct peptidase activities, described as the 'trypsin-like', 'chymotrypsin-like' and 'peptidylglutamylpeptide hydrolase' activities. However, it is not known which subunits are responsible for the different peptidase activities. The main aims of my study were (1) to establish which subunit(s) possesses the active site responsible for 'trypsin-like' activity, (2) to identify the catalytic amino acid residues responsible for this activity and (3) to determine whether all MCP particles possess these components. 'Protection' experiments with the peptide aldehyde leupeptin, which is a specific reversible inhibitor of the 'trypsin-like' activity, have identified one or two subunits which possess thiol groups essential for 'trypsin-like' activity. These thiol groups are probably not involved in catalysis but may be located very close to the active site responsible for 'trypsin-like' activity. An active site specific peptidyl chloromethane which specifically inactivates the 'trypsinlike' activity, labels two distinct subunits of 23-24 kDa. One of these polypeptides is also labelled by an active site specific peptidyl diazomethane for the 'chymotrypsin-like' activity, in addition to three other distinct polypeptides of 28-23 kDa. Together these results suggest that one active site is responsible for 'trypsin-like' activity while four distinct active sites are responsible for 'chymotrypsin-like' activity. Affinity chromotography was carried out using an immobilised specific inhibitor of the 'trypsin-like' activity. The results of these studies suggest that all MCP particles purified from rat liver possess the catalytic component responsible for the 'trypsin-like' activity.

There is increasing concern regarding alternative, sustainable energy sources, such as biofuels, to replace declining oil reserves. The abundance of lignocellulosic biomass makes it the only imaginable resource that can potentially substitute a substantial portion of the fossil fuels we use today, but current methods for producing biofuels from non-food crops are cost intensive and not economically viable. Synthetic biology provides several potential approaches for developing biologically mediated processes for the conversion of lignocellulosic biomass into biofuels. Such systems are based on engineered microbes that produce enzymes for catalysing the conversion of cellulose into fermentable sugars and subsequently into high value products. Effective degradation of cellulose requires multiple classes of enzyme working together. In naturally occurring cellulose degrading microbes, bioconversion is catalysed by a battery of enzymes with different catalytic properties. However, naturally occurring cellulases with multiple catalytic domains seem to be rather rare in known cellulose-degrading organisms. Using synthetic biology approaches, seven cellulases with multiple catalytic domains were engineered and tested to determine the usefulness of such chimeric enzymes to replace cloning of multiple enzymes for biomass conversion. Catalytic domains were taken from Cellulomonas fimi endoglucanases CenA, CenB and CenD, exoglucanase Cex, and β-glucosidase, Cfbglu as well as Cytophaga hutchinsonii cellodextrinase CHU2268. All fusions retained both catalytic activities of the parental enzymes. To investigate the benefits of fusion, Citrobacter freundii NCIMB11490 was transformed with either fused or non-fused enzymes and cultured with cellulose blotting papers as main carbon source. Cells expressing fusions of Cex with CenA or CenD reproducibly showed higher growth than cells expressing non-fused versions, as well as more rapid physical destruction of paper. The opposite was observed for the other combinations. Comparing two different Cex and CenA fusions, CxnA2, which contains two carbohydrate binding modules (CBMs), degraded filter paper faster and led to better growth than CxnA1, which contains only one CBM. It was observed that CxnA1 was exported to the supernatant of E. coli and C. freundii cultures, as also seen for Cex and CenA, although there is no clear biological mechanism for this. Monitoring of growth using colony counts is laborious, but the use of optical density is not possible for cellulose-based cultures as it is affected by the insoluble cellulose particles. The SYBR Green I/propidium iodide live/dead staining protocol was therefore evaluated for growth measurements and was found to allow rapid measurements of large numbers of samples. In conclusion, these studies have demonstrated a simple and useful method for making chimeric proteins from libraries of multiple parts. The results demonstrate that use of fusion proteins can improve biomass conversion in vivo, and could potentially reduce the necessity for cloning of multiple enzymes and improve product yields. A simple and effective method for monitoring growth of bacteria in turbid cultures using a fluorimeter has also been developed.

L'élaboration de méthodes de synthèse, basées sur l’utilisation d’espèces métalliques a été un sujet de tous les instances en chimie organique. Malgré l’efficacité des métaux utilisés en catalyse homogènes, leurs procédures de recyclage restent limitées. Ce pourquoi, une contrainte supplémentaire a été placée dans la conception de catalyseurs, pouvant offrir à la fois l'efficacité de la catalyse homogène et le recyclage de l’hétérogène. Dans ce contexte, les nanoparticules métalliques sont apparues comme objet phare, en raison de leurs propriétés physico-chimiques inégalées. On a découvert que les nanoparticules de métaux nobles présentaient des propriétés catalytiques similaires dans certains cas, aux complexes monoatomiques. De plus, les Au NPs ont montré une activité catalytique remarquable dans l'oxydation d’alcools activés sous O2. Nous avons donc envisagé des procédures multicatalytiques, basées sur les NPs d’Au. Notre choix d'utiliser des catalyseurs solides était pertinent, puisque les nano-catalyseurs, pour lesquels la fraction de sites actifs se trouve en surface, limitent les risques de cross-quenching. Ici, nous présentons trois nouveaux procédés bicatalytiques permettant l’accès, à des chromenes/quinoléines (53-93%) via une oxydation / Michael Addition/ aldolisation, combinant nanocatalyse et catalyse basique, l’accès à des ortho-THC (50-81%) via oxydation / arylation / cyclisation, combinant nanocatalyse et catalyse supportée, ainsi qu’une une oxydation / hydrolyse en cascade, pour accéder à l’HMLA (86%, sel 93%), un grand panel de produits d'activité biologique reconnue, utilisé en parfumerie ou visant une pré-industrialisation via la chimie en flux continu
Elaboration of synthetic methods based on metal-catalyzed reactions has been a hot topic in organic chemistry. Despite good efficiency, catalysis proceeding homogeneously, are limited in the operation of recovering/recycling of the catalysts. An important stress was placed to design catalysis, offering both the efficiency of homogeneous catalysts and the recyclability of heterogeneous catalysts. In this context, metal nanoparticles merged as a key tool, due to their unique physical and chemical properties. Notably, Au NPs have shown remarkable catalytic activity in the oxidation of activated alcohols under O2 atmosphere. Since now, the access to more complex molecules is the next step forward for this field, we envisioned multicatalytic roads, based on the oxidation of activated alcohols via supported Au NPs. Our choice of using solid catalysts was relevant, since nanostructured catalysts for which the fraction of active sites are located on the surface, limit the risk of cross-quenching. The latter carbonyl formed, could be further converted in situ, via tandem protocol. Herein, we developed novel, atom- and step-economical bicatalytic one-pot processes, to access substituted chromenes/quinolines (53-93%) by tandem oxidation/hetero-Michael addition/aldolisation combining nanocatalysis and base catalysis, ortho-THCs (50-81%) via tandem oxidation/arylation/cyclisation combining nanocatalysis and supported catalysts and a tandem cascade oxidation/hydrolysis to access HMLA (86%, sel 93%). A large panel of products of biological activity relevance, pertaining to the fragrance chemistry or aiming in some cases, pre-industrial scalability via continuous flow applications

Ce travail de thèse porte sur deux fonctions essentielles du reticulum endoplasmique (RE) : le contrôle qualité et la rétention des réticuloplasmines solubles qui vont échapper au flux endomembranaire de sécrétion. Dans une première partie de notre travail, nous avons étudié les mécanismes de rétention des protéines résidentes du RE. Notre stratégie a été d'utiliser la structure des N-glycannes associés à des protéines comme marqueur du transport dans le système endomembranaire de sécrétion de la cellule végétale. Ainsi, nous avons choisi deux glycoprotéines modèles : d'une part, une réticuloplasmine naturelle, la calréticuline de tabac, et d'autre part une réticuloplasmine artificielle constituée de l'invertase pariétale de carotte (Daucus carota) fusionnée en C-terminal à un tétrapeptide de rétention HDEL (InvHDEL). L'analyse de la structure des N-glycannes de la calréticuline de maïs ou de tabac montre que cette protéine est strictement retenue dans le RE. Par contre, la maturation golgienne des N-glycannes de l' InvHDEL montre que cette forme n'est pas strictement retenue dans ce compartiment mais échappe au RE pour être transportée jusqu'à l'appareil de Golgi puis recyclée par transport rétrograde du Golgi jusqu'au RE. Dans une seconde partie de notre étude, nous avons étudié le rôle de la N-glycosylation sur le transport et la stabilité des glycoprotéines végétales. Nous montrons que la N-glycosylation n'est pas nécessaire au transport des protéines et des glycoprotéines vers la vacuole. Par contre, les glycoprotéines ne sont pas transportées dans le compartiment extracellulaire si la N-glycosylation est inhibée. En particulier, l'étude de l'invertase pariétale de carotte a montré qu'en absence totale de glycosylation, cette protéine est rapidement dégradée dans un compartiment pré-golgien. Nous avons également montré que l'association d'une extension HDEL à l'extremité C-terminale de l'invertase de carotte permet de stabiliser cette protéine dans le RE des cellules de tabac, même lorsque cette glycoprotéine est produite sous une forme non glycosylée.

La mobilisation des proteines musculaires represente une adaptation metabolique fondamentale au cours de l'agression pour assurer la survie de l'organisme entier. La dysfonction musculaire induite par la fonte musculaire compromet l'evolution clinique et therapeutique, notamment chez les patients bpco. Nous avons analyse la prevalence et les consequences de la denutrition dans une population de patients (n = 78, sexe ratio, ages de) atteints d'affections pulmonaires chroniques parenchymateuses ou vasculaires en attente de transplantation pulmonaire. 72% etaient denutris (poids du corps < 90% ou index creatinine/taille < 60% des valeurs predites, isolement ou simultanement). La depletion de la masse maigre qui peut s'observer avec un poids normal dans 17% des cas, augmente le risque de deces des sujets en attente de greffe (31. 4% versus 11. 6% dans le groupe sans depletion musculaire, p<0. 05) et modifie l'evolution postoperatoire immediate. La relation entre fonte musculaire et l'importance de l'hypoxie suggere un lien entre oxygene et metabolisme proteique musculaire. Aussi, nous avons etudie les modifications du metabolisme musculaire squelettique (synthese et degradation des proteines) en hypoxie aigue dans un modele experimental d'hypoxie normobarique (fio2 : 0. 10). La fonte musculaire en hypoxie n'est pas a l'evidence induite par une augmentation de la proteolyse. Par contre, les donnees objectivent une reduction significative de la synthese proteique. Ainsi, en hypoxie, la fonte musculaire reflete uniquement la diminution de la synthese proteique sans activation de la proteolyse. Ces constatations contrastent avec les autres etats cataboliques etudies jusqu'a ce jour. Si l'hypoxie peut facilement expliquer l'absence de stimulation de la degradation des proteines puisqu'il s'agit d'un processus energetiquement couteux, les mecanismes moleculaires qui soutendent la regulation du metabolisme musculaire des proteines en situation d'hypoxie, restent a expliciter.

Le cycle cellulaire est un mecanisme par lequel les cellules se multiplient. Ce processus fait l'objet de controles. La progression des cellules a travers le cycle est regulee par les cdks qui sont activees par liaison aux cyclines et des reactions de phosphorylation/dephosphorylation. De plus, la regulation de ces complexes tout au long du cycle cellulaire est assuree par diverses proteines dont p21 w a f 1 / c i p 1 qui inhibe leur activite kinase et permet l'arret du cycle cellulaire. Pour comprendre les mecanismes de regulation de cet inhibiteur, nous avons isole et caracterise 4 proteines interagissant avec p21 : rch1 (proteine de transport dans le noyau), tcp1 (proteine chaperone), ki (proteine homologue des sous-unites de l'activateur du proteasome pa28) et 4/140 (proteine inconnue). Nous avons confirme in vitro les interactions de p21 avec ces 4 proteines et in vivo avec la proteine ki. Les resultats preliminaires obtenus nous ont pousse a nous interesser plus particulierement a ki. Cette proteine, localisee au niveau du noyau des cellules, possede une demi-vie superieure a 5h, un niveau constant au cours du cycle et 2 sites de liaison a p21 qu'elle stabilise. L'expression de la proteine ki dans les cellules nih3t3 synchronisees en phases g1 ou s ralentit la reprise du cycle cellulaire. L'effet inverse est observe lorsque les cellules sont bloquees en phase m. D'autre part, ki en stabilisant p21 empeche un arret des cellules nih3t3 dans les phases g1 et g2/m lorsque celles-ci sont irradiees aux rayons. Les resultats obtenus ont mis en evidence de nouvelles fonctions de ki. Cette proteine stabilise p21 en interagissant avec elle et augmente sa duree de vie en la protegeant, en partie, contre la destruction par le proteasome. La liaison des 2 proteines entre elles se fait notamment au niveau d'un domaine qui ne permet pas a p21 d'assurer son role d'inhibiteur du cycle cellulaire. Dans certaines conditions, cette liaison pourrait etre rompue par d'autres facteurs.

This thesis describes the development of novel synthetic methods in two areas of chemical research: Multicatalysis and the aromatic activation of alcohols. The first chapter, encompassing multicatalysis, reveals the design and realization of an innovative hydro-functionalization method. This method is examined in the context of designing multicatalytic processes to access privileged chemical architectures, which unite a nucleophilic addition event with the hydrofunctionalization reaction. The resulting multicatalytic methods capably effect the formation of complex heterocyclic compounds. The second chapter discloses an innovative paradigm for nucleophilic substitution involving aromatic cation activation of alcohols. The development of efficient chlorination and bromination methods promoted by cyclopropenium cations are discussed. The substrate scope and mechanism of the reaction are also examined. The successful demonstration of these methods established proof of concept and initiated further investigations of the aromatic cation activation strategy. The final chapter extends the concept of aromatic cation activation of alcohols to additional reaction manifolds. A dehydrative cyclization of diols employing aromatic cations is explored. The efficacy of alternative cyclopropenyl leaving groups is examined and the scope of viable nucleophiles for the aromatic activation strategy is extended. Along with Chapter 2, these seminal investigations have laid the foundation for future advances towards the realization of a general aromatic cation activation strategy.

One of the major drawbacks to traditional syntheses is the requirement for iterative synthesis, which is not only chemically inefficient and time-consuming, but environmentally unfriendly due to waste generated during purification procedures. A way to circumvent problems posed by iterative synthesis is through the development of multicatalytic protocols, in which multiple, distinct synthetic steps can be performed in one reaction pot. Saturated 5-membered oxygen- and nitrogen-containing heterocycles are extremely common structural motifs in many biologically important molecules--a multicatalytic synthetic strategy for their syntheses would be of incredible use. To that end, a bismuth(III) triflate-catalyzed hydroalkoxylation procedure was developed for the synthesis of substituted tetrahydrofurans. This operationally simple method successfully generated complex tetrahyrofurans in moderate to good diastereoselectivity with good functional group tolerance. An analogous hydroamination of non-basic N-tosyl amines was also developed and featured similar levels of diastereoselectivity and functional group compatibility. The methodology was part of a multicatalytic strategy combining nucleophilic additions to aliphatic aldehydes and N-tosyl imines to quickly generate complex 5-membered heterocycles in moderate to good diastereoselectivity. The palladium-pivalate catalytic system has emerged as one of the most efficient and general catalysts for the C-H arylation of arenes and heteroarenes with haloarene donors. Despite the importance of this class of catalytic reactions, the mechanistic understanding is limited by the lack of direct experimental evidence, especially in the context of Lewis basic heteroarene substrates. To address this problem, we chose the catalytic C-H arylation of 2-methylthiazole as a representative reaction for a detailed mechanistic study. Direct kinetic evidence was provided for the involvement of a palladium(II) pivalate species in the C-H arylation of heteroarenes by identifying the resting state of the catalyst - complex 2a [(Cy3P)(2-methylthiazole)Pd(Ph)(OPiv)] - and examining its reactivity. The pivalate ligand, in comparison to acetate, does not yield faster rates of C-H activation, but instead stabilizes the resting state of the catalyst against decomposition to inactive palladium species. An experimentally supported rationale for the superiority of the palladium(II) pivalate system in C-H arylation reactions was provided. The choice of phosphine ligand is an incredibly important aspect of catalyst design in many metal-catalyzed transformations, including direct arylations and cross-couplings. A relatively unexplored area of study was the effect of the phosphine ligand on the C-H metalation step of palladium-catalyzed direct arylation reactions. Through our studies and related studies in the literature, we can conclude that the phosphine ligand is generally deactivating toward deprotonative metalation (CMD/EMD) pathways, however the phosphine ligand is necessary in the C5 arylation of triazole and C2 arylation of thiazole, as well as substituted pyridines. In the case of azoles, arylation probably proceeds via a mechanism different to that of C5 arylations; the phosphine ligand stabilizes catalytic intermediates, affording efficient C2 arylation of azoles. In the case of pyridine, the major issue is that of catalyst decomposition; in approaching catalyst design, one must balance tuning of the reactivity of the palladium catalyst toward C-H metalation versus protecting the catalyst during prolonged reaction times and high reaction temperatures. Two common ligands in palladium catalysis, Cy3P and t-Bu3P, were directly compared in terms of their interaction with basic substrates. While complexes ligated to a single Cy3P ligand were able to accommodate basic heteroarenes in the palladium coordination sphere, complexes with the bulkier t-Bu3P ligand behaved very differently, which could have important ramifications on future catalyst design. Heteroaromatic substrates have typically provided challenges for the development of direct arylation protocols. However, how the properties of the substrate affect the rate-limiting metalation step of palladium-catalyzed direct arylation reactions was mostly unknown. Thus, we correlated the rates of C-H metalation of azoles and substituted pyridines with various intrinsic properties of heterocycles, such as aromaticity, and pKa. It was found that for the C5 arylation of azoles, a stronger correlation on the rate of metalation with pKa was observed. Degree of aromaticity appears to have little correlation with the rates of C-H metalation of azoles and pyridines.

Subcellular fractionation (together with immunocytochemical localisation studies) showed that the parasite Trypanosoma brucei brucei possesses a multicatalytic protease complex (MCPTb). This complex is predominantly cytosolic but some activity is also present in the nuclear fraction. MCP-Tb was isolated from T. b. brucei and compared to the properties of other proteasomes reported in the literature and to the 20S MCP isolated from bovine red blood cells (MCP-rbc). The isolation procedure employed four-steps: anion exchange chromatography on Q-Sepharose, adsorption chromatography on HA-Ultrogel, molecular exclusion chromatography on Sephacryl S-300 and glycerol density gradient sedimentation. The molecular mass of intact MCP-Tb was shown to be smaller than that of MCP-rbc. Separation of the different proteasome subunits by 2D-PAGE showed that MCP-Tb has 12 different polypeptide components compared to the 28 different polypeptide components of MCP-rbc. The N-terminal sequence of an MCP-Tb subunit showed that this subunit did not have any obvious sequence homology with the subunits of proteasomes from other cells. Furthermore, anti-MCP-Tb antibodies (which exhibited the in vitro inhibitory activity of MCP-Tb) did not cross-react with MCP-rbc showing that MCP-Tb and MCP-rbc are antigenically distinct. The basic enzymatic properties of MCP-Tb were fairly typical of other 20S proteasomes. MCP-Tb had multiple peptidase activities (identified as chymotrypsin-like, trypsin-like and peptidyl glutamylpeptide hydrolase activities) that are characteristic of proteasomes. Furthermore, the characteristics of inhibition by a variety of inhibitors were similar to those of other proteasomes, including MCP-rbc. The activities of 20S proteasomes from most cell types are activated by endogenous high molecular mass complexes such as the bovine 19S complex called PA700. These complexes form end-on associations with the 20S proteasome. However, no endogenous MCP-activator was found in T. b. brucei. Nevertheless, MCP-Tb was activated in an ATP-dependent manner by bovine PA700. Inhibition of the intrinsic phosphatase activity of PA700 inhibited the protease enhancing effect of PA700. Electron microscopic examination of negatively stained MCP-Tb and MCP-rbc showed particles that were morphologically indistinguishable. However, the MCP-Tb also exhibited unique end-on associations between individual units forming long (up to 200 nm) ribbon-like chains. Since access to the active sites of proteasomes occurs through the pores at the end of the complexes, this end-on association, when coupled to our observation of an apparent lack of an endogenous activator, suggests that T. b. brucei may have evolved an alternate mechanism for controlling their proteasome activity.
Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1999.

Part I of this thesis focuses on the development of novel synthetic methods and investigations into their incorporation into multicatalytic reactions. The first chapter describes the development of a bismuth(III)triflate catalyzed hydrocarboxylation reaction of unactivated alkenes to synthesize lactones. Efforts toward applying this new methodology in multicatalytic sequences are described. In the second chapter, the development of palladium(II) mediated oxidative formylation and ketonylation methods to construct complex aldehydes and ketones is presented. Investigations into the oxidative formylation mechanism revealed the formation of a stable acylpalladium hydride intermediate that could be manipulated in situ allowing for the formation of other functionality. These methods were shown to be compatible in multi-transformation processes leading to the synthesis of complex heterocyclic products in a single reaction vessel. The third chapter describes the total synthesis of members of the Tylophora alkaloid family of molecules using a key oxidative carbonylation step. Application of a tandem palladium(II) catalyzed aminochlorocarbonylation / indium(III) catalyzed Friedel-Crafts acylation led to the rapid construction of the key intermediate in these syntheses in a one-pot reaction. The concise syntheses of both 13a,alpha-secoantofine and antofine using this multicatalytic strategy are presented. The second part of this thesis describes the study of stable carbocations as catalysts for hydride transfer reactions. Both cyclopropenium and trityl catalysts are investigated in a reductive etherification method. A study of trityl catalyst structure and initial investigations into the development of chiral trityl catalysts are presented.

The first synthesis and full characterization of a new functionality, called the diaziridinium ion, is reported. The original synthetic intent behind its design was to explore its potential use as a non-metal based N-transfer reagent. During this study, we have uncovered a practical rearrangement to access 2,3-benzodiazepines reliably and efficiently. Efforts to achieve N-transfer from these species are described and are ongoing. We have identified the tropylium ion as a highly efficient organic-based amine oxidant and have demonstrated its practical use in a one-pot protocol for alpha-aminonitrile synthesis. We also report an application of this new oxidant towards an aza-Cope rearrangement. Finally, we report a multicatalytic method that uses bismuth(III) triflate to catalyze a nucleophilic addition to an aldehyde followed by hydroalkoxylation to generate highly functionalized tetrahydrofuran rings, a motif that is often encountered in natural product architectures.

Cette thèse comprend deux parties distinctes, dans lesquelles seront décrits tout d’abord, le développement d’un procédé multicatalytique en un seul pot d’une réaction de méthylénation suivie d’un couplage de Heck, puis dans un second temps, une étude vers la synthèse de l’Hodgsonox. Le premier thème de la thèse correspond à la mise en place d’un procédé en un seul pot, basé sur la méthodologie de méthylénation catalysée par un métal de transition, développée au sein du groupe du Pr. Lebel, et sur des couplages de Heck. Différentes études de compatibilité des réactifs mis en présence sont abordées, ainsi que le choix des conditions optimales (Pd(OAc)2 et P(o-tol)3) pour la réalisation d’un tel système qui ne requiert aucun isolement du produit intermédiaire. Il a été démontré que la présence de triphénylphosphine en excès inhibe la réaction de couplage de Heck, ce qui a finalement orienté notre choix vers les sels de cuivre pour la catalyse de la réaction de méthylénation. Le tandem séquentiel a ensuite été appliqué à la synthèse de divers stilbènes, notamment des composés dérivés du Resvératrol, molécule d’intérêt thérapeutique pour les maladies cardiovasculaires, et à la synthèse d’indanes substitués, avec un couplage intramoléculaire, avec de bons rendements. La deuxième partie de cette thèse traite de l’étude menée vers la synthèse de l’Hodgsonox. Cette molécule correspond à une nouvelle classe de sesquiterpènes tricycliques, comportant un dihydropyrane doté d’une fonction éther diallylique. Cette molécule représente un défi synthétique pour le groupe du Pr. Lebel, qui envisage de synthétiser les deux doubles liaisons terminales au moyen de la méthodologie de méthylénation développée au sein du groupe. L’Hodgsonox, dont la biosynthèse utilise la voie MEP, a un potentiel insecticide pour la croissance de la larve de la mouche verte d’Australie, Lucilia cuprina. La synthèse envisagée au cours de ces travaux est basée sur la formation préalable d’un cycle à 5 chaînons, comportant 3 centres stéréogéniques, puis sur la cyclisation du cycle pyranique au moyen d’une réaction d’insertion dans un lien O H. Un dédoublement cinétique dynamique sur une δ butyrolactone substituée permet de fixer la stéréochimie relative de deux centres chiraux dès la première étape. Le cycle à 5 chaînons est ensuite formé par métathèse après 6 étapes avec un rendement de 37%. Une addition conjuguée suivie d’une réaction de Saegusa et d’une réaction d’hydrosilylation introduit le groupement isopropyle de manière syn. Après mise en place d’un groupement céto-ester, un transfert de groupement diazonium permet de préparer le précurseur pour la réaction d’insertion dans un lien O-H. Le bicycle correspondant à la structure de base de l’Hodgsonox a été préparé au moyen de 16 étapes linéaires avec un rendement global de 12%.
This thesis is divided in two sections. The first topic to be discussed is the development of a multicatalytic one pot process of methylenation and Heck coupling reactions, and the second topic is the studies toward the synthesis of Hodgsonox. The first part of this thesis describes the development of a one pot process, based on the transition-metal catalyzed methylenation reaction reported by the Lebel group, and on Heck coupling reactions. The compatibility of reagents is studied and the optimal reaction conditions of the coupling reaction (Pd(OAc)2 et P(o tol)3) are described for this process, which does not require isolation of the alkene intermediate. The presence of excess triphenylphosphine inhibits the Heck coupling reaction, thus copper salts are used to catalyze the methylenation reaction. This tandem sequence was then used to synthesize different stilbenes, particularly hydroxylated (E) stilbenoids, analogues of Resveratrol, which are known to have a therapeutic activity against cardiovascular diseases, and substituted indanes, through an intramolecular Heck coupling reaction, all in good yields. The second part of this thesis describes the studies toward the synthesis of Hodgsonox. This molecule represents a new class of sesquiterpene with a cyclopenta[5,1-c]pyran ring system fused to an epoxide ring. The combination of a mono- and a 1,1-disubstituted double bond flanking the oxygenated carbon of the pyran ring is a unique structural feature, making the synthesis of this molecule a very attractive challenge. Hodgsonox also represents a good system to test the versatility of our metal-catalyzed methylenation reaction, since we propose to use this methodology to construct the two terminal alkenes from a dicarbonyl derivative. Hodgsonox, which is biosynthesized by the MEP pathway, exhibits activity against the larvae of the Australian green blowfly Lucilia cuprina. The synthesis planned during this work, is based on the prior formation of a 5-membered ring, with 3 stereogenic centers, followed by an O-H insertion reaction to cyclize the dihydropyran ring. A dynamic kinetic resolution of a substituted δ butyrolactone determines the relative stereochemistry of two chiral centers in the first step. The 5 membered cycle is then synthesized via a cross metathesis reaction, after 6 steps and a 37% global yield. A conjugated addition, followed by a Saegusa oxidation reaction and a hydrosilylation reaction gave the syn isopropyl group. After the formation of the ketoester functionality, a diazo transfer allows us to prepare the presursor for the OH insertion reaction. The bicycle, corresponding to the structural base of the Hodgsonox, was prepared in 16 linear steps in a 12 % global yield.