Добірка наукової літератури з теми "Chemo-enzymatic catalysis"

Deracemisation via chemo-enzymatic or multi-enzymatic approaches is the optimum substitute for kinetic resolution, which suffers from the limitation of a theoretical maximum 50% yield albeit high enantiomeric excess is attainable.

In this study, we present the synthesis of chiral fragrance aldehydes, which was tackled by a combination of chemo-catalysis and a multi-enzymatic in vivo cascade reaction and the development of a highly versatile high-throughput assay for the enzymatic reduction of carboxylic acids. We investigated a biocompatible metal-catalyzed synthesis for the preparation of α or β substituted cinnamic acid derivatives which were fed directly into the biocatalytic system. Subsequently, the target molecules were synthesized by an enzymatic cascade consisting of a carboxylate reduction, followed by the selective C-C double bond reduction catalyzed by appropriate enoate reductases. We investigated a biocompatible oxidative Heck protocol and combined it with cells expressing a carboxylic acid reductase from Neurospora crassa (NcCAR) and an ene reductase from Saccharomyces pastorianus for the production fragrance aldehydes.

Membranes with glycosylated surfaces are naturally biomimetic and not only have excellent surface hydrophilicity and biocompatibility, but have a specific recognition to target biomacromolecules due to the unique chemo-biological properties of their surface carbohydrates; however, they cannot be easily chemically produced on large scales due to the complex preparation process. This manuscript describes the fabrication of a polypropylene membrane with a glycosylated surface by a chemo-enzymatic strategy. First, hydroxyl (OH) groups were introduced onto the surface of microporous polypropylene membrane (MPPM) by UV-induced grafting polymerization of oligo(ethylene glycol) methacrylate (OEGMA). Then, glycosylation of the OH groups with galactose moieties was achieved via an enzymatic transglycosylation by β-galactosidase (Gal) recombinanted from E. coli. The fabricated glycosylated membrane showed surprisingly specific affinity adsorption to lectin ricinus communis agglutinin (RCA120). The chemo-enzymatic route is easy and green, and it would be expected to have wide applications for large-scale preparation of polymer membranes with glycosylated surfaces.

Multi-step cascade reactions have gained increasing attention in the biocatalysis field in recent years. In particular, multi-enzymatic cascades can achieve high molecular complexity without workup of reaction intermediates thanks to the enzymes’ intrinsic selectivity; and where enzymes fall short, organo- or metal catalysts can further expand the range of possible synthetic routes. Here, we present two enantiocomplementary (chemo)-enzymatic cascades composed of either a styrene monooxygenase (StyAB) or the Shi epoxidation catalyst for enantioselective alkene epoxidation in the first step, coupled with a halohydrin dehalogenase (HHDH)-catalysed regioselective epoxide ring opening in the second step for the synthesis of chiral aliphatic non-terminal azidoalcohols. Through the controlled formation of two new stereocenters, corresponding azidoalcohol products could be obtained with high regioselectivity and excellent enantioselectivity (99% ee) in the StyAB-HHDH cascade, while product enantiomeric excesses in the Shi-HHDH cascade ranged between 56 and 61%.

The enzymatic synthesis of trimeric sialyl Lewisx pentadecasaccharide (6), a 15-mer, from a trimannoside precursor required six different glycosyltransferase enzymes and four nucleotide donor sugars. Three N-acetylglucosaminyl residues were transferred from UDP-N-acetylglucosamine to a trimannoside by N-acetylglucosaminyltransferases I, II, and V, respectively. Galactosylation using β(1[Formula: see text]4) galactosyltransferase and UDP-galactose gave three N-acetyl lactosamine units in nonasaccharide 4. Sialylation of 4 with α(2[Formula: see text]3) sialyltransferase and CMP-N-acetylneuraminic acid was followed by fucosylation with α(1[Formula: see text]3) fucosyltransferase and GDP-fucose giving the 15-mer 6 in mg quantities. Compound 4 was also converted to a trimeric Lewisx dodecasaccharide 12-mer with α(1[Formula: see text]3) fucosyltransferase and GDP-fucose and to a trimeric α-2,6-sialyl N-acetyllactosamine dodecasaccharide 12-mer with α(2[Formula: see text]6) sialyltransferase and CMP-N-acetylneuraminic acid. Key words: glycosyltransferases, pentadecasaccharide, sialyl Lewisx.

L'extension de l'espace moléculaire chimique accessible à partir de la biomasse végétale par des méthodes douces et propres est un sujet d'actualité qui stimule la communauté scientifique afin de développer des produits biosourcés à faible impact environnemental et d'élargir le champ d'exploitation de la biomasse. La fonctionnalisation de la cellulose, le polysaccharide le plus abondant sur la planète, et/ou des cello-oligosaccharides telle que décrite dans cette thèse s'inscrit dans cette démarche. Notre objectif était de développer une méthode chimio-enzymatique impliquant l'action d'une laccase assistée par un médiateur pour oxyder des cello-oligosaccharides ou des fibres cellulosiques, suivie d'une amination réductrice pour greffer des composés aminés sur le matériau cellulosique. Dans ce but, nous avons d'abord démontré l'oxydation du cellobiose et du méthyl cellobiose en utilisant la laccase de Trametes versicolor et le TEMPO comme médiateur. Les conditions d'oxydation ont été optimisées avec le méthyl cellobiose et appliquées à un mélange de cello-oligosaccharides et au cellopentaose. En utilisant l'analyse LC/MS, nous avons montré qu'une large gamme de composés oxydés est obtenue et que la méthode est efficace pour produire des cello-oligosaccharides acides potentiellement intéressants pour les domaines biomédical et nutraceutique. Ensuite, nous avons montré que la réactivité du cellopentaose oxydé avec deux molécules aminées, la p-toluidine et la rhodamine 123 (un colorant aminé), permettait la liaison du composé aminé aux oligosaccharides. À l'aide des techniques LC/MS et MS/MS, nous avons mis en évidence la présence d'une liaison amine forte et covalente entre les colorants et le cellopentaose, élargissant ainsi l'espace chimique accessible par ce procédé hybride. Après avoir réalisé cette preuve de concept, nous avons tenté la teinture de fils de coton. Les fibres cellulosiques sont l'un des principaux matériaux textiles biosourcés et biodégradables. Cependant, le traitement chimique des textiles et notamment les méthodes chimiques utilisées pour fixer les colorants de manière covalente sont extrêmement polluants et nocifs pour la santé. Proposer des alternatives plus respectueuses de l'environnement est un défi mais d'un intérêt primordial pour une entreprise comme PILI, impliquée dans le projet de thèse, qui développe des colorants naturels en utilisant la biologie de synthèse. Ainsi, le potentiel du procédé hybride à deux étapes a été utilisé pour greffer avec succès la p-toluidine, la rhodamine 123 et le rouge acide 33 sur des fils de coton. La liaison covalente établie entre ces colorants et la fibre de coton a été prouvée pour la première fois. De plus, une bonne homogénéité et une bonne résistance au lavage ont été observées pour la teinture avec l'acid red 33, démontrant la robustesse et l'applicabilité de l'approche en situation réelle. Ces résultats originaux ont été brevetés. En testant d'autres colorants aminés, nous avons également montré que la solubilité, la réactivité et la structure du colorant aminé sont des paramètres importants à prendre en compte pour l'optimisation de la teinture, ce qui ouvre la voie à la synthèse à façon de nouveaux colorants aminés adaptés à ce procédé hybride prometteur
The extension of the chemical molecular space accessible from plant biomass by soft and clean methods is a timely topic that stimulates the scientific community in order to develop biobased products with low environmental impact and to widen the field of biomass exploitation. The functionalization of cellulose, the most abundant polysaccharide on the planet, and/or cello-oligosaccharides as described in this thesis is part of this approach. Our objective was to develop a chemo-enzymatic method involving the action of a mediator-assisted laccase to oxidize cello-oligosaccharides or cellulosic fibers, followed by reductive amination to graft amino compounds onto the cellulosic material. To this end, we first demonstrated the oxidation of cellobiose and methyl cellobiose using the laccase from Trametes versicolor and TEMPO as a mediator. Oxidation conditions were optimized with methyl cellobiose and applied to a cello-oligosaccharide mixture and cellopentaose. Using LC/MS analysis, we showed that a wide range of oxidized compounds is obtained and that the method is effective in producing acidic cello-oligosaccharides potentially of interest for the biomedical and nutraceutical fields. Then, we showed that the reactivity of oxidized cellopentaose with two aminated molecules, p-toluidine and rhodamine 123 (an aminated dye), allowed the binding of the amino compound to the oligosaccharides. Using LC/ MS and MS/MS techniques, we provided evidence for the presence of a strong, covalent amine bond between the dyes and cellopentaose, thus enlarging the chemical space accessible through this hybrid process. After completed this proof of concept, we attempted the dyeing of cotton threads. Cellulosic fibers are one of the main biosourced and biodegradable textile materials. However, chemical processing of textiles and especially the chemical methods used to covalently fix dyes are extremely polluting and harmful to health. Providing more eco-friendly alternatives is a challenge but of prime interest for a company like PILI, which was involved in the thesis project and is developing natural dyes using synthetic biology. Thus, the potential of the two-pot/two-step hybrid process was used to successfully graft p-Toluidine, rhodamine 123 and Acid Red 33 onto cotton thread. The covalent bond established between these dyes and the cotton fiber was proven for the first time. In addition, good homogeneity and wash-fastness were observed for acid Red 33 dyeing, demonstrating the robustness and applicability of the approach in real life. These original results have been patented. By testing other amino dyes, we also showed that the solubility, reactivity and structure of the aminated dye are important parameters to be addressed for dyeing optimization, which opens the way to the custom synthesis of new amino dyes suitable for this promising hybrid process

Le manuscrit présente la conversion du dioxyde de carbone en sucres C3 et C4 à l'aide de réactions en cascade chimio-enzymatiques stéréocontrôlées. Le processus repose sur une stratégie en deux étapes avec (i) la réduction catalytique et sélective à 4 électrons du CO2 en un dérivé bis(boryl)acétal suivi (ii) de couplage enzymatique C-C stéréocontrôlé du dérivé bis(boryl)acétal en sucres C3 et C4. La stratégie développée est sans précédent et représente une nouvelle approche pour l'utilisation du CO2 comme source Cn pour la synthèse de biomolécules énantiomériquement pures importantes sur le plan industriel. Le premier chapitre est une étude bibliographique décrivant (i) une introduction à la chimie des sucres avec un focus particulier dédié à la production de sucres à partir de CO2 et de formaldéhyde comme sources C1 et (ii) la réduction sélective et catalytique à quatre électrons du CO2 à l'aide d'hydroborane et d'hydrosilane utilisés comme réducteur pour la formation de dérivés bis(boryl)acétal et bis(silyl)acétal ainsi que leur utilisation comme sources de formaldéhyde ou substituts de formaldéhyde pour la synthèse de produits à haute valeur ajoutée. Le deuxième chapitre présente la synthèse et la réactivité des dérivés bis(boryl)acétal et bis(silyl)acétal. Notamment, un nouveau dérivé bis(boryl)acétal a été synthétisé avec succès et isolé à l'échelle du gramme. Le troisième chapitre décrit la bioconversion stéréocontrôlée du dérivé bis(boryl)acétal synthétisé à partir du CO2 en sucres. Notamment, une réaction enzymatique en cascade a été réalisée pour la production d'un sucre C4 énantiomériquement pur en utilisant le CO2 comme seule source de carbone
The manuscript presents the conversion of carbon dioxide into C3 and C4 carbohydrates using stereocontrolled chemo-enzymatic cascade reactions. The process relies on a two-step strategy with (i) the catalytic and selective 4-electron reduction of CO2 into a bis(boryl)acetal derivative followed by (ii) the stereocontrolled bio-catalyzed C-C coupling of the bis(boryl)acetal derivative into carbohydrates. The strategy developed is unprecedented and represents a new exciting approach for the use of CO2 as a Cn source for the synthesis of valuable industrially relevant enantiomerically pure biomolecules. The first chapter is a bibliographic study describing (i) an introduction to carbohydrate chemistry with a special focus dedicated to the production of carbohydrates from CO2 and formaldehyde as C1 sources and (ii) the selective and catalytic four-electron reduction of CO2 using hydroborane and hydrosilane as reductants for the formation of bis(boryl)acetal and bis(silyl)acetal derivatives and their use as formaldehyde sources or formaldehyde surrogates for the synthesis of value-added product. The second chapter presents the synthesis and reactivity of bis(boryl)acetal and bis(silyl)acetal derivatives. Notably, a new isolable bis(boryl)acetal derivative was successfully synthesized and isolated on a gram scale. The third chapter describes the stereocontrolled bioconversion of the bis(boryl)acetal derivative synthetized from CO2 into carbohydrates. Notably, an enzymatic cascade reaction was performed for the production of an enantiomerically pure C4 carbohydrate using CO2 as the only carbon source

"The procurement of sustainable technologies is the major driving force for current industrial development. The 12 principles of Green Chemistry are important guidelines for their development and the first one directs towards waste reduction instead of remediation. (...)"

Reductions and oxidations of carbonyl compounds under a variety of experimental conditions are introduced. We discuss the use of boron and aluminum hydrides, by examining chemo-, regio-, diastereo- and enantioselective processes and point to the advantages that may occur when applying flow chemistry. The regiochemistry in the reduction of α,β-unsaturated carbonyl compounds may provide allylic alcohols (1,2-reduction), saturated carbonyl compounds (1,4-reduction), or products from exhaustive reduction (1,2- and 1,4-reduction). Dissolving metal reductions, heterogeneous and homogeneous hydrogenations using rhodium, ruthenium, and iridium catalysts, reduction via hydrogen transfer reactions, and the hydrosilylation reactions are also discussed. The stereochemical aspects and the enantioselective reductions of carbonyl compounds are addressed, including protocols for their catalytic asymmetric reductions. Examples of enzymatic reductions of ketones, including some large-scale processes that make use of the directed enzymatic evolution strategy, are presented. The oxidation of aldehydes, ketones, and the Baeyer–Villiger, Favorskii, Wolff, Beckmann, and Schmidt rearrangements are presented. Examples of enzymatic Baeyer–Villiger oxidation are also discussed.