Produit naturel

Résumé

droite|vignette|Le paclitaxel (Taxol) est un produit naturel dérivé de l'if. Un produit naturel est un composé chimique ou une substance produite par un organisme vivant, c'est-à-dire qui se trouve dans la nature. Au sens le plus large, un produit naturel est toute substance produite par la vie. Les produits naturels peuvent également être préparés par synthèse chimique (semi-synthèse et synthèse totale) et ont joué un rôle central dans le développement du domaine de la chimie organique en fournissant des cibles synthétiques difficiles. Le terme a également été étendu à des fins commerciales pour désigner les cosmétiques, les compléments alimentaires et les aliments produits à partir de sources naturelles sans ingrédients artificiels ajoutés. Grâce aux améliorations techniques (programmes de criblage à haut débit, techniques de séparation et isolement), le nombre de produits naturels découverts au début du dépasse le million (nombre sur-évalué par rapport à ce qui est accessible). 5

Source officielle

https://fr.wikipedia.org/wiki/Produit_naturel

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The work presented in this thesis focuses on the synthesis of monoterpene indole alkaloids. The first part describes the divergent total synthesis of (-)-rhazinilam, (-)-leucomidine B and (+)-leuconodine F, three structurally distinct natural products of the Aspidosperma family. The key step involves the heteroannulation of an advanced tetrahydropyridine with bromoacetaldehyde or oxalyl chloride in order to afford the corresponding tetrahydroindolizine and 2,3-dioxopyrrole moieties, respectively. By fine tuning of the reaction conditions, the former was converted into rhazinilam while the latter led to the syntheses of leucomidine B and leuconodine F. In the case of leucomidine B, the development of a substrate-directed diastereoselective reduction of a sterically unbiased double bond is also discussed. The second part details the synthetic studies towards various members of the Sarpagan family. After the exploration of several strategies and indoles alkaloids, the enantioselective total synthesis of N(1)-demethyl-3,5-diepi-alstolactone was accomplished. This synthesis features three key points: 1) the incorporation of a vinyl ketone function in the C-2 position of indole by using the Liebeskind-Srogl coupling in order to afford, after ring-closing metathesis, an advanced eight-membered cyclic enone, 2) a highly diastereoselective intramolecular Michael addition and 3) the formation of an azabicyclo[3.3.1]nonane bridged system from the corresponding eight-membered ring via a dehydration / transannular cyclization process.

EPFL2017

Chargement

Aliphatic Carboxylic Acids as Coupling Partners in Carbon-Heteroatom Bond-Forming Reactions

Runze Mao

Carboxylic acids are one of the most suitable starting materials for synthesis. They are readily available and therefore inexpensive, stable and non-toxic. Many carboxylic acids can be obtained directly from natural resources, thus avoiding the extraction of fossil resources, such as oil or natural gas, in the production of chemicals. Furthermore, renewable carboxylic acids derived from biomass have a wide structural diversity (e.g., amino acids, fatty acids and sugar acids), which not only holds greater potential for the synthesis of complex molecules, but also advances the development of green chemistry. In this context, this thesis aims at establishing new carbon-heteroatom coupling reactions with carboxylic acids as versatile coupling partners. These reactions are hitherto unknown, which not only fill some of the gaps in synthetic organic chemistry, but also provide solutions for the rapid assembly of bioactive molecules. In order to overcome the challenge of forming C(sp3)-heteroatom bonds, Chapters 4, 5 and 6 detail the development of photoredox/copper bi-catalytic systems and their applications in decarboxylative C(sp3)-N and C(sp3)-O coupling reactions. These methods are not only compatible with numerous functional groups, but also allow for rapid late-stage functionalization. More importantly, these methods can simplify the pathway for building drug core skeletons, highlighting the potential of these methods to expedite drug discovery. To bridge the disconnection in the synthesis of trifluoromethylthioesters from carboxylic acids, Chapter 7 describes the establishment of a "umpolung" strategy and its application in the conversion of carboxylic acids to trifluoromethylthioesters. This approach provides the most concise synthetic pathway to date for the synthesis of trifluoromethylthioesters, which not only accommodates a variety of functional groups, but also allows for the rapid functionalization of carboxylic acid-containing natural products and drug molecules. In summary, this thesis illustrates how novel catalytic methods can be used to convert inexpensive, readily available and environmentally benign aliphatic carboxylic acids into high value-added compounds.

EPFL2020

Chargement

Total Synthesis of Aspidosperma Family Indole Alkaloids through the iORC Domino Process

Olivier Wagnières

This thesis describes a unified strategy for the synthesis of monoterpene indole alkaloids of the Aspidosperma family. These syntheses feature two key steps: (1) a palladiumcatalyzed decarboxylative vinylation that provides quick access to cyclopentene intermediates containing all of the carbons present in the natural products and (2) an integrated oxidation/reduction/cyclization (iORC) sequence for skeletal reorganisation that converts the cyclopentenes to the corresponding pentacyclic structures of the natural products. By incorporation of a geometric constraint to the iORC substrates, both the chemoselectivity (C7 versus N1 cyclization) and the stereoselectivity (trans- versus cis-fused ring system) of the cyclization process can be controlled. Using this method, we achieved the racemic total synthesis of aspidospermidine and dehydroaspidospermidine in seven steps; both of which feature a cis-fused ring system. We then accomplished a ten-steps synthesis of kopsihainanine A featuring a trans-fused ring system. The work towards the total synthesis of aspidoalbidine and kopsinitarine E using the same two key steps was attempted, but was not completed in the time provided. This PhD will also cover our synthetic efforts towards the alkaloidminfiensine, featuring a domino reduction/cyclization sequence performed prior to the development of the iORC process.

EPFL2015

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Aliphatic Carboxylic Acids as Coupling Partners in Carbon-Heteroatom Bond-Forming Reactions

Runze Mao

EPFL2020