Les bases esfingoides, aminoalcohols de cadena llarga, sovint es troben enllaçades a un àcid gras formant les anomenades ceramides. Aquestes ceramides constitueixen la part hidrofòbica essencial dels glicolípids, com -GalCer, iGB3 o KRN7000, que es troben a la membrana de les cèl·lules eucariotes i que participen en processos fisiològics importants involucrats en la prevenció de malalties com infeccions virals, infeccions microbianes, càncer, diabetis, malalties de Parkinson i Alzheimer entre d’altres. Dins el marc de la necessitat de desenvolupar noves metodologies de síntesi d’aquestes bases esfingoides, en la present tesi doctoral s’han desenvolupat tres nous mètodes sintètics, sent els mètodes estereoselectius més eficients fins el moment, basats en reaccions catalitzades per metalls de transició. / Glycosphingolipids are commonly found in eukaryotic cell membranes, plasma membranes and some intracellular organelles. They play a critical role in communication as shown promising bioactivities against diverse pathologies. Glycosphingolipids are constituted by a mono- or oligosaccharide moiety link to the ceramide part, which is a sphingoid base link to a fatty acid. Due to its importance, it is necessary to develop new methodologies to synthesize them. In this thesis, we developed three new synthetic methods based on stereoselective processes catalyzed by transition metal reactions.

Au cours de leur métabolisme, les céramides, produits de novo au niveau du réticulum endoplasmique, sont transportés vers l'appareil de Golgi pour être convertis en sphingomyéline. Le mode principal de ce transport implique la protéine cytosolique CERT (CERamide Transfer). La surexpression de CERT, responsable d'un abaissement du taux intracellulaire en céramide pro-apoptotique, a été associée au phénomène de résistance aux agents chimiothérapeutiques de plusieurs lignées de cellules tumorales. L'inhibition de CERT permet de resensibiliser ces lignées cellulaires aux agents anti-cancéreux. Cependant, une seule famille d'inhibiteurs de CERT est connue à ce jour : les HPAs. A l'extrémité C-terminale de la protéine, le domaine START contient le site de liaison du céramide nécessaire à l'activité de transport de CERT. A partir de structures cristallographiques, une méthode d'identification de nouveaux ligands, combinant des outils in silico et in vitro, a été développée. La jaspine B, des analogues HPAs et des iminosucres ont été mis à jour en tant qu'antagonistes potentiels de CERT par cette méthode. Certains des composés identifiés ont été synthétisés et évalués in vitro. Des sondes fluorescentes de la jaspine B ont été conçues afin d'approfondir la compréhension de son mécanisme d'inhibition. En parallèle, un test de liaison in vitro HTR-FRET a été développé, permettant le criblage haut-débit de la Chimiothèque Nationale Essentielle. / During its metabolism, ceramides, produced de novo in the endoplasmic reticulum, are transported to the Golgi complex to be converted into sphingomyelin. The main way of this transport involves the cytosolic CERT protein (Ceramide Transfer). Overexpression of CERT, responsible for a diminution of intracellular level of proapoptotic ceramide, is associated with the phenomenon of resistance to chemotherapeutic agents in several tumor cell lines. The CERT inhibition allows to resensitize these cell lines to anticancer drugs. Yet, only a single family of inhibitors is known to date: HPAs. Located at the C-terminal region of the protein, the START domain contains the binding site of ceramide necessary for the transport activity of CERT. Based on crystallographic structures, a method for the identification of new CERT ligands, combining in silico and in vitro tools, was developed. Jaspine B, HPAs analogs and iminosugars were identified as potential antagonists using this method. Some of these compounds were synthesized and evaluated in vitro. Fluorescent probes of jaspine B were designed for a better understanding of it mechanism of action. In parallel, an in vitro HTR-FRET binding assay was developed, allowing the high-throughput screening of the National Essential Compound Library.

The thesis entitled “Total synthesis of bio-active natural products microcarpalide, synargentolide A, jaspine B and anamarine.” demonstrates the utility of chiral pool tartaric acid as the source in the synthesis of bio-active natural products. The thesis was divided into four sections. Section I of the thesis deals with the enantiodivergent synthesis of microcarpalide from tartaric acid. Microcarpalide is a 10-membered lactone of polyketide origin isolated from the fermentation broths of an unidentified endophytic fungi, found to be weekly cytotoxic to mammalian cells and acts as a microfilament discrupting agent. Stereoselective approach for the synthesis of ()-microcarpalide is described from D- and L-tartaric acids, while enantiodivergent approach for the synthesis of both enantiomers is described from L-tartaric acid using ring closing metathesis as the Scheme 2: Enantiodivergent total synthesis of microcarpalide. In section II of the thesis, stereoselective synthesis of synargentolide A is described. Synargentolide A is a polyhydroxy -lactone, isolated from Syncolostemon argenteus, which was founf to exhibit cytotoxic and antitumor properties. Stereoselective synthesis of synargentolide A was accomplished, starting from L-tartaric acid employing, Keck and Brown allylations and ring closing metathesis, as the key steps. Scheme 3: Stereoselective total synthesis of ()-synargentolide A. Section III of the thesis deals with the synthesis of ()-jaspine B. Pachastrissamine (jaspine B), is an anhydrophytoshingosine derivative, isolated from marine sponges Pachastrissa and Jaspis speces. Pachastrissamine was shown to exhibit cytotoxicity (IC 50 0.01 g/mL) against P388, A549, HT29, and MEL28 cell lines. Enantioselective synthesis of jaspine B is accomplished from L-tartaric acid employing, Keck allylation, acid mediated formation of tetrahydrofuran, and olefin cross metathesis as the key reactions. In section IV of the thesis, enantioselective synthesis of ()-anamarine is described. Anamarine is a polyhydroxy -lactone isolated from the flowers and leaves of Peruvian hyptis, possessing cytotoxicity against human tumor cell lines. Enantioselective synthesis of -anamarine is accomplishedelaboration of hitherto unknown -keto phosphonate derived from tartaric acid amide. In an appendix for the thesis, enantiodivergent synthesis for 4-siloxy-pent-2-enone was described. The usefulness of asymmetric aldol reaction is exemplifiedin this section. hydroxy amide synthesized from crotonaldehyde is suitably elaborated to the diene which on RCM yielded 4-silyloxycyclopent-2-enone. Further synthetic modification of this compound afforded the other enantiomer. Scheme 6: Enantiodivergent synthesis of hydroxy cyclopentenones. (For structural formula pl the abstract pdf file)