Sulfation plays a critical role in the biosynthesis of small molecules, regulatory mechanisms such as hormone signaling, and detoxification processes (phase II enzymes). The sulfation reaction is catalyzed by a broad family of enzymes known as sulfotransferases (SULTs), which have been extensively studied in animals due to their medical importance, but also in plant key processes. Despite the identification of some sulfated metabolites in fungi, the mechanisms underlying fungal sulfation remain largely unknown. To address this knowledge gap, we conducted a comprehensive search of available genomes, resulting in the identification of 174 putative SULT genes in the Ascomycota phylum. Phylogenetic analysis and structural modeling revealed that these SULTs belong to the aryl sulfotransferase family, and they are divided into two potential distinct clusters of PAPS-dependent SULTs within the fungal kingdom. SULT genes from two marine fungi isolated from deep-sea hydrothermal vents, Hortaea werneckii UBOCC-A-208029 (HwSULT) and Aspergillus sydowii UBOCC-A-108050 SULT (AsSULT), were selected as representatives of each cluster. Recombinant proteins were expressed in Escherichia coli and biochemically characterized. HwSULT demonstrated high and versatile activity, while AsSULT appeared more substrate-specific. Here, HwSULT was used to sulfate the mycotoxin zearalenone, enhancing its cytotoxicity toward healthy feline intestinal cells.

Isocaloteysmannic acid (1), a new chromanone, was isolated from the leaf extract of the medicinal species Calophyllum tacamahaca Willd. along with 13 known metabolites belonging to the families of biflavonoids (2), xanthones (3–5, 10), coumarins (6–8) and triterpenes (9, 11–14). The structure of the new compound was characterized based on nuclear magnetic resonance (NMR), high-resolution electrospray mass spectrometry (HRESIMS), ultraviolet (UV) and infrared (IR) data. Its absolute configuration was assigned through electronic circular dichroism (ECD) measurements. Compound (1) showed a moderate cytotoxicity against HepG2 and HT29 cell lines, with IC₅₀ values of 19.65 and 25.68 µg/mL, respectively, according to the Red Dye method. Compounds 7, 8 and 10–13 exhibited a potent cytotoxic activity, with IC₅₀ values ranging from 2.44 to 15.38 µg/mL, against one or both cell lines. A feature-based molecular networking (FBMN) approach led to the detection of a large amount of xanthones in the leaves extract, and particularly analogues of the cytotoxic isolated xanthone pyranojacareubin (10).

Chemical investigation of ethyl acetate bark extracts of Indigofera ammoxylum red and white phenotypes led to the bio-guided isolation of four previously undescribed flavonoids, named (2S,3R)-3',7-dihydroxy-4',6-dimethoxyflavanol (1), (2S,3R)-6-methoxy-7-hydroxyflavanol (2), 2',3',7-trihydroxy-4',6-dimethoxyisoflavone (7) and 2',5' -dimethoxy-4',5,7-trihydroxyisoflavanone (8), along with 14 known compounds (3-6 and 9-18). The previously undescribed structures were characterized based on NMR, HRESIMS, UV and IR data. Published spectroscopic data were used to deduce the structure of the known compounds. Eleven of the 18 isolated metabolites were evaluated for anti-inflammatory activity and cytotoxic activity against human liver carcinoma cells and human colon and colorectal adenocarcinoma cells. All tested compounds showed an anti-inflammatory activity (IC₅₀ NO < 25 μg/mL), and compounds 2 and 3 were more selective than the positive control dexamethasone. Afromorsin (6) showed promising cytotoxic properties against both cancer cell lines (IC₅₀ 18.9 and 11.4 μg/mL). Feature-based molecular networking approach applied to bark and leaves extracts of the two phenotypes allowed to detect bioactive analogues, belonging to the families of flavones, isoflavones, flavanones, flavanols and flavonols, and to explore the chemodiversity of the species. The red and white phenotypes have a similar composition, whereas bark and leaves contain specific chemical entities. Finally, this approach highlighted a cluster of potentially bioactive and undescribed metabolites.

Hortaea werneckii is a halotolerant yeast, found in various habitats and which specialized metabolism remains largely unexplored. Moreover, its chemical response to high salinities has not been thoroughly investigated. To address this gap, a large-scale metabolomic study based on HPLC-HRMS/MS was conducted on 64 strains, collected from different habitats worldwide, and cultivated both on saline and non-saline media. The culture media salinity significantly modulated the strains metabolomes, suggesting the yeast exhibits a specific chemical response to high salt concentrations, potentially linked to halotolerance mechanisms. Additionally, the metabolomes were influenced by the ecological origin of the strains, with opportunistic pathogenic isolates producing distinct metabolites. Molecular networking revealed that H. werneckii synthesizes various chemical classes, including potential cytotoxic compounds, making this yeast a potentially interesting source of bioactive compounds. Hortein was detected as dominant and ubiquitous, emerging as a potential chemical marker for the species. This study highlights several compounds of interest, related to the chemical ecology and pathogenicity of H. werneckii . As most of them remain unidentified, future research should prioritize their isolation and identification, to improve our understanding of this extremophile organism and harness its potential in natural product discovery.

Ces travaux de thèse portent sur la valorisation pharmacologique de plantes médicinales de La Réunion. Deux axes ont été développés et menés en parallèle. Le premier axe avait pour objectif la recherche de composés bioactifs dans trois espèces endémiques des Mascareignes : Calophyllum tacamahaca, Indigofera ammoxylum et Pittosporum senacia. Pour ce faire, ces trois espèces ont tout d’abord été soumises à une étude chimique et biologique préliminaire. L’étude chimique a été réalisée à l’aide de différentes techniques analytiques telles que la CCM, la CLHP/DAD-CAD et la CLHP/DAD-SM. L’étude biologique a, quant à elle, permis d’évaluer les activités antiplasmodiale, anti-inflammatoire et cytotoxique des espèces. À l’issue de ces travaux préliminaires, deux espèces ont été mises en lumière : C. tacamahaca et I. ammoxylum. En effet, ces dernières ont présenté une composition chimique riche et diversifiée, ainsi que des propriétés biologiques significatives. Elles ont par conséquent été sélectionnées pour une étude phytochimique approfondie. L’extraction, l’isolement et l’identification de leurs métabolites spécialisés ont été réalisés au moyen de plusieurs techniques chromatographiques (SPE, CLHP...) et spectroscopiques (SMHR, RMN 1D et 2D...). Trente-quatre composés, appartenant à la famille des xanthones, des coumarines, des triterpènes et des composés phénoliques, ont été isolés de ces deux espèces, dont cinq molécules nouvelles et deux métabolites identifiés pour la première fois en tant que produits naturels. Parmi ces composés, deux ont montré une activité antiplasmodiale (la pancixanthone B et la pratenséine), trois une activité antiinflammatoire et sélective (le 6-méthoxy-7-hydroxyflavanol, la 3-(2',3'-dihydroxy-4'-méthoxyphényl)-5,7-dihydroxy-isoflavanone et la khrinone C) et huit une activité cytotoxique (trois inophyllums, trois triterpènes, la pyranojacareubine et l’afromorsine). Par ailleurs, l’approche bio-informatique des réseaux moléculaires appliquée aux extraits bruts de ces deux plantes a permis de détecter d’autres composés bioactifs, et d’évaluer la chimiodiversité de l’espèce I. ammoxylum. Le second axe avait pour objectif d’inscrire quatre plantes médicinales réunionnaises à la Pharmacopée française, afin que leurs vertus soient officiellement reconnues. Les monographies bibliographiques des espèces Pandanus utilis, Terminalia catappa, Tamarindus indica et Ravenala madagascariensis ont donc été rédigées et soumises à l’ANSM. Trois des espèces proposées ont ainsi été inscrites en liste A et une en liste B.