Solenn Ferron PhD defense

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Organic Chemistry & Interfaces (COrInt) team Abstract Lichens biosynthesize a wide variety of secondary metabolites, which are often specific. Among these metabolites, xanthones are a family of molecules comprising nearly 120 compounds in lichens, divided into four main structural groups. 1,350 species of lichens containing xanthones have been recorded, the majority of which are crustose lichens that produce chlorinated lichexanthones. These lichen-specific xanthones possess a 1,3,6-trihydroxy-8-methyl-9H-xanthen-9-one skeleton, their multiple chlorinations and methylations result in the existence of 64 isomers. The creation of a library of lichexanthones and the development of methods for identifying isomers using chromatographic techniques, hyphenated with spectroscopic techniques (UV, MS, NMR, HRMS/MS), have led to an analytical database for these compounds. Thus, it has been possible to define the chemosyndromes present in lichens of the genus Myriolecis, as well as to confirm the lichen origin of a pigment found in a medieval tapestry. Their polycyclic, aromatic and chlorinated structure shows an analogy with that of TCDD, and a study using a human cell model, combining in vitro and in silico approaches, demonstrated their activity on the Ah receptor as well as their enzymatic metabolism, in particular by CYP enzymes of the 1A family. CYPs are also found in lichens and are responsible for modulating the oxidation state of some secondary metabolites. The search for oxidized derivatives has led to the isolation and characterisation of two new lichexanthones. Jury Gérald Culioli, Professor, University of Avignon / Reviewer Laurence Nazabadioko, Professor, University of Reims / Reviewer Mehdi Beniddir, Professor, University of Paris-Saclay / Examiner David Guilet, Professor, University of Angers / Examiner Laurence Meslet-Cladière, Professor, University of Brest / Examiner Françoise Lohézic-Le Dévéhat, Associate Professor, University of Rennes / PhD Director Marylène Chollet-Krugler, Associate Professor, University of Rennes / PhD Co-Supervisor Contacts Solenn Ferron, solenn.ferron@univ-rennes.fr Françoise Lohézic-Le Dévéhat , francoise.le-devehat@univ-rennes.fr