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Recherche de molécules antimicrobiennes d'origine lichénique : Etude phytochimique de trois lichens & approche synthétique de deux composés actifs

Abstract : Phytochemical study of three lichens collected in Limousin, Usnea florida, Flavoparmelia caperata and Cladonia incrassata, led to the isolation and the structural identification of 16 secondary metabolites. First, these lichens were chosen after a preliminary screening performed on 17 species. Antimicrobial activity of acetone extracts was evaluated and bioassay-guided fractionation was performed. The two isomers of usnic acid, 3 dibenzofurans, 4 depsides, 3 depsidones, one aliphatic acid and one sterol were isolated. A trichlorinated xanthone, named cladoxanthone A, was extracted and identified for the first time in a natural source. A bioautographic protocol was used to evaluate antibacterial activities of these compounds on Staphylococcus aureus. MICs of the products obtained in sufficient amounts were determined by a broth microdilution method in parallel with Phenonip®, a preservative commonly used in cosmetic industry. Didymic and condidymic acids were found to be good candidates for use as preservatives. Secondly, owing to their potential industrial application, we explored synthetic routes for usnic acid and cladoxanthone A. Thus, the preparation of the key intermediate for access to usnic acid was optimized and the first coupling tests in the presence of a porphyrin were encouraging. Similarly, the proposed synthetic routes for cladoxanthone A are promising.
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Submitted on : Tuesday, August 18, 2015 - 11:47:16 AM
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Amandine Andraud-Dieu. Recherche de molécules antimicrobiennes d'origine lichénique : Etude phytochimique de trois lichens & approche synthétique de deux composés actifs. Biologie moléculaire. Université de Limoges, 2015. Français. ⟨NNT : 2015LIMO0029⟩. ⟨tel-01184892⟩

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