title: UV-protectant metabolites from lichens and their symbiotic partners.
abstract: Lichens are structurally complex symbiotic organisms that are exposed to a wide variety of external conditions (extreme temperatures, desiccation, UV radiation, etc.). These poikilohydric organisms have developed various mechanisms of photoprotection, such as light scattering, radiation screening, thermal dissipation, activation of antioxidant defense and macromolecules and membrane repair. These unique organisms produce a vast array of compounds, with more than 1000 secondary metabolites known. An important protective mechanism of lichens is the production of UV screening compounds, such as phenolic compounds (depsidones, depsides, diphenyl ethers), anthraquinones, xanthones or shikimic acid derivatives (calycin, mycosporines, scytonemin). Due to the harmful effects of the UVA wavelengths of sunlight, the search for new sunscreens remains important. We herein propose a review that focuses on the UV protectants from lichens and their symbiotic partners (lichenized fungi, green alga, cyanobacteria). In fact, lichens produce unique and/or efficient UV filters such as depsidones (lobaric acid, pannarin, etc.), depsides (atranorin, gyrophoric acid, etc.), diphenyl ethers (epiphorellic acids, buellin), bisxanthones (secalonic acids, etc.), mycosporines and MAAs, scytonemin along with classical pigments (melanin, carotenoids). We propose to classify these compounds with regard to their chemical structures and review the physicochemical properties that act as UV filters. While the most abundant lichen polyfunctionalized aromatic compounds, belonging to orsellinic derivatives, are UVB screens, these organisms produce strong UVA filters, e.g., calycin (pulvinic acid derivatives), bisxanthones (secalonic acids), scytonemin or mycosporines and MAAs with the latter ones exhibiting attractive properties as photoprotectants.
authors.affiliation: Equipe PNSCM «Produits Naturels - Synthèses - Chimie Médicinale» UMR CNRS 6226 Institut des Sciences chimiques de Rennes, UFR Sciences Pharmaceutiques et Biologiques, Univ. Rennes 1, Université Européenne de Bretagne, 2 Avenue du Pr. Léon Bernard, F-35043 Rennes, France. sophie.tomasi@univ-rennes1.fr.
authors.forename: Khanh-Hung
authors.initials: KH
authors.lastname: Nguyen
authors.forename: Marylène
authors.initials: M
authors.lastname: Chollet-Krugler
authors.forename: Nicolas
authors.initials: N
authors.lastname: Gouault
authors.forename: Sophie
authors.initials: S
authors.lastname: Tomasi
mesh_terms: D000880:Anthraquinones / Q000378:metabolism; D008011:Lichens / Q000737:chemistry / Q000378:metabolism; D015394:Molecular Structure; D010636:Phenols / Q000378:metabolism; D014466:Ultraviolet Rays
chemical_list: D000880:Anthraquinones; D010636:Phenols