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|Section2= }} Usnic acid is a naturally occurring dibenzofuran derivative found in several lichen species with the formula C18H16O7. It was first isolated by German scientist W. Knop in 1844〔Knop W. (1844) Chemisch-physiologische Untersuchung uber die Flechten. ''Justus Lieb. Ann. Chern'' 49: 103-124. 〕 and first synthesized between 1933-1937 by Curd and Robertson.〔A. Robertson and F. H. Curd. ''J. Chem. Soc.'' 1173 (1933)〕 Usnic acid was identified in many genera of lichens including ''Usnea'', ''Cladonia'', ''Hypotrachyna'', ''Lecanora'', ''Ramalina'', ''Evernia'', ''Parmelia'' and ''Alectoria''. Although it is generally believed that usnic acid is exclusively restricted to lichens, in a few unconfirmed isolated cases the compound was found in kombucha tea and non-lichenized ascomycetes. At normal conditions, usnic acid is a bitter, yellow, solid substance.〔 It is known to occur in nature in both the d- and l-forms as well as a racemic mixture. Salts of usnic acid are called usnates (e.g. copper usnate). ==Biological role in lichens== Usnic acid is a secondary metabolite in lichens whose role has not been completely elucidated. It is believed that usnic acid protects the lichen from adverse effects of sunlight exposure and deters grazing animals with its bitter taste. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Usnic acid」の詳細全文を読む スポンサード リンク
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