Lichens — symbiotic organisms of fungi and algae — contain a great number of organic compounds, the so-called lichen substances which are more or less typical of this group of cryptogames. The lichen substances comprise quite different classes of compounds like amino acid derivatives, sugar alcohols, aliphatic acids, γ-, δ- and macrocyclic lactones, monocyclic aromatic compounds, quinones, chromones, xanthones, dibenzofuranes, depsides, depsidones, depsones, terpenoids, steroids and carotenoids. This multitude of compounds made the study of their chemistry attractive from the early times of organic chemistry. Bebert (1831) isolated vulpinic acid in 1831, Alms (1832) picrolichenic acid in 1832, and Knop (1844) usnic acid in 1844. Gmelin (1858) published a review on lichen substances already in 1858.
KeywordsUsnic Acid Macrocyclic Lactone Chlorosulfonic Acid Lichen Substance Orsellinic Acid
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