The chemical structures of metabolic products of lichen have been much clarified by the investigations of Asahina, Asano and their collaborators.From the results of their works, the chemical structure of more than fifty lichenic constituents, including fatty acids, depsides, depsidones, pigments of pulvinic acid derivatives, anthraquinonesla), phenanthrene-quinonelb), xanthonlc) and diphenylene oxidesld) has been proved; they are so numerous and outstanding in their structure that they may well compose a special chemical group in natural products.Moreover, the investigations have brought out an interesting fact that a certain compound in the lichen has some antibiotic activity.Namely, Fuzikawa has reported the growth inhibiting effects, of depsides and phenol carboxylic acid • derivative against the molds growing in soy bean sauce (Shoyu)2).Asano et.al.3) have confirmed the antibacterial action of lichesteric acid and its derivatives against staphylococci.In United States, Burkholder and Evans4) showed by the Oxford Cup method the antibacterial effects of aqueous extract of Cladonia species against B. subtilis and Sarcina lutea.Stoll et, al. of Basel, examined many species of lichens and reported that usnic acid has particullarly high potency of antitubercular activity.In studies carried out at about the same time, we have been able to find .the high antibacterial action of usnic acid against acid fast bacilli and Staphylococcus aureus, and also it was noticed that there exists a certain relationship between the antibacterial effect and the chemical constitution of usnic acid and its derivatives.
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Shibata et al. (1948) studied this question.