From submerged cultures of Lachnella villosa, Lachnella sp. 541, and Peniophora laeta we isolated marasmic acid (1), a metabolite first described from surface cultures of Marasmius conigenus. The sesquiterpenoid exhibits potent antimicrobial and cytotoxic properties.In cells of the ascitic form of Ehrlich carcinoma RNA and DNA syntheses are preferentially inhibited. Marasmic acid inhibits RNA synthesis in isolated nuclei, but does not interfere with the transport of nucleoside precursors into the cells. RNA polymerase II and capping enzyme (mRNA guanylyltransferase), two enzymes of nucleic acid metabolism, are markedly affected after preincubation with marasmic acid. We assume that marasmic acid acts on nucleic acid syntheses by direct inhibition of some of the enzymes involved. This mode of action would also explain its mutagenic properties.The preparation and testing of two derivatives, 2 and 3, revealed that the a, n-unsaturated aldehyde is essential for the antimicrobial and cytotoxic activity of marasmic acid.In the course of the first extensive screening of basidiomycetes a highly potent antibacterial compound, marasmic acid, was isolated from cultures of Marasmius conigenusz).The sesquiterpenoid structure of marasmic acid was elucidated in 19663). GREENLEE and WOODWARD achieved the first total synthesis in 19764) and only recently new synthetic approaches have been published5). Except for some data on the antimicrobial activity in the first publication, the mode of action of this antibiotic had not been investigated.During our screening of basidiomycetes for antimicrobial and cytotoxic compounds, marasmic acid was detected in the culture broth of several, taxonomically not related species.In this report we wish to describe our studies on its biological activities both in whole cells and in cell-free preparations.
Results and DiscussionLachnella villosa, Lachnella sp. 541, and Peniophora laeta were grown in submerged culture in complex media as described earlier1).The antibiotic was extracted from the culture broth with ethyl acetate and purified by several chromatographic steps.The identity of the metabolite with marasmic acid was determined by MS and 1H NMR spectra.Authentic marasmic acid, kindly provided by P. DE MAYO, London, Canada, was used for comparison.Strobilurus stephanocystis (Hora) Sting. has been suggested by SINGER6) to be synonymous with M.conigenus (Pers. ex Fr.) Karst, from which marasmic acid had been first described. A strain of S. stephanocystis was therefore tested for the production of marasmic acid. None could be detected, our