Polyketides from cultured lichen mycobionts of Pseudopyrenula subnudata and their biosynthetic origin

Lichens are symbiotic organisms, composed of a fungus (mycobiont) and one or more algae and/or cyanobacteria (phytobiont). Lichens are well known to produce a wide range of characteristic secondary metabolites, namely, lichen substances, some of which are potentially useful and biologically active compounds. The majority of lichen substances are secondary metabolites of the fungal component, in symbiosis or in the aposymbiotic state. Our previous studies indicated that aposymbiotically cultivated lichen mycobionts under axenic conditions produce novel substances that differ from the secondary metabolites of intact lichens, but are structurally similar to fungal metabolites [1, 2]. Continuing our pursuit of novel bioactive metabolites from Vietnamese lichen-derived fungi [3], we cultivated spore-derived mycobionts of the crustose lichen Pseudopyrenula subnudata collected in Vietnam to isolate six new compounds from the cultures. The novel compounds 1-6 were polyketides closely related to versiol from the sponge-derived fungus, Aspergillus versicolor [4, 5]. Their structures were elucidated by spectroscopic and chemical means. The assembly pattern of acetate units in their biosynthesis was also studied by administration of sodium [1-¹³C]-acetate and sodium [1,2-¹³C₂]-acetate to the culture.

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