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Extracts from the Andean lichens Protousnea poeppigii and Usnea florida displayed antimicrobial activity against the pathogenic fungi Microsporum gypseum, Trichophyton mentagrophytes and T. rubrum with MIC values between 50 and 100 µg/mL. From the active extracts, four main metabolites were isolated and identified as the new depside, isodivaricatic acid, and the known metabolites 5-propylresorcinol, divaricatinic acid and usnic acid. Isodivaricatic acid and divaricatinic acid presented antifungal effect towards M. gypseum with a MIC of 50 µg/mL and against T. mentagrophytes and T. rubrum and with MIC values of 50 and 100 µg/mL, respectively. The new isodivaricatic acid was active towards Leishmania amazonensis, Leishmania brasiliensis and Leishmania infantum promastigotes with 100% lysis at 100 µg/mL. The activity of the new compound decreased on acetylation of the hydroxy groups as well as on methylation of the acid function. The structures were elucidated by spectroscopic means. The spectroscopic data of isodivaricatic acid are presented here for the first time. Copyright © 2007 John Wiley & Sons, Ltd.

Biotransformation of the diterpene jatrophone (1) by Aspergillus niger ATCC 16404 afforded the new diterpene 9β -hydroxyisabellione (2). The compounds were characterized by spectroscopic analysis. The cytotoxicity of the compounds as IC₅₀ values on AGS and lung fibroblasts was 2.4 and 2.8 μM for compound 1 and 53.1 and 260 μM for 2, respectively. Microbial transformation of 1 into compound 2 strongly reduced the cytotoxicity and enhanced the selectivity against AGS cells.