Antifungal activity of some coumarins obtained from species of Pterocaulon (Asteraceae)

Fractionation of antifungal hexane extracts of the aerial parts of three Pterocaulon spp., Pterocaulon alopecuroides, Pterocaulon balansae and Pterocaulon polystachyum (Asteraceae) from South Brazil traditionally used to treat animal mycoses, afforded the coumarins 5-methoxy-6,7-methylenedioxycoumarin, 7-(2',3'-epoxy-3'-methylbutyloxy)-6-methoxycoumarin, 6,7-methylenedioxycoumarin (ayapin), along with a mixture of 6-hydroxy-7-(3'-methylbutyl-2'-en-oxy)-coumarin (prenyletin) and 6-methoxy-7-(3'-methylbutyl-2'-en-oxy)-coumarin (prenyletin-methyl-ether). Among the different components of the active extracts, only the mixture of prenyletin and prenyletin-methyl-ether isolated from Pterocaulon polystachyum showed activity against Cryptococcus neoformans, Microsporum gypseum, Trichophyton rubrum and Trichophyton mentagrophytes. Nevertheless their MIC values were higher than the MIC of the original extracts, suggesting that the mixture but not only one compound would be the responsible for the activity detected in these Pterocaulon species.