Chemical and bioactive natural products from Microthyriaceae sp., an endophytic fungus from a tropical grass

In screening for natural products with antiparasitic activity, an endophytic fungus, strain F2611, isolated from above‐ground tissue of the tropical grass P aspalum conjugatum ( P oaceae) in P anama, was chosen for bioactive principle elucidation. Cultivation on malt extract agar ( MEA ) followed by bioassay‐guided chromatographic fractionation of the extract led to the isolation of the new polyketide integrasone B ( 1 ) and two known mycotoxins, sterigmatocystin ( 2 ) and secosterigmatocystin ( 3 ). Sterigmatocystin ( 2 ) was found to be the main antiparasitic compound in the fermentation extract of this fungus, possessing potent and selective antiparasitic activity against T rypanosoma cruzi , the cause of C hagas disease, with an IC 50 value of 0·13  μ mol l −1 . Compounds 2 and 3 showed high cytotoxicity against Vero cells ( IC 50 of 0·06 and 0·97  μ mol l −1 , respectively). The new natural product integrasone B ( 1 ), which was co‐purified from the active fractions, constitutes the second report of a natural product possessing an epoxyquinone with a lactone ring and exhibited no significant biological activity. Strain F2611 represents a previously undescribed taxon within the M icrothyriaceae ( D othideomycetes, A scomycota). Significance and Impact of the Study The present study attributes new antiparasitic and psychoactive biological activities to sterigmatocystin ( 2 ), and describes the structure elucidation of the new natural product integrasone B ( 1 ), which possesses a rare epoxyquinone with a lactone ring moiety. This is also the first report of sterigmatocystin ( 2 ) isolation in a fungal strain from this family, broadening the taxonomic range of sterigmatocystin‐producing fungi. The study also presents taxonomic analyses indicating that strain F 2611 is strongly supported as a member of the M icrothyriaceae ( A scomycota), but is not a member of any previously known or sequenced genus.