Biosynthetically Distinct Cytotoxic Polyketides from Setophoma terrestris

Sixteen polyketides belonging to diverse structural classes, including monomeric/dimeric tetrahydroxanthones and resorcylic acid lactones, were isolated from an organic extract of a fungal culture Setophoma terrestris (MSX45109) by bioactivity-directed fractionation as part of a search for anticancer leads from filamentous fungi. Of these, six were new: penicillixanthone B (5), blennolide H (6), 11-deoxyblennolide D (7), blennolide I (9), blennolide J (10), and pyrenomycin (16). The known compounds were: secalonic acid A (1), secalonic acid E (2), secalonic acid G (3), penicillixanthone A (4), paecilin B (8), aigialomycin A (11), hypothemycin (12), dihydrohypothemycin (13), pyrenochaetic acid C (14), and nidulalin B (15). The structures were elucidated by a set of spectroscopic and spectrometric techniques: the absolute configurations of compounds 1-10 were determined by ECD spectroscopy combined with time-dependent density functional theory (TDDFT) calculations, whereas a modified Mosher's ester method was used for compound 16. The cytotoxic activities of compounds 1-15 against the MDA-MB-435 (melanoma) and SW-620 (colon) cancer cell lines were evaluated. Compounds 1, 4, and 12 were the most potent, with IC50 values ranging from 0.16 to 2.14 M. When tested against a panel of bacteria and fungi, compounds 3 and 5 showed promising activity against the Gram-positive bacterium Micrococcus luteus, with MIC values of 5 and 15 gmL(-1), respectively.