Inducing Secondary Metabolite Production by Combined Culture of Talaromyces aculeatus and Penicillium variabile

Four new polyketides, penitalarins A-C (1-3) and nafuredin B (4), together with the known biogenetically related nafuredin A (5) were isolated from a mixed culture of a deep-sea-derived fungus Talaromyces aculeatus and a mangrove-derived fungus Penicillium variabile. Liquid chromatography/mass spectrometry analysis showed that none of compounds 1-5 was produced by either of the two fungi when cultured alone under the same condition. The structures of 1-4, including absolute configurations, were deduced based on the interpretation of MS, NMR data, and time-dependent density functional theory calculations of specific electronic circular dichroism spectra. Compounds 1-3 possess a 3,6-dioxabicyclo[3.1.0]hexane ring, and 4 showed cytotoxicity with IC50 values ranging from 1.2 to 9.8 mu M against a panel of human cancer cell lines.