An Unusual Meroterpenoid and Two New Steroids From Fungus <i>Penicillium fellutanum</i> and Their Bioactivities

An unusual clathrate-type meroterpenoid isoatlantinone A (1), two new steroids acrocalysterols E (2) and F (3), together with fifteen known compounds (4-18) were separated from a plant-associated fungus Penicillium fellutanum. Their structures and absolute configurations were established based on spectroscopic data (nuclear magnetic resonance and high-resolution electrospray ionization mass spectrometry), electronic circular dichroism and modified Mosher's method. Notably, compound 1 represents an unusual highly oxygenated meroterpenoid derivative with a unique caged bioxatetracyclo-[6.3.2.0^1,6.0^1,12]-tridecane ring system. All compounds were assessed in vitro for antifungal and cytotoxic activities. Intriguingly, compound 16 exhibited potent antifungal activity against Fusarium culmorum with a minimum inhibitory concentration value of 50 µM, similar to the positive control carbendazim. Furthermore, compound 3 displayed potent cytotoxic effects on HCC-1806, with a half-maximal inhibitory concentration (IC₅₀) value of 18.15 ± 1.05 µM, and compound 6 exhibited remarkable cytotoxic activities on RKO, with an IC₅₀ value of 11.61 ± 0.19 µM. Thus, strain P. fellutanum represents a novel resource of these bioactive compounds to be exploited.