An Unusual Meroterpenoid and Two New Steroids from Fungus Penicillium fellutanum 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 (NMR and HRESIMS), electronic circular dichroism (ECD) and modified Mosher's method. Notably, compound 1 represents an unusual highly oxygenated meroterpenoid derivative with a unique caged bioxatetracyclo-[6.3.2.01,6.01,12]-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 MIC value of 50 mM, similar to the positive control carbendazim. Furthermore, compound 3 displayed potent cytotoxic effects on HCC-1806, and IC50 value of 18.15 ± 1.05 μM, and compound 6 exhibited remarkable cytotoxic activities on RKO, with the IC50 value of 11.61 ± 0.19 μM. Thus, strain Penicillium fellutanum represents a novel resource of these bioactive compounds to be exploited.