Scabrosteroids A–D, Four Pyrrolidinone–Ergosterol Heterodimers from <i>Penicillium scabrosum</i> FXI744

Scabrosteroids A-D (<b>1</b>-<b>4</b>), four novel steroidal heterodimers, were isolated from <i>Penicillium scabrosum</i> FXI744. These compounds represent the first naturally occurring pyrrolidinone-ergosterol hybrids, linked by a C-3/C-3' bond between pyrrolidinone and ergosterol moieties. Their structural elucidation, including the determination of absolute configurations, was accomplished using HRESIMS, NMR, X-ray crystallography, and ECD calculation. A plausible biosynthetic pathway for these metabolites was proposed. Biological evaluation revealed that compounds <b>1</b>-<b>4</b> inhibited NO production with IC₅₀ values ranging from 9.5 to 14.4 μM, and compounds <b>1</b> and <b>4</b> also showed moderate <i>in</i> <i>vitro</i> immunosuppressive effects.