Ergopyrone, a Styrylpyrone-Fused Steroid with a Hexacyclic 6/5/6/6/6/5 Skeleton from a Mushroom Gymnopilus orientispectabilis

A styrylpyrone-fused ergosterol derivative, ergopyrone (1), was isolated and structurally characterized from a mushroom, Gymnopilus orientispectabilis, along with five biosynthetically related metabolites (2–6). Compound 1 features an unprecedented hexacyclic 6/5/6/6/6/5 skeleton that would be formed from ergosterol and styrylpyrone precursors via [3 + 2] cycloaddition. The chemical structure of 1 was elucidated by conventional spectroscopic and spectrometric data analysis coupled with computational methods including DP4+ probability and ECD simulation and an NOE/ROE-based interproton distance measurement technique via peak amplitude normalization for the improved cross-relaxation (PANIC) method. Plausible biosynthetic pathways of 1–6 are proposed, and compound 6 significantly regulated lipid metabolism in adipocytes through the upregulation of the mRNA expression of Adipsin, Fabp4, SREBP1, and ATGL.