Asperflotone, an 8(14→15)-abeo-Ergostane from the Sponge-Derived Fungus Aspergillus flocculosus 16D‑1

A novel 8(14→15)-abeo-ergostane-type steroid, asperflotone (1), and an ergostane steroid, asperfloroid (2), were isolated from the solid culture of Aspergillus flocculosus 16D-1. Their structures and absolute configurations were determined by high-resolution electrospray ionization mass spectrometry, 1D/2D NMR, X-ray crystallography, and quantum chemical calculations. Compound 1 is an unprecedented ergosteroid featuring a rearranged bicyclo[4.2.1]­non-2-ene ring system that could result from α-ketol rearrangement during biosynthesis. Compounds 1 and 2 showed inhibitory activity toward IL-6 production in the induced THP-1 cells.