Eringiacetal A, 5,6-seco-(5S,6R,7R,9S)-5,6:5,7:6,9-Triepoxyergosta-8 (14),22-diene-3β,7β-diol, an Unusual Ergostane Sterol from the Fruiting Bodies of Pleurotus eryngii.

A new rearranged ergostane-type steroid, named eringiacetal A (1), together with known compound 2, were isolated from the fruiting bodies of Pleurotus eryngii (Pleurotaceae). Its structure was fully elucidated by NMR spectroscopy and X-ray crystallography. Eringiacetal A (1) features an unprecedented 5,6-seco-(5S,6R,7R,9S)-5,6:5,7:6,9-triepoxyergosta-8(14),22-diene-3β,7β-diol. This is the first report of a 5,6-seco-ergostane-type steroid. A plausible biogenetic pathway of 1 from 2 is also described. Furthermore, isolated compounds were evaluated for inhibitory effects on nitric oxide (NO) production induced by lipopolysaccharide in macrophages. Compound 1 exhibited inhibitory activity on NO production (IC50 = 19.9 μM) accompanied by modest cytotoxicity (IC50 = 25.6 μM). Compound 2 did not have inhibitory effects on NO production or cytotoxicity (IC50 > 100 μM each).