Strophasterols E and F: Rearranged ergostane-type sterols from Pleurotus eryngii

Strophasterols E (1) and F (2) were isolated from the fruiting bodies of Pleurotus eryngii, together with four new ergostane-type sterols (3-6). Single-crystal X-ray diffraction analysis performed on the tris-p-bromobenzoate derivatives of compounds 1 and 2 allowed these two compounds to be identified as the structurally rare (22S,23R)- and (22S,23S)-5 alpha,6 alpha-epoxy-3 beta,7 beta,23-trihydroxy-15(14 -> 22)-abeo-ergost 8-en-14-one, respectively. The inhibitory effects on nitric oxide production of the six new steroids thus isolated from the fruiting bodies of P. eryngii were also evaluated.