Aspersteroids A–C, Three Rearranged Ergostane-type Steroids from Aspergillus ustus NRRL 275

Aspersteroid A (1), a highly rearranged 1(10 → 6)-abeo-18,22-cyclosterol, together with two new 18,22-cyclosterols (2 and 3), was isolated from the culture extract of Aspergillus ustus NRRL 275. Their structures were determined by spectroscopic analysis, X-ray diffraction, modified Mosher’s method, and Rh₂(OCOCF₃)₄-induced electronic circular dichroism experiments. Compound 1 represents a new carbon skeleton with an uncommon 6/6/6/5/5 ring system, which is presumably biosynthesized from A-ring scission, double 1,2-shifts, and C-18/C-22 cyclization. Compound 1 exhibited potent immunosuppressive and antimicrobial activities.