30-norlanostane triterpenoids and steroid derivatives from the endophytic fungus Aspergillus nidulans

Two undescribed 30-norlanostane triterpenoids, named nidulanoids A and B, one ergostane-type steroid with an unusual double bond between C-17 and C-20 designated (17E,22E,24R)-3β,5α-dihydroxyergosta-7,17,22-trien-6,16-dione, and one pregnane, (7Z,9Z,17Z)-,2α,3β-dihydroxypregna-7,9,17 (20)-trien-18-al, along with six known steroids were isolated from the extract of the fungus Aspergillus nidulans. Among them, nidulanosides A and B represents the first example of naturally occurred 30-norlanostane triterpenoids featuring a C9 side-chain moiety at C-17 and a hemiacetal system formed between C-3 and C-19, as an intermediate between lanostane and the regular steriods; the structure of (17E,22E,24R)-3β,5α-dihydroxyergosta-7,17,22-trien-6,16-dione possesses an untypical Δ17,20 double bond; meanwhile, (7Z,9Z,17Z)-,2α,3β-dihydroxypregna-7,9,17 (20)-trien-18-al represents the first example of C-21 steroid with an aldehyde group at C-13. Their structures and absolute stereochemistry were elucidated based on spectroscopic data, electronic circular dichroism (ECD) calculations, and single-crystal X-ray diffraction analysis. (7Z,9Z,17Z)-,2α,3β-dihydroxypregna-7,9,17 (20)-trien-18-al showed moderate inhibitory activities against rat brain cancer (PC12) cell lines, with IC50 value of 7.34 μM. This study enriches the diversified structures of triterpenoids and steroids analogues from A. nidulans and indicated (7Z,9Z,17Z)-,2α,3β-dihydroxypregna-7,9,17(20)-trien-18-al to be a promising lead compound against PC12 cell lines.