Bipolarsterol A, a steroid with an unprecedented 6/5/6/5 carbon skeleton from the phytopathogenic fungus Bipolaris oryzae

Abstract

Bipolarsterols A–H (1–8), eight undescribed steroids, were isolated from Bipolaris oryzae, along with nine known congeners. Their structures and absolute configurations were elucidated by comprehensive spectroscopic techniques, including NMR and ECD calculations. Compound 1 represents the first example of a 19(l0 → 5)-abeo-7(8 → 9)-abeo-ergostane, featuring an unusual spiro[4.5]decan-6-one system, and compound 2 is a new member of the rare steroid-phenylpropanoid hybrid class. Compound 5 showed remarkable cytotoxicity against HT29 cells with an IC₅₀ value of 5.8 μM. Compound 8 showed a significant inhibitory effect on NO production in RAW264.7 with an IC₅₀ value of 2.7 μM, through the inhibition of iNOS levels at the transcriptional and protein levels as well as the NF-κB pathway.