Highly modified steroids from Inonotus obliquus†
Six undescribed steroids were isolated from the fungus Inonotus obliquus. Notably, compounds 1 and 2 represented the first example of 8,14-seco-4-methylpregnane. By spectroscopic data analyses, quantum chemical calculations and DP4+ probability analysis, their structures were unambiguously determined. The absolute configurations of the compounds 1–6 were defined by comparison of their experimental and calculated electronic circular dichroism (ECD) spectra data. The structure of compound 1 was also confirmed by single-crystal X-ray diffraction. All isolated steroids were evaluated for their neuroprotective activities against H2O2-induced cell injury in human neuroblastoma SH-SY5Y cells, among which compound 2 showed moderate activity at 12.5 μM.