Five undescribed cassane diterpenoids were obtained from the seeds of Pterolobium macropterum. Their structures were established through extensive 1D and 2D NMR spectroscopy, and mass spectrometry. Their absolute configurations were assigned by electronic circular dichroism spectrum. Compounds 1 and 3 exhibited cytotoxic effects for the human glioma U251 cells with IC50 values of 28.48 ± 2.7 and 14.43 ± 7.8 μM, respectively.
Li et al. (Tue,) studied this question.