A new nemoralisin-type diterpenoid from Aglaia lawii

A new nemoralisin-type diterpenoid, nemoralisin O (1), along with ten previously identified compounds, was obtained from Aglaia lawii bark. Structural characterisation was performed using various spectroscopic techniques, with a focus on 1D and 2D NMR, and HR-ESI-MS analysis. The absolute stereochemistry of compound 1 was established by comparing its experimental ECD spectrum with theoretical ECD spectra of all eight possible stereoisomers using TD-DFT calculations, and by evaluating compatibility of calculated H-1 chemical shifts with experimental values using DP4 probability method. The cytotoxic effects of some isolated compounds on HepG2 human liver cancer cells and the inhibition of alpha-glucosidase were evaluated. Compounds 4, 5, and 6 exhibited weak cytotoxicity against HepG2 cells, and showed no inhibitory activity against alpha-glucosidase (IC50 > 256 mu g/ml).