Diterpenoids from the Aerial Parts of Isodon serra with Selective Cytotoxic Activity.

Four new diterpenoids, isodosins A-D ( 1 - 4 ), together with nine known compounds ( 5 - 13 ) were isolated and identified from the aerial parts of Isodon serra (Maxim.) Hara. The structures of the new diterpenoids were elucidated based on the analysis of HR-ESI-MS data, 1D/2D-NMR-spectroscopic data, and electronic circular dichroism (ECD) calculations. Cytotoxicities of compounds 2 , 3 , 5 , 6 , and 9 against the HepG2 and H1975 cell lines were evaluated with the MTT assay. As a result, compounds 2 , 3 , and 6 revealed higher levels of cytotoxicity against HepG2 cells than against H1975 cells. Moreover, compund 6 demonstrated the most efficacy in inhibiting the proliferation of HepG2 cells, with an IC ₅₀ value of 41.13 ± 3.49 μM. This effect was achieved by inducing apoptosis in a dose-dependent manner. Furthermore, the relationships between the structures and activities of these compounds are briefly discussed.