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 IC₅₀ 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.

The polyphenols from the TP fraction of I. serra exhibited potent hepatoprotective effects against t -BHP-induced hepatotoxicity both in vitro and in vivo .

Three new ent-kaurane diterpenoids, isodosins E–G (1–3), along with 20 known ones (4–23), were obtained from the aerial parts of Isodon serra (Maxim.) Hara.