6,7-seco-ent-Kaurane Diterpenoids from Isodon sculponeatus with Cytotoxic Activity

Six new 6,7‐seco‐ent‐kaurane diterpenoids, sculponeatins N–S (1–6, resp.), together with eleven known analogues, 7–17, were isolated from the aerial parts of Isodon sculponeatus. The structures of compounds 1–6 were elucidated by spectroscopic methods including extensive 1D‐ and 2D‐NMR experiments, as well as HR‐ESI‐MS analysis. All diterpenoids obtained were assayed for their cytotoxic activity against K562 and HepG2 human tumor cell lines. Among them, compound 1 showed the most significant cytotoxicity with the IC50 values of 0.21 and 0.29 μM, respectively. The structure–activity relationships are discussed.