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.