Bioactive abietane and ent-kaurane diterpenoids from Isodon tenuifolius

Three new abietane diterpenoids, isoabietenins A-C (1-3), and 13 new ent-kauranoids, tenuifolins A-M (4-16), along with four known compounds (17-20), were isolated from the aerial parts of Isodon tenuifolius. The structures of the new metabolites were established on the basis of detailed spectroscopic analysis. The absolute configurations of 1, 15, and 16 were confirmed by single-crystal X-ray diffraction. Selected compounds were evaluated for their cytotoxicity against a small panel of human tumor cell lines, and some compounds showed inhibitory effects. Furthermore, several isolates exhibited inhibitory activity against nitric oxide production in LPS-activated RAW264.7 macrophages.