Enmein-type 6,7-seco-ent-Kauranoids from Isodon sculponeatus

Fourteen enmein-type 6,7-seco-ent-kaurane diterpenoids, seven new ones (sculponins M–S, 1–7) and seven known compounds (8–14), were isolated from the aerial parts of Isodon sculponeatus. Compound 1 is the first example of an ent-kauranoid, possessing a 11,12-epoxy group, and compounds 6 and 7 have a rare 3,6-epoxy group. The structures were established primarily by NMR and MS methods, and the absolute configurations of 1, 3, and 6 were determined by single-crystal X-ray diffraction. Compound 14 showed significant cytotoxic activity against five human tumor lines, with IC50 values ranging from 1.0 to 3.5 μM, and it also inhibited NO production in LPS-stimulated RAW264.7 cells, with an IC50 value of 2.2 μM.