Cytotoxic ent-kaurene diterpenoids from three Isodon species

From Isodon loxothyrsa, one new diterpenoid, loxothyrin A, together with one known diterpenoid, adenolin B, from I.pleiophyllus, three known diterpenoids, coetsoidins A, B and G, and from I. adenoloma, one known diterpenoid, longikaurin F, were isolated. The structure determination of loxothyrin A, and the unambiguous NMR spectral assignments of the known compounds were made by a combination of 1D and 2D NMR techniques and computer modelling calculations. The isolates showed potent cytotoxic activities.