Three New 18-Oxygenated ent-Kaurane Diterpenoids from Isodon leucophyllus

Three new 18-oxygenated ent-kaurane diterpenoids, isoleuconins A-C (1–3) and ten known diterpenoids were isolated from the aerial parts of Isodon leucophyllus. The structures were elucidated by 1D and 2D NMR spectroscopic analysis. All of the compounds were evaluated for their cytotoxicity. Rabdokunmin A (13) showed significant cytotoxicity against HT-29 cells, with an IC50 value of 6.2 μM.