Cytotoxic ent-Kauranoids from the Medicinal Plant Isodon xerophilus

Bioassay-directed fractionation of the leaves of the medicinal plant Isodon xerophilusled to the isolation of a series of potential antitumor molecules. Thirteen new (1−13) and 23 (14−36) known diterpenoids were isolated and identified, representing ent-kauranoids of several structural types. The structures of 1−13were determined by means of spectroscopic studies. The absolute configurations of the new compounds were clarified by CD spectroscopic studies or were postulated on biogenetic grounds. All compounds obtained were evaluated for their cytotoxic activity against the K562, MKN45, and HepG2 cell lines. Compounds 1, 2, 11, 16−19, 23, 26−28, 30, and 32demonstrated significant cytotoxic activity for one or more cell lines.