Studies on the constituents of Leonurus sibiricus L.

Two new furanoditerpene-lactones, LS-1 (1) and LS-2 (2), were isolated along with four known furanoditerpene-lactones 3, 4, 5 and 6 from the aerial part of Leonurus sibiricus L. The structures of the new compounds were determined by spectroscopic means. Compounds 1-6 isolated here exhibited moderate cytotoxic activity (IC(50)=50-60 microg/ml) against leukemia cells (L 1210) in tissue culture.