Two novel ent-kaurane diterpenoids isolated from Isodon eriocalyx var. laxiflora

Two novel 3,6-epoxy-6,7:8,15-seco-7,20-olide-ent-kaurane diterpenoids laxiflorin F (1) and laxiflorin G (2) have been isolated from the leaves of Isodon eriocalyx var. laxiflora. The structure elucidation of 1 and 2 was accomplished by spectroscopic methods including 2D NMR analysis. The relative stereochemistry of 1 was established by single crystal X-ray crystallography, which also confirmed the novel carbon skeleton of the new ent-kaurane diterpenoid. Both compounds were tested for their cytotoxicity toward human leukemia K562 cells.