Two novel lathyrane-type diterpenoids, the Euphorbia factors L2a (1) and L2b (2), and their stereoisomer Euphorbia factor L2 (3) were obtained from seeds of Euphorbia lathyris. Both Euphorbia factors L2a and L2b possess an unprecedented trans-gem-dimethylcyclopropane as structural feature. Also, the Euphorbia factor L2a is the first example of a lathyrane diterpenoid with an endocyclic 12(Z)-double bond. The structures of the molecules and their absolute configurations were elucidated by comprehensive spectroscopic analyses, Cu-Kα radiation X-ray diffraction, and comparison with calculated electronic circular dichroism (ECD) data. The Euphorbia factor L2b exhibited an inhibitory effect against U937 cell line with an IC50 value of 0.87 μM.
