Two new toxic substances, euphoscopins A and B, have been isolated from the plant Euphorbia helioscopia L., and their absolute stereostructures also been elucidated on the basis of their spectral data coupled with an X-ray crystallographic analysis of the e-bromobenzoate readily obtained on treatment of euphoscopin A with p-bromobenzoyl chloride -pyridine. These antitumor substances belong to a group of jatrophone-type diterpenes. Many structural studies have been reported for antitumor activity on a number of polyoxygenated diterpenes including ingenol, phorbol, jatrophone and others.' Among them, however, only three substances having the jatrophone skeleton have been found in nature. 2 In addition, recently, Bohlmann and his co-workers isolated a new jatrophone-type diterpene, euphornin,3 from the plant Euphorbia maddeni B., and proposed a tentative stereostructure for this substance, in which the configuration at the ring junction of the bicyclic carbon skeleton is cis. This structural study prompted us to report our new results concerning about the isolation and the absolute stereostructures of two new polyoxygenated diterpenes, euphoscopins A and B. Fresh leaves and roots of the plant Euphorbia helioscopia L. (2.2 Kg) collected at Kanagawa, early in June, were immersed in MeOH at room temperature, and then the MeOH extract was concentrated and shaken with AcOEt. The AcOEt extract was directly chromatographed on silica gel (Mallinckrodt, 100 mesh). After elution of esters of higher fatty acids with CHC13, further elution with CHC13 -AcOEt (2 : 3) afforded a crude oil, which was further separated by repeating preparative TLC (kieselgel PF254) using hexane -Et20 (2 : 3), hexane -AcOEt (3 : 1) and/or CHC (1, l3 -AcOEt (10 : 1) to give two diterpenes, named euphoscopin A (1) and euphoscopin B (2 34 mg; 2, 77 mg). The physical data of these two substances are shown below.