The structure of ganervosin B, C22H30O6, a new diterpenoid from Rabdosia nervosa: an X‐ray study

C22H3006, M r = 390.5, orthorhombic, P212121, a = 7-714 (2), b = 9.555 (3), c-- 26.78 (1) A, V= 1973 (1)A 3, Z = 4, D x = 1.313 g cm -3, 2(Mo Ka) = 0.7107 A, g = 0.884 cm -1, F(000) = 840; R = 0.042 for 1646 diffraction data at room temperature. This compound is a new diterpenoid, ganervosin B (20,1- epoxymethano-21-ethoxy- 11 a-hydroxy-2,2-dimethyl-6- oxa- 18,19-dinor- 16-karene-7,15-dione), which has inter- nal strain in the D ring. This compound is expected to have anti-tumor activity. Introduction. In recent years, the chemical ingredients of Rabdosia have widely been studied, because some diterpenoids isolated from the plants of this genus have anti-tumor activity (Fujita & Node, 1984). The crystal structures of some anti-tumor drug molecules isolated from Rabdosia have been studied by means of X-ray diffractometry. It is found that the existence of interior stress in the molecule leads to an increase in the chemical reactivity of these drugs and probably bears a close relation to their anti-tumor activity (Chen, Wu & Cheng, 1987). Here, we report an X-ray study on the structure of ganervosin B, (1), a derivative of kaurane, a new diterpenoid from Rabdosia nervosa (Hemsl.), a species collected from the Wen Xian district of south Gansu province (Bai, 1987).