Rabdosia japonica

The biosynthesis of enmein (62) and oridonin (32), the major bitter principles in the leaves of Rabdosia japonica, has been investigated by E. Fujita and coworkers. It is thought to proceed by a pathway similar to that for cyclic diterpenoids in general, with e r-16-kaurene (116) as an important precursor. A biogenetic pathway and a classification of the Rabdosia diterpenoids based on the biogenesis were proposed 123). 

Secondly, the relative efficiencies of 15- and 7-mono-oxygenated kaurenes (195, 201) and 7,15-dioxygenated kaurene (204) as precursors were examined by use of the double-isotope technique (128). Thus, [17- " C]-and [18- HJ-labeled 7,15-dioxokaurene (204a, 204b) were prepared (127), and mixtures of (204b) and (201 a), of (204 a) and (201b), and of (204 b) and (195 a) were fed to Rabdosia japonica plants. The mono-oxo kaurenes (195, 201) were found to be more effectively incorporated into enmein and oridonin than the dioxo compound (204). 

The first report on antibacterial activity of Rabdosia constituents appeared in 1954, when it was discovered that a crystalline substance isolated from the ethanolic extract of Rabdosia japonica inhibited the growth of Gram-positive bacteria (i). Later two groups found that an extract of R, trichocarpa also had antibacterial and antitumor activities 131, 132). It was shown (133) that the activity was due to enmein. Dihydroenmein was inactive, while (9,(9-diacetylenmein remained active. Hence it was assumed that the biologically active site of enmein was the a-methylenecyclopentanone moiety (133). 

IsOBE, T., Y. Nod A, and T. Kubota The Constituents from Rabdosia japonica. Nippon Kagaku Kaishi 1982, 883. 

Nagao, Y., and E. Fujita Studies for Exploitation of the Biologically Active Components in Enmei-so (Rabdosia japonica Kara and R. trichocarpa Kudo) and Related Plants. Proc. Symp. Wakan-Yaku 13, 79 (1980). 

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