Biosynthesis of Sclareol, p-Sitosterol, and Oleanolic Acid from Mevalonic Acid-2-C”*

In previous studies of the incorporation of sodium acetateZ-Cl4 (1, 2) and sodium mevalonate-2-C14 (2) into &sitosterol and the acidic triterpenes of Salvia oficinalis, Cl4 from both precursors was found in sterol and triterpenes. The presence of sclareol (Fig. l), /3-sitosterol, oleanolic acid, and ursolic acid II (3, 4) in the plant Xalvia sclarea has afforded an opportunity to duplicate these observations in another species of Labiatae and to study the incorporation of an efficient isoprenoid precursor into a bicyclic triterpene. Little or no information is available on the biosynthesis and metabolism of diterpenes in higher plants (5). As in the previous work (1, 2), the use of a single plant for the simultaneous study of diterpene, sterol, and pentacyclic triterpene metabolism is advantageous. It cannot be assumed from data in the literature that an isoprenoid precursor like mevalonic acid will necessarily be incorporated into all terpenoid substances of higher plants. For this report, therefore, we were primarily interested in determining the extent to which mevalonic acid-2-C14 is incorporated into diterpene, sterol, and triterpene and the relative contribution of the precursor to the terpenoid substances in various organs. A preliminary report of this study has been published (6).