Isolation of Cneorubin X, an unusual diterpenoid from Ptaeroxylon obliquum (Ptaeroxylaceae).

The genera Ptaeroxylon and Cedrelopsis have been grouped together by Styles and Pennington into the Ptaeroxylaceae family due to similarity in their morphology and structure of the secondary xylem. The monospeci"c genus Ptaeroxylon had previously been placed in the Sapindaceae, the Rutaceae, and most popularly, in the Meliaceae families. The pollen of Cedrelopsis and Ptaeroxylon are very similar, unlike that of any Meliaceae pollen grain but similar to that of some Rutaceae (Styles and Pennington, 1975). The grouping together of Cedrelopsis and Ptaeroxylon is supported by chemical evidence: the wood of both was found to contain a variety of chromones and coumarins but no limonoids (Dean and Taylor, 1966; Dean et al., 1967a}c; McCabe et al., 1967; Eshiett and Taylor, 1968; Dean and Robinson, 1971). We have recently