Studies of some new Euphorbiaceae diterpenes.

Abstract

The heartwoods of two species of South African Euphorbiaceae have been chemically investigated. From Cleistanthus schlechteri three new diterpenes possessing the hitherto unknown ent-isopimara-8(14),15-diene skeleton were isolated. By means of chemical and spectroscopic methods these were shown to be 3a-hydroxy-ent isopimara-8(14),15-diene, I, 3a-hydroxy-ent-isopimara- 8(14},15-dien-12-one, II, and 3a,12a-dihydroxy-ent-isopimara- 8(14),15-diene, III. A biogenetic sequence has been proposed in which it is suggested that these compounds are probably the precursors of the major diterpenoid, cleistanthol, IV, previously isolated from this source. From the second species, Spirostachys africana, a new diterpenoid seco-acid, spirostachic acid, VIII, was obtained in addition to the beyerene derivatives previously reported. Mass spectral fragmentation patterns of the seco-acid and its methyl esters proved to be useful as a diagnostic tool in structure elucidations.