Diterpenes from Colophospermum mopane: "missing links" in the biogenesis of 9,13-epoxylabdanes.

Moponeol A (1) and moponeol B (2) were isolated from Colophospermum mopane along with a mixture of their corresponding aldehydes (3 and 4). These substances are primitive diterpenes that we view as the "missing links" in the biosynthesis of the 9,13-epoxylabdanes. The structures of 1 and 2 were elucidated by a combination of spectra (NMR and MS) of the isolates and their mono-p-bromobenzoyl derivatives. The structures of 3 and 4 were confirmed by their ready reduction to 1 and 2. The biosynthetic implications of the stereochemical assignments of these terpenoids are briefly discussed.