Biosynthesis of natural products. Part 4. Biosynthesis of enmein and oridonin from mono- or di-oxygenated kaurenoids
Incorporation of mono-oxygenated ent-kaur-1 6-ene derivatives (6a), (7a), and (8a) and dioxygenated derivatives (9a) and (12a) into both enmein (3) and oridonin (4) and those of C-20 or C-3 oxygenated ent-kaurene derivatives (13a), (14a), (15a), and (16a) into (3) by Isodon japonicus Hara have been demonstrated by the tracer experiments using the corresponding labelled compounds. It is probable, on the basis of the experimental results, that the positions in (3) and (4) which are similarly oxygenated are not necessarily oxygenated simultanously at an early stage in the biosynthetic route from ent-kaurene (1). However, control of the biosynthesis of enmein (3) may be initiated by the introduction of the C-3 oxygen-function of ent-kaurene (1) at an early stage.