STUDIES IN TERPENOID BIOSYNTHESIS .4. BIOSYNTHESIS OF KAURENOLIDES AND GIBBERELLIC ACID

Geranylgeraniol and (-)-labda-8,13-dien-15-ol pyrophosphate have been shown to act as precursors of (-)-kaurene, the kaurenolides, and gibberellic acid. The labelling pattern from 4-(R)-[4-3H]- and 2-[3H 2]-mevalonic acid in these tetracyclic diterpenes has been determined and this evidence is used to exclude (-)-pimara-7,8-and -8,9-dienes from the biosynthesis. (-)Pimara-8(14)-diene has been shown to be specifically incorporated into the kaurenolides and gibberellic acid. The stereochemistry of hydroxylation of ring A of the gibberellins has been shown to proceed with retention of configuration. The loss of the angular C-20 atom in the formation of the C-19 gibberellins does not involve the decarboxylation of a 4-, 4b-, or 10a-unsaturated acid.