Ginkgolide and bilobalide biosynthesis in Ginkgo biloba. II : Identification of a possible intermediate compound by using inhibitors of cytochrome P-450-dependent oxygenases

Abstract

The presence of diterpene hydrocarbons as biosynthetic intermediates in the formation of ginkgolides and bilobalide has been investigated in Ginkgo biloba seedlings. Diterpene hydrocarbons are present only in roots. as trace amounts (1-3 μg g -1 FW). Dehydroabietane is the main hydrocarbon compound. Two inhibitors of cytochrome P-450-dependent oxygenases, teteyclacis and clotrimazole, were supplied to the seedlings via the roots in order to deregulate the terpene pathway. As a consequence of the treatment with inhibitors, the ginkgolide and bilobalide content was lowered, both in roots and leave. A treatment with 10 mM tetcyclacis was more effective than a 100 mM clotrimazole treatment and resulted in a strong increase (up to 41 times of diterpene hydrocarbons in roots This increase concerned primarily dehydroabietane. 14 CO 2 feeding experiments. following 10 μM tetcyclacis treatment, showed that only dehydroabietane was highly labelled. The absence of labelling in both ginkgolides and bilobalide indicates that the oxygenation reactions leading to the end-products are fully inhibited. All together, these results support the existence of a precursor-product relationship between dehydroabietane and ginkgolides plus bilobalides. The biosynthesis of oxygenated terpenes in G. biloba proceeds via a hydrocarbon intermediate.