23 Geranylfarnesyl Pyrophosphateの酵素的閉環 : 無細胞系によるsesterterpeneの生合成研究

抄録

Mevalonic acid lactone and the chemically synthesized alltrans geranylfarnesyl pyrophosphate (14) are converted into a tricyclic sesterterpene alcohol, ophiobolin F, by the incubation with 100,000xg supernatant fraction from cell free system of eochliobolus heterostophus Mycelia of C. heterostrophus was ground in a mortar with sands in phosphate buffer containing MgCl_2, and the homogenate was centrifuged first at 1,000xg and then at 100,000xg for 1hr. The supernatant enzyme fraction was incubated with 2-^<14>C-MVA in the presence of ATP. It has been found that the enzymic reaction product was identical with ophiobolin F which was found to occur in crude metabolites of the fungi as a very minute amount. The structure and stereochemistry of ophiobolin F was established as 1 by the chemical correlation of it into ophiobolin C (2) whose absolute structure was known. All-trans-geranylfarnesyl pyrophosphate (14) and the terminal cis-isomer (15) were synthesized from geranyllinalool and were incubated with 100,000xg supernatant fraction under the same condition described above. It was found that only all-trans pyrophosphate ester was incorporated into the tricyclic alcohol 17. The data presented provide the first experimental evidence for the intermediary role of geranylfarnesyl pyrophosphate in the sesterterpene biosynthesis