Key Words: Ginkgolide derivatives / 1QEpiginkgolide derivatives / Ginkgo biloba L.3,14-Didehydro-10-hydroxyginkgolide[*1 (1) was prepared by 3c by means of a free-radical reduction with tri-n-butyltin reaction of 3,lO-dihydroxyginkgolide (3) (ginkgolide " A ) by hydride/u,u'-azobis(isobutyronitri1e) (AIBN). By heating the reaction with phosphoryl chloride in pyridine. Catalytic hy-14-epiginkgolides 2a and 2b and the ginkgolides 3a and 3b drogenation of 1 leads to 10-hydroxy-14-epiginkgolide (2a), in acetonitrile with DMAP an equilibrium on the side of the which was epimerized with 4-(dimethy1amino)pyridine ginkgolides was established. The constitution and configura-(DMAP) in acetonitrile to give 10-hydroxyginkgolide (3a). 14-tion of the compounds were proven by their 'H-and I3C-NMR Epiginkgolide (2d) and ginkgolide (3d) were obtained from spectra. 2a and 3a via the 10-0-phenylthiocarbonyl derivatives 2c and In 1971 we reported on the first studies toward the synthesis of the ginkgolide~[~'. These experiments were stopped because we were able to isolate the ginkgolides A, B and C in multigram quantities in that same year. Their constitution and configuration were established by X-ray Despite the undisputable methodical progress demonstrated by the multistep total synthesis of Corey and co-workers[61, it is of little interest as a practical route to ginkgolides.The ginkgolides show exceptional chemical properties.They are -despite the lactone rings -stable against acids but very susceptible to alkali. In this paper we report on the preparation of the ginkgolide skeleton 3d and its 14-epimer 2d in order to study their chemical and biological properties. be easily separated by flash chromatography on silica gel (toluene/acetone). Reaction of 2a/3a with 0-phenyl chlorothioformate and DMAP in acetonitrile leads to the 10-phenyloxy(thi0car-bonyl) derivatives 2c/3c. Free-radical reduction with tri-nbutyltin hydride and ap'-azobis(isobutyronitri1e) (AIBN) in toluene leads to 1Cepiginkgolide (2d) and ginkgolide (3d) 20

Herstellung von 1 ,lo-Dihydroxy-und 1,7,10-Trihydroxyginkgolid aus 1,3,7,10-Tetrahydroxyginkgolid