| abstract |
The invention relates to a process for the preparation of ginkgolide B from ginkgolide C and to ginkgolide B thus obtained, the process comprising the following succession of four steps: n protecting the 10-hydroxy group of ginkgolide C by conversion to an alkyl ester, the reaction being effected in dimethylformamide at a temperature of from 15° to 50° C. for from 4 to 10 hours; n activating the 7-hydroxy group of the resultant 10-protected ginkgolide C by conversion to a (R)thiocarbonyl ester, the activation being effected in basic conditions at a temperature of from 0° to 40° C. for from 1 to 24 hours; n deoxygenating the 7-activated group in the resultant 10-protected 7-activated ginkgolide C by treating it with tributyltin hydride or tris-(trimethylsilyl)silane, in an aprotic solvent, in the presence of a free-radical generator, the reaction being effected at a temperature of from 70° to 110° C. for from 15 minutes to 3 hours under inert atmosphere, and n cleaving the protecting group from the 10-hydroxy group of the resultant 10-protected ginkgolide B. |