26 十員環セスキテルペノイドの酵素によるエポキシ化反応

抄録

Germacradiene derivatives are thought to be precursors of a number of bicarbocyclic sesquiterpenoids. It is considered that the transformation from the former to the latter is initiated mainly by epoxidation of a double bond followed by cyclization of the resultant epoxide, during which the first epoxidation process must be stereospecific since it is conducted by an enzyme. Our interests on the stereospecificity of the reaction caused us to examine the enzymatic epoxidation using sesquiterpenoids of Curcuma zedoaria. Zederone (III), a constituent, is considered to be biosynthesized from furanodienone or isofuranodienone, the other constituents, each of which has been shown to be the 1: 1 mixture of the conformer I or II and its enantiomeric one, respectively. After the deduction of the conformation and absolute configuration of zederone as III A by spectral evidence, it is evident that the oxidation enzyme of the plant attacks stereospecifically on one (I) of the two enantiomeric conformers of furanodienone to afford zederone. On the other hand, fermentation of germacrone (V), another constituent of C. zedoaria, with the microbe Cunninghamella blakesleeana was carried out to yield two monoepoxides and a diepoxide whose conformations and absolute configurations have been deduced as VI, VII and VIII on the basis of the spectral evidence. Therefore, it is concluded that the oxidation enzyme induced by the microbe also has an affinity for one (V) of the two enantiomeric conformers, similar to I, selectively.