19 Shiromodiol-Diacetateの絶対構造

抄録

Three insect antifeedants, shiromodiol-diacetate, shiromodiol-monoacete and shiromool were isolated from the leaves of Parabenzoin trilobum Nakai. This report presents evidence which let us assign the absolute configuration (I) for shiromodiol-diacetate. On alkaline hydrolysis I, C_<19>H_<30>O_5 gave shiromodiol (II), C_<15>H_<26>O_3. Hydrogenation of II gave tetrahydro derivative (III). The comparison of the nmr of I and IV shows the presence of the partial structures (CH_3-C=CH, CH_3-C-O-CH) in I. On this basis, I has to be a monocarbocyclic compound. The spectral data of the oxidized products (V, VI, VII) suggest the presence of the partial structures, CH=C(CH_3)-CH_2-CH(OAc)- and CH_3-C-O-CH-CH(OAc)-CH in I. Moreover, dehydrogenation of I with Pd/C gave a 1.4.7-substituted azulene. This indicates that I has germacrane skeleton. Ozonolysis of I followed by the acid treatment, NaOH-AgNO_3 oxidation and NaIO_4 oxidation gave levulinic acid. Thus, the structure (I) was reasonably assigned to shiromodiol-diacetate. The relative configuration of I was assigned by the detailed analysis of the nmr spectrum of XI. The absolute configuration of I was finally established from the ORD of β,γ-unsaturated chromophore in V and VI.