31 うおとりしきぶ(Callicarpa candicans)の殺魚成分Callicarponeの構造

抄録

A fish-killing component, callicarpone, C_<20>H_<28>O_4, m.p. 111°, [α]^<23°>_D-188°, isolated from the leaf of Callicarpa candicans was proved to be represented by the structure I on the following evidences. The IR, UV and NMR spectral data suggested that I had one tertiary hydroxyl and ene-1,4-dione. Tetraol (IIa), obtained by lithium aluminum hydride reduction of I consisted of two secondary hydroxyls and 1,2-glycol of two tertiary hydroxyls, one of which was involved in α-hydroxy-isopropyl group. This finding, coupled with formation of chlorohydrin (III) showed an oxide ring attached to α-hydroxy-isopropyl group was present in I. It is, therefore, apparent that I is a tetracyclic diterpene. Treatment of I in methanol with sodium carbonate gave a diphenol A (IVa), C_<20>H_<28>O_4 and a smaller amount of diphenol B (Va), C_<17>H_<22>O_3. The structure of this rearranged product (IVa) was established by identifying IVh as 11-methoxy ferruginol methyl ether. As this rearrangement was assumed to be initiated by proton abstraction by base, placement of the oxide ring in 12, 13-position in I was required to explain the formation of IVa. Formation of Va as a minor product was also well explained by aromatization accompanied by liberation of acetone from I.