Studies on Fish-killing Components of Callicarpa candicans

A fish-killing component, which was named callicarpone, C₂₀H₂₈O₄, m.p. 111°C, ${\alpha ]}_{\text{D}}^{{23}^{°}}$ ?180° (chloroform) was isolated from the leaf of Callicarpa candicans and was found to have conjugated carbonyl groups, double bond and one hydroxyl group. The toxicity to fish was evaluated to be as strong as rotenone and ten times stronger than sodium pentachlorophenoxide.

It was deduced from the spectral data of callicarpone (I), the tetraol (IV), the chlorohydrin (VII) and the anhydro-diacetyl derivative (II) that I was a tricarbocyclic diterpene having an ene-l,4-dione and an α-hydroxy-isopropyl attached to an oxide ring. The structure of the rearranged product obtained by treatment with sodium carbonate was established to be IX by converting it to 11-methoxy-ferruginol methyl ether. As this rearrangement was assumed to be initiated by proton abstraction by base, the structure I was required for callicarpone to explain the formation of IX.