Structure of the diterpene clerodendrin A

Abstract

Clerodendrin A (I), a bitter principle of Clerodendron tricotomum Thunb. and an antifeeding repellent, is a diterpene with the clerodon skeleton as in clerodin (II). On oxidation with sodium periodate the dihydro-tetraol (XXVI) gave the acetal (XXVII). The formation of the acetal revealed the relative configuration of the epoxide ring and the 18-hydroxy-group. The c.d. and o.r.d. curves of the αβ-unsaturated ketone (XXXII), obtained by treatment of (XXVII) with manganese dioxide, showed a positive Cotton sign. Therefore, compound (I) has the configuration antipodal to that of clerodin. This was confirmed by X-ray analysis of the p-bromobenzoate of the chlorohydrin (XXII).