ON A NEW SYNTHESIS OF STERPURENE AND THE BIOACTIVITY OF SOME RELATED CHONDROSTEREUM-PURPUREUM SESQUITERPENE METABOLITES

Sterpurene, a sesquiterpene hydrocarbon metabolite of Chondrostereum p urpureum, a plant pathogen and potential mycoherbicide, was synthesize d by a six-step sequence, in 33% overall yield. The key steps were a t hermal [4 + 2] (Diels-Alder) cycloaddition of a ketene acetal diene wi th a conjugated eater dienophile, and a remarkably stereoselective [2 + 2] photocycloaddition of ethylene with the resulting conjugated keto ne. Several related, more highly oxygenated, metabolites isolated from culture filtrates of C. purpureum (cf. Ayer) were tested for toxicity to cells of a hybrid aspen, Populus deltoides X nigra. Their phytotox icity, at concentrations as low as 10 ppm, suggests that, like the end o-polygalacturonase produced by the fungus, these sesquiterpenes may b e partially responsible for the foliar lesions associated with infecti on of deciduous species by the pathogen.