ANTIMICROBIAL ABIETANE DITERPENOIDS FROM PLECTRANTHUS ELEGANS

Two novel abietane diterpenoids have been isolated from the aerial mat erial of Plectranthus elegans and identified as 11-hydroxy-12-oxo-7,9( 11),13-abietatriene and 7 lpha,11-dihydroxy-12-methoxy-8,11,13-abietat riene. Their structures were determined through rigorous use of spectr oscopic methods. Both inhibited spore germination of the fungus Clados porium cucumerinum, in direct bioautography, at a dose of 1 pg. The ne w diterpenes also inhibited the growth of Gram-positive bacteria, in t he concentration range 10-40 mu g ml(-1) in broth dilution assay. No e ffect was observed against Gram-negative bacteria. The ecological impl ications of these findings are discussed.