Biological activity of guanacastepene, a novel diterpenoid antibiotic produced by an unidentified fungus CR115

Fermentation extracts of culture CR115, an unknown plant endophyte original ly isolated from Costa Rica. were found to be active against antibiotic-res istant bacteria. The metabolite responsible for activity was identified as a novel diterpenoid antibiotic guanacastepene (mol. wt. 374.47 and mol. for mula C22H30O5). Mechanistic studies done in an E. coli imp strain suggested membrane damage as the primary mode of bactericidal action. This compound also lysed human RBCs and caused leakage of intracellular potassium from E. coli imp.