Actinomadurol, an Antibacterial Norditerpenoid from a Rare Actinomycete, Actinomadura sp. KC 191

A new secondary metabolite, actinomadurol (1), was isolated along with the known compound JBIR-65 (2) from a rare actinomycete, Actinomadura strain KC 191. The structure of 1 was established as a rare member of the bacterial C-19 norditerpenoid class by NMR data and ECD calculations. The absolute configuration of 2, which was previously reported without stereochemical analysis, was determined by using the modified Mosher’s method and ECD calculations. Actinomadurol (1) exhibited potent antibacterial activity against pathogenic strains, such as Staphylococcus aureus, Kocuria rhizophila, and Proteus hauseri (MIC = 0.39–0.78 μg/mL), whereas JBIR-65 (2) showed no antibacterial activity.