Two new tetracyclic diterpenes of the rarely reported cyclopiane class, conidiogenones H and I (1 and 2, resp.), along with five related congeners, conidiogenones B - D and F (3-5 and 6, resp.) and conidiogenol (7), were characterized from the culture extracts of Penicillium chrysogenum QEN-24S, an endophytic fungus derived from an unidentified marine red algal species of the genus Laurencia. The structures of these compounds were established on the basis of extensive spectroscopic analysis. The inhibitory activity of theses diterpenes against four bacteria and one pathogen fungus was evaluated. Conidiogenone B (3) showed potent activity against Methicillin resistant Staphylococcus aureus (MRSA), Pseudomonas fluorescens, P. aeruginosa, and Staphylococcus epidermidis (each with a MIC value of 8 μg/ml), while conidiogenol (7) showed obvious activity against P. fluorescens and S. epidermidis (each with a MIC value of 16 μg/ml). This is the first report on antimicrobial activity of cyclopiane diterpenes.

2011 Verlag Helvetica Chimica Acta AG, Zürich.