Emericellopsic acid, a helvolic acid derivative with a 6/5/7/5 tetracyclic skeleton from sponge-derived Emericellopsis maritima.

Emericellopsic acid (1), the first B/C ring-rearranged fusidane-type antibiotic possessing a 6/5/7/5-fused ring framework, together with seven known helvolic acid derivatives, was isolated from the sponge-associated fungus Emericellopsis maritima IMB18-123 cultivated with autoclaved Pseudomonas aeruginosa. The structure of 1 was determined by extensive spectroscopic data analysis combined with ECD calculation. Compound 1 exhibited moderate antimicrobial activities against Staphylococcus aureus and S. epidermidis with the minimum inhibition concentration of 4-8 μg ml.