Citrifelins A and B, Citrinin Adducts with a Tetracyclic Framework from Cocultures of Marine-Derived Isolates of Penicillium citrinum and Beauveria felina

Citrifelins A (1) and B (2), two citrinin adducts possessing a unique tetracyclic framework, were characterized from a coculture of marine-derived fungal isolates of Penicillium citrinum and Beauveria felina. Neither fungus produced these compounds when cultured alone under the same conditions. The structures of these adducts were elucidated on the basis of spectroscopic analysis, and the absolute configurations were assigned on the basis of TDDFT-ECD calculations. A hypothesis that adducts 1 and 2 might be derived from a citrinin derivative through a non-pericyclic Michael reaction is proposed. Compounds 1, 2, and 5 showed inhibitory activities against several human and aquatic pathogens.