Unstable Tetramic Acid Derivatives from the Deep-Sea-Derived Fungus EIODSF 008.

Seven new unstable tetramic acid derivatives, cladosporiumins I-O (⁻), together with the known analogue cladodionen () were isolated from the extract of the deep-sea-derived fungus EIODSF 008. Their structures were elucidated by spectroscopic analysis, quantum chemical calculations and ECD spectra. Compound was a Mg complex of tetramic acid derivative. In acidic solvent, could change to and , and could change to . In addition, , and existed as two exchangeable isomers, respectively. The structures of cladosporiumins E-H were reassigned as their Na complexes. The antibacterial and cytotoxic activities of ⁻ were also evaluated. However, because of their instability, all of the isolated compounds did not show significant antibacterial activity as the preliminary EtOAc extracts of the fungal strain.