Antimicrobial Polyketides from the Marine-Derived Fungus Spiromastix sp. SCSIO F190.

Three diphenyl ethers ( 1 - 3 ) and a cyclopentenone ( 4 ), together with seven known compounds ( 5 - 11 ), were isolated from the fermentation broth of the marine sediment-derived fungus Spiromastix sp. SCSIO F190. Compounds 3 and 4 were found to exist as a pair of atropisomers ( 3a , 3b ) and racemates ( 4a , 4b ), respectively. The planar structures of compounds 1 - 4 were elucidated on the basis of NMR and HRESIMS data sets. The absolute configurations of 2 and 3 were determined by spectroscopic and single-crystal X-ray diffraction analyses, whereas the configuration of 4 was determined by spectroscopic and chiral analyses. All compounds, except for 4 and 11 , displayed activities against various pathogenic bacteria. Notably, compounds 1 - 4 , especially 1 , exhibited strong activity against Gram-positive bacteria, including methicillin-resistant bacterial strains of Staphylococcus aureus (MRSA), Enterococcus faecalis ATCC 29212, and Bacillus subtilis BS01, with MIC values ranging from 0.5 to 4 μg/mL. Moreover, the structure-activity relationship analyses of the active compounds and their analogues revealed the critical structural features correlating to the observed antimicrobial activities, herein providing insights for antimicrobial drug development.