Isolation, Structure, and Antibacterial Activity of Phaeosphenone from a Phaeosphaeria sp. Discovered by Antisense Strategy

Ribosomal protein S4 (RPSD), a part of the ribosomal small subunit, is one of the proteins that is a part of the ribosomal machinery and is a potential new target for the discovery of antibacterial agents. Continued screening of microbial extracts using antisense-sensitized rpsD Staphylococcus aureus strain led to the isolation of a new dimeric compound, phaeosphenone (2). Compound 2 showed broad-spectrum antibacterial activity against Gram-positive bacteria, exhibiting MIC values ranging from 8 to 64 μg/mL. Phaeosphenone showed the highest sensitivity for Streptococcus pneumoniae (8 μg/mL) and inhibited the growth of Candida albicans with an MIC of 8 μg/mL. Phaeosphenone showed a modest selectivity for the inhibition of RNA synthesis over DNA and protein synthesis in S. aureus.