In the course of screening vancomycin-resistant enterococci (VRE), two new meroterpenoids, streptoquinolines A (1) and B (2), were isolated from a culture of terrestrial Streptomyces sp. TMPU-A0679. The structures of 1 and 2 were elucidated based on spectroscopic analyses, including NMR and MS, and were found to consist of a drimane-type sesquiterpene fused with a highly substituted quinoline moiety. Further structural comparisons and specific rotation data revealed that 1 and 2 were epimers at C-4'. Compounds 1 and 2 both exhibited selective antibacterial activity against Gram-positive bacteria, including VRE and methicillin-resistant Staphylococcus aureus, with minimum inhibitory concentrations ranging from 6.25 to 12.5 µg/mL. These results expand the structural and biological diversities of drimane-quinoline-type meroterpenoids and highlight their potential as lead compounds for the development of new antibacterial agents targeting drug-resistant Gram-positive pathogens.
Yagi et al. (Tue,) studied this question.