Chalcomycins from Marine-Derived Streptomyces sp. and Their Antimicrobial Activities.

Dihydrochalcomycin (1) and chalcomycin, (2), two known chalcomycins, and chalcomycin E (3), a new compound, were isolated from marine-derived Streptomyces sp. HK-2006-1. Their structures were elucidated by detailed spectroscopic and X-ray crystallographic analysis. The antimicrobial activities against Staphylococcus aureus, Escherichia coli, Candida albicans, and Aspergillus niger of 1-3 were evaluated. Compounds 1-2 exhibited activities against S. aureus with minimal inhibitory concentrations (MICs) of 32 µg/mL and 4 µg/mL, respectively. The fact that 1-2 showed stronger activity against S. aureus 209P than 3 indicated that the epoxy unit was important for antimicrobial activity. This structure-activity tendency of chalcomycins against S. aureus is different from that of aldgamycins reported in our previous research, which provide a valuable example for the phenomenon that 16-membered macrolides with different sugars do not have parallel structure-activity relationships.