Cytotoxic anthracycline and antibacterial tirandamycin analogues from a marine-derived Streptomyces sp. SCSIO 41399

Aranciamycin K (1) and isotirandamycin B (2) were isolated from a marine-derived Streptomyces sp. SCSIO 41399, along with the previously reported four anthracycline derivatives (3–6), and two known tirandamycin derivatives (7 and 8). Their structures including absolute configurations were determined by extensive analysis of their spectroscopic analysis and ECD calculation method. Most of the isolated compounds were tested for their cytotoxic, antibacterial, and antifungal activities. Compounds 2, 7 and 8 displayed potent bacteriostatic effects against Streptococcus agalactiae with MIC values of 11.5, 5.9 and 5.7 μM, respectively. Besides, compounds 3, 5 and 6 exhibited moderate in vitro cytotoxic activities against the K562 cell lines with IC50 values of 22.0 ± 0.20, 1.80 ± 0.01 and 12.1 ± 0.07 μM, respectively.