Bioactive constituents from marine-derived Streptomyces sp. NB-A13

Six new anthracyclines (1-6) were obtained by the investigation of the solid fermented extract of a marine-derived Streptomyces sp. NB-A13. The structures were elucidated on the basis of spectroscopic analysis, including 1D and 2D NMR, HRESIMS, UV and IR. The absolute configurations of compounds 1-5 were established by calculated electronic circular dichroism (ECD) using time dependent density functional theory. Among the isolates, four compounds (2, 3, 5 and 6) showed moderate cytotoxic activity against PC3 cells (prostate cancer cells) with IC50 values of 7.0 +/- 0.3 mu M, 0.92 +/- 0.05 mu M, 2.1 +/- 0.7 mu M and 9.8 +/- 0.7 mu M, respectively.