Kumemicinones A–G, Cytotoxic Angucyclinones from a Deep Sea-Derived Actinomycete of the Genus Actinomadura

Chemical investigation of the fermentation products of a deep sea water-derived actinomycete, Actinomadura sp. KD439, identified seven new angucyclinones, designated as kumemicinones A-G (1-7), together with the known SF2315B and miaosporone E. NMR and MS spectroscopic analyses, combined with X-ray crystallography and quantum chemical calculations of NMR chemical shifts and electronic circular dichroism (ECD) spectra, uncovered the structures of new angucyclinones as regioisomers of SF2315B at the allyl alcohol unit (1 and 2), an epoxy ring-opened γ-hydroxy enone isomer (3), a B/C-ring-rearranged product (4), or dimers with a new mode of bridging (5-7), adding new structural variation to this antibiotic group. The absolute configuration of SF2315B was also determined by comparison of ECD spectra with those of 1 and 2. All the angucyclinones exhibited cytotoxicity against P388 murine leukemia cells, with IC₅₀ values ranging from 1.8 to 53 μM.