Seco-Tetracenomycins from the Marine-Derived Actinomycete sp. 10-10.

Six new tetracenomycin congeners, saccharothrixones E⁻I (⁻) and 13-de--methyltetracenomycin X (), were isolated from the rare marine-derived actinomycete sp. 10-10. Their structures were elucidated by spectroscopic analysis and time-dependent density functional theory (TDDFT)-electronic circular dichroism (ECD) calculations. Saccharothrixones G () and H () are the first examples of tetracenomycins featuring a novel ring-A-cleaved chromophore. Saccharothrixone I () was determined to be a -tetracenomycin derivative with ring-B cleavage. The new structural characteristics, highlighted by different oxidations at C-5 and cleavages in rings A and B, enrich the structural diversity of tetracenomycins and provide evidence for tetracenomycin biosynthesis. Analysis of the structure⁻activity relationship of these compounds confirmed the importance of the planarity of the naphthacenequinone chromophore and the methylation of the polar carboxy groups for tetracenomycin cytotoxicity.