Iseoic acids and bisiseoate: three new naphthohydroquinone/naphthoquinone-class metabolites from a coral-derived Streptomyces

Two new naphthohydroquinone derivatives designated iseoic acids A ( 1 ) and B ( 2 ) and a new symmetrical glycerol bisester of naphthoquinonepropanoic acid designated bisiseoate ( 3 ) were isolated from the culture extract of a marine-derived actinomycete Streptomyces sp. DC4-5. The structures of 1–3 were determined by analyzing one- and two-dimensional NMR data and MS analytical data. The absolute configurations were determined by NOESY analysis and the phenylglycine methyl ester (PGME) method for 1 and by considering the structural similarity and biosynthesis for 2 and 3 . Compound 3 exhibited modest cytotoxicity against P388 murine leukemia cells with an IC 50 value of 19 μM.