Sarubicinols A-C, Cytotoxic Benzoxazoles from a Streptomyces .

A chemical investigation of Streptomyces sp. Hu186 afforded two known quinone antibiotics, sarubicin A ( 1 ) and sarubicin B ( 2 ), together with three unusual variants, sarubicinols A-C ( 3 - 5 ), and two new 1,4-naphthoquinone metabolites, sarubicin B 1 ( 6 ) and sarubicin B 2 ( 7 ). Compounds 3 - 5 possess a rare 2-oxabicyclo [2.2.2] substructure and a benzoxazole ring system. Their structures were elucidated using 1D and 2D nuclear magnetic resonance and high-resolution electrospray ionization mass spectrometry data. The absolute configurations of the side-chain moieties in 4 and 5 were solved by electronic circular dichroism calculations. Compounds 1 - 7 showed moderate cytotoxic activity against four tumor cell lines.