Naphthacemycins, novel circumventors of β-lactam resistance in MRSA, produced by Streptomyces sp. KB-3346-5. II. Structure elucidation.

Seventeen new compounds, naphthacemycins A1-A11, B1-B4 and C1-C2, were isolated from a cultured broth of Streptomyces sp. KB-3346-5 during screening for circumventors of β-lactam resistance in methicillin-resistant Staphylococcus aureus. Their structures were elucidated by spectroscopic studies, including NMR and X-ray crystallographic analysis. The naphthacemycin A series has a new skeleton displaying a 7-phenylnaphthacene-5,6,11(12H)-trione. In contrast, the quinone moiety of the A series is changed to dehydroxyquinol in the B series and to a semiquinone-like structure in the C series.