Antibacterial Spirotetronate Polyketides from an Actinomadura sp. Strain A30804.

Large scale cultivation and chemical investigation of an extract obtained from sp. resulted in the identification of six previously undescribed spirotetronates (pyrrolosporin B and decatromicins C-G; -), along with six known congeners, namely decatromicins A-B (-), BE-45722B-D (-), and pyrrolosporin A (). The chemical structures of compounds - were characterized via comparison with previously reported data and analysis of 1D/2D NMR and MS data. The structures of all new compounds were highly related to the spirotetronate type compounds, decatromicin and pyrrolosporin, with variations in the substituents on the pyrrole and aglycone moieties. All compounds were evaluated for antibacterial activity against the Gram-negative bacteria, and Gram-positive bacteria, and were investigated for their cytotoxicity against the human cancer cell line A549. Of these, decatromicin B (), BE-45722B (), and pyrrolosporin B () exhibited potent antibacterial activities against both Gram-positive (MIC between 1-3 μM) and Gram-negative bacteria (MIC values ranging from 12-36 μM) with weak or no cytotoxic activity against A549 cells.