Decatromicin B

New antibiotics designated decatromicins A and B were isolated from the culture broth of Actinomadura sp. MK73-NF4. They were purified by butyl acetate extraction, silica gel column chromatography, silica gel TLC and Sephadex LH-20 column chromatography. Decatromicins A and B inhibited growth of Gram-positive bacteria including methicillin-resistant Staphylococcus aureus (MRSA).

Large scale cultivation and chemical investigation of an extract obtained fromActimonadurasp. resulted in the identification of six previously undescribed spirotetronates (pyrrolosporin B and decatromicins C-G;7-12), along with six known congeners, namely decatromicins A-B (1-2), BE-45722B-D (3-5), and pyrrolosporin A (6). The chemical structures of compounds1-12were 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,Acinetobacter baumanniiand Gram-positive bacteria,Staphylococcus aureusand were investigated for their cytotoxicity against the human cancer cell line A549. Of these, decatromicin B (2), BE-45722B (3), and pyrrolosporin B (7) exhibited potent antibacterial activities against both Gram-positive (MIC90between 1-3 μM) and Gram-negative bacteria (MIC90values ranging from 12-36 μM) with weak or no cytotoxic activity against A549 cells.