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Seven new coralmycin derivatives, coralmycins C (<b>1</b>), D (<b>2</b>), E (<b>3</b>), F (<b>4</b>), G (<b>5</b>), H (<b>6</b>), and I (<b>7</b>), along with three known compounds, cystobactamids 891-2 (8), 905-2 (9), and 507 (10), were isolated from a large-scale culture of the myxobacteria <i>Corallococcus coralloides</i> M23. The structures of these compounds, including their relative stereochemistries, were elucidated by interpretation of their spectroscopic and CD data. The structure-activity relationships of their antibacterial and DNA gyrase inhibitory activities indicated that the <i>para</i>-nitrobenzoic acid unit is critical for the inhibition of DNA gyrase and bacterial growth, while the nitro moiety of the <i>para</i>-nitrobenzoic acid unit and the isopropyl chain at C-4 could be important for permeability into certain Gram-negative bacteria, including <i>Pseudomonas aeruginosa</i> and <i>Klebsiella pneumoniae</i>, and the &#946;-methoxyasparagine moiety could affect cellular uptake into all tested bacteria. These results could facilitate the chemical optimization of coralmycins for the treatment of multidrug-resistant Gram-negative bacteria.