A fermentation broth of an unidentified fungus (N983-46) was found to produce DNA gyrase inhibitors, CJ-12, 371 (1) and CJ-12, 372 (2). Following isolation by solvent extraction and silica gel and ODS (reverse phase) chromatographies, the structures were determined to be novel spiro-ketal compounds with S-configuration at position C-1. CJ-12, 371 and CJ-12, 372 inhibit both DNA supercoiling and relaxation mediated by Escherichia coli DNA gyrase. The interaction of these compounds with DNA gyrase appears to be novel in that the compounds inhibit supercoiling and relaxation without blocking religation; thus, no cleavage intermediate of double strand DNA is observed. Both compounds have antibacterial activity against several species of pathogenic Grampositive bacteria, with MICs between 25 and 100μg/ml. These results suggest that the antibacterial potency of CJ-12, 371 and CJ-12, 372 is attributed to the inhibition of DNA gyrase. However, the compounds did not inhibit DNA gyrase selectively, as they also inhibited eukaryotic topoisomerase II-mediated relaxation. Semi-synthetic modifications to the dihydroxy motif in CJ-12, 371 altered both gyrase- and topoisomerase Il-inhibitory activities, but did not enhance selectivity.
Japan Antibiotics Research Association