Fermentation, Isolation, Structural Elucidation and Biological Activities

A fermentation broth of an unidentified fungus (N983-46) was found to produce DNAgyrase 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-connguration at position C-l. CJ-12,371 and CJ-12,372 inhibit both DNA supercoiling and relaxation mediated by Escherichia coli DNAgyrase. The interaction of these compounds with DNAgyrase appears to be novel in that the compounds inhibit supercoiling and relaxation without blocking religation; thus, no cleavage intermediate of double strand DNAis observed. Both compounds have antibacterial activity against several species of pathogenic Grampositive bacteria, with MICs between 25 and 100^g/ml. These results suggest that the antibacterial potency of CJ-12,371 and CJ-12,372 is attributed to the inhibition of DNAgyrase. However, the compounds did not inhibit DNAgyrase selectively, as they also inhibited eukaryotic topoisomerase II-mediated relaxation. Semi-synthetic modifications to the dihydroxy motif in CJ-12,371 altered both gyraseand topoisomerase II-inhibitory activities, but did not enhance selectivity.