CJ-12371

Anteaglonialides A-F (1-6), bearing a spiro[6-(tetrahydro-7-furanyl)cyclohexane-1,2'-naphtho[1,8-de][1,3]-dioxin]-10-one skeleton, three new spirobisnaphthalenes, palmarumycins CE1-CE3 (7-9), nine known palmarumycin analogues, palmarumycins CP5 (10), CP4a (11), CP3 (12), CP17 (13), CP2 (14), and CP1 (15), CJ-12,371 (16), 4-O-methyl CJ-12,371 (17), and CP4 (18), together with a possible artifact, 4a(5)-anhydropalmarumycin CE2 (8a), and four known metabolites, O-methylherbarin (19), herbarin (20), herbaridine B (21), and hyalopyrone (22), were encountered in a cytotoxic extract of a potato dextrose agar culture of Anteaglonium sp. FL0768, an endophytic fungus of the sand spikemoss, Selaginella arenicola. The planar structures and relative configurations of the new metabolites 1-9 were elucidated by analysis of extensive spectroscopic data, and the absolute configuration of 1 was determined by the modified Mosher's ester method. Application of the modified Mosher's ester method combined with the NOESY data resulted in revision of the absolute configuration previously proposed for 10. Co-occurrence of 1-6 and 7-18 in this fungus led to the proposal that the anteagloniolides may be biogenetically derived from palmarumycins. Among the metabolites encountered, anteaglonialide F (6) and known palmarumycins CP3 (12) and CP1 (15) exhibited strong cytotoxic activity against the human Ewing's sarcoma cell line CHP-100, with IC50 values of 1.4, 0.5, and 1.6 μM, respectively.

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 Gram-positive bacteria, with MICs between 25 and 100 micrograms/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 II-inhibitory activities, but did not enhance selectivity.