Novel bioactive oxazolomycin isomers produced by streptomyces albus JA3453

Two novel oxazolomycin isomers, oxazolomycins B (2) and C (3), were isolated from the fermentation broth of an oxazolomycin-producing strain, Streptomyces albus JA3453. Both compounds are geometrical isomers of oxazolomycin (1), the configurations of their triene moieties being (4′E, 6′E, 8′E) (2) and (4′Z, 6′E, 8′E) (3) while that of oxazolomycin (1) is (4′Z, 6′Z, 8′E). Compounds 2 and 3 exhibited potent inhibitory activity against crown gall formation with the same MIC (0.8 μg/disk) as oxazolomycin. Compounds 2 and 3 showed no antibacterial activity against Agrobacterium tumefaciens, in contrast to oxazolomycin which has specific anti-A. tumefaciens activity.