New pyrrolobenzodiazepine antibiotics, RK-1441A and B. I. Biological properties.

Streptomyces griseus and bacteriophage B were used for an assay system detecting anti-bacteriophage antibiotics. Streptomyces sp. RK-1441 was found to produce antibacteriophage antibiotics, RK-1441A and B, which are pyrrolo[1,4]benzodiazepine group antibiotics related to neothramycin. Both RK-1441A and B had antibacteriophage activity. The former showed antimicrobial activity on a hypersensitive strain of E. coli for antitumor antibiotics, but the later did not show the activity. Restriction enzyme assay suggested that RK-1441A formed adducts with guanine residues in DNA strands. RK-1441B was not active in vitro, but it might be converted to the active form in host organisms.