Abstract
OPC- 19A, 9-fluoro-5-methyl-8-(4-methyl- 1 -piperazinyl)-6, 7-dihydro- 1-oxo-1H, 5H-benzo[ij]- quinolizine-2-carboxylic acid, and OPC-19B, 9-fluoro-5-methyl-8-(1-piperazinyl)-6, 7-dihydro-loxo- 1H, 5H-benzo[ij]quinolizine-2-carboxylic acid, are new synthetic naldixic acid-related antibiotics which belong to the group of quinolizine antibacterial agents. They inhibited the supercoiling of DNA catalyzed by Escherichia coli DNA gyrase. Introduction of transient doublestrand breaks into DNA by DNA gyrase was also observed in the presence of these antibiotics as well as oxolinic acid. The activities of subunit A of DNA gyrase purified from an OPC-19A resistant strain were insensitive to nalidixic acid as well as OPC-19A and OPC-19B, but sensitive to novobiocin which is known to inhibit the activity of subunit B of DNA gyrase. The targer molecule for OPC-19A and OPC-19B is, there fore, considered to be subunit A of DNA gyrase.
