Chiral DNA Gyrase Inhibitors. 3. Probing the Chiral Preference of the Active Site of DNA Gyrase. Synthesis of 10-Fluoro-6-methyl-6,7-dihydro-9-piperazinyl- 2H-benzo[a]quinolizin-20-one-3-carboxylic Acid Analogues

In pursuit of an apparent literature anomaly, S- and R-6-methyl-6,7-dihydro-2H-benzo[a]quinolizin-2-one-3-carboxylic acids (12 and 22) were synthesized by an unambiguous route from optically active norephedrines, and their antibacterial potencies were measured. Against Gram-negative microorganisms and DNA gyrase a preference for S-absolute configuration was found whereas R-absolute stereochemistry was more active against Gram-positives. These results are in partial conflict with an earlier report. In an attempt to enhance potency, racemic 10-fluoro-9-piperazinyl (35) and related analogues were synthesized by a novel route. The latter analogues were surprisingly unimproved in potency. The implications of these findings are briefly discussed.