SYNTHESIS AND BIOLOGICAL-ACTIVITY OF NEW QUINOLONE DERIVATIVES

A series of new quinolone derivatives bearing covalent modifications at the piperazine ring was synthesized and investigated for their biological properties. Two different types of substitutions at the level of the nitrogen at the 4' position were considered: introduction of a di- or tri-oxymethylene chain to modify steric hindrance and improve solubility in aqueous media or formation of a tertiary amide ending with a carboxylate group. In the latter case the net charge on the piperazine moiety changes from positive to negative at physiological conditions. In addition, a 'bis-quinolone' compound was examined, which lacks the piperazine ring and is also negatively charged at neutral pH. The new derivatives, except one, exhibited drug uptake, inhibition of DNA-gyrase activity and anti-bacterial potencies comparable to those of norfloxacin, and were modulated by the nature of the N4'-substituent. Besides indicating possible new modifications of the quinolone basic structure, the observation that substantially different substitution patterns at the same position did not cause impairment of biological activity suggests that the steric and electronic properties of this part of the molecule are not crucial for the recognition of DNA-gyrase.