Chapter 15. Quinolone Antibacterial Agents

Recent advances in the synthesis of N-containing heteroaromatics via heterogeneously transition metal catalysed cross-coupling reactions

N-containing heteroaromatics are important substructures found in numerous natural or synthetic alkaloids. The diversity of the structures encountered, as well as their biological and pharmaceutical relevance, have motivated research aimed at the development of new economical, efficient and selective synthetic strategies to access these compounds. Over more than 100 years of research, this hot topic has resulted in numerous so-called "classical synthetic methods" that have really contributed to this important area. However, when the selective synthesis of highly functional heteroaromatics like indoles, quinolones, indoxyls, etc. is considered these methods remain limited. Recently transition metal-catalysed (TM-catalysed) procedures for the synthesis of such compounds and further transformations, have been developed providing increased tolerance toward functional groups and leading generally to higher reaction yields. Many of these methods have proven to be the most powerful and are currently applied in target- or diversity-oriented syntheses. This review article aims at reporting the recent developments devoted to this important area, focusing on the use of heterogeneous catalysed procedures that include either the formation of the heterocyclic ring towards the nuclei or their transformations to highly substituted compounds.

Determination of enro?oxacin and its primary metabolite, cipro?oxacin, in pig tissues. Application to residue studies

A simple and sensitive HPLC method has been developed for the simultaneous determination of enrofloxacin (ENR) and ciprofloxacin (CIP) in pig tissue using difloxacin (DIF) as internal standard. Tissue sample preparations were carried out by adding phosphate buffer (pH 7.4, 0.1 m), followed by extraction with trichloromethane. Fluoroquinolones were separated on a reversed-phase column and eluted with aqueous buffer solution-acetonitrile (80:20, v/v). The concentrations of CIP, ENR and DIF eluted from the column, with retention times of 2.20, 2.73 and 4.38 min, respectively, were monitored by fluorescence detection at lambda(ex) 276 and lambda(em) 442 nm. The detection and quantitation limit were 8 and 25 ng/g, respectively, for both compounds. Standard curves were linearly related to concentration in the range 25-400 ng/g. The consequences of the introduction of minor reasonable variations (ruggedness studies) have also been analysed. Finally, the measurement of the tissue levels of ENR and CIP in the pig tissues after oral administration confirmed the utility of the proposed method.

Quinolone therapy in the management of infection after irradiation

Ionizing radiation increases the recipient's susceptibility to local and systemic infection by endogenous and exogenous microorganisms. Most infections involve fatal Gram-negative septicemia, but those associated with trauma may be polymicrobial. The use of quinolone antimicrobial agents in the treatment of these infections in irradiated mice is reviewed. Quinolones were effective in controlling systemic endogenous Gram-negative infection following irradiation. Supplementation of quinolone therapy with penicillin prevented treatment failures due to Streptococci, and increased survival. Quinolones were found also to be effective in management of systemic exogenous infections due to orally ingested Klebsiella pneumoniae and Pseudomonas aeruginosa. A 21-day course of therapy of K. penumoniae infection was superior to a 7-day therapy. The effectiveness of quinolones in the management of these infections may be attributed to local inhibition of the offending organism's growth within the gut lumen, while preserving the anaerobic gut flora and their systemic antibacterial activity. Administration of agents effective against anaerobic bacteria may be required for the management of polymicrobial infections. Supplementing antianaerobic therapy with a quinolone can control the Gram-negative bacterial component of the infection and prevent Enterobacteriaceae translocation and mortality. The availability of an oral, as well as parenteral, route of administration, the advantage of achieving selective inhibition of potential pathogens in the gut, and the ability to treat systemic infection make the quinolones promising agents for the therapy of endogenous and exogenous infections after irradiation.

The fluoroquinolone antibacterial agents

In summary, the last decade has been a highly fertile and productive period in quinolone medicinal chemistry, resulting in major improvements in potency, antibacterial spectra, oral absorption and pharmacokinetic properties as well as an increased knowledge of the molecular features important to conferring these various properties. Very recent discoveries concerning replacements for the 3-carboxylic acid moiety, previously thought to be uniquely essential for activity, to give highly potent antibacterials such as (83) illustrate the potential for new breakthroughs in this field. Among the major goals for future research remains the understanding of the potential cartilage toxicity associated with this class of agents, such that an agent useful for pediatric indications may be developed. Future studies can also be expected to further enhance and refine the level of current insight into the manner by which these agents inhibit the target enzyme on a molecular level.

Synthesis and in vitro antibacterial activity of some 1-(difluoromethoxyphenyl)quinolone-3-carboxylic acids

We report on the synthesis of N-1-phenylquinolones in which the difluoromethoxy moiety is utilized as a halogen replacement. The antibacterial activity is discussed with reference to N-1-halophenylquinolones.