Syntheses and biological activities of new N1-aryl substituted quinolone antibacterials

Canthin-4-ones as Novel Antibacterial Agents

Based on the chemotype of canthin-4-one alkaloids with moderate antimicrobial activity, a collection of variously substituted canthin-4-ones and desaza analogs were synthesized. Key steps in the syntheses were regioselective halogenations of (desaza) canthin-4-one, followed by Pd-catalyzed cross-coupling reactions. The in vitro screening for antimicrobial activity revealed that two 5-substituted canthin-4-ones (3-pyridyl, 2-bromophenyl) exhibit significant activity against Streptococcus entericus, coupled with high selectivity and the lack of cytotoxicity against mammalian cells. The intact canthin-4-one ring system was demonstrated to be essential for antibacterial activity.

The insulinotropic effect of fluoroquinolones

Antimicrobial fluoroquinolones induce, with strongly varying frequency, life-threatening hypoglycemias, which is explained by their ability to block K(ATP) channels in pancreatic B-cells and thus to initiate insulin secretion. In apparent contradiction to this, we observed that none of the fluoroquinolones in this study (gatifloxacin, moxifloxacin, ciprofloxacin, and a number of fluorophenyl-substituted compounds) initiated insulin secretion of perifused mouse islets when the glucose concentration was basal (5mM). Only when the glucose concentration was stimulatory by itself (10mM), the fluoroquinolones enhanced secretion. The fluoroquinolones were ineffective on SUR1 Ko islets, which do not have functional K(ATP) channels. All of these fluoroquinolones depolarized the membrane potential of mouse B-cells (patch-clamping in the whole-cell mode). Using metabolically intact B-cells (perforated-patch mode) however, 100microM of gatifloxacin, ciprofloxacin or moxifloxacin were unable to depolarize when the glucose concentration was 5mM, whereas other K(ATP) channel blockers (tolbutamide and efaroxan) remained effective. Only at a very high concentration (500microM) gatifloxacin and moxifloxacin, but not ciprofloxacin induced repetitive depolarizations which could be antagonized by diazoxide. In the presence of 10mM glucose all fluoroquinolones which enhanced secretion markedly elevated cytosolic calcium concentration ([Ca(2+)](i)). In the presence of 5mM glucose gatifloxacin and moxifloxacin at 500microM but not at 100microM elevated [Ca(2+)](i). It is concluded that fluoroquinolones in the clinically relevant concentration range are not initiators, but rather enhancers of glucose-induced insulin secretion. The block of K(ATP) channels appears necessary but not sufficient to explain the hypoglycemic effect of fluoroquinolones.

Synthesis and correlations between experimental and calculated lipophilic indices of new 1,2-benzisothiazole derivatives with potential antimicrobial activity

Five series of new hydrazones (1a-m, 2a-m, 3a-m, 4a-m, 5a-m) with potential antimicrobial activity were synthesized from cyclic (1 and 4) or acyclic (2, 3 and 5) 1,2-benzisothiazolylhydrazides and characterized. Condensation of the appropriate hydrazide with aldehydes afforded the designed compounds. Aldehydes carrying different hydrophobic substituents were used and the five series were designed so that the hydrophobicity also varied among congeners. Retention parameters were measured by HPLC employing a deactivated alkyl-bonded silica column and different eluent systems (methanol-aqueous buffer, acetonitrile-water). The hydrophobicity chromatographic parameters (log k') were compared with those provided by measurement of partitioning of solutes between n-octanol and water (log P), and with theoretical partition coefficients, calculated by a fragmental method and scaled according to the experimental values. Correlations between different hydrophobicity indices are reported and discussed.

Determination of protein binding of gyrase inhibitors by means of continuous ultrafiltration

In order to characterize the protein binding of a drug, it is necessary to have a method which is close to in vivo conditions and fast in the course of measurement. The continuous ultrafiltration fulfils both requirements for substances with a high extent of protein binding. In this study, 18 gyrase inhibitors in clinical practice, characterized by a lower extent of protein binding, were subjected to the titration procedure of the continuous ultrafiltration using bovine and human serum albumin (BSA, HSA), and human plasma. The results of the continuous ultrafiltration were found to be similar to those obtained by means of the 'classical' discontinuous ultrafiltration using plasma (correlation between continuous and discontinuous ultrafiltration r2 = 0.87). In the cases of pipemidic acid, enoxacin and rufloxacin, the continuous method gave approximately 20% lower degrees of protein binding than the discontinuous procedure, which utilizes plasma having the full range of proteins. It is likely that these drugs bind mainly to other proteins in plasma than HSA. This finding proves that this fast method is worthwhile in the whole range of protein binding.

Defluorinated sparfloxacin as a new photoproduct identified by liquid chromatography coupled with UV detection and tandem mass spectrometry

Photodegradation of sparfloxacin was observed by means of high-pressure liquid chromatography with UV detection and liquid chromatography coupled with UV detection and tandem mass spectrometry (LC-MS/MS). Three products were detected. Comparison with an independently synthesized derivative of sparfloxacin revealed the structure of one product which is believed to be 8-desfluorosparfloxacin. The second product is likely to be formed by the splitting off of a fluorine and a cyclopropyl ring. Thus, photodefluorination of quinolone antibacterial agents is found and proved for the first time by LC-MS/MS.

Plasma protein binding of gyrase inhibitors

Plasma protein binding of a wide range of gyrase inhibitors in clinical practice or trials has been determined by ultrafiltration to determine structure-protein binding relationships. The protein binding was independent of overall lipophilicity. In particular, the "western" part of the "quinolone" skeleton, consisting of a heterocyclus at position 7 and varying substituents at position 8, strongly influences the extent of protein binding, indicating that this part interacts with the plasma protein. In contrast, substituents in position N1 do not show an effect on the protein binding in this series of compounds.