The identification and characterization of hydrazinyl urea-based antibacterial agents through combinatorial chemistry.

An effort to identify novel inhibitors of peptidoglycan synthesis with antibacterial activity resulted in the discovery of a series of biaryl urea-based antibacterial agents through isolation of a by-product from a mixture-based combinatorial library of semi-carbazones and subsequent parallel synthesis efforts. The compounds were shown to possess broad spectrum antibacterial activity against gram-positive drug resistant pathogens, and showed apparent specificity for disruption of the bacterial cell wall biosynthesis pathway.

Quinolone resistance in Staphylococci: activities of new nonfluorinated quinolones against molecular targets in whole cells and clinical isolates.

The activity of three new, 8-methoxy-nonfluorinated quinolones (NFQs) against multiple-drug-resistant staphylococci was investigated. First, using Staphylococcus aureus strains containing point mutations in the serine 84-80 hot spots of the target genes (gyrA and grlA), cell growth inhibition potencies of the NFQs as a result of DNA gyrase and topoisomerase IV inhibition were estimated and compared with those of known fluoroquinolones. The NFQs and clinafloxacin showed higher affinities toward both the targets than ciprofloxacin, trovafloxacin and gatifloxacin. Furthermore, the ratio of the calculated affinity parameter for DNA gyrase to that for topoisomerase IV was lower in the case of the NFQs, clinafloxacin, and gatifloxacin than in the case of ciprofloxacin and trovafloxacin. These results suggest that the former group of quinolones is better able to exploit both the targets. Next, using clinical isolates of methicillin-resistant S. aureus (MRSA; n = 34) and coagulase-negative staphylococci (CoNS; n = 24), the NFQs and clinafloxacin were shown to be more potent (MIC at which 90% of the isolates are inhibited [MIC90] = 2 microg/ml for MRSA and 0.5 microg/ml for CoNS) than ciprofloxacin, trovafloxacin, and gatifloxacin (MIC90 = 16 to >64 microg/ml for MRSA and 4 to >32 microg/ml for CoNS). Bactericidal kinetics experiments, using two MRSA isolates, showed that exposure to the NFQs at four times the MIC reduced the bacterial counts (measured in CFU per milliliter) by > or =3 log units in 2 to 4 h. Overall, the NFQs and clinafloxacin were less susceptible than the other quinolones to existing mechanisms of quinolone resistance in staphylococci.

Use of combinatorial library screening to identify inhibitors of a bacterial two-component signal transduction kinase.

Bacterial resistance to antibiotics is emerging as a major concern to the medical community. The appearance of several antibiotic-resistant strains, including multidrug-resistant Staphylococcus aureus, raises the prospect that infections by these bacteria could soon become untreatable with currently available antibiotics. In order to address this problem, increased emphasis is being placed on the discovery of novel classes of antibacterial agents that inhibit novel molecular targets using sources of compounds not yet exploited for antibiotic drug discovery. Novel classes of compounds can now be rapidly investigated using combinatorial chemistry approaches. This report describes the identification of novel antibacterial compounds from a combinatorial library of N-acetylated, C-amidated D-amino acid hexapeptides. This library of compounds was screened for inhibitors of CheA, a member of the bacterial two-component signal transduction kinase family. Several peptides with apparent IC50 values in the low micromolar range were identified. In addition to inhibiting CheA, these peptides inhibited mammalian protein kinase C (from rat brain) with comparable potency. Finally, these peptides were also found to have significant antibacterial properties, although the true mechanism by which they exhibited inhibition of bacterial growth remains uncertain.