Despite recent progress in antithrombotic therapy, there is still an unmet medical need for safe and orally available anticoagulants. The coagulation enzyme Factor Xa (FXa) is a particularly promising target, and recent efforts in this field have focused on the identification of small-molecule inhibitors with good oral bioavailability. We identified oxazolidinone derivatives as a new class of potent FXa inhibitors. Lead optimization led to the discovery of BAY 59-7939 (5), a highly potent and selective, direct FXa inhibitor with excellent in vivo antithrombotic activity. The X-ray crystal structure of 5 in complex with human FXa clarified the binding mode and the stringent requirements for high affinity. The interaction of the neutral ligand chlorothiophene in the S1 subsite allows for the combination of good oral bioavailability and high potency for nonbasic 5. Compound 5 is currently under clinical development for the prevention and treatment of thromboembolic diseases.

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The multisubunit acetyl-CoA carboxylase, which catalyzes the first committed step in fatty acid biosynthesis, is broadly conserved among bacteria. Its rate-limiting role in formation of fatty acids makes this enzyme an attractive target for the design of novel broad-spectrum antibacterials. However, no potent inhibitors have been discovered so far. This report describes the identification and characterization of highly potent bacterial acetyl-CoA carboxylase inhibitors with antibacterial activity for the first time. We demonstrate that pseudopeptide pyrrolidine dione antibiotics such as moiramide B inhibit the Escherichia coli enzyme at nanomolar concentrations. Moiramide B targets the carboxyltransferase reaction of this enzyme with a competitive inhibition pattern versus malonyl-CoA (K i value ‫؍‬ 5 nM). Inhibition at nanomolar concentrations of the pyrrolidine diones is also demonstrated using recombinantly expressed carboxyltransferases from other bacterial species (Staphylococcus aureus, Streptococcus pneumoniae, and Pseudomonas aeruginosa). We isolated pyrrolidine dione-resistant strains of E. coli, S. aureus, and Bacillus subtilis, which contain mutations within the carboxyltransferase subunits AccA or AccD. We demonstrate that such mutations confer resistance to pyrrolidine diones. Inhibition values (IC 50 ) of >100 M regarding an eukaryotic acetyl-CoA carboxylase from rat liver indicate high selectivity of pyrrolidine diones for the bacterial multisubunit enzyme. The natural product moiramide B and synthetic analogues show broad-spectrum antibacterial activity. The knowledge of the target and the availability of facile assays using carboxyltransferases from different pathogens will enable evaluation of the antibacterial potential of the pyrrolidine diones as a promising antibacterial compound class acting via a novel mode of action.

Pyridochromanones were identified by high throughput screening as potent inhibitors of NAD ؉ -dependent DNA ligase from Escherichia coli. Further characterization revealed that eubacterial DNA ligases from Gramnegative and Gram-positive sources were inhibited at nanomolar concentrations. In contrast, purified human DNA ligase I was not affected (IC 50 > 75 M), demonstrating remarkable specificity for the prokaryotic target. The binding mode is competitive with the eubacteriaspecific cofactor NAD ؉ , and no intercalation into DNA was detected. Accordingly, the compounds were bactericidal for the prominent human pathogen Staphylococcus aureus in the low g/ml range, whereas eukaryotic cells were not affected up to 60 g/ml. The hypothesis that inhibition of DNA ligase is the antibacterial principle was proven in studies with a temperature-sensitive ligase-deficient E. coli strain. This mutant was highly susceptible for pyridochromanones at elevated temperatures but was rescued by heterologous expression of human DNA ligase I. A physiological consequence of ligase inhibition in bacteria was massive DNA degradation, as visualized by fluorescence microscopy of labeled DNA. In summary, the pyridochromanones demonstrate that diverse eubacterial DNA ligases can be addressed by a single inhibitor without affecting eukaryotic ligases or other DNA-binding enzymes, which proves the value of DNA ligase as a novel target in antibacterial therapy.Multiple drug resistance among bacterial pathogens is spreading even in developed countries and has made many currently available antibiotics ineffective (1). As a consequence the number of reports on therapy failures increases and treatment costs rise, causing a growing public health problem. Thus, the search for novel antibacterial classes with innovative mechanisms of action is crucial to keep pace with the innate adaptability of the bacterial population. From the information revealed by sequencing more than 80 bacterial genomes, many novel target ideas have emerged in the last decade. However, even classical target areas such as cell wall, protein, or DNA synthesis contain many vital reactions not exploited in antibacterial therapy so far.DNA ligases are promising target candidates because they are indispensable for many fundamental processes in DNA metabolism including the linkage of Okazaki fragments during replication, recombination processes, and repair pathways requiring resynthesis of DNA (2, 3). Their crucial function is emphasized by the fact that eukaryotic cells contain several isoenzymes and that viruses encode their own ligases (3, 4). The reaction catalyzed by the DNA ligases, the joining of nicked DNA strands, proceeds in three sequential nucleotidyl transfer reactions (2). The first step is the nucleophilic attack by the active site lysine on the AMP moiety of a cofactor, resulting in a covalent enzyme-AMP intermediate. The AMP is then transferred to the 5Ј-phosphate end of the nicked duplex DNA and finally released when the ligase catalyzes the attack by the adjacent...