New aminocoumarin antibiotics as gyrase inhibitors

The aminocoumarins novobiocin, clorobiocin and coumermycin A1 are structurally related antibiotics produced by different Streptomyces strains. They are potent inhibitors of bacterial gyrase. Their binding sites and their mode of action differ from those of fluoroquinolones such as ciprofloxacin. Novobiocin has been introduced into clinical use against Staphylococcus aureus infections, and S. aureus gyrase is particularly sensitive to inhibition by aminocoumarins, while topoisomerase IV is much less sensitive. Modern genetic techniques have allowed the engineering of the producer strains, resulting in a diverse range of new aminocoumarins, including compounds which are more active than the natural antibiotics as well as a compound which is actively imported across the cell envelope of Gram-negative bacteria. A further group of aminocoumarins are the simocyclinones which bind simultaneously to two different sites of gyrase and show a completely new mode of inhibition. Both the simocyclinones and the "classical" aminocoumarins strongly inhibit the fluoroquinolone-induced activation of RecA and thereby the SOS response in S. aureus. Therefore, a combination of aminocoumarins and fluoroquinolones strongly reduced the risk of resistance development and may offer new prospects in anti-infective therapy.