ABSTRACT
The DNA gyrase inhibitor cyclothialidine had been shown to be a valuable lead structure for the discovery of new antibacterial classes able to overcome bacterial resistance to clinically used drugs. Bicyclic lactone derivatives containing in their 12-14-membered ring a thioamide functionality were reported previously to exhibit potent antibacterial activity against gram-positive bacteria. Moderate in vivo efficacy, however, was demonstrated only for derivatives bearing hydrophilic substituents, which were found to have a favorable impact on pharmcokinetics, and to reduce metabolic degradation, in particular glucuronidation. The incorporation of an additional amide unit into the 14-membered monolactam-lactone scaffold of cyclothialidine analogues provided a new "dilactam" subclass of DNA gyrase inhibitors of inherently higher polarity. After adjusting their lipophilicity by methyl-halogen exchange at the benzene ring, compounds of this series did not require the thioamide functionality to exert a decent antibacterial potency and consequently exhibited improved pharmacokinetic properties resulting in a pronounced in vivo efficacy in a mouse septicaemia infection model.
Subject(s)
Lactams/chemistry , Lactones/chemistry , Peptides, Cyclic/chemistry , Peptides, Cyclic/pharmacology , Topoisomerase II Inhibitors , Animals , Anti-Bacterial Agents/chemical synthesis , Anti-Bacterial Agents/chemistry , Anti-Bacterial Agents/pharmacology , Bacteria/drug effects , DNA Gyrase/chemistry , Enzyme Inhibitors/chemical synthesis , Enzyme Inhibitors/chemistry , Enzyme Inhibitors/pharmacology , Mice , Microbial Sensitivity Tests , Models, Molecular , Peptides, Cyclic/chemical synthesis , Protein ConformationABSTRACT
Cyclothialidine (1, Ro 09-1437) is a potent DNA gyrase inhibitor that was isolated from Streptomyces filipinensis NR0484 and is a member of a new family of natural products. It acts by competitively inhibiting the ATPase activity exerted by the B subunit of DNA gyrase but barely exhibits any growth inhibitory activity against intact bacterial cells, presumably due to insufficient permeation of the cytoplasmic membrane. To explore the antibacterial potential of 1, we developed a flexible synthetic route allowing for the systematic modification of its structure. From a first set of analogues, structure-activity relationships (SAR) were established for different substitution patterns, and the 14-hydroxylated, bicyclic core (X) of 1 seemed to be the structural prerequisite for DNA gyrase inhibitory activity. The variation of the lactone ring size, however, revealed that activity can be found among 11- to 16-membered lactones, and even seco-analogues were shown to maintain some enzyme inhibitory properties, thereby reducing the minimal structural requirements to a rather simple, hydroxylated benzyl sulfide (XI). On the basis of these "minimal structures" a modification program afforded a number of inhibitors that showed in vitro activity against Gram-positive bacteria. The best activities were displayed by 14-membered lactones, and representatives of this subclass exhibit excellent and broad in vitro antibacterial activity against Gram-positive pathogens, including Staphylococcus aureus, Streptococcus pyogenes, and Enterococcus faecalis, and overcome resistance against clinically used drugs. By improving the pharmacokinetic properties of the most active compounds (94, 97), in particular by lowering their lipophilic properties, we were able to identify congeners of cyclothialidine (1) that showed efficacy in vivo.
