Interactions between penicillin-binding proteins (PBPs) and two novel classes of PBP inhibitors, arylalkylidene rhodanines and arylalkylidene iminothiazolidin-4-ones

Several non-beta-lactam compounds were active against various gram-positive and gram-negative bacterial strains. The MICs of arylalkylidene rhodanines and arylalkylidene iminothiazolidin-4-ones were lower than those of ampicillin and cefotaxime for methicillin-resistant Staphylococcus aureus M1339 and vancomycin-resistant Enterococcus faecium EF12. Several compounds were found to inhibit the cell wall synthesis of S. aureus and the last two steps of peptidoglycan biosynthesis catalyzed by ether-treated cells of Escherichia coli or cell wall membrane preparations of Bacillus megaterium. The effects of the arylalkylidene rhodanines and arylalkylidene iminothiazolidin-4-one derivatives on E. coli PBP 3 and PBP 5, Streptococcus pneumoniae PBP 2xS (PBP 2x from a penicillin-sensitive strain) and PBP 2xR (PBP 2x from a penicillin-resistant strain), low-affinity PBP 2a of S. aureus, and the Actinomadura sp. strain R39 and Streptomyces sp. strain R61 DD-peptidases were studied. Some of the compounds exhibited inhibitory activities in the 10 to 100 muM concentration range. The inhibition of PBP 2xS by several of them appeared to be noncompetitive. The dissociation constant for the best inhibitor (K-i = 10 muM) was not influenced by the presence of the substrate.