A series of pyrazolidine-3, 5-dione and 5-hydroxy-1 H-pyrazol-3 (2 H)-one inhibitors of Escherichia coli UDP-N-acetylenolpyruvyl glucosamine reductase (MurB) has been prepared. The 5-hydroxy-1 H-pyrazol-3 (2 H)-ones show low micromolar IC50 values versus E. coli MurB and submicromolar minimal inhibitory concentrations (MIC) against Staphylococcus aureus GC 1131, Enterococcus faecalis GC 2242, Streptococcus ...