Hybrid antibacterials. DNA polymerase-topoisomerase inhibitors.

Novel Gram-positive (Gram+) antibacterial compounds consisting of a DNA polymerase IIIC (pol IIIC) inhibitor covalently connected to a topoisomerase/gyrase inhibitor are described. Specifically, 3-substituted 6-(3-ethyl-4-methylanilino)uracils (EMAUs) in which the 3-substituent is a fluoroquinolone moiety (FQ) connected by various linkers were synthesized. The resulting "AU-FQ" hybrid compounds were significantly more potent than the parent EMAU compounds as inhibitors of pol IIIC and were up to 64-fold more potent as antibacterials in vitro against Gram+ bacteria. The hybrids inhibited the FQ targets, topoisomerase IV and gyrase, with potencies similar to norfloxacin but 10-fold lower than newer agents, for example, ciprofloxacin and sparfloxacin. Representative hybrids protected mice from lethal Staphylococcus aureus infection after intravenous dosing, and one compound showed protective effect against several antibiotic-sensitive and -resistant Gram+ infections in mice. The AU-FQ hybrids are a promising new family of antibacterials for treatment of antibiotic-resistant Gram+ infections.

Synthesis and antibacterial activity of 3-substituted-6-(3-ethyl-4-methylanilino)uracils.

Numerous 3-substituted-6-(3-ethyl-4-methylanilino)uracils (EMAU) have been synthesized and screened for their capacity to inhibit the replication-specific bacterial DNA polymerase IIIC (pol IIIC) and the growth of Gram+ bacteria in culture. Direct alkylation of 2-methoxy-6-amino-4-pyrimidone produced the N3-substituted derivatives, which were separated from the byproduct 4-alkoxy analogues. The N3-substituted derivatives were heated with a mixture of 3-ethyl-4-methylaniline and its hydrochloride to effect displacement of the 6-amino group and simultaneous demethylation of the 2-methoxy group to yield target compounds in good yields. Certain intermediates, e.g. the 3-(iodoalkyl) compounds, were converted to a variety of (3-substituted-alkyl)-EMAUs by displacement. Most compounds were potent competitive inhibitors of pol IIIC (K(i)s 0.02-0.5 microM), and those with neutral, moderately polar 3-substituents had potent antibacterial activity against Gram+ organisms in culture (MICs 0.125-10 microg/mL). Several compounds protected mice from lethal intraperitoneal (ip) infections with S. aureus (Smith) when given by the ip route. A water soluble derivative, 3-(4-morpholinylbutyl)-EMAU hydrochloride, given subcutaneously, prolonged the life of infected mice in a dose dependent manner.