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.

Intramolecular Diels-Alder Reaction of N-Alkyl-2-cyano-1-azadienes: A Study of the Eschenmoser Cycloreversion of Dihydrooxazines as a Route to N-Alkyl-2-cyano-1-azadienes.

In connection with the development of the intramolecular Diels-Alder reaction (IMDA) of 1-azadienes, the 5,6-dihydro-4H-1,2-oxazine 12has been evaluated as a synthon equivalent of the 2-cyano-1-azadiene system. It was found that the dihydrooxazonium salt 27, generated in situ from the cyclic hydroxamic acid derivative 26, is converted directly to azadiene 4a via tautomerization to the corresponding enamine and a particularly facile Eschenmoser type cycloreversion process. Conditions were subsequently found for the preparation of synthon 12. N-Alkylation of this intermediate with alkyl bromides in the presence of Ag(+) ion also resulted in direct formation of the 2-cyano-1-azadiene products 38a-dand 4a. Microwave irradiation of a benzene solution of azadiene 4a proved to be a convenient means to effect its IMDA conversion to indolizidine 5a. To avoid decomposition of azadiene 38c, its intramolecular cycloaddition giving 40 (60%) was achieved by flash vacuum thermolysis.

Reactivity of N-Phenyl-1-Aza-2-Cyano-1,3-Butadienes in the Diels-Alder Reaction.

It is found that N-phenyl-2-cyano-1-azadiene 4, prepared via a two-step, one-pot, sequence from acrylanilide, undergoes efficient [4 + 2] cycloaddition with a complete range of electron rich, electron poor, and neutral dienophiles under remarkably mild thermal conditions (90-120 degrees C for 20-48 h). Regiospecific formation of the alpha-cycloadduct wherein the dienophile substituent is alpha to nitrogen is observed for vinyl ethers and styrene, whereas the Diels-Alder reactions with methyl acrylate and methyl vinyl ketone (MVK) produce alpha/beta mixtures in which the alpha-cycloadduct is the major regioisomer (approximately 4-5:1). An essentially identical reaction pattern was observed in the Diels-Alder reaction of N-(p-methoxyphenyl)-2-cyano-1-azadiene 18 and the 4-methyl-substituted azadiene 27. For compound 19 derived from cycloaddition of 18 with ethyl vinyl ether, facile conversion to the dihydropyridine 21 through loss of EtOH on brief acid treatment was also noted. The 2,4-cis-disubstitution pattern confirmed by X-ray diffraction for the major cycloadduct 29 isolated from the reaction of 27 with styrene provides evidence for the endo mode of cycloaddition in the Diels-Alder reaction of N-phenyl(aryl)-2-cyano-1-azadienes. Calculation of the frontier orbital energies and coefficients, as well as the transition state geometries for the [4 + 2] cycloaddition of N-phenyl-2-cyano-1-azadiene 4 with methyl vinyl ether, styrene, and MVK were carried out at the RHF AM1 level (MOPAC, Version 5.0). The FMO treatment indicates that the reaction of 4 with methyl vinyl ether occurs under LUMO(diene) control, whereas in contrast, the corresponding cycloaddition with MVK occurs preferably under HOMO(diene) control. A high degree of asynchronicity is observed in the calculated transition states for reaction of 4 with the three representative dienophiles. In all cases the transition states leading to the alpha-cycloadducts are lower in energy than those giving the beta-products. However, at the AM1 level the exo cycloaddition mode is found to be the preferred, this result contrasting with experimental results for azadiene 27.