Synthesis and antibacterial activity of isomeric 6- and 7-acetyl-3-methyl-2-quinoxalinecarboxamide 1,4-dioxides

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Abstract
The synthesis, separation and structure determination of 6- and 7-acetyl-3-methyl-2-quinoxalinecarboxamide 1,4-dioxides are reported together with a comparison of their antibacterial activity. The structural assignment of these 6- and 7-acetyl isomers was based on NMR analysis of related mono-N-oxide derivatives, which were obtained by treatment of the quinoxaline 1,4-dioxides with acetic anhydride-acetic or trimethyl phosphite. The compounds were screened for in vitro and in vivo activity against Escherichia coli, Salmonella cholerae-suis, Pasteurella multocida and Streptococcus pyogenes. Although the isomers possessed similar activity, the 7-acetyl isomer was more active therapeutically in mice than the 6-acetyl isomer when administered parenterally.