Pyridoquinoxaline N-oxides. 2. Synthesis and antibacterial activity of tricyclic lactams

A series of novel 3,4-dihydropyrido[3,4-b]quinoxalin-1(2H)-one 5,10-dioxides was synthesized using an intramolecular amidation reaction. The lactams were screened in vitro and in vivo against Salmonella choleraesuis, Pasteurella multocida, and Escherichia coli. An N-methyl analogue was the most potent member of this series, with antibacterial activity comparable to that of the commercially important quinoxaline 1,4-dioxide carbadox.