Nitroimidazoles as anaerobic electron acceptors for xanthine oxidase

The rates of anaerobic nitroreduction of 15 nitroimidazoles by xanthine-xanthine oxidase were measured. The compounds studied were mainly 2-nitroimidazoles, including misonidazole and analogues of potential value in cancer therapy; most 5-nitroimidazoles such as metronidazole and nimorazole reacted too slowly for measurement under the conditions used. Using 0.1 mM nitroimidazole, reduction rates varied between ca. 4 and 680 nmole min-1 U-1 xanthine oxidase at 37 degrees and pH 7.4. These rates were correlated with the reduction potential characterizing one-electron reduction to the nitro radical-anion, and compared with those for other nitroaryl compounds and with reduction by free flavin mononucleotide.