Chemical and biological properties of acetyl derivatives of the hydroxylamino reduction products of metronidazole and dimetridazole.

Metronidazole and related 5-nitroimidazoles undergo reduction of their nitro group apparently to produce such reactive species as 5-hydroxylaminoimidazoles. To define the role of these species we have sought ways to prepare them by the catalytic reduction of metronidazole, dimetridazole and flunidazole. Although their respective 5-hydroxylaminoimidazoles were too unstable to be isolated directly, their O,N-diacetyl derivatives were isolable. Of these, the diacetyl derivative of the hydroxylamine derived from dimetridazole, O,N-diacetyl-1,2-dimethyl-5-hydroxylaminoimidazole (DiacDMH), was used for further study. DiacDMH was converted to its monoacetyl derivative, N-acetyl-1,2-dimethyl-5-hydroxylaminoimidazole (AcDMH), by enzymatic deacylation. Both DiacDMH and AcDMH were examined for bactericidal activity against such strains as Bacteroides fragilis, Clostridium perfringens, and Escherichia coli strain SR58, which are known to be sensitive to dimetridazole, as well as a variety of other bacteria. No bactericidal activity was detected, even in the presence of deacetylating enzymes. As the 5-hydroxylaminoimidazole itself could not be shown to form in these bacterial incubations, it remains uncertain whether or not the hydroxylamino functionality of a 5-nitroimidazole has bactericidal activity.