Properties of 2-hydroxylaminoimidazoles and their implications for the biological effects of 2-nitroimidazoles.

In aqueous solution, in the presence of ammonium chloride, N1-substituted 2-nitroimidazoles are readily reduced to the corresponding hydroxylamines. In air, under neutral conditions, analogous to the reactions of aromatic hydroxylamines, 2-hydroxylaminoimidazoles are converted to the azoxy derivatives via a base-catalyzed condensation reaction between the hydroxylamine and its oxidation product, the nitroso derivative. In nitrogen, rearrangement to form the 2-amino-4(5)hydroxyimidazole derivative followed by addition of water across the C4-C5 double bond to yield isomers of a 4,5-dihydro-4,5-dihydroxy derivative appears to be a major reaction. 2-hydroxylaminoimidazoles undergo a complex series of reactions with glutathione. The initial reaction is the formation of a labile conjugate involving an N-S-linkage. Subsequently in the presence of excess GSH, under neutral conditions, two stable conjugates identified as 2-amino-4-S-glutathionyl- and 2-amino-5-S-glutathionyl imidazoles are formed. Nucleophilic attack by GSH on the imidazole ring of a nitrenium ion is postulated as the initial step in the formation of the stable GSH conjugates as well as the 2-amino-4,5-dihydro dihydroxy derivative. The results provide a molecular mechanism for many of the biological effects of N1-substituted 2-nitroimidazoles in hypoxic mammalian cells.