4,5-Dihydro-4,5-dihydroxyimidazoles as products of the reduction of 2-nitroimidazoles. HPLC assay and demonstration of equilibrium transfer of glyoxal to guanine

Abstract

RICK PAN~CUCC~ and ROBERT A. MCCLELLAND. Can. J. Chem. 67, 2 128 (1 989). An HPLC method has been employed to study the electrochemical reduction (mercury cathode at -800 mV with respect to calomel electrode) of the 2-nitroimidazole benznidazole (N-benzyl-(2'-nitro-1'-imidazoy1)acetamide). The principal product of this reduction is the cyclic guanidiniurn ion 3c (protonated N-benzyl-(2'-amino-4',5'-dihydro-4',5'-dihydroxy-l'-imidazoyl)acetamide), which forms in a linear fashion as the nitroimidazole is reduced and accounts for 75% of the product upon completion of the reduction. To perform the HPLC analysis quantitatively an authentic sample of this product (isolated as cis:trans isomers) was prepared as the sulfate salt through the reaction of N-benzyl-2-guanidinoacetamide sulfate with aqueous glyoxal. The two isomers of 3c arise through the nonreductive decomposition of the 2-hydroxylaminoimidazole, which is the product of a four-electron reduction of the nitroimidazole. Analysis of high field 'H NMR spectra also showed that the two isomers of 3c were the principal products following electrochemical reduction, neutral aqueous zinc reduction, and radiation chemical reduction. Previous investigations using NMR of the reductions of misonidazole (3-methoxy-1-(2'-nitro-1'-imidazoy1)-2-propanol) and 1-methyl-2-nitroimidazole have shown that the corresponding dihydroimidazoles 3a and 36 are the major products. The agreement of these various NMR and HPLC results suggests that the formation of dihydroimidazoles 3 is a general phenomenon for model reductions of 2-nitroimidazoles in neutral aqueous solution. Previous workers have shown that 2-nitroimidazole reduction mixtures, when treated with guanine derivatives, form the adduct 4 derived from the guanine and glyoxal. This work demonstrates that this adduct is also formed when authentic samples of 3 a , 3 6 , and 3c are reacted with 2'-deoxyguanosine. A quantitative HPLC analysis, however, demonstrates that the reaction does not proceed to completion, and in fact the equilibrium for formation of 4 is unfavorable. This suggests that guanines are not useful derivatizing agents for the quantitative assay of "glyoxal-like" products formed in chemical or biological reductions of 2-nitroimidazoles.Key words: nitroimidazole, reduction of nitroimidazoles, glyoxal from nitroimidazoles.RICK PANICUCCI et ROBERT A. MCCLELLAND. Can. J. Chem. 67, 2128 (1989). On a utilisC une mtthode de CLHP pour Ctudier la rCduction Clectrochimique (cathode de mercure h -800 mV par rapport a l'tlectrode de calomel) de la 2-nitroimidazole benznidazole (N-benzyl-(2'-nitro-I '-imidazoy1)acttamide). Le produit principal de cette rCduction est l'ion guanidinium cyclique 3c (N-benzyl-(2'-amino-4',5'-dihydro-4',5'-dihydroxy-l'-imidazoyl)acCtamide protonC) qui se forme d'une faqon linCaire au fur et h mesure que le nitroimidazole est rtduit et qui forme 75% du produit ? I la fin de la riduction. Afin de rCaliser l'analyse quantitative par CLHP, on a prCparC un Cchantillon authentique de ce produit (is016 s...

Activation of Benznidazole by Trypanosomal Type I Nitroreductases Results in Glyoxal Formation

“…6G). The conversion of guanosine to the guanosine-glyoxal adduct is only partial, consistent with previous reports that the process is relatively inefficient in neutral aqueous solutions (32).…”

“…5). This reduction pattern is identical to that reported previously following the electrochemical reduction of benznidazole under neutral conditions and analogous to that observed during the cytochrome P450 reductase-mediated anaerobic reduction of the 2-nitroimidazole misonidazole (13,32). Throughout this pathway, several potentially cytotoxic and mutagenic moieties are produced (Fig.…”

“…S4B in the supplemental material) indicated that these two peaks corresponded to the cis and trans isomers of the 4,5-dihydro-4,5-dihydroxyimidazole derivative previously reported to be the product of the electrochemical reduction of benznidazole ( Fig. 3D) (32). These isomers are formed as a result of the 4-electron reduction of benznidazole to a hydroxylamine via a nitroso intermediate that, under neutral conditions, undergoes rearrangement through a nitrenium ion to form a hydroxy derivative (Fig.…”

“…6). However, as glyoxal release from the dihydro-dihydroxy metabolite of benznidazole is inefficient and does not account for all the DNA adducts detected by using the prodrug, the trypanocidal effects probably rely on the combined effects of several of its metabolites (32,37,44).…”

Slow delivery of a nitrification inhibitor (dicyandiamide) to soil using a biodegradable hydrogel of chitosan

“…Glyoxal is known to undergo oligomerisation upon loss of water and it can easily polymerise in the solid state (Loeffler et al, 2006;Nakajima et al, 2007). In addition, it is possible that glyoxal could react with the guanidine group of the DCD to form Schiff base glyoxal-DCD adducts (Panicucci and McClelland, 1989). These excess glyoxal compounds were partly removed from the C beads before the drying step by washing in a solution containing DCD.…”