Stable free radical and benzoquinone imine metabolites of an acetaminophen analogue.

V Fischer,R P Mason

doi:10.1016/s0021-9258(18)90961-0

Abstract

The enzymatic oxidation of the acetaminophen analogue 3',5'-dimethyl-4'-hydroxyacetanilide (3',5'-dimethylacetaminophen) with the horseradish peroxidase/hydrogen peroxide system forms a phenoxyl free radical metabolite. The structure of this free radical is established by a complete analysis of the ESR spectrum and confirmed by deuterium isotope substitution. Concomitant with phenoxyl radical formation, N-acetyl-3,5-dimethyl-p-benzoquinone imine was detected by optical spectroscopy. The free radical is also formed by comproportionation in solutions of the quinone imine containing added 3',5'-dimethylacetaminophen. In contrast to acetaminophen, the imine and radical metabolites are stable and can be detected without resort to rapid-mixing techniques. Factors leading to the increased stability of these metabolites relative to those formed from acetaminophen are discussed in terms of the toxicity of acetaminophen.

Highlights

N-C-CH, methylacetaminophen) with the horseradish peroxidaselhydrogen peroxide system forms a phenoxyl free radical metabolite
The free radical is formed by comproportionationin solutions of the quinone imine containing added 3’,5’-dimethy)acetaminophen.In contrast to acetaminophen, the imine and radical metabolites are stable and can be detected without resort to rapid-mixing techniques
Nitrosation of 2,6-diformation of a highly reactive metabolic species, the N-acetyl- methylphenol with sodium nitrite led to 2,6-dimethyl-4-nitrosop-benzoquinone imine, which is thought tobind covalently to protein in vivo

Summary

TKR JOURNAOFLBIOLOGICACLHEMISTRY

102&-10288,19& Printed in U.S.A. Stable Free Radical and Benzoquinone Imine Metabolites of an Acetaminophen Analogue*. N-C-CH, methylacetaminophen) with the horseradish peroxidaselhydrogen peroxide system forms a phenoxyl free radical metabolite. Factors leading to the increased stability of these metabolites relative to those in the 3’,5’-positions does not significantly change the metabolic pathway responsible for the toxic effects of acetaminophen. Both the radical formed from DMA and the corresponding quinone imine are more stable, so ESR and UV studies of this species were possible without the use of fastflow mixing techniques, which require liters of solutions [8]. To be of comparable toxicity to acetaminophen itself, whereas the 2’,6’-dimethyl-4’-hydroxyacetanilide,like N-methyl-

RESULTS

The resulting spectrum was identical to theone obtainedfrom m

ESR and UV spectroscopy have allowed us to detect the REFERENCES