Reactivity of glutathione adducts of 4-(dimethylamino)phenol. Formation of a highly reactive cyclization product.
During ferrihemoglobin formation, 4-(dimethylamino)phenol (DMAP), a potent cyanide antidote, forms a quinoid compound that is prone to sequential oxidation/addition reactions. In human red cells and hemoglobin solutions fortified with glutathione, a transient adduct has been isolated and identified as 4-(dimethylamino)-2-(glutathion-S-yl)phenol (2-GS-DMAP). This compound still formed ferrihemoglobin but differed from parent DMAP in that the reaction rate was roughly proportional to the oxygen concentration and exhibited a lag phase, pointing to a reactive autoxidation product. The compound was isolated and tentatively identified as an intramolecular cyclization product of 2-GS-DMAP. Formation of this product includes three reaction steps: (1) formation of a quinoid intermediate, (2) addition of the alpha-amino nitrogen atom of the glutamate residue to the aromatic ring, and (3) autoxidation of the cyclization product to give a highly reactive o-quinone imine. The isolated compound existed in two isomeric states (1H-NMR) which upon reduction could be separated by HPLC. The isolated reduced isomers mutually converted into each other. A model compound which was synthesized to mimic the most important structural features, 4-(dimethylamino)-6-[S-(2'-hydroxyethyl)-thio]-N-(2"-phenylethyl)-1,2- quinone imine, had a very similar visible spectum and exhibited an even higher ferrihemoglobin activity than the cyclization product. A similar phenomenon of intramolecular cyclization of a thioether of DMAP had been observed earlier: DMAP covalently bound to the SH groups of the beta-chains in hemoglobin formed a cross-link with the C-terminal histidine residue in the presence of oxygen but not in its absence.(ABSTRACT TRUNCATED AT 250 WORDS)
Ludwig
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Walther-Straub-Institute für Pharmakologie und Toxikologie, Ludwig-Maximilians-Universität München, Germany.
Eyer
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D000627:Aminophenols / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D005978:Glutathione / Q000737:chemistry*; D006454:Hemoglobins / Q000737:chemistry; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D010084:Oxidation-Reduction; D016339:Spectrometry, Mass, Fast Atom Bombardment; D013056:Spectrophotometry, Ultraviolet
D000627:Aminophenols; D006454:Hemoglobins; D005978:Glutathione; C020292:4-dimethylaminophenol