Formation of 4,4-Dialkoxycyclohexa-2,5-dienone N-(Thiol-S-yl)imine during Reaction of 4-Alkoxynitrosobenzenes with Thiols in Alcoholic Solvents

Abstract

During the interaction of nitrosoarenes with glutathione in aqueous media, intermediate generation of a highly resonance-stabilized sulfenamide cation has been repeatedly suggested. Most intermediates and end products could be explained by reactions of this sulfenamide cation with different nucleophiles such as excess thiol, solvent water, and metabolically produced arylamine. The present paper presents evidence for adduct formation of the sulfenamide cation with solvent alcohol at neutral pH. Sulfenamide cations generated from 4-nitrosophenetole and 4-nitrosoanisole, respectively, are strongly suggested to form the metastable ketals 4-ethoxy-4-methoxycyclohexa-2,5-dienone N-(glutathion-S-yl)imine and 4,4-dimethoxycyclohexa-2,5-dienone N-(glutathion-S-yl)imine, respectively, during reaction with solvent methanol. Reaction of the two sulfenamide cations in ethanol yielded 4,4-diethoxycyclohexa-2, 5-dienone N-(glutathion-S-yl)imine and 4-ethoxy-4-methoxycyclohexa-2, 5-dienone N-(glutathion-S-yl)imine, respectively. Although the metastability of the ketals did not allow isolation of pure solid material, chromatographic and chemical behavior as well as tandem MS fragmentation substantiate a ketal structure of these intermediates. To confirm the proposed structure, new compounds, 2, 6-dimethyl-4-nitrosophenetole, 2,6-dimethyl-4-nitrophenetole, 2, 6-dimethyl-4-phenetidine, and N-(glutathion-S-yl)-N-hydroxy-4-aminoacetophenone, were synthesized and included in supportive experiments. In summary, the detection of ketals corroborates once more the occurrence of a sulfenamide cation which obviously not only reacts with soft nucleophiles such as GSH but, to a limited extent, also reacts with hard nucleophiles. The toxicological significance of this result is discussed.

Additional Pathways of S-Conjugate Formation during Interaction of 4-Nitrosophenetole with Glutathione

“…The reported reactions of the NOPt-derived sulfenamide cation (also classified as N -sulfenylnitrenium ion) reveal striking similarity to other nitrenium ions. Except for the kinetic investigations of Kazanis and McClelland (), this correspondence was not noticed previously since the main products of other nitrosoarenes reacting with GSH were N -hydroxyarylamines, sulfinamides, sulfenamides, and arylamines, i.e., metabolites hardly resembling the product pattern of nitrenium ions.…”

“…Thus, 0.1 volume of MeOH was added to the incubates directly prior to sampling whereby recovery was raised to 93 ( 4%. Higher MeOH proportions were not used in order to maintain chromatographic resolution and to prevent reaction of the sulfenamide cation with alcohol (8). The profile of products obtained in the chromatograms is assumed to be representative for the time of sampling, since GSH separates quickly from the arylic compounds upon injection into the HPLC system (within less than 1 min); only the sulfenamides may decay to some extent during separation.…”

“…In physiological systems, low molecular weight nucleophiles such as GSH and H 2 O may not be the only sites of attack by the sulfenamide cation. Addition to nucleophilic sites of proteins and DNA has been discussed as well ( − ). However, the reactivity of the sulfenamide cation toward weak nucleophiles has been hardly studied and awaits a detailed characterization.…”

Direct and Nitroxyl (HNO)-Mediated Reactions of Acyloxy Nitroso Compounds with the Thiol-Containing Proteins Glyceraldehyde 3-Phosphate Dehydrogenase and Alkyl Hydroperoxide Reductase Subunit C

“…Similar reactions of aromatic C -nitroso compounds with glutathione and thiol-containing proteins including human serum albumin yield thiol oxidized products including N-aryl sulfinamides. 50, 59 Scheme 3 depicts a potential explanation for the exclusive formation of sulfinic acids from the reaction of 1 and 2 with thiol containing proteins. Acyloxy nitroso compounds behave like other electrophilic C -nitroso compounds and undergo nucleophilic thiol addition to yield an N-hydroxysulfenamide intermediate.…”

Differential activation of soluble guanylate cyclase by a series of aryl disulfanyl dinitrate esters

“…22 A sulfenyl nitrite (RSONO) could also form, since the migration of oxygen from nitrogen to sulfur has been reported, e.g., in the reaction of glutathione with nitrosoarenes to yield sulnamides (RSONHR'). 34 The nitrite intermediate can spontaneously release NO in aqueous solutions, 28 or rapidly transfer the NO group to thiols and generate nitrosothiols, which in the presence of trace transition metal ions quantitatively release NO. 35,36 GTN does not activate sGC in the absence of cysteine, and even acts as an antagonist of the sGC activation by NO, 6 an effect possibly due to GTN's capability to oxidize the ferrous-heme of sGC.…”