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Reactions of the NO redox forms NO + , • NO and HNO (protonated NO – ) with the melatonin metabolite N 1 ‐acetyl‐5‐methoxykynuramine
Author(s) -
Hardeland Rüdiger,
Backhaus Claudia,
Fadavi Azadeh
Publication year - 2007
Publication title -
journal of pineal research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.881
H-Index - 131
eISSN - 1600-079X
pISSN - 0742-3098
DOI - 10.1111/j.1600-079x.2007.00489.x
Subject(s) - chemistry , protonation , redox , metabolite , acetonitrile , trinitrotoluene , aqueous solution , solvent , nuclear chemistry , hydrogen peroxide , medicinal chemistry , inorganic chemistry , organic chemistry , biochemistry , ion , explosive material
The different NO redox forms, NO + , • NO and HNO (= protonated NO – ), were compared for their capabilities of interacting with the melatonin metabolite N 1 ‐acetyl‐5‐methoxykynuramine (AMK), using NO + SbF 6 – , PAPA‐NONOate and Angeli’s salt as donors of the respective NO species. Particular attention was paid to stability and possible interconversions of the redox forms. • NO formation was followed by measuring the decolorization of 2‐(trimethylammonio‐phenyl)‐4,4,5,5‐tetramethyl‐imidazoline‐1‐oxyl‐3‐oxide (TMA‐PTIO), at different pH values, at which NO + is, in aqueous solution, either highly unstable (pH 7.4) or relatively stable (pH 2.0). • NO donation by PAPA‐NONOate, as indicated by TMA‐PTIO decolorization, was similar at either pH and 3‐acetamidomethyl‐6‐methoxycinnolinone (AMMC) was formed as the major product from AMK, at pH 7.4 more efficiently than at pH 2.0. At pH 2.0, TMA‐PTIO decolorization by NO + SbF 6 – was much weaker than by PAPA‐NONOate, but AMMC was produced at substantial rates, whereas neither TMA‐PTIO decolorization nor AMMC formation was observed with the NO + donor at pH 7.4. As NO + is also stable in organic, especially aprotic solvents, NO + SbF 6 – was reacted with AMK in acetonitrile, ethanol, butanol, and ethyl acetate. In all these cases, AMMC was the only or major product. In ethyl acetate, N 1 ‐acetyl‐5‐methoxy‐3‐nitrokynuramine (AMNK) was also formed, presumably as a consequence of organic peroxides emerging in that solvent. Presence of tert ‐butylhydroperoxide in an ethanolic solution of NO + SbF 6 – and AMK also resulted in AMNK formation, in addition to AMMC and two red‐fluoresecent, to date unknown products. However, hydrogen peroxide enhanced • NO‐dependent AMMC production from AMK and also from N 1 ‐acetyl‐ N 2 ‐formyl‐5‐methoxykynuramine. HNO donation by Angeli’s salt (Na 2 N 2 O 3 ) also caused AMMC formation from AMK at pH 7.4, with a somewhat lower efficiency than PAPA‐NONOate, but no AMNK nor any other product was detected. Therefore, all three NO congeners are, in principle, capable of nitrosating AMK and forming AMMC, but in biological material the reaction with NO + is strongly limited by the extremely short life‐time of this redox form.