Reactivity of Sulfur-Centered Radicals with Indolinonic and Quinolinic Aminoxyls

Abstract

Indolinonic, phenylimino‐indolinonic and quinolinic aromatic aminoxyls readily react with sulfur‐centered radicals, generated upon reaction with p‐methylthiophenol at room temperature. The main product is the deoxygenated derivative i.e. the corresponding amine. The other compounds, obtained in low yields, are N‐substituted amines and amines substituted in a conjugated position with respect to the amino group by arylthiyl, arylsulphinyl, arylsulphonyl and arylsulphonyloxy radicals. The formation of the products are explained by the initial attack of the thiophenol radical onto the NO· function to give an unstable adduct which decomposes to aminyl and arylsulphinyl radicals. From here the reaction can take two different routes to give the products obtained.

Hydrogen Abstraction Ability of Different Aromatic Nitroxides

“…Our interest in this field has been mainly focused on aromatic indolinonic and quinolinic nitroxides, a series of nitroxides that exhibit a different behaviour towards radical species with respect to other nitroxides such as 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and 4-hydroxy-TEMPO. This more variegated reactivity is due to their ability to react not only with C-centred [1,2] or S-centred radicals (thiyls) [3] but also with O-centred radicals (peroxyl, [4] alkoxyl, [5] hydroxyl, [6] superoxide [6,7] ) and nitrogen monoxide, [8] as outlined in Scheme 1.…”

Fluorescence study on rat epithelial cells and liposomes exposed to aromatic nitroxides

“…In this context, we have been studying for some time the antioxidant effects of indolinonic aromatic nitroxides whose chemical properties differ to some extent from the most commonly used aliphatic nitroxides, such as piperidine and pyrrolidine derivatives. In the majority of cases, these compounds were shown to effectively protect the most biologically significant macromolecules, lipids (Antosiewicz et al, 1995(Antosiewicz et al, , 1997Damiani et al, 1994), proteins (Antosiewicz et al, 1995;Damiani et al, 2001a,b), DNA (Damiani et al, 1999a(Damiani et al, ,b,c, 2000Villarini et al, 1998) and intact cells (Gabbianelli et al, 1997;Falcioni et al, 1998) against free-radical induced damage. Nevertheless, information on the actual interaction of indolinonic nitroxides with biological structures, for example, membranes, is lacking, and this is of vital importance since the functional and structural properties, such as membrane fluidity, are important for the maintenance of cell integrity (Kimelberg, 1977).…”

Reaction of indolinonic aminoxyls with nitric oxide

“…The radical scavenging activity of indolinonic aminoxyls has now been well established; in fact, they are extremely versatile in reacting with oxygen-centered radicals (peroxyls, 1 alkoxyls, 2 hydroxyl, 3 superoxide 3,4 ), with sulfur-centered radicals (thiyls), 5 and with carbon-centered radicals 6 yielding products substituted on the benzene ring in the first two cases and alkylated hydroxylamines in the third. The above mentioned reactive oxygen radicals are all involved in a cascade of events that ultimately lead to conditions of 'oxidative stress' in biological systems.…”