V. A. Reznikov

Synthetic chemistry of stable nitroxides

Introduction to Nitroxide Chemistry. Generation and Chemical Properties of the Nitroxyl Group. Synthetic Chemistry of Stable Nitroxides. Complexes with Metal-Nitroxyl Group Coordination. New Approaches to Generation of Heterocyclic Nitroxides Using Organometal Reagents. References. Index.

Mechanistic studies of the reactions of nitrone spin trap PBN with glutathiyl radical.

We performed mechanistic studies of the reaction of PBN with the physiologically relevant glutathiyl radical, GS*, formed upon oxidation of the intracellular antioxidant, glutathione, GSH. The scavenging rate constant of GS* by PBN has been measured directly by laser flash photolysis and indirectly by competitive EPR of the spin adduct of PBN and another spin trap, DMPO (5,5-dimethyl-1-pyrroline N-oxide), and was found to be 6.7 x 107 M(-1) s(-1). Reverse decomposition of the paramagnetic PBN-glutathiyl radical adduct to the nitrone and thiyl radical was observed for the first time. The rate constant for the reaction of the monomolecular decomposition of the radical adduct was found to be 1.7 s(-1). Diamagnetic, EPR-invisible products of PBN adduct degradation were studied by 1H NMR and 19F NMR using newly synthesized fluorine-substituted PBN.

Stable nitroxyl radicals with a hydrogen atom at α-carbon atom of nitroxyl group

Nitroxyl radicals containing the diphenylmethyl group as one of the substituents at the nitroxyl group are stable compounds that can be isolated in an individual state.N-(2-Hydroxy-3-methyl-2-phenylcyclohexyl)-N-diphenylmethylnitroxyl was characterized by X-ray diffraction analysis for the first time.

Stable nitroxides with hydrogen at α-carbon of the nitroxyl group

Abstract The reactions of 1-hydroxy-3-imidazoline-3-oxides containing hydrogen in the 2-position with PhLi or PhMgBr lead to acyclic α-hydroxylaminooximes. The oxidation of the latter gives stable acyclic nitroxides with hydrogen at the α-carbon atom.

Metal complexes of the nitrile-substituted nitroxides

Abstract The chelates of the nitrile-substituted 3-imidazoline nitroxides with copper(II), cobalt(II), and nickel(II) have been synthesized and studied with X-ray diffraction and magnetic susceptibility measurements. The influence of the nitrile substituent on structural and magnetic features of the complexes are discussed.

Interaction of heterocyclic nitrones with organometallic reagents as a method for the synthesis of new types of nitroxides

Abstract The reactions of heterocyclic nitroxides: 3-imidazoline-3-oxides, 2H- (4H)-imidazole mono- and dioxides, dihydropyrazine-1,4-dioxides, with organometallic reagents and subsequent oxidation led to heterocyclic nitroxides of 3-(2)-imidazoline and 3-(2)-imidazoline-3-oxide, dihydropyrazine oxide, monocyclic imidazolidine biradicals and stable acyclic nitroxides with hydrogen at the α-carbon atom.

Synthesis and some properties of heterocyclic amidine derivatives of 3-imidazoline nitroxides

Abstract The interaction of 2,2,5,5-tetramethyl-3-imidazoline-3-oxide-1-oxyl with isocyanates leads to oxadiazolidine cycloadducts which are smoothly transformed into amidines - 4-R-amino-2,2,5,5-tetramethyl-3-imidazoline-1-oxyles when treated with nucleophilic reagents. This reaction was applied to the synthesis of some paramagnetic amidines containing various functional groups which may be used as spin labels having a pH-sensitive ESR spectrum. The mechanism of transformation of oxadiazolidines into amidines and the tautomeric equilibrium of the amidines synthesized are discussed.

A new series of lipophilic pH-sensitive spin probes

A series of new lipophilic spin probes with pH-dependent ESR spectra was synthesized: cyano-substituted enamino ketones, viz., derivatives of imidazolidine nitroxyl radicals. The use of these compounds makes it possible to measure the acidity of the medium in the pH 6—12 range.

Reactions of chloro-substituted enaminoketones,viz., derivatives of imidazolidine nitroxides, with sodium cyanide

The reactions of chloro-substituted enaminoketones,viz., derivatives of imidazolidine nitroxides, with sodium cyanide afford the corresponding nitriles. The reactions proceed through formation of epoxides. The structure of one of these epoxides was confirmed by X-ray diffraction analysis.

Mixed-ligand copper complexes with stable nitroxide — pseudotetrahedral tectons with the octahedral coordination core

Abstract The reaction of copper hexafluoroacetylacetonate (Cu(hfac) 2 ) with nitrile-substituted 3-imidazoline nitroxide enaminoketones (HL R ) or corresponding copper bis-chelates (CuL R 2 ) yields asymmetric chelates Cu(hfac)L R . Due to additional coordination of the nitrile and/or nitroxide groups to the copper atoms, the complexes form 3-D (R=i-Pr, Ph) and 2-D (R=n-Pr) coordination polymers. The key supramolecular feature of the complexes is that the Cu(hfac)L R molecules having the octahedral metal ion behave as pseudotetrahedral tectons giving rise to 3-D structures. Cryomagnetic investigation of the complexes showed that due to weak interactions through the nitrile bridge the magnetic dimensionality of the materials is lower than the structural one: 1-D for Cu(hfac)L i-Pr and 0-D for Cu(hfac)L n-Pr and Cu(hfac)L Ph .