Medium-dependent competitive pathways in the reactions of polyunsaturated fatty acids with nitric oxide in the presence of oxygen. Structural characterisation of nitration products and a theoretical insight

Reactions of methyl arachidonate and ethyl linoleate with NO in the presence of O-2 gave complex mixtures of products via interaction with NO2 and related nitrogen oxides. In cyclohexane, the reaction afforded chiefly nitroalkene and nitronitrate adducts, characterised by spectroscopic techniques. In 0.1 M phosphate buffer, pH 7.4, a different pattern of products was formed, comprising mainly conjugated hydroperoxide derivatives. Quantum mechanical calculations on a model 1,4-diene system suggested that medium-dependent changes in product distribution can be ascribed in part to solvation effects on the NO2-induced addition/H-atom abstraction competition, but reflect also a complex interplay of solvent-sensitive mechanisms. (C) 1999 Elsevier Science Ltd. All rights reserved.