Reactivity of (E)‐4‐Hydroxy‐2‐nonenal with Fluorinated Phenylhydrazines: Towards the Efficient Derivatization of an Elusive Key Biomarker of Lipid Peroxidation

Abstract

Abstract4‐Hydroxynonenal (4‐HNE) is a major product of the oxidation of ω‐6‐polyunstaturated lipids and an effector of radical‐mediated oxidative damage, whose analytical determination requires chemical derivatization. In this work, its reactivity with fluorinated phenylhydrazines was explored both under preparative and analytical settings. A five‐step synthesis of 4‐HNE on gram‐scale with an overall yield of 30 % is described. Reaction of 4‐HNE with ortho‐, meta‐, or para‐CF3‐phenylhydrazine, as well as with the 3,5‐di‐CF3, 2,4‐di‐CF3, or pentafluoro analogues, in MeCN with 0.5 mM TFA yields the corresponding hydrazones with rate constants kf of 2.8 ± 0.4, 1.7 ± 0.1, 3.0 ± 0.2, 0.6 ± 0.1, 0.5 ± 0.1, and 3.5 ± 0.5 M–1 s–1, respectively at 298 K. At higher temperatures, the hydrazones undergo intramolecular cyclization to form 1,6‐dihydropyridazines that, depending on the solvent and temperature, may further react with the hydrazine to yield tetrahydropyridazine adducts and their oxidation products. Other reaction products were isolated, depending on the reaction conditions, and the complex reactivity of 4‐HNE with the above nucleophiles is discussed. Due to the good yield and rate of formation of the hydrazone adducts, their stability and favorable UV absorbance, 2‐(trifluoromethyl)phenylhydrazine and 2,3,4,5,6‐pentafluorophenylhydrazine are the most interesting candidates for the development of rapid and efficient analytical derivatizations of 4‐HNE.