TY - JOUR T1 - One-electron redox reactions of pyrazolin-5-ones. A pulse radiolysis study of antipyrine and analogues. JF - Molecular Pharmacology JO - Mol Pharmacol SP - 377 LP - 380 VL - 28 IS - 4 AU - S V Jovanovic AU - P Neta AU - M G Simic Y1 - 1985/10/01 UR - http://molpharm.aspetjournals.org/content/28/4/377.abstract N2 - One-electron oxidation of several derivatives of pyrazolin-5-one, including the drug antipyrine, were studied by pulse radiolysis of aqueous solutions. All the compounds were found to be oxidized by Br2 rapidly (k approximately 3 X 10(8)-2 X 10(9) M-1 s-1) but considerably more slowly by weaker oxidants, such as peroxyl radicals. From redox equilibria using p-methoxyphenol and N,N,N',N'-tetramethyl-p-phenylenediamine as reference compounds, the one-electron oxidation potentials of the methyl-substituted 2-pyrazolin-5-ones were found to be in the range of 0.32-0.39 V versus normal hydrogen electrode. The relevance of these findings to the properties of the drug nafazatrom is discussed. Antipyrine was found to have a much higher oxidation potential, estimated as 1.2-1.5 V, which is rationalized on the basis of the phenyl substitution and lack of resonance stabilization of the radical cation. ER -