Oxidation of amides by laccase-generated aminoxyl radicals

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• 作者：Aless ; ra Coniglio ; Carlo Galli ; Patrizia Gentili ; Raffaella Vadalà
• 关键词：Laccase ; Mediators ; Oxidation ; Aminoxyl radicals ; Amides ; Semiempirical calculations
• 刊名：Journal of Molecular Catalysis B: Enzymatic
• 出版年：2008
• 出版时间：2 January 2008
• 年：2008
• 卷：50
• 期：1
• 页码：40-49
• 全文大小：743 K

文摘

The enzyme laccase from the fungus Trametes villosa catalyses the oxidation of two hydroxylamines (NOH), i.e., HPI (N-hydroxy-phthalimide) and HBT (1-hydroxy-benzotriazole), into their corresponding aminoxyl radicals (NO) PINO and BTNO. The ensuing oxidation of a few amides and lactames by PINO and BTNO has been investigated in buffered water solution (pH 5) at room temperature. The results from this chemo-enzymatic approach have been compared with a literature method that generates the aminoxyl radical PINO by the HPI/Co(II)/O₂ chemical system, and uses it for the oxidation of similar amides. The merits of the aminoxyl radicals PINO and BTNO have been comparatively assessed in the chemo-enzymatic method, and the mechanism investigated. A Hammett treatment of the relative reactivity of oxidation of X-substituted-N-acetylbenzylamides in competition experiments supports a rate-determining H-abstraction route. With a few of the investigated substrates, stereoelectronic effects have been uncovered, and a rationalisation of their contribution to the reactivity of the H-abstraction route is offered, and supported by semiempirical calculations.