The enzyme laccase from the fungus Trametes villosa catalyses the oxidation of two hydroxylamines ( NO H), i.e., HPI (N-hydroxyphthalimide) 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.
Oxidation of amides by laccase-generated aminoxyl radicals / Alessandra, Coniglio; Galli, Carlo; Gentili, Patrizia; Vadala', Raffaella. - In: JOURNAL OF MOLECULAR CATALYSIS B-ENZYMATIC. - ISSN 1381-1177. - 50:1(2008), pp. 40-49. [10.1016/j.molcatb.2007.09.022]
Oxidation of amides by laccase-generated aminoxyl radicals
GALLI, Carlo;GENTILI, Patrizia;VADALA', RAFFAELLA
2008
Abstract
The enzyme laccase from the fungus Trametes villosa catalyses the oxidation of two hydroxylamines ( NO H), i.e., HPI (N-hydroxyphthalimide) 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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
