Oxidative Deamination of Benzylamine by Electrogenerated Quinonoid Systems as Mimics of Amine Oxidoreductases Cofactors

Abstract

The reactions of a new type of quinonoid system with benzylamine have been investigated in methanol in order to mimic the reactions occurring in the course of the enzymatic oxidation of amines by quinone cofactors. Under strictly anaerobic conditions, unstable quinonoid species 1(ox)()-4(ox)() have been selectively electrogenerated using anodic-controlled potential electrolysis. Thus, we have demonstrated that 3,4-quinone 1(ox)() is incapable of deaminating benzylamine, while 3,4-iminoquinone species 3(ox)() and 4(ox)() act as efficient catalysts for the autorecycling oxidation of benzylamine: the reaction efficiency reached 64 turnovers. Additional mechanistic investigations reveal that the oxidation of benzylamine by our quinonoid model cofactors proceeds unambiguously via a transamination mechanism, as suggested for many enzymatic systems.

Symbiotic Transition‐Metal and Organocatalysis for Catalytic Ambient Amine Oxidation and Alkene Reduction Reactions

“…Secondly, chemistry that proceeds under ambient conditions is a key goal. Thus far, there have been examples of the use of biomimetic quinone molecules in catalytic amine redox transformations as electrochemical oxidants, as a single catalyst and with a Cu co‐catalyst, all of which require multi‐step synthesis of the quinone mediator and, in some cases, with sensitive synthetic intermediates that require attention en route.…”

Oxidation of Unactivated Primary Aliphatic Amines Catalyzed by an Electrogenerated 3,4‐Azaquinone Species: A Small‐Molecule Mimic of Amine Oxidases.

“…These results indicated that the 1 red /1 ox system behaved as a redox mediator for the indirect electrochemical oxidation of unactivated primary aliphatic amines to the corresponding alkylimines, according to the transamination mechanism reported in Scheme 2. [9] After exhaustive electrolysis, the catalyst 1 ox was lost irreversibly, as corroborated by the anodic current, which remained negligible upon further addition of amine substrate. Unstable alkylimine was isolated in terms of the corresponding aldehyde 2,4-dinitrophenylhydrazone (DNPH) obtained upon workup of the oxidized solution with 2,4-dinitrophenylhydrazine.…”

“…Recent intensive studies have shown that an electron transfer from the cofactor to the metal is not required during the catalytic turnover, so that the metal essentially stabilizes a reduced oxygen intermediate. [9] In contrast to other existing amine oxidase model cofactors, 1 ox was also very active toward aliphatic amines. [6] Substantial mechanistic information has been obtained through catalytic aerobic deamination of benzylamine mediated by synthetic models of natural quinones which confirm the occurrence of the transamination mechanism.…”

“…The catalytic cycle produced the reduced catalyst 1 red and N-benzylidenebenzylamine as the product of benzylamine oxidation in 3200 % yield (based on the initial concentration of 1 red ). [9] In contrast to other existing amine oxidase model cofactors, 1 ox was also very active toward aliphatic amines. Herein, we report for the first time the catalytic oxidation of unactivated primary aliphatic amines by a small-molecule enzyme mimic in the absence of a metal ion.…”

Eine gekreuzte Aldiminkupplung zur diastereoselektiven Synthese von unsymmetrischen 1,2‐Diaminen

“…Die Konfiguration der Hauptprodukte konnte mithilfe der in der Literatur beschriebenen charakteristischen 1 H-und 13 C-chemischen Verschiebungen sowie vergleichender NOE-Messungen an den diastereomeren FormaldehydAminalen der Diamine 4 a und 4 m zugeordnet werden. [19][20][21][22] Bei Versuchen zur Erhöhung der Diastereoselektivität der Reduktion fanden wir, dass über den Umweg einer Oxidation der Additionsprodukte zu den Diiminen 3 die synkonfigurierten Diamine 4 erhalten werden können, wenn [23] Dihydroxylierungen [24] oder Reduktionen [25] verwendet werden können. Setzt man bei der Reduktion mit BH 3 ·THF statt NaBH 4 Phthalsäure zu (Tabelle 2, Methode B), [26] entstehen hingegen die anti-konfigurierten Produkte.…”