Catalytic Oxidation Of Amines Research Articles

Catalytic Amine Oxidation under Ambient Aerobic Conditions: Mimicry of Monoamine Oxidase B.

The flavoenzyme monoamine oxidase (MAO) regulates mammalian behavioral patterns by modulating neurotransmitters such as adrenaline and serotonin. The mechanistic basis which underpins this enzyme is far from agreed upon. Reported herein is that the combination of a synthetic flavin and alloxan generates a catalyst system which facilitates biomimetic amine oxidation. Mechanistic and electron paramagnetic (EPR) spectroscopic data supports the conclusion that the reaction proceeds through a radical manifold. This data provides the first example of a biorelevant synthetic model for monoamine oxidase B activity.

Catalytic Amine Oxidation under Ambient Aerobic Conditions: Mimicry of Monoamine Oxidase B

The flavoenzyme monoamine oxidase (MAO) regulates mammalian behavioral patterns by modulating neurotransmitters such as adrenaline and serotonin. The mechanistic basis which underpins this enzyme is far from agreed upon. Reported herein is that the combination of a synthetic flavin and alloxan generates a catalyst system which facilitates biomimetic amine oxidation. Mechanistic and electron paramagnetic (EPR) spectroscopic data supports the conclusion that the reaction proceeds through a radical manifold. This data provides the first example of a biorelevant synthetic model for monoamine oxidase B activity.

Mechanistic study of amine oxidation catalysed by quinonoid cofactors

A kinetic study was performed on the oxidative deamination of benzylamine (BzAm) catalysed by pyrroloquinoline quinone (PQQ), a tryptophan tryptophylquinone analogue [3-methyl-4-(3′-methylindol-2′-yl)indole-6,7-dione; TTQa], and a topa quinone analogue (6-hydroxydopa quinone; TPQa) using high-performance liquid chromatography under aerobic conditions and cyclic voltammetry under anaerobic conditions. The overall kinetics are second-order in the quinone and BzAm concentrations and independent of the electron acceptors used (dioxygen under aerobic conditions and electrode under anaerobic conditions). The second-order rate constants vs. pH profiles are explained in terms of the acid dissociation of BzAm and the quinones, yielding pH-independent second-order rate constants, which are in the order TTQa > PQQ TPQa . Half-wave potentials of steady-state catalytic voltammograms are more positive than the redox potentials of the free quinones, indicating that the BzAm-reduced quinones are not quinols but the corresponding aminophenols, which are oxidized to iminoquinones. Iminoquinone forms of PQQ and TTQa exhibit lower catalytic activity compared with the quinone forms. The reaction rate of TTQa slows down with the time, while those of PQQ and TPQa are practically independent of the reaction time within a 15 min period. The diminished rate of TTQa is reasonably ascribed to slow hydrolysis of imino-TTQa to TTQa. Generation of the iminosemiquinone radical during the catalytic reactions is evidenced by EPR spectroscopic measurements. The significance of radical generation is discussed in the light of autoxidation of the aminophenols. All these results are interpreted well by a transamination mechanism. In addition, an asymmetric ortho-quinone structure is proposed to be important in catalytic amine oxidation activity, and the relatively low catalytic activity of free TPQa is ascribed to the contribution of a para-quinone-type electronic structure. On the basis of these results, a role for CuII is proposed as a transient intramolecular electron acceptor in copper amine oxidases to enhance the reactivity toward dioxygen through the generation of the imino-TPQ semiquinone and as a weak ligand in TPQ-containing amine oxidases making the TPQ cofactor bear an ortho-quinone-type electronic structure.

Synthetic Aspects of Metal‐Catalyzed Oxidations of Amines and Related Reactions

AbstractThe metabolism of amines is governed by a variety of enzymes such as amine oxidase, flavoenzyme, and cytochrome P‐450. A wide variety of compounds are produced such as ammonia and alkaloids in selective and clean oxidation reactions that proceed under mild reaction conditions. Simulation of the functions of these enzymes with simple transition metal complex catalysts may lead to the discovery of biomimetic, catalytic oxidations of amines and related compounds. Indeed, metal complex catalyzed oxidations have been found to proceed with high efficiency. The first section of this review discusses the dehydrogenative oxidations of amines with transition metal catalysts by transition metal catalysts that simulate amine oxidase. The second section highlights the catalytic oxidation of secondary amines to nitrones by simulation of flavoenzymes. The third section describes the simulation of the function of cytochrome P‐450 with lowvalent ruthenium complexes and peroxides. Biomimetic ruthenium‐catalyzed oxidations of tertiary amines, secondary amines, and other substrates such as amides, β‐lactams, nitriles, alcohols, alkenes, ketones, and even nonactivated hydrocarbons can be performed selectively under mild conditions. These three general approaches provide highly useful strategies for synthesis of fine chemicals and biologically active compounds such as alkaloids, amino acids, and β‐lactams.