Amines aldehydes, oxidation

While most alkaloids do not contain aldehydes when they enter mammalian, microbial, or plant tissues, this functional group may become important when formed as a metabolite of alcohols (via alcohol dehydrogenase) or amines (via oxidative dealkylation and oxidative deamination). Aldehyde dehydrogenases catalyze oxidation of aldehydes to the corresponding carboxylic acids. The physical properties, catalytic mechanism, and specificity of this group of enzymes has been reviewed (99). The general reaction catalyzed by aldehyde dehydrogenase is seen in Eq. (9). 

Kitamura S, Tatsumi K. Reduction of tertiary amine N-oxides by liver preparations function of aldehyde oxidase as a major N-oxide reductase. Biochem Biophys Res Commun 1984 121(3) 749-754. 

Interestingly, persulfate reacts differently with aliphatic and aromatic amines. Aliphatic primary amines are dehydrogenated to imines and further converted to aldehydes when reacted with peroxy disulfate , whereas aromatic primary amines are oxidized to nitroso compounds using potassium persulfate in the presence of H2SO4 (equation 14) °. 

Non-microsomal oxidations may be subdivided into amine oxidation, alcohol and aldehyde oxidation, dehalogenation, purine oxidation, and aromatization. 

Tertiary amines are oxidized to the corresponding nitrogen oxides. Tosyl hydrazones of ketones and aldehydes and imines are oxidized to the corresponding carbonyl compounds. Reactions have been carried out with small molecules and also with molecules that would not diffuse into the pore structure of the titanium silicates. As in the case of C—C bond cleavage, it is possible that these reactions take place on the outer surface of the catalyst crystals. 

Ozonolysis of alkenes in the presence of amine A-oxides resulted in reductive ozonolysis, i.e, the direct formation of aldehydes in high yields, avoiding the generation and isolation of ozonides or other peroxide products. Use of DMSO and tertiary amines improved the yield of aldehydes but some amount of ozonides remained. This... 

Although molybdenum and tungsten enzymes carry the name of a single substrate, they are often not as selective as this nomenclature suggests. Many of the enzymes process more than one substrate, both in vivo and in vitro. Several enzymes can function as both oxidases and reductases, for example, xanthine oxidases not only oxidize purines but can deoxygenate amine N-oxides [82]. There are also sets of enzymes that catalyze the same reaction but in opposite directions. These enzymes include aldehyde and formate oxidases/carboxylic acid reductase [31,75] and nitrate reductase/nitrite oxidase [83-87]. These complementary enzymes have considerable sequence homology, and the direction of the preferred catalytic reaction depends on the electrochemical reduction potentials of the redox partners that have evolved to couple the reactions to cellular redox systems and metabolic requirements. 

Primary amines are oxidized in the body by monoamine oxidase (MAO). MAO converts the amine to an imine, which is hydrolyzed to yield an aldehyde and ammonia. One function of MAO is to regulate the levels of the neurotransmitters serotonin and norepinephrine. Monoamine oxidase inhibitors prevent the oxidation (and inactivation) of these neurotransmitters, thereby elevating mood. MAO inhibitors were the first antidepressants, but they are used sparingly now because of numerous side effects. 

Figure 3.43 Use of an amine base with hydrogen peroxide to effect aldehyde oxidation.

Photochemical dehydrofragmentation has also been observed by Whitten et al. [16, 17] in PET reactions of aminoalcohols. The reaction is restricted to the geminate pair and the complimentary roles of reduced acceptor and oxidized donor facilitate chemical reaction in competition with back ET. The rapid fragmentation is dependent on the acceptor anion-radical induced deprotonation of the donor cation radical in the contact ion-pair and is strongly dependent on the structure of A [16]. The chemical transformation converts the aminoalcohol into the free amine, aldehyde and reduced electron acceptor. The efficiency of the PET induced fragmentation is affected by the stereochemistry of the aminoalcohol as well as the solvent [18]. Both the thioindigo (TI) and dicyanoanthracene (DCA) sensitized reactions are more efficient in nonpolar solvents such as benzene and... 

C. Silver-Mediated Amine, Imine, and Aldehyde Oxidation / 19... 

Amine concentrations can be determined by using either diamine oxidase or monoamine oxidase in which the amine is oxidized to an aldehyde, hydrogen peroxide, and ammonia with uptake of oxygen (Equation 17). 

Eq. (19). A tertiary amine N-oxide is O-lithiated and a-deprotonated with LDA, and the elimination of LiO follows immediately to form an iminium intermediate. The second a -deprotonation of the iminium intermediate generates an azomethine ylide 1,3-dipole. Hydrolysis of the iminium or azo-methine ylide 1,3-dipole. Hydrolysis of the iminium or azomethine ylide intermediate on a work-up procedure gives the aldehyde and secondary amine. 

An alternative oxidation using O2 and a RuCls catalyst converted pyridine to pyridine A-oxide. Bromamine-T and RuCls in aq. acetonitrile also oxidizes pyridine to the A-oxide. Tertiary amines are oxidized to the A-oxide with O2 and Fe203 in the presence of an aliphatic aldehyde. " Oxygen and a cobalt-Schiff base complex also oxidzes tertiary amines, including pyridine. ... 

The spectrum of applications of potassium permanganate is very broad. This reagent is used for dehydrogenative coupling [570], hydrox-ylates tertiary carbons to form hydroxy compounds [550,831], hydroxylates double bonds to form vicinal diols [707, 296, 555, 577], oxidizes alkenes to a-diketones [560, 567], cleaves double bonds to form carbonyl compounds [840, 842, 552] or carboxylic acids [765, 841, 843, 845, 852, 869, 872, 873, 874], and converts acetylenes into dicarbonyl compounds [848, 856, 864] or carboxylic acids [843, 864], Aromatic rings are degraded to carboxylic acids [575, 576], and side chains in aromatic compounds are oxidized to ketones [566, 577] or carboxylic acids [503, 878, 879, 880, 881, 882, 555]. Primary alcohols [884] and aldehydes [749, 868, 555] are converted into carboxylic acids, secondary alcohols into ketones [749, 839, 844, 863, 865, 886, 887], ketones into keto acids [555, 559, 590] or acids [559, 597], ethers into esters [555], and amines into amides [854, 555] or imines [557], Aromatic amines are oxidized to nitro compounds [755, 559, 592], aliphatic nitro compounds to ketones [562, 567], sulfides to sulfones [846], selenides to selenones [525], and iodo compounds to iodoso compounds [595]. 

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