Oxidative decarboxylation 382 Subject

In contrast, much is known about the catabolism of catecholamines. Adrenaline (epinephrine) released into the plasma to act as a classical hormone and noradrenaline (norepinephrine) from the parasympathetic nerves are substrates for two important enzymes monoamine oxidase (MAO) found in the mitochondria of sympathetic neurones and the more widely distributed catechol-O-methyl transferase (COMT). Noradrenaline (norepinephrine) undergoes re-uptake from the synaptic cleft by high-affrnity transporters and once within the neurone may be stored within vesicles for reuse or subjected to oxidative decarboxylation by MAO. Dopamine and serotonin are also substrates for MAO and are therefore catabolized in a similar fashion to adrenaline (epinephrine) and noradrenaline (norepinephrine), the final products being homo-vanillic acid (HVA) and 5-hydroxyindoleacetic acid (5HIAA) respectively. 

Oxidative decarboxylation.1 Sodium hypochlorite is known to effect oxidative decarboxylation of a-hydroxy carboxylic acids to form ketones and C02, but a hydroxyl group is not essential since trisubstituted acetic acids are also subject to this oxidation. Thus triphenylacetic acid is oxidized by NaOCl to triphenylmethanol and benzophenone. In the presence of a phase-transfer catalyst, the rate is enhanced... 

Grape compounds which can enter the yeast cell either by diffusion of the undissociated lipophilic molecule or by carrier-mediated transport of the charged molecule across the cell membrane are potentially subject to biochemical transformations by enzymatic functions. A variety of biotransformation reactions of grape compounds that have flavour significance are known. One of the earlier studied biotransformations in yeast relates to the formation of volatile phenols from phenolic acids (Thurston and Tubb 1981). Grapes contain hydroxycinnamic acids, which are non-oxidatively decarboxylated by phenyl acryl decarboxylase to the vinyl phenols (Chatonnet et al. 1993 Clausen et al. 1994). 

Oxidative decarboxylation of optically active l-methyl-2,2-diphenylcyclopropanecarboxylic acid (10) with lead tetraacetate in the presence of iodine leads to racemized 1-iodo-l-methy 1-2,2-diphenylcyclopropane (11) in 45% yield. Subjecting 10 to the Cristol-Firth modification of the Hunsdiecker reaction (bromine and mercuric oxide in carbon tetrachloride) leads to racemic 1-bromo-l-methyl-2,2-diphenylcyclopropane (12) however, the yield is poor (5 /o). ... 

The rate of ceric oxidation of substituted benzilic (2,2-diphenyi-2-hydroxyacetic) acid in sulfuric add, aqueous perchloric/acetic add and acetonitrile is the subject of two reports from Hanna and Sarac (1977a, b). The reaction proceeds like the other a-hydroxycarboxylic acids by oxidative decarboxylation, producing substituted benzo-phenones and COj. The primary interest in the first of these two reports (Hanna and Sarac 1977a) is in the organic chemical aspects of the reactions. However, it is observed that the relative rates vary with the media in the order H2SO4 > HC104/acetic acid > acetonitrile. Although little mechanistic information exists, it is apparent that the oxidation proceeds via an inner-sphere, electron transfer process. 

Dow has commercialized a 2-stage process from toluene. Benzoic acid is produced by liquid-phase oxidation in the presence of cobalt, and is then subjected to oxidative decarboxylation with a copper catalyst, again in the liquid phase ... 

An electrochemical oxidative decarboxylation in combination with an ester enolate Claisen rearrangement was reported by Wuts et al. (Scheme 5.2.26) [51]. A variety of allylic esters such as 97 was subjected to an Ireland-Qaisen rearrangement, and the resulting acids (98) obtained were submitted to electrolytic decarboxylation in a divided cell to afford ketals 99. The use of the divided cell was necessary to suppress side reactions such as alkene reduction. 

Glycolytic products can penetrate to the interior of the mitochondria frequently pyruvate will be captured and subjected to oxidative decarboxylation. In special tissues (such as the flight muscle of locusts), it is reported (Bucher and Zebe), the system dihydroxyacetone phosphate glycerol phosphate appears to function as a hydrogen transfer system between cytoplasm and mitochondria. The system aceto-... 

A large variety of organic oxidations, reductions, and rearrangements show photocatalysis at interfaces, usually of a semiconductor. The subject has been reviewed [326,327] some specific examples are the photo-Kolbe reaction (decarboxylation of acetic acid) using Pt supported on anatase [328], the pho-... 

Partenheimer showed (ref. 15) that when toluene was subjected to dioxygen in acetic acid no reaction occurred, even at 205 °C and 27 bar. He also showed that when a solution of cobalt(II) acetate in acetic acid at 113 °C was treated with dioxygen ca. 1 % of the cobalt was converted to the trivalent state. In the presence of a substituted toluene two reactions are possible formation of a benzyl radical via one-electron oxidation of the substrate or decarboxylation of the acetate ligand (Fig. 9). Unfortunately, at the temperatures required for a reasonable rate of ArCH3 oxidation (> 130 °C) competing decarboxylation predominates. As noted earlier, two methods have been devised to circumvent this undesirable... 

Reaction sequence E removed an extraneous oxygen by Sml2 reduction and installed an oxygen at C(15) by enolate oxidation. The C(l) and C(15) hydroxy groups were protected as a carbonate in Step E-5. After oxidation of the terminal vinyl group, the C-ring was constructed by a Dieckmann cyclization in Step F-4. After temporary protection of the C(7) hydroxy as the MOP derivative, the (1-ketoestcr was subjected to nucleophilic decarboxylation by phenylthiolate and reprotected as the BOM ether (Steps F-5, F- 6, and F-7). 

Volume 75 concludes with six procedures for the preparation of valuable building blocks. The first, 6,7-DIHYDROCYCLOPENTA-l,3-DIOXIN-5(4H)-ONE, serves as an effective /3-keto vinyl cation equivalent when subjected to reductive and alkylative 1,3-carbonyl transpositions. 3-CYCLOPENTENE-l-CARBOXYLIC ACID, the second procedure in this series, is prepared via the reaction of dimethyl malonate and cis-l,4-dichloro-2-butene, followed by hydrolysis and decarboxylation. The use of tetrahaloarenes as diaryne equivalents for the potential construction of molecular belts, collars, and strips is demonstrated with the preparation of anti- and syn-l,4,5,8-TETRAHYDROANTHRACENE 1,4 5,8-DIEPOXIDES. Also of potential interest to the organic materials community is 8,8-DICYANOHEPTAFULVENE, prepared by the condensation of cycloheptatrienylium tetrafluoroborate with bromomalononitrile. The preparation of 2-PHENYL-l-PYRROLINE, an important heterocycle for the synthesis of a variety of alkaloids and pyrroloisoquinoline antidepressants, illustrates the utility of the inexpensive N-vinylpyrrolidin-2-one as an effective 3-aminopropyl carbanion equivalent. The final preparation in Volume 75, cis-4a(S), 8a(R)-PERHYDRO-6(2H)-ISOQUINOLINONES, il lustrates the conversion of quinine via oxidative degradation to meroquinene esters that are subsequently cyclized to N-acylated cis-perhydroisoquinolones and as such represent attractive building blocks now readily available in the pool of chiral substrates. 

After oxidation of the vinyl group, the C ring is constructed by a Dieckmann cyclization. The resulting jS-keto ester is subjected to nucleophilic decarboxylation by phenylthiolate [step F (4-6)]. 

The acetyl-CoA transfers its acetyl group to oxaloace-tate, thereby generating citrate. In a cyclic series of reactions, the citrate is subjected to two successive decarboxylations and four oxidative events, leaving a four-carbon compound malate from which the starting oxaloacetate is regenerated. 

Although significant improvements have been made in the synthesis of phenol from benzene, the practical utility of direct radical hydroxylation of substituted arenes remains very low. A mixture of ortho-, meta- and para-substituted phenols is typically formed. Alkyl substituents are subject to radical H-atom abstraction, giving benzyl alcohol, benzaldehyde, and benzoic acid in addition to the mixture of cresols. Hydroxylation of phenylacetic acid leads to decarboxylation and gives benzyl alcohol along with phenolic products [2], A mixture of naphthols is produced in radical oxidations of naphthalene, in addition to diols and hydroxyketones [19]. 

Precursors of /1-alanine 3 biosynthesis are uracil 2, L-aspartate 4, and polyamines which are subjected to degradation in distinct ways - whereas uracil is metabolized by hydrogenation followed by hydrolysis, polyamines like spermine 1 are oxidized and L-aspartate is decarboxylated (Scheme 1.6.1). 

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