Acetic oxidative decarboxylation

Lead tetraacetate cupric acetate Oxidative decarboxylation Ethylene derivs. from carboxylic acids... 

It is worth noting that the carbon-carbon bond cleaved in the TCA pathway entered as an acetate unit in the previous turn of the cycle. Thus, the oxidative decarboxylations that cleave this bond are just a cleverly disguised acetate C—C cleavage and oxidation. 

A cursory inspection of key intermediate 8 (see Scheme 1) reveals that it possesses both vicinal and remote stereochemical relationships. To cope with the stereochemical challenge posed by this intermediate and to enhance overall efficiency, a convergent approach featuring the union of optically active intermediates 18 and 19 was adopted. Scheme 5a illustrates the synthesis of intermediate 18. Thus, oxidative cleavage of the trisubstituted olefin of (/ )-citronellic acid benzyl ester (28) with ozone, followed by oxidative workup with Jones reagent, affords a carboxylic acid which can be oxidatively decarboxylated to 29 with lead tetraacetate and copper(n) acetate. Saponification of the benzyl ester in 29 with potassium hydroxide provides an unsaturated carboxylic acid which undergoes smooth conversion to trans iodolactone 30 on treatment with iodine in acetonitrile at -15 °C (89% yield from 29).24 The diastereoselectivity of the thermodynamically controlled iodolacto-nization reaction is approximately 20 1 in favor of the more stable trans iodolactone 30. 

Potassium ferricyanide in oxidative decarboxylation, 40, 86 Potassium permanganate for oxidation of (trialkylmethyl)amines to tri-alkylnitromethanes, 43,87 Pregnenolone acetate, conversion to 3/3-acetoxyetienic acid, 42, 5 Propane, 2,2-dibotoxy-, 42,1 Propargylsuccinic anhydride, by-product in addition of maleic anhydride to allcne, 43, 27... 

Although Ce(IV) oxidation of carboxylic acids is slow and incomplete under similar reaction conditions , the rate is greatly enhanced on addition of perchloric acid. No kinetics were obtained but product analysis of the oxidations of -butyric, isobutyric, pivalic and acetic acids indicates an identical oxidative decarboxylation to take place. Photochemical decomposition of Ce(IV) carbo-xylates is highly efficient unity) and Cu(ll) diverts the course of reaction in the same way as in the thermal oxidation by Co(IIl). Direct spectroscopic evidence for the intermediate formation of alkyl radicals was obtained by Greatorex and Kemp ° who photoirradiated several Ce(IV) carboxylates in a degassed perchloric acid glass at 77 °K in the cavity of an electron spin resonance spectro-... 

Grootveld et al. (1994) employed this technique to investigate radiolytic, damage to biomolecules present in human body fluids. 7-Radiolysis of healthy or rheumatoid human serum (5.00 kGy) in the presence of atmospheric O2 gave rise to reproducible elevations in the concentration of NMR-detectable acetate, which are predominantly ascribable to the prior oxidation of lactate to pyruvate by OH radical followed by oxidative decarboxylation of pyruvate by radiolytically generated H2O2 and/or further OH radicals (Equations 1.7 and 1.8). 

However, at pH values closer to neutrality (i.e. at the mean salivary pH of 5.97), chlorite anion itself can effect the oxidative decarboxylation of pyruvate to acetate and CO2 (Equation 1.12). 

Oxidative decarboxylation of a-amino carboxylic acid The electrochemical oxidation of Al-acyl-a-amino acids (96) in MeOH affords N, O-acetals (98) through acyliminium intermediates (97) (Scheme 36) [121]. 

Surprisingly, the partial reduction of quinone 137 is best achieved by refluxing in acetic or propionic acids (yield 67%). Thereby the acids suffer oxidative decarboxylation (82CL701 85BCJ515). Two further unexpected routes are based on the redox reaction with cycloheptatriene (85BCJ2072) and electrolysis under the conditions of the cyclic voltammetry measurements (87BCJ2497), respectively. 

It is an acyl-CoA of the type mentioned in Section 1 and can also be formed from acetate, ATP, and coenzyme A. Although the human diet contains some acetic acid, the two major sources of acetyl-CoA in our bodies are the oxidative decarboxylation of pyruvate (Eq. 10-6) and the breakdown of fatty acid chains. Let us consider the latter process before examining the further metabolism of acetyl-CoA. 

One of the first persons to study the oxidation of organic compounds by animal tissues was T. Thunberg, who between 1911 and 1920 discovered about 40 organic compounds that could be oxidized by animal tissues. Salts of succinate, fumarate, malate, and citrate were oxidized the fastest. Well aware of Knoop s (3 oxidation theory, Thunberg proposed a cyclic mechanism for oxidation of acetate. Two molecules of this two-carbon compound were supposed to condense (with reduction) to succinate, which was then oxidized as in the citric acid cycle to oxaloacetate. The latter was decarboxylated to pyruvate, which was oxidatively decarboxylated to acetate to complete the cycle. One of the reactions essential for this cycle could not be verified experimentally. It is left to the reader to recognize which one. 

All parasitic flatworms capable of anaerobic metabolism favour malate as the primary mitochondrial substrate and the oxidative decarboxylations of first malate and then pyruvate generate intramitochondrial reducing power in the form of NADH (Fig. 20.1). In contrast, the pathways used to reoxidize intramitochondrial NADH are quite diverse and depend on the stage or species of parasite under examination, but in all cases, redox balance is maintained and electron-transport associated ATP is generated by the NADH-reduction of fumarate to succinate. In the cestode, hi. diminuta, succinate and acetate are the major end products of anaerobic malate dismutation and are excreted in the predicted 2 1 ratio. In the trematode F. hepatica, succinate is then further decarboxylated to propionate with an additional substrate level phosphorylation coupled to the decarboxylation of methylmalonyl CoA. F. hepatica forms primarily propionate and acetate as end products, again in a ratio of 2 1 to maintain redox balance. 

Fig. 1. Major thyroid hormones (3,5,3 ,5 -tetraiodothyronine or thyroxine, T4) and (3,5,3 triiodothy-ronine, T,) and other important iodothyronines (3,3,5 -triiodothyronine or reverse-T, r-T and 3,3 -diiodothyronine 3,3 -T2). T4 and T, are active, r-Tj and 3,3 -T, are inactive. The acetic derivatives of T4 (TETRAC) and T, (TRIAC) are produced by oxidative decarboxylation of the alanine side-chain and have thyromimetic activities.

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