Oxidation of Side Chain

The oxidation of the side chain of 5j -cholestane-3a,7a,12a-triol to yield cholic acid or rather cholyl coenzyme A entails an co-oxidation followed by a jS-oxidation (Fig. 2). Early investigations (71,72) showed that the mitochondrial fraction of rat and mouse liver homogenate catalyzed the conversion of 5jS-cholestane-3a,7a, 12a-triol into 5/5-cholestane-3a,7a, 12a,26-tetrol and, when supplemented with the 100,000g supernatant fluid, the further transformation of 5j -cholestane-3a,7a,12a,26-tetrol into 3a,7a,12a-trihydroxy-5/9-cholestanoic acid (Fig. 2). Suld et al. (72) showed that the conversion of 3a,7a,12a-trihydroxy-5/5-cholestanoic acid into cholic acid (cholyl coenzyme A), catalyzed by the mitochondrial fraction fortified with the 100,000g supernatant fluid, occurs with the release of propionic acid (propionyl coenzyme A). 

The 26-hydroxylation of 5/5-cholestane-3a,7a,12a-triol may be assumed to be stereospecific. Berseus (73) and Mitropoulos and Myant (74) have shown that the 26-hydroxylation of cholesterol, catalyzed by mitochondrial preparations from rat liver, is stereospecific. Mendelsohn and Mendelsohn 

Conversion of 5 -Cholestane-3aJa,12a,26-tetrol into 3a,7a,12a-Trihydroxy-5P cholestanoic Acid 

Conversion of 3a,7a,12a-Trihydroxy-5 -cholestanoic Acid into Cholic Acid 

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Oxidation of side chains. Aromatic nitro compounds that contain a side chain (e.g., nitro derivatives of alkyl benzenes) may be oxidised to the corresponding acids either by alkahne potassium permanganate (Section IV,9, 6) or, preferably, with a sodium dichromate - sulphuric acid mixture in which medium the nitro compound is more soluble. 

Oxidation of side chains. The oxidation of halogenated toluenes and similar compounds and of compounds with side chains of the type —CHjCl and —CH OH proceeds comparatively smoothly with alkaline permanganate solution (for experimental details, see under AromcUic Hydrocarbons, Section IV.9,6 or under Aromatic Ethers, Section IV,106). The resulting acid may be identified by a m.p. determination and by other teats (see Section IV,175). 

Figure 1.18 Reaction of proline, arginine, and lysine residues with hydroxyl radical results in oxidation of side-chain structures that form carbonyls. Both arginine and proline oxidation result in the same product.

Kinetics of oxidation of toluene and cumene to the corresponding a-hydroxy compounds by stoich. trani-[Ru(0)(bpy)(tpy)] VCH3CN were reported a two-electron hydride-ion transfer step may be involved [672]. Electro-oxidation of side-chains in alkylaromatics by [Ru(0)(bpy)(tpy)] (generated electrochemicaUy in situ from [Ru(OH)(bpy)(tpy)] V BuOH/water pH 6.8/Pt electrodes/50°C) was effected toluene gave benzoic acid and ethylbenzene gave acetophenone (Table 4.1) [673]. 

Within the body tissues the changes of caffeic acid are methylation of the hydroxyl group in the 3 position, p-oxidation of side chain and conjugation with glycine or glucuronic acid. 

Irradiation of powdered titanium dioxide suspended in solutions containing aromatic compounds and water under oxygen has recently been shown to induce hydroxylation of aromatic nuclei giving phenolic compounds and oxidation of side chains of the aromatic compounds (50-55). These reactions have been assumed to proceed through hydroxyl and other radical intermediates, but the mechanism for their generation, whether reactive free radicals result from oxidation of water, from reduction of oxygen, or from oxidation of the substrates on the surfaces of the excited titanium dioxide, has not been clear. 

Oxidation of Side Chains of Carbocyclic and Heterocyclic Aromatic Compounds... 

Biochemical oxidations of side chains proceed without degradation or with only limited degradation. Both ethylbenzene and butylbenzene, and even dodecylbenzene, give phenylacetic acid on incubation at 30 °C with Nocardia strain 107-332 (equation 182) [1071]. 

Aromatic Acids by Oxidation of Side Chains. German work on this subject is briefly reported on by Mittag (74, T J) and by Michel and Krey (7 ). 

Three patents issued in 1924 and 1925 are conspicuous as placing special emphasis upon the preparation of particular catalysts as suitable for reactions involving the partial oxidation of side chains present in aromatic nuclei. The first00 of these relates to the oxidation of aromatic hydrocarbons and their derivatives, viz., toluene, xylene, cymene, cumene, mesitylene, cresols, etc., together with their derivatives including nitro-... 

An important aspect is the oxidation of side-chain methyl to hydroxymethyl or aldehyde oxidation levels. The former can be achieved by reaction of the lithiated species with molecular oxygen, then qnenching with dimethyl sulfide in acetic acid. Conversion of methyl to the aldehyde oxidation level (see also 8.2) can be achieved by dibromination, then hydrolysis. ... 

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