Oxidative decarboxylation of amino acids

The first stage of the reaction is a special case of the oxidative decarboxylation of amino acids, for which two general mechanistic hypotheses are under discussion.This is followed by aromatiz-ation. A possible mechanism (241- 242- 243- 245) has been... 

Moc-Thr(OTBDMS)p(OMe)2 Oxidative Decarboxylation of Amino Acids Derivatives and Synthesis of l-Aminoalkylphosphonic Acid Esters 28 Typical Procedure 148 ... 

Oxidative decarboxylation of amino acids. A recent report by a Merck group " illustrates a reaclion which had previously been applied to natural amino acids."... 

Degradation Reactions. Oxidative decarboxylations of amino acids serve as a good example. Schizophyllum commune is capable of degrading phenylalanine to phenylacetic acid as well as other acids. 

Bi, thiamin oxidation-reduction potentials, hydroxylation reactions that require copper or iron Oxidative decarboxylation of amino acids,... 

The rates of oxidative decarboxylation of amino acids by the cop-per(III) complex [Cu(I06)2] increase with increasing pKb of the substrate. " Periodate inhibition in the rate law suggests formation of a complex between the amino acid and [CuflOe)] , which decomposes in... 

The oxidative decarboxylation of amino acids is performed by VO(OEt)Cl2 [117]. For example, 2-phenylglycine undergoes decarboxylative dehydrogenation, followed by oxidative esterification, to give ethyl benzoate as a major product (Scheme 2.54). 

Several of the B vitamins function as coenzymes or as precursors of coenzymes some of these have been mentioned previously. Nicotinamide adenine dinucleotide (NAD) which, in conjunction with the enzyme alcohol dehydrogenase, oxidizes ethanol to ethanal (Section 15-6C), also is the oxidant in the citric acid cycle (Section 20-10B). The precursor to NAD is the B vitamin, niacin or nicotinic acid (Section 23-2). Riboflavin (vitamin B2) is a precursor of flavin adenine nucleotide FAD, a coenzyme in redox processes rather like NAD (Section 15-6C). Another example of a coenzyme is pyri-doxal (vitamin B6), mentioned in connection with the deamination and decarboxylation of amino acids (Section 25-5C). Yet another is coenzyme A (CoASH), which is essential for metabolism and biosynthesis (Sections 18-8F, 20-10B, and 30-5A). 

The reaction of carboxylic acids with the PhI(OAc)2-iodine system may result in a decarboxylation ieading to the intermediate formation of a carbon-centered radical, which can be further oxidized to a carbocation and trapped by a nucleophile. This process has been utilized in several syntheses [97, 615,616, 617]. In a typical example, the oxidative decarboxylation of uronic acid derivatives 568 in acetonitrile under mild conditions affords acetates 569 in good yields (Scheme 3.225) [615]. A similar oxidative decarboxylation has been be used for the synthesis of 2-substituted pyrrolidines 571 from the cyclic amino acid derivatives 570 [616,617]. 

B188) and the realization that the oxidative desamination of amino acids 4 proceeds via 5 by a sequence involving the decarboxylation of an iminium-2-carboxylate (6 7), followed by desamination (7 8)... 

Pyridoxal phosphate is required for deamination, transamination, and decarboxylation of amino acids and also is involved in D-amino oxidation and in race-mization of the d- to the L-amino acid. Pyridoxal phosphate seems also to be required for diamine oxidase... 

Most of the vitamin Be in natural materials is present as phosphorylated derivatives of compounds I-III. Pyridoxal-5-phosphate (IV, Fig. i) was discovered in 1944 by Gale and Epps as an unidentified compound required for enzymatic decarboxylation of amino acids Gunsalus and co-workers subsequently showed it to be a phosphorylated pyridoxal -. Pyridoxamine-5-phosphate (V, Fig. i) was discovered by Rabinowitz and Snell by virtue of its differential activity in promoting growth of certain lactic acid bacteria. It is probable that pyridoxine-5-phosphate also occurs naturally, since it is both formed and oxidized to pyridoxal-5-phosphate by tissue enzymesi -. An unidentified conjugate of pyridoxine also occurs in cereal grains - . 

The enantiomorph of this deuteroamine, prepared by decarboxylation of a-deuteroglutamate in water, does not exchange deuterium with the solvent, under the same conditions. (a-Deuteroglutamate is prepared by enzyme-catalysed racemisation of d- or L-glutamate in deuterium oxide). Additional support for the stereospecificity of enzyme-catalysed decarboxylation of amino acids comes from experiments in which tyrosine was decarboxylated in DgO to give R-a-... 

Plants can use urea and a variety of relatively simple amines as a source of nitrogen. The first step in the metabolism of amines is probably oxidation to the corresponding aldehyde and ammonia (see section V.A). The amines occurring naturally in plants include methylamine, isoamylamine and other volatile amines, which are found in some flowering species. The route to these amines is not thought to involve decarboxylation of amino acids, but little is yet known with certainty about the metabolism of amines in plants. Glutamic decarboxylase activity has been detected in a wide variety of higher plants, consistent with the widespread distribution of the product of decarboxylation, y-aminobutyric acid. 

Aldehydes formed by the Strecker degradation (cf. 5.3.1.1 Table 5.16) can also be obtained as metabolic by-products of the enzymatic transamination or oxidative deamination of amino acids. First, the amino acids are converted enzymatically to a-keto acids and then to aldehydes by decarboxylation in a side reaction ... 

Finally, the name protoalkaloids is given to a group of N-containing substances of simple structure. Examples of these are biogenic amines which arise from the decarboxylation of amino acids and their oxidized, alkylated, or acylated derivatives. 

One important subgroup of the lyases are the decarboxylases. The decarboxylation of amino acids is assisted by pyridoxal phosphate as a prosthetic group, whereas in the decarboxylation of pyruvate to acetaldehyde, thiamine pyrophosphate (TPP) plays that role. Oxidative decarboxylation, lastly, depends on the cooperation of no fewer than five cofactors thiamine pyrophosphate, lipoic acid, coenzyme A, flavin-adenine dinucleotide, and nicotinamide-adenine dinucleotide. 

Histamine is formed by the enzymic decarboxylation of histidine. It is degraded by diamine oxidase (a flavoprotein) to give the aldehyde and NH3 and thus is inactivated. The reaction is analogous to oxidative deamination of amino acids. 

In the presence of oxygen, decarboxylation of amino acids is followed by oxidative deamination to an aldehyde due to the action of amine oxidase. The existence of such an enzyme in animal tissues was first observed in 1928 by Hare-Bernheim (76), who used tyramine as substrate and therefore chose the name tyraminase. It was shown later (20) that a great variety of primary, secondary, and tertiary amines was subject to attack by this enzyme and consequently the name amine oxidase or monoamine oxidase. in contrast to diamine oxidase, was introduced. Only amines-with... 

Strecker Degradation (Oxidative Deamination), Mild oxidizing agents such as aqueous sodium hypochlorite or aqueous A-bromosuccinimide, cause decarboxylation and concurrent deamination of amino acids to give aldehydes. 

Van Tamelen (I24a) has reported a useful and specific synthetic method for the production of enamines by the oxidative decarboxylation of N,N-dialkyl a-amino acids with sodium hypochlorite. 

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]. 

Phenylglycines are important components of the vancomycin/teicoplanin antibiotics, and the conforma-tionally restricted amino acids contribute to the unique architecture and biological function of these clinically important NRPs. 4-Hydroxyphenylglycine is produced from L-tyrosine in a pathway that involves three enzymes. In the key step, a nonheme iron oxidase catalyzes the oxidative decarboxylation of the a-keto acid derivative of L-tyrosine resulting in loss of carbon dioxide and generation of the phenylglycine carbon framework. 

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