Oxidation of L-phenylalanine

The fact that enzymes necessary to bring about the oxidation of L-phenylalanine were absent in the livers of two phenylpyruvics and were present in three controls34 has been demonstrated, but there is... 

Peptide-bond formation and transamination are the most general reactions of the standard amino acids, but individual amino acids often undergo reactions of more limited scope. One of the biosynthetic pathways to L-tyrosine is oxidation of L-phenylalanine. An arene oxide is an intermediate. 

The anaerobic metabolism of L-phenylalanine by Thauera aromatica under denitrifying conditions involves several steps that result in the formation of benzoyl-CoA (a) conversion to the CoA-ester by a ligase, (b) transamination to phenylacetyl-CoA, (c) a-oxidation to phenylglyoxalate, and (d) decarboxylation to benzoyl-CoA (Schneider et al. 1997). 

Both a synthetic lignin model substrate and the natural metabolites of the white-rot fungus were oxidized by this extracellular peroxidase. The possible roles of this nitrogen recycling system and the cinnamate pathway, which are involved in the secondary metabolism of L-phenylalanine in brown-rot and white-rot fungi, are discussed in relation to wood decay processes. 

One approach to unnatural amino acids is to use a readily available amino acid, such as L-phenyl-alanine, as the starting material. The Birch reduction of L-phenylalanine (1) was carried out with lithium in ammonia, followed by acylation of the amino group to produce compound 2, which was further esterihed to produce the cyclohexa-l,4-dienyl-L-alanine derivative 3 (Scheme 11.1). The ozonolysis step of the reaction was carried out at -78°C in a dichloromethane solution presaturated with ozone to reduce the extent of oxidation of the diene 3 to produce 4. Cyclization was then carried out by the introduction of either hydroxylamine hydrochloride to produce the isoxazol-5-ylalanine derivative 5 or phenylhydrazine to give a 1 1 mixture of (l-phenylpyrazol-3-yl)alanine derivative 6 and the (l-phenylpyrazol-2-yl)alanine derivative 7.4,5... 

In certain bacteria there is a specific nutritional requirement for D-amino acids which are found as components of cell structures or antimetabolites. Bacteria normally meet this need by the conversion of L-amino acids to D-amino acids and in the case of alanine, methionine and tryptophan the evidence suggests that these reactions are directly catalysed by amino acid racemases which have a cofactor requirement for pyridoxal phosphate . An oxidation-reduction cofactor may also be a general feature of racemases of this class. However, the mode of epimerisation of L-phenylalanine to D-phenylalanine necessary for the synthesis of some peptide antibiotics, proceeds in an entirely different way, which as yet has only been partially resolved. 

The oxidative metabolism of L-phenylalanine and L-tyrosine is of intrinsic interest from the medical point of view since a number of diseases resulting from inborn errors of metabolism are associated with this pathway. Some indication of the intermediates in the pathways of oxidative metabolism of L-phenylalanine and l-tyrosine indeed came first from a study of one such disease, alcaptonuria, in which the patient excretes homogentisic acid. Garrod recognised that these errors of metabolism were due to a congenital inability of the organism to carry out a particular enzyme transformation in the normal sequence of events it is a natural mutant. 

Under normal physiological conditions the bulk of L-phenylalanine is oxidatively metabolised by its initial transformation to L-tyrosine which is then oxidised to acetoacetate, fumarate and carbon dioxide Figure 4.1). The aryl hydroxylation reaction probably takes place in all higher animals and occurs in the liver . The same conversion... 

B.8 Batch Production of L-Phenylalanine and L-Aspartic Acid. Unit 900 B.9 Acrylic Acid Production via the Catalytic Partial Oxidation of Propylene B.IO Production of Acetone via the Dehydrogenation of Isopropyl Alcohol B.ll Production of Heptenes from Propylene and Butenes... 

One ammo acid often serves as the biological precursor to another L Phenylala nine is classified as an essential ammo acid whereas its p hydroxy derivative L tyro sine IS not This is because animals can convert L phenylalanine to L tyrosine by hydrox ylation of the aromatic ring An arene oxide (Section 24 7) is an intermediate... 

Phosphorus pentachloride, for conversion of pentaacetylgluconic add to add chloride, 41, 80 for oxidation of cycloheptatriene to tropylium fluoborate, 43, 101 with cyanoacetic acid, 41, 5 Phosphorus tribromide, reaction with 1.5-hexadien-3-ol, 41, 50 Phthalic anhydride, reaction with L-phenylalanine to yield N-phthalyl-L-phenylalanine, 40, 82 Phthalic monoperacid, 42, 77 N-Phthalyl-i.-alanine, 40, 84 N-Phthalyl-/3-alanine, 40, 84 N-Phthalylglycine, 40, 84 N-Phthalyl-l-/5-phenylalanine, 40, 82... 

The Jing group investigated their poly(L-lysine)-6-poly(L-phenylalanine) vesicles for the development of synthetic blood, since PEG-lipid vesicles were previously used to encapsulate hemoglobin to protect it from oxidation and to increase circulation time. They extended this concept and demonstrated that functional hemoglobin could be encapsulated into their vesicles. The same polypeptide material was also used to complex DNA, which caused the vesicles to lose their... 

Klein and Olsen126 studied the action of kojic acid on the enzymic oxidation of amino acids by the liver and kidney of rats. Low concentrations of kojic acid in vitro inhibited the oxidation of a number of D-amino acids, L-phenylalanine, and a few related compounds. Kojic acid was found to compete with D-amino acid oxidase for the substrate. 

Peroxidases have also been utilized for preparative-scale oxidations of aromatic hydrocarbons. Procedures have been optimized for hydroxylation of l-tyrosine, D-(-)-p-hydroxyphenylglycine, and L-phenylalanine by oxygen, di-hydroxyfumaric acid, and horseradish peroxidase (89). Lactoperoxidase from bovine milk and yeast cytochrome c peroxidase will also catalyze such hydroxylation reactions (89). 

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