Amino acids L-phenylalanine

The earliest references to cinnamic acid, cinnamaldehyde, and cinnamyl alcohol are associated with thek isolation and identification as odor-producing constituents in a variety of botanical extracts. It is now generally accepted that the aromatic amino acid L-phenylalanine [63-91-2] a primary end product of the Shikimic Acid Pathway, is the precursor for the biosynthesis of these phenylpropanoids in higher plants (1,2). 

Further, facilitated membrane separations by fixed-site heteropolysiloxane membranes for a mixture of seven amino acids provided a good selectivity (S = 9-10, calculated as flux ratio) for lypophilic amino acids (L-phenylalanine and L-leucine) (Figure 10.3) [30,31]. 

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. 

Based on these results, a simple and unique determination of 14 L-amino acids and glucose as substrates was developed. Thus, the calibration graph for a representative amino acid, L-phenylalanine was linear in the concentration range 1.0 x 10 6-2 x 10 8 M with a relative standard deviation of 5.78% and a correlation coefficient of 0.9974. The detection limit obtained was 1.05 X 10 8 M. In the case of glucose the calibration graph was linear in the concentration range 2.7 X 10 6-2.7 X 10 8 M with a relative standard deviation of 4.27% and a correlation coefficient of 0.9980. The detection limit was 2.7 X 10 8 M. The method was successfully applied to the determination of glucose in human blood serum. 

Proanthocyanidins and Procyanidins - In a classical study Bate-Smith ( ) used the patterns of distribution of the three principal classes of phenolic metabolites, which are found in the leaves of plants, as a basis for classification. The biosynthesis of these phenols - (i) proanthocyanidins (ii) glycosylated flavonols and (iii) hydroxycinnamoyl esters - is believed to be associated with the development in plants of the capacity to synthesise the structural polymer lignin by the diversion from protein synthesis of the amino-acids L-phenylalanine and L-tyro-sine. Vascular plants thus employ one or more of the p-hydroxy-cinnarayl alcohols (2,3, and 4), which are derived by enzymic reduction (NADH) of the coenzyme A esters of the corresponding hydroxycinnamic acids, as precursors to lignin. The same coenzyme A esters also form the points of biosynthetic departure for the three groups of phenolic metabolites (i, ii, iii), Figure 1. 

Although 2-phenylethanol can be synthesised by normal microbial metabolism, the final concentrations in the culture broth of selected microorganisms generally remain very low [110, 111] therefore, de novo synthesis cannot be a strategy for an economically viable bioprocesses. Nevertheless, the microbial production of 2-phenylethanol can be greatly increased by adding the amino acid L-phenylalanine to the medium. The commonly accepted route from l-phenylalanine to 2-phenylethanol in yeasts is by transamination of the amino acid to phenylpyruvate, decarboxylation to phenylacetaldehyde and reduction to the alcohol, first described by Ehrlich [112] and named after him (Scheme 23.8). 

The shikimate/arogenate pathway leads to the formation of three aromatic amino acids L-phenylalanine, L-tyrosine, and L-tryptophane. This amino acids are precursors of certain homones (auxins) and of several secondary compounds, including phenolics [6,7]. One shikimate/arogenate is thought to be located in chloroplasts in which the aromatic amino acids are produced mainly for protein biosynthesis, whereas the second is probably membrane associated in the cytosol, in which L-phenylalanine is also produced for the formation of the phenylpropanoids [7]. Once L-phenylalanine has been synthesized, the pathway called phenylalanine/hydroxycinnamate begins, this being defined as "general phenylpropanoid metabolism" [7]. 

Phenylketonuria. Phenylketonuria (PKU) is a genetic condition whose sufferers have an inability to metabolise the essential amino acid L-phenylalanine. Then1 intake of this amino acid from any source (e.g. milk, vegetables, meat and aspartame) must be strictly controlled from birth to adulthood. It is for this reason that an aspartame-containing product requires the statement that it contains a source of phenylalanine on the pack. 

Phenylpropanoids and flavonoids found in plants are predominantly derived from the aromatic amino acid L-phenylalanine originated in the shikimic acid... 

Beauvericin is a structural homolog of enniatins in which the branched-chain L-amino acid is substituted by the aromatic amino acid L-phenylalanine. Beauvericin synthetase, which has been isolated from the fungus Beauveria bassiana [54] and various strains of Fusaria [55], strongly resembles Esyn with respect to its molecular size and the reaction mechanism. In contrast to Esyn, which is only able to incorporate aliphatic amino acids, beauvericin synthetase exhibits high substrate specificity for aromatic amino acids such as phenylalanine. This capability is obviously caused by mutational alterations in the adenylation domain of this enzyme. 

Cinnamic acid and its derivatives found in plants originate from the aromatic amino acids L-phenylalanine and L-tyrosine by the elimination of ammonia. Some common natural cinnamic acid derivatives include -coumaric acid, caffeic acid, femlic acid, and sinapic acid. 

Not only the efficient removal of toxic heavy metals like hexavalent chromium (Cr(VI)), cadmium (Cd), zinc (Zn), nickel (Ni), etc., and other contaminants like phenol from industrial wastewaters [8-18] but also the recovery of valuable solutes from aqueous phases, for example, citric acid, carboxylic acids, amino acids, L-phenylalanine, etc. [19,20], are well-demonstrated applications of this technique. 

Both alkaloids have (+) and (-) forms but only the (-) hyoscyamine and (-) scopolamine are active. The biosynthetic pathway of tropane alkaloids, Fig. (1) is not totally understood, especially at the enzymatic level. Edward Leete has pioneered the biosynthetic studies of tropane alkaloid since 1950"s using whole plants and isotope labels [85-86]. The tropane alkaloid hyoscyamine is bioconverted by the enzyme H6H (hyoscyamine 6p-hydroxylase, EC 1.14.11.11) to scopolamine via 6p-hydroxyhyoscyamine. Hyoscyamine is the ester of tropine and (S)-tropic acid. The (S)-tropic acid moiety derives from the amino acid L-phenylalanine, while the bicyclic tropane ring derives from L-omithine primarily or L-arginine via tropinone. Tropinone is stereospecifically reduced to form either, tropine which is incorporated into hyoscyamine, or on the other hand into pseudotropine which proceeds to calystegines, a group of nortropane derivates that were first found in the Convolvulaceae family [87]. 

The LAT system has been used for the transport of various compounds to the brain. Variations in the cerebellum to plasma ratio at late times in 6-[18F]fluoro-L-DOPA studies are consistent with competitive binding of large neutral amino acids (LNAAs) for the LAT at the BBB (117). In addition, it was shown that oral administration of phenylalanine inhibited the uptake of an artificial amino acid [(1 lC)-aminocyclohexanecarboxylate] in human brain (118). Melphalan, a nitrogen mustard derivative of the neutral amino acid L-phenylalanine, was transported to the brain via the LAT system at the rat BBB. In addition, it was shown that melphalan competed with phenylalanine for the LAT system (119). 

The second mode of CSTR operation is that used by Thien (17) and by Li and Shrier (10). Here, both the external phase and the LM emulsion are in a continuous flow mode. The reactor effluents are sent to gravity settlers where the exterior phase is separated from the emulsion phase. The emulsion phase is then demulsified to recover the product followed by remulsification and recycle back to the reactor. Hatton and Wardius (48) have developed the advancing front model for the analysis of such staged LM operations. Thien (17) employed this scheme to remove the amino acid L-phenylalanine from simulated fermentation broth (dilute aqueous solution). 

From a broad variety of L-a-amino acids, L-phenylalanine as well as L-homophe-nylalanine were successfully produced using the amidase technology. 

Another comparable reaction is the asymmetric biocatalytic addition of ammonia to trans-cinnamic acid, 28 (Fig. 15) [38], This reaction represents a technically feasible process for the production of L-phenylalanine as has been shown by the Genex Corporation [38 a, b]. The amino acid L-phenylalanine is required in technical quantities as an intermediate, e.g., for the manufacture of the artificial sweetener aspartame. 

Soil is extremely rich in bacteria (10 —10 cells per g soil), which survive by utilizing nutrients and carbon sources present there. Naturally occurring aromatic compounds are present in soil from the breakdown of lignin from woody plants and phenylpropanoids found in plants the aromatic fraction of leached oil and coal as well as the aromatic amino acids L-phenylalanine, L-tyrosine, and L-tryptophan from protein breakdown (Figure 1). Man-made aromatic compounds include pesticides, detergents, oils, solvents, paints, and explosives. 

The amino acids L-phenylalanine and L-tyrosine are broken down via aromatic degradation pathways that are found in mammals and bacteria, to form organic acids that can be utilized for growth. These pathways are the only aromatic degradation pathways found in mammals, and are of some medical significance, since there are several inherited metabolic diseases (phenylketonuria, alkaptonuria, tyrosinemia) that are caused by mutations in enzymes in these pathways. 

Aromatic amino acid L-phenylalanine is a component of the artificial sweetener aspartame. It has been produced at 28gl in E. coli K12 by overexpressing feedback-resistant DAHP-synthase aroF ). However, it was found that overexpressing wild-type DAHP-synthase aroF ), which is tyrosine sensitive, and... 

Yoshida developed an enantioselective Michael addition reaction of a-branched aldehydes to p-nitroacrylates by using a primary a-amino acid, L-phenylalanine (Phe-OH), lithium salt 14 (Scheme 2.9). The obtained p-formyl-p -nitroesters were transformed into the corresponding cyclic amino acids in high yields via hydrogenolysis on Pd/C. 

In both bacteria and plants, two additional amino acids, phenylalanine and tyrosine, are formed from chorismic acid. From chorismate, two separate routes diverge and lead to the amino acids L-phenylalanine and L-tyrosine. However, the pathways in bacteria and plants are distinct and involve different intermediates. Both of these pathways pass through the same intermediate, prephenic acid (26) (Fig. 7.9) (Floss,... 

As an example of a molecule with diastereotopic ligands, consider the amino acid L-phenylalanine. The two protons at C-3 are diastereotopic, since substitution of either of them would generate a molecule with two chiral centers. Because the chiral center already present is 5, the two diastereomers would be the 2S,3R and the 25,35 stereoisomers. As in the case of enantiotopic protons, diastereotopic protons are designated pro-R or pro-S. The enzyme phenylalanine ammonia lyase catalyzes the conversion of phenylalanine to trans-cinnamic acid by a process involving anti elimination of the amino group and the 3-pro-S hydrogen. This stereochemical course has been demonstrated using deuterium-labeled L-phenyl-alanine as shown" ... 

Aromatic biosynthesis, aromatizatioa biosynthesis of compounds containing the benzene ring system. The most important mechanisms are 1. the shi-kimate/chorismate pathway, in which the aromatic amino acids, L-phenylalanine, L-tyrosine and L-trypto-phan, 4-hydroxybenzoic acid (precursor of ubiquinone), 4-aminobenzoie acid (precursor of folic acid) and the phenylpropanes, including components of lignin, cinnamic acid derivatives and flavonoids are synthesized and 2. the polyketide pathway (see Polyke-tides) in which acetate molecules are condensed and aromatic compounds (e.g. 6-methylsalicylic acid) are synthesized via poly-fl-keto acids. Biosynthesis of flavonoids (e.g. anthocyanidins) can occur by either pathway. 

Biosynthesis. The primary precursors of L. are con-iferyl, sinapyl and p-coumaiyl alcohoi, which are derived from 4-hydroxycinnamic acid. L. from conifers (i. e. from softwood) is derived chiefly from conifeiyl alcohol with variable but small proportions of sinapyl and p-coumaryl alcohol. L. from dicotyledonous an-giosperms (i.e. from hardwood), particularly deciduous trees, is formed chiefly from sinapyl (-44%) and coniferyl (-48 %) alcohol, with about 8 % p-cou-maryl alcohol. L. in grasses is formed from p-coumar-yl (-30%), coniferyl (-50%) and sinapyl (-20%) alcohol. These primary L. precursors are formed from the aromatic amino acids L-phenylalanine and L-tyro-sine by a series of reactions shown (Rg.). The first reaction is catalysed by L-Phenylalanine ammonia-lyase (EC 4.3.1.5) (see) this enzyme is induced by light in a process involving phytochrome, and it is of general importance in the synthesis of plant phenolic compounds from phenylalanine and tyrosine. 

The carbon skeleton of the amino acids L-phenylalanine and L-tyrosine is composed of a phenyl group linked to an n-propyl side chain (Fig. 266). A large number of secondary products, the phenylpropanoids, contain this fundamental structure. 

Structure 1 shows the structure of such a synthetic optically active polymer derived from the amino acid L-phenylalanine. 

It may be appropriate to say that in the above synthesis, use of unmodified E. coli gives the amino acids, L-phenylalanine, L-tyrosine and L-tryptophan via the formation of shikimic acid from dehydroshikimic acid (Scheme 6). 

Enantiospecific synthesis of 1,2,3,4-tetrahydroisoquinoline derivatives 826 and 827 can be accomplished from the amino acid L-phenylalanine 823. During the synthesis, both the amino and alcohol functions of phenylalaninol 824 are car-bonylated with methyl chloroformate, leading to the carbonate 825 in 99% yield (together with carbamate) [612]. 

Although the stmctures of Amaryllidaceae alkaloids are greatly diverse, they are considered to be biogenetically related and have a common precursor alkaloid norbelladine 2, which originally derived from the natural amino acids L-phenylalanine (Phe) and L-tyrosine (Tyr). Conventionally, according to molecule skeletons of the alkaloids, the large number of Amaryllidaceae alkaloids was classified mainly into nine different types, as represented by lycorine 1,... 

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