Amino enzymatic synthesis

Enzyme preparations from liver or microbial sources were reported to show rather high substrate specificity [76] for the natural phosphorylated acceptor d-(18) but, at much reduced reaction rates, offer a rather broad substrate tolerance for polar, short-chain aldehydes [77-79]. Simple aliphatic or aromatic aldehydes are not converted. Therefore, the aldolase from Escherichia coli has been mutated for improved acceptance of nonphosphorylated and enantiomeric substrates toward facilitated enzymatic syntheses ofboth d- and t-sugars [80,81]. High stereoselectivity of the wild-type enzyme has been utilized in the preparation of compounds (23) / (24) and in a two-step enzymatic synthesis of (22), the N-terminal amino acid portion of nikkomycin antibiotics (Figure 10.12) [82]. 

Enzymes are generally classified into six groups. Table 1 shows typical polymers produced with catalysis by respective enzymes. The target macromolecules for the enzymatic polymerization have been polysaccharides, poly(amino acid)s, polyesters, polycarbonates, phenolic polymers, poly(aniline)s, vinyl polymers, etc. In the standpoint of potential industrial applications, this chapter deals with recent topics on enzymatic synthesis of polyesters and phenolic polymers by using enzymes as catalyst. 

The reduction of a-hydroxynitriles to yield vicinal amino alcohols is conveniently accomplished with complex metal hydrides for example, lithium aluminum hydride or sodium borohydride [69]. However, it is still worth noting that a two-step chemo-enzymatic synthesis of (R)-2-amino-l-(2-furyl)ethanol for laboratory production was developed followed by successful up-scaling to kilogram scale using NaBH4/CF3COOH as reductant [70],... 

Figure 7.16 Enzymatic synthesis of the a-hydroxy-/3-amino acid moiety of (—)-hestatin... 

Cells grown in the presence of azide analogs of certain amino acids or sugars will incorporate these derivatives into proteins or carbohydrates through enzymatic synthesis using... 

The procedure can provide a higher amount of L-pipecolic acid in a shorter reaction time than the previously reported system, indicating that it is applicable in industrial production of L-pipecolic acid. A similar system was successfully employed in the enzymatic synthesis of several cyclic amino acids by our group. ... 

Yasuda, M., Ueda, M., Muramatsu, H., Mihara, H. and Esaki, N., Enzymatic synthesis of cyclic amino acids by A-methyl-L-amino acid dehydrogenase from Pseudomonas putida. Tetrahedron Asymmetry. 2006, 17, 1775. 

Thymine derivatives - 5-[7V-(2-Amino-4-hydroxy-6-methyl-5-pyrimidinyl-propyl)-p-carboxyanilinomethyl] uracil (XXXIII) was synthesized for study as a possible intermediate in the enzymatic synthesis of thymidylate. It is active as an enzyme inhibitor against thymidylate synthetase isolated from E. coli [298]. Certain thymine derivatives containing a 2-thioimidazole moiety (XXXIV, R = alkyl) inhibit growth of Ehrlich ascites carcinoma (fluid form) in mice [299]. 

Ac-Phc-Lys-OH, enzymatic synthesis, 156f Acesulfame K, stnicture, 7f Acetoin, in reactions of aldehydes with ammonium sulfide, 36-54 Acid chelators, 57-58 Acid synergism, description, 58 Acidic amino acid peptides, taste,... 

Fig. 5. Enzymatic synthesis of (i )-PAC catalysed by PDCZ.m., PDCS.c. and various mutants of PDCZ.m. in position 392 in a simplified batch reaction [170] (The amino acids which replace the original Trp-residue are indicated, respectively).

Fig. 21 Enzymatic synthesis of unnatural amino acids as building blocks for omapatrilat. (a-c) Enzymatic approaches to 6-oxonorleucine analogs...

The enzymatic synthesis of glycopeptides does not require protection of the functional groups of the amino acid side chains and sugar hydroxyls, because of the high stereoselectivity and regioselectivity of proteases. However, the substrate selectivity of these enzymes may limit a wider range of applications. 

The active form of folate is the tetrahydro-derivative that is formed through reduction by dihydrofolate reductase. This enzymatic reaction (Figure 29.5) is inhibited by trimethoprim, leading to a decrease in the folate coenzymes for purine, pyrimidine, and amino acid synthesis. Bacterial reductase has a much stronger affinity for trimethoprim than does the mammalian enzyme, which accounts for the drug s selective toxicity. [Note Examples of other folate reductase inhibitors include pyrimethamine, which is used with sulfonamides in parasitic infections (see p. 353), and methotrexate, which is used in cancer chemotherapy (see p. 378).]... 

Scheme 5.48. Enzymatic synthesis of 2-amino-3-hydroxy-l, 6-hexanedicarboxylic acids using serine hydroxymethyl transferases (SHMT). DEAD = diethyl azodicarboxylate.

This eoncept has been known for a long time in pure enzymatic synthesis, e.g. amino acid synthesis via hydantoins [1] or oxazolidinones [2]. Cyanohydrins [3] and lactols [4] are prone to in situ racemization as well and may serve as substrates in kinetic resolutions. 

There are two main routes for the production of D-amino acids chemical synthesis and enzymatic catalysis. As regards conventional chemical synthesis, unless asymmetrical starting compounds or catalysts are used, a mixture of the D- and L-stereoisomers is obtained in equal proportions. The racemic mixture is therefore optically inactive and the stereoisomers must be separated. The separation of the enantiomers by classical crystallization of diastereomeric salts is the most costly production step and in any case this method can only yield 50% of the desired enantiomer [3]. Enzymatic synthesis can solve the above problems, providing optical purity of the D-amino acid and a 100% yield, as well as mild, environment-friendly reaction conditions. 

Ikegami, R, Mizuno, M. and Murakoshi, I. (1990) Enzymatic synthesis of the thyrotoxic amino acid, mimosine, by cysteine synthase. Phytochemistry, 29,3461-6. 

The catalytic mechanisms and molecular recognition properties of peptide synthetases have been studied for several decades [169]. Nonribosomal peptides are assembled on a polyenzyme-protein template, first postulated by Lipmann [170]. The polyenzyme model was refined into the thiotemplate mechanism (Fig. 11) in which the amino acid substrates are covalently bound via thioester linkages to active site sulfhydryls of the enzyme and condensed via a processive mechanism involving a 4 -phosphopantetheine carrier [171-173].The presence of a covalently attached pantetheine cofactor was first established in a cell-free system that catalyzed enzymatic synthesis of the decapeptides gramicidin S and tyrocidine. As in the case of fatty acid synthesis, its role in binding and translocating the intermediate peptides was analyzed [174,175]. 

In principle, the use of amino acid or peptide esters as nucleophilic components in protease-catalyzed synthesis is possible, but with a drastically decreased efficiency. However, acyl transfer to arginine or lysine alkyl esters in ice using a-chymotrypsin with regard to its strong preference for basic residues in the P/ position enabled synthesis of a N-protected tripeptide ester in high yield (Scheme 7, see Section 4.2.1.2.2). Furthermore, it was found to be the method of choice in synthesizing new potential protease substrates (for proteases with a preference for basic residues in the Pj position). Neither enzymatic synthesis at room temperature nor synthesis in organic solvents has been shown to proceed in a successful manner. 

Maximizing DAHPS, PEPCxylase and SerSynth enzymatic flux ratios are expected to enhance the desired amino acids synthesis rates. Here, enzyme flux refers to the reaction rate facilitated by that enzyme. We opted to study two bi-objective scenarios. 

Several biosyntheses involve assembling building blocks such as amino acids and carboxylic acids. Parts of these assembly processes can show some substrate flexibility, allowing the enzymatic synthesis of un-natural analogues of normal fungal metabolites. One of the earliest examples was the variation of the penicillin side-chain brought about by replacing the phenylacetic acid of penicillin G with phenoxyacetic acid as in penicillin V. 

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