D-amino acid amidase

Recently it was reported that an a-amino-e-caprolactam racemase from Achro-mobacter obae can racemise a-amino acid amides efficiently. In combination with a D-amino acid amidase from Ochrobactrum anthropi L-alanine amide could be converted into D-alanine. This tour de force demonstrates the power of the racemase [84]. If racemic amide is used as a starting material the application of this racemase in combination with a d- or L-amidase allows the preparation of 100% d- or L-amino acid, a dynamic kinetic resolution instead of DSM s kinetic resolution (Scheme 6.24). 

Asano et al. have also purified a D-stereospecific amino acid amidase from another Ochrobadrum anthropi isolate137, 38i. Recently, a new amidase from Comamonas acidovorans has been reported that exhibits a broad substrate specificity and also d-amino acid amidase activity1391. In addition, a D-specific amidase has been identified in Arthrobacter sp. NJ-261401. In contrast to the D-selective enzymes of Ochrobadrum sp. and Comomonas acidovorans, the D-amide hydrolase identified in Arthrobacter sp. NJ-26 was very substrate specific a good hydrolysis rate was only observed for d-alanine amide. 

Discovery of D-Aminopeptidase, D-Amino Acid Amidase, and Alkaline o-Peptidase... 

D-Amino acid amidase (DaaA) 0. anthropi SV3 Ser Dynamic kinetic resolution... 

An alternative two-step biocatalytic route, first developed at Glaxo in the 1970s, utilized a D-amino acid oxidase and an amidase to provide 7-ACA under physiological conditions (Scheme 1.12). This process has since been established in several companies, with minor modifications. In fact, 7-ACA was manufactured by GSK at Ulverston (Cumbria, UK) using both the chemical and biocatalytic processes in parallel for a period of 2 years during which time the environmental benefits of the biocatalytic process were assessed (see Section 1.6). 

In the fine chemicals industry, enantiomerically pure amino acids are mainly produced by the aminoacylase process, the amidase process, and the hydantoinase/ carbamoylase process, all three of which are suitable for I- and D-amino acids. Dehydrogenases and transaminases are now becoming established for reduction processes. 

When eledoisin-related peptide was used as a substrate, the enzyme quickly released methionine-amide rather than methionine from the carboxy-terminus of-FIGLM-NH2. In this case, the P3 position was occupied by the hydrophobic amino acid isoleucine. Furthermore, when D-amino acid occupied the P3 position of the substrate, as in enkepharin-amide, the enzyme did not liberate a carboxy-terminal methionine-amide but acted only as amidase for this substrate. It can be concluded that the S3-P3 interaction is important in increasing... 

DSM developed a slightly different approach towards enantiopure amino acids. Instead of performing the Strecker synthesis with a complete hydrolysis of the nitrile to the acid it is stopped at the amide stage. Then a stereoselective amino acid amidase from Pseudomonas putida is employed for the enantioselective second hydrolysis step [83], yielding enantiopure amino acids [34, 77, 78]. Although the reaction is a kinetic resolution and thus the yields are never higher than 50% this approach is overall more efficient. No acylation step is necessary and the atom efficiency is thus much higher. A drawback is that the racemisation has to be performed via the Schiff s base of the D-amide (Scheme 6.23). 

The starting material for the acylase process is a racemic mixture of N-acetyl-amino acids 20 which are chemically synthesized by acetylation of D, L-amino acids with acetyl chloride or acetic anhydride in alkaU via the Schotten-Baumann reaction. The kinetic resolution of N-acetyl-D, L-amino acids is achieved by a specific L-acylase from Aspergillus oryzae, which only hydrolyzes the L-enantiomer and produces a mixture of the corresponding L-amino acid, acetate, and N-acetyl-D-amino acid. After separation of the L-amino acid by a crystallization step, the remaining N-acetyl-D-amino acid is recycled by thermal racemization under drastic conditions (Scheme 13.18) [47]. In a similar process racemic amino acid amides are resolved with an L-spedfic amidase and the remaining enantiomer is racemized separately. Although the final yields of the L-form are beyond 50% of the starting material in these multistep processes, the effidency of the whole transformation is much lower than a DKR process with in situ racemization. On the other hand, the structural requirements for the free carboxylate do not allow the identification of derivatives racemizable in situ therefore, the racemization requires... 

Several multi-ton industrial processes still use enzymatic resolution, often with lipases that tolerate different substrates. BASF, for example, makes a range of chiral amines by acylating racemic amines with proprietary esters. Only one enantiomer is acylated to an amide, which can be readily separated from the unreacted amine. Many fine chemicals producers also employ acylases and amidases to resolve chiral amino acids on a large scale. l-Acylases, for example, can resolve acyl d,l-amino acids by producing the I-amino acids and leaving the N-acyl-l-amino acid untouched after separation, the latter can be racemized and returned to the reaction. d-Acylase forms the alternative product. Likewise, DSM and others have an amidase process that works on the same principle d,l-amino acid amides are selectively hydrolyzed, and the remaining d-amino acid amide can be either racemized or chemically hydrolyzed. 

The enzymatic process uses water as the solvent and two immobilized enzymes as catalysts at room temperature. In a first step cephalosporin C is deaminated to a-ketoadipyl-7-ACA using a carrier-fixed D-amino acid oxidase in the presence of oxygen. Under reaction conditions the a-keto intermediate is oxidatively decarboxy-lated to glutaryl-7-ACA. In a second step the glutaryl-7-ACA is then hydrolyzed to 7-ACA by a carrier-fixed glutaryl amidase. 

Several methods to resolve racemic mixtures of a- amino acids have been worked out, including separation of diastereomeric salts by crystallization or amides by chromatography. Chiral HPLC on phases carrying d- and L-pro-line-copper complexes has been scaled up to 20 g quantities of amino acid race-mates. Resolution with immobilized amidases, which deacetylate only L-amino acid acetamides, and subsequent precipitation of the D-amino acid acetamides work on a 500-kg scale. All kinds of labels ( C, D) can thus be introduced... 

In 1935, Krebs published a technique for Isomer analysis that employs D-amino acid oxidase, an enzyme which selectively deaminates D-isomers. This method allowed measurement of D-amino acids via the resultant keto acids that were formed or by recovery of intact L-amino acids (28). Other enzymatic methods based on L-amino acid decarboxylases (25,43), L-amino acid acylases and amidases (44) also have been used. Other biologically-based techniques employing selective utilization of L-amino acids by microorganisms appeared as early as 1949 (29,30), but due to their complexity, have not been used widely. 

Investigation of the structure-function relationships in nitrilases was largely based on sequence analyses, homology modeling, and mutational studies, as the crystal structures of nitrile-hydrolyzing enzymes have not been available except for an aliphatic nitrilase from Pyrococcus abyssi [13]. Other crystallized members of the nitrilase superfamily (amidases, N-carbamoyl-D-amino acid amidohydrolases, etc. [9]) shared only low levels of identity with experimentally confirmed nitrilases. 

Since o-stereospecific amino acid amides and peptide hydrolases were previously unknown and were not targets of enz3unology, we started to screen for these enzymes and subsequently discovered three kinds that exhibited D-stereoselectivities for o-amino acid derivatives o-aminopeptidase [4], o-amino acid amidase [5], and alkaline o-peptidase [6] (Table 19.1). Ochrobactrum anthropi Cl-38 was isolated through an enridiment culture technique as a utilizer of o-alanine amide (o-Ala-NH ) as the sole... 

Ochrobactrum anthropi SV3 was isolated as a D-valine amide degrader after a 4-month acclimation of bacterial culture. The strain produced an enzyme that was characterized as o-amino acid amidase (DaaA) [5], Furthermore, Bacillus cereus DF4-B excreted alkaline o-peptidase (ADP), which acted on the synthehc oligopeptide D-phenylalanine tetramer (o-Phe). The enzyme was characterized as the first endopeptidase acting on D-amino acid-containing peptides by recognizing the second amino acid from its N-terminus under alkaline conditions [6]. 

In the kinetic resolution of amino acid amides with the use of amidases, such as DAP and DaaA, it is possible to synthesize D-amino acids by kinetic resolution, selectively from racemic acid amides [16]. An Escherichia coli transformant highly expressing DAP catalyzed the synthesis of 2.5M (about 220g/l) D-alanine from 5M racemic alanine amide in a 4.5-h reaction, d-2-Amino butyric acid, D-methionine, D-norvaline, and D-norleucine were S5mthesized in a similar manner. We have been successful in the evolution of DAP [17] and DaaA by mutations [18]. 

D-Amino Acid Amides by i-Amino Acid Amidase in the Presence of ACL Racemase... 

Komeda, H. and Asano, Y, "Gene cloning, nucleotide sequencing, and purification and characterization of the D-stereospecific amino-acid amidase from Ochrobactrum anthropi SV3." Eur.. Biochem., 267, 2028-2036 (2000). 

Asano, Y., Mori, T., Hanamoto, S., Kato, Y, and Nakazawa, A., "A new D-stereospecific amino acid amidase from Ochrobactrum anthropi." Biochem. Biophys. Res. Commun., 162, 470-474 (1989). 

Ma, D.Y, Wang, D.X., Pan, J. et al. 2008a. Nitrile biotransformations for the synthesis of highly enantioenriched P-hydroxy and P-amino acid and amide derivatives A general and simple but powerful and efficient benzyl protection strategy to increase enantiose-lectivity of the amidase. Journal of Organic Chemistry, 73 4087 091. 

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