Acylase process

A. S. Bommarius, M. Schwarm and K. Drauz, The membrane reactor for the acylase process -from laboratory results to commercial scale, Chim. Oggi 1996, 14(10), 61-64. 

The starting material for the acylase process is a racemic mixture of N-acetyl amino acids which are chemically synthesized, most conveniently by acetylation of... 

Figure 7.11 Acylase process with racemization (May, 2002). Conventional process racemization at pH 3, 80-100 °C novel process racemization with enzyme (NAAR), pH 7-8, 25 10 °C.

The acylase-catalyzed resolution of N-acetyl-D,L-amino acids to obtain enantiomerically pure i-amino acids (see Chapter 7, Section 7.2.1) has been scaled up to the multi-hundred ton level. For the immobilized-enzyme reactor (Takeda, 1969) as well as the enzyme membrane reactor technology (Degussa, 1980) the acylase process was the first to be scaled up to industrial levels. Commercially acylase has broad substrate specificity and sufficient stability during both storage and operation. The process is fully developed and allowed major market penetration for its products, mainly pharmaceutical-grade L-methionine and L-valine. 

The acylase process can also be applied for the production of D-amino acids. These amino acids are valuable building blocks in pharmaceutical chemistry and they can be prepared with high enantiopurity by the action of a D-N-acyl... 

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... 

Membrane technology is a well-established technology for the immobilization of enzymes [233] since Degussa [234] introduced a continuous acylase process employing an enzyme-membrane reactor for the enantiomeric production of pure L-amino acids in 1981. Polymer membranes configured into hollow-fiber modules are, by far, the most widely used membrane where the enzyme is held back by the low cutoff of the membrane. 

Since the early 1980s this process has been scaled-up to a production level of hundreds of tons per year. Fig. 6 shows the Degussa process for manufacturing l-methionine, l-6 [9 a]. The biocatalyst is produced in bulk quantities and its operational stability is high hence this continuous EMR-acylase process demonstrates high efficiency, especially on a large-scale [9]. 

In addition, the amino acylase process can be also applied in the production of other proteinogenic and non-proteinogenic L-amino acids such as L-valine and l-phenylalanine. It is worth noting that racemases have recently been developed by several companies which allow (in combination with the L-aminoacylases) an extension of the existing process towards a dynamic kinetic resolution reaction [10]. It should be mentioned that the same concept can be also applied for the synthesis of D-amino acids when using a D-aminoacylase as an enzyme. 

In the industrial acylase process, an increase of both substrate concentration and conversion is desired to reduce costs, but, as a thermodynamic principle, in cases of increasing mole number during the reaction, the equilibrium conversion decreases with rising substrate concentration. 

Stoppok E, Wagner F, Zadrazil F (1981). Identification of a penicillin V acylase processing fungus. Eur. I. Appl. Microbiol. Biotechnol. 13 60-61. 

Figure 5.16 shows the process scheme of the commercial acylase process. In a separation unit of several ultrafiltration modules in parallel, acylase is removed from the reactor outlet stream and recycled to the reactor. Subsequently,... 

The acylase process is a typical example of reaction and separation by membranes in a sequential mode. The process is fully developed up to industrial scale, yielding high-quality products at good cost effectiveness. 

Enzymatic resolution is another method applied for the production of l- as well as D-amino acids. The disadvantage of a resolution process, a maximal yield of 50%, can often be overcome by racemization of the unwanted enantiomer of the amino acid derivative (vide infra). Many resolution concepts have been developed and commercialized, e.g., the acylase process by Degussa and Tanabe [15], the D-hydantoinase process by Recordati and Ajinomoto [16], the aminoamidase processes of DSM, and different lipase-catalyzed processes [1,13b, 17]. 

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