Optically pure amino acid production enzymatic process

Table 1 Enzymatic Process for Optically Pure Amino Acid Production...

Hydantoinase process, outlined in Fig. 1, includes two hydrolases—hydantoin-hydrolyzing enzyme (hydantoinase) and AT-carbamoyl amino acid-hydrolyzing enzyme (carbamoylase)—and is one of the most efficient and versatile methods for the production of optically active a-amino acids. DL-5-Monosubstituted hydantoins, which are used as common precursors for the chemical synthesis of DL-a-amino acids [1], are the starting material of this enzymatic process. Keto-enol tautomerism is a typical feature of the hydantoin structure. Under neutral conditions, the keto form is dominant in alkaline solution, enolization between the 4 and 5 positions can occur, as has been concluded from the fact that optically pure hydantoins readily racemize. This feature is of practical relevance for the complete conversion of racemic hydantoin derivatives to optically pure L- or D-a-amino acids without any chemical racemization step. A variety of hydantoinase and carbamoylase with different stereospecificity were found. They are D-specific hydantoinase (D-hydantoinase), L-specific hydantoinase (L-hydantoinase), none-specific hydantoinase (DL-hydantoinase), D-specific carbamoylase (D-carbamoylase), and L-specific carbamoylase (L-carbamoylase). With the combination of these enzymes, optically pure amino acids are obtained from DL-5-monosubstituted hydantoins (Fig. 2). The wide substrate range of hydantoinases and carbamoylases also gives generality to the hydantoinase process. 

One of the most widely used enzymatic methods for D-amino acid production is the hydantoinase process [4]. The great advantage of this process is that, potentially, any optically pure D-amino acid can be obtained using the corresponding substrate from a wide spectrum of D,L-5-monosubstituted hydantoins, which are readily accessible by chemical synthesis [5]. In this cascade of reachons the chemically synthesized D,L-5-monosubstituted hydantoin ring is first hydrolyzed by a stereoselective hydantoinase enzyme (D-hydantoinase). Further hydrolysis of the resulting N-carbamoyl D-amino acid to the free D-amino acid is catalyzed... 

Although initially prepared and evaluated as a racemate, the NMDA antagonist activity was likely to reside primarily in a single enantiomer. The stereoselective nature of the NDMA receptor is well established, albeit not completely understood. Consequently, several attempts have been undertaken to develop synthetic protocols that would allow preparation of optically active compounds. Early reports of preparation of optically active co-amino-o-carboxyalkylphosphonic acids describe the preparation of (.S )-A P-3 from an optically active amino nitrile prepared by reaction of diethyl 1-formylphosphonate with hydrogen cyanide and (5)-(-)-a-methylbenzylamine. Acid hydrolysis, enrichment of the diastereomers by fractional recrystaUization, and debenzylation lead to the isolation of (.S )-A P-3 in 86% enantiomeric excess. " Recently reported procedures, which use chemoenzymatic processes, offer a more convenient and mild approach for the production of optically pure aminophosphonic acids. Enzymatic hydrolysis of amides using penicillinacylase (EC... 

Optically pure d- and L-a-amino acids are of increasing interest as precursors for semi-synthetic antibiotics, new herbicides, insecticides, and physiologically active peptides, and as chiral building blocks for chemical synthesis. For the production of optically active a-amino acids, enzymatic processes have been developed other than fermentation to cover a wide range of products, not only natural L-a-amino acids but also unnatural and D-a-amino acids (Table 1). 

---