Processes Using L-Hydantoinases

Resolution processes based on the use of hydantoinases have been well-known for a long time, in particular for the production of D-amino acids [16], By the 1970s 

Very recently, however, a remarkably improved whole-cell biocatalyst coexpressing an L-carbamoylase, a hydantoin racemase, and an L-hydantoinase has been developed which showed a 50-fold higher productivity and is suitable for large-scale applications [17]. A prerequisite of this efficient whole-cell biocatalyst, which is applied at Degussa, was the successful inversion of the enantiospecificity of a previously D-selective hydantoinase by means of directed evolution [18]. These improvements have already been confirmed at a m3-scale using a batch reactor concept [17]. 

The reaction concept with this new hydantoinase-based biocatalyst is economically highly attractive since it represents a dynamic kinetic resolution process converting a racemic hydantoin (theoretically) quantitatively into the enantiomerically pure L-enantiomer [19]. The L-hydantoinase and subsequently the L-carbamoylase hydrolyze the L-hydantoin, l-11, enantioselectively forming the desired L-amino acid, l-2. In addition, the presence of a racemase guarantees a sufficient racemiza-tion of the remaining D-hydantoin, d-11. Thus, a quantitative one-pot conversion of a racemic hydantoin into the desired optically active a-amino acid is achieved. The basic principles of this biocatalytic process in which three enzymes (hydan-toinase, carbamoylase, and racemase) are integrated is shown schematically in Fig. 9. 

It is worth noting that this whole-cell biocatalyst accepts a broad range of substrates, thus allowing access to numerous enantiomerically pure L-a-amino acids, l-2. Selected examples for successfully converted hydantoins are shown in Fig. 10. A further advantage of the hydantoinase-based technology is that hydantoins are readily accessible and economically attractive starting materials. 

The enantioselective ring-opening of lactams can also be used for an efficient production of L-amino acids, as has been demonstrated by the production process for L-lysine, l-16. For some years Tor ay s enzymatic process for L-lysine, l-16, was 

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