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174 7 Synergies of Chemistry and Biochemistry for the Production of -Amino Acids

Recent results on the use of dihydropyrimidinase/β-carbamoylase cascade
demonstrate that it constitutes an interesting biotechnological tool allowing the
total conversion of the natural substrates DHU and 5-METDHU into β-alanine and
α-methyl-β-alanine (3-AiBA). Additionally, α-phenyl-β-alanine has been produced
from its DHU derivatives. Both β-alanine derivatives were produced enantioen-
riched as (R)-α-phenyl-β-alanine (ee > 95%) and (R)-α-methyl-β-alanine (3-AiBA)
(ee > 90%) [44]. Analytical experiments with the tandem enzymes at high substrate
concentration provide evidence of total conversion without noticeable inhibition
effect. Thus, when 100 mM and 1 M solutions of 5-METDHU were hydrolyzed and
transformed totally into 3-AiBA, the former first reaction concentration required
a similar period of time as was observed in the small-scale experiment, while the
latter took only slightly longer.

7.5
Conclusions and Outlook
Apart from the interest of the isolated enzymes in the synthesis of enan-
2
3
tioenriched/enantiopure β -and β -amino acids (see above), our initial results
have shown for the first time that the mimetic tandem dihydropyrimidinase/β-
carbamoylase cascade might also be an interesting biotechnological tool for the
preparation of different β-alanine derivatives in an environmentally friendly
way [44]. More specifically, an analytical scale production of enantiomerically
enriched (R)-α-phenyl-β-alanine (ee > 95%) and (R)- α-methyl-β-alanine (ee > 90%)
was carried out using this bienzymatic system. The tandem also tolerates high
concentrations of substrate and product, which is another interesting characteristic
for a potential preparative scale-up. On the other hand, further studies should be
carried out to improve the economy of the substrate synthesis. The searching of
new enzymes with different substrate spectra and enhanced enantioselectivity will
allow increasing the versatility of this bienzymatic system in the future.

Acknowledgments

This work was supported by the Spanish Ministry of Education and Science,
the European Social Fund (ESF), and the European Regional Development Fund
(ERDF), through projects BIO2011-27842; by the Andalusian Regional Council of
Innovation, Science and Technology, through the project TEP-4691. European Sci-
ence Foundation has also supported this research through COST Action CM0701.
The authors thank Prof. Liisa Kanerva and Prof. Stefano Servi for the β-amino acid
derivatives synthesis.

References

1. Spiteller, R. and von Nussbaum, F. E. Juaristi and V.A. Soloshonok),
(2005) in Enantioselective Synthe- John Wiley & Sons, Inc, Hoboken, NJ,
sis of β-Amino Acids, 2nd edn (eds pp. 19–91.