3-(2,5-Cyclohexadienyl)-L-alanine (1,4-Dihydro-L-phenylalanine)
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Its Synthesis and Behaviour in the Phenylalanine Ammonia-Lyase Reaction

Conclusion and Acknowledgements
We have described for the first time the isolation of 1,4-dihydro-L-phenylalanine as minor product in the Birch reduction of L-phenylalanine. The yield could be improved to 3 % by changing the proton source from tert.-butanol to ethanol. Kinetic experiments showed that 2,5-dihydro-L-phenylalanine is a substrate (Km = 35.5 % of Km (phe), Vmax = 3.3 % of Vmax (phe)) and simultaneously a moderately good competitive inhibitor (Ki = 30.6 µM). 1,4-dihydro-L-phenylalanine was no substrate but a weaker competitive inhibitor (Ki = 157 µM). These results lend further support for the recently proposed mechanism of the PAL reaction [8,9].
Financial support from the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie is gratefully acknowledged. A.S. thanks the Land Baden-Württemberg for a scholarship for graduate students. We thank Professor G. E. Schulz for a recombinant plasmid harbouring the PAL gene changed into the codon usage of Escherichia coli.


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