1,4-Dihydro-l-phenylalanine—Its Synthesis and Behavior in the Phenylalanine Ammonia–Lyase Reaction

1,4-Dihydro-l-phenylalanine, a nonaromatic derivative of l-phenylalanine, has been isolated for the first time. It was synthesized as a yet unobserved minor product in the Birch reduction of l-phenylalanine. This is unexpected because it has an electron donor substituent at a reduced sp3-carbon atom of the ring system. Kinetic measurements with phenylalanine ammonia-lyase showed that 1,4-dihydro-l-phenylalanine is no substrate but a moderately good competitive inhibitor of the enzymatic reaction. This is in agreement with its predicted behavior and provides further evidence for the plausibility of the recently proposed mechanism of action of phenylalanine ammonia–lyase.