PHENYLALANINE AMMONIA-LYASES (PALs)
PALs catalyse the elimination of ammonia from L-phenylalanine, acting as a gateway enzyme to secondary metabolism. Although this reaction is of limited use in organic synthesis, the discovery of its reversibility opened up a completely new biocatalytic route to the preparation of optically pure L-amino acids. In the presence of high concentrations of ammonia, inexpensive and readily accessible arylacrylic acid derivatives can be converted into L-arylalanines with excellent yields and often perfect enantioselectivities. No cofactor regeneration is required, product isolation is extremely easy and the reaction proceeds with perfect atom economy, all factors that contribute to the scalability of PAL chemistry. In the past years, we have focused on the development of novel synthetic applications of PALs (and of the mechanistically related phenylalanine aminomutases) expanding their substrate scope and integrating them in chemo-enzymatic cascades.