The preparation of L-thienylalanine takes place by the hydantoin or azlactone route. 2-Hydroxy-3-thienylacrylic acids are used as starting material for the biotransformation. The innovative step comprises the transamination of the enol form of 2-hydroxy-3-thienylacrylic acids to give L-thienylalanines by means of the biotransformation. The transamination takes place in the presence of L-aspartic or L-glutamic acid as amino donor.
