Process for the biotechnological preparation of L-thienylalanines in enantiomerically pure form from 2-hydroxy-3-thienylacrylic acids

A method for making L-thienylalanine of the formula I ##STR4## in which R.sup.1 is hydrogen, a halogen radical, a nitro radical or a straight-chain or branched alkyl radial and the 2-amino-2-carboxyethyl radical is in the 2- or 3-position of the thiophene ring, or the salts of these compounds, which comprises;

• reacting a compound of formula II ##STR5## in which R.sup.1 has the above meanings and the 2-hydroxyacrylic acid radical is in the 2- or 3-position, with L-asparagine, L-glutamine, L-aspartic acid and/or L-glutamic acid using transaminase as a catalyst, wherein the transaminase is produced by Alcaligenes faecalis, Alcaligenes denitrificans, Pseudomonas paucimobilis, Serratia plymuthca, Agrobacterium tumefaciens, Enterobacter agglomerans, Streptomyces hygroscopicus, pigs heart, or Streptomyces viridochromogenes, to produce the compound of formula I and recovering the compound of formula I.