l-Thienylalanines were prepared via the hydantoin and azlactone routes with the key step consisting of the microbial transamination of 2-hydroxy-3-thienylacrylic with l-aspartic acid as amino donor. The transamination reaction was performed by a genetically engineered E. coli strain on scales up to 100 g of l-3-(2-thienyl) alanine 1a and is also applicable to the preparation of the isomeric amino acid 1b and some ring-substituted derivatives.
