Engineered Biocatalytic Synthesis of β-N-Substituted-α-Amino Acids

• Published in: Angewandte Chemie International Edition 2023-10, Vol.62 (43), p.e202311189-e202311189
• Main Authors: Villalona, Jairo, Higgins, Peyton M, Buller, Andrew R
• Format: Article
• Language: English
• Subjects: Amines; Amino acids; Amino Acids - chemistry; Biocatalysis; Biological activity; Catalysis; Directed evolution; Nucleophiles; Serine; Substitution reactions; Synthesis; Tryptophan; Tryptophan synthase
• ISSN: 1433-7851; 1521-3773; 1521-3773
• DOI: 10.1002/anie.202311189

Non-canonical amino acids (ncAAs) are useful synthons for the development of new medicines, materials, and probes for bioactivity. Recently, enzyme engineering has been leveraged to produce a suite of highly active enzymes for the synthesis of β-substituted amino acids. However, there are few examples of biocatalytic N-substitution reactions to make α,β-diamino acids. In this study, we used directed evolution to engineer the β-subunit of tryptophan synthase, TrpB, for improved activity with diverse amine nucleophiles. Mechanistic analysis shows that high yields are hindered by product re-entry into the catalytic cycle and subsequent decomposition. Additional equivalents of l-serine can inhibit product reentry through kinetic competition, facilitating preparative scale synthesis. We show β-substitution with a dozen aryl amine nucleophiles, including demonstration on a gram scale. These transformations yield an underexplored class of amino acids that can serve as unique building blocks for chemical biology and medicinal chemistry.