A Convergent, One-Step Biocatalytic Cascade for the Synthesis of Structurally Diverse Noncanonical Amino Acids

Noncanonical amino acids (ncAAs) are crucial building blocks for the development of peptide drugs. Despite their importance, a general and scalable approach to the synthesis of ncAA remains an unmet need in synthetic chemistry. Here, we report the development of a one-pot 4-enzyme cascade for the production of ncAAs starting from commodity aldehydes and glycine. This cascade, which leverages a phenylserine dehydratase enzyme engineered for stability and tolerance to high-substrate loading, generates up to 37 g/L of the target ncAA and fills an existing gap by providing a single platform technology for producing both l- and d- ncAAs, featuring both aromatic and aliphatic side-chains. Additionally, we provide a demonstration that by incorporating an alcohol dehydrogenase, the reaction can be run as a redox-neutral hydrogen-borrowing cascade to the desired ncAA from readily available alcohol starting materials and expand the scope to a β-methyl ncAA. This work represents a significant expansion of the scope and practical application of biocatalytic ncAA synthesis and will enable protecting-group-free access to a broad range of ncAA with fewer steps and less waste.