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.