Pyridoxal Radical Biocatalysis for the Stereoselective Production of Non-Canonical Amino Acids

Project Summary Biocatalysis represents a powerful emerging technology for the biomanufacturing of biologically active molecular agents and clinically significant therapeutics. Previously, the practice of biocatalysis is largely limited to the utilization and engineering of native enzymology from nature. New-to-nature enzymatic chemistries which are synthetically useful yet never encountered in biology remain largely underexploited. Combining biocatalysis and photochemistry, we propose a novel and generalizable photobiocatalysis strategy to reprogram diverse pyridoxal phosphate (PLP)-dependent enzymes as radical enzymes to catalyze stereoselective intermolecular radical reactions. Notably, these newly developed enzymatic reactions are not previously known in either biochemistry or organic chemistry. By merging photoredox catalysis powered by visible light and pyridoxal biocatalysis fine-tuned by directed evolution, a range of non-canonical amino acids that are often incorporated into medicines and therapeutic protein targets will be produced with excellent stereocontrol. By leveraging novel activation mechanisms involving open-shell PLP covalent intermediates, we will design and develop stereoselective biocatalytic radical C–C bond forming reactions at the a, b, or g position of abundant amino acid building blocks, furnishing an array of not easily accessible non-canonical amino acids, including those possessing a well-defined stereochemical dyad or triad which have remained out of the reach of traditional chemical and biological synthesis. Radical pyridoxal biocatalysis eliminates the need of tedious protecting group manipulation often required by traditional chemical synthesis, providing a modular, convergent and highly stereoselective approach to manufacturing biomedically valuable non-canonical amino acids.