Genetically encoded artificial photoenzymes for enantioselective [2 + 2] photocycloadditions

Photoenzymatic catalysis combines the strengths of photochemical activation and exceptional biocatalytic selectivity, enabling the exploration of new-to-nature enzyme activities and tackling enantioselectivity challenges associated with photoinduced radical reactions. To date, most reported photobiocatalytic systems rely on natural cofactors, such as nicotinamides and flavins. Our research team, along with others, has developed an alternative approach for designing artificial photoenzymes by incorporating synthetic photocatalysts (e.g., benzophenone) into protein scaffolds using genetic code expansion technology. These artificial triplet photoenzymes facilitate highly enantioselective [2 + 2] photocycloadditions, achieving over 99 % enantiomeric excess. This chapter provides detailed protocols for the preparation, screening, evolution, and catalysis of these artificial photoenzymes. The methodologies described can be adapted for other photobiocatalytic systems featuring artificial triplet photoenzymes, offering a general strategy for asymmetric photochemical transformations via energy transfer.