Artificial Enzymes Combining Proteins with Proline Polymers for Asymmetric Aldol Reactions in Water

Artificial enzymes, usually created by incorporating one or two abiological catalytic species into protein hosts, are becoming promising tools for biocatalysis. However, they are still far behind natural enzymes due to their limited active sites with low activity and selectivity. Here, we proposed a polymeric approach to generate artificial enzymes by combining proteins with organocatalytic polymers, in which multiple proline organocatalysts are grafted from protein scaffolds via atom-transfer radical polymerization. The resultant artificial polyenzymes, abbreviated as "ArPoly", have similar physicochemical properties as natural enzymes and proved to be effective aldolase mimics for the aqueous asymmetric aldol reaction, in which an optimal ArPoly gave rise to 33% conversion and 94% enantioselectivity. Therefore, we proved the concept of water-soluble proline-based organocatalyst for aqueous asymmetric aldol reactions. This success not only expands the toolbox of asymmetric organocatalysis but also opens other avenues in the field of artificial enzymes where a plethora of proteins/enzymes can be combined with various well-designed organocatalytic polymers for synthetically useful reactions.