Bridging between Organocatalysis and Biocatalysis: Asymmetric Addition of Acetaldehyde to β‐Nitrostyrenes Catalyzed by a Promiscuous Proline‐Based Tautomerase

Non-natural beauty: The enzyme 4-oxalocrotonate tautomerase (4-OT) promiscuously (i.e., with non-natural activity) catalyzes the Michael-type addition of acetaldehyde to nitrostyrene. Catalysis likely proceeds via enamine formation of the amino-terminal proline residue of 4-OT with acetaldehyde (see picture), reminiscent of organocatalysis. High stereoselectivity, low catalyst loading, and water as reaction medium characterize this methodology.