Chapter 5 - Imine Reductases for Chiral Amine Synthesis

Abstract

The discovery of imine reductases catalyzing the enantioselective reduction of unnatural imines leads to an effective method for the synthesis of chiral amine. The characterization and application of imine-reducing enzymes have been reviewed. Among them, Δ1-piperidine-2-carboxylate/Δ1-pyrroline-2-carboxylate reductases can be useful for the synthesis not only of cyclic amino acids but also of N-methyl-l-amino acids. Enantioselective imine reductases acting on unnatural imines afforded various five-, six-, and seven-membered ring cyclic amines with high optical purity. Furthermore, dihydroisoquinoline, dihydro-β-carboline, and indoles are acceptable as substrates, and the enantioselectivities of imine reductases for their substrates are very high. From X-ray crystal structure analyses, several imine reductases have been revealed to be NADPH-dependent homodimeric proteins with N-terminal Rossmann-fold motif, and the reaction mechanisms were proposed.