Stereocomplementary Synthesis of a Key Intermediate for Tofacitinib via Enzymatic Dynamic Kinetic Resolution‐Reductive Amination

Biocatalytic reductive aminations with NAD(P)H-dependent enzymes: enzyme discovery, engineering and synthetic applications

Chiral amines are pivotal building blocks for the pharmaceutical industry. Asymmetric reductive amination is one of the most efficient and atom economic methodologies for the synthesis of optically active amines. Among the various strategies available, NAD(P)H-dependent amine dehydrogenases (AmDHs) and imine reductases (IREDs) are robust enzymes that are available from various sources and capable of utilizing a broad range of substrates with high activities and stereoselectivities. AmDHs and IREDs operate via similar mechanisms, both involving a carbinolamine intermediate followed by hydride transfer from the co-factor. In addition, both groups catalyze the formation of primary and secondary amines utilizing both organic and inorganic amine donors. In this review, we discuss advances in developing AmDHs and IREDs as biocatalysts and focus on evolutionary history, substrate scope and applications of the enzymes to provide an outlook on emerging industrial biotechnologies of chiral amine production.

Structure-guided semi-rational design of an imine reductase for enantio-complementary synthesis of pyrrolidinamine

In this study, engineered imine reductases (IREDs) of IRED M5, originally from Actinoalloteichus hymeniacidonis, were obtained through structure-guided semi-rational design. By focusing on mutagenesis of the residues that directly interact with the ketone donor moiety, we identified two residues W234 and F260, playing essential roles in enhancing and reversing the stereoselectivity, respectively. Moreover, two completely enantio-complementary variants S241L/F260N (R-selectivity up to 99%) and I149D/W234I (S-selectivity up to 99%) were achieved. Both variants showed excellent stereoselectivity toward the tested substrates, offering valuable biocatalysts for synthesizing pyrrolidinamines. Its application was demonstrated in a short synthesis of the key intermediates of potential drug molecules leniolisib and JAK1 inhibitor 4, from cheap and commercially available pro-chiral N-Boc-piperidone 1 (2 and 3 steps, respectively).

Asymmetric Synthesis of Fused-Ring Tetrahydroisoquinolines and Tetrahydro-β-carbolines from 2-Arylethylamines via a Chemoenzymatic Approach

While chiral fused-ring tetrahydroisoquinoline (THIQ) and tetrahydro-β-carboline (THβC) scaffolds have attracted considerable interest due to their wide spectrum of biological activities, the synthesis of optically pure chiral fused-ring THIQs and THβCs remains a challenging task. Herein, a group of active imine reductases were identified to convert the imine precursors into the corresponding enantiocomplementary fused-ring THIQs and THβCs with high enantioselectivity and conversion, establishing an efficient and green chemoenzymatic approach to fused-ring alkaloids from 2-arylethylamines.