Chemoenzymatic Synthesis of Chiral Piperidines Using the Immobilized Transaminase ATA‐117 in Continuous Flow Reactors

Abstract

Nowadays, there is a growing need for streamlined and sustainable strategies to access chiral nitrogen heterocycles, whose stereodefined frameworks underpin their broad functional and pharmaceutical relevance. Herein, we report a robust continuous flow enzymatic protocol for the stereoselective synthesis of the natural alkaloid (–)‐pinidinone and demonstrate its applicability to the preparation of a small family of structurally diverse chiral 2,6‐disubstituted piperidines. The strategy relies on the enantioselective transamination of tailor‐made α , β ‐unsaturated ketones catalyzed by an immobilized form of ATA‐117, which triggers a spontaneous intramolecular aza‐Michael reaction, enabling rapid access to chiral cis ‐(2 R ,6 R )‐piperidine scaffolds under mild conditions. The enzyme, successfully immobilized on Eupergit C, showed good operational and storage stability while a dual‐flow feed configuration minimized the formation of imine and Michael‐type by‐products observed when a single stock solution of α , β ‐unsaturated ketone acceptor and isopropylamine (IPA) amino donor was employed. The optimized conditions (20 mM substrate, 200 mM IPA, 60 min residence time, 30 °C) allowed for complete conversion and high stereoselectivity, while an integrated in‐line work‐up improved automation and reduced manual handling. This study establishes a robust biocatalytic flow platform for the asymmetric synthesis of valuable nitrogen‐containing heterocycles.