Stereoselective Reduction of α‐Fluoro‐β‐keto Esters by NADH and NADPH‐Dependent Ketoreductases

Abstract

Racemic α‐fluoro‐β‐keto esters were stereoselectively transformed to α‐fluoro‐β‐hydroxy esters through dynamic reductive kinetic resolution (DYRKR) using commercially available NAD(P)H‐dependent ketoreductases. Aromatic, alkenyl, and alkyl substrates were all reduced in high optical purities and yields. For most substrates, either anti or syn diastereomers could be produced with high enantiomeric excess, depending on the enzyme employed. The enzyme reactions with ethyl α‐fluoroacetoacetate were conveniently monitored in real time by in situ 19F NMR spectroscopy. These commercially available enzymes provide convenient access to stereoisomers of α‐fluoro‐β‐hydroxy esters from easily accessible racemic substrates.

Stereoselective Reduction of α-Fluoro-β-ketoesters: Ketoreductases and Dynamic Reductive Kinetic Resolution

“…Students were initially assigned two enzymes from the Codexis Codex KRED Screening Kit based on previous results on the stereoselective reduction of racemic ethyl 2-fluoro-3-oxobutanoate with 24 different KREDs supplied by Codexis. 16 The goal was to provide students with a highly stereoselective KRED and another KRED that provided some amount of each stereoisomer as a "standard reference". The reaction is carried out on a small-scale, consistent with the screening protocol provided with the kit, using 2 mg of enzyme and 50 μmol of substrate.…”

Ketoreductase Catalyzed (Dynamic) Kinetic Resolution for Biomanufacturing of Chiral Chemicals

“…The C-F bond of α-fluoro-β-keto esters can affect the physical and chemical properties of the compound tremendously ( O'Hagan, 2008 ), and fluorine also has a great influence on the biological activity of pharmacologically active compounds and drugs ( Meanwell, 2018 ). Accordingly, Green and coworkers focus on selective catalytic reduction of α-fluoro-β-keto esters ( 23a-i ) by DKR ( Green et al, 2019 ) ( Figure 6A ). Using commercially available ketoreductases, most of the substrates could be reduced to corresponding α-fluoro-β-hydroxy esters in high optical purities and yields.…”