HHDH-Catalyzed Synthesis of Enantioenriched Fluorinated β-Hydroxy Nitrile─Process Advances through a Reaction Engineering Approach

This study explores halohydrin dehalogenase (HHDH) variant ISM-4 for the synthesis of enantioenriched fluorinated β-hydroxy nitrile, focusing on the reaction engineering perspective for the enhancement of process metrics. Detailed kinetic assessments, enzyme affinities, inhibitions, and deactivation dependency are integrated into a mathematical model, providing insights into ISM-4 limitations and optimal conditions for (S)-3-(4-fluorophenyl)-3-hydroxypropanenitrile's synthesis. By strategically feeding the substrate in a fed-batch or a repetitive-batch reactor, substantial improvements are achieved compared to the batch reactor, yielding the 75 and 145 mM desired product with ee > 90 and 80%, respectively. Additionally, findings from in silico simulations guided the selection of process conditions for a reaction on a 100 mL scale in a rotating-bed reactor with an immobilized catalyst, resulting in the 24.7 mM product (Y = 72%, ee 92%). This study highlights the important role of a reaction engineering approach in enhancing HHDH-catalyzed synthesis for scalable production of valuable enantioenriched building blocks.