Two-Step Synthesis of a Chiral Fluorinated Alcohol With Silica-Supported Enzyme RrADH in Batch and Continuous Flow Mode

Abstract

The growing demand for sustainable and efficient methods for synthesizing fine chemicals has increased interest in innovative approaches for accessing high-quality chiral building blocks, particularly fluoroalcohols, which are relevant for the production of active pharmaceutical ingredients (APIs). This study presents the complete integration of a two-step process in a continuous flow reactor system for the synthesis of (R)-2-fluoro-1-phenylethanol as a reference molecule. To this end, the individual reaction steps and technologies for the decarboxylative fluorination of 3-oxo-3-phenylpropanoic acid in aqueous media, followed by an enantioselective biocatalytic reduction of the prochiral intermediate phenacyl fluoride, were adapted and implemented in a compact laboratory system for performance demonstration. Alcohol dehydrogenase (ADH) from Rhodococcus ruber (RrADH) produced in a plant-derived BY2 cell-free expression system was used as the biocatalyst, which was immobilized via an imine bond on glutaraldehyde-modified silica supraparticles. The immobilized enzymes were used in batch mode for comprehensive kinetic studies of the enantioselective reduction, including evaluations of their operational and storage stability. Excellent enantiomeric excess (> 99.9%) and overall yields of up to 91% were achieved for both synthesis steps. These results are a prerequisite for the targeted and stable use of the enzyme in a continuously operated two-step process, which was achieved by using a serial micro batch reactor (SMBR) setup with a capillary reactor for precise temperature control. This study demonstrates the advantages of combining immobilized biocatalysts with continuous-flow operation for achieving high efficiency and selectivity in the synthesis of chiral fluoroalcohols. The integrated process provides a sustainable and versatile basis for future developments in the green synthesis of fluorinated building blocks relevant to pharmaceutical applications.

Abstract of "Two-Step Synthesis of a Chiral Fluorinated Alcohol With Silica-Supported Enzyme RrADH in Batch and Continuous Flow Mode" by Cermjani E, Nölke G, Fiore SD et al., https://doi.org/10.1002/chem.202503304, used under its Creative Commons Attribution license (CC-BY); markup removed, otherwise unmodified.