Continuous Flow Bioamination of Ketones in Organic Solvents at Controlled Water Activity using Immobilized ω-Transaminases.

Wesley Böhmer,Alexey Volkov,Francesco G Mutti,Karim Engelmark Cassimjee

doi:10.1002/adsc.201901274

Wesley Böhmer, Alexey Volkov + Show 2 more

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https://doi.org/10.1002/adsc.201901274

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Abstract

Compared with biocatalysis in aqueous media, the use of enzymes in neat organic solvents enables increased solubility of hydrophobic substrates and can lead to more favorable thermodynamic equilibria, avoidance of possible hydrolytic side reactions and easier product recovery. ω‐Transaminases from Arthrobacter sp. (AsR−ωTA) and Chromobacterium violaceum (Cv−ωTA) were immobilized on controlled porosity glass metal‐ion affinity beads (EziG) and applied in neat organic solvents for the amination of 1‐phenoxypropan‐2‐one with 2‐propylamine. The reaction system was investigated in terms of type of carrier material, organic solvents and reaction temperature. Optimal conditions were found with more hydrophobic carrier materials and toluene as reaction solvent. The system's water activity (aw) was controlled via salt hydrate pairs during both the biocatalyst immobilization step and the progress of the reaction in different non‐polar solvents. Notably, the two immobilized ωTAs displayed different optimal values of aw, namely 0.7 for EziG3−AsR−ωTA and 0.2 for EziG3−Cv−ωTA. In general, high catalytic activity was observed in various organic solvents even when a high substrate concentration (450–550 mM) and only one equivalent of 2‐propylamine were applied. Under batch conditions, a chemical turnover (TTN) above 13000 was obtained over four subsequent reaction cycles with the same batch of EziG‐immobilized ωTA. Finally, the applicability of the immobilized biocatalyst in neat organic solvents was further demonstrated in a continuous flow packed‐bed reactor. The flow reactor showed excellent performance without observable loss of enzymatic catalytic activity over several days of operation. In general, ca. 70% conversion was obtained in 72 hours using a 1.82 mL flow reactor and toluene as flow solvent, thus affording a space‐time yield of 1.99 g L−1 h−1. Conversion reached above 90% when the reaction was run up to 120 hours.

Highlights

The use of enzymes in laboratory and industrial scale organic synthesis has predominantly been restricted to either monophasic aqueous reaction media in presence of an optional water-miscible cosolvent or bi-phasic aqueousÀ organic media or reverse-micelles systems in which the enzyme is still dissolved in a significant amount of water.[1]
Many different enzyme families have been applied in neat organic solvents or supercritical gases over the last few decades,[2] whereas more recent contributions entail the use of ionic liquids[3] and deep eutectic solvents.[4]
We reported that wild-type ωTAs retain elevated catalytic activity for the amination of prochiral ketones in neat organic solvents when applied as lyophilized cell extracts.[22]

Summary

Introduction

The use of enzymes in laboratory and industrial scale organic synthesis has predominantly been restricted to either monophasic aqueous reaction media in presence of an optional water-miscible cosolvent or bi-phasic aqueousÀ organic media or reverse-micelles systems in which the enzyme is still dissolved in a significant amount of water.[1]. The immobilized (R)-selective transaminase was employed in a packed-bed flow reactor in a neat organic solvent showing high catalytic performance.

Results

Conclusion