Biocatalysis Under Reduced Pressure; Two-Step, One-Pot Amide Synthesis Using an Immobilised Transaminase/Lipase Cascade in Combination With By-Product Removal.

Immobilisation of biocatalysts has expanded their applicability under non-conventional conditions, particularly for compatibility in synthetic processes by improving stability in non-aqueous media and enabling reusability. The combination of biocatalysts in cascade reactions is often a useful strategy with significant advantages. However, the utility of cascades can be hindered by incompatibilities between enzymes and/or substrates and long reaction times. Herein, we describe the innovative use of a rotary evaporator for performing lipase-catalysed reactions under reduced pressure, facilitating the in situ evaporation of a volatile by-product and shifting the reaction equilibrium towards the desired product(s). This is demonstrated with an immobilised lipase-catalysed kinetic resolution of a chiral amine that yields products of high enantiopurity. Additionally, a two-step, one-pot biocatalytic cascade is developed by coupling the lipase with an immobilised, pyridoxal 5'-phosphate (PLP)-dependent transaminase (ATA). To address the challenges of combining these biocatalysts, we optimised the immobilisation support, solvent (organic/aqueous) and water content. Together, the enantioselective ATA/lipase cascade converts a prochiral ketone substrate to an amide with high yield and > 99% enantiomeric excess (%ee). This methodology demonstrates that biocatalysts can be readily combined for organic synthesis with standard laboratory apparatus and encourages a similar approach to be applied to other reactions.