Application of a Recombinant Escherichia coli Whole‐Cell Catalyst Expressing Hydroxynitrile Lyase and Nitrilase Activities in Ionic Liquids for the Production of ( S )‐Mandelic Acid and ( S )‐Mandeloamide

The conversion of benzaldehyde and cyanide into mandelic acid and mandeloamide by a recombinant Escherichia coli strain which simultaneously expressed an ( S )‐hydroxynitrile lyase (oxynitrilase) from cassava ( Manihot esculenta ) and an arylacetonitrilase from Pseudomonas fluorescens EBC191 was studied. Benzaldehyde exhibited a pronounced inhibitory effect on the nitrilase activity in concentrations ≥25 mM. Therefore, it was tested if two‐phase systems consisting of a buffered aqueous phase and the ionic liquid 1‐butyl‐1‐pyrrolidinium bis(trifluoromethanesulfonyl)imide (BMpl NTf 2 ) or 1‐butyl‐3‐methylimidazolium hexafluorophosphate (BMim PF 6 ) could be used for the intended biotransformation. The distribution coefficients of the substrates, intermediates and products of the reaction were determined and it was found that BMpl NTf 2 and BMim PF 6 were highly efficient as substrate reservoirs for benzaldehyde. The recombinant E. coli strain was active in the presence of BMpl NTf 2 or BMim PF 6 phases and converted benzaldehyde and cyanide into mandelic acid and mandeloamide. The two‐phase systems allowed the conversion of benzaldehyde dissolved in the ionic liquids to a concentration of 700 mM with product yields (=sum of mandelic acid and mandeloamide) of 87–100%. The cells were slightly more effective in the presence of BMpl NTf 2 than in the presence of BMim PF 6 . In both two‐phase systems benzaldehyde and cyanide were converted into ( S )‐mandeloamide and ( S )‐mandelic acid with enantiomeric excesses ≥94%. The recombinant E. coli cells formed, in the two‐phase systems with ionic liquids and increased substrate concentrations, higher relative amounts of mandeloamide than in a purely aqueous system with lower substrate concentrations.