Biotechnology Letters, Vol.43, No.1, 287-296, 2021
Synthesis of (R)-mandelic acid and (R)-mandelic acid amide by recombinantE. colistrains expressing a (R)-specific oxynitrilase and an arylacetonitrilase
Objectives Chiral 2-hydroxycarboxylic acids and 2-hydroxycarboxamides are valuable synthons for the chemical industry. Results The biocatalytic syntheses of (R)-mandelic acid and (R)-mandelic acid amide by recombinantEscherichia coliclones were studied. Strains were constructed which simultaneously expressed a (R)-specific oxynitrilase (hydroxynitrile lyase) from the plantArabidopsis thalianatogether with the arylacetonitrilase from the bacteriumPseudomonas fluorescensEBC191. In addition, recombinant strains were constructed which expressed a previously described acid tolerant variant of the oxynitrilase and an amide forming variant of the nitrilase. The whole cell catalysts which simultaneously expressed the (R)-specific oxynitrilase and the wild-type nitrilase transformed in slightly acidic buffer systems benzaldehyde plus cyanide preferentially to (R)-mandelic acid with ee-values > 95%. The combination of the (R)-specific oxynitrilase with the amide forming nitrilase variant gave whole cell catalysts which converted at pH-values <= pH 5 benzaldehyde plus cyanide with a high degree of enantioselectivity (ee > 90%) to (R)-mandelic acid amide. The acid and the amide forming catalysts also converted chlorinated benzaldehydes with cyanide to chlorinated mandelic acid or chlorinated mandelic acid amides. Conclusions Efficient systems for the biocatalytic production of (R)-2-hydroxycarboxylic acids and (R)-2-hydroxycarboxamides were generated.
Keywords:Biotransformations;Chiral synthesis;Nitrilase;Oxynitrilase;Hydroxynitrile lyase;Enzyme cascades