Aerobic synthesis of aromatic nitriles from alcohols and ammonia using galactose oxidase
The enzymatic synthesis of aromatic nitriles from alcohols and ammonia presents a valuable alternative to currently applied chemical methodologies. The synthesis of nitriles is traditionally accomplished through non-environmentally friendly approaches such as transition metal catalyzed cyanation, Sandmeyer reaction or Rosenmund-von Braun reaction. Biocatalytic routes towards the synthesis of nitriles utilize either cyanide in combination with aldehydes (e.g., hydroxynitrile lyases, halohydrin dehalogenases) or require previous in-situ formation of the substrate (aldoxime dehydratases). Ammoxidation is a more sustainable alternative, as it consumes molecular oxygen and ammonia as reagents.
Galactose oxidase (GOx) is a copper-dependent oxidoreductase that naturally catalyzes the aerobic oxidation of alcohol functions (as in galactose) to aldehydes. A variant of the GOx from Fusarium sp. (GOxM3-5) was evolved in the laboratory to perform the oxidation of benzylic primary and secondary alcohols to the related carbonyl compounds. We recently discovered that GOxM3-5 can also promiscuously catalyze the oxidation of aldehydes to nitriles in the presence of ammonia and air. Furthermore, we developed a concurrent, two-step biocatalytic cascade that exploits both the natural and promiscuous catalytic activities of GOx in order to perform the one-pot oxidation of primary alcohols into their corresponding nitriles. Finally, the biocatalytic process was applied for the preparative scale synthesis of 2’-fluorobenzonitrile from 2’-fluorobenzyl alcohol.