Biocatalytic Nitration of Phenols in Microemulsions at Elevated Temperatures using Enzymes Stabilized on Magnetic Beads

Enzymes as catalysts in organic syntheses can provide high regio- and stereo-selectivity, which is often not possible with chemical catalysts. Biocatalysis with iron heme enzymes has proven efficient when the enzyme is sequestered in thin films. An added feature is improved stability. For example, peroxidases chemically crosslinked in poly-lysine in films on silica nanoparticles were stable for 9 hrs or more at 90 oC, and were used for biocatalysis up to 90 °C. We show here for a series of para-substituted phenols, single nitro-phenol products can be selectively synthesized using biocatalytic magnetic beads coated with horseradish peroxidase (HRP) crosslinked in polylysine films. Nitrophenols moieties are important as synthetic intermediates and in drugs, for a series of para-substituted phenols, biocatalytic nitration gave average turnover numbers 1.8-fold larger at 75 °C than at 25 °C. For phenols giving <50% conversion after 1 hr at 25 °C, twice the nitration yield was achieved in 1 hr at 75 °C. Results indicate that this approach should be valuable as a general tool for biocatalytic chemical synthesis