Enzymatic nitration of phenols

Soybean peroxidase (SBP), an acidic peroxidase from the seed coat, has been shown to be an effective catalyst for the oxidation of a wide variety of o rganic compounds including phenols, non-phenolic aromatic compounds, aromat ic amines, and polycyclic aromatic hydrocarbons. We recently demonstrated t hat SBP could also oxidize inorganic compounds, e.g. bromide for the haloge nation of aromatic substrates [Enzyme Microb. Technol. 26 (2000) 337]. In t he present study, we expand the repertoire of SBP-catalyzed oxidation of in organic species and demonstrate that SBP can catalyze the nitration of a va riety of phenols in the presence of H2O2 and sodium nitrite. Using 4 ' -hyd roxy-3 ' -methylacetophenone as a model phenolic substrate, the influence o f various reaction parameters, including the nature of organic co-solvent, pH, and peroxide concentration, on enzyme activity and stability were asses sed. Nitration was directed to both ortho and para positions on the phenol, the latter occurring simultaneously with elimination of the ketone-contain ing substituent on the ring. Several other phenols were effective nitration substrates including 4-hydroxy-1-indanone, 7-hydroxycoumarin, and 2-hydrox y-5-methylbenzaldehyde. Nitration was also observed with horseradish peroxi dase, lipoxidase, lactoperoxidase, chloroperoxidase, and the peroxidase fro m Coprinus cinereus. (C) 2001 Elsevier Science B.V. All rights reserved.