NITRATION OF VERATRYL ALCOHOL BY LIGNIN PEROXIDASE AND TETRANITROMETHANE

Lignin peroxidase (LiP), from Phanerochaete chrysosporium, in the pres ence of H2O2 and tetranitromethane (TNM), oxidizes veratryl (3,4-dimet hoxybenzyl) alcohol (VA) (I) to veratraldehyde (IV), 4,5-dimethoxy-2-n itrobenzyl alcohol (VI), and 3,4-dimethoxy-nitrobenzene (VI). The form ation of these products is explained by a mechanism involving the one- electron oxidation of VA by LiP 60 produce the corresponding cation ra dical, which loses a proton to generate the benzylic radical. The latt er reduces TNM to generate the trinitromethane anion (VIII) and the ni trogen dioxide radical (. NO2). NO2 couples with the VA cation radical , and the subsequent loss of a proton leads to V. Alternatively, the a ttack of . NO2 at C-l of the VA cation radical, followed by aromatizat ion and loss of formaldehyde (VII), yields VI. Isotopic labeling exper iments confirm that V is generated by the reaction of . NO2 with the V A cation radical, rather than with the benzylic radical, The nitration of two other LiP substrates, 1,4-dimethoxybenzene (II) and tyrosine ( III), also was examined. Product analysis of reactions conducted in th e presence of H2O2 With these substrates indicated less nitrated produ ct was formed from 1,4-dimethoxybenzene and no nitrated product was fo rmed from tyrosine. However, significant amounts of nitrated products were formed from 1,1-dimethoxybenzene and tyrosine when glucose and gl ucose oxidase were used as an H2O2 source. These results suggest that a reductant, either the veratryl alcohol benzylic radical or superoxid e, is required in the reaction to reduce TNM to generate . NO2. These results provide further evidence for the formation of the VA cation ra dical and the first chemical evidence for the formation of the VA benz ylic radical in LiP-catalyzed reactions. (C) 1998 Academic Press.