Product identification of guaiacol oxidation catalyzed by manganese peroxidase

The mechanism underlying the oxidation of guaiacol (2-methoxyphenol) by manganese peroxidase (MnP) was studied by structural identification of the products. After separation by TLC, the products were characterized by NMR, GC–MS, and LC–MS. They were determined to be 3,3′-dimethoxy-4,4′-biphenol, a mixture of 3,3′-dimethoxy-4,4′-biphenoquinone and 3,5′-dimethoxy-4,4′-biphenoquinone, 6-methoxy-4-(4-hydroxy-3-methoxyphenyl)-1,2-benzoquinone, 3-(4-hydroxy-3-methoxy-phenyl)-5,3′-dimethoxy-4,4′-biphenol, and a mixture of 5-(4-hydroxy-3-methoxyphenyl)-3,3′-dimethoxy-4,4′-biphenoquinone and 3-(4-hydroxy-3-methoxyphenyl)-5,3′-dimethoxy-4,4′-biphenoquinone. From the direct GC–MS analysis, two other products were identified as 3-methoxy-catechol and 2-methoxy-1,4-benzoquinone. The reaction mechanism of MnP-catalyzed guaiacol oxidation is suggested on the basis of the structural information obtained for these products.