Substrate specificity of catechol oxidase from Lycopus europaeus and characterization of the bioproducts of enzymic caffeic acid oxidation1

The substrate specificity of catechol oxidase from Lycopus europaeus towards phenols is examined. The enzyme catalyzes the oxidation of o-diphenols to o-quinones without hydroxylating monophenols, the additional activity of tyrosinase. Substrates containing a -COOH group are inhibitors for catechol oxidase. The products of enzymic oxidation of caffeic acid were analyzed and isolated by HPLC with diode array detection. The neolignans of the 2,3-dihydro-1,4-benzodioxin type (3, 6–8), 6,7-dihydroxy-1-(3,4-dihydroxyphenyl)-2,3-dicarboxy-1,2-dihydronaphthaline (1) 6,7-dihydroxy-1-(3,4-dihydroxyphenyl)-3-carboxynaphthaline (5) and 2,6-bis-(3′,4′-dihydroxyphenyl)-1-carboxy-3-oxacyclo-(3,0)-pentan-2-on-1-ene (4) were formed. A reaction mechanism for the formation of (1, 4 and 5) is discussed.