Enzymatic systems using Cu-oxidases

Galactose oxidase (EC 1.1.3) in nature catalyzes the oxidation of D-galactose to D-galactohexodialdose (see Fig. 1, reaction 1). A detailed 

Despite its high selectivity in the oxidation of hexoses, GOase displays a rather broad substrate range for nearly all primary alcohols. In Table I the relative activities of alcohol substrates are given. As shown in the table, a-carbonyl alcohols as a class are the best substrates. Unsaturated or aromatic substrates constitute another reasonable good group of substrates. The inherent chemical reactivity of the alcohol is not a determinant in itself since substrates with comparable electronic properties differ markedly as substrates. For pyridine carbinols, the m- and p-derivatives are more reactive than the o-derivative. Remarkably m-substituted benzyl alcohols display larger reactivities than p-substituted benzyl alcohols. 

Whittaker performed quantitative structure-activity correlation studies and showed that within a series of m-substituted alcohols the rates correlate with Om- Thus the greater reactivity of m-methoxybenzyl alcohol relative to chloro- and nitro-benzyl alcohol is consistent with the electronic properties of the benzylic bond. This would correspond to hydrogen atom transfer as a key mechanistic step (see below). 

Relative Reactivities of Alcohol Substrates to be Oxidized by Galactose Oxidase 

Aliphatic alcohols a,P-Unsaturated alcohols Aromatic alcohols 

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