The oxidation of 7‐(p‐X‐phenyl)pteridin‐4‐ones (X = Me, H, Br, CN, NO₂) with free and immobilized xanthine oxidase

Abstract

Abstract. Bovine milk xanthine oxidase was used as a catalyst for the oxidation of various 7-(p-Xphenyl)pteridin-4-ones into 7-(p-X-phenyl)lumazines. On a preparative scale the derivatives with X = Br, CN and NO, were most conveniently oxidized with the free enzyme in a solution continuously fed with concentrated substrate. The lumazines obtained separated during the reaction and were easily isolated in good yield (> 90 %) and high purity by filtration. The compounds with X = H and OMe, on the other hand, were more conveniently oxidized with the immobilized enzyme, i.e. xanthine oxidase adsorbed to 1-octyl-substituted Sepharose 4B. Immobilized xanthine oxidase was used either as a suspension in a stirred batch reactor which was continuously fed with concentrated substrate, or packed in a column through which substrate solution was recirculated. After completion of the reaction the filtrate of the suspension, or the concentrated recirculation solution, respectively, were acidified and the product was collected in good yield (>90%) and high purity by filtration. The rate of oxidation was found to be influenced by the substituent X. The more electron attracting X, by either resonance or induction, the lower the reaction rate. Accordingly, a negative reaction constant p of --0.5 was calculated from the data for the free and immobilized enzyme. The enzyme-substrate complex formation, as reflected in the Michaelis constant K,, is largely determined by the hydrophobicity of the phenyl group.

Gratuitous induction of xanthine oxidase by 5,6-diaminouracil in continuously grown cells of Arthrobacter globiformis M4

“…Apart from hypoxanthine and xanthine which are oxidized to uric acid, several compounds structurally related to these natural substrates can be oxidized by enzyme preparations from bovine milk, chicken liver or from Arthrobacter sp. (Tramper et al 1979(Tramper et al , 1982. Immobilized enzyme preparations from Arthrobacter M4 have also been successfully used as a biocatalyst (De Meester et al 1987a, 1987b.…”