Enzymatic synthesis of novel antioxidant flavonoids by Escherichia coli cells expressing modified metabolic genes involved in biphenyl catabolism

The bpha1(2072)A2A3A4 gene cluster codes for a modified biphenyl dioxygenase holoenzyme with broad substrate specificity. In the previous report, we have shown the biotransformation of flavone, flavanone, 6-hydroxyflavone and 6-hydroxyflavanone by Streptomyces lividans cells carrying bphA1(2072)A2A3A4. In the present study, we successfully biotransformed chalcone and 7-hydroxyisoflavone, which are categorized with other groups of flavonoids, by using recombinant Escherichia coli cells expressing the same genes. We also biotransformed various flavonoids by E. coli cells expressing the bphB (dihydrodiol dehydrogenase) gene in addition to the bphA1(2072)A2A3A4 genes. Flavone, flavanone, 6-hydroxyflavone, 6-hydroxyflavanone, chalcone, and 7-hydroxyisoflavone, which were used as substrates, were converted with high efficiency to their corresponding diols, whose structures were determined by HREI-MS, 1H NMR and 13C NMR data. The antioxidative activity of these generated diol compounds was markedly higher than that of the substrates used.