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, H-1 NMR and C-13 NMR data. The antioxidative activity of these generated diol compounds was markedly higher than that of the substrates used. (C) 2003 Elsevier Science B.V. All rights reserved.