Biotransformation of Chrysin to Baicalein: Selective C6-Hydroxylation of 5,7-Dihydroxyflavone Using Whole Yeast Cells Stably Expressing Human CYP1A1 Enzyme.

Naturally occurring polyphenolic compounds are of medicinal importance because of their unique antioxidant, anticancer, and chemopreventive properties. Baicalein, a naturally occurring polyhydroxy flavonoid possessing a diverse range of pharmacological activities, has been used in traditional medicines for treatment of various ailments. Apart from its isolation from natural sources, its synthesis has been reported via multistep chemical approaches. Here, we report a preparative-scale biotransformation, using whole yeast cells stably expressing human cytochrome P450 1A1 (CYP1A1) enzyme that allows regioselective C6-hydroxylation of 5,7-dihydroxyflavone (chrysin) to form 5,6,7-trihydroxyflavone (baicalein). Molecular modeling reveals why chrysin undergoes such specific hydroxylation mediated by CYP1A1. More than 92% reaction completion was obtained using a shake-flask based process that mimics fed-batch fermentation. Such highly efficient selective hydroxylation, using recombinant yeast cells, has not been reported earlier. Similar CYP-expressing yeast cell based systems are likely to have wider applications in the syntheses of medicinally important polyphenolic compounds.