title: Reaction mechanism of oxidative rearrangement of flavanone in isoflavone biosynthesis.
abstract: Microsomes that were prepared from elicitor-treated Pueraria lobata cell cultures catalyzed the conversion of liquiritigenin, a flavanone, into daidzein, an isoflavone. The reaction was resolved into two steps. 2, 7, 4'-Trihydroxyisoflavonone was formed as a major product when liquiritigenin was incubated with carefully washed microsomes in the presence of NADPH. The structure of 2, 7, 4'-trihydroxyisoflavanone was confirmed by mass and 1H NMR spectroscopies. The enzyme responsible for this rearrangement reaction is a cytochrome P-450-dependent monooxygenase. Upon treatment with a soluble enzyme fraction 2, 7, 4'-trihydroxyisoflavone yielded daidzein quantitatively. The incorporation of 18O from 18O2 into the 2-hydroxy group of 2, 7, 4'-trihydroxyisoflavanone was demonstrated by the shift of molecular ion in its mass spectrum. Based on these observations a new reaction mechanism, hydroxylation associated with 1,2-migration, is proposed for the oxidative rearrangement reaction catalyzed by the cytochrome P-450 enzyme of Pueraria lobata.
authors.affiliation: Faculty of Pharmaceutical Sciences, University of Tokyo, Japan.
authors.forename: M F
authors.initials: MF
authors.lastname: Hashim
authors.forename: T
authors.initials: T
authors.lastname: Hakamatsuka
authors.forename: Y
authors.initials: Y
authors.lastname: Ebizuka
authors.forename: U
authors.initials: U
authors.lastname: Sankawa
mesh_terms: D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D006859:Hydrogen; D006900:Hydroxylation; D007529:Isoflavones / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D008861:Microsomes / Q000201:enzymology; D010944:Plants / Q000378:metabolism*
chemical_list: D007529:Isoflavones; D006859:Hydrogen; D003577:Cytochrome P-450 Enzyme System