Isoflavanones

Tsanuo MK, Hassanali A, Hooper AM, Khan Z, Kaberia F, Pickett JA, Wadhams LJ (2003) Isoflavanones from the allelopathic aqueous root exudate of Desmodium uncinatum. Phytochemistry 64 265-273... 

Examples of other antimicrobial isoflavonoids isolated from the Leguminoseae family also included two isoflavanones from Uraria picta (Jacq.) the isoflavones formononetin and afrormosin from the... 

Tanaka H, Hattori H, Oh-Uchi T, Sato M, Sako M, Tateishi Y, Rizwani GH. (2009) Three new isoflavanones from Erythrina costaricensis. Nat Prod Res 23 1089-1094. 

Rahman MM, Gibbons S, Gray AI. (2007) Isoflavanones from Uraria picta and their antimicrobial activity. Phytochemistry 68 1692-1697. 

Nkengfack, A.E. et al., Prenylated isoflavanone from Erythrina eriotricha, Phytochemistry, 40, 1803, 1995. 

The 2 -hydroxyisoflavones are reduced to the corresponding isoflavanones by a NADPH-dependent isoflavone reductase (IFR). The isoflavanones are the final isoflavonoid intermediates of pterocarpan biosynthesis. Variant IFR activities between species are thought to contribute to the stereochemistry of the pterocarpans produced, in particular, (-l-)-maackiain in P. sativum, (—)-maackiain in C. arietinum, (—)-3,9-dihydroxypterocarpan in G. max, and (—)-medicarpin in M. sativa. The (—) indicates 6aRllai stereochemistry. 

Based on analysis of enzyme preparations, the conversion of isoflavanones to pterocarpans was thought initially to be catalyzed by a single NADPH-dependent enzyme, termed the pterocarpan synthase (PTS). However, it was subsequently shown that in M. sativa the conversion of vestitone to medicarpin involves two enzymes, VR and 7,2 -dihydroxy-4 -methoxyisoflavanol (DMI) dehydratase (DMID). The reaction series from vestitone to the pterocarpan is thought to proceed by the VR-catalyzed reduction of vestitone to DMI, followed by the loss of water and formation of the C-O-C bridge between the heterocycle and the B-ring, catalyzed by DMID. 

Paiva, N.L. et al., Molecular cloning of isoflavone reductase from pea (Pisum sativum L.) evidence for a 3R-isoflavanone intermediate in (+)-pisatin biosynthesis. Arch. Biochem. Biophys., 312, 501, 1994. 

Berchemia zeyheri (Rhamnaceae), a tree native to southern Africa which is prized for its beautiful wood, known as pink ivory or red ivory. The complexity of the phenolic compounds present in heartwood extracts prompted their analysis as permethylated derivatives. Stereochemical features were determined by using both NMR and circular dichroism spectroscopy of the parent compounds and their degradation products. These methods were used successfully to obtain a full stereochemical description of the zeyherin epimers 374 and 375, ° which were first isolated in 1971 but not fully characterized at that time. Subsequent work has led to the discovery of further auronol dimers and novel heterodimers with flavanone or isoflavanone constituents as summarized in Table 16.15. ° ° °... 

Bekker, R., Brandt, E.V., and Ferreira, D., Bifiavonoids. Part 4. Structure and stereochemistry of novel flavanone- and the first isoflavanone-benzofuranone bifiavonoids. Tetrahedron, 55, 10005, 1999. 

Moreira, I.C. et al., Isoflavanone dimers hexaspermone A, B and C from Ouratea hexasperma. Phytochemistry, 35, 1567, 1994. 

Da-Cunha, E.V.L. et al., Eryvellutinone, an isoflavanone from the stem bark of Erythrina vellutina. Phytochemistry, 43, 1371, 1996. 

Delle Monache, G. et al.. Antimicrobial isoflavanones from Desmodium canian. Phytochemistry, 41, 537, 1996. 

DuBois, J.L. and Sneden, A.T., Dihydrolicoisoflavone, a new isoflavanone from Swartzia poly-phylla, Journal of Natural Products, 58, 629, 1995. 

Galeffi, C. et al., Two prenylated isoflavanones from Millettia pervilleana. Phytochemistry, 45, 189, 1997. 

Osawa, K. et ah, Isoflavanones from the heartwood of Swartziapolyphylla and their antibacterial activity against cariogenic bacteria. Chemical Pharmaceutical Bulletin, 40, 2970, 1992. 

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