Pterocarpans biosynthesis

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. 

Modification of isoflavonoid biosynthesis may have a wide range of applications for improving not only plant defense characters but also the health benefits of food for humans. With the exception of IFD (which may not be required in vivo), cDNA clones are available for all of the enzymes needed for the production of the isoflavonoid vestitone. Furthermore, as VR cDNAs have been cloned, only clones for the DMID are lacking for the biosynthetic branch of the antifungal pterocarpans. To date, experiments have focused on 2HIS, but there has also been success using IFR, I2 H, and I70MT. 

Tiemann, K. et al., Pterocarpan phytoalexin biosynthesis in elicitor-challenged chickpea (Cicer arietinum L.) cell cultures. Purification, characterization and cDNA cloning of NADPHnsofiavone oxidoreductase. Eur. J. Biochem., 200, 751, 1991. 

The biosynthesis of pterocarpans, which include well-known phytoalexins such as medicarpin in alfalfa (Medicago sativa) [Baker et al., 1989 Higgins, 1972 Oommen et al., 1994 He and Dixon, 2000] (Fig. 21.2), pisatin in pea... 

Akashi T, Koshimizu S, Aoki T, Ayabe S-I. 2006. Identification of cDNAs encoding pterocarpan reductase involved in isoflavan phytoalexins biosynthesis in Lotus japonicus by EST mining. FEBS Lett 580 5666-5670. 

Guo L, Dixon RA, Paiva NL. 1994b. The pterocarpan synthase of alfalfa Association and co-induction of vestitone reductase and 7,2 -dihydroxy-4 -methoxy-isoflavanol (DMI) dehydratase, the two final enzymes in medicarpin biosynthesis. FEBS Lett 356 221-225. 

Scheme 1.1 Pathway for the biosynthesis of the major classes of flavonoids. 1, Chalcone synthase 2, chalcone isomerase 3, flavone synthase 4, flavanone 3-hydroxylase 5, flavonol synthase 6, dihydroflavonol reductase 7, anthocyanidin synthase 8, anthocyanidin glucosyltransferase 9, chalcone-ketide reductase 10, chalcone isomerase 11, isoflavone synthase 12, isoflavone 2 -hydroxylase 13, isoflavone reductase 14, pterocarpan synthase 15, pterocarpan 6a-hydroxylase 16, prenyltransferase 17, prenylcyclase.

GUNIA, W., HINDERER, W., WITTKAMPF, U., BARZ, W Elicitor induction of cytochrome P450 monooxygenases in cell suspension cultures of chickpea and their involvement in pterocarpan phytoalexin biosynthesis. Z Natwforsch, 1991, 36c, 58-66. 

The pterocarpan pisatin was first isolated and characterized as a phytoalexin in Pi sum sativum in the early 1960s.234 235 Since then, structurally diverse phytoalexins have been reported from more than 30 families of higher plants. Much progress is also being made in studies on phytoalexin biosynthesis based on genomic information. 

Fig. 4 Biosynthesis of isoflavonoids (pterocarpans) via isoflavones from phenylpropanoid pathway...

Bearing these taxonomic conclusions in mind, an overview of likely biosynthetic relationships between the isoflavonoids discussed in this chapter was proposed [6] and is represented in Fig. (4). This emphasises those compounds whose occurrence is restricted to the 3 species in the proposed series Pinnatifida (C. bijugum, C. judaicum and C. pinnatifidum) and attempted to address the biosynthesis of these compounds, most notably arybenzofurans which are still missing from the latest versions of the isoflavonoid biosynthesis schemes because of the lack of persuasive biogenetic evidence. A 2 -hydroxyisoflavanol, the immediate precursor of isoflav-3-enes and pterocarpans, is shown as the first intermediate. Its... 

Isoflavonoids are metabolically derived from the flavanones. The central step is the migration from the C2 to the C3 of the aryl block, which constitutes the B ring of the flavanone intermediate. This reaction is catalysed by 2-hydroxyflavone synthase, a cytochrome P450. At the same time, the isoflavones are precursors of a substantial number of compounds involved in the biosynthesis of phytoalexins and pterocarpanes. 

BARZ, W., WELLE, R., Biosynthesis and metabolism of isoflavones and pterocarpan phytoalexins in chiekpea, soybean and phytopathogenic fungi, in ... 

C17H14O4, Mr 314.29, cryst., mp. 61 °C, (aJo -1-280° (C2H5OH). The 6a-hydroxy- pterocarpan (-F)-(6a/7,11 a/ )-P. is isolated from garden peas (Pisum sativum) infected with Sclerotinia spores and is a phy-toalexin. P. has antimycotic activity. The biosynthesis proceeds from maackiain, see pterocarpans. In pea tissue cultures ( - )-(6a I, 11 a/()-maackiain is converted to (-)-(6a5,lla5)-P. 

Barz, W. and R. Welle, Biosynthesis and metabolism of isofla-vones and pterocarpan phytoalexins in chickpea, soybean, and phytopathogenic fungi, in Phenolic Metabolism in Plants (H. A. Stafford and R. K. Ibrahim, eds.), Recent Advances in Phytochemistry Vol. 26, 139-164, Plenum Press, New York, 1992. 

Fig. 2.6 An overview of isoflavonoid biosynthesis in the Leguminosae based on recent findings. Partially characterized or uncertain steps are shown by the dotted arrows. 2HIS, 2-hydroxyisoflavanone synthase 2 OMT, 2 -0-methyltransferase (presumed) DMID, 7,2 -dihydroxy-4 -methoxyisoflavanol dehydratase HI4 OMT, hydroxyiso-flavanone 4 -0-methyltransferase I2 H, isoflavone 2 -hydroxylase IFR, isoflavone reductase PTR, pterocarpan reductase VR, vestitone reductase.

Biosynthesis of HydroxyphaseoUin.—The biosynthesis of a newly discovered pterocarpan (48)" has been investigated in disease-resistant soya bean hypo-cotyls. [U- C]Phenylalanine and [9- C]isoliquiritigenin were readily incorporated into (48). Label also appeared in daidzein, coumestrol, and spjagol (49). The biosynthetic pathway followed the generally expected route... 

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