Isoflavones compounds biosynthesis

The R. are generally toxic. They are soluble in organic solvents. Chemically the C20 or C23 compounds are chromanofiirochromones (see furocoumarins) or, respectively dichromanopyrones which can be considered as being derived tom the isoflavones for biosynthesis, see Lit.. The activity as an insecticide is based on an impairment of electron transport in the mitochondria caused by an inhibition of the citric acid cycle. 

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. 

Coumestans, such as (88), which possess a coumarin strac-ture, are derivatives of isoflavones (Fig. 11.28) most of the 31 known compounds of this stmctural type are restricted to the Fabaceae (Dewick, 1982,1988 Williams and Harbome, 1989b). Study of the biosynthesis of coumestans has been accomplished because elicitors stimulate synthesis of these compounds in plant cell cultures (Grisebach, 1985). The only known coumestan glycoside occurs in Eclipta alba (Asteraceae). 

The precursors of flavonoid biosynthesis include shikimic acid, phenylalanine, cinnamic acid, and p-coumaric acid. Shikimic acid acts as an intermediate in the biosynthesis of aromatic acid. The basic pathways to the core isoflavonoid skeletons have been established both enzymatically and genetically [16]. The synthesis of isoflavones can be broadly divided into three main synthetic pathways the formylation of deoxybenzoins, the oxidative rearrangement of chalcones and flavanones, and the arylation of a preformed chromanone ring. In leguminous plants, the major isoflavonoids are produced via two branches of the isoflavonoid biosynthetic pathway, and the different branches share a majority of common reactions [1]. Unlike the common flavonoid compotmds, which have a 2-phenyl-benzopyrone core structure, isoflavones, such as daidzein and genistein, are 3-phenyl-benzopyrone compounds. Biochemically, the synthesis of isoflavones is an offshoot of the flavonoids biosynthesis pathway. Several attempts have aimed to increase... 

Shoji T, Winz R, Iwase T et al (2002) Expression patterns of two tobacco isoflavone reductase-like genes and their possible roles in secondary metabolism in tobacco. Plant Mol Biol 50 427 40 Shoji T, Inai K, Yazaki Y et al (2009) Multidrug and toxic compound extrusion-type transporters implicated in vacuolar sequestration of nicotine in tobacco roots. Plant Physiol 149 708-718 Shoji T, Kajikawa M, Hashimoto T (2010) Clustered transcription factors regulate nicotine biosynthesis. Plant Cell 22 3390-3409... 

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