2 ,4 ,6 ,4-tetrahydroxychalcone

In addition to the bitter acids and essential oils, the flowers of hops offer a rich array of polyphenolic compounds, primarily chalcones and their accompanying flavanones, many of which are prenylated derivatives (Stevens et al., 1997,1999a, b). The most prominent flavonoid in all plants studied was xanthohumol [342] (3 -prenyl-6 -0-methylchalconaringenin chalconaringenin is 2, 4, 6, 4-tetrahydroxychalcone) (see Fig. 4.11 for structures 342-346). Several additional chalcones—variously adorned with 0-methyl and/or C-prenyl functions—were also encountered, along with their respective flavanones. Three new compounds were described in the Stevens et al. 

Recently, a new polyketide biosynthetic pathway in bacteria that parallels the well studied plant PKSs has been discovered that can assemble small aromatic metabolites.8,9 These type III PKSs10 are members of the chalcone synthase (CHS) and stilbene synthase (STS) family of PKSs previously thought to be restricted to plants.11 The best studied type III PKS is CHS. Physiologically, CHS catalyzes the biosynthesis of 4,2, 4, 6 -tetrahydroxychalcone (chalcone). Moreover, in some organisms CHS works in concert with chalcone reductase (CHR) to produce 4,2 ,4 -trihydroxychalcone (deoxychalcone) (Fig. 12.1). Both natural products constitute plant secondary metabolites that are used as precursors for the biosynthesis of anthocyanin pigments, anti-microbial phytoalexins, and chemical inducers of Rhizobium nodulation genes.12... 

The biological activity of isoprenylated chalcones from the Moraceae has been described both in original papers and reviews. Of particular interest is the potent 5-a-reductase inhibition shown by a geranylated chalcone (84) isolated from leaves of Artocarpus incisus The inhibitory effect is decreased by a factor of 2 when the geranyl substituent is lacking, as in butein (2, 4, 3,4-tetrahydroxychalcone). Compound 41, which was obtained from the leaves of Madura tinctoria together with four known isoprenylated flavonoids, showed inhibitory... 

Glucoside 2,3, 4, 4-Tetrahydroxychalcone C26H30O9 Madura tinctoria Moraceae 118... 

Glucoside (androechin) 2,4, 6, 4-Tetrahydroxychalcone (chalconaringeniri) C22H24O10 Andrographis echiodes Acantbaceae 121... 

Fig. (8). Selected HMBC (->) and NOE (<- ) correlations of isogemichalcone C (34), and comparison of, 3C NMR data of 3 -[y-hydroxymethyl-( )-y-inethylallyl]-2,4,2, 4 -tetrahydroxychalcone ll -O-coumarate(33),34,andgemichalconeC.

Their biosynthesis derives from the condensation of three acetyl units and of a derivative of hydroxycinnamic acid leading to the formation of a common intermediate, tetrahydroxychalcone. This chalcone is precursor of several compounds, the most important being the 4-oxo-flavonoids [19]. 

Flavonoid biosynthesis (Figure 3-7) is initiated from the condensation of / -coumaroyl-CoA (3.31) with three molecules malonyl-CoA (3.48), which is catalyzed by the enzyme chalcone synthase (CHS), and gives rise to 4,2, 4, 6 tetrahydroxychalcone (3.49). This compound can undergo a number of reactions that give rise to the different classes of compounds described in Section 3.6 of Chapter 1. 

Hayashi K, Nagematsu T, Honda S, Suzuki Y (1996) Butein (3,4,2 ,4 -tetrahydroxychalcone) ameliorates experimental anti-glomerular basement membrane antibody-associated glomerulonephritis. Eur J Pharmacol... 

Biochanin A (= 5,7-Dihydroxy-4 -methoxyisoflavone Pratensol) (isoflavone) Butein ( = 2, 4, 3,4-Tetrahydroxychalcone) (chalcone)... 

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