Biosynthesis of Flavonoids

The main flavonoid skeleton derives from the stepwise condensation of three molecules of malonyl CoA with one molecule of 4-coumaroyl CoA, a reaction catalyzed by chalcone synthase (CHS) to form naringenin (2, 4,4 ,6,-tetrahydroxy) chalcone, the common intermediate in the formation of all flavonoids with 5,7-dihydroxy (flavone numbering) A-ring substitution. In some plants, however, an NADP-dependent chalcone-ketide reductase coacts with CHS to form 6 -deoxychalcone, the precursor of 5-deoxyflavonoids. The resulting chalcones undergoe a stereospecific cyclization to the corresponding (2S) flavanones, the 

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Biosynthesis of Tea Flavonoids. The pathways for the de novo biosynthesis of flavonoids in both soft and woody plants (Pigs. 3 and 4) have been generally elucidated and reviewed in detail (32,51). The regulation and control of these pathways in tea and the nature of the enzymes involved in synthesis in tea have not been studied exhaustively. The key enzymes thought to be involved in the biosynthesis of tea flavonoids are 5-dehydroshikimate reductase (52), phenylalanine ammonia lyase (53), and those associated with the shikimate/arogenate pathway (52). At least 13 enzymes catalyze the formation of plant flavonoids (Table 4). 

Grisebach, H. and Grambow, H. J. 1968. Biosynthesis of flavonoids—XV. Occurrence and biosynthesis of flavonoids in Datisca cannabina. Phytochemistry 7 51-56. 

Heller W, Forkmann G (1994) Biosynthesis of flavonoids. In Harbome JB (ed) The flavonoids advances in research since 1986. Chapman and HaU, London, pp 499-536... 

Heller, W. and Forkmann, G., Biosynthesis of flavonoids, in The Flavonoids Advances in Research Since 1980, Harborne, J.B., Ed., Chapman Hall, London, 1988, 399. 

Winkel-Shirley, B., Biosynthesis of flavonoids and effects of stress, Curr. Opin. Plant Biol, 5, 218, 2002. 

Biogenetically, chalcones are the immediate precursors of flavanones, and some flavanones isomerize by ring opening into chalcones during isolation from plants or after chemical treatment with alkali. In turn, flavanones are intermediates in the biosynthesis of most other flavonoid groups, including flavones, flavonols, and isoflavonoids. For more information on the biosynthesis of flavonoids and flavanones in particular, the reader is referred to Chapter 3 and reviews by Heller and Forkmann. ... 

Forkmann, G. and Heller, W., Biosynthesis of flavonoids, in Comprehensive Natural Products Chemistry, Vol. 1, Barton, D., Nakanishi, K., and Meth-Cohn, O., Eds, Elsevier, Amsterdam, 1999, Chap. 1.26. 

The reader is referred to a number of texts for a detailed discussion of the biosynthesis of flavonoids (B-63MI22400, B-75MI22400, B-81MI22402), or of biosynthesis in general (B-63MI22401, B-64MI22402, B-78MI22401). 

In Arabidopsis the TT2, TT8, TTG1 and TTG2 genes have been shown to be regulatory genes controlling the biosynthesis of flavonoids. Walker et al. 

The biosynthesis of flavonoids, stilbenes, hydroxycinnamates, and phenolic acids involves a complex network of routes based principally on the shikimate, phenyl-propanoid, and flavonoid pathways (Figs. 1.35 and 1.36). These biosynthetic pathways constitute a complex biological regulatory network that has evolved in vascular plants during their successful transition on land and that ultimately is essential for their growth, development, and survival [Costa et al., 2003]. 

Hahlbrock H, Grisebach H. 1975. Biosynthesis of flavonoids. In Harborne JB, Mabry TJ, Mabry H, Eds. The Flavonoids. San Diego Academic Press, PP. 866-915. 

Ebel, J. Hahlbrock, K. (1982). Biosynthesis of flavonoids. In The Flavonoids Advances in Research, ed. J.B. Harborne T.J. Mabry, pp. 641-79. London Chapman and Hall. 

Forkmann G and Heller W (1999) Biosynthesis of flavonoids. Comprehensive Natural Products Chemistry, Vol 1. Elsevier, Amsterdam, pp 713-748. 

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