Phenylpropanoids from

Cardono ML, Garcia B, Pedro JR, Sinisterra JF (1990) Flavonoids, Flavonolignans and a Phenylpropanoid from Onopordon corymbosum. Phytochemistry 29 629... 

K Yoshikawa, H Kinoshita, Y Kan, S Arihara. Neolignans and phenylpropanoids from the rhizomes of Coptis japonica var dissecta. Chem Pharm Bull 43 578-581, 1995. 

Cytotoxicity of diterpenes from Hedychium coronarium and antitumor activity against sarcoma 180A of phenylpropanoids from Alpinia galanga and of bisabolane sesquiterpenes from Curcuma xanthorrhiza have been reviewed [203]. 

Miyazawa, M., and M. Hisama. 2003. Antimutagenic activity of phenylpropanoids from clove (Syzygium aromaticum).. Agric. Food Chem. 51(22) 6413-6422. 

Ma, Z. Hano, Y. Nomma, T. Chen, Y. Alkaloids and phenylpropanoids from Peganum nigellastrum. 

Ichikawa M., Ryu K., Yoshida J., Ide N., Kodera Y., Sasaoka T., Rosen R.T. Identification of six phenylpropanoids from garlic skin as major antioxidants, /ournfl/ of Agricultural and Food Chemistry, 51 7313-7317 (2003). 

Ichikawa, M., Ryu, K., Yoshida, J. et al (2003) Identification of six phenylpropanoids from garlic skins as major antioxidants. /. Agric. Food Chem., 51, 7313-7317. 

B, cytotoxic tetrameric phenylpropanoids, from the ophiuroid Ophiocoma scolopendrina. J. Oig. Chem., 74,4396-4399. 

According to a widely accepted concept, lignin [8068-00-6] may be defined as an amorphous, polyphenoHc material arising from enzymatic dehydrogenative polymerization of three phenylpropanoid monomers, namely, coniferyl alcohol [485-35-5] (2), sinapyl alcohol [537-35-7] (3), and /)-coumaryl alcohol (1). 

In addition, it has been discovered that there are naturally occurring enzymes that facilitate Diels-Alder type reactions within certain metabolic pathways and that enzymes are also instrumental in forming polyketides, isoprenoids, phenylpropanoids, and alkaloids (de Araujo et al., 2006). Agresti et al. (2005) identified ribozymes from RNA oligo libraries that catalyzed multiple-turnover Diels-Alder cycloaddition reactions. 

Precursors of phenylpropanoids are synthesized from two basic pathways the shikimic acid pathway and the malonic pathway (see Fig. 3.1). The shikimic acid pathway produces most plant phenolics, whereas the malonic pathway, which is an important source of phenolics in fungi and bacteria, is less significant in higher plants. The shikimate pathway converts simple carbohydrate precursors into the amino acids phenylalanine and tyrosine. The synthesis of an intermediate in this pathway, shikimic acid, is blocked by the broad-spectrum herbicide glyphosate (i.e., Roundup). Because animals do not possess this synthetic pathway, they have no way to synthesize the three aromatic amino acids (i.e., phenylalanine, tyrosine, and tryptophan), which are therefore essential nutrients in animal diets. 

Many secondary phenolic compounds are derived from the amino acids phenylalanine and tyrosine and therefore contain an aromatic ring and a three-carbon side chain (see Fig. 3.3). Phenylalanine is the primary substrate for phenylpropanoid synthesis in most higher vascular plants, with tyrosine being used to a lesser extent in some plants. Because of their common structure, compounds derived from these amino acids are collectively called phenylpropanoids. 

Simple phenolic compounds include (1) the phenylpropanoids, trans-cinnamic acid, p-coumaric acid and their derivatives (2) the phenylpropanoid lactones called coumarins (Fig. 3.4) and (3) benzoic acid derivatives in which two carbons have been cleaved from the three carbon side chain (Fig. 3.2). More complex molecules are elaborated by additions to these basic carbon skeletons. For example, the addition of quinic acid to caffeic acid produces chlorogenic acid, which accumulates in cut lettuce and contributes to tissue browning (Fig. 3.5). 

Flavonoids are the largest class of phenylpropanoids in plants. The basic flavonoid structure is two aromatic rings (one from phenylalanine and the other from the condensation of three malonic acids) linked by three carbons (Fig. 3.6). Chalcone is converted to naringenin by the enzyme chalcone isomerase, which is a key enzyme in flavonoid synthesis. This enzyme, like PAL and chalcone synthase (CHS), is under precise control and is inducible by both internal and external signals. Naringenin is the... 

Ring B and the central three-carbon bridge forming the C ring (see Fig. 5.1) originate from the amino acid phenylalanine, itself a product of the shikimate pathway, a plastid-based process which generates aromatic amino acids from simple carbohydrate building blocks. Phenylalanine, and to a lesser extent tyrosine, are then fed into flavonoid biosynthesis via phenylpropanoid (C6-C3) metabolism (see Fig. 5.1). 

WISMAN, E., HARTMANN, U., SAGASSER, M., BAUMANN, E., PALME, K., HAHLBROCK, K., SAEDLER, H., WEISSHAAR, B., Knock-out mutants from an En-1 mutagenized Arabidopsis thaliana population generate phenylpropanoid biosynthesis phenotypes, Proc. Natl. Acad. Sci. USA, 1998,95,12432-12437. 

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