Phenylpropanoid derivatives

The functions of phenylpropanoid derivatives are as diverse as their structural variations. Phenylpropanoids serve as phytoalexins, UV protectants, insect repellents, flower pigments, and signal molecules for plant-microbe interactions. They also function as polymeric constituents of support and surface structures such as lignins and suberins [1]. Therefore, biosynthesis of phenylpropanoids has received much interest in relation to these functions. In addition, the biosynthesis of these compounds has been intensively studied because they are often chiral, and naturally occurring samples of these compounds are usually optically active. Elucidation of these enantioselective mechanisms may contribute to the development of novel biomimetic systems for enantioselective organic synthesis. 

Phenylalanine Ammonia-Lyase. The building units of lignin are formed from carbohydrate via the shikimic acid pathway to give aromatic amino acids. Once the aromatic amino acids are formed, a key enzyme for the control of lignin precursor synthesis is phenylalanine ammonia-lyase (PAL) (1). This enzyme catalyzes the production of cinnamic acid from phenylalanine. It is very active in those tissues of the plant that become lignified and it is also a central enzyme for the production of other phenylpropanoid-derived compounds such as flavonoids and coumarins, which can occur in many parts of the plant and in many different organs (35). Radioactive phenylalanine and cinnamic acid are directly incorporated into lignin in vascular tissue (36). 

Figure 1. Phenylalanine ammonia-lyase (PAL) involvement in the biosynthesis of phenylpropanoid-derived secondary metabolites in plants and Ba-sidiomycetes.

Cuendet, M., Potterat, O., and Hostettmann, K., Flavonoids and phenylpropanoid derivatives from Campanula barbata. Phytochemistry, 56, 631, 2001. 

Ngadjui, B.T. et al., Prenylated flavones and phenylpropanoid derivatives from roots of Dorstenia psilurus. Phytochemistry, 48, 733, 1998. 

Volatile compounds are often involved in long distance attraction and are especially important as attractants and repellents (as defined by Kogan, ). One major class of volatile materials, essential oils, is comprised of complex mixtures of terpenes, phenylpropanoid derived compounds and a number of esters, alcohols, aldehydes, ketones, acids, and hydrocarbons. The constituent compounds are mostly of low to medium molecular weight and generally not highly oxygenated. Some of the biological properties of these compounds have been reviewed (17,41,46,55,56). 

Funk C, Brodelius P (1992) Phenylpropanoid metabolism in suspension cultures of Vanilla planifolia Andr. IV Induction of vanillinic acid formation. Plant Physiol 99 256-262 Funk C, Brodelius P (1994) Vanilla planifolia Andrews in vitro biosynthesis of vanillin and other phenylpropanoids derivatives. In Bajaj YPS (ed) Biotechnology in agriculture and forestry. Medicinal and aromatic plants VI, vol 26. Springer, Berlin Heidelberg New York, pp 377-402... 

If, as a criterion of value to the study of lignin depolymerization by alkaline hydrolysis, the maximum yield of oxygen-bearing, phenylpropanoid derivatives is chosen, then the conditions of such a study have been optimized here at a treatment severity corresponding to a reaction temperature of 300°C for 1 hour. Under these conditions, 20% of the lignin is recovered as ether-solubles of which 55% is identifiable as monomeric derivatives. The rest of this material probably consists of dimeric-type compounds not identified by capillary gas chromatography. 

Ververidis F, Trantas E, Douglas C, Vollmer G, Kretzschmar G, Panopoulos N. 2007a. Biotechnology of flavonoids and other phenylpropanoids-derived natural products. Part I Chemical diversity impact, impa on plant biology and human health. Biotechnol J 2 1214-1234. 

According to Proteau et al., condensation of two subunits of tryptophan and two phenylpropanoid-derived units would explain the biogenetic pathway to form the symmetrical structure of scytonemin (123) [146]. No syntheses of 123 have been reported. 

Corroborative evidence for the structures of various coumarinolignans, deduced almost exclusively from spectroscopic evidence, has been provided by their appropriate synthesis. The synthesis of this group of natural products has been achieved mainly through oxidation (chemical or enzymatic) of appropriate coumarin and phenylpropanoid derivatives, although other methods are also known. 

Figure 4.2 Structures of some phenylpropanoid-derived fragrance compounds.

Ververidis, R, Trantas, E., Douglas, G., Vollmer, G., Kretzschmar, G., Panopoulos, N. (2007b) Biotechnology of flavonoids and other phenylpropanoid-derived natural products. Part II Reconstruction of multienzyme pathways in plants and microbes. Biotechnol.., 2,1235-49. 

Flavonoids are one of the largest classes of phenylpropanoid-derived plant specialized metabolites, with 10,000 different members. They consist of two main groups, the 2-phenylchromans (flavonoids flavanones, flavones, flavonols, flavan-3-ols, anthocy-anidins) and the 3-phenylchromans (isoflavonoids isoflavones, iso-flavans, pterocarpans). Some flavonoids and their metabolites exhibit positive effects for disease therapy and chemoprevention [218,219],... 

Essential oil obtained from the fresh rhizomes oiA. conchigera showed the presence of twelve terpenoids by GC-MS analysis, and the major component was chavicol acetate [44]. 1-Hydroxychavicol acetate [45], 4-acetoxycinnamyl alcohol and 4-acetoxycinnamyl acetate [46] were isolated from the aqueous layer obtained from the steam distillation of the rhizomes. Phenylpropanoid derivatives, chavicol acetate and eugenol acetate were present in the fruit of the plant [47]. In addition to four known diaryIheptanoids 40,41,43 and 44, and two known flavonoids, 3,5,7-trihydroxyflavone and 3,5,7-trihydroxy-4 -methoxyflavone, a new diarylheptanoid 54 was isolated from the rhizomes of the same plant [48]. 

From a quantitative point of view, the main phenolics are phenylpropanoid derivatives which accumulate as esters, flavonoids, or are polymerized as lignins (Ref. l). All these products may be synthesized in the same organ from cinnamic acids via their cinnamoyl-coenzyme A thioesters (Ref. 23). Consequently, the following reactions may indeed occur simultaneously ... 

A number of phenylpropanoid-derived compounds are capable of inhibition of seed germination and seedling growth of other plants. Dihydrocinnamic acid (79), from Ceratiola ericoides (Empetraceae), a common plant in the Florida scrub, was shown to inhibit both germination and growth of Schizachyrium scoparium (little blue stem, Poaceae), Leptochloa dubia (Poaceae), Rudbeckia hirta (As-... 

Fig. 8.22. Phenylpropanoid-derived compounds with allelopathic activity.

Several phenylpropanoid derivatives have been identified as contributing to the adaptogenic activity (adaptability to stress) in species such as Eleuthrococcus senticosus, Rhodiala rosea and Ocimum... 

Chakraborty M, Karun A, Mitra A (2009) Accumulation of phenylpropanoid derivatives in chitosan-induced cell suspension culture of Cocos nucifera. J Plant Physiol 166 63... 

Three different metabolic pathways are known to be involved in the synthesis of different classes of phenolic compounds, namely, (1) (Ce — C3) phenylpropanoid derivatives produced by the shikimate/chorismate pathway (2) side chain elongated phenylpropanoids, flavonoids (Ce - C3 - Cg), and few quinones synthesized by the acetate/malOTiate or polyketide pathway and (3) the aromatic terpenoids synthesized throu the acetate/mevalonate pathway. 

Phytoalexins are low molecular weight products which are produced in response to elicitors such as microbial, herbivorous or environmental stimuli (Poulev et al. 2003). Once plants detect a pathogen signal, a complex mixture of secondary metabolites is produced to control the invader. These molecules are synthesized de novo, and thus involve the activation of certain genes and enzymes required for their synthesis (Kuc 1995). Phytoalexins are chemically diverse and may include many chemical classes such as simple phenylpropanoid derivatives, alkaloids, gly-costeroids, flavonoids, isoflavonoids, various sulphur products, terpenes and polyketides (Hammerschmidt 1999). There is no boundary between phytoalexins and phytoanticipins, and in one plant species a certain chemical can function as a phytoalexin, whereas it has the function of a phytoanticipin in another species (Junghanns et al. 1998). It is important to point out that the distinction between phytoanticipins and phytoalexins is not based on their chenucal structure but rather on how they are produced. Thus, the same chemical may serve as both phytoalexin and phytoanticipin, even in the same plant (VanEtten et al. 1994). 

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