Phenylpropanoid

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4-Coumaroyl-CoA is the central biosynthetic precursor to phenylpropanoids (shown in protonated state) 4-Coumaroyl-CoA.svg
4-Coumaroyl-CoA is the central biosynthetic precursor to phenylpropanoids (shown in protonated state)
Phenylalanine L-Phenylalanin - L-Phenylalanine.svg
Phenylalanine
Tyrosine L-Tyrosin - L-Tyrosine.svg
Tyrosine

The phenylpropanoids are a diverse family of organic compounds that are biosynthesized by plants from the amino acids phenylalanine and tyrosine in the shikimic acid pathway. [1] Their name is derived from the six-carbon, aromatic phenyl group and the three-carbon propene tail of coumaric acid, which is the central intermediate in phenylpropanoid biosynthesis. From 4-coumaroyl-CoA emanates the biosynthesis of myriad natural products including lignols (precursors to lignin and lignocellulose), flavonoids, isoflavonoids, coumarins, aurones, stilbenes, catechin, and phenylpropanoids. [2] The coumaroyl component is produced from cinnamic acid.

Contents

Phenylpropanoids are found throughout the plant kingdom, where they serve as essential components of a number of structural polymers, provide protection from ultraviolet light, defend against herbivores and pathogens, and also mediate plant-pollinator interactions as floral pigments and scent compounds.

Hydroxycinnamic acids

Cinnamic acid Zimtsaure - Cinnamic acid.svg
Cinnamic acid

Phenylalanine is first converted to cinnamic acid by the action of the enzyme phenylalanine ammonia-lyase (PAL). Some plants, mainly monocotyledonous, use tyrosine to synthesize p-coumaric acid by the action of the bifunctional enzyme Phenylalanine/tyrosine ammonia-lyase (PTAL). A series of enzymatic hydroxylations and methylations leads to coumaric acid, caffeic acid, ferulic acid, 5-hydroxyferulic acid, and sinapic acid. Conversion of these acids to their corresponding esters produces some of the volatile components of herb and flower fragrances, which serve many functions such as attracting pollinators. Ethyl cinnamate is a common example.

Cinnamic aldehydes and monolignols

Coniferyl alcohol Coniferol.svg
Coniferyl alcohol

Reduction of the carboxylic acid functional groups in the cinnamic acids provides the corresponding aldehydes, such as cinnamaldehyde. Further reduction provides monolignols including coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol, which vary only in their degree of methoxylation. The monolignols are monomers that are polymerized to generate various forms of lignin and suberin, which are used as a structural component of plant cell walls.

Safrole Safrole acsv.svg
Safrole

The phenylpropenes, phenylpropanoids with allylbenzene (3-phenylpropene) as the parent compound, are also derived from the monolignols. Examples include eugenol, chavicol, safrole, and estragole. These compounds are the primary constituents of various essential oils.

Coumarins and flavonoids

Umbelliferone Umbelliferone acsv.svg
Umbelliferone

Hydroxylation of cinnamic acid in the 4-position by trans-cinnamate 4-monooxygenase leads to p-coumaric acid, which can be further modified into hydroxylated derivatives such as umbelliferone. Another use of p-coumaric acid via its thioester with coenzyme A, i.e. 4-coumaroyl-CoA, is the production of chalcones. This is achieved with the addition of 3 malonyl-CoA molecules and their cyclization into a second phenyl group. Chalcones are the precursors of all flavonoids, a diverse class of phytochemicals.

Stilbenoids

trans-resveratrol Resveratrol.svg
trans-resveratrol

Stilbenoids, such as resveratrol, are hydroxylated derivatives of stilbene. They are formed through an alternative cyclization of cinnamoyl-CoA or 4-coumaroyl-CoA.

Sporopollenin

Phenylpropanoids and other phenolics are part of the chemical composition of sporopollenin. It is related to cutin and suberin. [2] This ill-defined substance found in pollen is unusually resistant to degradation. Analyses have revealed a mixture of biopolymers, containing mainly hydroxylated fatty acids, phenylpropanoids, phenolics and traces of carotenoids. Tracer experiments have shown that phenylalanine is a major precursor, but other carbon sources also contribute. It is likely that sporopollenin is derived from several precursors that are chemically cross-linked to form a rigid structure.

See also

Related Research Articles

<span class="mw-page-title-main">Cinnamic acid</span> Chemical compound

Cinnamic acid is an organic compound with the formula C6H5-CH=CH-COOH. It is a white crystalline compound that is slightly soluble in water, and freely soluble in many organic solvents. Classified as an unsaturated carboxylic acid, it occurs naturally in a number of plants. It exists as both a cis and a trans isomer, although the latter is more common.

<span class="mw-page-title-main">Methoxsalen</span> Chemical compound

Methoxsalen, sold under the brand name Oxsoralen among others, is a medication used to treat psoriasis, eczema, vitiligo, and some cutaneous lymphomas in conjunction with exposing the skin to ultraviolet (UVA) light from lamps or sunlight. Methoxsalen modifies the way skin cells receive the UVA radiation, allegedly clearing up the disease. Levels of individual patient PUVA exposure were originally determined using the Fitzpatrick scale. The scale was developed after patients demonstrated symptoms of phototoxicity after oral ingestion of methoxsalen followed by PUVA therapy. Chemically, methoxsalen belongs to a class of organic natural molecules known as furanocoumarins. They consist of coumarin annulated with furan. It can also be injected and used topically.

<span class="mw-page-title-main">Umbelliferone</span> Chemical compound

Umbelliferone, also known as 7-hydroxycoumarin, hydrangine, skimmetine, and beta-umbelliferone, is a natural product of the coumarin family.

Shikimic acid, more commonly known as its anionic form shikimate, is a cyclohexene, a cyclitol and a cyclohexanecarboxylic acid. It is an important biochemical metabolite in plants and microorganisms. Its name comes from the Japanese flower shikimi, from which it was first isolated in 1885 by Johan Fredrik Eykman. The elucidation of its structure was made nearly 50 years later.

<span class="mw-page-title-main">Rutin</span> Chemical compound

Rutin is the glycoside combining the flavonol quercetin and the disaccharide rutinose. It is a flavonoid glycoside found in a wide variety of plants, including citrus.

<span class="mw-page-title-main">Hesperidin</span> Chemical compound

Hesperidin is a flavanone glycoside found in citrus fruits. Its aglycone is hesperetin. Its name is derived from the word "hesperidium", for fruit produced by citrus trees.

<span class="mw-page-title-main">Apigenin</span> Chemical compound

Apigenin (4′,5,7-trihydroxyflavone), found in many plants, is a natural product belonging to the flavone class that is the aglycone of several naturally occurring glycosides. It is a yellow crystalline solid that has been used to dye wool.

<span class="mw-page-title-main">Kaempferol</span> Chemical compound

Kaempferol (3,4′,5,7-tetrahydroxyflavone) is a natural flavonol, a type of flavonoid, found in a variety of plants and plant-derived foods including kale, beans, tea, spinach, and broccoli. Kaempferol is a yellow crystalline solid with a melting point of 276–278 °C (529–532 °F). It is slightly soluble in water and highly soluble in hot ethanol, ethers, and DMSO. Kaempferol is named for 17th-century German naturalist Engelbert Kaempfer.

<i>p</i>-Coumaric acid Chemical compound

p-Coumaric acid is an organic compound with the formula HOC6H4CH=CHCO2H. It is one of the three isomers of hydroxycinnamic acid. It is a white solid that is only slightly soluble in water but very soluble in ethanol and diethyl ether.

<span class="mw-page-title-main">Daidzein</span> Chemical compound

Daidzein is a naturally occurring compound found exclusively in soybeans and other legumes and structurally belongs to a class of compounds known as isoflavones. Daidzein and other isoflavones are produced in plants through the phenylpropanoid pathway of secondary metabolism and are used as signal carriers, and defense responses to pathogenic attacks. In humans, recent research has shown the viability of using daidzein in medicine for menopausal relief, osteoporosis, blood cholesterol, and lowering the risk of some hormone-related cancers, and heart disease. Despite the known health benefits, the use of both puerarin and daidzein is limited by their poor bioavailability and low water solubility.

<span class="mw-page-title-main">Sinapyl alcohol</span> Chemical compound

Sinapyl alcohol is an organic compound structurally related to cinnamic acid. It is biosynthetized via the phenylpropanoid biochemical pathway, its immediate precursor being sinapaldehyde. This phytochemical is one of the monolignols, which are precursor to lignin or lignans. It is also a biosynthetic precursor to various stilbenoids and coumarins.

<span class="mw-page-title-main">Flavones</span> Class of flavonoid chemical compounds

Flavones are a class of flavonoids based on the backbone of 2-phenylchromen-4-one (2-phenyl-1-benzopyran-4-one).

In enzymology, a trans-cinnamate 2-monooxygenase (EC 1.14.13.14) is an enzyme that catalyzes the chemical reaction

In enzymology, a trans-cinnamate 4-monooxygenase (EC 1.14.14.91) is an enzyme that catalyzes the chemical reaction

<span class="mw-page-title-main">Phenylalanine ammonia-lyase</span>

The enzyme phenylalanine ammonia lyase (EC 4.3.1.24) catalyzes the conversion of L-phenylalanine to ammonia and trans-cinnamic acid.:

Coumaroyl-coenzyme A is the thioester of coenzyme-A and coumaric acid. Coumaroyl-coenzyme A is a central intermediate in the biosynthesis of myriad natural products found in plants. These products include lignols, flavonoids, isoflavonoids, coumarins, aurones, stilbenes, catechin, and other phenylpropanoids.

The biosynthesis of phenylpropanoids involves a number of enzymes.

<span class="mw-page-title-main">Umbellic acid</span> Chemical compound

Umbellic acid is a hydroxycinnamic acid. It is an isomer of caffeic acid.

<span class="mw-page-title-main">5-Hydroxyferulic acid</span> Chemical compound

5-Hydroxyferulic acid is a hydroxycinnamic acid.

Phenylalanine/tyrosine ammonia-lyase (EC 4.3.1.25, PTAL, bifunctional PAL) is an enzyme with systematic name L-phenylalanine(or L-tyrosine):trans-cinnamate(or trans-p-hydroxycinnamate) ammonia-lyase. This enzyme catalyses the following chemical reaction

References

  1. Barros J, Serrani-Yarce JC, Chen F, Baxter D, Venables BJ, Dixon RA (2016). "Role of bifunctional ammonia-lyase in grass cell wall biosynthesis". Nat. Plants. 2 (6): 16050. doi:10.1038/nplants.2016.50. PMID   27255834. S2CID   3462127.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  2. 1 2 Vogt, T. (2010). "Phenylpropanoid Biosynthesis". Molecular Plant. 3: 2–20. doi: 10.1093/mp/ssp106 . PMID   20035037.