![L-Tyrosin - L-Tyrosine](https://upload.wikimedia.org/wikipedia/commons/4/40/L-Tyrosin_-_L-Tyrosine.svg)
The phenylpropanoids are a diverse family of organic compounds that are synthesized by plants from the
amino acid
Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha a ...
s
phenylalanine and
tyrosine
-Tyrosine or tyrosine (symbol Tyr or Y) or 4-hydroxyphenylalanine is one of the 20 standard amino acids that are used by cells to synthesize proteins. It is a non-essential amino acid with a polar side group. The word "tyrosine" is from the G ...
.
Their name is derived from the six-carbon, aromatic phenyl group and the three-carbon propene tail of
coumaric acid Coumaric acid is a phenolic derivative of cinnamic acid
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. Cl ...
, which is the central intermediate in
phenylpropanoid biosynthesis The biosynthesis of phenylpropanoids involves a number of enzymes.
From amino acids to cinnamates
In plants, all phenylpropanoids are derived from the amino acids phenylalanine and tyrosine.
Phenylalanine ammonia-lyase (PAL, a.k.a. phenylalanine/t ...
. From
4-coumaroyl-CoA
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 (precursors to lignin and lign ...
emanates the biosynthesis of myriad natural products including
lignols (precursors to
lignin and
lignocellulose
Lignocellulose refers to plant dry matter (biomass), so called lignocellulosic biomass. It is the most abundantly available raw material on the Earth for the production of biofuels. It is composed of two kinds of carbohydrate polymers, cellulose a ...
),
flavonoids
Flavonoids (or bioflavonoids; from the Latin word ''flavus'', meaning yellow, their color in nature) are a class of polyphenolic secondary metabolites found in plants, and thus commonly consumed in the diets of humans.
Chemically, flavonoids ...
,
isoflavonoids,
coumarin
Coumarin () or 2''H''-chromen-2-one is an aromatic organic chemical compound with formula . Its molecule can be described as a benzene molecule with two adjacent hydrogen atoms replaced by a lactone-like chain , forming a second six-membered h ...
s,
aurones
An aurone is a heterocyclic chemical compound which is a type of flavonoid. There are two isomers of the molecule, with (''E'')- and (''Z'')-configurations. The molecule contains a benzofuran element associated with a benzylidene linked in posi ...
,
stilbenes,
catechin
Catechin is a flavan-3-ol, a type of secondary metabolite providing antioxidant roles in plants. It belongs to the subgroup of polyphenols called flavonoids.
The name of the catechin chemical family derives from ''catechu'', which is the tanni ...
, and phenylpropanoids.
The coumaroyl component is produced from
cinnamic acid
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 na ...
.
Phenylpropanoids are found throughout the plant kingdom, where they serve as essential components of a number of structural polymers, provide protection from
ultraviolet light
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nanometer, nm (with a corresponding frequency around 30 Hertz, PHz) to 400 nm (750 Hertz, THz), shorter than that of visible light, but longer than ...
, defend against
herbivores
A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...
and
pathogen
In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ ...
s, and also mediate
plant-pollinator interactions
A pollination network is a bipartite mutualistic network in which plants and pollinators are the nodes, and the pollination interactions form the links between these nodes. The pollination network is bipartite as interactions only exist between ...
as floral pigments and scent compounds.
Hydroxycinnamic acids
Phenylalanine is first converted to
cinnamic acid
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 na ...
by the action of the
enzyme
Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...
phenylalanine ammonia-lyase
The enzyme phenylalanine ammonia lyase (EC 4.3.1.24) catalyzes the conversion of L-phenylalanine to ammonia and ''trans''-cinnamic acid.:
:L-phenylalanine = ''trans''-cinnamate + NH3
Phenylalanine ammonia lyase (PAL) is the first and committed ...
(PAL). Some plants, mainly
monocotyledonous
Monocotyledons (), commonly referred to as monocots, ( Lilianae ''sensu'' Chase & Reveal) are grass and grass-like flowering plants (angiosperms), the seeds of which typically contain only one embryonic leaf, or cotyledon. They constitute one of ...
, use
tyrosine
-Tyrosine or tyrosine (symbol Tyr or Y) or 4-hydroxyphenylalanine is one of the 20 standard amino acids that are used by cells to synthesize proteins. It is a non-essential amino acid with a polar side group. The word "tyrosine" is from the G ...
to synthesize
p-coumaric acid by the action of the bifunctional enzyme
Phenylalanine/tyrosine ammonia-lyase
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 che ...
(PTAL). A series of enzymatic
hydroxylations and
methylations leads to
coumaric acid Coumaric acid is a phenolic derivative of cinnamic acid
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. Cl ...
,
caffeic acid
Caffeic acid is an organic compound that is classified as a hydroxycinnamic acid. This yellow solid consists of both phenolic and acrylic functional groups. It is found in all plants because it is an intermediate in the biosynthesis of lignin, one ...
,
ferulic acid
Ferulic acid is a hydroxycinnamic acid, an organic compound with the formula (CH3O)HOC6H3CH=CHCO2H. The name is derived from the genus ''Ferula'', referring to the giant fennel ('' Ferula communis''). Classified as a phenolic phytochemical, ferul ...
,
5-hydroxyferulic acid, and
sinapic acid
Sinapinic acid, or sinapic acid (Sinapine - Origin: L. Sinapi, sinapis, mustard, Gr., cf. F. Sinapine.), is a small naturally occurring hydroxycinnamic acid. It is a member of the phenylpropanoid family. It is a commonly used matrix in MALDI mass ...
. Conversion of these acids to their corresponding
ester
In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides a ...
s produces some of the volatile components of herb and flower
fragrance
An aroma compound, also known as an odorant, aroma, fragrance or flavoring, is a chemical compound that has a smell or odor. For an individual chemical or class of chemical compounds to impart a smell or fragrance, it must be sufficiently ...
s, which serve many functions such as attracting
pollinators.
Ethyl cinnamate
Ethyl cinnamate is the ester of cinnamic acid and ethanol. It is present in the essential oil of cinnamon. Pure ethyl cinnamate has a "fruity and balsamic odor, reminiscent of cinnamon with an amber note".
The ''p''-methoxy derivative is report ...
is a common example.
Cinnamic aldehydes and monolignols
Reduction of the
carboxylic acid functional groups in the cinnamic acids provides the corresponding aldehydes, such as
cinnamaldehyde
Cinnamaldehyde is an organic compound with the formula(C9H8O) C6H5CH=CHCHO. Occurring naturally as predominantly the ''trans'' (''E'') isomer, it gives cinnamon its flavor and odor. It is a phenylpropanoid that is naturally synthesized by the sh ...
. Further reduction provides
monolignol
Monolignols, also called lignols, are the source materials for biosynthesis of both lignans and lignin and consist mainly of paracoumaryl alcohol (H), coniferyl alcohol (G) and sinapyl alcohol (S). These monolignols differ in their degree of me ...
s including
coumaryl alcohol,
coniferyl alcohol
Coniferyl alcohol is an organic compound with the formula HO(CH3O)C6H3CH=CHCH2OH. A colourless or white solid, it is one of the monolignols, produced via the phenylpropanoid biochemical pathway. When copolymerized with related aromatic compounds, ...
, and
sinapyl alcohol
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 ...
, which vary only in their degree of
methoxy
In organic chemistry, a methoxy group is the functional group consisting of a methyl group bound to oxygen. This alkoxy group has the formula .
On a benzene ring, the Hammett equation classifies a methoxy substituent at the ''para'' position a ...
lation. The monolignols are monomers that are
polymer
A polymer (; Greek '' poly-'', "many" + ''-mer'', "part")
is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...
ized to generate various forms of
lignin and
suberin
Suberin, cutin and lignins are complex, higher plant epidermis and periderm cell-wall macromolecules, forming a protective barrier. Suberin, a complex polyester biopolymer, is lipophilic, and composed of long chain fatty acids called suberin aci ...
, which are used as a structural component of plant cell walls.
The
phenylpropene
Phenylpropene is the organic compound with the formula C6H5CH2CH=CH2. It is a colorless liquid. The compound consists of a phenyl group attached to allyl. Phenylpropene isomerizes to trans-propenylbenzene.
In plant biochemistry, the phenylpro ...
s, including
eugenol
Eugenol is an allyl chain-substituted guaiacol, a member of the allylbenzene class of chemical compounds. It is a colorless to pale yellow, aromatic oily liquid extracted from certain essential oils especially from clove, nutmeg, cinnamon, ...
,
chavicol
Chavicol (''p''-allylphenol) is a natural phenylpropene, a type of organic compound. Its chemical structure consists of a benzene ring substituted with a hydroxy group and a propenyl group. It is a colorless liquid found together with terpenes i ...
,
safrole
Safrole is an organic compound with the formula CH2O2C6H3CH2CH=CH2. It is a colorless oily liquid, although impure samples can appear yellow. A member of the phenylpropanoid family of natural products, it is found in sassafras plants, among oth ...
and
estragole
Estragole (''p''-allylanisole, methyl chavicol) is a phenylpropene, a natural organic compound. Its chemical structure consists of a benzene ring substituted with a methoxy group and an allyl group. It is an isomer of anethole, differing with res ...
, are also derived from the monolignols. These compounds are the primary constituents of various
essential oils.
Coumarins and flavonoids
Hydroxylation of
cinnamic acid
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 na ...
in the 4-position by
trans-cinnamate 4-monooxygenase
In enzymology, a trans-cinnamate 4-monooxygenase () is an enzyme that catalyzes the chemical reaction
:trans-cinnamate + NADPH + H+ + O2 \rightleftharpoons 4-hydroxycinnamate + NADP+ + H2O
The 4 substrates of this enzyme are trans-cinnamate, ...
leads to
''p''-coumaric acid, which can be further modified into hydroxylated derivatives such as
umbelliferone
Umbelliferone, also known as 7-hydroxycoumarin, hydrangine, skimmetine, and ''beta''-umbelliferone, is a natural product of the coumarin family.
It absorbs ultraviolet light strongly at several wavelengths. There are some indications that this ch ...
. Another use of ''p''-coumaric acid via its
thioester
In organic chemistry, thioesters are organosulfur compounds with the functional group . They are analogous to carboxylate esters () with the sulfur in the thioester playing the role of the linking oxygen in the carboxylate ester, as implied by t ...
with
coenzyme A, i.e.
4-coumaroyl-CoA
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 (precursors to lignin and lign ...
, is the production of
chalcones. This is achieved with the addition of 3
malonyl-CoA molecules and their cyclization into a second
phenyl
In organic chemistry, the phenyl group, or phenyl ring, is a cyclic group of atoms with the formula C6 H5, and is often represented by the symbol Ph. Phenyl group is closely related to benzene and can be viewed as a benzene ring, minus a hydrogen ...
group.
Chalcones are the precursors of all
flavonoids, a diverse class of
phytochemicals.
Stilbenoids
Stilbenoid
Stilbenoids are hydroxylated derivatives of stilbene. They have a C6–C2–C6 structure. In biochemical terms, they belong to the family of phenylpropanoids and share most of their biosynthesis pathway with chalcones. Most stilbenoids are prod ...
s, such as
resveratrol, are hydroxylated derivatives of
stilbene Stilbene may refer to one of the two stereoisomers of 1,2-diphenylethene:
* (''E'')-Stilbene (''trans'' isomer)
* (''Z'')-Stilbene (''cis'' isomer)
See also
* Stilbenoid
Stilbenoids are hydroxylated derivatives of stilbene. They have a C6– ...
. They are formed through an alternative cyclization of
cinnamoyl-CoA or
4-coumaroyl-CoA
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 (precursors to lignin and lign ...
.
Sporopollenin
Phenylpropanoids and other
phenolics are part of the chemical composition of
sporopollenin
270px, SEM image of pollen grains
Sporopollenin is one of the most chemically inert biological polymers. It is a major component of the tough outer (exine) walls of plant spores and pollen grains. It is chemically very stable and is usually well ...
. It is related to
cutin
Cutin is one of two waxy polymers that are the main components of the plant cuticle, which covers all aerial surfaces of plants. It is an insoluble substance with waterproof quality. Cutin also harbors cuticular waxes, which assist in cuticle st ...
and
suberin
Suberin, cutin and lignins are complex, higher plant epidermis and periderm cell-wall macromolecules, forming a protective barrier. Suberin, a complex polyester biopolymer, is lipophilic, and composed of long chain fatty acids called suberin aci ...
.
[ This ill-defined substance found in pollen is unusually resistant to degradation. Analyses have revealed a mixture of biopolymers, containing mainly hydroxylated ]fatty acid
In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, ...
s, 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
*Apiole
Apiole is a phenylpropene, also known as apiol, parsley apiol, or parsley camphor. Its chemical name is 1-allyl-2,5-dimethoxy-3,4-methylenedioxybenzene. It is found in the essential oils of celery leaf and all parts of parsley. Heinrich Christo ...
* Asarone
*Chavicol
Chavicol (''p''-allylphenol) is a natural phenylpropene, a type of organic compound. Its chemical structure consists of a benzene ring substituted with a hydroxy group and a propenyl group. It is a colorless liquid found together with terpenes i ...
* Dillapiole
*Elemicin
Elemicin is a phenylpropene, a natural organic compound, and is a constituent of several plant species' essential oils.
Natural occurrence
Elemicin is a constituent of the oleoresin and the essential oil of ''Canarium luzonicum'' (also referred ...
*Estragole
Estragole (''p''-allylanisole, methyl chavicol) is a phenylpropene, a natural organic compound. Its chemical structure consists of a benzene ring substituted with a methoxy group and an allyl group. It is an isomer of anethole, differing with res ...
*Eugenol
Eugenol is an allyl chain-substituted guaiacol, a member of the allylbenzene class of chemical compounds. It is a colorless to pale yellow, aromatic oily liquid extracted from certain essential oils especially from clove, nutmeg, cinnamon, ...
*Methyl eugenol
Methyl eugenol (allylveratrol) is a natural chemical compound classified as a phenylpropene, a type of phenylpropanoid. It is the methyl ether of eugenol and is important to insect behavior and pollination. It is found in various essential oils.
...
*Myristicin
Myristicin is a naturally occurring compound found in common herbs and spices, the most well known being nutmeg. It is an insecticide, and has been shown to enhance the effectiveness of other insecticides in combination. Myristicin is also a pre ...
* Eleutheroside
Eleutherosides are a diverse group of chemical compounds that were isolated from roots of the herb ''Eleutherococcus senticosus'' which is commercially offered mostly as extracts. Eleutheroside A is a saponin and sterol glycoside while other eleuth ...
s
References
*
{{Phenylpropanoids
*