Phenylpropanoid

Phenylpropanoids are organic chemical compounds with a typical carbon backbone, which are composed of a Benzolaromaten and a chain of three carbon atoms, and often contribute both hydroxy and methoxy groups on the aromatic ring. Many phenylpropanoids are natural substances that are formed in plants and microorganisms via the shikimate pathway involving phenylalanine as an intermediate. Phenylpropanoids are, in addition to the terpenes, a common ingredient of essential oils and represent the majority of naturally occurring phenolic natural products or their precursor dar. Among the known members of the group of phenylpropanoids include anethole, apiol, cinnamaldehyde, Dillapiol and estragole.

Occurrence

Phenylpropanoids are a very common class of phytochemicals, which represents the majority of the naturally occurring phenols and aromatic compounds and their biosynthetic precursor are. The structural spectrum is very broad and they perform diverse biological functions.

As an example of the biological function of the flavonoids could be mentioned, which provide protection against ultraviolet radiation and flower pigments for many species. Or the biopolymer lignin, which gives the plant tissue stability.

Cinnamic acids

A key intermediate of most phenylpropanoids are the cinnamic acid or different hydroxy or Methoxyzimtsäuren dar. However, in many plants, they provide a final product in the form of conjugates Represents the presence of certain compounds is often limited to a certain number of species.

The cinnamic acids are produced biosynthetically from phenylalanine by the enzyme phenylalanine ammonia lyase (PAL). A number of enzymatic hydroxylation and methylation then leads to the cinnamic acid derivatives, such as coumaric acid, caffeic acid, ferulic acid, 5 - hydroxyferulic acid and 4-hydroxy -3 ,5- dimethoxycinnamic acid. The esters of cinnamic acids are volatile compounds with bitter or flowery fragrance and are used for attracting pollinating insects. An example of this is the cinnamate.

Cinnamaldehydes and monolignols

Reducing the carboxylic acid group in the cinnamic acids leads initially to the corresponding aldehydes, such as cinnamic aldehyde. By a further step of reducing the corresponding alcohol, such as coumaryl alcohol, coniferyl alcohol and is then produced which are called monolignols. These monolignols can lignins or Suberinen which polymerize as cell walls of plants are important.

The phenylpropenes such as eugenol, safrole and estragole are derivatives of monolignols and are constituents of essential oils.

Coumarins and flavonoids

Hydroxylation of cinnamic acid by the enzyme, cinnamate -4- hydroxylase, the p- coumaric acid which results by further hydroxylation at the 2- position of umbelliferone. The 2- hydroxylated compounds can now be cyclized via coumaryl -CoA to the coumarins. Flavonoids are also produced via the p -coumaric acid. First, the coumaryl -CoA is produced from coumaric acid. With the help of chalcone synthase reacts with three molecules of malonyl -CoA to chalcone. A isomerase then transferred in this flavone, are biosynthesized from which all flavonoids.

Stilbenoids

Stilbenoids such as resveratrol are hydroxylated derivatives of stilbene. They are formed by an alternative cyclization of cinnamic acid -CoA or coumaryl -CoA.