Umbellic acid (2,4-dihydroxycinnamic acid) is a

hydroxycinnamic acid Hydroxycinnamic acids (hydroxycinnamates) are a class of aromatic acids or phenylpropanoids having a C6–C3 skeleton. These compounds are hydroxy derivatives of cinnamic acid. In the category of phytochemicals that can be found in food, there ...

. It is an isomer of

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 ...

. It is a precursor in the

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 ...

biosynthesis pathway. Umbelliferone is a

phenylpropanoid The phenylpropanoids are a diverse family of organic compounds that are synthesized by plants from the amino acids phenylalanine and tyrosine. Their name is derived from the six-carbon, aromatic phenyl group and the three-carbon propene tail of ...

and as such is synthesized from L-phenylalanine, which in turn is produced via the

shikimate pathway The shikimate pathway (shikimic acid pathway) is a seven-step metabolic pathway used by bacteria, archaea, fungi, algae, some protozoans, and plants for the biosynthesis of folates and aromatic amino acids (tryptophan, phenylalanine, and tyrosine) ...

. Phenylalanine is lysated into

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 n ...

, followed by

hydroxylation In chemistry, hydroxylation can refer to: *(i) most commonly, hydroxylation describes a chemical process that introduces a hydroxyl group () into an organic compound. *(ii) the ''degree of hydroxylation'' refers to the number of OH groups in a ...

cinnamate 4-hydroxylase 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, ...

to yield 4-coumaric acid. The 4-coumaric acid is again hydroxylated by cinnamate/coumarate 2-hydroxylase to yield 2,4-dihydroxy-cinnamic acid followed by a bond rotation of the unsaturated bond adjacent to the

carboxylic acid In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an R-group. The general formula of a carboxylic acid is or , with R referring to the alkyl, alkenyl, aryl, or other group. Carboxylic ...

group. Finally an intramolecular attack from the hydroxyl group of C2' to the carboxylic acid group closes the ring and forms the

lactone Lactones are cyclic carboxylic esters, containing a 1-oxacycloalkan-2-one structure (), or analogues having unsaturation or heteroatoms replacing one or more carbon atoms of the ring. Lactones are formed by intramolecular esterification of the co ...

umbelliferone. :

\xrightarrow

\xrightarrow

\xrightarrow

\longrightarrow

The enzyme 4-hydroxycinnamate decarboxylase, induced in bacteria species such as ''

Klebsiella oxytoca ''Klebsiella oxytoca'' is a Gram-negative, rod-shaped bacterium that is closely related to '' K. pneumoniae'', from which it is distinguished by being indole-positive; it also has slightly different growth characteristics in that it is able to gr ...

'', works also with p-coumaric acid analogs such as E-2,4-dihydroxycinnamic acid.

References

External links

{{Hydroxycinnamic acid Hydroxycinnamic acids Resorcinols Vinylogous carboxylic acids