Chlorogenic acid (CGA) is an ester of caffeic acid and quinic acid, an intermediate in lignin biosynthesis.The term “chlorogenic acids” refers to a family of related polyphenolic esters, including hydroxycinnamic acids (caffeic, ferulic, and p-coumaric acids) and quinic acids. Despite the “chlorine” in the name, chlorogenic acid does not contain chlorine.Instead, the name comes from the Greek χλωρός (khloros, light green) and -γένος (ghenos, suffix, meaning “to produce”), which relates to the green color produced when chlorogenic acids oxidize.
Structurally, chlorogenic acid is an ester of caffeic acid with the 3-hydroxyl group of L-quinic acid.Isomers of chlorogenic acid include caffeoyl esters at other hydroxyl sites on the quinic acid ring: 4-O-caffeoylquinic acid (cryptochlorogenic acid or 4-CQA) and 5-O-caffeoyl quinic acid Acylquinic acid (neochlorogenic acid or 5-CQA).The epimer at position 1 has not been reported.Structures with multiple caffeic acid groups are called isochlorogenic acids and are found in coffee.There are several isomers such as 3,4-dicaffeoylquinic acid and 3,5-dicaffeoylquinic acid and chamomile (1,5-dicaffeoylquinic acid)
Biosynthesis and natural occurrence
The biosynthetic precursor of chlorogenic acid is 4-coumaroyl-CoA, which contains a hydroxyl group on the aromatic ring, which in turn is produced from cinnamic acid. Hydroxylation of coumarin, the installation of a second hydroxyl group, is catalyzed by cytochrome P450 enzymes.Chlorogenic acids are found in the bamboo Moso bamboo as well as in many other plants, such as the shoots of heather (Calluna vulgaris).
Chlorogenic acid and related compounds cryptochlorogenic acid and neochlorogenic acid are found in the leaves of Hibiscus sabdariffa.Isomers of chlorogenic acid were found in potatoes.Chlorogenic acids are found in the pulp of eggplant,peaches, plums and coffee beans.
Research and security
Chlorogenic acid is undergoing preliminary research on its possible biological effects.Chlorogenic acid has not been approved as a prescription drug or food additive and is considered a safe ingredient in food or beverages.There is insufficient evidence to determine whether it is safe or effective for human health, and its use in high doses, such as excessive consumption of green coffee, may have adverse effects.Chlorogenic acid has been studied as a possible chemical sensitizer involved in respiratory sensitization to certain plant materials.
The atomic numbering of chlorogenic acids may be ambiguous.In 1976, following IUPAC guidelines, the order of atomic numbering on the quinic acid ring was reversed, resulting in 3-CQA becoming 5-CQA and 5-CQA becoming 3-CQA.This article uses the unique original numbering before 1976 (3-CQA for chlorogenic acid and 5-CQA for neochlorogenic acid).Since then, researchers and manufacturers have diverged, and both numbering systems are in use.Even the 1976 IUPAC recommendations are not entirely satisfactory when applied to some less common chlorogenic acids.