Protocatechuic acid

Protocatechuic acid
IUPAC name 3,4-Dihydroxybenzoic acid
Other names 3,4-Dihydroxybenzoic acid, PCA
Identifiers
CAS number	99-50-3 Y
PubChem	72
ChemSpider	71 Y
EC number	202-760-0
DrugBank	DB03946
ChEBI	CHEBI:36062 Y
ChEMBL	CHEMBL37537 Y
RTECS number	UL0560000
Jmol-3D images	Image 1
SMILES C1=CC(=C(C=C1C(=O)O)O)O
InChI InChI=1S/C7H6O4/c8-5-2-1-4(7(10)11)3-6(5)9/h1-3,8-9H,(H,10,11) Y Key: YQUVCSBJEUQKSH-UHFFFAOYSA-N Y
Properties
Molecular formula	C7H6O4
Molar mass	154.12 g/mol
Appearance	light brown solid
Density	1.54 g/cm3
Melting point	221 °C; 430 °F; 494 K (decomp.)
Solubility in water	1.24 g/100 mL
Solubility	soluble in ethanol, ether insoluble in benzene
Acidity (pKa)	4.48 [1]
Hazards
MSDS	MSDS
NFPA 704	0 2 0
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Infobox references

UV visible spectrum of protocatechuic acid

Protocatechuic acid (PCA) is a dihydroxybenzoic acid, a type of phenolic acid. It is a major metabolite of antioxidant polyphenols found in green tea. It has mixed effects on normal and cancer cells in in vitro and in vivo studies.^[2]

Biological effects

Protocatechuic acid (PCA) is antioxidant and anti-inflammatory. PCA extracted from Hibiscus sabdariffa protected against chemically-induced liver toxicity in vivo. In vitro testing documented antioxidant and anti-inflammatory activity of PCA, while liver protection in vivo was measured by chemical markers and histological assessment.^[3]

PCA has been reported to induce apoptosis of human leukemia cells, as well as malignant HSG1 cells taken from human oral cavities,^[4] but PCA was found to have mixed effects on TPA-induced mouse skin tumours. Depending on the amount of PCA and the time before application, PCA could reduce or enhance tumour growth.^[5] Similarly, PCA was reported to increase proliferation and inhibit apoptosis of neural stem cells.^[6] In an in vitro model using HL-60leukemia cells, protocatechuic acid showed an antigenotoxic effect and tumoricidal activity.^[7]

Occurrence in nature

Protocatechuic acid can be isolated from the stem bark of Boswellia dalzielii.^[8]

The hardening of the protein component of insect cuticle has been shown to be due to the tanning action of an agent produced by oxidation of a phenolic substance. In the analogous hardening of the cockroach ootheca, the phenolic substance concerned is protocatechuic acid.^[9]

in foods

Açaí oil, obtained from the fruit of the açaí palm (Euterpe oleracea), is rich in protocatechuic acid (630 ± 36 mg/kg).,^[10] Protocatechuic acid also exists in the skins of some strains of onion as an antifungal mechanism, increasing endogenous resistance against smudge fungus. It is also found in Allium cepa (17,540 ppm).^[11]

PCA occurs in roselle (Hibiscus sabdariffa), which is used worldwide as a food and beverage.^[3]

Protocatechuic acid is also found in mushrooms such as Agaricus bisporus^[12] or Phellinus linteus.^[13]

Metabolism

Protocatechuic acid is one of the main catechins metabolites found in humans after consumption of green tea infusions.^[14]

Enzymes

Biosynthesis enzymes

• 3-Dehydroshikimate dehydratase
• (3S,4R)-3,4-dihydroxycyclohexa-1,5-diene-1,4-dicarboxylate dehydrogenase
• Terephthalate 1,2-cis-dihydrodiol dehydrogenase
• 3-hydroxybenzoate 4-monooxygenase
• 4-hydroxybenzoate 3-monooxygenase (NAD(P)H)
• 4-sulfobenzoate 3,4-dioxygenase
• Vanillate monooxygenase
• 3,4-dihydroxyphthalate decarboxylase
• 4,5-dihydroxyphthalate decarboxylase

Protocatechuic acid biosynthesis

Degradation enzymes

The enzyme protocatechuate decarboxylase uses 3,4-dihydroxybenzoate to produce catechol and CO₂.
The enzyme protocatechuate 3,4-dioxygenase uses 3,4-dihydroxybenzoate and O₂ to produce 3-carboxy-cis,cis-muconate.

See also

• Ethyl protocatechuate

References