Gallic Acid

Biotechnological Production

The production of gallic acid is challenging. Conventionally, it has been produced by acid hydrolysis of tannic acid. However, this process is expensive due to low yields and high impurities. To overcome this problem, microbial production of gallic acid has been suggested. For example, in a solid-state fermentation of Teri pod cover powder containing tannin using Rhizopus oryzae, a yield of 90.9 % based on the tannin content of 58 % of the substrate was observed. In a submerged culture of Aspergillus aceleatus DBF9 growing on a medium with 3 % tannin, a maximal product concentration of 6.8 g.L-1 was reported. With tannic acid, even higher product concentrations of up to 25 g.L-1, a yield of 0.83 g of gallic acid per gram of tannic acid, and a productivity of 0,56 g.L-1.h-1 were shown using Apergillus fischeri MTCC 150 in submerged cultivation. An alternative is the enzymatic hydrolysis of tannic acids using tannase produced by microorganisms (e.g. Aspergillus fischeri or R. oryzae). For example, propyl gallate could be produced using a tannase from Emericela nidulans immobilized on ionic and covalent supports.

Air & Water Reactions

Sparingly water soluble

Reactivity Profile

Phenols, such as Gallic acid, do not behave as organic alcohols, as one might guess from the presence of a hydroxyl (-OH) group in their structure. Instead, they react as weak organic acids. Phenols and cresols are much weaker as acids than common carboxylic acids (phenol has Ka = 1.3 x 10^[-10]). These materials are incompatible with strong reducing substances such as hydrides, nitrides, alkali metals, and sulfides. Flammable gas (H2) is often generated, and the heat of the reaction may ignite the gas. Heat is also generated by the acid-base reaction between phenols and bases. Such heating may initiate polymerization of the organic compound. Phenols are sulfonated very readily (for example, by concentrated sulfuric acid at room temperature). The reactions generate heat. Phenols are also nitrated very rapidly, even by dilute nitric acid.

Health Hazard

Inhalation of dust may irritate nose and throat. Contact with eyes or skin causes irritation.

Fire Hazard

Flash point data for Gallic acid are not available. Gallic acid is probably combustible.

Flammability and Explosibility

Notclassified

Biochem/physiol Actions

Gallic acid is a water soluble phenolic acid present in grapes and in the leaves of many plants. Gallic acid esters, such as tannins, catechin gallates and aliphatic gallates are potent antioxidants in vitro. However, gallic acid itself also appears to have antioxidant, anticarcinogenic and antiangiogenic activity in vitro.

Side effects

It is a weak carbonic anhydrase inhibitor.

Metabolism

Biosynthesis Chemical structure of 3,5- didehydro shikimate Gallic acid is formed from 3-dehydro shikimate by the action of the enzyme shikimate dehydro genase to produce 3,5-didehydro shikimate. This latter compound tautomerizes to form the redox equivalent gallic acid, where the equilibrium lies essentially entirely toward gallic acid because of the coincidently occurring aromatization. Degradation Gallate dioxygenase is an enzyme found in Pseudomonas putida that catalyzes the reaction : gallate + O2 → (1E)-4-oxobut-1-ene-1,2,4-tri carboxylate. Gallate decarboxylase is another enzyme in the degradation of gallic acid. Conjugation Gallate 1-beta-glucosyltransferase is an enzyme that uses UDPglucose and gallate, whereas its two products are UDP and 1-galloylbeta- D-glucose.

Purification Methods

Crystallise gallic from water. The tri-O-acetyl derivative has m 172o (from MeOH), and the anilide has m 207o(from EtOH). [Beilstein 10 H 470, 10 IV 1993.]

Esters

Also known as galloylated esters: Methyl gallate Ethyl gallate, a food additive with E number E313 Propyl gallate, or propyl 3,4,5-trihydroxybenzoate, an ester formed by the condensation of gallic acid and propanol Octyl gallate, the ester of octanol and gallic acid Dodecyl gallate, or lauryl gallate, the ester of dodecanol and gallic acid Epicatechin gallate, a flavan-3-ol, a type of flavonoid, present in green tea Epigallocatechin gallate (EGCG), also known as epigallocatechin 3-gallate, the ester of epigallocatechin and gallic acid, and a type of catechin Gallocatechin gallate (GCG), the ester of gallocatechin and gallic acid and a type of flavan-3ol Theaflavin-3-gallate, a theaflavin derivative.

General Description

Gallic acid is a trihydroxybenzoic acid derivative with notable pharmacological properties, including potential roles as a liver-protective agent, an antidiabetic compound (as seen in its involvement in penta-O-galloyl-D-glucopyranose), and an inhibitor of α-synuclein aggregation in neurodegenerative diseases. Its structure allows for chemical modifications, such as amide derivatization, to enhance lipophilicity and blood-brain barrier penetration, improving therapeutic efficacy. Additionally, gallic acid serves as a key intermediate in synthesizing bioactive compounds, demonstrating its versatility in medicinal chemistry and material science applications.

Definition

ChEBI: A trihydroxybenzoic acid in which the hydroxy groups are at positions 3, 4, and 5.