What is cinnamic acid?

Cinnamic acid is an organic compound with the formula C6H5CH=CHCOOH. 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 naturally in a number of plants. It exists as both a cis and a trans isomer, but the trans form is the one most often found in nature and is the article of commerce. It is obtained from cinnamon bark and balsam resins such as storax. It was first isolated in 1872 by F. Beilstein (of Handbook of Organic Chemistry fame) and A. Kuhlberg. It is synthesized by the Perkin reaction between Ac2O and PhCHO.

Occurrence and production

Biosynthesis

Cinnamic acid is a central intermediate in the biosynthesis of a myriad of natural products including lignols (precursors to lignin and lignocellulose), flavonoids, isoflavonoids, coumarins, aurones, stilbenes, catechin, and phenylpropanoids. Its biosynthesis involves the action of the enzyme phenylalanine ammonia-lyase (PAL) on phenylalanine.

Natural occurrence

It is obtained from oil of cinnamon, or from balsams such as storax. It is also found in shea butter. Cinnamic acid has a honey-like odor; it and its more volatile ethyl ester (ethyl cinnamate) are flavor components in the essential oil of cinnamon, in which related cinnamaldehyde is the major constituent.

Synthesis

Cinnamic acid was first synthesized by the base-catalysed condensation of acetyl chloride and benzaldehyde, followed by hydrolysis of the acid chloride product. In 1890, Rainer Ludwig Claisen described the synthesis of ethyl cinnamate via the reaction of ethyl acetate with benzaldehyde in the presence of sodium as base. Another way of preparing cinnamic acid is by the Knoevenagel condensation reaction. The reactants for this are benzaldehyde and malonic acid in the presence of a weak base, followed by acid-catalyzed decarboxylation. It can also be prepared by oxidation of cinnamaldehyde, condensation of benzal chloride and sodium acetate (followed by acid hydrolysis), and the Perkin reaction. The oldest commercially used route to cinnamic acid involves the Perkin reaction

Other names

(2E)-3-Phenylacrylic acid (IUPAC Name); (E)-3-Phenylprop-2-enoic acid; 3-Phenyl-, 2-propenoic acid; (2E)-3-phenyl-2-propenoic acid; (E)-3-phenyl-2-propenoic acid; 3-phenyl-acrylic acid; 3t-phenyl-acrylic acid; beta-Phenylacrylic Acid; (Trans)-3-phenyl-propenoic acid; trans-beta-Carboxystyrene; trans-Cinnamic Acid

Biological Significance of AOB Phenolic Compounds

Cinnamic acid is found in most green plants, and it has low toxicity. It is used in flavors and in the manufacturing of the methyl, ethyl, and benzyl esters for the perfume industry. It is also a precursor to the sweetener aspartame. Cinnamic acid has been reported to exhibit antioxidant and antibacterial activities. This acid and its hydroxylated derivatives have also been reported to have antifungal activity, preventing fungal spore germination and antityrosinase enzyme activity with potential skin-whitening activity. Like other phenolic acids, such as gallic acid, cinnamic acid has reported anticancer activity. It induces cytostasis and reverses malignant properties of human tumor cells in vitro; it is a differentiation inducer for melanoma cells disrupts cytoskeleton and induces apoptosis and proliferation of nasopharyngeal carcinoma cells and leukemic cells in vitro. The hydroxylated cinnamic acid derivative p-coumaric acid has antioxidant properties and is believed to reduce the risk of stomach cancer by reducing the formation of carcinogenic nitrosamines. Also, para-coumaric acid found in honey has in vitro antiinflammatory activity. Ellagic acid, phenolic acids, and flavonoids in Malaysian honey extracts demonstrate in vitro antiinflammatory activity. Several dihydroxycinnamic acids, including ferulic acid, chlorogenic acid, caffeic acid, and curcumin, were found to inhibit tumor promotion in mouse skin induced by the tumor promoter 12-O-tetradecanoylphorbol-13-acetate. In addition, ferulic acid exhibited antitumor activity against breast cancer cells.