Cinnamic acid

Cinnamic acid, 3 -phenyl-2-propenoic acid, is a non-toxic, unsaturated carboxylic acid that occurs naturally in various plants. It is a non-toxic, unsaturated carboxylic acid with the linear structural pattern C6H5-CH=CH-COOH that occurs naturally in various plants and has a characteristic cinnamon odor. Cinnamic acid occurs in 2 stereosiomeric forms (cis- and trans-cinnamic acid) whereby only trans-cinnamic acid plays a role in nature.

Alongside cinnamaldehyde and eugenol, cinnamic acid is responsible for the aroma of cinnamon.
Cinnamic acid is poorly soluble in cold water, but easily soluble in ethanol, ether and fatty oils. Free or esterified, trans-cinnamic acid is found in balsams, resins and essential oils (Peru balsam, storax, cassia oil, etc.).

Cinnamic acid is no longer known to be used medicinally. Formerly used as a remedy against tuberculosis. In the cosmetics industry, cinnamic acid is used as an odor corrector and preservative. Cinnamic acid, and even more so its oxidation products and esters, are relevant contact allergens.

Cinnamic acid methyl ester has been shown in animal experiments to inhibit AMPA receptors (AMPA receptors are ionotropic glutamate receptors in vertebrates and consist of three major subtypes - AMPA, kainate and NMDA receptors. They mediate the majority of fast excitatory neurotransmission at chemical synapses of the central nervous system). AMPA receptors are involved in the development of neuropathic pain in the spinal cord (Gui Y et al. (2018).

1. Gui Y et al. (2018) Methyl cinnamate alleviated CCI-induced upregulation of spinal AMPA receptors and pain hypersensitivity by targeting AMPK. Eur J Pharmacol 833:183-189.

2. Letizia CS et al.(2005) Fragrance material review on cinnamic acid. Food Chem Toxicol 43:925-943.
3. Srivastava D et al. (2009) Identification of the constituents of balsam of peru in tomatoes. Dermatitis 20:99-105.