The natural product is trans-cinnamaldehyde. The molecule consists of a benzene ring attached to an unsaturated aldehyde. As such, the molecule can be viewed as a derivative of acrolein. Its color is due to the π → π* transition: increased conjugation in comparison with acrolein shifts this band towards the visible.
Pathway for the biosynthesis of trans-cinnamaldehyde.
The biosynthesis of cinnamaldehyde begins with deamination of L-phenylalanine into cinnamic acid by the action of phenylalanine ammonia lyase (PAL). PAL catalyzes this reaction by a non-oxidative deamination. This deamination relies on the MIO prosthetic group of PAL. PAL gives rise to trans-cinnamic acid.
In the second step, 4-coumarate–CoA ligase (4CL) converts cinnamic acid to cinnamoyl-CoA by an acid–thiol ligation. 4CL uses ATP to catalyze the formation of cinnamoyl-CoA. 4CL effects this reaction in two steps. 4CL forms a hydroxycinnamate–AMP anhydride, followed by a nucleophile attack on the carbonyl of the acyl adenylate.
Cinnamoyl-CoA is reduced by NADPH catalyzed by CCR (cinnamoyl-CoA reductase) to form cinnamaldehyde.
Cinnamaldehyde is also known as a corrosion inhibitor for steel and other ferrousalloys in corrosive fluids such as hydrochloric acid. It is believed that this is achieved by polymerization to form a protective film on the metal surface. It can be used in combination with additional components such as dispersing agents, solvents and other surfactants. Cinnamaldehyde is also a potent inducer of apoptosis via ROS-mediated mitochondrial permeability transition in human promyelocytic leukemia HL-60 cells. Some early evidence shows that cinnamaldehyde blocks formation of Tau protein aggregation into neurofibrillary tangles, a major pathology in Alzheimer's Disease.  Cinnamaldehyde also has antimicrobial properties. Cinnamaldehyde is also a TRPA1 activator, and can excite a subset of sensory neurons that are mainly cold-sensitive neurons, to cause nociceptive behavior in mice. Cinnamaldehyde has been found to improve metabolic health by acting directly on adipocytes and inducing them to start burning energy through a process called thermogenesis. Scientists had previously observed that cinnamaldehyde appeared to protect mice against obesity and hyperglycemia, but the mechanisms underlying these effects were not well understood. Researchers are currently investigating cinnamaldehyde as a potential anti-obesity drug.
Numerous derivatives of cinnamaldehyde are commercially useful. Dihydrocinnamyl alcohol, which occurs naturally but is produced by double hydrogenation of cinnamaldehyde, is used to confer the fragrances of hyacinth and lilac. Cinnamyl alcohol similarly occurs naturally and has the odor of lilac, but can be also produced starting from cinnamaldehyde. Dihydrocinnamaldehyde is produced by the selective hydrogenation of the alkene subunit. α-Amylcinnamaldehyde and α-hexylcinnamaldehyde are important commercial fragrances, but they are not prepared from cinnamaldehyde.
Cinnamaldehyde is used in agriculture because of its low toxicity, but it is a skin irritant.
^"Cinnamon". Transport Information Service. Gesamtverband der Deutschen Versicherungswirtschaft e.V. Retrieved 2007-10-23.
^Gutzeit, Herwig (2014). Plant Natural Products: Synthesis, Biological Functions and Practical Applications. Wiley. pp. 19–21. ISBN978-3-527-33230-4.
^Koukol, J.; Conn, E. E. (1961-10-01). "The metabolism of aromatic compounds in higher plants. IV. Purification and properties of the phenylalanine deaminase of Hordeum vulgare". The Journal of Biological Chemistry. 236: 2692–2698. ISSN0021-9258. PMID14458851.
^Kong, Jian-Qiang (2015-07-20). "Phenylalanine ammonia-lyase, a key component used for phenylpropanoids production by metabolic engineering". RSC Advances. 5 (77): 62587–62603. doi:10.1039/C5RA08196C. ISSN2046-2069.
^Beuerle, Till; Pichersky, Eran (2002-03-15). "Enzymatic Synthesis and Purification of Aromatic Coenzyme A Esters". Analytical Biochemistry. 302 (2): 305–312. doi:10.1006/abio.2001.5574. PMID11878812.
^Wengenmayer, Herta; Ebel, Jurgen; Grisebach, Hans (1976). "Enzymic Synthesis of Lignin Precursors. Purification and Properties of a Cinnamoyl-CoA:NADPH Reductase from Cell Suspension Cultures of Soybean (Glycine max)". European Journal of Biochemistry. 65 (2): 529–536. doi:10.1111/j.1432-1033.1976.tb10370.x. ISSN0014-2956. PMID7454.
^Friedman, M.; Kozuekue, N.; Harden, L. A. (2000). "Cinnamaldehyde content in foods determined by gas chromatography-mass spectrometry". Journal of Agricultural and Food Chemistry. 48 (11): 5702–5709. doi:10.1021/jf000585g. PMID11087542.
^Cheng, Sen-Sung; Liu, Ju-Yun; Tsai, Kun-Hsien; Chen, Wei-June; Chang, Shang-Tzen (2004). "Chemical Composition and Mosquito Larvicidal Activity of Essential Oils from Leaves of Different Cinnamomum osmophloeum Provenances". Journal of Agricultural and Food Chemistry. 52 (14): 4395–4400. doi:10.1021/jf0497152. PMID15237942. Lay summary – Science Daily (July 16, 2004).
^Ma, W.-B.; Feng, J.-T.; Jiang, Z.-L.; Zhang, X. (2014). "Fumigant Activity of 6 Selected Essential Oil Compounds and Combined Effect of Methyl Salicylate And trans-Cinnamaldehyde Against Culex pipiens pallens". Journal of the American Mosquito Control Association. 30 (3): 199–203. doi:10.2987/14-6412R.1. PMID25843095.
^Growcock, F. B. (1989). "Inhibition of Steel Corrosion in HCl by Derivatives of Cinnamaldehyde". Corrosion. 45 (12): 1003–1007. doi:10.5006/1.3585007.
^Growcock, F. B.; Frenier, W. W.; Andreozzi, P. A. (1989). "Inhibition of Steel Corrosion in HCl by Derivatives of Cinnamaldehyde". Corrosion. 45 (12): 1007–1015. doi:10.5006/1.3585008.
^Ka, Hyeon; Park, Hee-Juhn; Jung, Hyun-Ju; Choi, Jong-Won; Cho, Kyu-Seok; Ha, Joohun; Lee, Kyung-Tae (2003). "Cinnamaldehyde induces apoptosis by ROS-mediated mitochondrial permeability transition in human promyelocytic leukemia HL-60 cells". Cancer Letters. 196 (2): 143–152. doi:10.1016/s0304-3835(03)00238-6. PMID12860272.
^López, P.; Sánchez, C.; Batlle, R.; Nerín, C. (2007). "Vapor-Phase Activities of Cinnamon, Thyme, and Oregano Essential Oils and Key Constituents against Foodborne Microorganisms". J. Agric. Food Chem. 55 (11): 4348–4356. doi:10.1021/jf063295u. PMID17488023.
^Bandell, M; Story, G. M.; Hwang, S. W.; Viswanath, V.; Eid, S. R.; Petrus, M. J.; Earley, T. J.; Patapoutian, A. (2004). "Noxious cold ion channel TRPA1 is activated by pungent compounds and bradykinin". Neuron. 41 (6): 849–857. doi:10.1016/s0896-6273(04)00150-3. PMID15046718.
^Zucca, P.; Littarru, M.; Rescigno, A.; Sanjust, E. (2009). "Cofactor recycling for selective enzymatic biotransformation of cinnamaldehyde to cinnamyl alcohol". Bioscience, Biotechnology, and Biochemistry. 73 (5): 1224–1226. doi:10.1271/bbb.90025. PMID19420690.
^Olsen, R. V.; Andersen, H. H.; Møller, H. G.; Eskelund, P. W.; Arendt-Nielsen, L (2014). "Somatosensory and vasomotor manifestations of individual and combined stimulation of TRPM8 and TRPA1 using topical L-menthol and trans-cinnamaldehyde in healthy volunteers". European Journal of Pain. 18 (9): 1333–42. doi:10.1002/j.1532-2149.2014.494.x. PMID24664788.