Thujaplicins were discovered in the mid-1930s and purified from theheartwood ofThuja plicata Donn ex D. Don, commonly called as Western red cedar tree.[5] These compounds were also identified in the constituents ofChamaecyparis obtusa, another species from theCupressaceae family.C. obtusa is native to East Asian countries includingJapan andTaiwan, and is also known asTaiwan hinoki, from which the β-thujaplicin was first isolated in 1936 and received its name,hinokitiol. Thujaplicins were the first naturaltropolones to be made synthetically, byRalph Raphael and colleagues, and the β-thujaplicin was the first non-benzenoid aromatic compound identified, byTetsuo Nozoe and colleagues.[4][5] The resistance of the heartwood of the tree todecay was the main reason prompting to investigate its content and identify the compounds responsible for antimicrobial properties.[4] β-thujaplicin gained more scientific interest beginning in the 2000s.[6] Later, iron-binding activity of β-thujaplicin was discovered and the molecule has been ironically nicknamed as “Iron Man molecule”,[7] because the first name ofTetsuo Nozoe can be translated into English as “Iron Man”.[6]
Thujaplicins belong to tropolones containing an unsaturated seven-membered carbon ring. Thujaplicins aremonoterpenoids that arecyclohepta-2,4,6-trien-1-one substituted by ahydroxy group at position 2 and anisopropyl group at positions 3, 4 or 5.[17] These compounds areenols and cyclicketones. They derive from a hydride of acyclohepta-1,3,5-triene. Thujaplicins are soluble in organic solvents and aqueousbuffers. Hinokitiol is soluble inethanol,dimethyl sulfoxide,dimethylformamide with a solubility of 20, 30 and 12.5 mg/ml, respectively.[18] β-thujaplicin provides acetone on vigorous oxidation and gives the saturated monocyclic diol upon catalytic hydrogenation.[19] It is stable to alkali and acids, forming salts or remaining unchanged, but does not convert to catechol derivatives. The complexes made of iron and tropolones display high thermodynamic stability and has shown to have a stronger binding constant than the transferrin-iron complex.[20]
There are threeisomers of thujaplicin, with theisopropyl group positioned progressively further from the two oxygen atoms around the ring: α-thujaplicin, β-thujaplicin, and γ-thujaplicin.[4] β-Thujaplicin, also calledhinokitiol, is the most common in nature.[21] Each exists in twotautomeric forms, swapping thehydroxyl hydrogen to the other oxygen, meaning the two oxygensubstituents do not have distinct "carbonyl" vs "hydroxyl" identities. The extent of this exchange is that thetropolone ring isaromatic with an overall cationic nature, and the oxygen–hydrogen–oxygen region has an anionic nature.[citation needed]
Tropolone and thujaplicins exhibit potent suppressive activity onenzymatic browning due to inhibition ofpolyphenol oxidase andtyrosinase. This have been shown in experiments on different vegetables, fruits, mushrooms, plants and other agricultural products.[11] Prevention of darkening has also been elicited onseafood products.[24]
Owing to their antibacterial activities against various microbes colonizing and affecting the skin, thujaplicins, including alsothujaplicinol, are used in skin care and hair growth products,[25] and are especially popular in Eastern Asia.[citation needed]
Considering their antifungal activity against many plant-pathogenicfungi, andpesticidal andinsecticidal properties, the role of thujaplicins in agriculture is evolving, including their use in the management of different plant diseases and for controlling thepostharvest decay.[9][29]
^Chedgy, Russell J.; Lim, Young Woon; Breuil, Colette (May 2009). "Effects of leaching on fungal growth and decay of western redcedar".Canadian Journal of Microbiology.55 (5):578–586.doi:10.1139/W08-161.PMID19483786.
^Chedgy, R. (2010).Secondary Metabolites of Western Red Cedar (Thuja plicata). Lambert Academic Publishing.ISBN978-3-8383-4661-8.
^abcdCook, J. W.; Raphael, R. A.; Scott, A. I. (1951). "149. Tropolones. Part II. The synthesis of α-, β-, and γ-thujaplicins".J. Chem. Soc.:695–698.doi:10.1039/JR9510000695.
^Zhao, J.; Fujita, K.; Yamada, J.; Sakai, K. (1 April 2001). "Improved β-thujaplicin production in Cupressus lusitanica suspension cultures by fungal elicitor and methyl jasmonate".Applied Microbiology and Biotechnology.55 (3):301–305.doi:10.1007/s002530000555.PMID11341310.S2CID25767209.
^Chedgy, Russell J.; Daniels, C.R.; Kadla, John; Breuil, Colette (1 March 2007). "Screening fungi tolerant to Western red cedar (Thuja plicata Donn) extractives. Part 1. Mild extraction by ultrasonication and quantification of extractives by reverse-phase HPLC".Holzforschung.61 (2):190–194.doi:10.1515/HF.2007.033.S2CID95994935.
^Soung, Min-Gyu; Matsui, Masanao; Kitahara, Takeshi (September 2000). "Regioselective Synthesis of β- and γ-Thujaplicins".Tetrahedron.56 (39):7741–7745.doi:10.1016/S0040-4020(00)00690-6.
^Pietra, Francesco (August 1973). "Seven-membered conjugated carbo- and heterocyclic compounds and their homoconjugated analogs and metal complexes. Synthesis, biosynthesis, structure, and reactivity".Chemical Reviews.73 (4):293–364.doi:10.1021/cr60284a002.
^Aladaileh, Saleem; Rodney, Peters; Nair, Sham V.; Raftos, David A. (December 2007). "Characterization of phenoloxidase activity in Sydney rock oysters (Saccostrea glomerata)".Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology.148 (4):470–480.doi:10.1016/j.cbpb.2007.07.089.PMID17950018.
^Aharoni, Y.; Copel, A.; Fallik, E. (June 1993). "Hinokitiol (β-thujaplicin), for postharvest decay control on 'Galia' melons".New Zealand Journal of Crop and Horticultural Science.21 (2):165–169.Bibcode:1993NZJCH..21..165A.doi:10.1080/01140671.1993.9513763.
^Vanitha, Thiraviam; Thammawong, Manasikan; Umehara, Hitomi; Nakamura, Nobutaka; Shiina, Takeo (3 September 2019). "Effect of hinokitiol impregnated sheets on shelf life and quality of "KEK-1" tomatoes during storage".Packaging Technology and Science.32 (12):641–648.doi:10.1002/pts.2479.S2CID202995336.
_cyclization.svg)
![[icon]](/mt/?noimg=&dark=on&url=https%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aWiki_letter_w_cropped.svg)
