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Alpha-thujaplicin tautomers.png
Beta-thujaplicin tautomers.png
β-Thujaplicin (hinokitiol)
Gamma-thujaplicin tautomers.png
3D model (JSmol)
EC Number
  • β:207-880-7
PubChem CID
  • α:InChI=1S/C10H12O2/c1-7(2)8-5-3-4-6-9(11)10(8)12/h3-7H,1-2H3,(H,11,12)
  • β:InChI=1S/C10H12O2/c1-7(2)8-4-3-5-9(11)10(12)6-8/h3-7H,1-2H3,(H,11,12)
  • γ:InChI=1S/C10H12O2/c1-7(2)8-3-5-9(11)10(12)6-4-8/h3-7H,1-2H3,(H,11,12)
  • α:CC(C)C1=C(C(=O)C=CC=C1)O
  • β:CC(C)C1=CC(=O)C(=CC=C1)O
  • γ:CC(C)C1=CC=C(C(=O)C=C1)O
Molar mass 164.204 g·mol−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Thujaplicins (isopropyl cycloheptatrienolones) are a series of tropolone-related chemical substances that have been isolated from the softwoods of the trees of Cupressaceae family. [1] These compounds are known for their antibacterial, antifungal, and antioxidant properties. [2] [3] They were the first natural tropolones to be made synthetically. [4]



Thuja plicata Donn ex D. Don (Western red cedar) - a tree belonging to the Cupressaceae family from which thujaplicins were first purified Thuja plicata Vancouver.jpg
Thuja plicata Donn ex D. Don (Western red cedar) – a tree belonging to the Cupressaceae family from which thujaplicins were first purified

Thujaplicins were discovered in the mid-1930s and purified from the heartwood of Thuja plicata Donn ex D. Don, commonly called as Western red cedar tree. [5] These compounds were also identified in the constituents of Chamaecyparis obtusa , another species from the Cupressaceae family. C. obtusa is native to East Asian countries including Japan and Taiwan, and is also known as Taiwan hinoki, from which the β-thujaplicin was first isolated in 1936 and received its name, hinokitiol. Thujaplicins were the first natural tropolones to be made synthetically, by Ralph Raphael and colleagues, and the β-thujaplicin was the first non-benzenoid aromatic compound identified, by Tetsuo Nozoe and colleagues. [4] [5] The resistance of the heartwood of the tree to decay 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 of Tetsuo Nozoe can be translated into English as “Iron Man”. [6]

Occurrence and isolation

Tjujaplicins are found in the heartwood of the conifer trees belonging to the Cupressaceae family, including Chamaecyparis obtusa (Hinoki cypress), Thuja plicata (Western red cedar), Thujopsis dolabrata var. hondai (Hinoki asunaro), Juniperus cedrus (Canary Islands juniper), Cedrus atlantica (Atlas cedar), Cupressus lusitanica (Mexican white cedar), Chamaecyparis lawsoniana (Port Orford cedar), Chamaecyparis taiwanensis (Taiwan cypress), Chamaecyparis thyoides (Atlantic white cedar), Cupressus arizonica (Arizona cypress), Cupressus macnabiana (MacNab cypress), Cupressus macrocarpa (Monterey cypress), Juniperus chinensis (Chinese juniper), Juniperus communis (Common juniper), Juniperus californica (California juniper), Juniperus occidentalis (Western juniper), Juniperus oxycedrus (Cade), Juniperus sabina (Savin juniper), Calocedrus decurrens (California incense-cedar), Calocedrus formosana (Taiwan incense-cedar), Platycladus orientalis (Chinese thuja), Thuja occidentalis (Northern white-cedar), Thuja standishii (Japanese thuja), Tetraclinis articulata (Sandarac). [8] [9] [10] [11]

Thujaplicins can be produced in plant cell suspension cultures, [12] [13] or can be extracted from wood using solvents and ultrasonication. [14]


Thujaplicins can be synthesized by cycloaddition of isopropylcyclopentadiene and dichloroketene, 1,3-dipolar cycloaddition of 5-isopropyl-1-methyl-3-oxidopyridinium, ring expansion of 2-isopropylcyclohexanone, regiocontrolled hydroxylation of oxyallyl (4+3) cycloadducts, from (R)-(+)-limonene regioselectively by several steps, and from troponeirontricarbonyl complex by few steps. [15] [16] The synthesis pathway of β-thujaplicin from troponeirontricarbonyl complex is found below:

Biosynthesis of beta-thujaplicin from troponeirontricarbonyl complex.svg

The synthesis pathway of β-thujaplicin by electro-reductive alkylation of substituted cycloheptatrienes is shown below:

Biosynthesis of beta-thujaplicin through electroreductive alkylation.svg

The synthesis pathway of β-thujaplicin through ring expansion of 2-isopropylcyclohexanone is shown below:

Biosynthesis of beta-thujaplicin from 2-isopropylcyclohexanone.svg

The synthesis pathway of β-thujaplicin through oxyallyl cation [4+3] cyclization (Noyori's synthesis) is shown below:

Biosynthesis of b-thujaplicin through oxyallyl cation (4+3) cyclization.svg


Thujaplicins belong to tropolones containing an unsaturated seven-membered carbon ring. Thujaplicins are monoterpenoids that are cyclohepta-2,4,6-trien-1-one substituted by a hydroxy group at position 2 and an isopropyl group at positions 3, 4 or 5. [17] These compounds are enols and cyclic ketones. They derive from a hydride of a cyclohepta-1,3,5-triene. Thujaplicins are soluble in organic solvents and aqueous buffers. Hinokitiol is soluble in ethanol, 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 three isomers of thujaplicin, with the isopropyl group positioned progressively further from the two oxygen atoms around the ring: α-thujaplicin, β-thujaplicin, and γ-thujaplicin. [4] β-Thujaplicin, also called hinokitiol, is the most common in nature. [21] Each exists in two tautomeric forms, swapping the hydroxyl hydrogen to the other oxygen, meaning the two oxygen substituents do not have distinct "carbonyl" vs "hydroxyl" identities. The extent of this exchange is that the tropolone ring is aromatic with an overall cationic nature, and the oxygen–hydrogen–oxygen region has an anionic nature.[ citation needed ]

Beta-thujaplicin aromaticity.png

Biological properties

Insecticidal and pesticidal activity

Thujaplicins are shown to act against Reticulitermes speratus (Japanese termites), Coptotermes formosanus (super termites), Dermatophagoides farinae (dust mites), Tyrophagus putrescentiae (mould mites), Callosobruchus chinensis (adzuki bean weevil), Lasioderma serricorne (cigarette beetle). [9] [22] [11]

Hinokitiol has also shown some larvicidal activities against Aedes aegypti (yellow fever mosquito) and Culex pipiens (common house mosquito), and anti-plasmodial activities against Plasmodium falciparum and Plasmodium berghei . [11]

Antioxidant activity

Chelating and ionophore activity

Thujaplicins, as other tropolones, demonstrate chelating activity, acting as an ionophore by binding different metal ions. [23]

Anti-browning activity

Tropolone and thujaplicins exhibit potent suppressive activity on enzymatic browning due to inhibition of polyphenol oxidase and tyrosinase. This have been shown in experiments on different vegetables, fruits, mushrooms, plants and other agricultural products. [11] Prevention of darkening has also been elicited on seafood products. [24]


Skin care and cosmetics

Owing to their antibacterial activities against various microbes colonizing and affecting the skin, thujaplicins, including also thujaplicinol, are used in skin care and hair growth products, [25] and are especially popular in Eastern Asia.[ citation needed ]

Oral care

Hinokitiol is used in various oral care products, including toothpastes and oral sprays. [25] [26]

Veterinary medicine

Due to its antifungal activity against Malassezia pachydermatis , it is used in eardrop formulations for external otitis in dogs. [27] [28]


Considering their antifungal activity against many plant-pathogenic fungi, and pesticidal and insecticidal properties, the role of thujaplicins in agriculture is evolving, including their use in the management of different plant diseases and for controlling the postharvest decay. [9] [29]

Food additive

Thujaplicins are used as food additives in Japan. [30] Due to its suppressive activity on food browning and the inhibitory activity against bacteria and fungi causing food spoilage (such as Clostridium perfringens , Alternaria alternata , Aspergillus niger , Botrytis cinerea , Fusobacterium species, Monilinia fructicola and Rhizopus stolonifer ), hinokitiol is also used in food packaging as a shelf-life extending agent. [31] [32] [33] Thujaplicinol, a tropolone, is also used in Japan as a food additive in small amount.

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Cedrus, with the common English name cedar, is a genus of coniferous trees in the plant family Pinaceae. They are native to the mountains of the western Himalayas and the Mediterranean region, occurring at altitudes of 1,500–3,200 m in the Himalayas and 1,000–2,200 m in the Mediterranean.

<span class="mw-page-title-main">Juniper</span> Genus of plants

Junipers are coniferous trees and shrubs in the genus Juniperus of the cypress family Cupressaceae. Depending on the taxonomy, between 50 and 67 species of junipers are widely distributed throughout the Northern Hemisphere, from the Arctic, south to tropical Africa, throughout parts of western, central and southern Asia, east to eastern Tibet in the Old World, and in the mountains of Central America. The highest-known juniper forest occurs at an altitude of 4,900 metres (16,100 ft) in southeastern Tibet and the northern Himalayas, creating one of the highest tree lines on earth.

Cypress is a common name for various coniferous trees or shrubs of northern temperate regions that belong to the family Cupressaceae. The word cypress is derived from Old French cipres, which was imported from Latin cypressus, the latinisation of the Greek κυπάρισσος (kyparissos). Cypress trees are a large classification of conifers, encompassing the trees and shrubs from the cypress family (Cupressaceae) and many others with the word cypress in their common name. Many cypress trees have needle-like, evergreen foliage and acorn-like seed cones.

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<i>Thuja plicata</i> Species of conifer

Thuja plicata is a large evergreen coniferous tree in the family Cupressaceae, native to the Pacific Northwest of North America. Its common name is western redcedar in the U.S. or western red cedar in the UK, and it is also called pacific red cedar, giant arborvitae, western arborvitae, just cedar, giant cedar, or shinglewood. It is not a true cedar of the genus Cedrus. T. plicata is the largest species in the genus Thuja, growing up to 70 metres (230 ft) tall and 7 m (23 ft) in diameter. It mostly grows in areas that experience a mild climate with plentiful rainfall, although it is sometimes present in drier areas on sites where water is available year-round, such as wet valley bottoms and mountain streamsides. The species is shade-tolerant and able to establish in forest understories and is thus considered a climax species. It is a very long-lived tree, with some specimens reaching ages of well over 1,000 years.

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<span class="mw-page-title-main">Hinokitiol</span> Chemical compound

Hinokitiol (β-thujaplicin) is a natural monoterpenoid found in the wood of trees in the family Cupressaceae. It is a tropolone derivative and one of the thujaplicins. Hinokitiol is used in oral and skin care products, and is a food additive used in Japan.

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<span class="mw-page-title-main">Cedrol</span> Chemical compound

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