Borneol is a bicyclicorganic compound and a terpene derivative. The hydroxyl group in this compound is placed in an endo position. The exo diastereomer is called isoborneol. Being chiral, borneol exists as enantiomers, both of which are found in nature: d-borneol (also written (+)-borneol, dextroborneol, dexborneol) and l-borneol (or (−)-borneol, levoborneol).
Both borneol and isoborneol belong to the category of 2-bornanol, a derivative of bornane. Some sources such as PubChem and CHEBI use the term borneol to refer to the entire category of 2-bornanols while others such as KEGG use the term borneol to refer to the compounds with endo hydroxyl only.
It is one of the chemical compounds found in castoreum. This compound is gathered from the beaver's plant food.[6]
Synthesis
Borneol can be synthesized by reduction of camphor by the Meerwein–Ponndorf–Verley reduction (a reversible process). For flavoring purposes, a racemic mixture of camphor is used as starting material, leading to a racemic mixture of borneol and isoborneol. The chirality can be controlled by changing the chirality of camphor: (+)-camphor gives (−)-isoborneol and (+)-borneol.[7]
Borneol is synthesized using DMAPP as the starting material. DMAPP is then converted to GPP, which is acted upon by a bornyl diphosphate synthase to yield a bornyl diphosphate. A phosphatase then removes the phosphate groups, yielding borneol.[12]
The chirality of borneol in a plant depends on the preferred chirality of the bornyl diphosphate synthase. Synthases for either chirality have been sequenced.[12][13]
As mentioned above, both enantiomers of borneol occur in nature. Whereas d-borneol (+) was the enantiomer that used to be the most readily available commercially, the more commercially available enantiomer now is l-borneol (-).
Borneol generates a TRPM8-mediated cooling sensation similar to, but weaker than, menthol. It is more effective at activating TRPM8 at lower temperatures.[14]
Laevo-borneol (-) is used in perfumery. It has a balsamic odour type with pine, woody and camphoraceous facets.
Medical uses
Dextro-borneol (dexborneol) is used in edaravone/dexborneol, a drug approved in China for stroke. It is approved in intravenous (2021) and sublingual (2025) forms. The intravenous combination was approved on the basis of trials showing it to be superior to edavarone alone.[16][17]
Volume 1 of the modern Chinese Pharmacopoeia, which deals with TCM and modernized TCM, lists uses for both enantiomers as well as the synthetic racemer.[11]
Borneol is widely used in ophthalmic preparations in China, though little is known about its exact function.[14]
Toxicology
Borneol may cause eye, skin, and respiratory irritation; it is harmful if swallowed.[18] Acute exposure may cause headache, nausea, vomiting, dizziness, lightheadedness, and syncope. Exposure to higher levels or over a longer period of time may cause restlessness, difficulty concentrating, irritability, and seizures.[19]
Skin irritation
Borneol has been shown to have little to no irritation effect when applied to the human skin at doses used in fine fragrance formulation.[20] Skin exposure can lead to sensitization and a future allergic reaction even to small quantities.[19]
Derivatives
The bornyl group is a univalent radical C10H17 derived from borneol by removal of hydroxyl and is also known as 2-bornyl.[21] Isobornyl is the univalent radical C10H17 that is derived from isoborneol.[22]Bornyl acetate is the acetateester of borneol.
The norborneols are derived from borneol and isoborneol by the removal of methyl groups, analogous to the change from bornane to norbornane.
The epiborneols and isoepiborneols are analogously derived from epicamphor.[23]
↑Lide, D. R., ed. (2005). CRC Handbook of Chemistry and Physics (86thed.). Boca Raton, Florida: CRC Press. p.3.56. ISBN0-8493-0486-5.
↑Gerhardt, C. (1842). "Sur la transformation de l'essence de valériane en camphre de Bornéo et en camphre des laurinées" [On the transformation of the essence of valerian into Borneo camphor and into laurel camphor]. Comptes rendus. 14: 832–835. From p. 834: "Je donne, par cette raison, à l'hydrogène carboné de l'essence de valériane, le nom de bornéène, et, au camphre lui-même, celui de bornéol." (I give, for this reason [namely, that the compound that Gerhardt had obtained from valerian oil was identical to that obtained by Pelouze from camphor from Borneo], to the hydrocarbon from valerian essence, the name bornéène, and, to camphor itself, that of borneol.)
↑Lincoln, D. E.; Lawrence, B. M. (1984). "The volatile constituents of camphorweed, Heterotheca subaxillaris". Phytochemistry. 23 (4): 933–934.
↑Begum, A.; Sandhya, S.; Shaffath Ali, S.; Vinod, K. R.; Reddy, S.; Banji, D. (2013). "An in-depth review on the medicinal flora Rosmarinus officinalis (Lamiaceae)". Acta Scientiarum Polonorum: Technologia Alimentaria. 12 (1): 61–73. PMID24584866.
↑Wong, K. C.; Ong, K. S.; Lim, C. L. (2006). "Composition of the essential oil of rhizomes of Kaempferia galanga L.". Flavour and Fragrance Journal. 7 (5): 263–266. doi:10.1002/ffj.2730070506.
↑The Beaver: Its Life and Impact. Dietland Muller-Schwarze, 2003, page 43 (book at google books)
↑Yang, Ming-Yeh; Khine, Aye Aye; Liu, Jen-Wei; Cheng, Hui-Chen; Hu, Anren; Chen, Hao-Ping; Shih, Tzenge-Lien (November 2018). "Resolution of isoborneol and its isomers by GC/MS to identify "synthetic" and "semi-synthetic" borneol products". Chirality. 30 (11): 1233–1239. doi:10.1002/chir.23017. PMID30222211.
↑Li, Fangping; Huang, Shilin; Mei, Yu; Wu, Bingqi; Hou, Zhuangwei; Zhan, Penglin; Hou, Zhihao; Huang, Wenjie; Zhao, Junliang; Wang, Jihua (October 2022). "Genome assembly provided new insights into the Cinnamomum burmannii evolution and D-borneol biosynthesis differences between chemotypes". Industrial Crops and Products. 186 115181. doi:10.1016/j.indcrop.2022.115181.
↑Xingxing, Liu; Xi, Zhang; Xiali, Guo; Shangji, Gong; Xiangmei, Jiang; Yuxin, Fu; Liping, Luo (2014). "Multivariate Analyses of Volatile Chemical Composition in Leaves of Different Cinnamomum camphora Chemotypes". Chinese Bulletin of Botany. 49 (2): 161. doi:10.3724/SP.J.1259.2014.00161.
↑Robertson, JS; Hussain, M (June 1969). "Metabolism of camphors and related compounds". The Biochemical journal. 113 (1): 57–65. doi:10.1042/bj1130057. PMID4308838.
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