Borneol is a

bicyclic A bicyclic molecule () is a molecule that features two joined rings. Bicyclic structures occur widely, for example in many biologically important molecules like α-thujene and camphor. A bicyclic compound can be carbocyclic (all of the ring ...

organic compound Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...

and a

terpene Terpenes () are a class of natural products consisting of compounds with the formula (C5H8)n for n ≥ 2. Terpenes are major biosynthetic building blocks. Comprising more than 30,000 compounds, these unsaturated hydrocarbons are produced predomi ...

derivative. The

hydroxyl In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydroxy ...

group in this compound is placed in an '' endo'' position. The exo diastereomer is called

isoborneol Isoborneol is a bicyclic organic compound and a terpene derivative. The hydroxyl group in this compound is placed in an ''Endo-exo isomerism, exo'' position. The endo diastereomer is called borneol. Being chiral, isoborneol exists as enantiomers. ...

. Being chiral, borneol exists as

enantiomer In chemistry, an enantiomer (Help:IPA/English, /ɪˈnænti.əmər, ɛ-, -oʊ-/ Help:Pronunciation respelling key, ''ih-NAN-tee-ə-mər''), also known as an optical isomer, antipode, or optical antipode, is one of a pair of molecular entities whi ...

s, both of which are found in nature: ''d''-borneol (also written (+)-borneol) and ''l''-borneol (or (−)-borneol).

Reactions

Borneol is

oxidized Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is ...

to the

ketone In organic chemistry, a ketone is an organic compound with the structure , where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group (a carbon-oxygen double bond C=O). The simplest ketone is acetone ( ...

(

camphor Camphor () is a waxy, colorless solid with a strong aroma. It is classified as a terpenoid and a cyclic ketone. It is found in the wood of the camphor laurel (''Cinnamomum camphora''), a large evergreen tree found in East Asia; and in the kapu ...

Occurrence

The compound was named in 1842 by the French chemist Charles Frédéric Gerhardt. Borneol can be found in several species of '' Heterotheca'', '' Artemisia'', ''Rosmarinus officinalis'' (

rosemary ''Salvia rosmarinus'' (), commonly known as rosemary, is a shrub with fragrant, evergreen, needle-like leaves and white, pink, purple, or blue flowers. It is a member of the sage family, Lamiaceae. The species is native to the Mediterranean r ...

) ''

Dipterocarpaceae Dipterocarpaceae is a family (biology), family of flowering plants with 22 genera and about 695 known species of mainly lowland tropical forest trees. Their distribution is pantropical, from northern South America to Africa, the Seychelles, India ...

'', ''

Blumea balsamifera ''Blumea balsamifera'' is a flowering plant belonging to the genus ''Blumea'' of the family Asteraceae. It is also known as Ngai camphor and sambong (also sembung). Description In the Philippines, where it is most commonly known as sambong, ''B ...

'' and ''

Kaempferia galanga ''Kaempferia galanga'', commonly known as kencur, aromatic ginger, sand ginger, cutcherry, is a monocotyledonous plant in the ginger family, and one of four plants called galangal. It is found primarily in open areas in Indonesia, southern C ...

''. It is one of the chemical compounds found in

castoreum Castoreum is a yellowish exudate from the castor sacs of mature beavers used in combination with urine to territorial marking, scent mark their territory. Both beaver sexes have a pair of castor sacs and a pair of anal glands, located in two c ...

. This compound is gathered from the beaver's plant food.

Synthesis

Borneol can be synthesized by reduction of

by the Meerwein–Ponndorf–Verley reduction (a reversible process). Industrially, a racemic mixture of camphor is used, leading to a racemic mixture of borneol and

. The chirality can be controlled by changing the chirality of camphor: (+)-camphor gives (−)-isoborneol and (+)-borneol. Reduction of camphor with

sodium borohydride Sodium borohydride, also known as sodium tetrahydridoborate and sodium tetrahydroborate, is an inorganic compound with the formula (sometimes written as ). It is a white crystalline solid, usually encountered as an aqueous basic solution. Sodi ...

(fast and irreversible) gives instead the

diastereomer In stereochemistry, diastereomers (sometimes called diastereoisomers) are a type of stereoisomer. Diastereomers are defined as non-mirror image, non-identical stereoisomers. Hence, they occur when two or more stereoisomers of a compound have di ...

. :

Natural sources

Industrially, natural (+)-borneol is produced from ''

Cinnamomum burmanni ''Cinnamomum burmanni'' (or ''Cinnamomum burmannii''), also known as Indonesian cinnamon, Padang cassia, Batavia cassia, or korintje, is one of several plants in the genus ''Cinnamomum'' whose bark is sold as the spice cinnamon. It is an evergre ...

'' (one specific chemotype) and ''

Cinnamomum camphora ''Camphora officinarum'' is a species of evergreen tree indigenous to warm temperate to subtropical regions of East Asia, including countries such as China, Taiwan, Vietnam, Korea, and Japan. It is known by various names, most notably the camph ...

''.右旋 (+)左旋 (-)合成 (racemic synthetic)
Natural (-)-borneol occurs in ''

''.

Biosynthesis

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. The chirality of borneol in a plant depends on the preferred chirality of the bornyl diphosphate synthase. Synthases for either chirality have been sequenced. A downstream product is

of either chirality, a reaction catalyzed by (+)-borneol dehydrogenase or (−)-borneol dehydrogenase.

Uses

Whereas ''d''-borneol was the

that used to be the most readily available commercially, the more commercially available enantiomer now is ''l''-borneol, which also occurs in nature. (+)-Borneol from ''

Dipterocarpus '' D. retusus'' in Köhler ''Dipterocarpus'' is a genus of flowering plants and the type genus of family Dipterocarpaceae. ''Dipterocarpus'' is the third-largest and most diverse genus among the Dipterocarpaceae. The species are well known for ...

'' spp. is used in

traditional Chinese medicine Traditional Chinese medicine (TCM) is an alternative medicine, alternative medical practice drawn from traditional medicine in China. A large share of its claims are pseudoscientific, with the majority of treatments having no robust evidence ...

. An early description is found in the

Bencao Gangmu The ''Bencao gangmu'', known in English as the ''Compendium of Materia Medica'' or ''Great Pharmacopoeia'', is an encyclopedic gathering of medicine, natural history, and Chinese herbology compiled and edited by Li Shizhen and published in the ...

. Borneol is a component of many

essential oil An essential oil is a concentrated hydrophobic liquid containing volatile (easily evaporated at normal temperatures) chemical compounds from plants. Essential oils are also known as volatile oils, ethereal oils, aetheroleum, or simply as the ...

s and it is a natural

insect repellent An insect repellent (also commonly called "bug spray" or "bug deterrent") is a substance applied to the skin, clothing, or other surfaces to discourage insects (and arthropods in general) from landing or climbing on that surface. Insect repellent ...

. It also generates a

TRPM8 Transient receptor potential cation channel subfamily M (melastatin) member 8 (TRPM8), also known as the cold and menthol receptor 1 (CMR1), is a protein that in humans is encoded by the ''TRPM8'' gene. The TRPM8 channel is the primary molecular ...

-mediated cooling sensation similar to

menthol Menthol is an organic compound, specifically a Monoterpene, monoterpenoid, that occurs naturally in the oils of several plants in the Mentha, mint family, such as Mentha arvensis, corn mint and peppermint. It is a white or clear waxy crystallin ...

. Laevo-borneol is used in perfumery. It has a balsamic odour type with pine, woody and camphoraceous facets. Dextro-borneol (dexborneol) is used in edaravone/dexborneol, a drug approved in China for stroke.

Toxicology

Borneol may cause eye, skin, and respiratory irritation; it is harmful if swallowed. 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.HAZARDOUS SUBSTANCE FACT SHEET
(PDF)

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. Skin exposure can lead to sensitization and a future

allergic reaction Allergies, also known as allergic diseases, are various conditions caused by hypersensitivity of the immune system to typically harmless substances in the environment. These diseases include Allergic rhinitis, hay fever, Food allergy, food al ...

even to small quantities.

Derivatives

The bornyl group is a univalent radical C₁₀H₁₇ derived from borneol by removal of hydroxyl and is also known as 2-bornyl. Isobornyl is the univalent radical C₁₀H₁₇ that is derived from isoborneol. The

structural isomer In chemistry, a structural isomer (or constitutional isomer in the IUPAC nomenclature) of a compound is a compound that contains the same number and type of atoms, but with a different connectivity (i.e. arrangement of bonds) between them. The ...

fenchol is also a widely used compound derived from certain

s. Bornyl acetate is the

acetate An acetate is a salt formed by the combination of acetic acid with a base (e.g. alkaline, earthy, metallic, nonmetallic, or radical base). "Acetate" also describes the conjugate base or ion (specifically, the negatively charged ion called ...

ester In chemistry, an ester is a compound derived from an acid (either organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group () of that acid is replaced by an organyl group (R). These compounds contain a distin ...

of borneol.

Notes and references

External links

NIST datasheet including full spectroscopic data

{{GABAAR PAMs Secondary alcohols Monoterpenes GABAA receptor positive allosteric modulators Bicyclic compounds Cyclopentanes Substances discovered in the 19th century