What are the properties of Terpenes in supplements?

Terpenes are a class of natural products consisting of compounds with the formula (C₅H₈)_n. Comprising more than 30,000 compounds, these unsaturated hydrocarbons are produced predominantly by plants, particularly conifers. Terpenes are further classified by the number of carbons: monoterpenes (C₁₀), sesquiterpenes (C₁₅), diterpenes (C₂₀), etc. A well known monoterpene is alpha-pinene, a major component of turpentine.

Still more numerous than terpenes is a class of compounds called “terpenoids”. Terpenoids are terpenes that have been modified with (usually oxygen-containing) functional groups. The terms terpenes and terpenoids are used interchangeably. Both have strong and often pleasant odors, which may protect their hosts or attract pollinators. The inventory of terpenes and terpenoids is estimated at 55,000 chemical entities.

Terpenes may be classified by the number of isoprene units in the molecule; a prefix in the name indicates the number of isoprene pairs needed to assemble the molecule. Commonly, terpenes contain 2, 3, 4 or 6 isoprene units; the tetraterpenes (8 isoprene units) form a separate class of compounds called carotenoids; the others are rare. The classification is formalistic only; nothing may be inferred about their properties, uses or occurrence.

• Hemiterpenes consist of a single isoprene unit. Isoprene itself is considered the only hemiterpene, but oxygen-containing derivatives such as prenol and isovaleric acid are hemiterpenoids.
• Monoterpenes consist of two isoprene units and have the molecular formula C₁₀H₁₆. Examples of monoterpenes and monoterpenoids include geraniol, terpineol (present in lilacs), limonene (present in citrus fruits), myrcene (present in hops), linalool (present in lavender), hinokitiol (present in cypress trees) or pinene (present in pine trees). Iridoids derive from monoterpenes. Examples of iridoids include aucubin and catalpol.
• Sesquiterpenes consist of three isoprene units and have the molecular formula C₁₅H₂₄. Examples of sesquiterpenes and sesquiterpenoids include humulene, farnesenes, farnesol, geosmin. (The sesqui- prefix means one and a half.)
• Diterpenes are composed of four isoprene units and have the molecular formula C₂₀H₃₂. They derive from geranylgeranyl pyrophosphate. Examples of diterpenes and diterpenoids are cafestol, kahweol, cembrene and taxadiene (precursor of taxol). Diterpenes also form the basis for biologically important compounds such as retinol, retinal, and phytol.
• Sesterterpenes, terpenes having 25 carbons and five isoprene units, are rare relative to the other sizes. (The sester- prefix means two and a half.) An example of a sesterterpenoid is geranylfarnesol.
• Triterpenes consist of six isoprene units and have the molecular formula C₃₀H₄₈. The linear triterpene squalene, the major constituent of shark liver oil, is derived from the reductive coupling of two molecules of farnesyl pyrophosphate. Squalene is then processed biosynthetically to generate either lanosterol or cycloartenol, the structural precursors to all the steroids.
• Sesquarterpenes are composed of seven isoprene units and have the molecular formula C₃₅H₅₆. Sesquarterpenes are typically microbial in their origin. Examples of sesquarterpenoids are ferrugicadiol and tetraprenylcurcumene.
• Tetraterpenes contain eight isoprene units and have the molecular formula CC₄₀H₆₄40H₆₄. Biologically important tetraterpenoids include the acyclic lycopene, the monocyclic gamma-carotene, and the bicyclic alpha- and beta-carotenes.
• Polyterpenes consist of long chains of many isoprene units. Natural rubber consists of polyisoprene in which the double bonds are cis. Some plants produce a polyisoprene with trans double bonds, known as gutta-percha.
• Norisoprenoids, such as the C₁₃-norisoprenoid 3-oxo-α-ionol present in Muscat of Alexandria leaves and 7,8-dihydroionone derivatives, such as megastigmane-3,9-diol and 3-oxo-7,8-dihydro-α-ionol found in Shiraz leaves (both grapes in the species Vitis vinifera) or wine (responsible for some of the spice notes in Chardonnay), can be produced by fungal peroxidases or glycosidases.