Farnesene

The term farnesene refers to a set of six closely related chemical compounds which all are sesquiterpenes. α-Farnesene and β-farnesene are isomers, differing by the location of one double bond. α-Farnesene is 3,7,11-trimethyl-1,3,6,10-dodecatetraene and β-farnesene is 7,11-dimethyl-3-methylene-1,6,10-dodecatriene. The alpha form can exist as four stereoisomers that differ about the geometry of two of its three internal double bonds (the stereoisomers of the third internal double bond are identical). The beta isomer exists as two stereoisomers about the geometry of its central double bond.

All four of the α-farnesene stereoisomers are reported to occur in nature with (E,E)-α-Farnesene the most common isomer. It is found in the coating of apples, and other fruits, and it is responsible for the characteristic green apple odour[1] and more extensively described as "citrus, herbal, lavender, bergamot, myrrh, neroli, green, woody, vegetable, floral".[2] Its oxidation by air forms compounds that are damaging to the fruit. The oxidation products injure cell membranes which eventually causes cell death in the outermost cell layers of the fruit, resulting in a storage disorder known as scald. α-Farnesene is also the chief compound contributing to the scent of gardenia, making up ~65% of the headspace constituents.[3]

Another stereoisomer, (Z,E)-α-Farnesene (CAS 26560-14-5), has been isolated from the oil of perilla.[4] Both the (E,E) and (Z,E)-α-Farnesene isomers are known insect semiochemicals; they act as alarm pheromones in termites[5] or food attractants for the apple tree pest, the codling moth.[6] The (E,Z)-α-Farnesene isomer (CAS 28973-98-0) is also found in plants sources.[7]

β-Farnesene has one naturally occurring isomer. The E isomer is a constituent of various essential oils. It is also released by aphids as an alarm pheremone upon death to warn away other aphids.[8] Several plants, including potato species, have been shown to synthesize this pheromone as a natural insect repellent.[9] Recently renewable aviation fuel (synthetic iso-paraffin) has been produced through c6 sugars being converted to Farnesene, which is then hydrotreated. Making it a highly promising biofuel precursor.

## See also

* Farnesol
* Geranylfarnesol
* Nerolidol
* Prenylation
* Terpene

## References

1. ↑ HUELIN, F.E.; Murray, K.E. (18 June 1966). "α-Farnesene in the Natural Coating of Apples". Nature 210 (5042): 1260–1261. doi:10.1038/2101260a0. PMID 5967802. Bibcode: 1966Natur.210.1260H.
2. ↑ "alpha-farnesene". Scents and Flavors. https://scentsandflavors.com/database/9dbb51a7-9588-4c1f-8546-cda6e04927c4.
3. ↑ Liu, BZ; Gao, Y (September 2000), "Analysis of headspace constituents of Gardenia flower by GC/MS with solid-phase microextraction and dynamic headspace sampling", Chinese Journal of Chromatography 18 (5): 452–455, PMID 12541711
4. ↑ "(Z,E)-alpha-farnesene". Scents and Flavors. https://scentsandflavors.com/database/9dbb572c-9de3-4321-bdc7-27c177fdf5aa#organoleptic-properties.
5. ↑ Šobotník, J.; Hanus, R.; Kalinová, B.; Piskorski, R.; Cvačka, J.; Bourguignon, T.; Roisin, Y. (April 2008), "(E,E)-α-Farnesene, an Alarm Pheromone of the Termite Prorhinotermes canalifrons", Journal of Chemical Ecology 34 (4): 478–486, doi:10.1007/s10886-008-9450-2, PMID 18386097, Bibcode: 2008JCEco..34..478S
6. ↑ Hern, A.; Dorn, S. (July 1999), "Sexual dimorphism in the olfactory orientation of adult Cydia pomonella in response to alpha-farnesene", Entomologia Experimentalis et Applicata 92 (1): 63–72, doi:10.1046/j.1570-7458.1999.00525.x, Bibcode: 1999EEApp..92...63H
7. ↑ "(E,Z)-alpha-farnesene". Scents and Flavors. https://scentsandflavors.com/database/9dbb572c-94b4-453c-84db-53fcdba6adae#organoleptic-properties.
8. ↑ Gibson, R. W.; Pickett, J. A. (14 April 1983), "Wild potato repels aphids by release of aphid alarm pheromone", Nature 302 (5909): 608–609, doi:10.1038/302608a0, Bibcode: 1983Natur.302..608G
9. ↑ Avé, D. A.; Gregory, P.; Tingey, W. M. (July 1987), "Aphid repellent sesquiterpenes in glandular trichomes of Solanum berthaultii and S. tuberosum", Entomologia Experimentalis et Applicata 44 (2): 131–138, doi:10.1111/j.1570-7458.1987.tb01057.x, Bibcode: 1987EEApp..44..131A

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