Furanocoumarin

The furanocoumarins, or furocoumarins, are a class of organic chemical compounds produced by a variety of plants. Most of the plant species found to contain furanocoumarins belong to a handful of plant families. The families Apiaceae and Rutaceae include the largest numbers of plant species that contain furanocoumarins. The families Moraceae and Fabaceae include a few, widely distributed plant species that contain furanocoumarins.[1]

Psoralen
Angelicin
Two furanocoumarin isomers

Generally furanocoumarins are most abundant in plants that have flowered and in ripe seeds and fruits.[1] (An exception is the common fig where furanocoumarins are found chiefly in the milky sap of the leaves and shoots but not the fruits.[2]) During the early stages of plant growth their presence is not easily detected.

Structure

The chemical structure of furanocoumarins consists of a furan ring fused with a coumarin. The furan ring may be fused in various ways producing several different isomers. The parent compounds of the most common isomers are psoralen and angelicin. Derivatives of these two compounds are referred to respectively as linear and angular furanocoumarins,[3] so called since they exhibit a linear or angular chemical structure.

Biosynthesis

The compounds are biosynthesized partly through the phenylpropanoid pathway and the mevalonate pathway, which is biosynthesized by a coupling of dimethylallyl pyrophosphate (DMAPP) and 7-hydroxycoumarin (umbelliferone).

Effects

Direct toxicity

Many furanocoumarin compounds are toxic. The phytochemicals enter the nucleus of epithelial cells and form a bond (crosslinking) with the DNA when exposed to UV, which causes the cells to die. The result is known as phytophotodermatitis, a serious skin inflammation.

Furanocoumarins may be produced by plants as a defense mechanism against predators such as insects and mammals.[4][5] It is also likely that furanocoumarins are related to a plant's natural defense against fungal attack.[6] In particular, the linear furanocoumarins (psoralen, bergapten, and methoxsalen), which occur naturally in Apiaceae, Rutaceae, and other plant families, are known to be toxic to fungi.[7] Plants that cause phytophotodermatitis usually contain linear furanocoumarins.[6]

Furanocoumarins are found in the sap of plants such as Ammi majus, parsnip, and giant hogweed. At least 36 species of the genus Heracleum in the family Apiaceae are known to contain one or more furanocoumarin compounds.[8]

Medication interactions

Furanocoumarins have other biological effects as well. For example, in humans, bergamottin and 6',7'-dihydroxybergamottin are responsible for the "grapefruit juice effect", in which these furanocoumarins affect certain P450 liver and gut enzymes, such as the inhibition of CYP3A4 which either activates or deactivates many drugs, thus leading to higher or lower levels in the bloodstream.[9] Furanocoumarins have various effects which can specifically increase or decrease (depending on the drug) the blood levels of many pharmaceuticals in ways that can be life-threatening and so FDA approved drugs will include warnings for grapefruit.

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See also

References
  1. Pathak, M. A.; Daniels Jr., Farrington; Fitzpatrick, T. B. (September 1962). "The Presently Known Distribution of Furocoumarins (Psoralens) in Plants". Journal of Investigative Dermatology. 39 (3): 225–239. doi:10.1038/jid.1962.106. PMID 13941836.
  2. Zaynoun, S. T.; Aftimos, B. G.; Abi Ali, L.; Tenekjian, K. K.; Khalidi, U.; Kurban, A. K. (July 1984). "Ficus carica; isolation and quantification of the photoactive components". Contact Dermatitis. 11 (1): 21–25. doi:10.1111/j.1600-0536.1984.tb00164.x. PMID 6744838. Cited in McGovern and Barkley 2000, section Phytophotodermatitis.
  3. IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version:  (2006–) "furanocoumarins". doi:10.1351/goldbook.F02558 IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version:  (2006–) "furocoumarins". doi:10.1351/goldbook.F02562
  4. Berenbaum, May (June 14, 2010). "Furanocoumarins as potent chemical defenses".
  5. Cox, George W. (2004). Alien species and evolution: the evolutionary ecology of exotic plants, animals, microbes, and interacting native species. Island Press. p. 125. ISBN 978-1-55963-009-2.
  6. McGovern, Thomas W.; Barkley, Theodore M. (2000). "Botanical Dermatology". The Electronic Textbook of Dermatology. Internet Dermatology Society. Section Phytophotodermatitis. Retrieved November 29, 2018.
  7. Camm, E. L.; Wat, C. K.; Towers, G. H. N. (1976). "An assessment of the roles of furanocoumarins in Heracleum lanatum". Can. J. Bot. 54 (22): 2562–2566. doi:10.1139/b76-275.
  8. Mitchell, John; Rook, Arthur (1979). Botanical Dermatology: Plants and Plant Products Injurious to the Skin. Vancouver: Greengrass. pp. 692–699.
  9. Kakar, SM; Paine, MF; Stewart, PW; Watkins, PB (2004). "6',7'-Dihydroxybergamottin contributes to the grapefruit juice effect". Clinical Pharmacology and Therapeutics. 75 (6): 569–579. doi:10.1016/j.clpt.2004.02.007. PMID 15179411.
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