Eugenol/ˈjuːdʒɪnɒl/ is an allyl chain-substituted guaiacol, a member of the allylbenzene class of chemical compounds.[2] It is a colorless to pale yellow, aromatic oily liquid extracted from certain essential oils especially from clove, nutmeg, cinnamon, basil and bay leaf.[3][4][5][6] It is present in concentrations of 80–90% in clove bud oil and at 82–88% in clove leaf oil.[7] Eugenol has a pleasant, spicy, clove-like scent.[8] The name is derived from Eugenia caryophyllata, the former Linnean nomenclature term for cloves. The currently accepted name is Syzygium aromaticum.[9]
Eugenol and thymol possess general anesthetic properties. Like many other anesthetic agents, these 2-alkyl(oxy)phenols act as positive allosteric modulators of the GABAA receptor. Although eugenol and thymol are too toxic and not potent enough to be used clinically, these findings led to the development of 2-substituted phenol anesthetic drugs, including propanidid (later withdrawn) and the widely used propofol.[12] Eugenol and the structurally similar myristicin, have the common property of inhibiting MAO-A and MAO-B in vitro.[13][14]
In humans, complete excretion occurs within 24 hour and metabolites are mostly conjugates of eugenol.[15]
It is attractive to males of various species of orchid bees, which apparently gather the chemical to synthesize pheromones; it is commonly used as bait to attract and collect these bees for study.[21] It also attracts female cucumber beetles.[22]
Eugenol and isoeugenol, which both are floral volatile scent compounds, are catalyzed by a single type of enzyme in the genus Gymnadenia and the gene encoding for this enzyme is the first functionally characterized gene in these species.[23] Eugenol is an ingredient in some insecticides.[2]
Clove oil is common as an anaesthetic for use on aquarium fish as well as on wild fish when sampled for research and management purposes.[24][25] Where readily available, it presents a humane method to euthanise sick and diseased fish either by direct overdose or to induce sleep before an overdose of eugenol.[26]
Eugenol is subject to restrictions on its use in perfumery[28] as some people may become sensitised to it, however, the degree to which eugenol can cause an allergic reaction in humans is disputed.[29]
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^Tsuchiya H (August 2017). "Anesthetic Agents of Plant Origin: A Review of Phytochemicals with Anesthetic Activity". Molecules. 22 (8): 1369. doi:10.3390/molecules22081369. PMC6152143. PMID28820497.
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