| Humulene | |
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2,6,6,9-Tetramethyl-1,4-8-cycloundecatriene |
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Other names
alpha-Caryophyllene; 3,7,10-Humulatriene[1] |
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| Identifiers | |
| CAS number | 6753-98-6 |
| PubChem | 5281520 |
| ChemSpider | 4444853 |
| ChEBI | CHEBI:5768 |
| ChEMBL | CHEMBL251280 |
| Jmol-3D images | Image 1 |
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| Properties[2] | |
| Molecular formula | C15H24 |
| Molar mass | 204.35 g mol−1 |
| Appearance | Pale yellowish green clear liquid |
| Density | 0.886 g/cm3 |
| Boiling point |
106-107 °C at 5 mmHg |
| Hazards | |
| MSDS | MSDS |
| LD50 | >48 mg/kg |
| (verify) (what is: /?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| Infobox references | |
Humulene, also known as α-humulene or α-caryophyllene, is a naturally occurring monocyclic sesquiterpene, which is a terpenoid consisting of 3 isoprene units. It is found in the essential oils of Humulus lupulus (hops) from which it derives its name.[3] It is an isomer of β-caryophyllene, and the two are often found together as a mixture in nature. It is also found in Lindera strychnifolia, and is one of the chemical compounds that contribute to the taste of the spice Vietnamese coriander. It also contributes to the characteristic aroma of Cannabis sativa, where it is present in the essential oil of the plant.
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Humulene is one of many sesquiterpenoids that are derived from farnesyl diphosphate (FPP). The biosynthesis begins with the loss of diphosphate from FPP under the action of sesquiterpene synthesis enzymes, generating an allylic cation that is highly susceptible to intramolecular attacks.[4]
This biosynthesis can be mimicked in the lab by preparing allylic stanane from farnesol, termed Corey synthesis. There are diverse ways to synthesize humulene in the laboratory, involving differing closures of the C-C bond in the macrocycle. The McMurry synthesis uses a titanium-catalyzed carbonyl coupling reaction; the Takahashi synthesis uses intramolecular alkylation of an allyl halide by a protected cyanohydrin anion; the Suginome synthesis utilizes a geranyl fragment; and the de Groot synthesis synthesizes humulene from a crude distillate of eucalyptus oil.[5] Humulene can also by synthesized using a combination of four-component assembly and palladium-mediated cyclization, outlined below. This synthesis is noteworthy for the simplicity of the C−C bond constructions and cyclization steps, which it is believed will prove advantageous in the synthesis of related polyterpenoids.[6]
Humulene is one of the essential oils made in the flowering cone of the hops plant. The concentration of humulene varies among different varieties of the plant. Humulene and its reaction products in the brewing process of beer is gives many beers their “hoppy” aroma. Noble hop varieties have been found to have higher levels of humulene, while other bitter hop varieties contain low levels.[7] Multiple epoxides of humulene are produced in the brewing process. In a scientific study involving GC/MS analysis of samples and a trained sensory panel, it was found that the hyrdrolysis products of humulene epoxide II specifically produces a “hoppy” aroma in beer.[8][9]
Humulene has been found to produce anti-inflammatory effects, and has potential to be an effective treatment or management tool for inflammatory diseases. It produces similar effects to dexamethazone, and was found to decrease the edema formation caused by histamine injections. Humulene also produced important inhibitory effects on tumor necrosis factor-α (TNFα) and interleukin-1 β (IL1B) generation in carrageenan-injected rats.[10]