Sesquiterpene

Big Sagebrush (Artemisia tridentata) contains sesquiterpene lactones which are sesquiterpenoids (built from three isoprene units) and contain a lactone ring, hence the name. These compounds are found in many other plants and can cause allergic reactions and toxicity if overdosed, particularly in grazing livestock.

Phallus indusiatus, in Cooktown, Queensland, Australia, which produces two novel sesquiterpenes

Sesquiterpenes are a class of terpenes that consist of three isoprene units and have the empirical formula C₁₅H₂₄. Like monoterpenes, sesquiterpenes may be acyclic or contain rings, including many unique combinations. Biochemical modifications such as oxidation or rearrangement produce the related sesquiterpenoids.

Sesquiterpenes are found naturally in plants and insects, as semiochemicals, e.g. defensive agents or pheromones.

Acyclic

The reaction of geranyl pyrophosphate with isopentenyl pyrophosphate results in the 15-carbon farnesyl pyrophosphate which is an intermediate in the biosynthesis of sesquiterpenes such as farnesene. Oxidation of farnesene then provides sesquiterpenoids such as farnesol.

File:Farnesylpyrophosphat.svg

Farnesyl pyrophosphate

Monocyclic

There are more cyclic sesquiterpenes than cyclic monoterpenes because of the increased chain length and additional double bond. In addition to common six-membered ring systems such as is found in zingiberene (a constituent of the oil from ginger), cyclization of one end of the chain to the other end can lead to macrocyclic rings such as humulene.

Bicyclic

δ-Cadinene, a sesquiterpene

The cadinenes contain two fused six-membered rings. Caryophyllene, a component of many essential oils such as clove oil, contains a nine-membered ring fused to a cyclobutane ring.

Vetivazulene and guaiazulene are aromatic bicyclic sesquiterpenoids.

Tricyclic

With the addition of a third ring, the possible structures become increasingly varied. Examples include longifolene, copaene and the alcohol patchoulol.

Dictyophorine A and B

Two sesquiterpenes named dictyophorine A and B were identified from the fungus Phallus indusiatus. These compounds are based on the eudesmane skeleton (a common structure found in plant-derived flavors and fragrances), and they are the first eudesmane derivatives isolated from fungi. The dictyophorines promote the synthesis of nerve growth factor in astroglial cells.

External links

• Sesquiterpenes at the US National Library of Medicine Medical Subject Headings (MeSH)