- Sesquiterpene
Sesquiterpenes are a class of
terpene s that consist of threeisoprene units and have the molecular formula C15H24. Likemonoterpenes , sesquiterpenes may be acyclic or contain rings, including many unique combinations. Biochemical modifications such as oxidation or rearrangement produce the related sesquiterpenoids.Acyclic
Biosynthetically, when
geranyl pyrophosphate reacts withisopentenyl pyrophosphate , the result is the 15-carbonfarnesyl pyrophosphate which is an intermediate in the biosynthesis of sesquiterpenes such asfarnesene . Oxidation can then provide sesquiterpenoids such asfarnesol . Sesquiterpenes are found naturally in plants as defensive agents.Monocyclic
With the increased chain length and additional double bond, the number of possible ways that cyclization can occur is also increased and there exist a wide variety of cyclic sesquiterpenes. In addition to common six-membered ring systems such as is found in
zingiberene , a consitituent of the oil fromginger , cyclization of one end of the chain to the other end can lead to macrocyclic rings such ashumulene .Bicyclic
In addition to common six-membered rings such as in the
cadinene s, one classic bicyclic sesquiterpene iscaryophyllene , from the oil ofclove s, which has a nine-membered ring andcyclobutane ring. Additional unsaturation provides aromatic bicyclic sesquiterpenoids such asvetivazulene andguaiazulene .Tricylic
With the addition of a third ring, the possible structures become increasingly varied. Examples include
longifolene ,copaene and the alcoholpatchoulol .
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