Sesquiterpenes

Sesquiterpenes

Approximately 5000 sesquiterpenes have been reported.

Most appear to be derived from mevalonic acid, but in a few cases sesquiterpenes have been shown to come from the DOXP pathway (e.g., in Matricaria).

Sesquiterpenes are found in most plants and many fungi accumulate sesquiterpenes as well

the biosynthesis is not as well worked out as for monoterpenes, but all trans- or E-farnesyl pyrophosphate or diphosphate appears to be the intermediate in the biosynthesis of almost all other sesquiterpenes.

E-Farnesyl pyrophosphate or diphosphate ----> most sesquiterpenes

IPP is added by a prenyl transferase.

FPP-synthetase forms E-farnesyl pyrophosphate or diphosphate. An ionization mechanism is involved. The stereochemistry is pretty well nailed down.

geranyl-OPP is an intermediate, but may exist only in combination with the enzyme. The biosynthesis of sesquiterpenes is isolated from that of mono- and/or diterpenes. These last two types of terpenes are associated with plastids, whereas sesquiterpene biosynthesis is cytosolic.

FPP is a branch point leading to the synthesis of triterpenes and sterols ... and polyisoprenes.

Acyclic sesquiterpenes


These are derived by modification of uncyclized E-farnesyl pyrophosphate or diphosphate.

Cyclization by cyclases


The steps of cyclization to many of the major skeletal types probably occur through the action of specific cyclases. To date, only a few of these cyclases have been characterized.

The cyclases from Pogostemon cablin (patchouly) are probably the rate controlling step in the formation of cyclic products.

At least 80 major structural types are known. This suggests that a large number of cyclases may exist.

The results of the rearrangements and cyclizations are similar to those predicted by Wagner-Meerwein rearrangements, as in the case of monoterpenes.

Mono-, bi-, tricyclic sesquiterpenes are all common in plants and fungi.


Allelopathy


A number of sesquiterpenes are involved in plant-plant interactions.

Fungal pheromones


Compounds such as sirenin are involved in attraction of gametes in fungi of the genus Allomyces.

Phytoalexins


Several sesquiterpenoid phytoalexins have been described, mostly from the family Solanaceae.

Phytotoxins


Sesquiterpenes from fungal pathogens are sometimes active as phytotoxins, i.e., compounds that break down host tissues and release nutrients for the pathogens.

Allomones


Many sesquiterpenes play defensive roles in plant-insect and plant-fungal interactions.

Insect-related compounds

allomones

Pheromones. A number of sesquiterpenes play pheromonal roles in insects. In most cases, these involve compounds synthesized by the insects themselves, although some plant compounds may be modified or occasionally serves as components or mimics.

Juvenile hormone and mimics. Juvenile hormones in insects are biosynthesized from mevalonic acid, homomevalonic acid and related precursors. At present, juvenile hormones don't appear to occur in plants, although there are plant compounds, many of them being sesquiterpenes, that have juvenile hormone activity in insects. These mimics probably serve as allomones by interfering with normal insect development.

Essential oils


Although monoterpenes predominate in most essential oils, many also contain sesquiterpenes. This should not be interpreted as indicating that two compound classes are found in the same places in the plants, however, as this may be an artifact of the isolation process.

Picrotoxins

Some of the most complex known sesquiterpenes are picrotoxins that are found in a variety of plant families. These compounds are found in honey made by bees from plants in the Coriariaceae in New Zealand among other sources. Compounds of this series tend to be extremly toxic to humans.

Sesquiterpene lactones

Approximately 4000 sesquiterpene lactones are now known. These compounds are restricted in distribution, many have pronounced bitter taste to people, and most are relatively non-volatile crystalline solids.

Sesquiterpene Lactone Biosynthesis


The biosynthesis of this group of compounds is imperfectly known. Some steps have been examined, but many probable enzymes and intermediates have not been studied. Little known about the steps.

Distribution


Sesquiterpene lactones are most common in members of the Asteraceae (Compositae), but they are also found in the Apiaceae (Umbelliferae), and in the Magnoliaceae and its relatives.

Systematic studies


The chemistry and distribution of sesquiterpene lactones has been used to study relationships of plants in the Asteraceae.

Activity


Many of these lactones are biologically active. Some different kinds of activity include:

plant growth regulators

allelopathy

allomones

chemotactic agents

medicinal

antitumor


Related Images

Miscellaneous sesquiterpenes

Farnesyl pyrophosphate biosynthesis

Farnesyl pyrophosphate isomers

Acyclic sesquiterpenes

Origin of major sesquiterpene skeletal types 1

Origin of major sesquiterpene skeletal types 2

Monocyclic sesquiterpenes

Biosynthesis of eudesmanes and germacranes

Biosynthesis of patchoulene isomers

Cadinene biosynthesis

Bioactive sesquiterpenes

Sesquiterpene phytoalexins

Sesquiterpene phytotoxins

Insect antifeedant sesquiterpenes

Gossypol and related sesquiterpenes

Insect-derived sesquiterpenes

Marine sesquiterpenes

Insect pheromones and bioactive sesquiterpenes

Juvenile hormone biosynthesis and juvenile hormone mimics

Additional bioactive sesquiterpenes

More Bioactive Sesquiterpenes

Picrotoxinin biosynthesis

Sesquiterpene lactones 1

Sesquiterpene lactones 2

Bioactive sesquiterpene lactones

Proposed sesquiterpene lactone biosynthesis

Systematically useful sesquiterpene lactones


Lecture Slides

Plants with Sesquiterpenes



© David S. Seigler, Integrative Biology 425, Plant Secondary Metabolism, Department of Plant Biology, 265 Morrill Hall, 505 S. Goodwin Ave., University of Illinois, Urbana, Illinois 61801, USA. 217-333-7577. seigler@life.uiuc.edu.