isoprene

Definition: Isoprene, short for isoterpene (see terpene), is a common organic compound with the formula CH2=C(CH3)CH=CH2 (C5H8).

Isoprene (short for isoterpene), or 2-methyl-1,3-butadiene, is a common organic compound with the formula CH2=C(CH3)CH=CH2.

Under standard conditions it is a colorless liquid. However, this compound is highly volatile because of its low boiling point.

Isoprene (C5H8) is the monomer of natural rubber and also a common structure motif to an immense variety of other naturally occurring compounds, collectively termed the isoprenoids.

Molecular formula of isoprenoids are multiples of isoprene in the form of (C5H8)n, and this is termed the isoprene rule. The functional isoprene units in biological systems are dimethylallyl diphosphate (DMADP) and its isomer isopentenyl diphosphate (IDP).

The singular terms “isoprene” and “terpene” are synonymous whereas the plurals “isoprenes” or “terpenes” refer to terpenoids (isoprenoids).

It is formally described as 2-methyl-1,3-butadiene, showing that it is structurally related to butadiene. This colourless liquid is the precursor (monomer) to an immense variety of naturally-occurring compounds ranging from camphor to natural rubber.

Isoprene (C5H8) is a common synonym for the chemical compound 2-methylbuta-1,3-diene and is an important biological material. Isoprene is a common structural motif in biological systems.

Isoprene is formed naturally in animals and plants and is generally the most common hydrocarbon found in the human body.

The estimated production rate of isoprene in the human body is 0.15 µmol/kg/h, equivalent to approximately 17 mg/day for a 70 kg person. Isoprene is also common in low concentrations in many foods.

In humans

Isoprene is generally the most common hydrocarbon found in the human body. The estimated production rate of isoprene in the human body is 0.15 µmol/kg/h, equivalent to approximately 17 mg/day for a 70 kg person. Isoprene is also common in low concentrations in many foods.

It is a common structural motif in biological systems. The terpenes (for example, the carotenes are tetraterpenes) are derived from isoprene, as are the terpenoids and coenzyme Q.

Also derived from isoprene are phytol, retinol (vitamin A), tocopherol (vitamin E), dolichols, and squalene. Heme A has an isoprenoid tail, and lanosterol, the sterol precursor in animals, is derived from squalene and hence from isoprene.

The functional isoprene units in biological systems are dimethylallyl pyrophosphate (DMAPP) and its isomer isopentenyl pyrophosphate (IPP), which are used in the biosynthesis of terpenes and lanosterol derivatives.

In virtually all organisms, isoprene derivatives are synthetised by the HMG-CoA reductase pathway. Addition of these chains to proteins is termed isoprenylation.

Terpens

The terpenes (for example, the carotenes are tetraterpenes) are derived from isoprene, as are the terpenoids and coenzyme Q.

Also derived from isoprene are phytol, retinol (vitamin A), tocopherol (vitamin E), dolichols, and squalene.

Heme A has an isoprenoid tail, and lanosterol, the sterol precursor in animals, is derived from squalene and hence from isoprene.

The functional isoprene units in biological systems are dimethylallyl pyrophosphate (DMAPP) and its isomer isopentenyl pyrophosphate (IPP), which are used in the biosynthesis of terpenes and lanosterol derivatives.

In virtually all organisms, isoprene derivatives are synthetised by the HMG-CoA reductase pathway.

Isoprenylation

Addition of these chains to proteins is termed isoprenylation.

HMG-CoA reductase inhibitors

Mevalonate is a precursor to isopentenyl pyrophosphate (IPP), which combines with its isomer, dimethylallyl pyrophosphate (DMAPP), in repeating alternations to form isoprene (or polyprenyl) chains.

HMG-CoA reductase inhibitors, also known as the group of cholesterol-lowering drugs called statins, inhibit the synthesis of mevalonate.

Statins are used to lower cholesterol, which is synthesized from the 15-carbon isoprenoid, farnesyl pyrophosphate, but also inhibit all other isoprenes, including coenzyme Q10.

In plants

Isoprene is produced in the chloroplasts of leaves of certain tree species through the DMAPP pathway; the enzyme isoprene synthase is responsible for its biosynthesis.

The amount of isoprene released from isoprene-emitting vegetation depends on leaf mass, leaf area, light (particularly photosynthetic photon flux density, or PPFD), and leaf temperature.

Thus, during the night, little isoprene is emitted from tree leaves whereas daytime emissions are expected to be substantial ( 5–20 mg/m2/h) during hot and sunny days.

Isoprene is produced in the chloroplasts of leaves of certain tree species through the DMAPP pathway; the enzyme isoprene synthase is responsible for its biosynthesis.

The amount of isoprene released from isoprene-emitting vegetation depends on leaf mass, leaf area, light (particularly photosynthetic photon flux density), and leaf temperature. Thus, during the night, little isoprene is emitted from tree leaves while daytime emissions are expected to be substantial ( 5-20 mg/m2/h) during hot and sunny days.

Natural rubber is a polymer of isoprene - most often cis-1,4-polyisoprene - with a molecular weight of 100,000 to 1,000,000.

Some natural rubber sources called gutta percha are composed of trans-1,4-polyisoprene, a structural isomer which has similar, but not identical properties.

Isoprene was first isolated by thermal decomposition of natural rubber. It is most readily available industrially as a byproduct of the thermal cracking of naphtha or oil, as a side product in the production of ethylene. About 20M kg are produced annually. About 95% of isoprene production is used to produce cis-1,4-polyisoprene—a synthetic version of natural rubber.

Derived from isoprene

 terpenes

• carotenes are tetraterpenes

 terpenoids
 coenzyme Q
 phytol
 retinol (vitamin A)
 tocopherol (vitamin E)
 dolichols
 squalene
  heme A (isoprenoid tail)
 lanosterol (sterol precursor derived from squalene)

In virtually all organisms, isoprene derivatives are synthetised by the HMG-CoA reductase pathway.

Isoprenylation

Addition of isoprene chains to proteins is termed isoprenylation.

See also

 biosynthesis of cholesterol
 hydrocarbon
 isoprenylation