C5H8, IUPAC 2-methylbuta-1,3-diene, a liquid, boiling point 34°C. Natural rubber may be considered an addition polymer of isoprene. It is also the basic structural unit of terpene molecules.
At room temperature, isoprene is a colorless liquid which is highly flammable and easily ignited. The United States Department of Transportation considers isoprene a hazardous material and requires special marking, labeling, and transportation for it. About 95% of isoprene production is used to produce cis-1,4-polyisoprene - a synthetic version of natural rubber.
Natural rubber is a polymer of isoprene - most often cis-1,4-polyisoprene - with a molecular weight of 100,000 to 1,000,000.
Biological roles and effects
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 15 µmol/kg/h, equivalent to approximately 17 mg/day for a 70 kg person. The amount of isoprene released from isoprene-emitting vegetation depends on leaf mass, leaf area, light (particularly photosynthetic photon flux density), and leaf temperature.
With a global biogenic production in the range of 350–500 Tg of carbon/year, isoprene has a large impact on atmospheric processes and is thus an important compound in the field of Atmospheric Chemistry. Isoprene affects the oxidative state of large air masses, is an important precursor for ozone, a pollutant in the lower atmosphere. Furthermore, isoprene forms secondary organic aerosols through photooxidation with OH radicals which also have wide-ranging health effects, particularly for the respiratory tract, and reduce visibility due to light scattering effects. Because of its atmospheric importance, much work has been devoted to emission studies from isoprene-emitting vegetation, and, kinetic and mechanistic studies of isoprene oxidation via OH radicals, ozone, and NO3 radicals. 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.
According to the United States Department of Health and Human Services Eleventh Edition Report on Carcinogens, isoprene is reasonably expected to be a human carcinogen. No adequate human studies of the relationship between isoprene exposure and human cancer have been reported. Mevalonate is a precursor to isopentenyl pyrophosphate, which combines with its isomer, dimethylallyl pyrophosphate, in repeating alternations to form isoprene (or polyprenyl) chains.
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. This flow chartshows the biosynthesis of isoprenes, and the point at which statins act to inhibit this process.
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