Diterpenes are a class ofterpenes composed of fourisoprene units, often with the molecular formula C20H32. They are biosynthesized by plants, animals and fungi via theHMG-CoA reductase pathway, withgeranylgeranyl pyrophosphate being a primary intermediate. Diterpenes form the basis for biologically importantcompounds such asretinol,retinal, andphytol. Some diterpenes areantimicrobial andanti-inflammatory.[1][2]
As with most terpenes a huge number of potential structures exists, which may be broadly divided according to the number of rings present.
| Number of rings | Examples |
|---|---|
| 0 | Phytane |
| 1 | Cembrene A |
| 2 | Sclarene,Labdane |
| 3 | Abietane,Taxadiene |
| 4 | Stemarene,Stemodene |
Diterpenes are derived from the addition of oneIPP unit toFPP to formgeranylgeranyl pyrophosphate (GGPP). From GGPP, structural diversity is achieved mainly by two classes of enzymes; the diterpene synthases andcytochromes P450. Several diterpenes are produced by plants andcyanobacteria. GGPP is also the precursor for the synthesis of thephytane by the action of the enzyme geranylgeranyl reductase. This compound is used for the biosynthesis oftocopherols and thephytyl functional group is used in the formation ofchlorophylla,ubiquinones,plastoquinone andphylloquinone.[3]
Diterpenes are formally defined as beinghydrocarbons and thus contain no heteroatoms. Functionalized structures should instead be called diterpenoids,[4] although in scientific literature the two terms are often used interchangeably. Although a wide range of terpene structures exist, few of them are biologically significant; by contrast, diterpenoids possess a rich pharmacology and include important compounds such asretinol,phytol ortaxadiene.
Taxanes are class of diterpenoids featuring ataxadiene core. They are produced by plants of the genusTaxus (yew trees) and are widely used aschemotherapy agents.[5]
