**5.6. Triterpenes**

They consist of *six isoprene* units and have the molecular formula C30H48 (see **Figure 13**). The linear triterpene squalene, the major constituent of shark liver oil, is derived from the reductive coupling of two molecules of farnesyl pyrophosphate. Triterpenes constitute a significant portion of the lipid substances of all plants; more than 4000 triterpenoids have been isolated. These compounds are precursors to steroids in both plants and animals. Both triterpenes and steroids occur free, as glycosides or in other combined forms. The structures of triterpenes and steroids may be subdivided into about 40 major types [1]. β-Boswellic acids (ursanetype triterpene) and α-boswellic acids (oleanane-type triterpene) that are isolated from the oleo-gum-resin of *Boswellia carterii* are known for their anti-inflammatory and anti-rheumatic activities [38].

**Figure 13.** Example of triterpene.

One group of compounds showing a range of interesting biological activity is the quassinoids isolated from *Quassia amara*. These are degradation and rearrangement products of triterpenes. Quassia is used as a bitter tonic, as an insecticide and as an enema for the expulsion of thread worms.

Terpenes also include sesquarterpenes (*seven isoprene* units, C35H56), tetraterpenes (*eight isoprene* units, C40H64) as well as polyterpenes and norisoprenoids (long chains of *many isoprene* units.
