Isoprenoids, sometimes called terpenes, are a large and diverse class of naturally-occurring organic chemicals similar to terpenes, derived from five-carbon isoprene units assembled and modified in thousands of ways. Most are multicyclic structures that differ from each other not only in functional groups, but also in their basic carbon skeletons. These lipids can be found in all classes of living things, and they are the largest group of natural products. About 60% of known natural products are terpenoids.
Terpenoids from the plant are used widely for their aromatic qualities and play a role in traditional herbal remedies. Terpenoids contribute to the scent of eucalyptus, the flavors of cinnamon, cloves and ginger, the yellow color in sunflowers, and the red color in tomatoes. Known terpenoids include citral, menthol, camphor, salvinorin A in the Salvia divinorum plant, the cannabinoids found in cannabis, ginkgolide and bilobalide found in Ginkgo biloba, and the curcuminoids found in turmeric and mustard seed.
Steroids and sterols in animals are biologically produced from terpenoid precursors. Terpenoids are sometimes added to proteins, for example, to improve their attachment to the cell membrane; This is known as isoprenylation.
Isoprenoids are hydrocarbons resulting from the condensation of several 5-carbon isoprene units. The isoprene unit has the formula CH2 = C (CH3) CH = CH2. Terpenoids can be viewed as modified terpenes, in which methyl groups have been moved or removed, or oxygen atoms have been added. Like terpenes, terpenoids can be classified according to the number of isoprene units used:
- Hemiterpenoids, 1 isoprene unit (5 carbons).
- Monoterpenoids, 2 isoprene units (10C).
- Sesquiterpenoids, 3 isoprene units (15C).
- Diterpenoids, 4 isoprene units (20C) (for example ginkgolides).
- Sesterterpenoids, 5 isoprene units (25C).
- Triterpenoids, 6 isoprene units (30C) (for example, sterols).
- Tetraterpenoids, 8 isoprene units (40C) (eg carotenoids).
- Polyterpenoid with a higher number of isoprene units.
Terpenoids can also be classified according to the number of cyclic structures they contain. The Salkowski test can be used to identify the presence of terpenoids.
Meroterpenes are any compound, including many natural products, that have a partial terpenoid structure.
