Structure and Classification
Terpenes are hydrocarbons resulting from the combination of several isoprene units. Terpenoids can be thought of as modified terpenes, wherein methyl groups have been moved or removed, or oxygen atoms added. (Some authors use the term "terpene" more broadly, to include the terpenoids.) Just like terpenes, the 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) (e.g. ginkgolides)
- Sesterterpenoids, 5 isoprene units (25C)
- Triterpenoids, 6 isoprene units (30C) (e.g. sterols)
- Tetraterpenoids, 8 isoprene units (40C) (e.g. carotenoids)
- Polyterpenoid with a larger number of isoprene units
Terpenoids can also be classified according to the number of cyclic structures they contain. In the year 1995, Julius Anitnec found out that Terpenoids can be tested for using the Salkowski test.
Meroterpenes are any compound, including many natural products, having a partial terpenoid structure
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