Oleanane
From Wikipedia, the free encyclopedia
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| Names | |
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| IUPAC name
Oleanane[1] | |
| Systematic IUPAC name
(4aR,6aR,6bR,8aS,12aS,12bR,14aR,14bS)-2,2,4a,6a,6b,9,9,12a-Octamethyldocosahydropicene | |
| Identifiers | |
| ChEBI | |
| ChemSpider | |
PubChem CID |
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| UNII | |
CompTox Dashboard (EPA) |
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| Properties | |
| C30H52 | |
| Molar mass | 412.746 g·mol−1 |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Oleanane is a natural triterpenoid. It is commonly found in woody angiosperms and as a result is often used as an indicator of these plants in the fossil record. It is a member of the oleanoid series, which consists of pentacyclic triterpenoids (such as beta-amyrin and taraxerol[verification needed]) where all rings are six-membered.
Oleanane is a pentacyclic triterpenoid, a class of molecules made up of six connected isoprene units. The naming of both the ring structures and individual carbon atoms in oleanane is the same as in steroids. As such, it consists of a A, B, C, D, and E ring, all of which are six-membered rings.[2][failed verification]
The structure of oleanane contains a number of different methyl groups, that vary in orientation between different oleananes. For example, in 18-alpha-oleanane contains a downward facing methyl group for the 18th carbon atom, while 18-beta-oleanane contains an upward facing methyl group at the same position.
A and B rings of the oleanane structure are identical to that of hopane. As a result, both molecules produce a fragment of m/z 191. Because this fragment is often used to identify hopanes, oleanane can be mis-identified in hopane analysis.
Synthesis
Like other triterpenoids, are formed from six combined isoprene units.[2] These isoprene units can be combined via a number of different pathways. In eukaryotes (including plants), this pathway is the mevalonate (MVA) pathway. For the formation of steroids and other triterpenoids the isoprenoids are combined into a precursor known as squalene, which then undergoes enzymatic cyclization to produce the various different triterpenoids, including oleanane.[2]
Once the oleananes have been transported into rocks or sediments they will undergo further alteration before they are measured.
Measurement in Rock Samples
Oleananes can be identified in extracts from rock samples (or plants) using GC/MS. A GC/MS is a gas chromatograph coupled with a mass spectrometer. The sample is first injected into the system, then run through as chromatographic column. How fast a material moves through a chromatographic column depends on how long it spends in each of the two stages there. Compounds that partition more into the mobile phase will move faster as opposed to compounds that partition more into the stationary phase. The result of this is a separation of different organic molecules based on their retention time in the GC.
After being separated by the GC, the compounds can then be analyzed by a mass spectrometer. Each compound will contain a characteristic mass spectrum, based on the fragments it splits into during ionization in the mass spectrometer. This means that the GC can not only separate different types of molecules, it can also identify them.
As mentioned above, they have a characteristic mass fragment at m/z = 191, and thus will appear in the same selected ion chromatograph (SIC) as hopanes. This can help one identify them in GC/MS datasets.