Sterane

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Numbering of the C atoms. In steranes the side chain at C-17 varies.

Steranes constitute a class of

biomarkers for the presence of eukaryotes in past ecosystems because steroids are nearly exclusively produced by eukaryotes.[3] In particular, cholestanes are diagenetic products of cholesterol in animals, while stigmastanes are diagenetic products of stigmasterols in algae and land plants.[1] However, some bacteria are now known to produce sterols and it is inferred that the ultimate origin of sterol biosynthesis is in bacteria.[4] Sterols are produced via protosterols that are direct cyclization compounds of squalene by the catalysis of oxidosqualene cyclase.[4] All known sterols in eukaryotes are enzymatically extensively modified from protosterols, while organisms that only produce protosterols are not known. The oldest record of modified steranes are in sedimentary rocks deposited ca. 720–820 million years ago.[5] In contrast, diagenetic products of protosterols (called protostanes and cyclosteranes) are widely distributed in older Proterozoic rocks and imply the presence of extinct proto-eukaryotes and/or sterol-producing bacteria before the evolution of crown-group eukaryotes.[6]

Steranes may be rearranged to diasteranes during diagenesis (C-27 to C-30, rearrangement at C-18 and C-19, no R at C-24). Oils from clastic source rocks tend to be rich in diasteranes.

Cholesterol and its derivatives (such as progesterone, aldosterone, cortisol, and testosterone), are common examples of compounds with the cyclopentanoperhydrophenanthrene nucleus.

See also

References

  1. ^ .
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  3. ^ "About biomarkers". The Summons Lab, Massachusetts Institute of Technology (MIT). November 2006. Archived from the original on 24 April 2020. Retrieved 8 October 2009.
  4. ^
    PMID 34131078
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