CHOLESTANE (STEROID)

I. CHOLESTANE

                                                                           

cholestane structure                               IUPAC numbering

Cholestane : a crystalline saturated steroid hydrocarbon C₂₇H₄₈ obtained from cholesterol by reduction 

This is some cholestane:

                                 (+)-4-cholestan-3-one 98%

        
                                      5 aplha cholestan 3 ol

5 aplha cholestan 3 one crist.

                                     5 cholestane 3 one

                                 5 alpha cholestan 97 %

                                 cholestan 3b 5a 6b triol

                                      cholestane 5 aplha          

II. NORCHOLESTANE

norcholestane

Cholestane can be C₂₇ to C₃₀ and is a sterane without the R group on its chain. Norcholestane, a cholestane with one carbon missing, has some interesting uses as a biomarker. Only three series of these C₂₆ steranes are known: 21-, 24- and 27-norcholestane. 24-norcholestane has a particular source or depositional environment meaning, whereas 21- and 27- are markers for maturity. 

24-norcholestane

use as a biomarker

This compound probably has a direct biological source as corresponding sterols are commonly found in recent marine sediments. They may be associated with diatoms, or diagenetic processes having to do with diatom blooms. 24-norcholestane has been used to distinguish between marine and nonmarine sediments. In addition, the concentration of 24-nor versus the 27-norcholestanes increases in specific periods of the geological record since the Jurassic. Thus, abundances may be used as an age-diagnostic biomarker for post-Jurassic rocks and oils. 

specificity as a biomarker

specific for biological source, depositional environment and age


21- and 27-norcholestane

use as a biomarker

These compounds appear to have no direct sterol precursors, and are probably degradation products of steroids of higher carbon numbers. The ratio of C₂₁ to the sum of all the norcholestanes may be used as a maturity parameter. 

ratios considered

C₂₄ / the sum of all the norcholestanes

C₂₁ / the sum of all the norcholestanes