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Synthesis of 26-methyl cholestane and identification of cryostanes in mid-Neoproterozoic sediments.

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Title: Synthesis of 26-methyl cholestane and identification of cryostanes in mid-Neoproterozoic sediments.
Authors: Adam, Pierre1 padam@unistra.fr, Schaeffer, Philippe1, Brocks, Jochen J.2
Source: Organic Geochemistry. Jan2018, Vol. 115, p246-249. 4p.
Subjects: Cholestanes, Marine sediments, Steranes, Gas chromatography, Mass spectrometry, Molecular clock
Abstract: The biomarker distributions of mid-Neoproterozoic sediments (800–717 million yr, Ma) from various locations are characterized by the occurrence, besides cholestane isomers, of a novel series of C 28 steranes, whereas classical C-24 alkylated steranes are absent. These unusual C 28 steranes, termed cryostanes, seem to be restricted to pre-Snowball Earth sediments. We report their conclusive identification as 26-methyl cholestanes based on comparison of gas chromatographic (GC) behavior and mass spectrum of the last eluting cryostane isomer with those of a 26-methyl 5α(H),14α(H),17α(H),20 R -cholestane standard obtained by way of synthesis. Sterols methylated at C-26 seem to be restricted to some demosponges and, based on molecular clock estimates, demosponges may have emerged in the time interval 800–700 Ma. A sponge origin of cryostanes is thereby conceivable, making cryostanes the oldest molecular markers for animals. However, other biological sources need to be explored, including the wide variety of eukaryotic protists. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
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Abstract:The biomarker distributions of mid-Neoproterozoic sediments (800–717 million yr, Ma) from various locations are characterized by the occurrence, besides cholestane isomers, of a novel series of C 28 steranes, whereas classical C-24 alkylated steranes are absent. These unusual C 28 steranes, termed cryostanes, seem to be restricted to pre-Snowball Earth sediments. We report their conclusive identification as 26-methyl cholestanes based on comparison of gas chromatographic (GC) behavior and mass spectrum of the last eluting cryostane isomer with those of a 26-methyl 5α(H),14α(H),17α(H),20 R -cholestane standard obtained by way of synthesis. Sterols methylated at C-26 seem to be restricted to some demosponges and, based on molecular clock estimates, demosponges may have emerged in the time interval 800–700 Ma. A sponge origin of cryostanes is thereby conceivable, making cryostanes the oldest molecular markers for animals. However, other biological sources need to be explored, including the wide variety of eukaryotic protists. [ABSTRACT FROM AUTHOR]
ISSN:01466380
DOI:10.1016/j.orggeochem.2017.11.006