Letter | Published:

Stereochemistry of some steranes from geological sources

Abstract

THE steranes present in crude oils and sedimentary rocks are believed to be derived from the sterols of ancient organisms. Their precise structure and stereochemistry may give important clues about the nature of the original biological materials and about the geochemical processes which they have undergone. Examination of synthetic steranes1,2 has led us to question the adequacy of reported3–6 identifications, using only gas–liquid chromatography (GC) and mass spectroscopy (MS), of steranes such as 5α-cholestane, 5α-ergostane, and 5α-stigmastane ( =5α-sitostane) in geological samples. The last two, in particular, seem incompletely identified, since the configuration at C-24 has been ignored (although it is of phylogenetic importance in modern organisms7,8), and since we find that epimers at C-24, that is II and III, IV and V, are indistinguishable using GC and MS. The use of the names 5α-ergostane and 5α-stigmastane in geochemical work both for steranes of undetermined configuration at C-24 and for synthetic samples of defined configuration is confusing. In the absence of clear IUPAC/IUB rules, we have adopted the names shown in Fig. 1.

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