Diatoms as a source for 4-desmethyl-23,24-dimethyl steroids in sediments and petroleum |
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Authors: | Sebastiaan W Rampen Stefan Schouten Ben Abbas Anna AM Noordeloos Jan AJ Geenevasen |
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Institution: | a NIOZ Royal Netherlands Institute for Sea Research, Departments of Marine Organic Biogeochemistry and Biological Oceanography, P.O. Box 59, 1790 AB Den Burg, The Netherlands b University of Amsterdam, Van‘t Hoff Institute for Molecular Sciences, Nieuwe Achtergracht 129, 1018 WS Amsterdam, The Netherlands |
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Abstract: | Analysis of the sterol composition of more than 100 diatom cultures, representing all major marine diatom orders, indicates that this group of algae may be an important source for 4-desmethyl-23,24-dimethyl steroids in sediments and petroleum, as their precursors, i.e. 4-desmethyl-23,24-dimethyl sterols, were present in 22 of the cultures. The phylogenetic positions of diatom species that produce 4-desmethyl-23,24-dimethyl sterols show that, within the centric diatoms, only a specific group of diatoms is able to produce these sterols, while within the pennate diatoms, a phylogenetic relationship between 4-desmethyl-23,24-dimethyl sterol-producing diatoms is less apparent. Based on the phylogenetic relationship, it is suggested that diatoms inherited the ability of producing these sterols from a single common ancestor, which originated between 150 and 100 Ma ago. Co-injection of an authentic 23R,24R-dimethyl-5α-cholestane standard with extracts confirmed its presence in sediments. We also tentatively identified three other 4-desmethyl-23,24-dimethyl sterane isomers having different side-chain stereo-configurations and observed that some of the isomers co-elute with other steranes including 24-ethyl-5α-cholestane. |
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