Functionalized biological precursors of tricyclic terpanes: information from sulfur-bound biomarkers in a Permian tasmanite

Abstract

Desulfurization of the aromatic and polar maltene fractions of a tasmanite oil shale extract with Raney Ni yielded a series of tricyclic terpanes extending to C 40. We suggest that the C 40 homologs are derived from tetraterpenoid biological precursor(s) in the tasmanite, and were formed by biochemical cyclization of a C 40 polyprenol. It is likely that many of the lower carbon number tricyclic terpanes in these samples are early diagenetic alteration products of these C 40 precursors. Tricyclic terpane series in other samples that terminate at C 30 or C 45 (or higher) could be derived from biochemical cyclization of other polyprenols of different lengths in related microbiota. The desulfurization products indicate that tricyclic terpanes in the tasmanite extract derive from biological precursor(s) with functionalities in both the ring system and the side chain. Novel desulfurization products included substantial amounts of mono-unsaturated tricyclic terpenes (tentatively identified as 8,13-dimethyl-14-alkylpodocarp-13-enes, primarily C 39) and a C 21 acyclic isoprenoid, probably derived from the side chain of a C 40 tricyclic terpenoid. These data suggest that phytane, and possibly other isoprenoids in these samples, may partially derive from the side chain of lower-carbon-number tricyclic terpenoids.