Synthesis and NMR characterisation of novel highly cyclised polyprenoidhydrocarbons from sediments

We report here on the identification of two novel hexacyclic alkanes (C33 and C35) occurring in bitumen. The C35 compound 1 was identified by comparison with a standard obtained by synthesis involving a biomimetic proton-induced extensive cyclisation of an acyclic heptaprenoid. This cascade cyclisation allows the formation of eleven asymmetric centres present in the natural compound in only one step. The C33 analogue 2 was identified by NMR studies after isolation from the saturated hydrocarbon fraction of a bituminous rock. Both compounds are “orphan” molecular fossils of biological lipids of unknown origin formed by the extensive cyclisation of higher regular polyprenoids.