Synthesis and NMR characterisation of novel highly cyclised polyprenoid hydrocarbons from sediments

Abstract

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.