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

We report here on the identification of two novel hexacyclic alkanes (C-33 and C-35) occurring in bitumen. The C-35 compound 1 was identified by compa rison with a standard obtained by synthesis involving a biomimetic proton-i nduced extensive cyclisation of an acyclic heptaprenoid. This cascade cycli sation allows the formation of eleven asymmetric centres present in the nat ural compound in only one step. The C-33 analogue 2 was identified by NMR s tudies after isolation from the saturated hydrocarbon fraction of a bitumin ous rock. Both compounds are "orphan" molecular fossils of biological lipid s of unknown origin formed by the extensive cyclisation of higher regular p olyprenoids.