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.