Occurrence of precursors of regular tricyclopolyprenoids in recent sediments

[structure: see text] Two novel C24 tricyclic alkenes of the cheilanthane series have been isolated from the solvent extract of a sulfur-rich recent sediment and their structures determined by NMR studies. They represent the first example of functionalized tricyclic hydrocarbons structurally related to the tricyclopolyprenanes widespread in ancient sediments and petroleum identified in recent sediments.