Abstract
A novel tetrahydrophenanthrene derivative 1 (1,1,7,8-tetramethyl-1,2,3,4-tetrahydrophenanthrene), formed from the triterpenoid tetrahymanol 2a by dehydration, ring A and B degradation and aromatisation during sediment diagenesis, has been isolated from a 180 Ma old marine sedimentary rock and identified by 1H and 13C NMR spectroscopy and mass spectrometry.