A novel series of benzohopanes widespread in sediments

A novel series (C31---C35) of benzohopanes cyclized at the C(16) position has been characterized by gas chromatography-mass spectrometry and NMR structural elucidation of the usually predominant C31 member, the 4′-methylbenzo[16,17,21]-22,29,30-trinorhop-16-ene isolated from the Messel shale (Germany). These biological markers of bacterial origin seem to be widely distributed in sediments and to show low specificity with regard to the depositional environment, although they are well represented in evaporites. Up to now, they have been detected only in thermally immature samples, which could reflect either a relative fragility or other possibilities of transformation as compared to the regular benzohopanes cyclised at C(20).