Two tetracyclic triterpene-derived hydrocarbons, des-E-D : C-friedo-25
-norhopa-5,7,9-triene 1 and des-E-D: C-friedohop-8-ene 8, have been is
olated from an Italian Triassic black shale and identified by MS and N
MR spectrosropy. Their structure, the occurrence in the sediment of th
eir ring A methylated counterparts, as well as carbon isotopic data in
dicate that these compounds originate from bacterial hopanoids. Their
formation most probably involves a sedimentary rearrangement of a func
tionalised des-E-hopane intermediate. This hypothesis was further subs
tantiated by experiments in which 8 was formed from (18alphaH)des-E-ho
pan-17alpha-ol 10 by treatment with K-10 montmorillonite clay. In addi
tion, some minor unsaturated hydrocarbons formed as by-products are al
so present in sediments.