REARRANGED DES-E-HOPANOID HYDROCARBONS IN SEDIMENTS AND PETROLEUM

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.