A NEW CLASS OF NATURAL-PRODUCTS REVEALED BY 3-BETA-ALKYL STERANES IN PETROLEUM

THE polycyclic hydrocarbons steranes and hopanes are nearly ubiquitous in petroleum, and their relative resistance to degradation makes them useful as 'biomarkers' for assessing the maturity and history of the oil. Steranes represent the reduced form of sterols, which serve as membrane rigidifiers in eukaryotic organisms; similarly, hopanes derive from hopanols, which serve the same function in prokaryotes. We have identified several homologous series of steranes with alkyl side chains (C1 to C6) at the 3-beta-position. These compounds, when liberated from the polar fractions of the oils by deuterated Raney nickel desulphurization, give fragmentation mass spectra indicating that the 3-alkyl side chains of the precursor steroids contained several functional groups. 3-beta-pentyl steranes are anomalously abundant in many samples. These data suggest that the precursors represent a new class of steroids, alkylated at the C-3 position with a polyhydroxy n-alkane. These precursors may have been formed by the bacterial addition of a ribose sugar to DELTA-2-sterenes, diagenetic alteration products of steroids synthesized by eukaryotes, 3-alkyl steroids might substitute for hopanols (of prokaryotic origin) in bacterial membranes 1.