25th International Meeting on Organic Geochemistry IMOG 2011

P-067
C21-C23 steroidal tricyclic terpanes from bitumen of Olenek field
(East Siberia)
Vladimir Kashirtsev
Trofimuk Institute of Petroleum Geology and Geophysics SB RAS, Novosibirsk, Russian Federation
(corresponding author:KashircevVA@ipgg.nsc.ru)
Jiang Zhusheng et al. [1], V.Kashirtsev [2] identified
(by GCMS, m/z 219) unusual biomarkers associated
with biodegraded oils and natural bitumen. In the first
case, researchers studied the oils of Kelamayi oilfield
(China) interpreted the structures of the C28 and C29
as de-A-steroidal tricyclic hydrocarbons. In the
another case author considered close or similar
hydrocarbons C27,C28 and C29 from Olenek bitumen
field like structures 8-14 sekosteranes. S.Norden,
J.Christoffers and J.Rullkotter had attempted a
synthesis 5-methyl-19-nor -4,5-seco-sterane [3].
Tricyclic compounds having common structural
features with the aforementioned secosteranes, they
have been found along with regular pregnanes (Fig.
1). The mass spectra of these compounds are
characterized by molecular ions at m/z 290, 304 and
318, with a base peak m/z 219, indicating that they
originate from C21, C22 and C23 tricyclanes. Features
of the fragmentation under electron impact (m/z 95
instead m/z 97; mz/ 262 instead m/z 263,264 and m/z
219) indicate that the rings A, B and D are not broken
by C-C bonds.
The Permian bitumen from Olenek field underwent
the strongest biological oxidation (rank 8 by Peters et
al. [4]) they virtually lack normal and branched
alkanes. The concentrations of terpanes are much
higher than those acyclic hydrocarbons.
Chromatograms scanned by ions m/z 123, 177, and
191 show that regular hopanes are almost completely
transformed to a homologous series of 25norhopanes,
with a predominance of 25-noradiantane
C28 [5]. Normally demethylated hopanes represent
biomarkers of intensely biodegraded oils (rank 8).
Among the identified terpanes, a homologus series of
secohopanes (C-ring opened i.e. hopanes with a
broken chain between carbon atoms 8 and 14) is of
special interest. These variations suggest that the
microbial biodegradation of terpanes proceeds along
to different pathway: oxidation of the alkyl side chain
and alteration cyclic core.
On the other hand, 8-14-secohopanes and steroidal
tricyclic terpanes can be primary compounds
synthesized in minor quantities by prokaryotes during
the OM transformation. They appear to be the most
resistant to biodegradation, and their significant
"residual" amounts are due to the bacterial utilization
of labile hydrocarbons in the pool.
Fig 1. Mass-chromatogram of saturated HC from
the natural bitumens of Olenek field (by m/z 217,218
and m/z 219). Lower part is mass-spectrum for the
peak H (C23H42).
References
[1] Jiang Zhusheng, Fowler M.G., Lewis C.A. and
Philp R.P. (1990) Organic Geochemistry, 15, .35-46.
[2] Kashirtsev V.A. (2009) The 24-th IMOG Abstracts,
529.
[3] .Norden S, Christoffers J. and Rullkӧtter J (2009).
The 24-th IMOG Abstracts, 526.
[4] Peters K.E., Walters C.C., Moldowan M.(2005)
The biomarker guide. Cambridge UP, vol.1,2,1155.
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