Jean M. Trendel

Novel triterpene-derived hydrocarbons of arborane/fernane series in sediments. Part I.

Abstract Three aromatic polycyclic hydrocarbons were isolated from Eocene shales and the Permian Kupferschiefer, and their molecular structures established by 1D and 2D NMR spectroscopy. These compounds (des-A-arbora-5,7,9- triene; 24,25-dinorarbora-1,3,5(10),9(11)-tetraene; 24,25-dinorarbora-1,3,5,7,9-pentaene) derive from microbial transformations of pentacyclic triterpenes oxygenated at C-3 belonging to the arborane or fernane families.

A novel series of benzohopanes widespread in sediments

Abstract A novel series (C 31 C 35 ) of benzohopanes cyclized at the C(16) position has been characterized by gas chromatography-mass spectrometry and NMR structural elucidation of the usually predominant C 31 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).

Isoarborinol through geological times: Evidence for its presence in the Permian and Triassic

Abstract Optical rotation measurements and HPLC chiral separations using a β-cyclodextrin phase, performed on aromatic hydrocarbons isolated from diverse geological sources, and belonging to the arborane or fernane triterpenoid series, have shown that isoarborinol, one of the possible biological precursors, was abundantly present at the time of deposition of Permian and Triassic sediments. This fact considerably reinforces the hypothesis that arborane derivatives in sediments, often found in abundance in lacustrine or lagoonal environments, must originate from microorganisms such as aerobic bacteria or algae rather than from angiosperms, a group of higher plants whose evolution dates from the Cretaceous and currently believed to be the principal source of isoarborinol.

Polar constituents of organic matter rich marls from evaporitic series of the Mulhouse basin

Abstract A suite of marl samples from the evaporitic series of the Mulhouse basin (France; Lower Oligocene) was studied for its biomarker content, in particular its polar constituents. Novel series of 3-carboxyalkyl steranes and 15-oxo triaromatic ketones were identified by synthesis. The 3-carboxyalkyl steranes probably originate from highly polar precursors yet unreported in living organisms. Our data suggest that micro-algae could be the major source of these compounds which seem to be indicators of high algal input rather than characteristic of evaporitic environments. The 15-oxo triaromatic ketones could be oxidation products of triaromatic steroid hydrocarbons formed during diagenesis, although their formation during work-up procedure could not be excluded.

Novel Thiophene Derived from Higher Plant Triterpenes in Sediments.

Abstract A novel thiophene 1 derived from higher plant triterpenoids of the oleanane series was detected in sediments deposited in evaporitic environments and identified by synthesis.

An unusual aromatization process of higher plant triterpenes in sediments

Abstract The NMR structural elucidation of D:B -friedo-3-methyl-24-noroleana-1,3,5(10)-triene (3-methyl-24-nor-friedela-1,3,5(10)-triene) isolated from the Messel shale (Germany) highlights an unusual ring-A aromatization process occurring during diagenesis of higher plant 3-oxygenated triterpenes. This process, which involves the shift of one of the gem -dimethyl groups at C(4) to C(3), instead of its commonly observed elimination, is probably induced by structural features of the precursors (most likely the Δ 5 or Δ 5(10) -gluten-3-ones). An acid(clay)-catalysed enone-benzene transposition can indeed account for a direct abiotic ring- A aromatization of such precursors.

Rearranged des-E-hopanoid hydrocarbons in sediments and petroleum

Abstract 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 isolated from an Italian Triassic black shale and identified by MS and NMR spectroscopy. Their structure, the occurrence in the sediment of their ring A methylated counterparts, as well as carbon isotopic data indicate that these compounds originate from bacterial hopanoids. Their formation most probably involves a sedimentary rearrangement of a functionalised des-E-hopane intermediate. This hypothesis was further substantiated by experiments in which 8 was formed from (18αH)-des-E-hopan-17α-ol 10 by treatment with K-10 montmorillonite clay. In addition, some minor unsaturated hydrocarbons formed as by-products are also present in sediments.

Spiro-triterpenes from clay-catalysed rearrangement of hopenes: NMR structural elucidation and occurrence in a recent sediment

Acidic K-10 montmorillonite clay-catalysed rearrangement of hop-22(29)-ene 5 and of hop-17(21)-ene 6 leads to the formation of small quantities of various fernenes and of new compounds, the 14-methyl-13,15-cyclo-B′:A′-neo-26-nor-14,15-seco-18α-gammacer-7-ene 8 and its Δ8- and Δ9(11)-isomers 9 and 10, the structures of which have been established by MS and NMR spectroscopy. This novel hopane skeleton transposition also operates on bacterial sedimentary hopenes, as shown by GC-MS investigations of the alkene fraction from a recent lacustrine sediment.

Baccharane (18,19-secolupane): A rare triterpenoid skeleton widespread in Triassic sediments and petroleum from the Adriatic Basin

Abstract Baccharane (18,19-secolupane) 1, a triterpenoid skeleton seldom encountered in living organisms, has been characterized together with 17βH-des-E-lupane 2, one of its minor degradation products, in Italian Triassic sediment and crude oil samples from the Adriatic Basin by synthesis of standards. Reports of baccharane-derived triterpenoids in the field of natural products are scant and up to now restricted to terrestrial plants (angiosperms and ferns). In this regard, sedimentary baccharane derivatives may indicate a continental contribution (ferns?) to fossil organic matter; but they may also represent a contribution of as yet undetermined marine microorganisms, as has been proposed for dammarenes and dammaranes. Alternatively, they could be the bio/geochemical transformation products of biosynthetically closely related precursors such as lupane- or dammarane-type triterpenoids. The apparently restricted occurrence of baccharane derivatives in geological samples (up to now detected only in Triassic sediments of the Adriatic Basin) confers upon these compounds great value as correlation parameters and possibly as source indicators.