Org. Geochem. Vol. 8, No. 4, pp. 293-297, 1985 0146-6380/85 $3.00 + 0.00 Printed in Great Britain. All rights reserved Copyright 1985 Pergamon Press Ltd

Petroleum isoprenoid hydrocarbons derived from catagenetic degradation of Archaebacterial lipids

J. ALBAIGI~S 1, J. BORBON l and W. WALKER II 2 llnstitute of Bio-Organic Chemistry (CSIC), Jorge Girona Salgado, 18-26, Barcelona-34, Spain.

2Bodega Marine Laboratory, University of California, Berkeley, CA 94720, U.S.A.

(Received 24 April 1984; accepted 5 March 1985)

Abstract--The three GC coeluting C40 bis-phytanes with head-to-tail, tail-to-tail and head-to-head linkages considered to be archaebacterial markers, have been recognized in petroleum by enhanced mass-fragrnentography. Supporting evidence has been obtained by the simultaneous occurrence of two C2~-C24 series of isoprenoid and quasi-isoprenoid hydrocarbons that are supposedly formed during the catagenetic degradation of the isomeric C40 isoprenoids. The C2~-C24 quasi-isoprenoid hydrocarbons have been identified conclusively for the first time by comparison with authentic standards.

Key words: archaebacterial lipids, acyclic isoprenoids, synthesis of isoprenoids, mass spectra, petroleum oils

INTRODUCTION

Acyclic isoprenoids constitute a rather complex family of biological indicators in petroleum. Even though there is good evidence that the planktonic chlorophyll a is the predominant source for the regular isoprenoids below C20 (Didyk et al., 1978), the recent discovery in sediments and petroleums of diphytanyl glycerol ethers (Chappe et al., 1982), which are the main components of the membrane lipids in Archaebacteria, suggests that a substantial contribution from these organisms can also be ex- pected. This possibility has been strengthened by the concurrent identification of other lipids unique to Archaebacteria such as diglycerol tetraethers, con-

taining two C40 head-to-head isoprenoid chains (Fig. 1, I and IV; R~OX, where X = hydrophilic group) (Tornabene and Langworthy, 1979; De Rosa et al., 1977).

A series of structurally related long chain iso- prenoids (I-IV; R=H) have also been isolated from geological sources (Kimble et al., 1974; Albaig6s et al., 1978; Dastillung and Corbet, 1978; Moldowan and Seifert, 1979; Albaig+s, 1980; Chappe et al., 1980; Brassell et al., 1981; McEvoy et al., 1981). However, the precise origin of some of these hydrocarbons (II-I I I) and their fate in the geosphere are still poorly understood.

We report in this paper the identification of C2~ C24 quasi-isoprenoid alkanes (1'~/) in petroleum. The

vCz3(5') I ~Cz l ( 1' )

I I R R

Cz3(3 I - 7 [

, Czl(1)m I I I I I I I I

I t ~ I " -C22(2 ' ) L Cz 4(4,) I I

C24(4) / I l l

IV Fig. 1. Structures of C,~ isoprenoid alkanes (R-~-H) identified in Amposta crude oil (Miocene, Spain).

Dashed lines indicate lower homologs conclusively identified in this paper.

293

294 J. ALBAIG[S et al.

simultaneous occurrence of these compounds with the C2~-C24 (1~1) isoprenoid series provides evidence of the catagenetic degradation of three C40 isomeric isoprenoid hydrocarbons (I-III) considered to be bacterial or Archaebacterial markers. These markers which coelute in gas chromatography were also identified in the same petroleum samples by enhanced mass-fragmentography.

EXPERIMENTAL

Sample preparation and analysis

The crude oils belong to the off-shore fields Am- posta and Tarraco, in the Western Mediterranean, and are reservoired respectively in Lower Cretaceous and Upper Jurassic limestones. They have been recognized to be dissimilar (Albaigrs and Torradas, 1977) although the actual source of the Amposta oil remains unpublished. However, the possible source rocks in the area (Middle Miocene and Mesozoic) consist in carbonates generated in a restricted marine environment, which provide favourable conditions for the preservation of biological markers.

Branched-alkane fractions of these crudes were obtained in the usual way: silica-gel column chro- matography, urea and thiourea adduction of the saturated fractions and alumina column chro- matography of the latter adduct (Albaigrs, 1980).

Gas chromatographic analysis of extracts and ref- erence compounds was carried out in a Carlo Erba FW 4160 GC instrument equipped with glass capil- lary columns (25 m x 0.25 mm. i.d.) coated with SE- 52 (Bayona and Albaigrs, 1982).

The COM-GC-MS system comprised a GC Finnigan 9610, equipped with a 30 m x 0.3 mm i.d. DB-5 fused silica column (J&W Scientific), linked to a Finnigan 4023 MS with an INCOS data system. Operating conditions are given elsewhere (Bayona et al., 1983; Albaigrs et al., 1983).

Preparation of reference compounds

The regular C24 isoprenoid (4) was produced by hydrogenation (PtO2) of the allylic alcohol obtained in a Grignard reaction between phytaldehyde and butyl bromide, in a manner similar to that described previously for other homologs in the series (Albaigrs et al., 1978) (yield 53%; RIAp i .... L 2145; MS in Fig. 4).

The quasi-isoprenoid hydrocarbons C2~ (1'), C22 (_2') and C24 (4') were synthesized following the scheme outlined-in Fig. 3, basically a coupling (via Wittig reactions) of the adequate syntons, a series of methyl ketones, using the trimethylene-bis- triphenylphosphonium-ylide (Friedich and Henning, 1959) (m.p. 334-336C). 6-Methyloct-5-en-2-one (E + Z) was produced in 78% yield by a Carroll sequence (Mori et al., 1969) from 3-methylpenten-3-ol; homologation of this ketone by the ylide of (4,4-ethylenedioxy)-pentyltriphenyl- phosphonium iodide (m.p. 217-218C) (Cavill et aL,

1969) rendered 6,10-dimethyldodeca-5,9-dien-2-one (51% yield). Pentan-2-one and heptan-2-one were commercially available (Fluka, A.G.). Products from the Wittig reactions, namely the alkene C21H36 and two alkene mixtures, in the case of C22 and C24 hydrocarbons, were hydrogenated with PtO2 as the catalyst. After purification by silica-gel chro- matography (eluent: n-pentane), the C2~ isoprenoid (_1') was obtained in pure form (23% yield with respect to the corresponding ketone; RIAp ~ .... L 1982), whereas the C22 (_2') and C24 (4') isoprenoids were obtained in mixtures of hydrocarbons with abun- dance of 50 and 54% respectively, when the high and low molecular weight ketones were reacted in a 2:1 ratio (absolute yield 15-18% and RIAp i .... L 1978 and 2156, respectively).

RESULTS AND DISCUSSION

The C40 bis-phytane (I) and C27-C39 isoprenoid hydrocarbons resulting from its catagenetic de- gradation have been identified in several petroleums (Moldowan and Seifert, 1979; Albaigrs, 1980). How- ever, in examining the branched-alkane fractions previously isolated from the Spanish Amposta and Tarraco crude oils (Albaigrs, 1980) we realized that the chromatographic peak corresponding to bis- phytane (I) was composed of more than one com- pound (Albaigrs et al., 1981). Using high resolution gas chromatography-mass spectrometry and passing the recorded signal through smoothing and peak enhancement, we proved the presence of three main components (Fig. 2A). These were identified as the head-to-head bis-phytane (I, R=H), the regular C40-isoprenoid (II) and the tail-to-tail C40-isoprenoid (lycopane, III) by reference to the retention times and mass spectra of standard compounds (Chappe et al., 1980; Albaigrs et al., 1978; Kimble et al., 1974). In addition, at slightly higher retention times we ob- served two other peaks (IV and V; Fig. 2B), with very similar spectra containing fragment ions at m/z 165, 166, 167, 194 and 195, which are characteristic of C40 saturated isoprenoids with one pentacyclic ring (Chappe et al., 1980). The mass spectrum of the first of these compounds appeared to be identical to that reported for the hydrocarbon IV (R=H), produced during the degradation of kerogen (Chappe et al., 1980). The structural relationship of this hydro- carbon (IV) to the isoprenoid moieties of glycerol tetraethers found in Archaebacteria (De Rosa et al., 1977) provides, as in the case of bis-phytane (I; R=H), additional evidence of the contribution of these micro-organisms to the formation of petroleum.

The biological sources of the regular (240 isoprenoid (II) and of lycopane (III) are unclear. They could be formed by diagenetic reduction of polyprenols and carotenoids (e.g. lycopene or spirilloxanthin) re- spectively, which is compatible with the processes occurring during the formation of petroleum. But, as their structure resembles the widely distributed

Petroleum isoprenoid hydrocarbons from archaebacterial lipids 295

II

_ __91 ~ V ~ 4200

70:00

IV

V

i

~.~--,,,...-- ,,. (B) - - , , , . - ' i -A , , ",'~',

RIC

. . . . I . . . . I ' ' ' ' i 4250 4300 4350 4400 4450 70:50 71:40 72:30 73:20 74:10

Fig. 2. Enhanced (A) and partially reconstructed (B) (~m/z 166, 167, 194, 195) gas chromatograms of an isoprenoid fraction of Amposta crude oil. (Column: fused silica DB-5, 30 m (J&W); temperature:

60-300C at 2C/min; Finnigan Incos data system). Peaks are identified in Fig. 1.

(A)

450o 4550 Scan 75:00 75:50 Time

0 0

+ OEt = OH

I . - - ( ~3PCH2CH 2

0 2.-- H2/PtO 2

1.- I- [~L-~ 0 /DMSO - +po 3 OY

2.-- p - -TsOH

5- 5-

i. (~3PCH2CH2CH2P~3)2Br- /DMSO-

4,- C21H44(1' )

1. (~3PCHzCH2CHzPOa)2Br - /DMSO- ,, 2. Hz/PI"O 2

l C22H46 (2 ') C24H 50 (4 ' )

Fig. 3. Synthetic pathways for isoprenoids C21H44 (1'), C22H46 (2') and C24H50 (4').

296 J. ALBAIG~S et al.

_I

Fx2 1'

267 296

2'

197 211

127 141 267 281 310

4'

197 239 I 127 169 I , 267 =~9

~ ~ ou= 338

113

I / [ 18a 253 323 338

100 200 300

Fig. 4. Mass spectra of isoprenoid hydrocarbons synthesized and identified in petroleum. Numbers refer to Fig. 1.

Archaebacterial isoprenoids previously described, a more direct biological origin is also conceivable. Lycopane has been identified in several geological settings (Dastillung and Corbet, 1978; McEvoy et aL, 1981; Brassell et al., 1981); and in the recent sedi- ments where it has been reported, methanogenic activity has also been documented (Brassell et aL, 1981). Moreover, Ourisson et aL (1982) have suggested the existence of different families of polyterpenoid compounds in the membranes of microorganisms yet to be identified.

On the other hand, petroleum is formed at a depth where thermal degradation of organic matter be- comes important (Tissot and WeRe, 1978). Hence, degradation products of the parent hydrocarbons would be expected to occur. In light of this, we have focused our attention on the hydrocarbons 1-4 and 1'-4' (Fig. 1). The regular series C2~-C23 (1-3) has been reported in crude oils (Han and Calvin, 1969; Albaigrs and Torradas, 1977) and in shale (Spyckerelle et al., 1972), and has been attributed to the catagenetic degradation of regular isoprenoid hydrocarbons (Albaigrs et al., 1978). However, the formation of the C22 member of this series by this process in highly unlikely, requiring simultaneous cleavage of two geminal C-C bonds. The presence of the C22 member (2) in ancient sediments has been considered to indicate a contribution from lycopane (Han and Calvin, 1969). The presence of the C24 homolog (4) would support this hypothesis; we were

able to identify a constituent with mass spectra and retention time corresponding to an authentic stan- dard.

Other standards, the quasi-isoprenoid hydro- carbons C21H44 (l'), C22H46 (2') and C24H50 (4'), were synthesized according to the scheme outlined in Fig. 3 and then analyzed by GC-MS and high resolution gas chromatography.

The mass spectra (see Fig. 4) and retention indices on two different columns (Apiezon L and DB-5) were found to be identical to those of the corresponding peaks in alkane fractions isolated from the Spanish crude oils.

The C23 member of the series (3'), recognized on the basis of the mass spectrometric data, was found only in minor quantities. This fact strongly suggests that the origin of these C21-C24 quasi-isoprenoid hydro- carbons is from catagenetic degradation of the regu- lar isoprenoid II, although their formation from a parent head-to-head isoprenoid (1) cannot be com- pletely ruled out. This implies that there is no func- tional group in the original molecule that may induce a preferential cleavage at one end, as is the case of liberation of phytol from kerogen. Thus, we favor the idea that the regular isoprenoid II is of direct biolog- ical origin, as is probably true with lycopane (III). The formation of quasi-isoprenoid aikanes not significantly different from the normal isoprenoid alkanes was also predicted by mathematical models (Waples and Tornheim, 1978) which assumed that

Petroleum isoprenoid hydrocarbons from archaebacterial lipids 297

cracking of a pre-existing isoprenoid hydrocarbon occurs preferentially at the more highly substituted carbon atoms, and terminal cleavage yielding meth- ane takes place less frequently.

Acknowledgement--This work was partially supported by the Spanish-North American Cooperative Project No. 793028.

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