Isoprenoid alkanes

McKenna EJ, RE Kallio (1971) Microbial metabolism of the isoprenoid alkane pristane. Proc Natl Acad Sci USA 68 1552-1554. 

First reported from petroleum in 1963 (268, 269), acyclic isoprenoid alkanes have now been identified in crude oils from three continents (270-273), and in one crude oil all 12 isoprenoid hydrocarbons from C14 to C25 as well as head-to-tail conformations, have been found... 

Calvin, M., Occurrence of Isoprenoid Alkanes in a Precambrian Sediment, in Advances in Organic Geochemistry, pp. 41-74, Pergamon, Oxford, 1966. 

Advances in petroleum characterization at the molecular structure level by GC-MS methods renewed interest in OSC. Within the past few years, at least one-thousand new and novel OSC that previously were not known to be present in petroleum and bitumens have been reported. Tentative molecular structures inferred from GC-MS and other techniques have been confirmed in many cases by synthesis of authentic reference-compounds. The difficult and time-consuming synthetic work has been crucial in validating many of the novel structures. Another key finding has been that immature bitumens and crude oils (samples that have not received significant thermal stress) differ markedly from the previously known OSC in that they have carbon-skeletons resembling ubiquitous biomarker hydrocarbons (e.g., n-alkanes, isoprenoid alkanes, steranes, and hopanes). This similarity, of course, suggests that the hydrocarbons and OSC have common biogenic precursors. 

A major goal in organic geochemistry is to reconstruct depositional environments of the geological past based on qualitative and quantitative analyses of biological markers in sediments. Classes of hydrocarbons such as n-alkanes, isoprenoid alkanes, steranes and hopanes are routinely used for this purpose (1). 

In summary, Raney Ni desulfurisation of the polar fraction of the Northern Apennines Marl further supports the presence of (poly)sulfide-linked phytanyl, docosanyl and cholestanyl moieties (some of them with additional intramolecular sulfur linkages) in the resin fraction as proposed from the pyrolysis experiments. In addition, a number of other structural units are revealed e.g. pentakishomohopane, carotenoids, n-alkanes and isoprenoid alkanes. The reason why these structural units are not revealed by the pyrolysis experiments may be (i) their much lower relative abundance (e.g.9 other n-alkanes and isoprenoid alkanes), (ii) their attachment in the macromolecules by more than one (poly)sulfide linkage, which make their release from the macromolecule by flash pyrolysis unlikely ([Pg.522]

Isoprenoid Alkanes. Early work su ested (Nooner and Oro, 1967 Gelpi and Oro, 1970a) that nearly all carbonaceous chondrites contain the isoprenoid alkanes pristane and phytane (2-,6-,10-,14-tetramethyl-pentadecane and -hexadecane). These two hydrocarbons, which may formally be r arded as tetramers of isoprene, CHj C(CH3)CH CH2, serve as biological markers on Earth, being derived mainly... 

Stranger C. (1993) The structure of a new C25 isoprenoid alkane biomarker from diatomaceous microbial communities. Aust. J. Chem. 46, 907-915. 

The natiue of the higlier-molecular-weight aliphatic hydrocarbons from the Murchison has been controversial. Kvenvolden et al. [33] detected a wide variety of coeluting isomers dominated by polycyclic aliphatic structures. Oro el al. [41] reported Cg to Cis metliyl and dimetliyl alkanes, alkenes, and cycloalkanes. Studier et al. [42] detected straight-chain alkanes with some isoprenoidal hydrocarbons. It is now widely believed that straight-chain alkanes were the dominant components of the ahphatic fraction in the solar nebula. However, Cronin and Pizzarello [43] analyzed organic materials from the Murchison under less environmental contamination and concluded lliat tire n-alkanes, methyl alkanes, and isoprenoid alkanes reported in the Murchison were terrestrial contaminants. Tliese authors identified Cis to C30 cyclic alkanes as the major indigenous alipliatic components. 

Each of these groups of phases includes the numerous items of various trade names, different average molecular weights, viscosity, thermal stability, and so forth, but all of them are very close to each other by polarity. Up to the middle of the 1970s, the preferred nonpolar phase was squalane (isoprenoid alkane C30H62). This phase is no longer used because of its low thermal stability (only about 110°C). However, this obsolete phase maintains its importance as a nonpolar standard in gas chromatography. Other phases may be characterized by differences of RI values of specially selected test compounds between the phase under consideration and squalane, for example ... 

This paper presents data on isolation and identification of the following types of geolipids from the Aleksinac oil shale, a Miocene lake sediment n-al-kanes, iso- and/or anteiso-alkanes, aliphatic iso-prenoid alkanes, polycyclic isoprenoid alkanes, aromatic hydrocarbons, saturated unbranched, aliphatic isoprenoid, hopanoic, and aromatic mono- and poly-carboxylic acids, fatty acid methyl esters, aliphatic y- and 6-lactones, cyclic y-lactones, aliphatic methyl- and isoprenoid ketones, and the triterpenoid ketone adiantone. Possible origin of the identified compound classes is discussed, particularly of those which had not been identified previously as geolipids. 

Branched Alkanes. 2,6,10,14-Tetramethyl-hexadecane (phytane) and 2,6,10,14-tetramethyl-pentadecane (pristane) were found in considerable amounts (3). The dominance of phytane over pristane was observed. Other aliphatic isoprenoid alkanes C15 (2,6,10-trimethyl-dodecane, farnesane), C-, (2,6,10-trimethyl-tridecane), and C-g (2,6,10-trimethyl-pentaaecane) were also identified (4). In tne thiourea adduct of the branched-cyclic fraction, a homologous... 

Table II. Isoprenoid Alkanes Found in the Aleksinac Shale Bitumen...

Most of the geolipids so far identified in the oil shale from Aleksinac represent well known and ubiquitous constituents of sediments n-alkanes, iso- and anteiso-alkanes, aliphatic and cyclic isoprenoid alkanes including steranes, triterpanes and tetrater-panes, aromatic hydrocarbons, and aliphatic, hopanoic and aromatic acids. Moreover, several classes of compounds were identified which were also known as constituents of some ancient sediments but were not found to be ubiquitous, such as aliphatic isoprenoid ketones, aliphatic methyl ketones and the triterpenoid ketone adi-antone. 

J.-F. Rontani (1991). Identification by GC/MS of acidic compounds produced during the photosenitized oxidation of normal and isoprenoid alkanes in seawater. Int. J. Environ. Anal Chem., 45,1-9. 

Acyclic isoprenoidal alkanes may be important constituents, particularly pristane (2,6,10,14-tetra-methylpentadecane) and phytane (2,6,10,14-tetra-methylhexadecane) (Fig. 4.23a). Unfortunately, the term isoalkane is sometimes used to describe all the branched alkanes and not just the 2-methylalkanes. Acyclic alkanes normal surface conditions, while those up to C15 are liquids. The n-alkanes with >15 C atoms tend to be viscous liquids grading into solid waxes (the transition depending upon the ambient temperature). 

Botryococcane, a saturated C34 isoprenoidal alkane, is a particularly useful source- and environment-specific indicator. It appears to be derived only from the alga Botryococcus braunii, which is widely distributed in... 

Highly branched C20, C25, C30 and C35 isoprenoidal alkanes and their alkene counterparts with 1—4 double bonds (Fig. 2.18) occur widely in Recent marine and... 

The approximate unity ratio for even- and odd-numbered alkanes is an example, as are the homologous series of Ci2-C22 isoprenoid alkanes. As previously mentioned, marine organisms have a strong predominance of odd-numbered Ci5 through C2i alkanes. 

Pristane, 2,6,10,14-Tetramethylpentadecane nor-phytane Robuoy. C. H mol wt 268.51. C 84,98%, H 15.02%. Isoprenoid alkane obtained from the unsaponifiable fraction of shark liver oil where it occurs to an extent of 14% Tsujimoto. J. Soc. Chem. Ind. 51, 3 7T (1932) Sorensen, Mehllum, Acta Chem. Scand. 2, 140 (1948). Identity with norphytane Pliva, Sorensen, ibid. 4, 846 (1950), Isoln from patroleum crude oils Bendoraitis et al. Anal Chem. 34, 49 (1962) from wool wax Mold et al. Nature 199, 283 (1963). Synthesis from phytol Sorensen, Sorensen, Acta... 

In contrast, Figure 6 also shows cross plots of normal and isoprenoid alkane and tetracyclic alkane parameters for the end member oils and... 

Mackenzie, A. S., Patience, R. L., Maxwell, J. R., Vandenbroucke, M. Durand, B. 1980. Molecular parameters of maturation in the Toarcian shales, Paris Basin, France. I. Changes in configuration of acyclic isoprenoid alkanes, steranes, and triterpanes. Geochimica et Cosmochimica Acta, 44, 1709-1721. 

In the sediments of the Nansha Islands waters, compositional characteristics of nalkanes, isoprenoid alkanes, alkanes, steranes, and hopanes indicate that they come from marine planktons. Lower Pr/Ph ratios show that the depositing environment is anoxic. With increasing burial depth, the relationship of diagenetic transformation between hopenes and hopanes and that between hopane isomers are found (Duan et al., 1996). 

Table 5.20. n-Alkane and isoprenoid alkane parameters (Duan et al., 1998) (With permission from Dnan Y)... 

---