Isoprenoids acyclic

Diaz-Perez AL, AN Zavala-Hernandez, C Cervantes, J Campos-Garcia (2004) The gnyRDBHAL cluster is involved in acyclic isoprenoid degradation in Pseudomonas aeruginosa. Appl Environ Microbiol 70 5102-5110. 

Larcher, A. V., Alexander, R., Rowland, S. J. and Kagi, R. I. (1986) Acid catalysis of alkyl hydrogen exchange and configurational isomerisation reactions acyclic isoprenoid acids. Organic Geochemistry 10, 1015. 

Another relevant feature of the gas chromographic profile is the acyclic isoprenoid hydrocarbon pattern that is made evident with capillary columns or by the inclusion of the saturated fraction in 5 A (0.5 nm) molecular sieves or in urea. The predominant peaks usually correspond to the C19 (pristaine) and C20 (phytane) isomers, which ratios serve as an identification parameter [87], although the series extends to lower and higher homologues. 

All the above fingerprints exhibit a different usefulness for characterising oils. Their variation between crudes and their resistance to the sea weathering processes are not enough, in many cases, for providing the unequivocal identification of the pollutant. The n-paraffins can, apparently, be removed by biodegradation, as can the lower acyclic isoprenoids at respectively slower rates. 

Acyclic isoprenoid Present in the marine en- Saturated forms reported alkanes vironment but often un- from recent marine sedi-... 

Acyclic isoprenoid Abundant and widely dis-fatty acids tributed generally unsaturated 46)... 

Only the Green River oil shale and Scottish torbanite have so far yielded acyclic isoprenoid fatty acids (129,143,276-278). 

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... 

Risatti, J.B., Rowland, S.J., Yon, D., and Maxwell, J.R. (1984) Sterochemical studies of acyclic isoprenoids—XII. Lipids of methanogenic bacteria and possible contributions to sediments. In Advances in Organic Geochemistry (Schenck, P.A., and de Leeuw, J.W., eds.), pp. 93-103, Pergamon Press, Oxford, UK. 

The pentane-soluble portion of asphaltene thermolyzed at 300° C has been found to contain a full complement of n-alkanes, acyclic isoprenoids, small ring saturated and small ring aromatic compounds, typical of unbiodegraded conventional crude oil (8). However, in all cases only a small fraction of the degraded asphaltene can be analyzed in this manner, and therefore the question of the size and homogeneity of the remaining hydrocarbon units remains unresolved. 

The mobile Jt-electrons of unsaturated systems, responsible for the stabilization of the carbocations, provide equally efficient stabilization for carbanions. Consequently, a retrosynthetic cleavage of a benzylic, allylic, or propargylic C-C bond has additional merits since the resulting fragments can be visualized as either an electrophile or a nucleophile. The dual synthetic value of the allylic moiety has been extensively utilized in the synthesis of a large number of natural acyclic isoprenoids. The structures of many of these compounds look like they were purposely tailored for this type of retrosynthetic analysis. In fact, the 1,5-diene system, usually present in their structure (Scheme 2.19), immediately suggests the cleavage of its central C-3-C-4 bond, which leads to two allylic precursors. 

Rowland S. J. (1990) Production of acyclic isoprenoid hydrocarbons by laboratory maturation of methanogenic bacteria. Org. Geochem. 15, 9—16. 

Regular acyclic isoprenoids (6) I21 to l30 probable source is halophilic Archaea abundant in evaporitic environments. Grice et al. (1998b)... 

Brassell S. C., Wardroper A. M. K., Thomson I. D., Maxwell J. R., and Eglinton G. (1981) Specific acyclic isoprenoids as biological markers of methanogenic bacteria in marine sediments. Nature 290, 693-696. 

Balaban, A.T., Barasch, M. and Marcus, S. (1980b). Picture Grammars in Chemistry. Generation of Acyclic Isoprenoid Structures. MATCH (Comm.Math.Comp.Chem.), 8,193-213. 

CycUzation of isoprenoids.1 Acyclic isoprenoids can be cyclized in 30-60% yield by treatment with 1.2-2.0 eq. of mercuric trifluoroacetate in nitromethane or acetonitrile at -20° to 0°. After 5- 30 min. the reaction mixture is treated with 2 eq. of NaBH4 in 3 M NaOH solution at 0°. An example is the cyclization of trans-geranylacetone (1) to 2,5,5,9-tetramethylhexahydrochromene (2). 

We have investigated the variations in two groups of biomarker compounds, acyclic isoprenoids and polycycloalkanes (steranes and triterpanes), in gas chromatograms of oils produced... 

Very recently it was demonstrated that tocopherol moieties in kerogen are likely precursors of prist-l-ene (Figure 7) (30). This idea was supported by the fact that tocopherols are widely distributed in photosynthetic tissues and that they also occur as such in several recent sediments (31). It is tempting to conclude that during "natural pyrolysis" the generated pristene will be transformed to the well known component, pristane, in ancient sediments and oils. This example nicely illustrates that we have to be very careful when we conclude that acyclic isoprenoid hydrocarbons such as pristane originate from the chlorophyll side chain, phytol, based solely on structural similarities. 

Vandenbergh, P.A. and A.M. Wright. 1983. Plasmid involvement in acyclic isoprenoid metabolism by Pseudomonas putida. Appl. Environ. Microbiol. 45 1953-1955. 

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