Correlation of stereoisomerism in present day and geologically ancient isoprenoid fatty acids

Novel branched-chain fatty acids in certain fish oils

Methyl-branched fatty acids, which are usually minor components (equal or less than 0.1%) in fish oils, were concentrated in the non-urea-complexing fraction along with polyunsaturated fatty acids during the enrichment of omega-3 fatty acids from certain fish oils via the urea complexation process. The methyl-branched fatty acids in the omega-3 polyunsaturated fatty acid concentrates, which were prepared from three fish body oils, were characterized by gas chromatography and gas chromatography/mass spectrometry. Among the major branched-chain fatty acids expected and identified were the known isoprenoid acids--mainly 4,8,12-trimethyltridecanoic, pristanic, and phytanic--and the well-known iso and anteiso structures. Two novel phytol-derived multimethyl-branched fatty acids, 2,2,6,10,14-pentamethylpentadecanoic and 2,3,7,11,15-pentamethylhexadecanoic, were identified in redfish (Sebastes sp.) oil. These two fatty acids were absent in oils from menhaden (Brevoortia tyrannus) and Pacific salmon (mixed, but mostly from sockeye, Oncorhynchus nerka). The major branched-chain fatty acid in the salmon oil, 7-methyl-7-hexadecenoic acid, was also present to a moderate extent in menhaden oil. A novel vicinal dimethyl-branched fatty acid, 7,8-dimethyl-7-hexadecenoic was detected in all of the fish oils examined, but was most important in the salmon oil. Three monomethyl-branched fatty acids, 11-methyltetradecanoic acid, and 11- and 13-methylhexadecanoic, hitherto undescribed in fish lipids, were also detected in salmon, redfish and menhaden oils.

Isoprenoid fatty acids from marine sponges. Are sponges selective?

The burrowing sponges Anthosigmella varians and Spheciospongia vesparium were found to be rich in the isoprenoid phospholipid fatty acid 4,8,12-trimethyltridecanoic (5.2% and 23%, respectively, of the total fatty acid composition), while the burrowing sponge Chondrilla nucula and the demosponge Agelas dispar contained the acid 3,7,11,15-tetramethylhexadecanoic (13.8% and 8.6%, respectively, of the total phospholipid fatty acid composition). No other isoprenoid fatty acid was found, and the two acids described in this work did not occur concomitantly in the same sponge.

Copepod Fecal Pellets as a Source of Dihydrophytol in Marine Sediments

Dihydrophytol(3,7,11,15-tetramethylhexadecanol) was identified in the nonsaponified lipid fraction of fecal pellets from the copepod Calanus helgolandicus fed in the laboratory on a unialgal diet. Direct deposition in the fecal pellets of certain zooplankton species may explain the presence of dihydrophytol in marine sediments. Microbial reduction of phytol in sediment cores does not account for the origin of this compound in all sedimentary environments.

Chemical Fossils: The Geological Fate of Steroids

Steroids are used to illustrate some of the significant advances that have been made in recent years in understanding the biological origin and geological fate of the organic compounds in sediments. The precursor sterols are transformed, initially by microbial activity and later by physicochemical constraints, into thermodynamically more stable saturated and aromatic hydrocarbons in mature sediments and petroleums. The steps in this transformation result in a complex web linking biogenesis, diagenesis, and catagenesis. Indeed, the complexity and variety of biological lipids such as the steroids are evidently matched in the corresponding geolipids. The extent of preservation of the biochemical imprint in the structures and stereochemistry of these geolipids, even over hundreds of millions of years, is startling, as is the systematic and sequential nature of the geochemical changes they evidently undergo. This new understanding of molecular organic geochemistry has applications in petroleum geochemistry, where biological marker compounds are valuable in the assessment of sediment maturity and in correlation work.

Microbial metabolism of the isoprenoid alkane pristane

The "inert" hydrocarbon pristane (2,6,10,14-tetramethylpentadecane) can be utilized as the sole source of carbon and energy for growth of a coryneform soil isolate. Identification of the metabolites 4,8,12-trimethyltridecanoic acid and alpha-methylglutaric acid indicates that two pathways of fatty acid metabolism operate in this bacterial strain. The widespread use of pristane as a biological marker appears to be predicated on its structural similarity to phytol and its apparent stability, which may be only a reflection of the inability of microorganisms to carry out its anaerobic destruction.

A bacterium capable of using phytol as its sole carbon source, isolated from algal sediment of Mud Lake, Florida

A species of Flavobacterium that consistently attacks pure phytol and can use it as a sole source of carbon has been isolated from the blue-green algal sediment of Mud Lake, Florida. Biochemical tests demonstrate that this bacterium also readily uses various other organic compounds. This bacterium may account for the degradation products of chlorophyll and its side chain phytol, which have been found in the Mud Lake algal sediment. Phytol and its degradation products play a role in Refsum's disease, but phytol is also the most promising precursor of the isoprenoid hydrocarbons found in oil shale of the Green River Formation (Eocene) of Colorado, Utah, and Wyoming. The discovery of this species of Flavobacterium is a significant product of a protracted study of the bacteriology, phycology, zoology, and geochemistry of the algal sediment forming in Mud Lake, which is believed to be a modern analogue of the kind of algal sediment that, through geologic time, became oil shale.