User:Lalatheplatypus/Desmosterol
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| Names | |
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| IUPAC name
3S,8S,9S,10R,13R,14S,17R)-10,13-dimethyl-17-[(2R)-6-methylhept-5-en-2-yl]-2,3,4,7,8,9,11,12,14,15,16,17-dodecahydro-1H-cyclopenta[a]phenanthren-3-ol
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| Other names
Desmosterol
24-Dehydrocholesterol Cholesta-5,24-dien-3β-ol | |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Desmosterol (Cholesta-5,24-dien-3β-ol) is a lipid present in the membrane of phytoplankton. These are autotrophic organisms which undergo photosynthesis and rely on sunlight for energy, living in shallower waters. Structurally, desmosterol has a similar backbone to cholesterol, with the exception of an extra double bond in the structure of desmosterol. This is seen biologically through the synthesis of cholesterol in the human body, as desmosterol is the immediate precursor to cholesterol.
Background
Desmosterol is classified as a cholestadienol, a subgroup of a wider known group of sterols, which are organic compounds naturally occurring in eukaryotes.
Desmosterol was first described and isolated in 1955 from chick embryo sterol with a 2% yield and postulated as being a biological precursor to cholesterol by Stokes et al.
The first known isolation of desmosterol in invertebrates was published in 1957 by Fagerlund and Idler. This new sterol was isolated in large amounts from balanus glandula, a barnacle species found on the North American Pacific coast.
Additionally, small amounts of desmosterol have been found in other crustaceans such as lobster and shrimp in the homarus americanus and pandalus borealis species. This strengthens the conclusion that desmosterol must be created exogenously as crustaceans have not been seen to biosynthesise sterols. [1]
Biological Occurence
Desmosterol has been largely found within a large population of marine invertebrates. Major sources include: , which has led to the idea of an exogenous origin of desmosterol in phytoplankton.
Biosynthesis
There are two major pathways for cholesterol biosynthesis, being the Kandutsch-Russell and Bloch pathways. The Bloch pathway, named after Konrad Bloch, occurs naturally alongside the mevalonate pathway in humans within the cell.
Preservation
Desmosterol has been seen to biologically oxygenate to cholesterol in cell cultures.[2] The presence of desmosterol in oceans and lakes has potential to diagnose anoxic conditions and for studying trends in steroid chemistry during the early stages of diagenesis.[3] Desmosterol has been found in samples of Rhizosolenia setigera Brightwell in Western Svalbard[4] and from surface sediment off the Peruvian Shelf sediment-water interface.[3]
Measurement techniques
chemical constants, thin-layer and gas-liquid chromatography, ozonolysis, infrared, NMR, and mass spectra
GC-MS
Samples from water sources are first extracted and partially purified before analysis. Sterols are commonly first derivatised after purification. Lipid extracts can be separated into their fragments by ionisation using Gas Chromatography followed by Mass Spectroscopy analysis. Based on characteristically different retention times of the ions, individual highly branched isoprenoids can be identified. To identify sterols, mass spectra can be compared and contrasted with published data.[4] Desmosterol has a characteristic m/z peak at 384.
Thin Layer Chromatography
The top layer of sedimentary rock can be extracted to form a extract containing all the fatty acid components. Extracts can be separated into different bands of hydrocarbons, acyclic ketones, cyclic ketones, alcohols, and sterols by TLC using silica gel. More polar compounds dissolve better to the silica gel phase and are retained on the plate for longer compared to less polar compounds. These compounds are often subsequently analysed by capillary gas chromatography and GC-MS.[3]
Case Study: Western Svalbard
Case Study: Peruvian Shelf
Diatoms and Silicoflagellates are classes of phytoplankton present in sedimentary material from the sediment water interface in the Peruvian Shelf region. Mineralogical analysis of these suggested large volumes of phytoplankton. Researchers at the University of Bristol examined the sterol composition of these sedimentary rocks which have gone through oxygen depletion, leading to anoxic conditions. These conditions have enhanced preservation of lipids present during the time of formation, around 1 year prior, and limited degradation of these compounds.
Analysis of this sediment sample after extraction, TLC, and GC-MS showed small amounts of desmosterol along with abundant levels of cholesteryl decanoate, an ester of cholesterol. Compared to the Namibian Shelf,
References
- ^ Gagosian, Robert (1974). Summary of Investigations Conducted in 1974. Massachusetts: Woods Hole Oceanographic Institution. pp. C-16.
- ^ Saucier, S. E.; Kandutsch, A. A.; Gayen, A. K.; Nelson, J. A.; Spencer, T. A. (1990-12). "Oxygenation of desmosterol and cholesterol in cell cultures". Journal of Lipid Research. 31 (12): 2179–2185. ISSN 0022-2275. PMID 2090711.
{{cite journal}}: Check date values in:|date=(help) - ^ a b c Smith, D.J.; Eglinton, G.; Morris, R.J.; Poutanen, E.L. (1983). "Aspects of the steroid geochemistry of an interfacial sediment
from the Peruvian upwelling". Oceanologica Acta. 6 (2): 211–219.
{{cite journal}}: line feed character in|title=at position 63 (help) - ^ a b Belt, Simon T.; Brown, Thomas A.; Smik, Lukas; Tatarek, Agnieszka; Wiktor, Józef; Stowasser, Gabriele; Assmy, Philipp; Allen, Claire S.; Husum, Katrine (2017-08-01). "Identification of C25 highly branched isoprenoid (HBI) alkenes in diatoms of the genus Rhizosolenia in polar and sub-polar marine phytoplankton". Organic Geochemistry. 110: 65–72. doi:10.1016/j.orggeochem.2017.05.007. ISSN 0146-6380.