Dinosterol
From Wikipedia, the free encyclopedia
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| Names | |
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| IUPAC name
(22E)-4α,23-Dimethyl-5α-ergost-22-en-3β-ol | |
| Systematic IUPAC name
(1R,3aS,3bS,5aS,6S,7S,9aR,9bS,11aR)-6,9a,11a-Trimethyl-1-[(2R,3E,5R)-4,5,6-trimethylhept-3-en-2-yl]hexadecahydro-1H-cyclopenta[a]phenanthren-7-ol | |
| Identifiers | |
3D model (JSmol) |
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| ChemSpider | |
PubChem CID |
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| UNII | |
CompTox Dashboard (EPA) |
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| Properties | |
| C30H52O | |
| Molar mass | 428.745 g·mol−1 |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Dinosterol (4α,23,24-trimethyl-5α-cholest-22E-en-3β-ol) is a 4α-methyl sterol that is produced by several genera of dinoflagellates and is rarely found in other classes of protists.[1] The steroidal alkane, dinosterane, is the 'molecular fossil' of dinosterol, meaning that dinosterane has the same carbon skeleton as dinosterol, but lacks dinosterol's hydroxyl group and olefin functionality. As such, dinosterane is often used as a biomarker to identify the presence of dinoflagellates in sediments.
Dinosterol is a C30 sterol characterized by four fused rings (three six-membered and one five-membered), seven methyl groups, an olefin in its side-chain, and a secondary alcohol.[2] The double bond in the side chain is located at the 22 position, and dinosterol's methyl groups are at the 20, 23, 24 and 25 positions of the side chain. The structure of dinosterol is established as 4α,23,24-trimethyl-5α-cholest-22-en-3β-ol.
Dinosterol contains an unusual pattern of side-chain alkylation with methyl groups at C-23 and C-24. This substitution motif was thought to be unique to dinoflagellate sterols, until Volkman et al. (1993) found a diatom belonging to the genus Navicula, which contains several 4-methyl sterols including dinosterol.[1]
Biosynthesis
4-Methyl sterols are intermediates in the biosynthesis of 4-desmethyl sterols and are known to accumulate under anaerobic conditions.[1] The synthesis of dinosterol begins with the cyclization of squalene to lanosterol, but then diverges from cholesterol biosynthesis. The biosynthesis of dinosterol's side chain has been investigated in dinoflagellates using methionine-[CD3].[4] The sequence of side-chain alkylations is thought to be initiated by the formation of 4α,24-dimethyl-5α-cholest-24(28)-en-3β-ol, followed by reduction to 4α,24-dimethyl-5α-cholestan-3β-ol, then introduction of the Δ22-double bond to form 4α,24-dimethyl-5α-cholest-22E-en-3β-ol and then methylation at C-23 to form 4α23,24-trimethyl- 5α-cholest-22E-en-3β-ol (dinosterol).[4]
In a study on dinosterol side chain synthesis in the marine heterotrophic dinoflagellate, Crypthecodinium cohnii, the dinoflagellates were cultured with methionine-[CD3]. GC-MS analysis revealed that the C-23 methyl group contained three deuterium atoms that were introduced by transmethylation from methionine. The C-24 methyl group contained only two deuterium atoms, consistent with a 24-methylenesterol intermediate, which is reduced to the resulting 24-methyl side chain.[5] This mechanism has been previously reported in fungi,[6] a chrysophyte alga[7] and a diatom.[8] Importantly, no deuterium was incorporated into cholesterol or cholesta-5,7-dien-3β-ol, which are the major 4-methyl-sterols in Crypthecodinium cohnii. A suggested biosynthetic mechanism for side chain alkylations at C-23 and C-24 in dinosterol has been proposed.[5]
Biological occurrence
Dinoflagellates are the primary source of dinosteral. Dinoflagellates are unicellular, aquatic organisms that live in both marine and inland environments and are a prominent constituent of phytoplankton. Dinoflagellates are often characterized by their uncommon sterol distribution, dominated by 4α-methyl sterols derived from lanosterol rather than cycloartenol.[1] In many cases, the most abundant sterol in dinoflagellates is dinosterol.[10] Dinosterol is often used a biomarker in geochemical research because it is produced almost exclusively by dinoflagellates and is found in many environments.[11] In addition to several species of dinoflagellates, dinosterol has also been isolated from the diatom Nivicula sp. (CS-46c) collected from Port Hacking, New South Wales, Australia.[12]
Preservation and diagenesis
Steroids are often preserved in petroleum as saturated and aromatic steroidal hydrocarbons that result from transformations occurring during diagenesis. After senescence of steroids from aquatic producers, they undergo rapid re-mineralization under aerobic conditions in the upper water column.[13] A small percentage of the intact sterols produced in the euphotic zone endure diagenesis, where microbial mediated transformations effectively yield compounds that can then be related back to their parent sterols and are more stable in the geologic record.[14] The preservation of sterols is often limited, but is enhanced by anaerobic conditions during their deposition and subsequent diagenesis, in particular, early sulfurization and reduction mediated by sulfur species.[15][16]
Intact dinosterol has been reported from sediments of the presumed late Jurassic age, possibly due to incomplete degradation of lipids in the water column under high productivity conditions in the presence of sulfate reducers.[17][18] These transformations are controlled by microbial activity and low temperature physiochemical reactions.[19] Thermodynamically driven abiotic physicochemical reactions further alter the steroids by causing complete aromatization, isomerization and cracking of the steroids.[20] These more stable compounds co-exist with their precursor sterols and their intermediate diagenetic products can only occur in immature sediments when incomplete microbial degradation has occurred.[13]
