Stereochemical Aspects of the Synthesis of 1,2‐Epoxides

Berti, G.

doi:10.1002/9780470147160.ch2

Cited by 127 publications

(12 citation statements)

References 254 publications

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“…Such compounds can be formed by the adding of a peroxyl radical to a double bond [42], followed by a fast intramolecular homolytic substitution [43]. In the case of monounsaturated fatty acids (such as cis -vaccenic acid), such a formation is very unlikely.…”

Section: Resultsmentioning

confidence: 99%

Photochemical Production and Behavior of Hydroperoxyacids in Heterotrophic Bacteria Attached to Senescent Phytoplanktonic Cells

Petit

Sempéré

Vaultier

et al. 2013

IJMS

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The photooxidation of cellular monounsaturated fatty acids was investigated in senescent phytoplanktonic cells (Emiliania huxleyi) and in their attached bacteria under laboratory controlled conditions. Our results indicated that UV-visible irradiation of phytodetritus induced the photooxidation of oleic (produced by phytoplankton and bacteria) and cis-vaccenic (specifically produced by bacteria) acids. These experiments confirmed the involvement of a substantial singlet oxygen transfer from senescent phytoplanktonic cells to attached bacteria, and revealed a significant correlation between the concentration of chlorophyll, a photosensitizer, in the phytodetritus and the photodegradation state of bacteria. Hydroperoxyacids (fatty acid photoproducts) appeared to be quickly degraded to ketoacids and hydroxyacids in bacteria and in phytoplanktonic cells. This degradation involves homolytic cleavage (most likely induced by UV and/or transition metal ions) and peroxygenase activity (yielding epoxy acids).

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Section: Resultsmentioning

confidence: 99%

Photochemical Production and Behavior of Hydroperoxyacids in Heterotrophic Bacteria Attached to Senescent Phytoplanktonic Cells

Petit

Sempéré

Vaultier

et al. 2013

IJMS

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“…8). Epoxides may be formed by classical addition of a peroxyl radical to a double bond (Berti, 1973) and subsequent fast intramolecular homolytic substitution (Fossey et al, 1995 double bonds (Schaich, 2005). In the case of monounsaturated fatty acids, such a formation is thus very unlikely.…”

Section: Biotic and Abiotic Alteration Of Monounsaturated Fatty Acidsmentioning

confidence: 99%

Degradation state of organic matter in surface sediments from the Southern Beaufort Sea: a lipid approach

et al. 2012

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Abstract. For the next decades significant climatic changes should occur in the Arctic zone. The expected destabilisation of permafrost and its consequences for hydrology and plant cover should increase the input of terrigenous carbon to coastal seas. Consequently, the relative importance of the fluxes of terrestrial and marine organic carbon to the seafloor will likely change, strongly impacting the preservation of organic carbon in Arctic marine sediments. Here, we investigated the lipid content of surface sediments collected on the Mackenzie basin in the Beaufort Sea. Particular attention was given to biotic and abiotic degradation products of sterols and monounsaturated fatty acids. By using sitosterol and campesterol degradation products as tracers of the degradation of terrestrial higher plant inputs and brassicasterol degradation products as tracers of degradation of phytoplanktonic organisms, it could be observed that autoxidation, photooxidation and biodegradation processes act much more intensively on higher plant debris than on phytoplanktonic organisms. Examination of oxidation products of monounsaturated fatty acids showed that photo-and autoxidation processes act more intensively on bacteria than on phytodetritus. Enhanced damages induced by singlet oxygen (transferred from senescent phytoplanktonic cells) in bacteria were attributed to the lack of an adapted antioxidant system in these microorganisms. The strong oxidative stress observed in the sampled sediments resulted in the production of significant amounts of epoxy acids and unusually high proportions of monounsaturated fatty acids with a trans double bond. The formation of epoxy acids was attributed to peroxygenases (enzymes playing a protective role against the deleterious effects of fatty acid hydroperoxides in vivo), while cis/trans isomerisation was probably induced by thiyl radicals produced during the reaction of thiols with hydroperoxides. Our results confirm the important role played by abiotic oxidative processes in the degradation of marine bacteria and do not support the generally expected refractory character of terrigenous material deposited in deltaic systems.

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“…However, only the thermodynamically less favorable cis-oxirane 8 is obtained as reaction product. The remarkable diastereospecificity of the Darzens reaction is well known 3,4 and can be rationalized in terms of an equilibrium between the two aldol addition products and kinetic control in the cyclization step by a favorable orbital overlap in the transition state of the oxirane formation from the threo diastereomer. In order to test the suggested pathway leading to compound 8 a mixture of the α-oxoester 7 and the α-bromoester 4 were reacted in the presence of an equimolar amount of base.…”

Section: Discussionmentioning

confidence: 99%

Unexpected course of a Williamson ether synthesis

Zeller

Haiß²,

Hartmann³

et al. 2006

Arkivoc

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The Williamson ether synthesis between the sodium salt of methyl mandelate and methyl α-bromophenylacetate was reinvestigated. In addition to the expected ether product cis-dimethyl 2,3-diphenyloxirane-2,3-dicarboxylate, methyl phenylacetate and methyl phenylglyoxylate were obtained. Their formation is explained by an initial α-elimination producing an α-oxo-carbene from the α-bromoester. This is followed by a hydride transfer from the sodium salt of methyl mandelate to the carbenic intermediate furnishing the enolate of methyl phenylacetate as reduction product and methyl phenylglyoxylate as oxidation product. Finally, the methyl phenylglyoxylate reacts with the enolate of the α-bromoester in a diastereospecific Darzens condensation to the cis-oxirane (cis-conformation confirmed by single crystal structure analysis). In this series of parallel and sequential reactions, the sodium salt of methyl mandelate displays 3 modes of action: nucleophile (ether synthesis), base (α-elimination) and hydride donor (redox process).

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Stereochemical Aspects of the Synthesis of 1,2‐Epoxides

Cited by 127 publications

References 254 publications

Photochemical Production and Behavior of Hydroperoxyacids in Heterotrophic Bacteria Attached to Senescent Phytoplanktonic Cells

Photochemical Production and Behavior of Hydroperoxyacids in Heterotrophic Bacteria Attached to Senescent Phytoplanktonic Cells

Degradation state of organic matter in surface sediments from the Southern Beaufort Sea: a lipid approach

Unexpected course of a Williamson ether synthesis

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