Search results for "acids"
showing 10 items of 3520 documents
Redox Biochemistry of the Genetic Code.
2021
New findings on the chemistry of the amino acids, their role in protein folding, and their sequential primordial introduction have uncovered concealed causalities in genetic code evolution. The genetically encoded amino acids successively provided (i) membrane anchors, (ii) halophilic protein folds, (iii) mesophilic protein folds, (iv) metal ligation, and (v) antioxidation.
Peroxydation in vivo et in vitro des acides gras polyinsaturés
2007
It is well admitted that polyunsaturated fatty acids are the most sensitive fatty acids to oxidative damage because of their high number of double bonds. This concept could not be confirmed by in vitro, animal, or human studies since unexpected or even contradictory results were obtained. The explanation of that is probably related to the methods evaluating lipid peroxidation whose relevance is not always established, but especially to movements of polyunsaturated fatty acids within lipoproteins that results in their protection. This short review aims to discuss the main results related to this topic.
Influence of nitrogen status in wine alcoholic fermentation
2019
Nitrogen is an essential nutrient for yeast during alcoholic fermentation. Nitrogen is involved in the biosynthesis of protein, amino acids, nucleotides, and other metabolites, including volatile compounds. However, recent studies have called several mechanisms that regulate its role in biosynthesis into question. An initial focus on S. cerevisiae has highlighted that the concept of "preferred" versus "non-preferred" nitrogen sources is extremely variable and strain-dependent. Then, the direct involvement of amino acids consumed in the formation of proteins and volatile compounds has recently been reevaluated. Indeed, studies have highlighted the key role of lipids in nitrogen regulation in…
Nickel‐Mediated Photoreductive Cross Coupling of Carboxylic Acid Derivatives for Ketone Synthesis**
2021
A simple photochemical, nickel-catalyzed synthesis of ketones starting from carboxylic acids is presented. Hantzsch-ester (HE) functions as a cheap, green and strong photoreductant upon visible-light excitation to facilitate radical generation and also engages in the Ni-catalytic cycle to restore the reactive species. With this dual role, HE allows for the coupling of a large variety of radicals (1°,2°, benzylic, α-oxy & α-amino) with aroyl and alkanoyl moieties, a new feature in the synthesis of ketones through dual nickel photoredox catalysis. With both precursors deriving from abundant carboxylic acids, this protocol is a welcome addition to the organic chemistry toolbox. The reactio…
The mechanism of formation of 3H,9H-Pyrano[3,4-b]indol-3-ones from 3-indolalkanoic acids
1991
The mechanism of the formation of 1-methyl-3H,9H-pyrano[3,4-b]indol-3-one (4) from the corresponding 3-indolacetic acid 1 is discussed. The suggested mechanism is substantiated by the isolation of a stable intermediate 2 and its transformations in the presence of acetic anhydride and/or Lewis acids.
Evidence for essential primary amino groups in a bacterial coupling factor F1ATPase.
1980
Abstract We have found that the binding of pyridoxal-5′-phosphate to 6 primary amino groups leads to the inactivation of the enzyme. A preferential reaction of pyridoxal-5′-phosphate with the α-subunits of this enzyme can be demonstrated. The reactivity of the amino groups is influenced by various effectors. In the presence of ATP the inhibition of the ATPase activity is noncompetitive.
Interaction between 24-hydroxycholesterol, oxidative stress, and amyloid-β in amplifying neuronal damage in Alzheimer’s disease: three partners in cr…
2011
All three cholesterol oxidation products implicated thus far in the pathogenesis of Alzheimer's disease, 7β-hydroxycholesterol, 24-hydroxycholesterol, and 27-hydroxycholesterol, markedly enhance the binding of amyloid-beta (Aβ) to human differentiated neuronal cell lines (SK-N-BE and NT-2) by up-regulating net expression and synthesis of CD36 and β1-integrin receptors. However, only 24-hydroxycholesterol markedly potentiates the pro-apoptotic and pro-necrogenic effects of Aβ(1-42) peptide on these cells: 7β-hydroxycholesterol and 27-hydroxycholesterol, like unoxidized cholesterol, show no potentiating effect. This peculiar behavior of 24-hydroxycholesterol at physiologic concentrations (1 μ…
Characterization of waxes used in pictorial artworks according to their relative amount of fatty acids and hydrocarbons by gas chromatography.
2005
A study attempted to characterize natural waxes used in pictorial works of art was carried out by means of gas chromatography. The analytical treatment requires prior hydrolysis of the waxes to release the fatty acids (FA) (myristic (myr), palmitic (pal), oleic (ole), stearic (ste), araquidic (ara), behenic (beh), lignoceric (lig), cerotic (cer)) from the main esters of the waxes. The formation of volatile derivatives of the fatty acids was carried out by derivatization with ethyl choroformate (ECF). This derivatization reagent was chosen due to the speed, safety and quantitativity of the reaction. The analyzed hydrocarbons were n-eicosane, n-heneicosane, n-docosane, n-tricosane, n-tetracos…
Enantioselective Synthesis of α-Quaternary Amino Acids by Alkylation of Deprotonated α-Aminonitriles.
2015
A series of α-quaternary arylglycines were prepared in high optical purity (up to 98% ee) by α-alkylation of deprotonated α-aminonitriles derived by the Strecker reaction from (4S,5S)-5-amino-2,2-dimethyl-4-phenyl-1,3-dioxane. The procedure includes only chromatographic purification of the final products and is devoid of chromatography or crystallization operations on intermediates to raise the optical purity.
ChemInform Abstract: Synthesis of (E)- and (Z)-29-Methylidyne-2,3-oxidosqualene Derivatives as Inhibitors of Liver and Yeast Oxidosqualene Cyclase.
2010
The synthesis of (E)- and (Z)-29-methylidyne-2,3-oxidosqualene derivatives is described starting from the C22 and C17 squalene aldehyde monobromohydrins. The conversion was achieved by means of a Wittig reaction, followed by desilylation of the terminal acetylene. For trisubstituted 1,3-enynes, preliminary alkylation with a suitable allyl bromide was performed. A new procedure for the synthesis of squalene aldehyde C27, C22 and C17 monobromohydrins is also described. Some of the new compounds behaved as inhibitors of pig liver and yeast oxidosqualene cyclase and were time-dependent inhibitors of the animal enzyme.