Search results for "accions"
showing 10 items of 70 documents
Does the Sun Shine byppor CNO Fusion Reactions?
2002
We show that solar neutrino experiments set an upper limit of 7.8% (7.3% including the recent KamLAND measurements) to the fraction of energy that the Sun produces via the CNO fusion cycle, which is an order of magnitude improvement upon the previous limit. New experiments are required to detect CNO neutrinos corresponding to the 1.5% of the solar luminosity that the standard solar model predicts is generated by the CNO cycle.
Asymmetric Michael Addition in Synthesis of β-Substituted GABA Derivatives
2022
γ-Aminobutyric acid (GABA) represents one of the most prolific structural units widely used in the design of modern pharmaceuticals. For example, β-substituted GABA derivatives are found in numerous neurological drugs, such as baclofen, phenibut, tolibut, pregabalin, phenylpiracetam, brivaracetam, and rolipram, to mention just a few. In this review, we critically discuss the literature data reported on the preparation of substituted GABA derivatives using the Michael addition reaction as a key synthetic transformation. Special attention is paid to asymmetric methods featuring synthetically useful stereochemical outcomes and operational simplicity. This research was funded by the National Na…
Synthesis of Multisubstituted 1,4-Dihydrobenzoxazin-2-ones through a One-Pot Nucleophilic N-Alkylation/C-Alkylation of Cyclic α-Imino Esters
2017
A nucleophilic N-alkylation of 2-oxobenzoxazine-2-carboxylates with organozinc reagents with good selectivities and in moderate to good yields is described. Moreover, the synthesis of multisubstituted 1,4-dihydrobenzoxazine-2-ones bearing a tetrasubstituted carbon atom via a one-pot N-alkylation/C-alkylation reactions is reported.
Catalytic Asymmetric Reactions Involving the Seven-Membered Cyclic Imine Moieties Present in Dibenzo[b,f][1,4]oxazepines
2018
The dibenzo[b,f][1,4]oxazepine scaffold is a privileged structure in medicinal chemistry that displays a wide variety of biological and pharmacological activities. However, catalytic asymmetric methodologies for the synthesis of chiral dibenzo[b,f][1,4]oxazepine derivatives are scarce in the literature. This microreview presents an overview of enantioselective reactions in which these cyclic seven-membered imines are used as electrophiles, including their substrate scope, limitations and application to the synthesis of related compounds.
Nucleo-cytoplasmic shuttling of RNA-binding factors: mRNA buffering and beyond.
2022
Gene expression is a highly regulated process that adapts RNAs and proteins content to the cellular context. Under steady-state conditions, mRNA homeostasis is robustly maintained by tight controls that act on both nuclear transcription and cytoplasmic mRNA stability. In recent years, it has been revealed that several RNA-binding proteins (RBPs) that perform functions in mRNA decay can move to the nucleus and regulate transcription. The RBPs involved in transcription can also travel to the cytoplasm and regulate mRNA degradation and/or translation. The multifaceted functions of these shuttling nucleo-cytoplasm RBPs have raised the possibility that they can act as mRNA metabolism coordinator…
Organocatalytic asymmetric addition of naphthols and electron-rich phenols to isatin-derived ketimines: highly enantioselective construction of tetra…
2015
A quinine-derived thiourea organocatalyst promoted the highly enantioselective addition of naphthols and activated phenols to ketimines derived from isatins. The reaction afforded chiral 3-amino-2-oxindoles with a quaternary stereocenter in high yields (up to 99%) with excellent enantioselectivity (up to 99% ee). To the best of our knowledge, this transformation is the first highly enantioselective addition of naphthols to ketimines
Cutinases: Characteristics and Insights in Industrial Production
2021
Cutinases (EC 3.1.1.74) are serin esterases that belong to the α/β hydrolases superfamily and present in the Ser-His-Asp catalytic triad. They show characteristics between esterases and lipases. These enzymes hydrolyze esters and triacylglycerols and catalyze esterification and transesterification reactions. Cutinases are synthesize by plant pathogenic fungi, but some bacteria and plants have been found to produce cutinases as well. In nature they facilitate a pathogen’s invasion by hydrolyzing the cuticle that protects plants, but can be also used for saprophytic fungi as a way to nourish themselves. Cutinases can hydrolyze a wide range of substrates like esters, polyesters, triacylglycero…
Metal-Free Diastereo- and Enantioselective Dearomative Formal [3 + 2] Cycloaddition of 2-Nitrobenzofurans and Isocyanoacetate Esters
2022
The diastereo- and enantioselective dearomative formal [3 + 2] cycloaddition of 2-nitrobenzofurans and α-aryl-α-isocyanoacetate esters provides tricyclic compounds bearing the 3a,8b-dihydro-1H-benzofuro[2,3-c]pyrrole framework with three consecutive stereogenic centers. The reaction was enabled by a cupreine-ether organocatalyst. The reaction products were obtained with almost full diastereoselectivity and with excellent enantiomeric excesses for a number of substituted 2-nitrobenzofurans and isocyanoacetates.
Two Consecutive Magneto-Structural Gas-Solid Transformations in Non-Porous Molecular Materials
2018
Modification of the magnetic properties in a solid-state material upon external stimulus has attracted much attention in the recent years for their potential applications as switches and sensors. Within the field of coordination polymers, gas sorption studies typically focus on porous solids, with the gas molecules accommodating in the channels. Here we present a 1D non-porous coordination polymer capable of incorporating HCl gas molecules, which not only causes a reordering of its atoms in the solid state but also provokes dramatic changes in the magnetic behavior. Subsequently, a further solid-gas transformation can occur with the extrusion of HCl gas molecules causing a second structural…
Iodide-Photocatalyzed Reduction of Carbon Dioxide to Formic Acid with Thiols and Hydrogen Sulfide.
2016
The photolysis of iodide anions promotes the reaction of carbon dioxide with hydrogen sulfide or thiols to quantitatively yield formic acid and sulfur or disulfides. The reaction proceeds in acetonitrile and aqueous solutions, at atmospheric pressure and room temperature by irradiation using a low-pressure mercury lamp. This transition-metal-free photocatalytic process for CO2 capture coupled with H2 S removal may have been relevant as a prebiotic carbon dioxide fixation.