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PubMed Journals Articles About "Novel Ring Shaped Reaction Pathway With Interconvertible Intermediates" RSS

03:26 EST 15th December 2019 | BioPortfolio

Novel Ring Shaped Reaction Pathway With Interconvertible Intermediates PubMed articles on BioPortfolio. Our PubMed references draw on over 21 million records from the medical literature. Here you can see the latest Novel Ring Shaped Reaction Pathway With Interconvertible Intermediates articles that have been published worldwide.

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Showing "novel ring shaped reaction pathway with interconvertible intermediates" PubMed Articles 1–25 of 15,000+

A novel ring-shaped reaction pathway with interconvertible intermediates in chitinase A as revealed by QM/MM simulation combined with a one-dimensional projection technique.

Substrate-assisted catalysis (SAC), a mechanism of chitin hydrolysis by chitinases belonging to the glycoside hydrolase family 18 (GH18), has been studied experimentally and theoretically for several decades. However, the detailed reaction mechanism in chitinase A (ChiA) remains unclear at the atomic level. In this study, we investigated glycosylation, the first step of SAC, of ChiA obtained from Serratia marcescens (SmChiA), using QM/MM simulations combined with a one-dimensional projection (ODP) technique...


Synthesis of an Emissive Spectacle-Shaped Hexanuclear Rhenium(I) Complex.

Ring-shaped multinuclear Re(I) complexes (Re(I) rings) have the potential to function as useful units in multifarious photofunctional compounds because of their flexibility in molecular design and various photofunctions. The first synthetic example of the coupling reaction using a Re(I) ring as a building block to synthesize a novel spectacle-shaped hexanuclear complex is reported herein. This complex shows an efficient intramolecular energy transfer to accumulate the excitation energy into the central Re(I...

Ring-shaped meniscus formation may arise from the regenerative response to meniscectomy during growth spurts: A case report.

Ring-shaped meniscus is very rare and generally considered to be a congenital malformation. Here, we report a case of newly formed ring-shaped meniscus-like tissue following arthroscopic partial meniscectomy for a complete discoid lateral meniscus.


Disrotatory Ring-Opening of Furans Gives Stereocontrol.

The ring-opening of 2-methylfuran catalyzed by the Lewis acid catalyst tris(pentafluorophenyl)borane in the presence of hydrosilanes was studied by using quantum chemical methods. In a previous study, it was suggested that the stereoselective formation of the product is due to a nucleophilic vinylic substitution (SV) during the reaction. Our calculations show that the pathway involving the SV reaction is energetically not accessible. Instead, the intramolecular C-O bond cleavage is found to be much more fav...

Synthesis of Medium-Ring-sized Benzolactams by Using Strong Electrophiles and Quantitative Evaluation of Ring-size Dependency of the Cyclization Reaction Rate.

Benzolactams with medium-sized rings were synthesized via electrophilic aromatic substitution reaction of carbamoyl cations (R1R2N+=C=O) in good to high yields without dilution. These reactions were utilized to quantitatively examine the extent of retardation of medium-sized ring formation, compared to 5- or 6-membered ring formation. The order of reaction rates of formation of cyclic benzolactams is 6- > 5- > 7- > 8- > 9-membered ring at 25ºC. The present reaction provides a route to 8- and 9-membered ben...

Carbon dots from citric acid and its intermediates formed by thermal decomposition.

Thermal decomposition of citric acid is one of the most common syntheses of fluorescent C-dots; the reaction pathway is, however, quite complex and the details are still far from being understood. For instance, several intermediates form during the process and they also give rise to fluorescent species. In the present work, the formation of fluorescent C-dots from citric acid has been studied as a function of reaction time by coupling infrared analysis, X-ray photoelectron spectroscopy, liquid chromatograph...

Concise construction of the ACDE ring system of calyciphylline A-type alkaloids via 5+2 cycloaddition.

A concise route for construction of the ACDE ring skeleton in calyciphylline A-type alkaloids was developed using an intramolecular [5+2] cycloaddition reaction of an oxidopyrylium species bearing a tetrasubstituted olefin. Key to the success of this reaction was the combination of acid and base, which accelerated the construction of this skeleton containing a spiro ring and vicinal quaternary carbon centers. The resultant tricyclic ADE ring compound was converted to an ACDE ring model through C-H oxidation...

Mechanism of Photoinduced Dihydroazulene Ring-Opening Reaction.

The photoinduced ring-opening reaction is a key process in the functioning of dihydroazulene/vinylheptafulvene (DHA/VHF) photoswitches. Over the years, the mechanism of this reaction has been extensively debated. Herein, by means of nonadiabatic trajectory dynamics simulations and quantum chemistry calculations, we present the first detailed and comprehensive investigation on the mechanism of the photoinduced ring-opening reaction of DHA. The results show the crucial role of the excited-state ring planariza...

1,3-Difunctionalization of Aminocyclopropanes via Dielectrophilic Intermediates.

We report an oxidative ring-opening strategy to transform acyl, sulfonyl or carbamate protected aminocyclopropanes into 1,3-dielectrophilic carbon intermediates bearing a halide atom (Br, I) and a N,O-acetal. Replacing the alkoxy group of the N,O-acetal can be achieved under acidic conditions via an elimination-addition pathway, while substitution of the halides by nucleophiles can be done under basic conditions via a SN2 pathway, generating a wide range of 1,3-difunctionalized propylamines. A proof of conc...

Access to Enantiopure Advanced Intermediates en Route to Madangamines.

The synthesis of enantiopure ABCE and ABCD tetracyclic advanced intermediates en route to madangamine alkaloids and studies for the construction of the triunsaturated 15-membered D ring of madangamine B and the saturated 13-membered D ring of madangamine E are reported.

Yttrium Manganese Oxide Phase Stability and Selectivity Using Lithium Carbonate Assisted Metathesis Reactions.

In solid-state chemistry, stable phases are often missed if their synthesis is impractical, such as when decomposition or a polymorphic transition occurs at relatively low temperature. In the preparation of complex oxides, reaction temperatures commonly exceed 1000 °C with little to no control of the reaction pathway. Thus, a prerequisite for exploring the synthesis of complex oxides is to identify reactions with intermediates that are kinetically competent at low temperatures, as provided by assisted meta...

Preparation of dihydroxy polycyclic aromatic hydrocarbons and activities of two dioxygenases in the phenanthrene degradative pathway.

Dihydroxy phenanthrene, fluoranthene, and pyrene derivatives are intermediates in the bacterial catabolism of the corresponding parent polycyclic aromatic hydrocarbon (PAH). Ring-opening of the dihydroxy species followed by a series of enzyme-catalyzed reactions generates metabolites that funnel into the Krebs Cycle with the eventual production of carbon dioxide and water. One complication in delineating these pathways and harnessing them for useful purposes is that the initial enzymatic processing produces...

Mechanism and Selectivity of the Oxidative Ring Contraction of Cyclic α-Formyl Ketones.

The oxidative contraction of α-formal ketone to form continuous all carbon chiral centers promoted by H 2 O 2 is widely used in natural product total synthesis. Typically, using this transformation, the chiral cyclic ketones were obtained as the major products and the ring-opening products as the minor products. Herein, DFT computations have been used to investigate the detailed reaction mechanism and the chemoselectivity. In addition with the widely accepted mechanism of H 2 O 2 -catalyzed transformation,...

Tandem Wittig Reaction-Ring Contraction of Cyclobutanes: A Route to Functionalized Cyclopropanecarbaldehydes.

An original tandem reaction consisting of a Wittig reaction-ring contraction process between α-hydroxycyclobutanone and phosphonium ylides has been developed. Highly functionalized cyclopropanecarbaldehydes are obtained in good to high yield.

Scholl-Type Cycloheptatriene Ring Closure of 1,4,9,12-Tetraarylfenestrindanes: Reactivity and Selectivity in the Construction of Fenestrane-Based Polyaromatic Saddles.

The Scholl-type cyclodehydrogenation generating up to four cycloheptatriene rings around a fenestrindane core leads to novel, saddle-shaped polyaromatic hydrocarbon derivatives. In this article, we present the results of in-depth experimental and computational works on the oxidative cyclization of various 1,4,9,12-tetraarylfenestrindanes. In particular, the kinetic control of the four-step cyclization of the electronically activated tetrakis(3,4-dimethoxyphenyl) derivative is elucidated. The reasons for the...

Characterization of initial reaction intermediates in heated model systems of glucose, glutathione, and aliphatic aldehydes.

To understand the effect of lipid degradation on Maillard formation of meaty flavors, initial reaction intermediates in model systems of glucose-glutathione with hexanal, (E)-2-heptenal, or (E,E)-2,4-decadienal were identified by HPLC-MS and by NMR. Besides Amadori compounds, hemiacetals and thiazolidines via addition of sulfhydryl to carbonyl or to the conjugated olefinic bond were found. Concentrations of all intermediates increased with reaction time while degradation of the intermediates with a glutathi...

Construction of BCDEF Core of Andilesin C.

A synthetic study toward the BCDEF core skeleton of andilesin C is presented. Key elements involved iron-promoted intramolecular perezone-type [5 + 2] cycloaddition to install the BCD ring system simultaneously in a one-step, copper-catalyzed intramolecular cyclopropanation followed by BiCl-promoted retro-aldol reaction to construct ring E and a one-pot manipulation involving reduction, lactonization, and isomerization to introduce the lactone ring F. We finally synthesized the congested BCDEF ring system o...

Exposing the delocalized Cu-S π bonds on Au24Cu6(SPhtBu)22 nanocluster and its application in ring opening reaction.

Bimetallic nanomaterials are of major importance in catalysis. In this study, we synthesized a novel Au-Cu bimetallic nanocluster and found it effective to catalyze the epoxide ring opening reaction. The catalyst was analyzed by SCXRD and ESI-MS to be Au24Cu6(SPhtBu)22 (Au24Cu6 for short). Six copper atoms were found to exclusively occupy the surface positions in two groups with three atoms for each, and each group was bonded with three thiolate ligands to give a planar motif reminiscent of a benzene ring. ...

Modelling an adult human head on a donut-shaped gel head support for pressure ulcer prevention.

Patients who are stationary endure prolonged pressures and shear loads at contact areas between their body and the support surface, which over time may cause pressure ulcers (PUs). Donut-shaped gel head supports are commonly used to protect the occiput, which is among the most common anatomical sites for PUs; however, the biomechanical efficacy of these devices is unclear. To investigate their effects on scalp tissues, we have used our three-dimensional anatomically realistic finite element model of an adul...

Hydrogen by Deuterium Substitution in an Aldehyde Tunes the Regioselectivity by a Nonheme Manganese(III)-Peroxo Complex.

Mononuclear nonheme Mn(III)-peroxo complexes are important intermediates in biology, and for instance take part in the oxygen activation by Photosystem II. Herein, we present work on two novel isomeric biomimetic side-on Mn(III)-peroxo intermediates with bispidine ligand system and reactivity patterns with aldehydes. The complexes are characterized with UV-Visible and mass spectrometric techniques and reaction rates with cyclohexane carboxaldehyde (CCA) have been measured. The reaction gives an unusual regi...

Synthetic Approach to the ABCD Ring System of Anticancer Agent Fredericamycin A via Claisen Rearrangement and Ring-Closing Metathesis as Key Steps.

A new synthetic strategy to the ABCD ring system of the anticancer agent fredericamycin A (NSC-305263) was realized by the Diels-Alder reaction and olefin metathesis as key steps. The tactics developed here for the construction of the ABCD ring system also involve double Claisen rearrangement followed by a retro-Diels-Alder reaction and ring-closing metathesis. The metathesis approach performs a key role in the construction of A and D rings of the ABCD core unit. More importantly, ABCD fragment synthesis wa...

Far away from flatland. Synthesis and molecular structure of di- and tri-hetera3.3.npropellanes - advanced analogues of morpholine/piperazine.

An approach to di- and trihetera[3.3.n]propellanes (n = 2-4) - advanced morpholine and piperazine analogues - is developed. The key step of the reaction sequence included [3+2] cycloaddition reaction of unsaturated vicinal dicarboxylic acid derivatives and generated in situ azomethine ylide resulting in the formation of the pyrrolidine ring. One more heteroaliphatic ring (i.e. pyrrolidine or tetrahydrofuran) was annelated by nucleophilic cyclization of appropriate 1,4-dielectrophilic intermediates. 11 examp...

Theoretical Analysis of Competing Pathways for Carbon-Hydrogen Activation of Cyclopentadienyl-Triphenylphosphine-Iridium in Benzene.

Density functional theory (DFT) calculations are used to evaluate alternative reaction mechanisms when the photochemically produced (η-CMe)IrPPh oxidatively adds a C-H bond from either a benzene solvent molecule or a phenyl group of the phosphine ligand. Experimentally, the ortho-metalated complexes produced from intramolecular C-H activation and the hydridophenyl complexes produced from intermolecular C-H activation form in a ratio of 53:47 (Janowicz, A. H.; Bergman, R. G. . , , 352-354). Both products ar...

Theoretical investigation of oxidation of NO (NO + ½ O → NO) on surfaces of nickel-doped nanocages (Ni-C and Ni-BN).

In present study, the NO oxidation on Ni-carbon nanocage and Ni-boron nitride nanocage surfaces was investigated. The Ni-C and Ni-BN catalysts can oxidize the NO molecule by Langmuir-Hinshelwood (LH) and Eley-Rideal (ER) mechanisms. In this study, the NO molecule was joined to Ni atom of the Ni-surface-O* and Ni-surface-O* to generate the intermediates with low barrier energies. It can be concluded that the cis-Ni-surface-ONOO* complex in the ER pathway is more stable than four-elements-ring complex in LH p...

Second-Coordination Sphere Effect on the Reactivity of Vanadium-Peroxo Complexes: A Computational Study.

Vanadium-oxo and vanadium-peroxo complexes are common intermediates in biology and are, for instance, found in the catalytic cycle of vanadium haloperoxidases. In biomimetic chemistry synthetic models have been created that mimic the structural features of the coordination environment of these vanadium-oxo and vanadium-peroxo species. Recently, two novel vanadium-oxo complexes were trapped and characterized with a trigonal bipyramidal ligand design with either a solvent exposed vanadium center or the vanadi...


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