Preliminary study of mechanism of action of SN38 derivatives. Physicochemical data,evidence of interaction and alkylation of DNA octamer d(GCGATCGC)2

The synthesis of water‐soluble SN38 derivatives is presented, and their stability in solutions used during drug development studies has been investigated. A preliminary study of mechanism of action of 9‐aminomethyl SN38 is presented. Using NMR techniques, the interaction of the oligomer d(GCGATCGC)₂ is studied, showing that the terminal GC base pairs are the main site of interaction. Using pulsed field gradient spin echo and mass spectroscopy, evidence of a spontaneous alkylation reaction of the DNA oligomer with SN38 derivatives is presented. A proposed mechanism of reaction is suggested. Copyright © 2016 John Wiley & Sons, Ltd.     

Coupures thermiques du type retro-Diels et Alder—II : Une nouvelle synthese du (±) jasmonate de methyle

A synthesis is described of methyl dl-jasmonate and jasmonic acid, from endo-tricyclo [5,2,1,0^2.6] 3,8-decadiene-5-one, by standard procedures in 18% yield overall. One of the main steps is a retro-Diels Alder reaction. Some variations of this sequence are presented.     

An efficient ultrasound-promoted method for the synthesis of bis(indole) derivatives

In this paper, the reaction of indole with electron-deficient alkenes in aqueous media is reported. This procedure allows the synthesis of bis(indole) derivatives in good to high yields at 90 °C under silent and ultrasound irradiation conditions. Short reaction times and high yields of desired products are the main advantages of the presented procedure. This reaction catalyzed by 12-tungstophosphoric acid is operationally simple and considers environmental aspects by avoiding toxic catalysts and solvents.     

Artificial-intelligence-based interpretation of feature sensitivities of the Belousov-Zhabotinsky reaction

A new approach is presented for analyzing kinetic models of relaxation-type oscillatory systems on the basis of numerical data. Feature sensitivities of the length of the two kinetic states of the Belousov-Zhabotinsky (BZ) reaction with respect to the rate constants of the model are explained by means of a logic-based inference system. The main kinetic roles of the individual reaction steps on the relaxing components are revealed, and a consistent interpretation of the kinetic states is given by this process. Both the high and the low set of rate constants were studied. According to our analysis, the bromous acid-hypobromous acid reaction is an important Br^? producing step of the model, and in the case of the low set, the bromate-bromous acid reaction is not the rate-determining step of the bromous acid autocatalysis.     

Chemical relaxation study of the heterogeneous silicon-hydrogen system under plasma conditions

The chemical relaxation technique consists of measuring the response of a chemical system to a small disturbance of an equilibrium or a nonequilibrium steady state. Since, for a small perturbation, the response of any complex and stable system is linear, rate constants of elementary processes under actual plasma conditions can be evaluated directly from the relaxation data. Applications of this technique to the kinetic study of the formation and decomposition of silane are presented and compared with previous data obtained by a flow method. In addition, relaxation data are presented which show that the main reaction channel of silance decomposition in glow discharges is the electron-impact-induced fragmentation into SiH₂ radicals (or ions) and H₂ molecules.     

Transition-metal-free Suzuki-type coupling reactions: scope and limitations of the methodology

The scope and limitations of the transition-metal-free Suzuki-type coupling of aryl halides and arylboronic acids to form biaryls are presented. Confirmation that the reaction is indeed metal-free is presented. The effects of changing base, solvent, reaction temperature, phase-transfer catalyst, and substrate are shown and the implications of these results discussed in terms of their impact on the synthetic versatility of the methodology. The main findings are that the reaction works well for aryl bromides, water is necessary as a solvent for the reaction, the optimum temperature for the reaction is 150 degrees C, the reaction is best performed by using microwave promotion with the exception of an electron-poor aryl bromide example where conventional heating may be used, only limited boronic acids can be used as coupling partners, sodium carbonate is the best base for the reaction, tetrabutylammonium bromide proves to be the best phase-transfer catalyst for the reaction, the reaction is limited to couplings between aryl halides and aryl boronic acids with sp(2)-sp(3) couplings proving ineffective, and NaBPh(4) can be used in the place of phenylboronic acid as a phenylating agent.     

Online ATR-IR investigations and mechanistic understanding of the carbonylation of epoxides - the selective synthesis of lactones or polyesters from epoxides and CO

In situ ATR-IR spectroscopy is applied as a powerful tool to study the factors that control the reaction of epoxides with carbon monoxide in the presence of [Lewis acid]⁺[Co(CO)₄]⁻ salts. Based on these investigations, a consistent mechanistic scheme is presented, comprising the main lactone and polyester products and minor components, e.g., acetone and crotonic acid derivatives. β-Alkoxy-acyl-cobalttetracarbonyl species are shown to be key intermediates from which two reaction routes start in dependence of the applied Lewis acid (LA). Labile LA-alkoxy combinations favor a backbiting process of the oxygen function on the Co-acyl bond, primarily producing lactone products. More stable LA-alkoxy entities are unreactive toward PO conversion and afford a polymerization reaction after the addition of a nucleophile. In that case, the Lewis acid remains bonded to the chain end.     

Total synthesis of stagonolide B

Asymmetric total synthesis of nonenolide stagonolide-B has been presented in this Letter. The main highlight of our synthetic strategy is the application of hydroxynitrile lyase (ParsHNL) mediated asymmetric synthesis of cyanohydrin, Sharpless asymmetric dihydroxylation, cross metathesis (CM) reaction, stereoselective Keck allylation reaction and Yamaguchi macrolactonization at a late stage enables us to achieve the synthesis of the target molecule in an efficient way.     

Cluster size-dependent mechanisms of the CO + NO reaction on small Pdn (n < or = 30) clusters on oxide surfaces

The CO + NO reaction (2CO + 2NO --> N(2) + 2CO(2)) on small size-selected palladium clusters supported on thin MgO(100) films reveals distinct size effects in the size range Pd(n) with n < or = 30. Clusters up to the tetramer are inert, while larger clusters form CO(2) at around 300 K, and this main reaction mechanism involves adsorbed CO and an adsorbed oxygen atom, a reaction product from the dissociation of NO. In addition, clusters consisting of 20-30 atoms reveal a low-temperature mechanism observed at temperatures below 150 K; the corresponding reaction mechanism can be described as a direct reaction of CO with molecularly adsorbed NO. Interestingly, for all reactive cluster sizes, the reaction temperature of the main mechanism is at least 150 K lower than those for palladium single crystals and larger particles. This indicates that the energetics of the reaction on clusters are distinctly different from those on bulklike systems. In the presented one-cycle experiments, the reaction is inhibited when strongly adsorbed NO blocks the CO adsorption sites. In addition, the obtained results reveal the interaction of NO with the clusters to show differences as a function of size; on larger clusters, both molecularly bonded and dissociated NO coexist, while on small clusters, NO is efficiently dissociated, and hardly any molecularly bonded NO is detected. The desorption of N(2) occurs on the reactive clusters between 300 and 500 K.     

Reactions of Organometallic Reagents with Halogenophosphazene Cyclic Trimers,Tetramers, and High Polymers

Abstract

Three main mechanistic pathways are now evident when Grignard, organolithium, organocopper, or transition metal anions are used as reagents for reactions with halogeno-phosphazenes-substitution, metal-halogen exchange, and skeletal cleavage. Use of these reaction pathways allows the synthesis of species such as I-X. A general mechanistic theory of these reactions is presented, together with an application of these mechanisms to macromolecular synthesis.     

Unexpected but Easy Synthesis of a Dihydrophosphadiazaazulene

Abstract

The title compound is the main product of the 2:1 reaction of DMAD with diazaphosphinines. The supposed mechanisms with intermediates and related products will be presented.     

Recent Developments in Kramers’ Theory of Reaction Rates

In this short review, we provide an update of recent developments in Kramers’ theory of reaction rates. After a brief introduction stressing the importance of this theory initially developed for chemical reactions, we briefly present the main theoretical formalism starting from the generalized Langevin equation and continue by showing the main points of the modern Pollak, Grabert and Hänggi theory. Kramers’ theory is then sketched for quantum and classical surface diffusion. As an illustration the surface diffusion of Na atoms on a Cu(110) surface is discussed showing escape rates, jump distributions and diffusion coefficients as a function of reduced friction. Finally, some very recent applications of turnover theory to different fields such as nanoparticle levitation, microcavity polariton dynamics and simulation of reaction in liquids are presented. We end with several open problems and future challenges faced up by Kramers turnover theory.     

醛与有机锌的不对称加成反应机理研究进展

醛与有机锌试剂的加成反应是近年来醛不对称加成研究的热点.本文综述并讨论了该类体系的两大类反应机理的微观过程,分析了两大类机理的根本不同之处.     

New facts concerning the reaction of K, K(15-crown-5)2 with phenyl glycidyl ether: unexpected formation of potassium cyclopropoxide

A new mechanism of the reaction of K⁻, K⁺(15-crown-5)₂ with phenyl glycidyl ether is presented. The linear ether bond is attacked only to a small extent, if at all. As the main reaction path the oxirane bond in the β-position is cleaved, followed by the γ-elimination of potassium phenoxide and the formation of potassium cyclopropoxide. Crown ether ring opening also occurs in reactions with organometallic intermediates.     

The local structure of molecular reaction intermediates at surfaces

A critical review is presented of the results of (experimental) quantitative structural studies of molecular reaction intermediates at surfaces; i.e. molecular species that do not exist naturally in the gas phase and, in most cases, are implicated in surface catalytic processes. A brief review of the main experimental methods that have contributed to this area is followed by a summary of the main results. Investigated species include: carboxylates, RCOO- (particularly formate, but also deprotonated amino acids); methoxy, CH(3)O-; carbonate, CO(3); ethylidyne, CH(3)C-; NH(x) and SO(x) species; cyanide, CN. As far as possible in the limited range of systems studied, a few general trends are identified (108 references).     

Die Reaktion von 1,2-Epoxy-octan mit 2-Dimethylamino-äthanol

2-Dimethylaminoethanol reacts with 1,2-epoxyoctane presumably via a hydrogen-bonded complex to form a quaternary ammonium compound which exhibits a fair stability at lower temperatures. At higher temperatures the quaternary structure decomposes with the resulting formation of a wide variety of products. Most of the products have been identified and a reasonable mechanistic picture for their formation is presented. The main products of the reaction are 1-(ß-dimethylaminoethoxy)-2-octanol (IIIa) and 1-dimethylamino-2-octanol (IV), the latter being formed according to several pathways concurrently with ethylene oxide, 2-methyl-4-hexyl-1, 3-dioxolane (VI), and 2-hexyl-1, 4-dioxane (VII). Some of the higher molecular weight products are secondary products resulting from the action of epoxide on the primary reaction products IIIa and IV. The relative amount of each product formed depends on the ratio of starting materials and reaction temperature. In the presence of an additional hydroxylic solvent such as ethanol, the solvent enters also into the reaction.     

Kinetics and molecular weights distribution study of neodymium-catalyzed polymerization of 1,3-butadiene

The homopolymerization of 1,3-butadiene in a stirred batch reactor with the catalytic system Nd octoate/diethyl-aluminium chloride/triisobutyl-aluminium in n-heptane was studied. The effect of various reaction conditions on especially high conversion and molecular weight is reported. Polymerization is shown to be first order with respect to both monomer and neodymium. Molecular weights are high and broadly distributed. Chain transfer to triisobutylaluminium is the main factor governing molecular weight development. A mechanism of polymerization is presented with the chain transfer process incorporated. © 1995 John Wiley & Sons, Inc.     

Catalytic and Mechanistic Developments of the Nickel(II) Pincer Complex-Catalyzed Hydroarsination Reaction

Synthetic challenges have significantly slowed the development of the catalytic asymmetric hydroarsination reaction despite it being a highly attractive C−As bond formation methodology. In addition, there is a poor understanding of the main reaction steps in such reactions which limit further development in the field. Herein, key intermediates of the hydroarsination reaction catalyzed by a PCP Ni^II-Cl pincer complex are presented upon investigating the reaction with DFT calculations, conductivity measurements, NMR spectroscopy, and catalytic screening. The novel Ni–Cl–As interaction proposed was then contrasted against known Ni^II-catalyzed hydrophosphination reactions to highlight dissimilarities between them even though P and As share a close group relationship. Lastly, the asymmetric hydroarsination of nitroolefins was further developed to furnish a library of chiral organoarsines in up to 99 % yield and 80 % ee under mild conditions (−20 °C to RT) between 5 to 210 mins.     

The insertion and extrusion of heterosulfur bridges. VII. Desulfurization of phenanthro[4,5-bcd]thiophene by means of methanol and a molybdena catalyst

Phenanthro[4,5-bcd]thiophene ( 1 ) is converted into phenanthrene ( 2 ) (50%) and a mixture of methylphenanthrenes ( 3 ) (12%) by means of methanol and a sulfided cobaltous oxide-molybdic oxide-aluminum oxide catalyst (CMA-1) at 450° in a flow system. Similarly, 2 gives 3 ; and 4-methylphenanthrene yields 2 plus 3 (main component 3-methylphenanthrene) under the same reaction conditions. Mechanisms of the reactions are discussed. A facile chromatographic separation for 1- and 4-keto-1,2,3,4-tetrahydrophenanthrenes is presented.     

Improving the Stability of Maleimide–Thiol Conjugation for Drug Targeting

Maleimides are essential compounds for drug conjugation reactions via thiols to antibodies, peptides and other targeting units. However, one main drawback is the occurrence of thiol exchange reactions with, for example, glutathione resulting in loss of the targeting ability. A new strategy to overcome such retro-Michael exchange processes of maleimide–thiol conjugates by stabilization of the thiosuccinimide via a transcyclization reaction is presented. This reaction enables the straightforward synthesis of stable maleimide–thiol adducts essential in drug-conjugation applications.