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Zhen Zhang, Cheng Li, Shao-Hua Wang, Fu-Min Zhang, Xue Han, Yong-Qiang Tu, Xiao-Ming Zhang
A novel and efficient tandem SN2' nucleophilic substitution/oxidative radical cyclization reaction of aryl substituted allylic alcohols with 1,3-dicarbonyl compounds has been developed by using Mn(OAc)3 as an oxidant, which enables the expeditious synthesis of polysubstituted dihydrofuran (DHF) derivatives in moderate to high yields. The use of weakly acidic hexafluoroisopropanol (HFIP) as the solvent rather than AcOH has successfully improved the yields and expanded the substrate scope of this type of radical cyclization reactions...
March 23, 2017: Organic & Biomolecular Chemistry
Ren Zhao, Wenjun Lu
A β-mesylation of primary sp(3) C-H bonds from simple amides with methanesulfonic anhydride (Ms2O) has been established successfully at 80 °C in a Pd(OAc)2 (catalyst)/K2S2O8 (oxidant)/CF3CH2OH (solvent) system. These amide substrates involve N-monosubstituted linear, branch, or cyclic alkanes, and electron-deficient benzyl compounds. The β-mesylated amide products can be converted easily to β-fluoroamides or β-lactams through inter- or intramolecular SN2 processes.
March 22, 2017: Organic Letters
Arthi Ravi, Syed Zahid Hassan, Ajithkumar N Vanikrishna, Kana M Sureshan
Triflates of myo-inositol undergo facile solvolysis in DMSO and DMF yielding SN2 products substituted with O-nucleophiles; DMF showed slower kinetics. Axial O-triflate undergoes faster substitution than equatorial O-triflate. By exploiting this difference in kinetics, solvent-tuning and sequence-controlled nucleophilysis, rapid synthesis of three azido-inositols of myo-configuration from myo-inositol itself has been achieved.
March 22, 2017: Chemical Communications: Chem Comm
Jian Long Li, Hong Wei Shi, Qi Wang, Yong Hai Chai, Jun Yang
A substrate-stereocontrolled synthesis of the ABC tricyclic system of daphnicyclidin A is developed. The key reactions include an efficient tandem N-allylation-SN2' reaction to assemble 2,3,4-cis trisubstituent pyrrolidine ring C and two intramolecular Horner-Wadsworth-Emmons reactions to construct cycloheptanone ring A and piperidine ring B.
March 15, 2017: Organic Letters
Przemyslaw Dopieralski, Jordi Ribas-Arino, Padmesh Anjukandi, Martin Krupicka, Dominik Marx
The reduction of disulfides has a broad importance in chemistry, biochemistry and materials science, particularly those methods that use mechanochemical activation. Here we show, using isotensional simulations, that strikingly different mechanisms govern disulfide cleavage depending on the external force. Desolvation and resolvation processes are found to be crucial, as they have a direct impact on activation free energies. The preferred pathway at moderate forces, a bimolecular SN2 attack of OH(-) at sulfur, competes with unimolecular C-S bond rupture at about 2 nN, and the latter even becomes barrierless at greater applied forces...
February 2017: Nature Chemistry
Thayanne Monteiro Ramos-Oliveira, Camila Vieira Silva, Paula Mendes Acatauassu Nunes, Cecília Pedroso Turssi, Peter Rechmann, Patricia Moreira de Freitas
This in situ study aimed to investigate the effect of a tin-containing fluoride solution in preventing enamel erosion. Also, its effects on the partly demineralized zone were assessed for the first time. Thirteen volunteers participated in this 2-phase study, wearing removable intra-oral appliances containing four sterilized bovine enamel slabs, for 8 days, where 2 treatment protocols were tested using samples in replicas (n = 13): CO - no treatment (negative control) and FL - AmF/NaF/SnCl2 solution (500 ppm F-, 800 ppm Sn2+, pH = 4...
March 6, 2017: Brazilian Oral Research
Laureen Bonnat, Laure Bar, Beatrice Gennaro, Hugues Bonnet, Olivier Jarjayes, Fabrice Thomas, Jerome Dejeu, Eric Defrancq, Thomas Lavergne
G-rich DNA oligonucleotides derived from the promoter region of the HIV-1 Long Terminal Repeat (LTR) were assembled onto an addressable cyclopeptide platform through sequential oxime ligation, thiol-iodoacetamide SN2 reaction and copper-catalyzed azide-alkyne cycloaddition reactions. The resulting conjugate was shown to fold into a highly stable antiparallel G4 architecture as demonstrated by UV, circular dichroism (CD), and NMR spectroscopic analysis. The binding affinities of six state-of-the-art G4 binding ligands toward the HIV G4 structure were compared to those obtained with a telomeric G4 structure and a hairpin structure...
March 6, 2017: Chemistry: a European Journal
Allan J Canty, Alireza Ariafard, Nicole M Camasso, Andrew T Higgs, Brian F Yates, Melanie S Sanford
This report describes a computational study of C(sp(3))-OR bond formation from Pd(IV) complexes of general structure Pd(IV)(CH2CMe2-o-C6H4-C,C')(F)(OR)(bpy-N,N') (bpy = 2,2'-bipyridine). Dissociation of (-)OR from the different octahedral Pd(IV) starting materials results in a common square-pyramidal Pd(IV) cation. An SN2-type attack by (-)OR ((-)OR = phenoxide, acetate, difluoroacetate, and nitrate) then leads to C(sp(3))-OR bond formation. In contrast, when (-)OR = triflate, concerted C(sp(3))-C(sp(2)) bond-forming reductive elimination takes place, and the calculations indicate this outcome is the result of thermodynamic rather than kinetic control...
March 14, 2017: Dalton Transactions: An International Journal of Inorganic Chemistry
Ward van der Stam, Jaco J Geuchies, Thomas Altantzis, Karel H W van den Bos, Johannes D Meeldijk, Sandra Van Aert, Sara Bals, Daniel Vanmaekelbergh, Celso de Mello Donega
Colloidal CsPbX3 (X = Br, Cl, and I) perovskite nanocrystals (NCs) have emerged as promising phosphors and solar cell materials due to their remarkable optoelectronic properties. These properties can be tailored by not only controlling the size and shape of the NCs but also postsynthetic composition tuning through topotactic anion exchange. In contrast, property control by cation exchange is still underdeveloped for colloidal CsPbX3 NCs. Here, we present a method that allows partial cation exchange in colloidal CsPbBr3 NCs, whereby Pb(2+) is exchanged for several isovalent cations, resulting in doped CsPb1-xMxBr3 NCs (M= Sn(2+), Cd(2+), and Zn(2+); 0 < x ≤ 0...
March 10, 2017: Journal of the American Chemical Society
Dipak Patel, Md Shahriar Al Hossain, Wenbin Qiu, Hyunseock Jie, Yusuke Yamauchi, Minoru Maeda, Mike Tomsic, Seyong Choi, Jung Ho Kim
An efficient cooling system and the superconducting magnet are essential components of magnetic resonance imaging (MRI) technology. Herein, we report a solid nitrogen (SN2) cooling system as a valuable cryogenic feature, which is targeted for easy usability and stable operation under unreliable power source conditions, in conjunction with a magnesium diboride (MgB2) superconducting magnet. The rationally designed MgB2/SN2 cooling system was first considered by conducting a finite element analysis simulation, and then a demonstrator coil was empirically tested under the same conditions...
March 2, 2017: Scientific Reports
Janina Kuduk-Jaworska, Jerzy J Jański, Szczepan Roszak
The results of computational simulation of reaction courses mimicking the transformation of carboplatin from pro-drug into its active shape, responsible for cytotoxic effect, are reported. Implementing the density functional theory (DFT) calculations and the supermolecular approach, we explored the pathways representing two disparate models of carboplatin bioactivation: (1) based on paradigm of carboplatin aquation, and (2) based on new hypothesis that transformation is controlled by electron-transfer processes...
February 11, 2017: Journal of Inorganic Biochemistry
Víctor Rojas-Cervellera, Lluís Raich, Jaakko Akola, Carme Rovira
The labeling of proteins with heavy atom clusters is of paramount importance in biomedical research, but its detailed molecular mechanism remains unknown. Here we uncover it for the particular case of the anti-influenza N9 neuraminidase NC10 antibody against a glutathione-coated gold cluster by means of ab initio QM/MM calculations. We show that the labeling reaction follows an associative double SN2-like reaction mechanism, involving a proton transfer, with low activation barriers only if one of the two distinct peptide/peptidic ligands (the one that occupies the side position) is substituted...
February 17, 2017: Nanoscale
Sankar K Guchhait, Neha Hura, Archana P Shah
A step-economical access to polysubstituted aminoimidazoles has been accomplished via alkene vicinal C-N bonds formation of 2-bromo-2-alkenones with guanidine avoiding its NH-protection/derivatization prerequisite for electronic modulation. The approach has excellent substrate scope, is amenable to diverse guanidine-containing substrates, and introduces distinctive substitutions/functionalities into aminoimidazole core. It is also applicable to preparation of fused-imidazoles. The reaction involves a tandem pathway of aza-Michael addition, SN2, and a unique redox-neutral process, as evident by spectroscopic study and control experiments...
February 20, 2017: Journal of Organic Chemistry
Athanasios Zavras, Hossein Ghari, Alireza Ariafard, Allan J Canty, Richard A J O'Hair
Gas-phase reactivity of the copper hydride anions [CuH2](-) and [Cu2H3](-) toward a range of neutral reagents has been examined via multistage mass spectrometry experiments in a linear ion trap mass spectrometer in conjunction with isotope labeling studies and Density Functional Theory (DFT) calculations. [CuH2](-) is more reactive than [Cu2H3](-), consistent with DFT calculations, which show it has a higher energy HOMO. Experimentally, [CuH2](-) was found to react with CS2 via hydride transfer to give thioformate (HCS2(-)) in competition with the formation of the organometallic [CuCS2](-) ion via liberation of hydrogen; CO2 via insertion to produce [HCuO2CH](-); methyl iodide and allyl iodide to give I(-) and [CuHI](-); and 2,2,2-trifluoroethanol and 1-butanethiol via protonation to give hydrogen and the product anions [CuH(OCH2CF3)](-) and [CuH(SBu)](-)...
February 10, 2017: Inorganic Chemistry
Chunjie Ni, Yuwen Zhang, Yading Hou, Xiaofeng Tong
DABCO-catalyzed formal (3+3) annulations of β'-acetoxy allenoates with indoline-2-thiones are described, which provide facile access to thiopyrano[2,3-b]indole under mild reaction conditions. The reaction might proceed via the SN2'-SN2'-type process between β'-acetoxy allenoate and indole-2-thiolate with the assistance of the DABCO catalyst and K2CO3 additive, followed by intramolecular Friedel-Crafts reaction at the 3-position of indole and central carbon of allene.
February 10, 2017: Chemical Communications: Chem Comm
Marc Esser, Stefan Maintz, Richard Dronskowski
Plotting materials on bi-coordinate maps according to physically meaningful descriptors has a successful tradition in computational solid-state science spanning more than four decades. Equipped with new ab initio techniques introduced in this work, we generate an improved version of the treasure map for phase-change materials (PCMs) as introduced previously by Lencer et al. which, other than before, charts all industrially used PCMs correctly. Furthermore, we suggest seven new PCM candidates, namely SiSb4 Te7 , Si2 Sb2 Te5 , SiAs2 Te4 , PbAs2 Te4 , SiSb2 Te4 , Sn2 As2 Te5 , and PbAs4 Te7 , to be used as synthetic targets...
January 27, 2017: Journal of Computational Chemistry
Takahiro Suzuki, Soichiro Watanabe, Susumu Kobayashi, Keiji Tanino
(+)-Iso-A82775C is a proposed biosynthetic precursor of the chloropupukeananin family and an important intermediate for related natural products. The first enantioselective total synthesis of (+)-iso-A82775C (18 steps, 2.2% overall yield) toward the eventual biomimetic total synthesis of chloropupukeananin is described. The key steps are (1) the enantioselective Diels-Alder reaction of 4-bromo-3-hydroxy-2-pyrone with methyl 2-chloroacrylate using cinchonine as an organocatalyst and (2) the anti-selective Cu-mediated SN2' reaction to afford the axially chiral vinylallene moiety...
January 27, 2017: Organic Letters
C V da Silva, T M Ramos-Oliveira, T F Mantilla, P M de Freitas
Although several studies have demonstrated the efficacy of AmF/NaF/SnCl2 solution in inhibiting dental erosion progression, measures for further improvement in its effectiveness are paramount. Thus, this in situ study evaluated whether the protective effect promoted by the AmF/NaF/SnCl2 solution would be enhanced by increasing its frequency of use. The study was conducted with 12 volunteers, a 4-phase (5 days each) randomized, crossover model. Extraoral erosive challenges (0.5% citric acid, pH 2.6, 6 × 2 min/day) and rinsing protocol (1 or 2 × 2 min/day) were performed...
2017: Caries Research
David W Roberts, Aynur Aptula, Anne Marie Api
Epoxides are known or proposed to be involved in skin sensitization in various ways. Some are encountered directly, and others have been shown to be formed abiotically and metabolically from various unsaturated chemicals. They can react as SN2 electrophiles. To date no quantitative mechanistic models (QMMs) are known for skin sensitization potency of this subcategory of SN2 electrophiles. Here we have considered the reaction mechanistic chemistry of epoxides and combined published experimental kinetic data (rate constants k for reaction with a cysteine-based peptide) together with calculated hydrophobicity data (logP) to derive a QMM correlating potency in the local lymph node assay (LLNA), expressed as EC3, with a relative alkylation index (RAI, calculated as logk + 0...
February 20, 2017: Chemical Research in Toxicology
Subha Pratihar, Xinyou Ma, Zahra Homayoon, George L Barnes, William L Hase
In a direct dynamics simulation, the technologies of chemical dynamics and electronic structure theory are coupled so that the potential energy, gradient, and Hessian required from the simulation are obtained directly from the electronic structure theory. These simulations are extensively used to (1) interpret experimental results and understand the atomic-level dynamics of chemical reactions; (2) illustrate the ability of classical simulations to correctly interpret and predict chemical dynamics when quantum effects are expected to be unimportant; (3) obtain the correct classical dynamics predicted by an electronic structure theory; (4) determine a deeper understanding of when statistical theories are valid for predicting the mechanisms and rates of chemical reactions; and (5) discover new reaction pathways and chemical dynamics...
February 9, 2017: Journal of the American Chemical Society
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