Thorpe-Ingold acceleration of oxirane formation is mostly a solvent effect

Kinetics of Glutathione Depletion and Antioxidant Gene Expression as Indicators of Chemical Modes of Action Assessed in Vitro in Mouse Hepatocytes with Enhanced Glutathione Synthesis

Here we report a vertically integrated in vitro - in silico study that aims to elucidate the molecular initiating events involved in the induction of oxidative stress (OS) by seven diverse chemicals (cumene hydroperoxide, t-butyl hydroperoxide, hydroquinone, t-butyl hydroquinone, bisphenol A, Dinoseb, and perfluorooctanoic acid). To that end, we probe the relationship between chemical properties, cell viability, glutathione (GSH) depletion, and antioxidant gene expression. Concentration-dependent effects on cell viability were assessed by MTT assay in two Hepa-1 derived mouse liver cell lines: a control plasmid vector transfected cell line (Hepa-V), and a cell line with increased glutamate-cysteine ligase (GCL) activity and GSH content (CR17). Changes to intracellular GSH content and mRNA expression levels for the Nrf2-driven antioxidant genes Gclc, Gclm, heme oxygenase-1 ( Hmox1), and NADPH quinone oxidoreductase-1 ( Nqo1) were monitored after sublethal exposure to the chemicals. In silico models of covalent and redox reactivity were used to rationalize differences in activity of quinones and peroxides. Our findings show CR17 cells were generally more resistant to chemical toxicity and showed markedly attenuated induction of OS biomarkers; however, differences in viability effects between the two cell lines were not the same for all chemicals. The results highlight the vital role of GSH in protecting against oxidative stress-inducing chemicals as well as the importance of probing molecular initiating events in order to identify chemicals with lower potential to cause oxidative stress.

A computational study of the influence of methyl substituents on competitive ring closure to α- and β-lactones

gem-Dimethyl substitution at C3 enhances the preference for β-lactone formation from 2-chlorosuccinate but methylation at C2 almost favours α-lactone.

N-Sulfonyl α-imino ester-derived chiral oxaziridines: catalytic asymmetric synthesis and application as a modular chiral organic oxidant

A novel class of chiral N-sulfonyl oxaziridines is catalytically prepared and introduced for use as highly reactive and enantiospecific oxidants.

Application of a BOSS-Gaussian interface for QM/MM simulations of Henry and methyl transfer reactions

Hybrid quantum mechanics and molecular mechanics (QM/MM) computer simulations have become an indispensable tool for studying chemical and biological phenomena for systems too large to treat with QM alone. For several decades, semiempirical QM methods have been used in QM/MM simulations. However, with increased computational resources, the introduction of ab initio and density function methods into on-the-fly QM/MM simulations is being increasingly preferred. This adaptation can be accomplished with a program interface that tethers independent QM and MM software packages. This report introduces such an interface for the BOSS and Gaussian programs, featuring modification of BOSS to request QM energies and partial atomic charges from Gaussian. A customizable C-shell linker script facilitates the interprogram communication. The BOSS-Gaussian interface also provides convenient access to Charge Model 5 (CM5) partial atomic charges for multiple purposes including QM/MM studies of reactions. In this report, the BOSS-Gaussian interface is applied to a nitroaldol (Henry) reaction and two methyl transfer reactions in aqueous solution. Improved agreement with experiment is found by determining free-energy surfaces with MP2/CM5 QM/MM simulations than previously reported investigations using semiempirical methods.

On the understanding of BF3·Et2O-promoted intra- and intermolecular amination and oxygenation of unfunctionalized olefins

BF₃·Et₂O was found to be effective for the amination and oxygenation of unfunctionalized olefins. In the presence of 3 equiv. of BF₃·Et₂O, intra- and intermolecular amination and oxygenation reactions could be realized in up to 99% isolated yields.

QM/MM investigation on 1,3-dipolar cycloadditions of the phthalazinium dicyanomethanide with three different dipolarophiles on water and in solution

An "on water" environment, describing the reactions with insoluble reactants in water, has been reported to give high yields of products compared to organic solvents. The 1,3-dipolar cycloadditions of phthalazinium dicyanomethanide 1 with three different dipolarophiles, methyl vinyl ketone (MVK), methyl acrylate (MAC), and styrene (STY), have been investigated using QM/MM calculations in water, acetonitrile, and acetonitrile-water solvent mixtures, as well as at the vacuum-water interface. Monte Carlo statistical mechanics simulations utilizing the free-energy perturbation theory and PDDG/PM3 for the QM method have been used. The transition structures for all three reactions do not show large variations among different solvents. However, the calculated free energies of activation at the interface are found to be higher than those calculated in bulk water. Computed energy pair distributions and radial distribution functions reveal a uniform loss of hydrogen bonds for the reactants and transitions states in progressing from bulk water to the vacuum-water interface. The hydrophobic effects in the reactions of 1 with MVK and MAC are similar for both, and weaker than the effect in the reaction with STY. According to the results in water-acetonitrile mixtures at different molar ratios, it is clear that the special hydrogen bonding effects are the main reason which leads to the rapid rate enhancement in progressing from a water-acetonitrile molar ratio of 0.9 : 0.1 to pure water. New insights into solvent effects for 1,3-dipolar cycloadditions are presented herein.

Distinct chemoselectivities in the platinum-catalyzed 1,2-carboalkoxylations of 5-alkoxypent-1-yn-3-ol derivatives

Two distinct Pt-catalyzed carboalkoxylations of alkynes are reported. The cycloisomerization of 5-alkoxypent-1-yn-3-ol derivatives 5 produces 2,6-dioxabicyclo[3.1.0]hexanes 6; the mechanism is postulated to involve a hydroxyl-triggered [3.3]-sigmatropic allyl rearrangement. As the same catalysis is extensible to their tertiary alcohol analogues 7, distinct dihydrofuranyl alcohols 8 were obtained through a [3.3]-allyl rearrangement that is not assisted by the hydroxyl group.