Nanoengineered Design of inside-Heating Hot Nanoreactor Surrounded by Cool Environment for Selective Hydrogenations.

Catalysts with designable intelligent nanostructure may potentially drive the changes in chemical reaction techniques. Herein, a multi-function integrating nanocatalyst, Pt-containing magnetic yolk-shell carbonaceous structure, having catalysis function, microenvironment heating, thermal insulation, and elevated pressure into a whole is designed, which induces selective hydrogenation within heating-constrained nanoreactors surrounded by ambient environment. As a demonstration, carbonyl of α, ß-unsaturated aldehydes/ketones are selectively hydrogenated to unsaturated alcohols with a >98% selectivity at a nearly complete conversion under mild conditions of 40 °C and 3 bar instead of harsh requirements of 120 °C and 30 bar. It is creatively demonstrated that the locally increased temperature and endogenous pressure (estimated as ≈120 °C, 9.7 bar) in the nano-sized space greatly facilitate the reaction kinetics under an alternating magnetic field. The outward-diffused products to the "cool environment" remain thermodynamically stable, avoiding the over-hydrogenation that often occurs under constantly heated conditions of 120 °C. Regulation of the electronic state of Pt by sulfur doping of carbon allows selective chemical adsorption of the CO group and consequently leads to selective hydrogenation. It is expected that such a multi-function integrated catalyst provides an ideal platform for precisely operating a variety of organic liquid-phase transformations under mild reaction conditions.

Effect of nano-TiO2 particle size on the bonding performance and film-forming properties of starch-based wood adhesives.

The effect of nano-TiO2 particle size on the properties of starch-based wood adhesives was studied in this work. Our findings indicate that a smaller size of nano-TiO2 particles corresponds with a larger specific surface area and more hydroxyl sites on the particle surface that interact with latex molecules, forming a more compact network structure. Therefore, the bonding performance and water resistance of the adhesive were enhanced. In addition, rheology results showed that the adhesive behaves as a pseudoplastic fluid. Small-angle X-ray scattering and energy dispersive spectroscopy confirmed the good compatibility and dispersion of nano-TiO2 in the adhesive films. Diffusing wave spectroscopy and scanning electron microscopy showed that smaller TiO2 particles were more favorable for the formation of smoother and denser films. These results are of great significance for improving the structure and properties of starch-based wood adhesives and preparing high-performance environmentally friendly biobased adhesives.

Asymmetric Nucleophilic Allylation of α-Chloro Glycinate via Squaramide Anion-Abstraction Catalysis: SN1 or SN2 Mechanism, or Both?

The nucleophilic substitution mechanism of enantioselective allylation of α-chloro glycinate catalyzed by squaramide organocatalysts was studied using density functional theory. Based on a comprehensive study of SN1 and SN2 pathways of a catalyst-free reaction, we found that the catalytic reaction slightly favors the SN1 mechanism, instead of the previously proposed SN2 mechanism. Further investigation of different leaving groups and nucleophiles revealed that this is not limited to the present reaction, and the SN1 mechanism might have been generally overlooked. For the squaramide-catalyzed reactions, the SN1 mechanism was predicted to be preferred. However, the rate-determining step of the SN1 pathway has changed from the chloride-leaving step to the C-C bond-formation step. Therefore, a first-order dependence on both substrates was predicted, in agreement with the observed second-order kinetics. Intriguingly, the lowest-energy enantioselective transition states (TSs) originate from different pathways; R-inducing TS corresponds to the SN1 pathway, while S-inducing TS corresponds to SN2. The calculated enantiomeric excesses of two squaramide catalysts agree well with the experimental values. Given the ubiquity of nucleophilic substitution reactions in chemistry and biology, we believe that our finding will inspire more studies that will lead to an improved mechanistic understanding of important chemical reactions, and it may even lead to better catalysts.

Copper-Catalyzed Cascade Cyclization Reactions of Diazo Compounds with tert-Butyl Nitrite and Alkynes: One-Pot Synthesis of Isoxazoles.

A novel copper-catalyzed [3 + 2] cycloaddition reaction of alkynes with nitrile oxides generated in situ from the coupling reaction of copper carbene and nitroso radical has been developed. The three-component reaction provides a simple and efficient method for the construction of isoxazoles in a highly regioselective manner in a single step. On the basis of the experimental results and density functional theory calculations, a catalytic cycle (CuI-CuII-Cu0-CuI) for this cascade cyclization reaction is proposed.

Chiral Phosphoric Acid-Catalyzed Enantioselective Direct Arylation of Iminoquinones: A Case Study of the Model Selectivity.

Chiral phosphoric acid (CPA)-catalyzed enantioselective arylation reactions have attracted immense attention recently. However, the preferential activation model in the stereodetermining step is controversial, and hence, the origin of enantioselectivity is still far from being understood. Two stereochemical models are provided on the basis of the asymmetric arylations of iminoquinones with naphthylamines (reaction 1) or naphthols (reaction 2) catalyzed by (R/S)-TRIP to explain the high enantioselectivity and the effect of CPAs scaffolds. Unexpectedly, our calculations reveal that substrate naphthylamines or naphthols prefer enantioselective aminal formation model II or 1,4-addition model I, respectively, which is the reverse of Tan's and Xu's model. The different noncovalent and steric interactions between catalysts and substrates are responsible for the observed model preference. Moreover, the enantioselectivity arises from distortion (reaction 1) and noncovalent interactions (reaction 2) that discriminate between the diastereomeric transition states. We further investigated the effect of SPINOL-based CPAs on the enantioselectivity and found that the more rigid skeleton and a smaller binding pocket lead to lower enantioselectivity as compared with that of BINOL-based CPA. The new insights into the reaction activation model rationalize the stereoselectivity outcome of direct asymmetric arylation reactions, and our general model can be extended to related transformations.

Withanolides and aromatic glycosides isolated from Nicandra physaloides and their anti-inflammatory activity.

Two new withanolides (1-2) together with five known ones (3-7), and three known aromatic glycosides (8-10) were isolated from the dried stems and leaves of Nicandra physaloides, an edible and medicinal plant. Their structures were identified by extensive spectroscopic analyses or comparison with literature data. The absolute configuration of 2 was assigned via X-ray crystallography. Compound 1 with a spiroketal moiety is relatively unusual in withanolides. Aromatic glycosides (8-10) showed potent inhibitory activity against LPS-induced nitric oxide production in RAW 264.7 macrophages, with IC50 values from 4.69 to 16.12 µM.

Mechanistic insight on water and substrate catalyzed the synthesis of 3-(1H-indol-3-yl)-2-(4-methoxybenzyl)isoindolin-1-one: Driving by noncovalent interactions.

The mechanisms of the synthesis of 2-substituted-3-(1H-indol-3-yl)-isoindolin-1-one derivatives have been investigated theoretically under unassisted, self-assisted, and water-assisted conditions. Being different from previously proposed catalyst-free by Hu et al., our results show that the title mechanism can be altered and accelerated by solvent and substrate 2. Two types of mechanisms have been developed by DFT calculations differ in the reaction sequence of substrates 1 with 3 (M1) or 2 (M2) followed by 2 (M1) or 3 (M2), and water-assisted M1 is the most favored one. It was found that the nucleophilicity of substrate 3 is stronger than that of 2. Our calculations suggest that the water-assisted pathway in M1 is the most favorable case, which undergoes nucleophilic addition and H-shift, C-N bond formation and water elimination, and intramolecular cyclization and water elimination. The rate-determining step is the nucleophilic attack process. Moreover, we also explored the effect of nucleophilic attack of the nitrogen of (4-methoxyphenyl)methanamine on hydroxyl or carbonyl group carbon of phthalaldehydic acid on the activation energy. More importantly, we found that water molecules play a critical role in the whole reaction, not only act as solvent but also as an efficient catalyst, proton shuttle, and stabilizer to stabilize the structures of transition states and intermediates via π···H-O, O···H-N, O···H-C, and O···H-O interactions. The origin of the different reactivity of M1 and M2 is ascribed to the pivotal noncovalent interactions exist between catalyst (water and substrate 2) and reactants. © 2018 Wiley Periodicals, Inc.

Terpenoids from Vitex trifolia and their anti-inflammatory activities.

A new diterpenoid glucoside, (3S,5S,6S,8R,9R,10S)-3,6,9-trihydroxy-13(14)-labdean-16,15-olide 3-O-ß-D-glucopyranoside (1), and a new iridoid glucoside, (1S, 5S,6R,9R)-10-O-p-hydroxybenzoyl-5,6ß-dihydroxy iridoid 1-O-ß-D-glucopyranoside (2), along with six known compounds (3-8) were isolated from Vitex trifolia L.. Their structures were elucidated by extensive spectroscopic analysis. All these isolated compounds were evaluated for their inhibitory effects on nitric oxide production in LPS-induced RAW 264.7 macrophages. Compounds 2, 4, 5, and 7 showed moderate inhibitory activities with IC50 values of 90.05, 88.51, 87.26, and 76.06 µM, respectively.

Farnesyl phenolic enantiomers as natural MTH1 inhibitors from Ganoderma sinense.

Cancer cells are more addictive to MTH1 than normal cells because of their dysfunctional redox regulations. MTH1 plays an important role to maintain tumor cell survival, while it is not indispensable for the growth of normal cells. Farnesyl phenols having a coumaroyl substitution are rather uncommon in nature. Eight farnesyl phenolic compounds with such substituent moiety (1-8), including six new ones, ganosinensols E-J (1-6) were isolated from the 95% EtOH extract of the fruiting bodies of Ganoderma sinense. Four pairs of enantiomers 1/2, 3/4, 5/6 and 7/8 were resolved by HPLC using a Daicel Chiralpak IE column. Their structures were elucidated from extensive spectroscopic analyses and comparison with literature data. The absolute configurations of C-1' in 1-6 were assigned by ECD spectra. These compounds were predicted to have high binding affinity to MTH1 through virtual ligand screening. The enzyme inhibition experiments and cell-based assays confirmed their inhibitory effects on MTH1. Furthermore, siRNA knockdown experiments and the cellular thermal shift assay (CETSA) confirmed that the farnesyl phenolic enantiomers specifically bound with MTH1 in intact cells. Meanwhile, the low cytotoxicity of 1-8 on normal human cells further verified their good selectivity and specificity to MTH1. These active structures are expected to be potential anti-cancer lead compounds.

Mechanistic investigation on N → Cα → O relay via non-Brook rearrangement: reaction conditions promote synthesis of furo[3,2-c]pyridinones.

A comprehensive density functional theory investigation was employed to disclose the effect of reaction conditions on the mechanism and effective anion relay sequence of a NaH promoted non-Brook rearrangement of benzaldehyde and 1-cinnamoylcyclopropanecarboxamides. Two main mechanisms were explored under four different reaction conditions: Na+-assisted and nH2O-Na+, 2H2O-DMSO-Na+, and Na+-DMSO co-assisted, and the difference relies on the reaction sequence between the concerted ring-opening and recyclization and electrophilic addition. Being different from previous reports, a cooperative participation of water, solvent DMSO and counterion Na+ is revealed in the preferential mechanism. The preferred scenario undergoes five major steps: deprotonation, aza-Michael addition, electrophilic addition, NaOH elimination and a concerted ring-opening and recyclization step. The rate-determining step is the concerted ring-opening and recyclization process with an energy barrier of 30.2 kcal mol-1. We found that the effective anion relay of a non-Brook rearrangement order is N → Cα → O rather than the previously proposed aza-oxy-carbanion. Meanwhile, a mixed type of ARC chemistry through a novel non-Brook rearrangement was disclosed. Moreover, the non-covalent interactions between substrate and reactant extensively affect the anion relay process by hydrogen-bonding (O-HO and C-HO) and electrostatic (Na+O) interactions. Thus, our results provide insightful clues to the mechanism of the reaction condition catalyzed non-Brook rearrangement reaction.

Constituents from Apium graveolens and their anti-inflammatory effects.

A phthalide glycoside, (3R, 4R)-4-O-ß-D-glucopyranosyl-senkyunolide (1), and a megastigmane glycoside, (6S, 7R)-3-oxo-megastigma-4, 8-dien-7-O-ß-D-glucoside (2), along with two known aglycones (3-4), were isolated from the 70% EtOH extract of fresh whole grass of Apium graveolens L. Their structures were elucidated by extensive spectroscopic analysis. All of these compounds were tested for their inhibitory effects on nitric oxide (NO) production in the RAW 264.7 macrophages. Among them, compounds 3 and 4 showed potent inhibitory activity against LPS-induced nitric oxide production in RAW 264.7 macrophages, with IC50 values of 24.0 ± 2.1 µM and 28.6 ± 2.4 µM, respectively.

Physapubescin, a natural withanolide as a kidney-type glutaminase (KGA) inhibitor.

Kidney-type glutaminase (KGA) is over expressed in many kinds of cancers that converts glutamine to glutamate for supplying energy, and has become an object for targeted cancer therapy. The structure-based virtual ligand screening identified physapubescin, a withanolide purified from Physalis pubescens L., as a possible inhibitor of KGA with low binding energy. Enzyme inhibition experiments and cell-based assays further confirmed its inhibitory effects on KGA activity, suggesting potential applications of physapubescin and its derivatives as KGA inhibitors.

Two pairs of farnesyl phenolic enantiomers as natural nitric oxide inhibitors from Ganoderma sinense.

Four new farnesyl phenolic compounds, ganosinensols A-D (1-4) were isolated from the 95% EtOH extract of the fruiting bodies of Ganoderma sinense. Two pairs of enantiomers, 1/2, and 3/4 were isolated by HPLC using a Daicel Chiralpak IE column. Their structures were elucidated from extensive spectroscopic analyses and comparison with literature data. The absolute configurations of 1-4 were assigned by ECD spectra. All of these isolated compounds showed potent inhibitory activity against LPS-induced nitric oxide production in RAW 264.7 macrophages, with IC50 values from 1.15 to 2.26µM.