Berberine inhibits gluconeogenesis in spontaneous diabetic rats by regulating the AKT/MAPK/NO/cGMP/PKG signaling pathway.

This work was aimed to investigate the action mechanism of berberine (BBR) on gluconeogenesis. The effects of BBR were examined in rat primary hepatocytes and confirmed in vivo in spontaneous diabetic rats. Protein levels were assessed by Western blot. Immunofluorescence staining was utilized for visualizing protein expression, while qRT-PCR helped for the determination of gene expression at the mRNA level. Besides, cGMP concentration was measured using ELISA, whereas NO level was assessed by spectrophotometry. BBR inhibited gluconeogenesis by downregulating G6Pase and PEPCK via inhibition of CREB phosphorylation. Moreover, BBR enhanced NO and cGMP concentrations, leading to the activation of the NO/cGMP/PKG signaling via activating AKT1/MAPK axis. The in vivo experiments were consistent with the findings obtained in vitro. Hence, BBR represents a drug candidate for diabetic patients and its mechanism of action may be driven via the AKT/MAPK/NO/cGMP/PKG pathway.

Late-Stage Diversification of Peptides via Pd-Catalyzed Site-Selective δ-C(sp2)-H Fluorination and Amination.

Site-selective C-H fluorination is an attractive strategy for directly transforming inert C-H bonds into C-F bonds, yet it remains a significant challenge. Herein, we have developed an efficient and versatile strategy for site-selective fluorination and amination of phenylalanine-containing peptides via late-stage Pd-catalyzed δ-C(sp2)-H activation, providing a valuable tool for the in situ synthesis of fluorinated indoline scaffolds within peptides.

Mechanistic Insights Into the Rhodium-Catalyzed C-H Alkenylation/Directing Group Migration and [3+2] Annulation: A DFT Study.

The mechanism of the rhodium-catalyzed C-H alkenylation/directing group migration and [3+2] annulation of N-aminocarbonylindoles with 1,3-diynes has been investigated with DFT calculations. On the basis of mechanistic studies, we mainly focus on the regioselectivity of 1,3-diyne inserting into the Rh-C bond and the N-aminocarbonyl directing group migration involved in the reactions. Our theoretical study uncovers that the directing group migration undergoes a stepwise ß-N elimination and isocyanate reinsertion process. As studied in this work, this finding is also applicable to other relevant reactions. Additionally, the role of Na+ versus Cs+ involved in the [3+2] cyclization reaction is also probed.

Recent advances in computational studies on Cu-catalyzed aerobic reactions: cooperation of copper catalysts and dioxygen.

O2, one of the ideal oxidants, suffers from low solubility, low oxidizability, low selectivity and a triplet ground state when applied in organic synthesis. Biomimetic copper catalysis has been demonstrated to be a powerful method for activating and transforming O2 to conduct aerobic reactions for a long time. On the other hand, the structures of Cu-O2 complexes are complex with diverse downstream reactions, whereas active copper intermediates were rarely identified by experimental methods, making the mechanisms of many Cu-catalyzed aerobic reactions far from clear. In this context, computational studies emerged as an effective alternative to mechanistic studies on Cu-catalyzed aerobic reactions. This review introduces the relevant computational studies since 2012, focusing on showing the cooperation of copper catalysts and O2 in dehydrogenation, oxygenation and coupling reactions.

Computational Study Revealing the Mechanistic Origin of Distinct Performances of P(O)-H/OH Compounds in Palladium-Catalyzed Hydrophosphorylation of Terminal Alkynes: Switchable Mechanisms and Potential Side Reactions.

Pd-catalyzed hydrophosphorylation of alkynes with P(O)-H compounds provided atom-economical and oxidant-free access to alkenylphosphoryl compounds. Nevertheless, the applicable P(O)-H substrates were limited to those without a hydroxyl group except H2P(O)OH. It is also puzzling that Ph2P(O)OH could co-catalyze the reaction to improve Markovnikov selectivity. Herein, a computational study was conducted to elucidate the mechanistic origin of the phenomena described above. It was found that switchable mechanisms influenced by the acidity of substrates and co-catalysts operate in hydrophosphorylation. In addition, potential side reactions caused by the protonation of PdII-alkenyl intermediates with P(O)-OH species were revealed. The regeneration of an active Pd(0) catalyst from the resulting Pd(II) complexes is remarkably slower than the hydrophosphonylation, while the downstream reactions, if possible, would lead to phosphorus 2-pyrone. Further analysis indicated that the side reactions could be suppressed by utilizing bulky substrates or ligands or by decreasing the concentration of P(O)-OH species. The presented switchable mechanisms and side reactions shed light on the co-transformations of P(O)-H and P-OH compounds in the Pd-catalyzed hydrophosphorylation of alkynes, clarify the origin of the distinct performances of P(O)-H/OH compounds, and provide theoretical clues for expanding the applicable substrate scope of hydrophosphorylation and synthesizing cyclic alkenylphosphoryl compounds.

Distinctive Mechanistic Scenarios and Substituent Effects of Gold(I) versus Copper(I) Catalysis for Hydroacylation of Terminal Alkynes with Glyoxal Derivatives.

Density functional theory (DFT) calculations have been conducted to study the mechanisms, substituent effects, and the role of bases in Au- and Cu-catalyzed hydroacylation of terminal alkyne with glyoxal derivatives. The two reactions, despite being catalyzed by the same group of transition metals, follow distinctive reaction mechanisms. Through the detailed DFT calculations, insights into the mechanisms are obtained, and the substituent effects and the role of the bases are understood.

Insights into α-Alkynylation and α-Allenylation of Aldehydes under the Synergisitic Catalysis of Gold/Amine: A DFT Study.

A mechanistic investigation of α-alkynylation and α-allenylation of aldehydes under the synergistic catalysis of AuCl/amine was performed using density functional theory (DFT) calculations. For such a reaction that delivers two products, this study reveals that the reaction undergoes such a mechanistic mode: reactants → alkynyl product → allenyl product, implying that the allenyl product cannot be obtained directly from reactants. The product ratio obtained experimentally was rationalized based on the computed results that both products can reversibly interconvert with AuCl as the catalyst and with N-containing Lewis bases as additives such as 4,5-diazafluorenone. For the relative stability of alkynyl versus allenyl compounds, unsaturated substituents are found to favor the allenyl compounds.

Noncovalent Interaction- and Steric Effect-Controlled Regiodivergent Selectivity in Dimeric Manganese-Catalyzed Hydroarylation of Internal Alkynes: A Computational Study.

Selective hydroarylation of internal alkynes catalyzed by a dimeric manganese complex provides a powerful strategy for the construction of multisubstituted alkenes. In this work, density functional theory (DFT) calculations and experimental studies were carried out to explore the mechanism and origin of regiodivergent hydroarylation of internal alkynes reported by our group. The results demonstrate that this reaction first proceeds via a bimetallic mechanism to generate the active catalyst that subsequently undergoes a monometallic mechanism to run the three-stage catalytic cycle: alkyne migratory insertion, protonation, and active catalyst regeneration. Alkyne migratory insertion is considered as the regioselectivity-determining step. Energy decomposition analyses on insertion transition states suggest that the interaction between the substrate and catalyst is mainly responsible for the observed exclusive γ-selectivity of 1a, while the deformation of these two sections induced by the sterically hindered phenyl group and aryl group accounts for the complete ß-position arylation of 1e. The decrease of γ-selectivity with the regulation of a tertiary alcohol motif in 1a originates from the reduced noncovalent interaction. The computational results provide important insights into the origin of regiodivergent selectivities and useful information for further designing and adjusting the strategy in Mn-catalyzed alkyne hydroarylation.

Palladium-Catalyzed Regioselective B(3,4)-H Acyloxylation of o-Carboranes.

We disclose herein an efficient regioselective B(3,4)-H activation via a ligand strategy, affording B(3)-monoacyloxylated and B(3,4)-diacyloxylated o-carboranes. The identification of amino acid and phosphoric acid ligands is crucial for the success of B(3)-mono- and B(3,4)-diacyloxylation, respectively. This ligand approach is compatible with a broad range of carboxylic acids. The functionalization of complex drug molecules is demonstrated. Other acyloxyl sources, including sodium benzoate, benzoic anhydride, and iodobenzene diacetate, are also tolerated.

Ligand-Controlled Regiodivergent Cyanoboration of Internal Allenes by Copper Catalysis.

The first copper-catalyzed regiodivergent cyanoboration of internal allenes with B2 pin2 (bis(pinacolato)diboron) and NCTS (N-cyano-N-phenyl-p-toluenesulfonamide) derivatives is reported. The ß,γ- and α,ß-cyanoborylated products were synthesized with high regio- and stereo-selectivity. Computational studies revealed that nucleophilic addition of allylcopper or related intermediates on cyanation reagent is the regio- and stereo-determining step, while transmetalation with B2 pin2 is the rate-determining step. The nucleophilic addition step proceeds via inner-sphere mechanism in the CuI /P(o-tol)3 and CuI /Xantphos (P(o-tol)3 =tris(o-methylphenyl)phosphine, Xantphos=4,5-bis(diphenylphosphino)-9,9-dimethylxanthene) catalytic systems and via outer-sphere mechanism in the CuII /Xantphos catalytic system, respectively.

Transient Stabilization Effect of CO2 in the Electrochemical Hydrogenation of Azo Compounds and the Reductive Coupling of α-Ketoesters.

The carbon dioxide (CO2 ) capture and utilization has attracted a great attention in organic synthesis. Herein, an unpresented transient stabilization effect (TSE) of CO2 is disclosed and well applied to the electrochemical hydrogenation of azo compounds to hydrazine derivatives. Mechanistic experiments and computational studies imply that CO2 can capture azo radical anion intermediates to protect the hydrogenation from potential degradation reactions, and is finally released through decarboxylation. The promotion effect of CO2 was further demonstrated to work in the preliminary study of electrochemical reductive coupling of α-ketoesters to vicinal diol derivatives. For the electrochemical reductive reactions mentioned above, CO2 is indispensable. The presented results shed light on a different usage of CO2 and could inspire novel experimental design by using CO2 as a transient protecting group.

Metabolic analysis of early nonalcoholic fatty liver disease in humans using liquid chromatography-mass spectrometry.

BACKGROUND: Nonalcoholic fatty liver disease (NAFLD) is a common metabolic disease that affects 20-30% of individuals worldwide. Liver puncture remains the gold standard for the diagnosis of liver diseases despite limitations regarding invasive nature and sample variability. It is of great clinical significance to find noninvasive biomarkers to detect and predict NAFLD. OBJECTIVE: The aims of this study were to identify potential serum markers in individuals with early-stage NAFLD and to advance the mechanistic understanding of this disease using a high-throughput mass spectrometry-based untargeted metabolomics approach. METHODS: One hundred and twelve patients with early-stage NAFLD aged 18-55 were recruited according to the guidelines. The control group included 112 healthy participants. The demographic, anthropometric, clinical and laboratory data of all participants were systematically collected. Serum samples were obtained after an overnight fast. The comprehensive serum metabolomic analysis was performed by ultra-performance liquid chromatography-Orbitrap mass spectrometry. The resultant data was processed by Compound Discover and SIMCA-P software to validate the potential biomarkers. Significantly altered metabolites were evaluated by variable importance in projection value (VIP > 1) and ANOVA (p < 0.01). Pathway analysis was performed using MetaboAnalyst 4.0. RESULTS: The liver function test of early NAFLD patients showed no statistical differences to control group (p > 0.05). However, obvious differences in blood lipids were observed between subjects with NAFLD and controls (p < 0.001). In total, 55 metabolites showed significant changes in experimental group were identified. The area under curve (AUC) values deduced by receiver operating curve (ROC) analysis indicated that these newly identified biomarkers have high predictability and reliability. Of these, 15 metabolites with AUC greater than 0.9 were of great diagnostic value in early NAFLD patients. CONCLUSION: In this study, a total of 15 serum metabolites were found to strongly associate with early NAFLD. These biomarkers may have great clinical significance in the early diagnosis of NAFLD, as well as to follow response to therapeutic interventions.

Double-Regiodetermining-Stages Mechanistic Model Explaining the Regioselectivity of Pd-Catalyzed Hydroaminocarbonylation of Alkenes with Carbon Monoxide and Ammonium Chloride.

Pd-catalyzed hydroaminocarbonylation (HAC) of alkenes with CO and NH4Cl enables atom-economic and regiodivergent synthesis of primary amides, but the origin of regioselectivity was incorrectly interpreted in previous computational studies. A density functional theory study was performed herein to investigate the mechanism. Different from the previous proposals, both alkene insertion and aminolysis were found to be potential regioselectivity-determining stages. In the alkene insertion stage, 2,1-insertion is generally faster than 1,2-insertion irrespective of neutral or cationic pathways for both P(tBu)3 and xantphos. Such selectivity results from the unconventional proton-like hydrogen of the Pd-H bond in alkene insertion transition states. For less bulky alkenes, aminolysis with P(tBu)3 shows low selectivity, while linear selectivity dominates in this stage with xantphos due to a stronger repulsion between xantphos and branched acyl ligands. It was further revealed that the less-mentioned CO concentration and solvents also influence the regioselectivity by adjusting the relative feasibilities of CO-involved steps and NH3 release from ammonium chloride, respectively. The presented double-regiodetermining-stages mechanistic model associated with the effects of ligands, CO concentration, and solvents well reproduced the experimental selectivity to prove its validity and illuminated new perspectives for the regioselectivity control of HAC reactions.

Regioselective Synthesis of Tetrasubstituted Benzenes via Co-Catalyzed Cycloaddition of Alkynyl Ketones and 2-Acetylpyridines.

A Co(II)-catalyzed cycloaddition reaction of alkynyl ketones and 2-acetylpyridines using 2,2'-bipyridine as the ligand has been developed. These reactions have been realized through Co-catalyzed reductive coupling of two molecules of 2-acetylpyridine followed by regioselective insertion of the alkynone. It is the first example of regioselective cyclotrimerization of one molecule of alkyne and two molecules of monoketone to polysubstituted benzene derivatives in good to excellent yields. A mechanism involving the formation of a cobaltacyclopentane via homocoupling of 2-acetylpyridines is proposed, and it is supported by the DFT calculations.

Mechanism and Origin of Chemoselectivity of Ru-Catalyzed Cross-Coupling of Secondary Alcohols to ß-Disubstituted Ketones.

Ru-catalyzed cross-coupling of secondary alcohols with only byproducts H2 and H2O provides a green synthetic strategy to prepare ß-disubstituted ketones. Density functional theory (DFT) calculations were performed with the coupling of 1-phenylethanol and cyclohexanol as a model reaction to gain deeper mechanistic insights herein. The mechanistic details of the main reaction and the key steps of possible side reactions were clarified, and the obtained results are consistent with reported selectivity. Hydrogenation of α,ß-unsaturated ketones and dehydrogenation of ruthenium hydride intermediate are direct chemoselectivity-determining stages. The hydrogenation via 1,4-addition generates more stable intermediates, being favored over that via 1,2-addition, and thus avoids the formation of alkene products. The conjugation and π-π stacking effects of phenyl and the weak electronic effect of alkyls explain the dominance of specific ketone products in the hydrogenation stage. Hydrogenation of ketone products is kinetically operative but not exergonic enough to stop the irreversible dihydrogen release in an open reaction system, and thus alcohol products are absent. Furthermore, water evaporation in aldol condensation is found to be a double-edged sword, as it can accelerate the hydrogenation stage to prevent α,ß-unsaturated ketones from being the main products but decrease the selectivity therein from thermodynamics overall.

Mechanism and Origin of Ligand-Controlled Chemo- and Regioselectivities in Palladium-Catalyzed Methoxycarbonylation of Alkynes.

Pd-catalyzed alkoxycarbonylation of alkynes provided a redox-neutral method to selectively access branched/linear α,ß-unsaturated monoesters and 1,4-dicarboxylic acid diesters. Herein, a systematic computational study was performed to elucidate the mechanism and origin of ligand-controlled chemo- and regioselectivities. It is found that the catalytic cycle, including hydrometallation, carbon monoxide insertion, and methanolysis, is more likely than that involving palladium alkoxycarbonyl intermediates. Both hydrometallation and methanolysis stages are important to determine the chemo- and regioselectivities. Hydrometallation proceeds via anti-Markovnikov-selective migratory insertion or Markovnikov-selective ligand-participated electrophilic addition. A flexible bidentate phosphine ligand slows down migratory insertion due to the stronger trans effect of the CO ligand but accelerates the ligand-participated electrophilic addition by adopting better orbital orientations. On the other hand, a ligand-participated mechanism and an unrevealed mechanism involving ketene intermediates can promote methanolysis, whereas ligands with large bite angles or bulky substituents are detrimental to methanolysis. On the basis of these mechanistic foundations, the influence of the flexibility, basicity, bite angle, and steric hindrance of ligands on chemo- and regioselectivities was clarified. The present study provided more universal and deeper mechanistic insights into Pd-catalyzed alkoxycarbonylation reactions and shed light on the superior regulation performance of the bifunctional pyridyl-containing phosphine ligands.

One-Pot Methylenation-Cyclization Employing Two Molecules of CO2 with Arylamines and Enaminones.

One-pot methylenation-cyclization employing two molecules of CO2 with enaminones and primary aromatic amines was discussed for the first time to access cyclized products. This 1,5,7-triazabicyclo[4.4.0]dec-5-ene and ZnCl2-catalyzed procedure was characterized by the selective conversion of two molecules of CO2 into methylene groups in a multicomponent cyclization reaction. According to the computational study and control experiments, the reaction might proceed through the generation of bis(silyl)acetal and condensation of arylamine and aza-Diels-Alder processes. Moreover, the resulting products will probably be potential organic building blocks with adjustable photophysical properties.

C-H Activation versus Ring Opening and Inner- versus Outer-Sphere Concerted Metalation-Deprotonation in Rh(III)-Catalyzed Oxidative Coupling of Oxime Ether and Cyclopropanol: A Density Functional Theory Study.

The Rh(III)-catalyzed oxidative coupling of oxime ether (S1) and cyclopropanol (S2) with Cu(II) as the oxidant features the combination of C-H activation and strained ring opening. The sequential order of C-H activation versus ring opening was investigated with the aid of density functional theory calculations. Prior ring opening due to the release of ring strain is found to be favored over the prior C-H activation. For the prior ring-opening mechanisms, the outer-sphere concerted metalation-deprotonation (CMD) mechanism in C-H bond activation is energetically favored. The outer-sphere CMD mechanism proposed in this work favors solvent effects and affords the N→Rh binding that allows a directing role of the Schiff base group. In conclusion, the reaction was suggested to undergo prior ring opening followed by C-H activation via the outer-sphere CMD mechanism.

Mechanism and Origin of Stereoselectivity of Pd-Catalyzed Cascade Annulation of Aryl Halide, Alkene, and Carbon Monoxide via C-H Activation.

The combination of carbon monoxide with palladium chemistry has been demonstrated to be a promising tool for the synthesis of carbonyl compounds, and relative mechanistic studies are desirable to take this field one step further. In this manuscript, density functional theory calculations were performed to investigate the mechanism and origin of stereoselectivity of Pd-catalyzed cascade annulation of aryl iodide, alkene, and carbon monoxide to access the core of cephanolides B and C. It was found that the favorable mechanism proceeds via oxidative addition of Ar-I bond, migratory insertion of the C═C bond, CO insertion into the Pd-(sp3) bond, Ar-H activation, and C(sp2)-C(sp2) reductive elimination. The Ar-H activation is the rate-determining step and goes through an I-assisted outer-sphere concerted metalation-deprotonation mechanism. The C═C bond insertion is irreversible and controls the stereoselectivity. In contrast, other two pathways involving the direct Ar-H activation after the C═C bond insertion is less favored because of the following difficult CO insertion on the palladacycle intermediate. Further calculations well reproduced the experimental results, which supports the rationality of our computation. Meanwhile, the influence of the steric effect of three substitution sites on the stereoselectivity was disclosed, which should be helpful to the further experimental design in the synthesis of analogues.

Mechanistic Insights into the Chemo- and Regio-Selective B(C6F5)3 Catalyzed C-H Functionalization of Phenols with Diazoesters.

The Lewis acidic B(C6F5)3 was recently demonstrated to be effective for the C-H alkylation of phenols with diazoesters. The method avoids the general hydroxyl activation in transition-metal catalysis. Ortho-selective C-H alkylation occurs regardless of potential para-selective C-H alkylation and O-H alkylation. In the present study, a theoretical calculation was carried out to elucidate the reaction mechanism and the origin of chemo- and regio-selectivity. It is found that the previously proposed B(C6F5)3/N or B(C6F5)3/C bonding-involved mechanisms are not favorable, and a more favored one involves the B(C6F5)3/C═O bonding, rate-determining N2 elimination, selectivity-determining electrophilic attack, and proton transfer steps. Meanwhile, the new mechanism is consistent with KIE and competition experiments. The facility of the mechanism is attributed to two factors. First, the B(C6F5)3/C═O bonding reduces the steric hindrance during electrophilic attack. Second, the bonding forms the conjugated system by which the LUMO energy is reduced via the electron-withdrawing B(C6F5)3. The ortho-selectivity resulted from the greater ortho-C-C (than para-C-C) interaction and the O-H···O and O-H···F hydrogen-bond interaction during electrophilic attack. The greater C-C (than C-O) interaction and the π-π stacking between the benzene rings of phenol and diazoester concerted contribute to the chemo-selective C-H alkylation.