Latest ArticlesTo overcome the shortcomings of single component carrier supported platinum (Pt)-based catalysts, herein, we demonstrate the fabrication of alumina combined mesoporous carbon to prepare a series of alumina-carbon composites and their corresponding Pt-based catalysts. The alumina-carbon composites Al@PhFC are synthesized by using phloroglucinol-formaldehyde resin as carbon source and aluminum acetylacetone as the aluminum source. Further, the effect of alumina content on the properties of the composites is investigated. The composites and catalysts are characterized by using XRD, XPS, N2 sorption, and TEM. The Pt/Al@PhFC-1.8 composite with appropriate amounts of alumina, pore diameter, and moderate Pt nanoparticle size, resulted in 99.5% of conversion efficiency and 77.4% of optical selectivity in the asymmetric hydrogenation of ethyl 2-oxo-4-phenylbutanoate (EOPB). Interestingly, this composite can be used more than 20 times without a significant decrease in its performance.
Palladium-catalyzed highly meta-selective C -H iodination of phenylacetic acid, benzylphosphonate and benzylsulfonate scaffolds with molecular I2 is developed using a pyridine-type template. The practical ester linkages enable the directing template easily installed and readily removed. The substrate scope is broad, and alkyl, methoxyl, trifluomethyl, and halo substituents are compatible with this reaction. Further transformations of ibuprofen iodide intermediates by Pd-catalyzed C -C and C-heteroatom bond formation illustrate the broad utility of this method.
Direct C(sp3)-H functionalization of N-unprotected aliphatic amines represents one of the most efficient and straightforward strategies for amine synthesis. Despite some recent progress in this field, the NH2-directed γ-C(sp3)-H arylation of primary aliphatic amines except α-amino esters remained an unmet challenge. In this report, we established a simple and efficient method for site-selective C(sp3)-H arylation of primary aliphatic amines by aryl iodides. In the presence of only 5 mol% Pd(OAc)2, a wide range of aliphatic amines including O-benzyl and O-silyl amino alcohols were arylated at γ-or δ-positions by aryl iodides containing a broad scope of functional groups. The synthetic application of this method had also been demonstrated by large-scale synthesis, the synthesis of a fingolimod analogue, and the conjugation with natural D-menthol and fluorescent 1, 8-naphthalimide.
Dipyrrolyldiketone difluoroboron complexes (BONEPYs) were synthesized by condensation of the corresponding pyrroles and malonyl chloride followed by treatment with BF3·OEt2. The aryl-substituted pyrrole is introduced to form a cyclic system in order to investigate anion binding studies. In BONEPYs 1-3 the o-H of the aryl group forms hydrogen bonding with F- to give a more table complex. In contrast, the intramolecular hydrogen-bonded BONEPYendo-4 is more stable than its exo isomer. While adding F-, the hydrogen bonds must be broken first to give 4·(3)F-. Owing to the electron-rich group (-OMe), the o-H of the phenyl group can hardly interact with F- via hydrogen bonding to give the less stable complex 4·(5)F-. The energy differences between the different conformations were calculated using DFT methods, which is consistent to the experimental observations.
An efficient method was developed for the conjugate addition of water to various α, β-unsaturated ketones by using bismuth(Ⅲ) chloride as a catalyst. The reactions proceeded smoothly in the presence of a catalytic amount of BiCl3 (20 mol%) in aqueous media to furnish a variety of synthetically useful β-hydroxyl ketones in moderate to good yields. Apart from water molecule, various alcohols could also be employed as nucleophiles to react with α, β-unsaturated ketones, leading to β-alkoxyl ketones in modest to high yields. In addition, the mild reaction conditions also entailed the conjugate addition reactions to proceed with the tolerance to a range of functional groups.
(±)-Crataegusnorin A (1a/1b) and B (2a/2b), two pairs of rare 8, 9'-epoxy-type norlignan enantiomers featuring a γ-butyrolactone ring, were isolated from the fruit of Crataegus pinnatifida. Their structures were determined via extensive spectroscopic analyses. Gauge-independent atomic orbital (GIAO) NMR chemical shift calculations, combined with the advanced statistical method DP4+ were employed to establish the relative configurations of four compounds. Next, chiral separation was accomplished by chiral chromatographic column and the absolute configurations of the four compounds were unambiguously assigned by comparison between their experimental electronic circular dichroism curves with the quantum-mechanically calculated curves based on time-dependent density functional theory (TDDFT). All the isolates were evaluated for their neuroprotective activities against H2O2-induced cell injury in human neuroblastoma SH-SY5Y cells. The results showed that two pairs of enantiomers 1a/1b and 2a/2b displayed diff; erent effect on neuroprotective activity. Among them, compound 2a displayed the most potent neuroprotective effect. Further flow cytometry analysis indicated that 2a could protect SH-SY5Y cells from oxidative damage through inhibiting cell apoptosis.
HYL derived from the venom of the solitary bee Hylaeus signatus (Hymenoptera:Colletidae) is an α-helical antimicrobial peptide with 16 residues. To explore whether HYL can be applied in anti-tumor therapy, we synthesized HYL and further modified its structure by using a solid-phase synthesis method, and then evaluated their antitumor activities. Firstly, we identified the key residues of HYL by alanine scanning strategy, and then a series of stapled peptides were synthesized by hydrocarbon stapling strategy without destroying the key residues. All the stapled peptides of HYL showed significant improvement not only in α-helicity, but also in antitumor activity and protease resistance when compared to the parent peptide HYL. The results showed that hydrophobicity and amphiphilicity are important factors affecting the antitumor activity of HYL, and the stapling strategy can significantly affect the proteolytic stability and helicity of HYL. What's more, we find that the stapled peptides HYL-14, HYL-16 and HYL-18 show a promising prospect for novel anti-tumor drug development.
This study presents a facile strategy for the formation of highly substituted butterfly 1, 4-adducts/9, 10-adducts via the Diels-Alder reaction of benzyne intermediates. The method achieves very good to excellent yields of the respective anthracene derivatives under mild conditions. This practical protocol is compatible with a variety of sensitive functional groups and provides access to difunctionalized bridge 1, 4-adducts/9, 10-adducts.
A Sc(OTf)3-catalyzed [3 + 3] cycloaddition of 2, 2'-diester aziridines with β-(indol-2-yl)-α, β-unsaturated ketones was developed, affording polysubstituted tetrahydro-γ-carbolines in single diastereoisomers in good to excellent yields.
The effective valuation of catalyst supports in the catalytic oxidation makes the contribution to understand the support effect of great interest. Here, the role of active substrate in the performance and stability of Cu-Fe-Co ternary oxides was studied towards the complete catalytic oxidation of CO. The Cu-Fe-Co oxide thin films were deposited on copper grid mesh (CUGM)using one-step pulsed-spray evaporation chemical vapor deposition method. Crystalline structure and morphology analyses revealed nano-crystallite sizes and dome-top-like morphology. Synergistic effects between Cu, Fe and Co, which affect the surface Cu2+, Fe3+, Co3+ and chemisorbed oxygen species (O2- and OH-) of thin films over the active support and thus result in better reducibility. The thin film catalysts supported on CUGM exhibited attractive catalytic activity compared to the ternary oxides supported on inert grid mesh at a high gas hourly space velocity. Moreover, the stability in time-on-stream of the ternary oxides on CUGM was evaluated in the CO oxidation for 30 h. The adopted deposition strategy of ternary oxides on CUGM presents an excessive amount of adsorbed active oxygen species that play an important role in the complete CO oxidation. The catalysts supported on CUGM showed better catalytic conversion than that on inert grid mesh and some literature-reported noble metal oxides as well as transition metal oxides counterparts, revealing the beneficial effect of the CUGM support in the improvement of the catalytic performance.
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