Synthesis of a highly hydrophobic cyclic decapeptide by solid-phase synthesis of linear peptide and cyclization in solution

A general method was described to synthesize a highly hydrophobic cyclic peptide,cyclo[LWLWLWLWLQ]where underlines indicate D-configuration of the amino acid,by a two-step solid-phase/solution synthesis strategy.The linear decapeptide was assembled by standard Boc chemistry on solid-phase and subsequently cyclized in solution with high efficiency and reproducibility. In subsequent purification by semi-preparative HPLC,50%(v/v) DMF/H_2O was employed as the solvent to overcome the difficulty of solubilization...

Polymer-support Selenium-induced Electrophilic Cyclization:Solid-phase Synthesis of Flavonoids

The Lewis acid mediated polystyrene supported selenium cyclization of chalcones and oxidative cleavage of selenium resins flavonoids in good yields and purities have been reported. induced intramolecular gave the corresponding

STUDIES ON THE REACTION OF SULFUR,SELENIUM AND TELLURIUM WITH SODIUM HYDROXIDE UNDER PHASE TRANSFER CATALYSIS(Ⅱ).A CONVENIENT METHOD FOR THE SYNTHESIS OF BI(ACYL)DISULFIDES

A simple and general method for the synthesis of bi(acyl)disulfides is reported.Sulfur is allowed to react with sodium hydroxide to give sodium disulfide at 65℃ under PTC,which can react with acyl halides to afford bi(acyl)disulfides in good to excellent isolated yields.The effects of solvents and phase transfer catalysts are discussed.

Structure, synthesis, and catalytic properties of nanosize cerium-zirconium-based solid solutions in environmental catalysis

Nanosize cerium-zirconium solid solution(CZO)with a special fluorite structure has received an increasing research interest due to their remarkable advantages such as excellent oxygen storage capacity and great flexibility in their composition and structure.By partial metal(including rare earth,transition,alkaline earth or other metal)doping into CZO,the physicochemical properties of these catalytic materials can be controllable adjusted for the study of specific reactions.To date,nanosize CZO has been prepared by co-precipitation,sol-gel,surfactant-assisted approach,solution combustion,micro-emulsion,high energy mechanical milling,etc.The advent of these methodologies has prompted researchers to construct well-defined networks with customized micromorphology and functionalities.In this review,we describe not only the basic structure and synthetic strategies of CZO,but also their relevant applications in environmental catalysis,such as the purification for CO,nitrogen oxides(NOx),volatile organic compounds(VOC),soot,hydrocarbon(HC),CO2 and solid particulate matters(PM),and some reaction mechanisms are also summarized.

Hydrothermal Synthesis, Structural Characterization and Catalysis Property of a Zr-substituted Polyoxometalate Based on [Zr2(μ-OH)2(α-Si W11O39)2]^10- Building Blocks

A new Zr-substituted polyoxometalate（POM） [（CH3）4N]6H2Cs2（H2O）4[Zr2（μ2-OH）2（α-SiW11O39）2]·27H2O（1） was prepared by the reaction of K10[A-α-SiW9O（34）]·25H2O with ZrCl4 in 0.5 mol/L NaAc-HAc（Ac = CH3COO^-） buffer solution（pH = 4.5）. 1 was characterized by elemental and thermogravimetric analyses, powder X-ray diffraction and single-crystal X-ray diffraction. The title compound crystallizes in monoclinic system, space group P21/m with a = 13.1865（16）, b = 20.964（3）, c = 21.432（3） A^°, V = 5923.9（12） A^°3, Z = 2, Dc = 3.833 mg/m^3, μ = 22.175 mm^-1, F（000） = 6116, the final R = 0.0697 and wR = 0.1959 for 10319 observed reflections with I 〉 2σ（I）. Single-crystal X-ray structure analysis reveals that 1 exhibits a one-dimensional chain structure based on sandwiched-type POM anions [Zr2（μ2-OH）2（α-SiW11O（39））2]^10- linked by Cs＋cations. In addition, catalytic tests indicate that 1 provides a sufficient driving force for the conversion from thioethers to sulfoxides/sulfones by H2O2.

Facile Synthesis of [1,2,4]Triazolo[4,3-a]pyrazin-3-amines via Oxidative Cyclization of 1-(Pyrazin-2-yl)guanidine Derivatives

In this study, we applied a novel, mild, and convenient synthetic method involving the oxidative cyclization of 1-(pyrazin-2-yl)guanidine derivatives to produce [1,2,4]triazolo[4,3-a ]pyrazin-3-amines. We optimized the reaction procedure to easily obtain 5-chloro-[1,2,4]triazolo[4,3-a ]pyrazin-3-amine. Various types of halogenated pyrazines can successfully undergo this process. We synthesized a series of 1-(pyrazin-2-yl)guanidines and [1,2,4]triazolo[4,3-a ]pyrazin-3-amines, and then elucidated their structures based on their ~1H-NMR, ^(13)C-NMR, ESI-HRMS, and nuclear Overhauser effect spectra.

Stereodivergent synthesis ofα-fluoroα-azaarylγ-butyrolactones via cooperative copper and iridium catalysis

The development of stereodivergent synthetic methods to access all four stereoisomers of biologically importantα-fluoroγ-butyrolactones containing vicinal stereocenters is of great importance and poses a formidable challenge owing to ring strain and steric hindrance.Herein,a novel asymmetric[3+2]annulation ofα-fluoroα-azaaryl acetates with vinylethylene carbonate was successfully developed through Cu/Ir-catalyzed cascade allylic alkylation/lactonization,affording a variety of enantioenrichedα-fluoroγ-butyrolactones bearing vicinal stereogenic centers with high reaction efficiency and excellent levels of both stereoselectivity and regioselectivity(up to 98%yield,generally>20:1 dr and>99%ee).Notably,all four stereoisomers of these pharmaceutically valuable molecules could be accessed individually via simple permutations of two enantiomeric catalysts.In addition,other azaaryl acetates bearingα-methyl,α-chlorine orα-phenyl group were tolerated well in this transformation.Reaction mechanistic investigations were conducted to explore the process of this bimetallic catalysis based on the results of reaction intermediates,isotopic labelling experiments,and kinetic studies.

An Efficient and Convenient Cyclization Method for the Synthesis of Flavans

A convenient cyclization method for the flavans synthesis is described. BF3 was used for the first time as an efficient catalyst to effect the cyclization of 1,3-diarylpropan-1-ols.

Asymmetric Synthesis of Dihydrospirotryprostatin B via a Silica Gel-Mediated Cyclization of Tryptamine-Ynamide

Comprehensive Summary An asymmetric synthesis of dihydrospirotryprostatin B was achieved in 15 steps(8 purifications)from L-tryptophan.The main feature of our synthetic strategy is the efficient construction of spirocyclic oxindole intermediate containing a chiral quaternary carbon center,involving the silica gel-mediated cyclization of tryptamine-ynamide and oxidation under neat conditions.

Recent progress on the synthesis of defective UiO-66 for thermal catalysis

Zirconium terephthalate UiO-66 has aroused great interest in catalysis since it exhibits significant flexibility and compatibility for accommodating a high number of defects as well as exceptional thermal and chemical stability.Until now,many works have focused on the modulations of the Zr6-oxo clusters in UiO-66 in terms of diverse synthesis,advanced characterizations,and their catalytic applications.To achieve high catalytic efficiency,it is still highly desired for rationally constructing and modulating the Zr6-oxo clusters with exposed catalytic sites and diverse microenvironments for advanced catalysis.In this review,we provide a comprehensive summary of recent progress on the synthesis of defective UiO-66,qualitative and quantitative characterizations,as well as a logical overview of heterogeneous catalytic applications over the past few years.Finally,the outlooks for the research paradigm of defective UiO-66 are discussed.

Modular synthesis of β-amino acids from alkenes,amines,and CO_(2) via photoredox/copper dual catalysis

The conversion of industrial waste into value-added chemicals represents a compelling approach to bolster sustainability efforts.Among the primary components of greenhouse gases,carbon dioxide(CO_(2))stands as an ideal C_(1) source owing to its abundance,renewability,and non-toxic nature.

Shape-Controlled Synthesis of Platinum-Based Nanocrystals and Their Electrocatalytic Applications in Fuel Cells

To achieve environmentally benign energy conversion with the carbon neutrality target via electrochemical reactions, the innovation of electrocatalysts plays a vital role in the enablement of renewable resources. Nowadays, Pt-based nanocrystals(NCs) have been identified as one class of the most promising candidates to efficiently catalyze both the half-reactions in hydrogen-and hydrocarbonbased fuel cells. Here, we thoroughly discuss the key achievement in developing shape-controlled Pt and Pt-based NCs, and their electrochemical applications in fuel cells. We begin with a mechanistic discussion on how the morphology can be precisely controlled in a colloidal system, followed by highlighting the advanced development of shape-controlled Pt, Pt-alloy, Pt-based core@shell NCs, Pt-based nanocages, and Pt-based intermetallic compounds. We then select some case studies on models of typical reactions(oxygen reduction reaction at the cathode and small molecular oxidation reaction at the anode) that are enhanced by the shape-controlled Pt-based nanocatalysts. Finally, we provide an outlook on the potential challenges of shape-controlled nanocatalysts and envision their perspective with suggestions.

Asymmetric Synthesis of Anti-tuberculosis-specific Drug TBAJ-876 through Synergistic Li/Li Catalysis

TBAJ-876, developed by TB Alliance, a novel anti-tuberculosis-specific drug, has entered Phase II clinical trials. Herein, the first asymmetric synthesis of TBAJ-876 has been realized using synergistic Li/Li catalysis with excellent yield of 95% and 88 : 12 er (99.6 : 0.4 er, 10 : 1 dr after simple recrystallization). Furthermore, DFT calculations and 7Li-NMR analysis illustrated the mechanism of the synergistic reaction: a chiral Li-complex activates the nucleophile to control the stereoselectivity, while the other achiral Li-complex activates the electrophile to catalyze the carbonyl addition reaction. Additionally, this protocol has been successfully carried out at 5 gram-scale, showing its industrial potential.

Modular synthesis of 1,4-diketones through regioselective bis-acylation of olefins by merging NHC and photoredox catalysis

Efficient and modular synthesis of structurally diverse 1,4-diketones from readily available building blocks represents an essential but challenging task in organic chemistry.Herein,we report a multi-component,regioselective bis-acylation of olefins by merging NHC organocatalysis and photoredox catalysis.With this protocol,a broad range of 1,4-diketones could be rapidly assembled using bench-stable feedstock materials.The robustness of this method was further evaluated by sensitivity screening,and good reproductivity was observed.Moreover,the diketone products could be readily converted into functionalized heterocycles,such as multi-substituted furan,pyrrole,and pyridazine.Mechanistic investigations shed light on the NHC and photoredox dual catalytic radical reaction mechanism.

Synthesis of n-Butyl Acetate by Microwave Irradiation Under the Assistance of Solid-Liquid Phase Transfer Catalysis Without Solvent

Introduction Microwave irradiation has been very widely used in heating, cooking and brewing. Several papers which describe the use of domestic microwave ovens to perform rapid organic synthesis in solution have been published. The high heating efficiency gives rise to remarkable rate of reaction and dramatic reduction of reaction time. Nevertheless, its application seems to be limited to these procedures because of

Synthesis of 1,2:4,5-di-O-Isopropylidene-3-C-Cyano-β-D-ribo-hex-2-ulo Pyranose by Phase Transition Catalysis

Introduction The cyano branched carbohydrates are useful, versatil intermediaries for the synthesis of branched sugars having biological activity in nature. Owing to the good yield, mild reaction conditions and high stereospecificity, the phase transition catalysis(PTC)method has been widely used to the syntheses of C-

Synthesis of p-nitrophenol under normal pressure with A-1 phase transfer catalysis

p nitrophenol is synthesized using p nitrochlorobenzene and sodium hydroxide with phase transfer catalyst. Several reaction factors, such as catalyst type, the amounts of catalysts and sodium hydroxide, the concentration of sodium hydroxide solution as well as reaction time, affect greatly the yield of p nitrophenol. The optimum reaction conditions are as follows: A 1 used as phase transfer catalyst whose consumption is 6% (mole fraction) of p nitrochlorobenzene; the molar ratio of sodium hydroxide to p nitrochlorobenzene is 3:1; the concentration of sodium hydroxide solution is 50% (mass fraction). Nitrobenzene, whose molar amount is 2.45 times as much as that of p nitrochlorobenzene; reaction time is 7 h at 140 ℃ under normal pressure. The final yield of p nitrophenol is 83.6%.

SYNTHESIS OF DIARYL ETHERS THROUGH PHASE TRANSFER CATALYSIS WITH POTASSIUN FLUORIDE COATED ALUMINA AS A STRONG BASE

Seven diaryl ethers were synthesized with potassium fluoride coated alumina as a strong base and the addition of catalytic amount of PTC. The yield of diaryl ethers with addition of PTC was much higher than that without PTC.A discussion of the catalysis mechanism was given in this paper.

SYNTHESIS OF 1-O-ACYL-2,3,4-TRI-O-ACETYL-β-D-XYLO-AND ARABINOPYRANOSES BY PHASE TRANSFER CATALYSIS

The acetylated xylo-and arabinopyranosyl esters(1-8) were obtained in high yields with stereoselectivity by phase-transfer catalyzed (PTC) synthesis, and their structures were confirmed by elemental analysis and IR,^(1)H-NMR spectral data.