A rapid and efficient microwave-assisted synthesis of hydantoins and thiohydantoins

The present paper describes studies on the synthesis of the antiepileptic drug phenytoin, and of structurally related derivatives. First, the influence of the solvent has been investigated in the microwave-assisted synthesis of the drug, resulting in a yield improvement and a cleaner reaction. Second, a two-step reaction is described to synthesize selectively and in high yields phenytoin. The first step consists in microwave activation of the reaction of benzil with thiourea, the second step includes the conversion of the resulting 2-thiohydantoin to phenytoin using hydrogen peroxide. Moreover, microwave activation is a very convenient method for the synthesis of 3-alkylated phenytoin derivatives, resulting in a much more selective method than the previously reported procedure using alkylating agents.     

Microwave-assisted combined Mitsunobu reaction-Claisen rearrangement and microwave-assisted phenol oxidation: rapid synthesis of 2,6-disubstituted-1,4-benzoquinone natural products

Microwave irradiation of a phenol, an allylic alcohol, di-isopropyl azodicarboxylate and triphenylphosphine at 220-240 °C for 30 min results in a combined Mitsunobu reaction and Claisen rearrangement to give the rearranged 2-allylphenol. Following the first detailed study of microwave-assisted phenol oxidation, rapid syntheses of the natural products primin and 2-methoxy-6-pentadecyl-1,4-benzoquinone (four reaction steps, total reaction time 1 h) were achieved using this combined Mitsunobu-Claisen strategy in combination with two further microwave-assisted steps (alkene hydrogenation and phenol oxidation).     

Amberlite IR-120 catalyzed,microwave-assisted rapid synthesis of 2-aryl-benzimidazoles

An expeditious synthesis of 2-aryl-benzimidazoles by the condensation of o-phenylenediamine with various araldehydes is described. This greener protocol is catalyzed by Amberlite IR-120, and proceeds efficiently in the absence of any organic solvent under microwave irradiation within 3–5 min.     

Barium manganate in microwave-assisted oxidation reactions: synthesis of lactones by oxidative cyclization of diols

Microwave irradiation of a range of diols at 150 °C in acetonitrile in the presence of three equivalents of barium manganate facilitates a novel tandem oxidation/heterocyclocondensation to give the corresponding lactone, including both small and medium ring lactones, in only one hour and in high yield without the need for chromatographic purification.     

Optimization and application of microwave-assisted acid hydrolysis for rapid quantification of protein oxidation markers using LC-MS

Simple and efficient microwave-assisted acid hydrolysis (MAAH) of proteins was used for rapid quantification of α-aminoadipic semialdehyde (AAS) and γ-glutamic semialdehyde (GGS) as major protein oxidation markers. The precursor amino acid residues corresponding to AAS and GGS in oxidized proteins were derivatized by reductive amination with sodium cyanoborohydride (NaCNBH₃) and p-aminobenzoic acid (ABA) followed by MAAH to generate the marker derivatives AAS-ABA and GGS-ABA. The quantification was performed using electrospray ionization liquid chromatography-mass spectrometry (ESI LC-MS). The important parameters for hydrolysis were optimized, which include the temperature, the reaction time, the acid concentration and volume as well as the microwave power. Compared to the conventional acid hydrolysis of 18-24 h using 6-12 M HCl at 110 °C applied commonly in the literature and also in this work, MAAH of proteins can be completed as fast as in only 2-10 min and, additionally, with a 3-5 times higher yield of the final derivatization products. Furthermore, a better agreement between the ratio of the detected derivatization products and the theoretical yields from the studied protein has also been achieved, which indicates that MAAH may serve as a more reliable method of acid hydrolysis for this purpose than that with conventional thermal heating. The MAAH method is demonstrated to be a time-saving, reproducible and efficient technique for studying AAS and GGS as protein oxidation markers using LC-MS.     

Porous Ni/NiO nanohybrids for electrochemical catalytic glucose oxidation

The remarkable development of nanotechnology and nanoscience has greatly promoted the vigorous development of the field of nanomaterials. This study explores a porous cuboid Ni/NiO composite nanomaterial obtained by calcining NiC_2O_4·2H_2O under a N_2 environment. The composite affords direct electrochemical activity and good electrocatalytic properties. Compared to uncalcined precursor, the porous Ni/Ni O obtained after calcination exhibited higher catalytic activity for glucose oxidation with higher sensitivity. Moreover, because of its regular cube structure the as-synthesized Ni/Ni O exhibited improved electrochemical stability. Such porous Ni/Ni O nanocubes represent promising glucose catalyst with high sensitivity and selectivity, improved stability and fast amperometric response.     

The synthesis of temperature-sensitive PMMA-coating PNIPAM particles via a rapid microwave-assisted polymerization

PMMA-coating PNIPAM particles were prepared via a rapid microwave-assisted polymerization. The PMMA shell was found to have a limitation on the movement of PNIPAM chains, which resulted in a reversible swelling and shrinking. The swelling-shrinking processes of particles were traced by laser light scattering, and the swelling factor of particles was found to be 1.63 with an average radius of 83.4 nm in the swelling state and of 70.8 nm in the shrinking state.     

Barium manganate in microwave-assisted oxidation reactions: synthesis of solvatochromic 2,4,6-triarylpyrimidines

Synthesis of 2,4,6-trisubstituted pyrimidines by tandem oxidation/heterocyclocondensation of propargylic alcohols and amidines is effected rapidly and efficiently under microwave dielectric heating using barium manganate as oxidant. Irradiation at 150 °C in ethanol–acetic acid for 45 min results in dramatic improvements in yield over the corresponding manganese dioxide-mediated method and establishes a rapid route to triarylpyrimidines in order to investigate their photophysical properties.     

Chitosan-mediated synthesis of carbon nanotube-gold nanohybrids

Metal-nanotube nanohybrids were produced by in situ synthesis and stabilization of gold nanoparticles on chitosan-functionalized carbon nanotubes. The formation of gold nanoparticles from tetrachloroauric acid was observed after only a few minutes of contact with the functionalized nanotubes, at room temperature. These results suggest that adsorption of chitosan at the surface of carbon nanotubes permits smooth reduction of the metallic salt and efficient anchoring of gold nanoparticles to the nanotubes.

     

Enhancement of combinatorial chemistry by microwave-assisted organic synthesis

It was in the 1980 s that the first papers in which the use of either combinatorial methods or microwave heating in organic chemistry were published. Unlike combinatorial chemistry, which quite readily became an accepted method, particularly in the pharmaceutical industry, it is only now that microwave heating is truly gaining acceptance. Our aim in this review is to attempt to rationalize this slow acceptance and to show the benefits to be gained by employing microwave heating in tandem with combinatorial chemistry. We will also give a number of examples of successful applications.     

Microwave synthesis of supported Au and Pd nanoparticle catalysts for CO oxidation

We report the microwave synthesis and characterization of Au and Pd nanoparticle catalysts supported on CeO2, CuO, and ZnO nanoparticles for CO oxidation. The results indicate that supported Au/CeO2 catalysts exhibit excellent activity for low-temperature CO oxidation. The Pd/CeO2 catalyst shows a uniform dispersion of Pd nanoparticles with a narrow size distribution within the ceria support. A remarkable enhancement of the catalytic activity is observed and directly correlated with the change in the morphology of the supported catalyst and the efficient dispersion of the active metal on the support achieved by using capping agents during the microwave synthesis. The significance of the current method lies mainly in its simplicity, flexibility, and the control of the different factors that determine the activity of the nanoparticle catalysts.     

Rapid microwave-assisted solid-phase glycopeptide synthesis

Coupling of glycosylated Fmoc-Thr or Fmoc-Ser with N-terminal amino acids on a resin proceeded smoothly under microwave irradiation for 20 min with much higher efficiency (98% yield per coupling) than found in more general conditions. Compared with a conventional protocol, the present method greatly reduces the time required for solid-phase glycopeptide synthesis from 4 days to 7 h, as is the case with the synthesis of Muc-1-related 20-residue glycopeptide carrying five core-2 trisaccharide chains. [structure: see text]     

Chromonic/Silica nanohybrids: synthesis and macroscopic alignment

Some dye molecules self-aggregate to exhibit a lyotropic columnar liquid crystal state (chromonic liquid crystal) via pi stacking in relatively highly concentrated aqueous solutions. In this work, the chromonic liquid crystal structure was immobilized, for the first time, with silica networks by way of the sol-gel condensation process. The immobilization of the columnar structure was successfully attained in the presence of 2-(2-aminoethoxy)ethanol, which favorably mediates the interface between the anionic charge of the dye aggregates and the silica network. Without this molecule, the sol-gel process gave rise to a transformation from columnar to lamellar structure. Both spin-coating and dip-coating methods gave essentially the same results. In the dip-coated films, the dye molecules were aligned over a large area with orientation orthogonal to the lifting direction.     

Trifluoroacetic anhydride-catalyzed oxidation of isonitriles by DMSO: a rapid, convenient synthesis of isocyanates

A smooth and efficient oxidation of isonitriles to isocyanates by sulfoxides is catalyzed by trifluoroacetic anhydride. With use of DMSO as the oxidant and 5 mol·% TFAA (dichloromethane, -60 to 0 °C), the process is complete in a few minutes, forming dimethyl sulfide as the only byproduct. The newly formed isocyanates may be used directly or isolated in high purity by solvent evaporation.     

Total synthesis of endothelin 1 by microwave-assisted solid phase method

<正>A microwave-assisted solid phase synthesis for endothelin 1 is presented.Reduced endothelin 1 was synthesized efficiently on Wang resin under microwave irradiation using Fmoc/tBu orthogonal protection strategy.The whole peptide was cleaved from the resin and two disulphide bridges were formed under air oxidation at room temperature.The purity and efficiency of synthesizing the peptide is much higher than other methods used before.     

Rapid synthesis of LiFePO4 nanoparticles by microwave-assisted hydrothermal method

Lithium iron phosphate (LiFePO₄) nanoparticles have been successfully prepared via microwave-assisted hydrothermal route within ultrashort synthesis-time condition. Electrochemical data reveal that the as-synthesized LiFePO₄ after a post-synthesis heat treatment in an inert atmosphere have excellent rate capability and cycling stability. Ultrashort synthesis-time and higher yield show a possibility of scaling up for industrial production.     

Total synthesis of human urotension-Ⅱ by microwave-assisted solid phase method

Human urotension-Ⅱwas synthesized efficiently on Wang resin under microwave irradiation using Fmoc/tBu orthogonal protection strategy.Disulphide bridge was formed on solid phase with the irradiation of microwave,then the whole peptide was cleaved from the resin.The purity of crude peptide cyclized under microwave irradiation was higher than that under room temperature.     

微波辅助水相有机合成研究进展

微波辅助水相有机合成结合了水为溶剂和微波加热的特点,具有反应速率快、产率高、绿色环保等优点.本文介绍了近几年来微波辅助水相(过热水,T≥100 ℃)有机合成的研究进展,主要包括过碳-碳键形成反应、碳-杂键形成反应、环加成反应、Mannich反应、脱保护反应等.并展望了该领域今后的发展方向.