Coupling Reactions of Alkynylsilanes Mediated by a Cu(I) Salt: Novel Syntheses of Conjugate Diynes and Disubstituted Ethynes

Reaction of 1-trimethylsilylalkyne with copper(I) chloride in a polar solvent, DMF, at 60 degrees C under an aerobic conditions smoothly undergoes homo-coupling to give the corresponding symmetrical 1,3-butadiynes in 70-99% yields. In addition, (arylethynyl)trimethylsilanes are found to couple with aryl triflates and chlorides in the presence of Cu(I)/Pd(0) (10 mol %/5 or 10 mol %) cocatalyst system to give the corresponding diarylethynes in 49-99% yields. The cross-coupling reaction is applied to a one-pot synthesis of the corresponding unsymmetrical diarylethynes from (trimethylsilyl)ethyne via sequential Sonogashira-Hagihara and the present cross-coupling reactions using two different aryl triflates. The reactions of (arylethynyl)trimethylsilanes with aryl(chloro)ethynes in the presence of 10 mol % of CuCl also yield the corresponding unsymmetrical 1,3-butadiynes in 43-97% yields.     

An efficient direct alpha-alkylation of ketones with primary alcohols catalyzed by [Ir(cod)Cl]2/PPh3/KOH system without solvent

alpha-Alkylation of ketones was successfully achieved by the reaction of ketones with alcohols catalyzed by iridium complexes in the presence of a small amount of base. For example, 2-octanone was allowed to react with butanol under the influence of [Ir(cod)Cl]2/PPh3/KOH to give 6-dodecanone in good yield. The reaction was found to proceed by using a 1:1 mixture of ketone and alcohol without use of any solvent.     

Voltammetric sensing of sugar by an electrode covered with wheat germ agglutinin/chitin film

The binding between wheat germ agglutinin (WGA) and N-acetylglucosamine at the electrode covered with chitin film was investigated with voltammetry. Chitin, β-1,4-poly-N-acetylglucosamine, is one of the biolpolymers which have a high biocompatibility. WGA is immobilized to the surface of chitin film by the affinity of WGA to N-acetylglucosamine residue of chitin. To investigate the binding event of WGA on the chitin modified electrode, N-acetylglucosamine labeled with an electroactive compound was prepared. The binding causes the changes in the electrode response of labeled sugar. The peak current of labeled sugar decreased due to the specific binding with WGA on the chitin film modified at the electrode. N-Acetylglucosamine was successfully determined by using the competitive reaction with labeled sugar to WGA on the chitin film electrode.     

Voronoi space division of a polymer: topological effects, free volume, and surface end segregation

In order to investigate the topological effects of chain molecules, united-atom molecular dynamics simulations of a 500-mer polyethylene linked by 50 hexyl groups (a grafted polymer having 52 ends) are carried out and analyzed in terms of Voronoi space division. We find that the volume of a Voronoi polyhedron for a chain end is larger than that for an internal or junction atom, and that it is the most sensitive to temperature, both of which suggest higher mobility of chain ends. Moreover, chain ends dominantly localize at the surface of the globule: The striking evidence is that while the ratio of surface atoms is only 24% of all atoms, the ratio of ends at the surface is 91% out of all ends. The shape of Voronoi polyhedra for internal atoms is prolate even in the bulk, and near the surface it becomes more prolate. We propose the concept of bonding faces, which play a significant role in the Voronoi space division of covalently bonding polymers. Two bonding faces occupy 38% of the total surface area of a Voronoi polyhedron and determine the prolate shape.     

Sorption behavior and inventory of alpha-emitters on the surfaces of spent nuclear fuel cladding

Alpha-emitters on the surfaces of Zircaloy-4 cladding of PWR spent nuclear fuel have been examined at fuel burnup of 6900, 29,400 and 38,100 MWd/t. The amount of -emitter on the inner and outer surfaces of cladding increased with fuel burnup, whereas the amount of plutonium on the outer surface remained roughly constant. The distribution of -activity in the cladding varied with fuel burnup. The ratio of -activity on the outer surface to total -activity of the cladding decreased from about 50% at fuel burnup of 6900 MWd/t to 3% at fuel burnup of 38,100 MWd/t. The inventory of the -activity in unit weight of cladding was found to be 4.75·10² and 4.35·10⁴ Bq/g-cladding at fuel burnup of 6900 and 38,100 MWd/t, respectively. Adsorptive ability of the outersurface of irradiated cladding was about one order of magnitude greater than that of unirradiated Zircaloy-4 for -emitters and some of the fission products except ruthenium.     

Molecular transformations of unsaturated thiacrown ethers

Unsaturated thiacrown ethers with 15, 18, and 21 members were oxidized to sulfoxides by the reaction with m-CPBA. The reaction with t-BuOCl at -20 degrees C also afforded sulfoxides, whereas the reaction at room temperature yielded cis-trans isomerized compounds. The cis-trans isomerized compound was also obtained by the photochemical reaction or by the reaction with NCS and NCP. Meanwhile, the reaction with NBS and NBP provided an acetal via 1,2-bridged bromonium intermediate.     

Improved method for large-scale purification of brain gangliosides by Q-sepharose column chromatography. Immunochemical detection of C-series polysialogangliosides in adult bovine brains

A new chromatographic method for separation of bovine brain gangliosides has been developed using Q-Sepharose. Gangliosides were separated based not only on their sialic acid numbers but also on the sialic acid molecular species and chain lengths of the skeletal oligosaccharide portions. The following results indicate that this column chromatography has practical advantages in separating mixtures of gangliosides, especially positional isomers and molecular species with N-acetyl- or N-glycolylneuraminic acid. (1) the loading capacity of Q-Sepharose for gangliosides was very high; (2) most major gangliosides such as GM1, GD1a, GD1b, GT1b and GQ1b were isolated in a single step; (3) these major gangliosides were clearly separated from gangliosides containing, N-glycolylneuraminic acid when examined using Hanganutziu-Deicher antibody; (4) polysialogangliosides that have four or more sialic acid residues were isolated efficiently. It was shown by the combination of Q-Sepharose column chromatography with thin-layer chromatography/enzyme immunostaining that adult bovine brains possess C-series polysialogangliosides as minor components which are known as embryonic molecules in avian and mammalian brains.     

A generalization of maillet and demyanenko determinants for the Cyclotomic Zp-Extension

LetK be an imaginary abelian number field. By means of a generalization of Maillet and Demyanenko determinants we give a relative class number formula for an intermediate field of the cyclotomic ℤp-extension ofK. The degree of the generalized determinant is a half of the degree ofK over ℚ.     

Lewis acid-catalyzed ring-opening reactions of semicyclic N,O-acetals possessing an exocyclic nitrogen atom: mechanistic aspect and application to piperidine alkaloid synthesis.

Ring-opening reactions of semicyclic N,O-acetals possessing an exocyclic nitrogen atom with silicon-based nucleophiles (silyl enol ethers, ketene silyl acetals, allylic silanes, and trimethylsilyl cyanide) were systematically studied for the first time. It was found that the reactions were effectively catalyzed by a Lewis acid, trimethylsilyl trifluoromethanesulfonate (TMSOTf), to afford 1,4- and 1,5-amino alcohols in high yields. In reactions of 3-oxygen functionalized semicyclic N,O-acetals, high 1,2-syn-diastereoselectivity was obtained. By 1H NMR experiment, the formation of the O-trimethylsilylated ring-opened product was observed as the initial product. Furthermore, the epimerization between the diastereomers of a 3-benzyloxy semicyclic N,O-acetal suggested the transient formation of an acyclic iminium ion species as a reactive intermediate. It was also found that 3-acetoxy and 3-benzyloxy N,O-acetals showed a tendency for the larger nucleophile to provide higher syn-selectivity, while 3-tert-butyldiphenylsilyloxy N,O-acetals showed the opposite tendency. These stereochemical outcomes can be rationalized by assuming four transition state models for the acyclic iminium ion intermediate. The synthetic utility of the reaction has been demonstrated in the diastereoselective synthesis of piperidine alkaloids, (+)-isofebrifugine and (+/-)-sedacryptine.