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41.
A convergent synthesis of the A-F ring segment of yessotoxin and adriatoxin was achieved via the intramolecular allylation of an α-chloroacetoxy ether and subsequent ring-closing metathesis. 相似文献
42.
Shoichi Katsuta Hirokazu Wakabayashi Mariko Tamaru Yoshihiro Kudo Yasuyuki Takeda 《Journal of solution chemistry》2007,36(4):531-547
Equilibria concerning picrates of tetraalkylammonium ions (Me4N+, Et4N+, Pr4N+, Bu4N+, Bu3MeN+) in a dichloromethane−water system have been investigated at 25 ∘C. The 1:1 ion-pair formation constants (K
IP,o
o) in dichloromethane at infinite dilution were conductometrically determined. The distribution constants (K
D
o) of the ion pairs and the free cations between the solvents were determined by a batch-extraction method. The K
IP,o
o value varies in the cation sequence, Bu4N+ ≈ Pr4N+ ≈ Et4N+ < Bu3MeN+ < < Me4N+; this trend is explained by the electrostatic cation−anion interaction taking into account the structures of the ion pairs
determined by density functional theory calculations. For the ion pairs of the symmetric R4N+ cations, there is a linear positive relationship between log10
K
D
o and the number of methylene groups in the cation (N
CH
2). The ion pair of asymmetric Bu3MeN+ has a higher distribution constant than that expected from the above log10
K
D
o
versus
N
CH
2 relationship. These cation dependencies of log10
K
D
o for the ion pairs are explained theoretically by using the Hildebrand-Scatchard equation. For all the cations, the log10
K
D
o value of the free cation increases linearly with N
CH
2; the variation of log10
K
D
o is discussed by decomposing the distribution constant into the Born-type electrostatic contribution and the non-Born one,
and attributed to the latter that is governed by the differences in the molar volumes of the cations. The cation dependencies
of the ion-pair extractability and ion pairing in water are also discussed.
An erratum to this article can be found at 相似文献
43.
[reaction: see text] We describe an efficient synthesis of di-branched heptasaccharide 1 having phytoalexin elicitor activity in soybeans by one-pot glycosylation. The synthesis involves chemo- and regioselective sequential six-step glycosylations using seven independent building blocks and sequential removal of acyl- and benzyl ether-type protecting groups. The coupling of seven building blocks requires only four chemoselective activitable leaving groups of glycosyl donors. Both the glycosylation and deprotection reactions can be achieved utilizing a parallel manual synthesizer. 相似文献
44.
Oishi T Hagiwara K Kinumi T Yamakawa Y Nishijima M Nakamura K Arimoto H 《Organic & biomolecular chemistry》2003,1(15):2626-2629
The effects of Soto's 'beta-sheet breaker peptide' and its polymer on PrPSc formation in ScN2a cells were investigated. Surface plasmon resonance study indicated that direct binding between PrP(81-145) and the 'beta-sheet breaker peptide' is not specific and may not play a major role in the inhibition of PrPSc formation. 相似文献
45.
Precipitation temperature-total polymer concentration diagrams for toluene solutions of two styrene-acrylonitrile copolymers different in chemical composition and their mixtures were determined and then triangular phase diagrams of this system were constructed from these diagrams. It is speculated from the triangular phase diagrams and experimentally shown that the copolymer may be effectively fractionated by chemical composition in this system. 相似文献
46.
Cross‐Coupling of Organolithium with Ethers or Aryl Ammonium Salts by C−O or C−N Bond Cleavage
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Ze‐Kun Yang Dong‐Yu Wang Hiroki Minami Hiroyuki Ogawa Takashi Ozaki Dr. Tatsuo Saito Dr. Kazunori Miyamoto Dr. Chao Wang Prof. Dr. Masanobu Uchiyama 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(44):15693-15699
Various aryl‐, alkenyl‐, and/or alkyllithium species reacted smoothly with aryl and/or benzyl ethers with cleavage of the inert C?O bond to afford cross‐coupled products, catalyzed by commercially available [Ni(cod)2] (cod=1,5‐cyclooctadiene) catalysts with N‐heterocyclic carbene (NHC) ligands. Furthermore, the coupling reaction between the aryllithium compounds and aryl ammonium salts proceeded under mild conditions with C?N bond cleavage in the presence of a [Pd(PPh3)2Cl2] catalyst. These methods enable selective sequential functionalizations of arenes having both C?N and C?O bonds in one pot. 相似文献
47.
Takeshi Takeda Shuichi Kuroi Makoto Ozaki Akira Tsubouchi 《Phosphorus, sulfur, and silicon and the related elements》2013,188(5-6):1291-1296
Abstract Trialkylsilyl group-directed regioselective transformations of alkynyl thioacetals to alkynylcyclopropanes and enynes are described. 相似文献
48.
Chihiro Manri Takahide Yokoi Hirokazu Nishida 《Applied biochemistry and biotechnology》2017,182(2):609-623
Extracellular vesicles (EV), typified by exosomes or microvesicles, are expected to be effective diagnostic markers for cancers. The sizes of the vesicles range from 20 to 1000 nm, but the size-dependent variations of the contents of EVs are still poorly understood. We succeeded in the size-selective harvesting of the vesicles by utilizing the molecular weight-dependent characteristics of a variety of polyethylene glycols (PEG) as precipitating reagents and analyzed the antigens displayed on the surfaces of the vesicles and the miRNAs included in the vesicles from each size group. As a result, the relatively larger (<100 nm) particles precipitated by PEG5k clearly exhibited the greatest amount of epithelial cell adhesion molecule (EpCAM), from both breast cancer (MCF-7) and colon cancer (HCT116) cells, and a larger quantity of microRNA (miRNA) specific to breast cancer cells (miRNA155 for MCF-7) seemed to be contained in the PEG-precipitated particles. The results demonstrated that the quantities of both the tumor-specific miRNA and protein were similarly distributed among the several classes of the size-sorted EVs and that the size-selective harvesting of EVs may be informative for strategic analyses towards the diagnoses of cancers. 相似文献
49.
50.
The anomalous temperature dependence of the sign of the spontaneous polarization in a biphenyl ester series of ferroelectric liquid crystals is reported. The reversal of the sign of the spontaneous polarization in the chiral smectic C phase of 2MBNCBC ((S)-2′-methylbutyl-4′-n- nonylcarbonyloxy-(l,l′-biphenyl)-l-carboxylate) is observed at T m. This anomaly is studied in detail as functions of the length of the terminal alkyl chain, the applied electric field, the frequency and the applied hydrostatic pressure. T m has been confirmed to depend on the length of the terminal chain and the applied pressure. However, it is independent of the applied field and the measuring frequency. In the mixture of these compounds, this anomaly is also observed. 相似文献