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991.
992.
993.
994.
Y Kasai N Michihata H Nishimura T Hirokane H Yamada 《Angewandte Chemie (International ed. in English)》2012,51(32):8026-8029
Quite strained: The total synthesis of (+)-davidiin, an ellagitannin with more substituents in axial than in equatorial positions, requires a conformational lock of the glucose, induced by steric repulsion between adjacent bulky silyloxy groups. This conformational lock played a pivotal role in 1)?the β-selective formation of the glycosyl ester at the anomeric position, 2)?the formation of the 1,6-HHDP bridge, and 3)?the complete control of axial chirality in the aryl-aryl coupling. 相似文献
995.
Yamada Y Miyahigashi T Ohkubo K Fukuzumi S 《Physical chemistry chemical physics : PCCP》2012,14(30):10564-10571
Photocatalytic hydrogen evolution has been made possible by using oxalate as a carbon-neutral electron source, metal nanoparticles as hydrogen-evolution catalysts and the 2-phenyl-4-(1-naphthyl)quinolinium ion (QuPh(+)-NA), which forms the long-lived electron-transfer state upon photoexcitation, as a photocatalyst. The hydrogen evolution was conducted in a deaerated mixed solution of an aqueous buffer and acetonitrile (MeCN) [1:1 (v/v)] by photoirradiation (λ > 340 nm). The gas evolved during the photocatalytic reaction contained H(2) and CO(2) in a molar ratio of 1:2, indicating that oxalate acts as a two-electron donor. The hydrogen yield based on the amount of oxalate reached more than 80% under pH conditions higher than 6. Ni and Ru nanoparticles as well as Pt nanoparticles act as efficient hydrogen-evolution catalysts in the photocatalytic hydrogen evolution. The photocatalyst for hydrogen evolution can be used several times without significant deactivation of the catalytic activity. Nanosecond laser flash photolysis measurements have revealed that electron transfer from oxalate to the photogenerated QuPh˙-NA˙(+), which forms a π-dimer radical cation with QuPh(+)-NA [(QuPh˙-NA˙(+))(QuPh(+)-NA)], occurs followed by subsequent electron transfer from QuPh˙-NA to the hydrogen-evolution catalyst in the photocatalytic hydrogen evolution. Oxalate acts as an efficient electron source under a wide range of reaction conditions. 相似文献
996.
Sato Y Zhang Y Seino T Sugimoto T Nishizawa S Teramae N 《Organic & biomolecular chemistry》2012,10(20):4003-4006
We report on highly selective binding of a naphthyridine derivative with a trifluoromethyl group to cytosine opposite an abasic site in DNA duplexes; the binding-induced fluorescence quenching is applicable to the analysis of a C-related single-base mutation in DNAs amplified by PCR. 相似文献
997.
Yuki Goto Yusuke Matsuki Masakazu Nishida Shigeki Oyama Katsumi Chikama Hideo Sawada 《Colloid and polymer science》2012,290(1):11-21
Two kinds of fluoroalkyl end-capped vinyltrimethoxysilane oligomer [RF-(VM)
n
-RF] silica nanocomposites containing biphenylene units were prepared by the sol-gel reactions of the corresponding oligomer
with biphenylene-bridged ethoxysilanes or 4,4′-biphenol under alkaline conditions, respectively. One is the fluorinated oligomer/silica
nanocomposites containing biphenylene units [RF-(VM-SiO2)
n
–RF/Ar-SiO
2
], of whose biphenylene units were incorporated into nanocomposite cores through the siloxane bondings, and the other is the
fluorinated oligomer/silica nanocomposites containing biphenylene units [RF-(VM-SiO2)
n
–RF/Biphenol], of whose biphenylene units were directly encapsulated into nanocomposite cores through the sol–gel process. Interestingly,
the shape of RF-(VM-SiO2)
n
–RF/Ar-SiO
2
nanocomposites is morphologically controlled cubic particles; although the shape of RF-(VM-SiO2)
n
–RF/Biphenol nanocomposites is spherically fine particles. Thermogravimetric analyses 2H magic-angle spinning nuclear magnetic resonance, Ultraviolet visible, and fluorescent spectra showed that biphenylene units
in RF-(VM-SiO2)
n
–RF/Ar-SiO
2
nanocomposites have a flammable characteristic after calcinations at 800 °C; in contrast, biphenylene units in RF-(VM-SiO2)
n
–RF/Biphenol nanocomposites have a nonflammable characteristic even after calcination at 800 °C. X-ray photoelectron spectroscopy analyses
of these two kinds of fluorinated nanocomposites showed that nonflammable characteristic toward biphenylene units in the silica
gel matrices is due to the formation of ammonium hexafluorosilicate during the sol–gel process. 相似文献
998.
Iwao Okamoto Yusuke Takahashi Mika Sawamura Mio Matsumura Hyuma Masu Kosuke Katagiri Isao Azumaya Masanori Nishino Yukari Kohama Nobuyoshi Morita Osamu Tamura Hiroyuki Kagechika Aya Tanatani 《Tetrahedron》2012,68(27-28):5346-5355
Redox-induced conformational alteration of N-aryl-N-phenylamides, in which the N-aryl group consists of a hydroquinone–p-quinone system, was examined. The reduced form bearing a dihydroxyphenyl or dimethoxyphenyl group exists mainly in the E-form, whereas the oxidized form bearing a N-benzoquinone moiety takes the Z-form both in the crystal and in solution. This redox-induced conformational alteration is associated with a marked change in optical properties. This system appears to have suitable properties for use in external redox stimulus-responsive functional switching. 相似文献
999.
Haruhisa Kikuchi Yusuke Matsuo Yasuhiro Katou Yuzuru Kubohara Yoshiteru Oshima 《Tetrahedron》2012,68(43):8884-8889
From the fruiting bodies of Dictyostelium polycephalum, we obtained four aromatic compounds: dictyobiphenyl A (1) and B (2) and dictyoterphenyl A (3) and B (4). The synthesis of 1–4 was performed to confirm the structures and obtain sufficient material for biological evaluation. Compound 3 was the first example of nitrogen-containing natural m-terphenyls, and the isolation of novel classes of compounds such as 3 shows that cellular slime molds are promising sources in natural product chemistry. Moreover, dictyoterphenyl A (3) showed cancer cell-selective antiproliferative activity (IC50 2.3–8.6 μM). 相似文献
1000.
Junya Chiba Wataru Shirato Yusuke Yamade Byung-Soon Kim Shinya Matsumoto Masahiko Inouye 《Tetrahedron》2012,68(44):9045-9049
A large-scale synthesis was carried out for alkynyl C-nucleotide oligomers in order to clarify the structural details of the artificial DNA. A liquid-phase synthesis by means of phosphoramidite methodology enabled us to handle ~0.1 g of the DNA oligomers possessing a pseudouracil derivative (T*) as a non-natural nucleobase. 1H NMR measurements in aqueous media were carried out for the oligomers, succeeded in the accurate assignments of the protons accompanying with determination of the coupling constants (J values). These J values revealed that average conformation of the alkynylribose rings in the DNA was substantially biased toward the S-type conformers (2T1/E1/OT1). X-ray crystal analysis of the non-natural nucleoside also supported the S-type conformation (2E/2T1) as seen in natural B-DNA. 相似文献