A novel convenient method for the generation of thiocarbonyl ylides from readily accessible starting materials and the first synthetic application of in situ generated ylides in the synthesis of silyl enol and dienol ethers, accompanied by C-C bond formation, is described. Under completely neutral conditions without any catalyst or additive, thermal reactions of S-alpha-silylbenzyl thioesters in sealed tubes at 180 degrees C provided silyl enol and dienol ethers in good to excellent yields with high stereoselectivities. This procedure consists of a multistep reaction in a one-pot process, i.e., 1,4-silatropy of S-alpha-silylbenzyl thioesters to give thiocarbonyl ylides, 1,3-electrocyclization of the ylides to give thiiranes, and the extrusion of sulfur from thiiranes to give silyl enol and dienol ethers. 相似文献
A new general method for the synthesis of a variety of 1-azasugars with a nitrogen atom at the anomeric position is described. The readily available chiral N-Boc-5-hydroxy-3-piperidene 3 is transformed to isofagomine (2), homoisofagomine (13), and 5'-deoxyisofagomine (14) via stereoselective epoxidation and regioselective ring-cleavage in a highly stereocontrolled manner. In addition, the synthesis of all four stereoisomers of 3,4,5-trihydroxypiperidines (18-21) classified as 1-azasugar-type glycosidase inhibitors was stereoselectively achieved from the (chiral) piperidene 3. 相似文献
To obtain adsorbents for boron(III) derived from a natural polymer, two forms (powder and fiber) of N-methylglucamine-type cellulose derivatives were newly synthesized. After the graft polymerization of two forms of cellulose with vinyl monomer having epoxy groups, the N-methylglucamine-type cellulose derivatives were obtained by the reaction of the grafted cellulose with N-methylglucamine. The adsorption capacities of the cellulose derivatives for boron(III) were the same levels as that of a commercially available N-methylglucamine-type polystyrene resin. However, the cellulose derivatives adsorbed boron(III) more quickly than the polystyrene resin. The adsorption and desorption of boron(III) with a column method using the cellulose fiber were achieved at a higher flow rate than that using the polystyrene resin. In addition, the boron(III), adsorbed on the cellulose fiber column, was quantitatively recovered with dilute hydrochloric acid in 20- and 200-fold increased concentrations. Consequently, it was found that the cellulose derivatives were superior to the polystyrene resin as adsorbents for boron(III) for treatment of a large quantity of wastewater. 相似文献
The invariant mass spectra of phi-->K+K- are measured in 12 GeV p+A reactions in order to search for the in-medium modification of phi mesons. The observed K+K- spectra are well reproduced by the relativistic Breit-Wigner function with a combinatorial background shape in three betagamma regions between 1.0 and 3.5. The nuclear mass number dependence of the yields of the K+K- decay channel is compared to the simultaneously measured e+e- decay channel for carbon and copper targets. We parameterize the production yields as sigma(A)=sigma0Aalpha and obtain alphaphi-->K+K- -alphaphi-->e+e- to be 0.14+/-0.12. Limits are obtained for the partial decay widths of the phi mesons in nuclear matter. 相似文献
The line widths of the β-NMR spectra of the short-lived β emitters 8Li and 12N implanted in a single crystal of Al have been measured precisely for the first time as a function of crystal orientation.
The NMR line widths were compared with the theoretical van Vleck values of the dipolar broadening. As a result, it was found
that 8Li mainly sits in substitutional sites, while 12N sits in tetrahedral interstitial sites, in Al.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
Hyperfine interactions of 8Li impurity nucleus imbedded in ferromagnetic Ni metal were studied using the β-NMR technique. Two kinds of hyperfine fields
B82 were found, corresponding to two different final sites of Li atoms in the Ni lattice. The nuclear spin-lattice relaxation
times T1 of 8Li in Ni were also determined for each field. Temperature dependencies of B82 and T1 were observed to deduce these values at T=0 K that can be compared with those calculated recently by Akai et al.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
The dipolar broadening of the NMR on short-lived β-emitter 8Li implanted in single crystal Cu has been observed as a function of crystal orientation at several temperatures. From the
orientation angle dependence of the line width, it was found that the main component of the 8Li occupies substitutional site, while about 30% of 8Li occupies octahedral interstitial site at temperatures below 300 K.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
Summary: A cyclodextrin‐peptide hybrid bearing coumarin and fluorescein on the peptide side chain has been designed and synthesized as a novel chemosensor molecule utilizing fluorescence resonance energy transfer (FRET). Inclusion of coumarin into β‐cyclodextrin protects this system against fluorescent quenching, so that FRET occurs though donor and acceptor moieties nearby. FRET is diminished upon the addition of various guest compounds, suggesting that this system is useful for detecting molecules in aqueous solution.
A cyclodextrin‐peptide hybrid bearing coumarin and fluorescein on the peptide side chain. 相似文献
A cyclodextrin‐peptide hybrid (CD‐peptide) bearing three units of γ‐cyclodextrin, cholic acid, and a dansyl fluorophore in the side chain has been prepared. In this novel CD‐peptide, the cholic acid unit acts as an internal guest and forms an intramolecular inclusion complex with γ‐cyclodextrin in the CD‐peptide. This intramolecular complex works as a host‐guest bridge in the CD‐peptide and remarkably stabilizes the α‐helix structure of the CD‐peptide. 相似文献
An α‐helix peptide (17 amino acids) bearing γ‐cyclodextrin (γ‐CD) and two naphthyl units (γ‐N217) was designed and prepared as a new type of chemosensor. The α‐helix peptide with γ‐CD sandwiched between two naphthyl moieties exhibits excimer emission by inserting the two naphthalene moieties into the γ‐CD cavity from the opposite sides in the side chain of the peptide. The two reference peptides, which have one naphthalene moiety and one γ‐CD unit, exhibit only monomer fluorescence and have larger binding constants for the examined guests than γ‐N217. 相似文献