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81.
Ptilomycalin A and crambescidins, novel marine guanidine alkaloids, have a unique pentacyclic guanidine structure, and exhibit a considerable array of biological activities. The first method developed for the synthesis of the pentacyclic guanidine core structure involved successive 1,3-dipolar cycloaddition reactions and resulted in the first total synthesis of crambescidin 359. The synthesis of other pentacyclic guanidine derivatives has been based on this methodology and applied as tools for studying biological activities, and as chemical reaction catalysts. 相似文献
82.
T. Hashimoto Y. Uezu F. Ishizuka H. Washio 《Journal of Radioanalytical and Nuclear Chemistry》1993,173(1):87-97
A selective extraction of the correlated events due to three kinds of short-lived -decay events,216Po (145 ms),217At (32.3 ms) and215Po (1.78 ms), from other random background events were examined by using a time interval analysis (TIA) from the viewpoint of detection sensitivity. In the theoretical treatment based on the probability and statistics, it was clarified that the detection sensitivity proportionally increased with shortening half-lives in the following order,215Po>217At>216Po. In the experiments, pulses from a liquid scintillator owing to -decay events were analyzed using a multiple TIA technique and resulted in the highest sensitivity of219Rn–215Po pairs in the actinium series. Thus, the multiple TIA method was applied to the practical determination of219Rn–215Po pairs in natural samples. 相似文献
83.
[formula: see text] The conformation of the retinal chromophore in rhodopsin is central for understanding the visual transduction process. The absolute twist around the 12-s bond of the chromophore in rhodopsin has been determined by studies with 11-cis-locked 11,12-cyclopropylretinal analogues (11S,12R)-2 and (11R,12S)-3, enantioselectively synthesized with the aid of an enzyme. The finding that enantiomer 2 binds to opsin while the other 3 does not defines the absolute sense of twist around the 12-s bond. 相似文献
84.
Yamamura K Houda Y Hashimoto M Kimura T Kamezawa M Otani T 《Organic & biomolecular chemistry》2004,2(9):1413-1418
Intramolecular reaction of 2-tropylio-3-(5-substituted 2-furyl)benzothiophenes (3), prepared from the corresponding 2-cycloheptatrienyl-3-(5-substituted 2-furyl)benzothiophenes (2), afforded the beta-(azuleno[1,2-b]benzothienyl)-alpha,beta-unsaturated ketones (4), which are otherwise difficult to obtain, in moderate yields. The reaction involves a ring-opening process of the furan ring by intramolecular attack of the tropylium ion onto the 2-position of the furan ring. Similarly, beta-(azuleno[2,1-b]benzothienyl)-alpha,beta-unsaturated ketones (8) were obtained from the corresponding 3-tropylio-2-(5-substituted 2-furyl)benzothiophenes (7) albeit in lower yields. The molecular and crystal structures of the methyl ketone derivative, 8a, are discussed on the basis of X-ray structure analysis. 相似文献
85.
Two novel nucleosides, mycalisines A and B, have been isolated from a marine sponge and their structures elucidated as 4-amino-5-cyano-7-(3--methyl-5-deoxy-β-D--pent-4-enofuranosyl)-pyrrolo[2,3-]pyrimidine and 5-cyano-7-(3--methyl-5-deoxy-β-D--pent-4-enofuranosyl)-pyrrolo[2,3-]pyrimidine-4-one, respectively. Both compounds inhibit cell division of fertilized starfish eggs. 相似文献
86.
Ruslim C Hashimoto M Matsunaga D Tamaki T Ichimura K 《Langmuir : the ACS journal of surfaces and colloids》2004,20(1):95-100
The inherent chromonic lyotropic liquid crystalline properties of a dye have been manipulated to fabricate multi-axial micropolarizing thin films by means of the photoalignment technique. The dye aqueous solution is deposited on a photopatterned polymer film to result in the macroscopic alignment of the dye molecules, followed by drying at ambient temperature. The solid polarizing dye layers thus produced exhibit very a high contrast ratio and degree of polarization in the region of visible light. Addition of a small amount of surfactant to the dye solution is a prerequisite for the generation of a nematic chromonic phase and for the formation of homogeneous thin dye layers on the polymer film. The correlation between the optical and surface morphological properties of the dye layers is discussed. 相似文献
87.
Seiichi Nakamura Jun Inagaki Tomohiro Sugimoto Yasuyuki Ura Shunichi Hashimoto 《Tetrahedron》2002,58(52):10375-10386
An efficient, highly stereoselective synthesis of the C10–C31 (BCDEF ring) portion of pinnatoxin A has been achieved utilizing tandem double hemiketal formation/intramolecular hetero-Michael addition to construct the 6,5,6-dispiroketal (BCD ring) system and subsequent intramolecular ketalization to form the 5,6-bicycloketal (EF ring) system as key steps. 相似文献
88.
Watanabe M Ikagawa A Wang H Murata K Ikariya T 《Journal of the American Chemical Society》2004,126(36):11148-11149
Well-defined chiral Ru amido complexes promoted asymmetric Michael addition of 1,3-dicarbonyl compounds including malonates, beta-keto esters, and 1,3-diketones to nitroalkenes to give the corresponding adducts with excellent ees and in excellent yields. 相似文献
89.
Hiroyoshi Nakajima Katsuhiro Yamada Yuki Iseki Satoru Hosoda Ayako Hanai Yasunori Oumi Toshiharu Teranishi Tsuneji Sano 《Journal of polymer science. Part A, Polymer chemistry》2003,41(24):3324-3332
Polypropylene (PP)/Ti-MCM-41 nanocomposites were prepared by isospecific propylene polymerization with Ti-MCM-41/Al(i-C4H9)3 catalyst. The cross polarization/magic angle spinning (CP/MAS) 13C NMR spectrum of the composite was similar to that of the conventional isotactic PP, and the decrease in the pore volume of Ti-MCM-41 in the nanocomposites, as measured by N2 adsorption, was consistent with the value calculated from the weight loss in the thermogravimetric analysis (TGA) curve; both these facts attest to propylene polymerization within the mesopores of Ti-MCM-41. Alkali treatment followed by extraction with o-dichlorobenzene allows us to extract the confined PP out of the Ti-MCM-41 mesopores. Although the PP/Ti-MCM-41 nanocomposites do not exhibit a crystalline melting point, the same PP when extracted from the mesopores showed a clear melting point at 154.7 °C; this indicates that the crystallization of PP confined in mesopores is strongly hindered. For the PP polymerized within the confinement, the molecular weight (Mw) and molecular weight distribution (Mw/Mn) were 84,000 and 4.3, respectively; these values were considerably smaller than those of the PP polymerized concurrently outside the Ti-MCM-41 mesopores (Mw = 200,000–450,000, Mw/Mn = 40–75). Therefore, the confinement also has a marked effect on the molecular weight of the PP. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3324–3332, 2003 相似文献
90.
Enami S Yamanaka T Hashimoto S Kawasaki M Tonokura K 《The journal of physical chemistry. A》2005,109(27):6066-6070
The reactions of Cl atoms with RI (R = n-C3H7, n-C4H9, cyclo-C6H11, C6H5, C6F5, and p-CH3C6H4) have been studied using cavity ring-down spectroscopy at a temperature range of 233-313 K and at 100 Torr total pressure of N2 diluent. Visible absorption spectra of the RI-Cl adducts were recorded at 440-520 nm at 263 K. The yields of the adducts were temperature-dependent. There was no discernible reaction of the adducts in the presence of 100 Torr of O2 at 263 K. Theoretical calculations were performed for C4H9I-Cl and C6H5I-Cl for quantitative explanation of the absorption spectra and the strength of the I-Cl bonds in the charge-transfer complexes. Evidence for the adduct formation following the reaction of Cl with C6H5Br was sought but not found at 440 and 520 nm. 相似文献