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71.
The C-12˜C-17 segment
of (+)-aplasmomycin (
) was synthesized stereoselectively starting from (−)-malic acid based on the stereoselective ketone reduction. 相似文献
72.
Hiroshi Takeuchi Makoto Nakagawa Takayuki Saito Toru Egawa Kiyoshi Tanaka Shigehiro Konaka Toshiyuki Mitsuhashi 《International journal of quantum chemistry》1994,52(6):1339-1348
The energy spectra of free water molecules were measured at scattering angles 2θ ranging from 10.5° to 75.7°, using an angle-dispersive-type diffractometer and synchrotron radiation as an X-ray source. A silicon (111) monochrometer was used to obtain incident X-rays with the wavelengths of (1.543/n) Å (n = 1,3,4,5). Observed inelastic scattering peaks are clearly separated from eleastic ones at s values [s = (4π/λ) sin Å] larger than 8 Å?1. The increase of the separation with an increasing s value was consistent with the classical theory of the Compton shift. The total (elastic plus inelastic) intensities were obtained over a range of s = 0.74–5.0 Å?1. Experimental difference intensities Δσee and Δσne were obtained separately by combining the X-ray and high-energy electron scattering data. The experimental results are in reasonable agreement with the theoretical intensities calculated from SCF and CI molecular wave functions with a basis set of double-zeta plus polarization functions. © 1994 John Wiley & Sons, Inc. 相似文献
73.
Chiral resolution of native DL-tartaric acid was achieved by ion-pair capillary electrophoresis (CE) using an aqueous-ethanol background electrolyte with (1R,2R)-(-)-1,2-diaminocyclohexane (R-DACH) as a chiral counterion. Factors affecting chiral resolution and migration time of tartaric acid were studied. By increasing the viscosity of the background electrolyte and the ion-pair formation, using organic solvents with a lower relative dielectric constant, resulted in a longer migration time. The optimum conditions for both high resolution and short migration time of tartaric acid were found to be a mixture of 65% v/v ethanol and 35% v/v aqueous solution containing 30 mM R-DACH and 75 mM phosphoric acid (pH 5.1) with an applied voltage of -30 kV at 25 degrees C, using direct detection at 200 nm. By using this system, the resolution (Rs) of racemic tartaric acid was approximately 1. The electrophoretic patterns of tartaric and malic acids suggest that two carboxyl groups and two hydroxyl groups of tartaric acid are associated with the enantioseparation of tartaric acid by the proposed CE method. 相似文献
74.
[reaction: see text] We describe an efficient template-directed photoligation of oligodeoxynucleotides (ODNs) using alpha-5-cyanovinyldeoxyuridine (alpha(C)U). An efficient photoligation was produced by photoirradiation of an ODN containing alpha(C)U at the 3' end with an ODN containing thymine at the 5' end in the presence of a template ODN. This photoligation method is a new and efficient way to synthesize branched ODNs. 相似文献
75.
Akai S Kawashita N Satoh H Wada Y Kakiguchi K Kuriwaki I Kita Y 《Organic letters》2004,6(21):3793-3796
[reaction: see text] The reactions of (phenylsulfinyl)furans or -thiophenes with carbon nucleophiles in the presence of trifluoroacetic anhydride allowed the nucleophilic installation of carbon functional groups on the furan and thiophene nuclei with complete regioselectivity. 相似文献
76.
Reactions of polyatomic organic radicals with gas phase ions have been studied at thermal energy using a flowing afterglow-selected ion flow tube (FA-SIFT) instrument. A supersonic pyrolysis nozzle produces allyl radical (CH2CHCH2) and ortho-benzyne diradical (o-C6H4) for reaction with ions. We have observed: [CH2CHCH2 + H3O+ --> C3H6+ + H2O], [CH2CHCH2 + HO- --> no ion products], [o-C6H4 + H3O+ --> C6H5+ + H2O], and [o-C6H4 + HO- --> C6H3- + H2O]. The proton transfer reactions with H3O+ occur at nearly every collision (kII approximately with 10(-9) cm3 s(-1)). The exothermic proton abstraction for o-C6H4 + HO- is unexpectedly slow (kII approximately with 10(-10) cm3 s(-1)). This has been rationalized by competing associative detachment: o-C6H4 + HO- --> C6H5O + e-. The allyl + HO- reaction proceeds presumably via similar detachment pathways. 相似文献
77.
HUANG Wei-Ping ZHANG Xin-Jie WU Shi-HuaMA Shu-Yin ZHANG Shu-Ji ZHAO Wei-Jun 《天然气化学杂志》1997,6(3):252-257
IntroductionIn1962,N.V.Kutepow'SgroupfirstusedcomplexesofFe,CoandNiascatalyststocatalyzecarboXylationofethanoltopreparepropanoicacidanditsderivants.Thereactionpressurewashighandtheyieldwaslow.LateronPaulalsandhiscolleagueusedabC13andiodineascatalyst,which… 相似文献
78.
Morimasa Saito 《Analytical and bioanalytical chemistry》1995,351(2-3):148-153
Relative sensitivity factors (RSF) (Fe=1) were determined for steel, aluminium and copper standard samples by direct current glow discharge mass spectrometry using Kr and Xe as discharge gas. In general, the RSF values in Kr and Xe were higher than in Ar; however for S and P in Kr gas and P, As and Se in Xe gas they were considerably lower. This decrease is related to the relative importance of the Penning ionization process in overall ionization of the sputtered species. The results showed the percentage of Penning ionization to account for 75.6–82.0% for Se, As and P and 64.2% for S. 相似文献
79.
H. Ohta K. Jinno Y. Saito J. C. Fetzer W. R. Biggs J. J. Pesek M. T. Matyska Y. -L. Chen 《Chromatographia》1996,42(1-2):56-62
Summary The temperature-dependency of the separation of fullerenes in liquid chromatography (LC) has been examined using various alkyl bonded stationary phases. It has been found that a maximum retention temperature exists with long alkyl bonded stationary phases, whereas there is no similar effect with the newly synthesized alkyl bonded phases which have two phenyl groups at the base of the bonded phase. The interpretation of the retention behavior of fullerenes in the low temperature region on alkyl bonded stationary phases is discussed using information obtained by CP-MAS solid-state NMR spectroscopy and LC. 相似文献
80.