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191.
Kitajima M Hashimoto K Yokoya M Takayama H Aimi N Sakai SI 《Chemical & pharmaceutical bulletin》2000,48(10):1410-1412
A new gluco indole alkaloid, 3,4-dehydro-5-carboxystrictosidine, was obtained from Peruvian U?a de Gato (Cat's Claw, original plant: Uncaria tomentosa) together with two known gluco indole alkaloids. This compound was the first example of isolation of a gluco monoterpenoid indole alkaloid having a 3,4-dihydro-beta-carboline ring system from nature. A characteristic feature of the compound was the quick replacement of the methylene hydrogens on C-14 with deuterium that was observed when it was dissolved in CD3OD. We demonstrated a similar proton-deuterium exchange on a model compound, 1-methyl-3,4-dihydro-gamma-carboline, in CD3OD solution. 相似文献
192.
Hayashi M Hashimoto Y Yamamoto Y Usuki J Saigo K 《Angewandte Chemie (International ed. in English)》2000,39(3):631-633
Convenient access to cyclopentenones is provided by catalytic intra- and intermolecular Pauson - Khand reactions in the presence of octacarbonyldicobalt and tributylphosphane sulfide (see scheme). In contrast to other reactions of this type, they proceed under mild conditions (70 degrees C, 1 atm CO), and commercially available [Co(2)(CO)(8)] can be used without further purification. 相似文献
193.
The effect of a geometrical relationship between a grain boundary (GB) plane and a tensile axis on intergranular fatigue cracking along 3(1 1 2) twin boundaries has been investigated in Fe-30%Cr alloy crystals. Fatigue experiments were carried out on the three kinds of the specimens containing the 3(1 1 2) twin boundary. It was found that the fatigue cracking behavior was sensitive to the geometry of the GB plane. In a specimen where both the GB plane and a slip vector lying in the GB plane in adjacent grains are inclined to the tensile axis at 45°, the fatigue cracks were nucleated preferentially along the twin boundary at a stress amplitude of 170 MPa. The specimen with the GB plane normal to the tensile axis showed that the fatigue crack was initiated from a slip band formed within a constituent grain at a stress amplitude of 300 MPa. When the GB plane was inclined to the tensile axis but the slip vector lying in the GB plane was normal to the tensile axis, development of additional slips formed perpendicular to the GB plane were observed at a specific site of the GB. Initiation of intergranular fatigue cracks at the site was recognized at a stress amplitude of 250 MPa. It can be suggested that the GB plane normal to the tensile axis provides the highest fatigue performance among them. The difference in the cracking property among these specimens could be understood in terms of the effective Schmid factor derived from elastically incompatible stress. 相似文献
194.
Kazuhiko Saigo Yukihiko Hashimoto Kazushi Kinbara Atsushi Sudo 《Journal of Chemical Sciences》1996,108(6):555-573
The review describes the mechanism of chiral discrimination of racemic amines upon crystallization and the induction of chirality
in organic reactions by using them as chiral auxiliaries. In order to form conglomerates, which can be resolved into the two
enantiomers upon alternative seeding, both formation and packing of 21-columns are essentially very important. On the other hand, in order to achieve high efficiency in resolution through diastereomeric
salt formation, which is the most practical method, one of a pair of diastereomeric salts derived from a racemic amine and
an enantiomerically pure resolving agent should at least have two 21-columns and planar boundary surfaces in its crystal structure. On the basis of this knowledge, we developed several artificial
chiral auxiliaries such as erythro-2-amino-1,2-diphenylethanol,cis-2-amino-1-acenaphthenol, andcis-2-amino-3,3-dimethyl-1-indanol. These were found to be very efficient chiral auxiliaries in asymmetric inductions: alkylation
of chiral imines, catalytic borane-reduction, and alkylation of chiral N-acylated oxazolidinone. 相似文献
195.
Hargovind Rathore Toshihiro Hashimoto Kikuo Igarashi Haruo Nukaya Dwight S. Fullerton 《Tetrahedron》1985,41(23):5427-5438
As part of a continuing study of cardiac g1ycos1des,1,2 stereoselective syntheses of the four possible glucosides of digitoxigenin were developed via the thermodynamically produced tetra-O-benzyl-D- and L-glucosyl α-trichloroacetaimidates 2α and 11α, and the kinetically produced β-trichloroacetaimidates 2β and 11β. A 58%:19% isolated yield ratio of α-D and β-D benzyl protected glycosides 6 and 3 could be obtained in 30 minutes reaction at ?10°. Halide ion catalysis with a 2:1 excess of tetra-O-benzyl-α-D-glucopyranosyl bromide for 14 days in methylene chloride at room temperature gave a 39%:11% ratio of 6 and 3, along with 43% of recovered digitoxigenin. Debenzylation of the D-glucosides required milder conditions (20% Pd/C, atmospheric pressure, 45 min-1 hr) than the L-glucosides (40% Pd/C, 2 hr) but yields were typically 80% for both groups. 相似文献
196.
197.
Charge transport properties of β-LiAl were studied in the composition range of 48.0–50.2 at.% Li. Measurements were made on single crystal samples and down to the liquid He temperature. The resistivity changes linearly with temperature above 125 K, with a thermal coefficient of 72–95nΩ cm K?1. The Matthiessen law was obeyed very well. A component dependent on temperature, which was described by the Grüneisen formula, is insensitive to a change of the chemical composition. On the other hand, the residual resistivity depends largely on the composition and contributes up to 58% of the total resistivity in Li0.498. It is chiefly due to the substituted Li atoms on the Al sublattice. 相似文献
198.
199.
Let denote the set of all Hadamard matrices of order n. For , define the weight of H to be the number of 1's in H and is denoted by w(H). For a subset , define the maximal weight of Γ as w(Γ) = max{w(H) | H?Γ}. Two Hadamard matrices are equivalent if one of them can be transformed to the other by permutation and negation of rows and columns, and the equivalence class containing H is denoted by [H]. In this paper, we shall derive lower bounds for w([H]), which are best possible for n ? 20. We shall also determine the exact value of . 相似文献
200.
The change in the light-scattering patterns upon deforming two-dimensional disordered spherulites is shown to arise from four effects occurring upon stretching: (1) the change in shape of the spherulite, (2) the change in average orientation of the optic axes of the scattering volume elements, (3) the change in deviation of the optic axis orientation angle from its average value, and (4) the change in the distance over which this deviation is correlated. The effects of these contributions upon the experimental scattering patterns are analyzed. 相似文献