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1.
N-Deacetylcolchiceine ( 7 ), readily available from colchicine ( 1 ), was converted into N-trifluoroacetyl-deacetylcolchiceine ( 8 ). Methylation of 8 with methyl iodide in the presence of potassium carbonate afforded a mixture of N-trifluoroacetyl-demecolcine ( 10 ) and its isomer 11 . The mixture of 10 and 11 was detrifluoroacetylated and separated by chromatography to afford demecolcine ( 2 ) and isodemecolcine ( 12 ). A more practical route to 2 started with 8 , and gave N-trifluoroacetyl-deacetylcolchicine ( 13 ) and its isomer 14 after O-methylation with diazomethane. N-Methylation of 13 and 14 with methyl iodide and potassium carbonate afforded 10 and 11 . The overall yield in the conversion of colchicine ( 1 ) into demecolcine ( 2 ) via 7, 8 and 13 was 55%. 相似文献
2.
F. Capraro C. Gros 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(1):35-40
Using the density matrix renormalization group technique, we evaluate the low-energy spectrum (ground state and first excited
states) of the anisotropic antiferromagnetic spin-one-half chain under magnetic fields. We study both homogeneous longitudinal
and transversal fields as well as the influence of a transversal staggered field on the opening of a spin-gap. We find that
only a staggered transversal field opens a substantial gap.
Received 16 April 2002 / Received in final form 4 July 2002 Published online 17 September 2002 相似文献
3.
A synthesis of twista-4,9-diene ( 17 ) from tricyclo[4.3.1.03,8]dec-4-en-10-one ( 2 ) is described. 相似文献
4.
Let M be a II 1-factor with trace τ, the finite dimensional subspaces of L 2(M, τ) are not just common Hilbert spaces, but they have an additional structure. We introduce the notion of a cyclic linear space by taking these additional properties as axioms. In Sect. 3 we formulate the following problem: “does every cyclic Hilbert space embed into L 2(M, τ), for some M?”. An affirmative answer would imply the existence of an algorithm to check Connes’ embedding Conjecture. In Sect. 4 we make a first step towards the answer of the previous question. 相似文献
5.
[reaction: see text]. Room-temperature ionic liquids, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium bromide, and 1-butyl-3-methylimidazolium chloride, are used as "green" recyclable alternative to chlorinated solvents for the stereoselective halogenation of alkenes and alkynes. 相似文献
6.
Ali Bicer Robert M. Capraro Mary M. Capraro 《International Journal of Mathematical Education in Science & Technology》2018,49(5):705-720
The purpose of this paper is to demonstrate Hispanic students’ mathematics achievement growth rate in Inclusive science, technology, engineering, and mathematics (STEM) high schools compared to Hispanic students’ mathematics achievement growth rate in traditional public schools. Twenty-eight schools, 14 of which were Texas STEM (T-STEM) academies and 14 of which were matched non-STEM schools, were included in this study. A hierarchical linear modelling method was conducted. The result of the present study revealed that there was no difference in Hispanic students’ mathematics achievement growth rate in T-STEM academies compared to Hispanic students’ mathematics achievement growth rate in comparison schools. However, in terms of gender, the results indicated that female Hispanic students in T-STEM academies outperformed female Hispanic students in comparison schools in their mathematics growth rate. 相似文献
7.
(+)-(1S, 3S, 6S, 8S)-and (?)-(1R, 3R, 6R, 8R)-4, 9-Twistadiene: Synthesis and Absolute Configuration A synthesis and the determination of the absolute configuration of (+)-(1S, 3S, 6S, 8S)- and (?)-(1R, 3R, 6R, 8R)-4, 9-twistadiene ((+)- and (?)- 4 , respectively) is described. Their chiroptical properties are compared with those of saturated twistane ((+)- and (?)- 5 ) as well as with those of the unsaturated and saturated 2, 7-dioxatwistane analogs (+)- and (?)- 9 , and (+)- and (?)- 10 , respectively, which also are compounds of known absolute configurations. 相似文献
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9.
The purpose of this study is to compare students’ mathematics achievement growth rate in Texas science, technology, engineering, and mathematics (T‐STEM) academies to students’ mathematics achievement growth rate in traditional public high schools. Forty‐six schools, 23 of which were T‐STEM academies and 23 of which were matched non‐STEM schools, were included in this study. A hierarchical linear modeling method was conducted. The result of the present study revealed that there was no difference in students’ mathematics achievement growth rate in T‐STEM academies compared to students’ mathematics achievement growth rate in comparison schools. However, in terms of ethnicity, the results indicated that African American and Hispanic students in T‐STEM academies outperformed African American and Hispanic students in comparison schools on their mathematics growth rate. 相似文献
10.