A practical asymmetric synthesis of ortho-substituted 4-pyrazolyl-2-ethylamines

A reliable three-step synthesis of ortho-substituted 4-pyrazolyl-2-ethylamines starting from a pyrazole methyl ketone and N-tert-butanesulfinylamine is described. Strongly dehydrating conditions were required to form the N-tert-butanesulfinyl ketimines, but these intermediates were stable to aqueous work-up and chromatography. Reduction of N-tert-butanesulfinyl ketimines with L-selectride®, or Super-hydride®, in THF afforded excellent yields and diastereoselectivities of the sulfinamides, which were converted into chiral amines with methanolic HCl. The 4-pyrazolyl-2-ethylamines from these investigations are attractive building blocks for medicinal chemists, as they exhibit low molecular weight, and low calculated octanol-water partition coefficient (c Log P values), while disrupting planarity with three-dimensional character. For example, the amine products were utilized in structure-activity studies of the human transient receptor potential vanilloid 1 (TRPV1/VR1).     

香菇多糖L-2A的结构表征

从香菇子实体中提取纯化得到香菇多糖级分L-2A,利用紫外光谱、红外光谱、凝胶渗透色谱和气相色谱分析其结构特征.香菇多糖L-2A糖含量为90.14%;重均分子量是2.03×10 5道尔顿;具有D-葡萄吡喃糖构型,单糖组成主要是由吡喃型葡萄糖组成;香菇多糖L-2A多糖含有o-糖苷键,且主要是o-Ser连接方式;具有与刚果红结合的螺旋结构.香菇多糖L-2A为首次从香菇子实体中分离得到.     

THE PROTONATION OF A RETINYL SCHIFF BASE

The hydrogen bonding-protonation equilibrium for retinyl Schiff base/propionic acid or 3-chloropropionic acid systems was examined by Fourier transform infrared spectroscopy in non polar solutions at temperatures ranging from 25 degrees C to about -150 degrees C. The spectra give evidence for the gradual increase in the degree of protonation as temperature is lowered. The bearing of this on applying low temperature spectroscopic results to physiological conditions in rhodopsin research is discussed.     

Linear dynamical systems with integer constraints

We study properties of dynamic discrete-time linear systemswith the input or the state constrained to have integer components.The reachability of input-constrained systems is investigated,and consistency conditions for state-constrained systems aregiven.     

钾蒸气中的偶极禁戒双光子共振四波混频和混合激发能量转移受激辐射

本文首次报道了由钾分子-原子系统的混合激发和碰撞能量转移过程产生4F→3D受激辐射以及由钾原子的4S→4F偶极禁戒双光子共振产生4F→3D受激辐射和四波混频的研究结果。     

液氦温区两级4K脉冲管制冷机数值模拟

为模拟和动态显示工作在液氦温区的两级4K脉冲管制冷机内部工作过程和参数变化规律,发展了一种新的欧拉法-拉格朗日法数值计算模型。采用拉格朗日方法,直接跟踪脉冲管中气体微元随周期性压力波动的具体运行轨迹;采用欧拉法,直接模拟蓄冷器内部的动态参数变化。本文简单介绍该模型,并模拟了一典型两级4 K脉冲管制冷机各参数的变化情况,分析了多层磁性蓄冷材料对制冷机性能的影响情况。     

[H_2N(C_2H_4)_2NH_2]_4(H_3O)[PMo_2~VMo_6~(VI)V_4~(IV)O_(40)(V~(IV)O)_2]·H_2O: A New Highly Reduced, Bicapped Pseudo-Keggin Vanadylpolymolybdophosphate

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GLOBAL ANALYSIS OF THE TIME-RESOL VED FLUORESCENCE OF α-CHYMOTRYPSINOGEN A AND α-CHYMOTRYPSIN POWDERS AS A FUNCTION OF HYDRATION

The time-resolved tryptophyl fluorescence of alpha-chymotrypsin A and alpha-chymotrypsin in the crystalline state and in buffer solution at room temperature was analyzed globally. Triple-exponential decay functions are necessary to adequately describe the tryptophyl fluorescence decay surfaces of the protein powders as a function of hydration and in solution. The fluorescence lifetimes of alpha-chymotrypsinogen A (tau 1 = 0.32, tau 2 = 1.30 ns, tau 3 = 3.98 ns) and alpha-chymotrypsin(tau 1 = 0.66 n s, tau 2 = 2.26 ns, tau 3 = 5.40 ns) are constant over the entire hydration range. The spectral positions of the decay-associated spectra of the hydrated powders do not shift as a function of hydration. This indicates that the structures of the zymogen and the active enzyme are unaffected by hydration. The lifetimes of alpha-chymotrypsinogen A in phosphate buffer pH 7.4 are tau 1 = 0.37 ns, tau 2 = 1.17 ns and tau 3 = 3.44 ns while the respective values of alpha-chymotrypsin are tau 1 = 0.47 ns, tau 2 = 1.40 and tau 1 = 3.89 ns.     

A Note on Sampling from Combinations of Distributions

A rejection technique is described for sampling from a combinationof distributions with negative weights for some of the components.