立体异构体

Cephalotaxine ester of 2-oxo-6-methylheptanoic acid was treated with lithium diisopropylamide and Me O-(1-methoxyisopropyl)glycolate to give a mixture of homoisoharringtonine and its stereoisomers with 56% yield. The four stereoisomers separated by TLC showed identical mass spectra and almost superimposed IR but with different 1H NMR spectra. The configuration of the 2'-C and 3'-C of the four isomers were postulated based upon their 1H NMR spectra as compared with the 1H NMR spectra of isoharringtonine and its stereoisomers.

2-氧代-6-甲基庚酰基三尖杉碱(3)与0-(1-甲氧基异丙基)羟基乙酸甲酯(4)在强碱性试剂二异丙胺锂存在下，起亲核加成反应，反应中间体5在室温用酸性丙酮水解，得到一种新的三尖杉酯类生物碱一一高异三尖杉酯碱(6c)及其立体异构体(6a、6b、6d)的混合物，产率56%、通过制备薄层层析分得这四个立体异构体，它们的1H NMR和异三尖杉酯碱及其立体异构体的1H NMR类似，推定了它们的绝对构型。

A solution of one stereoisomer of a given monosaccharide rotates plane-polarized light to the left and is called the levorotatory isomer, designated

一特定单糖的一种立体异构体溶液使平面偏振光向左旋转称为左旋，标记为

A solution of one stereoisomer of a given monosaccharide rotates plane- polarize d light to the left and is called the levorotatory isomer, designated

一特定单糖的一种立体异构体溶液使平面偏振光向左旋转称为左旋，标记为

Serum levels of ADMA and its stereoisomer, symmetrical dimethylarginine, were determined using high-performance liquid chromatography.

使用高效液相色谱法测定ADMA及其立体异构体对称二甲基精氨酸的血清浓度。

Uses: Lutein, and its naturally occurring stereoisomer zeaxanthin, is used as part of a general carotenoid defense against oxidative stress, whether solar or metabolic.

用途： 叶黄素和其立体异构体玉米黄质，作为常规类胡萝卜素的一部分，用于防止来自日光的或者来自新陈代谢的氧化压力。

The optical activity of a stereoisomer is expressed quantitatively by its optical rotation, The specific rotation 〖α〗D25C of an optically active compound is defined thus

立体异构体的光学活性是以旋光度定量表示的，光学活性物质的比旋光度〖α〗D25C是这样定义的

The other stereoisomer rotates plane-polarized light to the same extent but to the right and is called the dextrorotatory isomer, designated.

另一立体异构体使平面偏振光向右旋转称为右旋，标记为。

The other stereoisomer rotates plane- polarize d light to the same extent but to the right and is called the dextrorotatory isomer, designated.

另一立体异构体使平面偏振光向右旋转称为右旋，标记为。

Diltiazem is an important coronary vasodilating drug and contains two chiral centers while only the (2S, 3S)-isomer has the desired activity.

地尔硫卓是重要的心血管药物，在其分子结构中含有2个手性中心，可产生4个立体异构体，其中只有(2S， 3S)－异构体具有药理活性，因此其立体选择性合成具有很大的挑战性。

The combined acids , LHZZS,XDZZS and SLZZS, one of four fractions in montan resins from montan waxes from Liaohu, Xundian and Shulan brown coal respectively, were derived by CH 2N 2 to methyl esters and their chemical constituents and structural characteristic were studied on GC-MS.

结果显示，树脂结合酸均以正构烷酸为主要成份，其分布为C1 2 ～C2 8，高含量的正构烷酸集中在低碳数一端，C2 0 含量最高，其次为C1 6 ，而舒兰结合酸中，正构烷酸占绝对优势，且C1 6 为最高含量的化合物；去氢松香酸在每一个样品中含量较低，其它三环二萜酸，如松脂酸、三达松脂酸等异构体或立体异构体含量也非常低；具有五环三萜骨架的酸性物质，在潦浒、舒兰结合酸中比较丰富，其含量超过寻甸结合酸；在低碳数一端，存在着各种支链烷酸及苯甲酸、苯酚及取代物。

As she looked at Warrington's manly face, and dark, melancholy eyes, she had settled in her mind that he must have been the victim of an unhappy attachment.

每逢看到沃林顿那刚毅的脸，那乌黑、忧郁的眼睛，她便会相信，他一定作过不幸的爱情的受害者。

Maybe they'll disappear into a pothole.

也许他们将在壶穴里消失