立体异构

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 rather more complex case is that of steric isomerism.

更复杂的情形是立体异构问题。

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

John Cornforth (b. 1917) and Vladimir Prelog (1906-98) shared a 1975 Nobel Prize for work on stereochemistry and stereoisomerism of alkaloid s, enzymes, antibiotics, and other natural compounds.

康福思和普雷洛格在立体化学以及生物碱、、抗生素和其它天然化合物的立体异构方面做了许多工作，因而共获1975年的诺贝尔奖。

John Cornforth (b. 1917) and Vladimir Prelog (1906-98) shared a 1975 Nobel Prize for work on stereochemistry and stereoisomerism of alkaloids, enzymes, antibiotic s, and other natural compounds.

康福思和普雷洛格在立体化学以及生物碱、、抗生素和其它天然化合物的立体异构方面做了许多工作，因而共获1975年的诺贝尔奖。

The generating results of our system were compared with the published,results of DENDRAL and SEMAMI systems, and they were consistent with eachother.

目前本系统对于含C、N、P、S与Si等元素由于不对称中心、不对称轴引起的立体异构和几何异构均能进行穷举生成。

The invention includes all sterioisomeric forms, including individual diastereoisomers and enantiomers of the compound of formula as well as racemic and non-racemic mixtures thereof.

本发明包括式化合物所有的立体异构形式，包括单个的非对映异构体和对映异构体，及其外消旋的和非外消旋的混合物。

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。

According to the clear water experiment, aeration performance of the new equipment is good with high total oxygen transfer coefficient and oxygen utilization ratio.

曝气设备的动力效率在叶轮转速为120rpm～150rpm时取得最大值，此时氧利用率和充氧能力也具有较高值。

The environmental stability of that world - including its crushing pressures and icy darkness - means that some of its most famous inhabitants have survived for eons as evolutionary throwbacks, their bodies undergoing little change.

稳定的海底环境─包括能把人压扁的压力和冰冷的黑暗─意谓海底某些最知名的栖居生物已以演化返祖的样态活了万世，形体几无变化。