手性NMR位移试剂在有机磷酰胺酯类杀虫剂对映异构体测定中的应用

本工作利用手性位移试剂Eu(hfc)Eu(tfc)_3和Pr(hfc)_3对通式为剂进行了~1H、~(13)C和~(31)P NMR研究,观察了对映异构体在手性条件下在NMR谱图上的反映。结果表明,在手性位移试剂作用下,用~1H NMR谱仅能测定结构简单例如R为CH_3的化合物的光学纯度,但采用~(31)P{~1H}技术则可方便有效地测定结构复杂的该类化合物的光学纯度。本工作还对硫酮式和硫醇式两类硫代磷酰胺酯与手性位移试剂的络合模型作了初步讨论。     

手性溶剂-NMR法测定2,4-滴丙酸对映体纯度的定量分析

研究了手性溶剂法测定2,4-滴丙酸的^1H、^13C谱,在满足NMR准确定量所要求的分离度和信噪比的条件下,能准确测定手性化合物的对映体纯度。比较了以对映体百分含量（R％）和对映体过量（ee）表示手性农药的对映体纯度的差别,发现以对映体百分含量代替对映体过量来表示手性农药的对映体纯度更为准确。     

纤维素键合手性固定相拆分喹禾灵对映体

采用Chiralpak IC(纤维素-三(3,5-二氯苯基氨基甲酸酯)键合在5μm硅胶上)键合型手性柱,建立了喹禾灵对映体的高效液相色谱拆分方法。系统考察了流动相组成、流速和柱温对喹禾灵对映体分离效果的影响。结果表明,在正己烷-异丙醇(95∶5,体积比)为流动相,流速1.0 mL/min,柱温25℃的条件下,喹禾灵对映体能获得基线分离,分离度Rs为3.97,R-构型先出峰,两对映体的检出限均为0.045 mg/L,定量下限均为0.15 mg/L。在15～35℃柱温范围内,lnα对1/T Van’t Hoff曲线呈良好的线性关系,相关系数(r2)大于0.99,分离因子α随温度升高而降低,焓变差和熵变差热力学参数显示,喹禾灵对映体的拆分过程受焓控制。     

H-NMR—位移试剂法研究α-氨基酸及α-取代胺的构型和对映体含量

本文报道了在研究α—氨基酸及α—取代苄胺的不对称合成中,用核磁共振波谱法和手性位移试剂—Eu(hfc)_3给出′H—NMR谱。利用OCH_3基团的明显单蜂,在加入以上位移试剂后,单峰向低场位移,分别在5和7ppm左右分裂成二个峰,其积分值可计算e.e值。由于Eu(hfc)_3为R构型,它同被测样品分别生成R—R,R—s构型的络合物,前者的位移较后者快,从而可确定样品的R和s构型的位置。     

手性试剂TMPEA用于手性酮对映体纯度测定的研究

β-三氟甲基-β甲氧基β-苯基乙胺（TMPEA）是含氨基功能团的手性试剂[1]．由于胺可将按酸转变成酸胺，该试剂已成功地用于手性有机酸对映体的纯度测定[2]．考虑到胺同样可将醛酮转变成亚胺，本文进一步探讨了TMPEA用于手性醒酮对映体纯度测定的可行性．用R－（－）－TMPEA及dl－TMPAE分别与下列4种手性酮反应，制备相应的非对映异构亚胶：比较光活亚胺及相应的非对映异构体混合物亚腔的NMR谱，可确定各组非对映异构亚胺‘HNMR位移差（以OCH为探针基团）和’‘FNMR的位移差（以CF为探针基团）（表1）．TablelCheffiicalshif…     

3-苯基异香豆冉酮衍生物的不对称Mannich反应研究

研究了双功能手性硫脲-叔胺催化剂催化的3-苯基异香豆冉酮衍生物与N-保护亚胺的不对称Mannich反应,高收率、高对映选择性(88%~98%)地合成了一系列具有连续季碳叔碳手性中心的新化合物,其结构经1HNMR和13C NMR表征。     

酰基辅酶A : 胆固醇酰基转移酶抑制剂Beauveriolide I的全合成

报道了酰基辅酶A:胆固醇酰基转移酶抑制剂beauveriolideI的全合成.BeauveriolideI结构中的饱和脂肪酸具有两个相邻的手性中心,是合成的关键中间体,以(4R)-4-苄基-3-丙酰基-2-噁唑烷酮和3-苄氧丙醛为起始原料制备得到.Beauveriolide I的结构经1HNMR,13CNMR,MS和IR谱确定.     

核磁共振技术测定联萘酚的对映体纯度

手性联萘酚((±)-BINOL)制备是国内高校常开设的一个实验,其产品的对映体纯度测试是实验的重要一环。以2-甲酰基苯硼酸和(S)-(?)-1-苯乙胺的混合物作为手性试剂与联萘酚发生Bull-James Assembly反应,以此设计了核磁共振氢谱(¹H NMR)测定联萘酚对映体纯度的实验。实验结果表明,通过反应生成的对映体混合物的核磁信号,能准确地计算出(±)-BINOL的对映体纯度。以选定的苯环氢核信号计算出的(R)-BINOL含量与理论ee值有着良好的线性关系(R²=0.9999)。此实验方法能够快速完成大量学生样品的测量,同时大大减少实验废液的产生量。学生通过此实验可对核磁共振技术有更进一步的了解。     

3种芳香连二醇对映体的毛细管区带电泳手性拆分及其光学纯度分析

以磺化环糊精为毛细管区带电泳(CZE)手性选择剂,成功地分离了3种烯烃的不对称二羟化产物苯基乙二醇、β-甲基苯基-乙二醇和1,2-二苯基乙二醇对映体;考察了不同手性选择剂及其浓度、背景电解质pH值、操作电压等因素对分离的影响,优化了分离条件;对该3种芳香连二醇对映体样品进行了光学纯度检查,并与HPLC测定结果作比较,评价该方法的准确性。结果表明:两批样品中对映体过量(ee)测定值与HPLC法结果相一致,CZE方法简单、准确、分离度好,可用于该芳香连二醇中性化合物的手性拆分和ee值的测定。     

不对称合成——Ⅱ.(R)-O-甲基-α-甲基丝氨酸衍生物的对映选择合成

本文报道以L-缬氨酸为手征性助剂,DL-丙氨酸为原料,(3S,6SR)-2,5-二甲氧基-3-异丙基-6-甲基-3,6-二氢吡嗪(1)为杂环中间体,(2R,3SB)-O-甲基-a-甲基丝氨酸甲酯衍生物的对映选择合成。在丁基锂作用下,化合物1转变成锂衍生物(2),它与醛类化合物(3)作用可得具有很高立体选择性的羰基加成物(4)。羰基化合物以C-3位异丙基的反式进入1的C-6位,即在C-6位引入(R)-构型。为避免4水解时的反醛醇缩合反应,必须对其羟基加以保护,然后才能经水解合成O-甲基-a-甲基丝氨酸衍生物(6)。用加入手征性位移试剂Eu(hfc)_3的~1H NMR谱测定了对映体过量百分数。     

NMR determination of enantiomeric composition of 1-substituted 3-amino-1,2-dicarba-closo-dodecaboranes using Eu(hfc)3

Experimental conditions for determination of enantiomeric composition of 1-substituted 3-aminocarboranes by ¹H and ¹³C NMR spectroscopy using chiral shift reagent Eu(hfc)₃ have been found.     

Determination of enantiomeric excess by 13C NMR spectroscopy

Oxazolidine derivatives of β-amino alcohols such as ephedrine have been resolved by ¹³C NMR spectroscopy using Eu(hfc)₃ as a chiral shift reagent. The method is quantitative in the determination of enantiomeric excess, and is advantageous where ¹H NMR is of limited use owing, for example, to significant line broadening.     

Enantiomeric differentiation of oxygenated p-menthane derivatives by 13C NMR using Yb(hfc)3

The (13)C NMR behaviour of 21 p-menthanic terpene bearing an oxygenated function (alcohol, ketone, acetate) was examined in the presence of a chiral lanthanide shift reagent (Yb(hfc)(3)). For each monocyclic compound, we measured the lanthanide-induced shift (LIS) on the signals of the carbons and the splitting of signals allowing the enantiomeric differentiation. Some general features were found about their LIS behaviour: experimental data establishing distinct patterns for carvomenthone-like compounds and menthone-like compounds. The enantiomeric splitting was observed for the majority of signals in the spectrum of each compound. In the case of alcohols and acetates, the influence of the relative stereochemistry (cis vs trans) of isopropyl(ene) and the binding function was discussed.     

A new chiral lanthanide NMR probe for the determination of the enantiomeric purity of alpha-hydroxy acids and the absolute configuration of alpha-amino acids in water

A water-soluble, enantiopure lanthanide complex, SSS-[Ln x L3], has been assessed as an effective chiral derivatizing agent for the determination of the enantiomeric purity of alpha-hydroxy acids in aqueous solution. The complex displays superior chemical shift non-equivalence (DeltaDeltadelta approximately 2-11 ppm) for the diastereomeric resonances of interest compared to lanthanide shift reagents reported in the literature (DeltaDeltadelta <0.1 ppm, typically). 1H NMR studies have also revealed that SSS-[Ln x L3] can be used to determine the absolute configuration of alpha-amino acids at physiological pH, in water. The ability of SSS-[Ln x L3] to signal anion binding and, in particular, to distinguish between diastereomers through optical techniques such as lanthanide luminescence and circular dichroism has also been assessed.     

Resolution of (±)-2,3-Dihydro-2-phenyl-4(1H)-Quinolone

The resolution of (±)-2,3-dihydro-2-phenyl-4(1H)-quinolone into individual enantiomers was achieved using the optically active oxo reagent (-)-5-(α-phenethyl)-semioxamazide. The enantiomeric purity was checked by ¹H-NMR using the chiral lanthanide shift reagent Eu(hfc)₃.     

Enantiomeric NMR signal separation mechanism and prediction of separation behavior for a praseodymium (III) complex with (S,S)-ethylenediamine-N,N-disuccinate

Because choice of chiral nuclear magnetic resonance (NMR) shift reagents and concentration conditions have been made empirically by trials and errors for chiral NMR analyses, the prediction of NMR signal separation behavior is an urgent issue. In this study, the separation of enantiomeric and enantiotopic ¹H and ¹³C NMR signals for α-amino acids and tartaric acid was performed by using the praseodymium(III) complex with (S,S)-ethylenediamine-N,N′-disuccinate ((S,S)-EDDS). All the present D-amino acids exhibited larger downfield shift of their α-protons and α-carbons compared with those for the corresponding L-amino acids in common. This regularity is applicable to absolute configurational assignment and determination of optical purity of amino acids. The chemical shifts of β-protons of d - and l -alanine fully bound with the Pr(III) ((S,S)-EDDS) complex (δ_bs) and the adduct formation constants of both enantiomers (Ks) were obtained by dependences of the observed downfield shifts of the β-protons on the total concentrations of the respective enantiomers in the presence of a constant concentration of the Pr(III) complex. The difference in the K values was found to be predominant determining factor for the enantiomeric signal separation. The chemical shifts of both enantiomers (δs) and the enantiomeric signal separations (Δδs) under given conditions could be calculated from the δ_b and K values. Furthermore, prediction of the signal separation behavior was enabled by using the calculated δ values and the signal broadening obtained by dependences of the half-height widths of the observed signals on the bound/free substrate concentration ratios for the respective enantiomers.     

Helical chirality in hexamethylene triperoxide diamine

The primary explosive hexamethylenetriperoxide diamine has previously been found to exist in the solid state as a racemic mixture of helically chiral, threefold symmetric enantiomers; another enantiomeric pair of low-energy conformers has been predicted, but has never been observed. We show by solution 2D NMR at 14 T, in achiral solution and by addition of chiral shift reagents, that all four optically isomeric conformers coexist at slow equilibrium on the NMR timescale at room temperature, and can be observed. Calculations of the 1H and 13C NMR chemical shifts using gauge-including atomic orbital methods are in excellent agreement with experiment; thermochemical calculation of the free energies in solution are in somewhat worse agreement, but correctly predict the relative stability of the conformers. Analysis of the effects of chiral shift reagents on the NMR spectra suggests that discrimination between chiral isomers is primarily around the molecular equator, around which the enantiomeric gauche O--O linkages are arrayed.     

Observing the enantiomeric 1H chemical shift non-equivalence of several α-amino ester signals using tris[3-(trifluoromethylhydroxymethylene)-(+)-camphorato]samarium(III): a chiral lanthanide shift reagent that causes minimal line broadening

The chiral lanthanide shift reagent, tris[3-(trifluoromethylhydroxymethylene)-(+)-camphorato]samarium(III) [Sm(tfc)₃], was shown to resolve the ¹H NMR signals of the enantiomers of α-amino esters without causing serious line broadening. This distinctive feature of Sm(tfc)₃ made it possible to examine the enantiomeric chemical shift non-equivalence of several protons in ester substrates, increasing the reliability of the empirical assignment of the absolute configuration as compared to earlier techniques.     

Chiral imines prepared from 1-(2-aminoalkyl)aziridines as novel chiral shifts reagents for efficient recognition of acids

Optically pure, chiral imines synthesized from the corresponding aldehydes and 1-(2-aminoalkyl)aziridines in good chemical yields, have been assessed as an NMR chiral shift reagents for effective discrimination of the signals of some acids (mandelic acid and its derivatives and N-protected amino acid). The title compounds have proven to be very useful for the determination of enantiomeric purity and absolute configuration of the aforementioned acid derivatives.