高效液相色谱-圆二色检测法分析甲霜灵的对映体纯度

以手性农药甲霜灵为研究对象,使用非手性高效液相色谱在不拆分对映体的条件下,利用圆二色检测器所测的各向异性系数(g)测定手性对映体纯度。实验结果表明,g与对映体过剩率(ee)具有良好的线性关系;通过比较g所测ee与手性色谱所测的ee,二者所测ee相对平均偏差小于3.0%,说明该方法具有较高的准确性,可应用于手性化合物对映体纯度的测定。     

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。     

气相色谱手性固定相进展

1966年Gil-Av等人首次用手性固定相在毛细管柱上分离了氨基酸对映体。至今这种方法已发展为研究和分离对映体的一种重要技术,并愈来愈多地用于天然产物绝对构象(外激素、香料成分等)的测定,不对称选择合成中对映体纯度及过剩量测定,手性药物中对映体纯度的测定,手性化合物在化学转移机理等方面的研究。目前气相色谱中用于分离对映体的     

键合型纤维素类手性固定相高效液相色谱法拆分对映异构体

制备了一种键合型纤维素-三苯基氨基甲酸酯手性固定相。在正相色谱条件下，拆分了九种结构不同的外消旋对映体，实验发现，在流动相中添加四氢呋喃有利于手性化合物拆分，而衍生化官能团可参与手性识别过程，在反相色谱条件下，此固定相同样具有手性拆分能力。研究结果表明，随着流动相中乙腈浓度的增加，对映体的保留值明显减小，但对映异构体的选择性却变化不大。在流动相中使用低pH值，能有效抑制酸性化合物的解离，从而显著增强其手性识别能力；对于中性化合物，流动相中pH对手性分离影响不大。     

测定手性有机酸对映体纯度的新试剂

用NMR技术测定微量手性化合物的对映体纯度,已有多种方法。其中,加手性镧化物位移试剂法适用面最广,但对有机酸,结果常不理想。另一种使用较广的方法是加手性试剂,将样品中两对映体转变成非对映异构体,然后比较非对映基因NMR信号的强度,确定原样品中对映体的组成比例。国外已出售的手性试     

气相色谱法手性拆分氯代和溴代环氧苯乙烷

用手性毛细管气相色谱法(使用2，6-戊基-3-丙基-γ-环糊精柱，Chiraldex G-PN)对3种溴代环氧苯乙烷和3种氯代环氧苯乙烷对映体进行了拆分,初步讨论了对映体在该手性毛细管柱上的保留行为,已用于此类化合物对映体过量值(ee值)的测定．     

NMR手性位移试剂Eu(facam)3的应用

应用核磁共振波谱法来测定有机化合物的光学对映体含量是很有意义的。通常,它有三种方法:①应用手性溶剂,②被测对映体形成非对映异构体方法,③手性位移试剂。Pirkle等应用的手性溶剂方法,虽可推测绝对构型,但往往由于对映位化学位移差值较小,不易准确测定含量。一般应用最广的Mosher试剂(光学活性α-甲氧基α-三氟甲基苯乙酸,MTPA)形成非对映异构体的方法,仅局限于测定醇或胺类化合物,此法有时还需普通位移试剂配合使用。手性位移试剂则可直接测定对映体的光学纯度。 1970年Whitesides和Lewist首先合成了手性位移试剂三-(3-叔丁基羟基亚甲基-d-樟脑)     

气相色谱法手性拆分氯代和溴代环氧苯乙烷

用手性毛细管气相色谱法 (使用 2 ,6 戊基 3 丙基 γ 环糊精柱 ,ChiraldexG PN)对 3种溴代环氧苯乙烷和 3种氯代环氧苯乙烷对映体进行了拆分 .初步讨论了对映体在该手性毛细管柱上的保留行为 .已用于此类化合物对映体过量值 (ee值 )的测定     

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。     

在对映体水平上测定土壤中烯效唑的方法

目前使用的农药中约25％是手性化合物.手性农药对映体的生物活性往往有很大差异,例如常用的三唑类植物生长调节剂烯效唑(Uniconazole),其S体的活性是R体的7倍.但目前绝大多数手性农药是以消旋体形式使用的.对于手性农药,目前的研究工作主要集中在其作为农药的生物活性的对映体选择性上,而对其环境行为的对映体选择性研究则很少,缺乏在对映体水平上测定环境介质.     

Quantitative chiral analysis of phthaloylglutamic acid and related analogs by a single ratio kinetic method using electrospray ionization and matrix-assisted laser desorption techniques

A rapid method for quantitative chiral analysis of phthaloylglutamic acid and its dimethyl ester by Cook's kinetic method is demonstrated using electrospray ionization (ESI) and matrix-assisted laser desorption techniques. Transition-metal-bound complex ions containing the chiral phthaloylglutamic acid and its dimethyl ester are generated by ESI mass spectrometry and subjected to collision-induced dissociation. The ratio of the two competitive dissociation rates is related to the enantiomeric composition of the drug mixture. A seven-point calibration curve, derived from the kinetic method, allowed rapid quantitation of the enantiomeric excess of drug mixtures. In this paper, matrix-assisted laser desorption/ionization (MALDI) coupled with the linear ion trap (LIT) technique is evaluated for its applicability as a complementary technique to ESI for chiral discrimination and quantitation.     

Chiral and isomeric analysis by electrospray ionization and sonic spray ionization using the fixed-ligand kinetic method

The fixed-ligand version of the kinetic method has been used for chiral and for isomeric analysis by studying the dissociation kinetics of transition metal-bound trimeric cluster ions ([(M(II) + L(fixed)-H)(ref*)(An)](+), where M(II) is a transition metal, L fixed is a fixed (non-dissociating) ligand, ref* is a reference ligand and An is the analyte. The trimeric cluster ions are readily generated by electrospray ionization (ESI) or sonic spray ionization (SSI). The size of the fixed ligand, L- Phe-Gly-L-P he-Gly, is chosen based on previous results but with the inclusion of aromatic functionality to increase chiral recognition. Improved chiral/isomeric differentiation results from enhanced chiral/isomeric interactions (metal-ligand and ligand-ligand) due to the fixed ligand. As shown in the cases of chiral dipeptides (D-Ala-D-Ala/L-Ala-L-Ala), sugars (D/L-glucose, D/L-mannose) and isomeric tetrapeptides (L-Ala-Gly-Gly-Gly/Gly-Gly -Gly-L-Ala), improved chiral/isomeric discrimination by factors from three to six were obtained by the fixed ligand procedure. Chiral recognition is independent of the concentrations of the analyte, the reference ligand, the fixed ligand and the transition metal salt, a great advantage for practical applications. In addition to increased chiral distinction, the simplified dissociation kinetics also contribute to improved accuracy in chiral quantification, in comparison with data obtained by investigating the dissociation kinetics of simple trimeric cluster ions [M(II)(ref*)2(An) H](+). Accurate determination of enantiomeric excess (ee) is demonstrated by enantiomeric quantification of D-Ala-D-Ala/L-Ala-L-Ala down to 2% ee. Both ESI and SSI allow chiral quantification with similar accuracies. The performance of chiral analysis experiments is not limited to ion trapping devices such as quadrupole ion trap mass spectrometers by a hybrid quadrupole-time of flight (Q-ToF) mass spectrometer is shown to provide an alternative choice. The fixed-ligand kinetic method is not restricted to any particular kinds of isomers and, hence, represents a general procedure for improving molecular recognition and chiral analysis in the gas phase.     

Chiral discrimination of D- and L-amino acids using iodinated tyrosines as chiral references: Effect of iodine substituent

L-Tyrosine and iodinated L-tyrosines, i.e., 3-iodo-L-tyrosine and 3,5-diiodo-L-tyrosine, are successfully used as chiral references for the chiral discrimination of aliphatic, acidic, and aromatic amino acids. Chiral discrimination is achieved by investigating the collision-induced dissociation spectra of the trimeric complex [Cu(II)(ref)(2)(A) - H](+) ion generated by electro spraying the mixture of D- or L-analyte amino acid (A), chiral reference ligand (ref) and M(II)Cl(2) (M = Ni and Cu). The relative abundances of fragment ions resulted by the competitive loss of reference and analyte amino acids are considered for measuring the degree of chiral discrimination by applying the kinetic method. The chiral discrimination ability increases as the number of iodine atom increases on the aromatic ring of the reference and the discrimination is better with Cu when compared with Ni. A large chiral discrimination is obtained for aliphatic and aromatic amino acids using iodinated L-tyrosine as the reference. Computational studies on the different stabilities of the diastereomeric complexes also support the observed differences measured by the kinetic method. The suitability of the method in the measurement of enantiomeric excess over the range of 2% to 100% ee with relative error 0.28% to 1.6% is also demonstrated.     

Quantitative determination of the enantiomeric composition of thalidomide solutions by electrospray ionization tandem mass spectrometry

Rapid and simple chiral analysis of thalidomide solutions is demonstrated by using electrospray ionization tandem mass spectrometry and analysis of cluster ion dissociation by the kinetic method. Average deviations of 1% between the actual and experimental enantiomeric compositions are observed.     

Kinetic method for the simultaneous chiral analysis of different amino acids in mixtures

The kinetic method has been extended to enantiomeric excess (ee) determinations on amino acids present in mixtures. Singly charged trimeric clusters [Cu(II)(ref*)(2)(A(m)) - H](+) are readily generated by electrospraying solutions containing Cu(II), a chiral reference ligand (ref*), and the amino acids (analytes A(m), m = 1-3). A trimeric cluster ion for each amino acid is individually mass-selected and then collisionally activated to cause dissociation by competitive loss of either the reference ligand or the analyte. For each analyte in the mixture, as shown from separate experiments, the logarithm of the ratio of the fragment abundances for the complex containing one enantiomer of this analyte expressed relative to that for the fragments of the corresponding complex containing the other enantiomer is linearly related to the enantiomeric composition of the amino acid. Formation and dissociation of each trimeric complex ion are shown to occur independently of the presence of other analytes. Chiral selectivity appears to be an intrinsic property and the chiral selectivity R(chiral(m)) measured from the mixture of analytes is equal to R(chiral) measured for the pure analyte. The sensitive nature of the methodology and the linear relationship between the logarithm of the fragment ion abundance ratio and the optical purity, characteristic of the kinetic method, allow the determination of chiral impurities of less than 2% ee in individual compounds present in mixtures by simply recording the ratios of fragment ion abundances in a tandem mass spectrum.     

Chiral recognition of zinc(II) ion complexes composed of bicyclo[3.3.0] octane-2,6-diol and <Emphasis Type="Italic">s</Emphasis>-Naproxen probed by collisional-induced dissociation

Chiral recognition of racemic bicyclo[3.3.0] octane-2,6-diol(B) was achieved in the gas phase using s-Naproxen(A) as reference, using the kinetics of competitive unimolecule dissociation of tetrameric zinc(II)-bound complexes by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometer(ESI-FTMS). As undergoing a mild competitive collision-induced dissociation(CID) experiment with a constant pressure argon gas introduced by leak valve, the tetrameric cluster ion [A(2)B(2)Z(n)(II)-H](+) forms only two trimeric ions and R(chiral) is subsequently obtained in the kinetic method. Further studies obtained the difference of Gibbs free energy of [ABZ(n)(II)-H](+)(Delta Delta G(ABZn(II)-H](+))) by dissociating [A(2)BZ(n)(II)-H](+), resulting two fragment ions [ABZ(n)(II)-H](+) and [A(2)Z(n)(II)-H](+), which can be established to a linear relationship between Delta Delta G([ABZn(II)-H](+)) and R(chiral)' basing on the kinetic method. The value of R(chiral)' suggested that Delta Delta G([ABZn(II)-H](+)) could be regarded as zero. Meanwhile, dissociation of [AB(2)Z(n)(II)-H](+) generated only one daughter ion [ABZ(n)(II)-H](+) in a stable pressure. Thus, a linear relationship was established between the difference of Gibbs free energy of [AB(2)Z(n)(II)-H](+)(Delta Delta G([AB(2)Zn(II)-H](+))) and R(chiral)" if the Delta Delta G([ABZn(II)-H](+)) can be negligible. Because there is also a linear relationship of R(chiral) in the tetrameric ion [A(2)B(2)Z(n)(II)-H](+) and the Gibbs energy difference of trimeric cluster ion [A(2)BZ(n)(+)(II)-H](Delta Delta G([A(2)BZn(II)-H](+))) plus that of [AB(2)Z(n)(II)-H](+), Delta Delta G([A(2)BZ(n)(II)-H]+]) is easy to be calculated in the dissociation process of tetrameric ion. Stable of R(chiral), R(chiral)' and R(chiral)" under different pressures show T(eff) does not affect the chiral recognition of cluster ions in the condition selected. If an only-one-daughter-ion fragment process of [A(2)BZ(n)(II)-H](+) was existed, R(chiral)' relating to this dissociation would be calculated just like R(chiral)" of [AB(2)Z(n)(II)-H](+) does. Conclusion was obtained that [A(2)BZ(n)(II)-H](+) makes more contribution to chiral recognition of tetrameric ion measured by kinetic method than [AB(2)Z(n)(II)-H](+) does as R(chiral)' and R(chiral)" were applied as index to evaluate the Gibbs free energy difference of these two trimeric cluster ions. Further discussion shows that steric interactions and pi-pi stacking interactions are the major factors responsible for the observed efficient chiral recognition in this system.     

Characterization of interaction kinetics between chiral solutes and human serum albumin by using high-performance affinity chromatography and peak profiling

Peak profiling and high-performance columns containing immobilized human serum albumin (HSA) were used to study the interaction kinetics of chiral solutes with this protein. This approach was tested using the phenytoin metabolites 5-(3-hydroxyphenyl)-5-phenylhydantoin (m-HPPH) and 5-(4-hydroxyphenyl)-5-phenylhydantoin (p-HPPH) as model analytes. HSA columns provided some resolution of the enantiomers for each phenytoin metabolite, which made it possible to simultaneously conduct kinetic studies on each chiral form. The dissociation rate constants for these interactions were determined by using both the single flow rate and multiple flow rate peak profiling methods. Corrections for non-specific interactions with the support were also considered. The final estimates obtained at pH 7.4 and 37°C for the dissociation rate constants of these interactions were 8.2-9.6 s(-1) for the two enantiomers of m-HPPH and 3.2-4.1 s(-1) for the enantiomers of p-HPPH. These rate constants agreed with previous values that have been reported for other drugs and solutes that have similar affinities and binding regions on HSA. The approach used in this report was not limited to phenytoin metabolites or HSA but could be applied to a variety of other chiral solutes and proteins. This method could also be adopted for use in the rapid screening of drug-protein interactions.     

Microcanonical analysis of the kinetic method. the meaning of the "apparent entropy"

A rigorous analysis of the kinetic method is carried out using Rice-Ramsperger-Kassel-Marcus (RRKM) theory of microcanonical statistical unimolecular dissociation rates. The model employs a kinetics treatment appropriate for metastable ion dissociation. Proton-bound alkoxide dimer anions are used as model systems, with realistic vibrational and rotational parameters calculated by ab initio methods for the cluster ion and transition states leading to the competitive dissociation channels. The numerical simulations show that the kinetic method plots of ln(I2/I1) versus AAH are nearly linear but can exhibit significant curvature. The apparent entropy obtained in the extended kinetic method is not approximately equal to the thermodynamic entropy difference for dissociation, AAS(T), or for activation, deltadeltaS++(T), either at the effective temperature or at any fixed equilibrium temperature. Instead, the apparent entropy term can be related to the ratio of the microcanonical sum of states of the dissociation transition states for the kinetically selected internal energy of the dissociating ions.     

Chiral quantification of D-, L-phenylglycine mixture using mass spectrometric kinetic method

A novel mass spectrometric method is applied to rapid, accurate, quantitative analysis of chiral phenylglycine. Transition-metal-bound complex ions containing the chiral phenylglycine are generated by electrospray ionization mass spectrometry and subjected to collision-induced dissociation. The ratio of the two competitive dissociation rates is related to the enantiomeric composition of the mixture, allowing the determination of enantiomeric contamination in the intermediates.     

Differentiation and quantitation of isomeric dipeptides by low-energy dissociation of copper(II)-bound complexes

Application of the kinetic method based on the dissociation of transition metal centered cluster ions is extended from chiral analysis (Tao, W. A.; Zhang, D.; Nikolaev, E. N.; Cooks, R. G. J. Am. Chem. Soc. 2000, 122, 10598) to quantitative analysis of isomeric mixtures, including those with Leu/Ile substitutions. Copper(II)-bound complexes of pairs of peptide isomers are generated by electrospray ionization mass spectrometry and the trimeric complex [CuII(ref)2(A) - H]+ (analyte A, a mixture of isomeric peptides; reference compound ref, usually a peptide) is caused to undergo collisional dissociation. Competitive loss of the neutral reference compound or the neutral analyte yields two ionic products and the ratio of rates of the two competitive dissociations, viz. the product ion branching ratio R is shown to depend strongly on the regiochemistry of the analyte in the precursor [CuII(A)(ref)2 - H]+ complex ion. Calibration curves are constructed by relating the branching ratio measured by the kinetic method, to the isomeric composition of the mixture to allow rapid quantitative isomer analysis.