高效液相色谱手性固定相的研究VI. 间隔基结构对L-缬氨酸玻丁酰胺型手性固定相拆分效果的影响

本文合成一系列含不同结构间隔基的L-缬氨酸叔丁酰胺型键合硅胶手性固定相, 将其用于高效液相色谱拆分α-氨基烃基膦酸衍生物, N-乙酰基-β-二茂铁基丙氨酸乙酯、N-叔丁氧羰基亮氨酰亮氨酸甲酯、N-乙酰基-α-氨基酸甲酯等对映异构体。结果表明: 制得的固定相对以上化合物对映异构体均有不同程度的拆分效果。间隔基刚性增强, 一般对拆分产生不利影响。间隔基为旋光活性酒石酰基的固定相拆分化合物范围减少, 但对某些类化合物对映体的拆分效果有所增强。     

高效液相色谱手性固定相的研究 Ⅵ.间隔基结构对L-缬氨酸叔丁酰胺型手性固定相拆分效果的影响

本文合成一系列含不同结构间隔基的L-缬氨酸叔丁酰胺型键合硅胶手性固定相,将其用于高效液相色谱拆分α-氨基烃基膦酸衍生物,N-乙酰基-β-二茂铁基丙氨酸乙酯、N-叔丁氧羰基亮氨酰亮氨酸甲酯、N-乙酰基-α-氨基酸甲酯等对映异构体.结果表明:制得的固定相对以上化合物对映异构体均有不同程度的拆分效果.间隔基刚性增强,一般对拆分产生不利影响.间隔基为旋光活性酒石酰基的固定相拆分化合物范围减少,但对某些类化合物对映体的拆分效果有所增强.     

高效液相色谱手性固定相的研究V——二肽叔丁酰胺型手性固定相拆分α-氨基酸、二茂铁基氨基酸及二肽衍生物对映异构体

本文应用高效液相色谱(L,L)-二肽叔丁酰胺型键合硅胶手性固定相拆分N-乙酰基-α-氨基酸甲酯、N-乙酰基-β-二茂铁基丙氨酸乙酯及N-叔丁氧羰基亮氨酰亮氨酸甲酯等对映异构体、结果表明:部分固定相对氨基酸衍生物对映异构体有拆分效果;大部分固定相对二茂铁基丙氨酸衍生物对映异构体有较好拆分效果;所有固定相对由(D,D)-及(L,L)-亮氨酰亮氨酸衍生物构成的外消旋体均有良好的拆分效果,分离系数最高达1.79。本文对部分化合物对映异构体的拆分机制进行了初步探讨。     

高效液相色谱手性固定相的研究Ⅴ——二肽叔丁酰胺型手性固定相拆分α-氨基酸、二茂铁基氨基酸及二肽衍生物对映异构体

]本文应用高效液相色谱(L，L)-二肽叔丁酰胺型键合硅胶手性固定相拆分N-乙酰基--氨基酸甲酰、N-乙酰基--二茂铁基丙氨酸乙酯及N-叔丁氧羰驶基亮氨酰亮氨酸甲酯等对映异构体、结果表明：部分固定相对氨基酸衍生物对映异构体有拆分效果；大部分固定相对二茂铁基丙氨酸衍生物对映异构体有较好拆分效果；所有固定相对由（D，D）-及（L，L）-亮氨酰亮氨酸衍生物构成的外消旋体均有良好的拆分效果，分离系数最高达1.79。本文对部分化合物对映异构体的拆分机制进行了初步探讨。     

高效液相色谱手性固定相的研究Ⅴ——二肽叔丁酰胺型手性固定相拆分α-氨基酸、二茂铁基氨基酸及二肽衍生物对映异构体

 ]本文应用高效液相色谱(L，L)-二肽叔丁酰胺型键合硅胶手性固定相拆分N-乙酰基--氨基酸甲酰、N-乙酰基--二茂铁基丙氨酸乙酯及N-叔丁氧羰驶基亮氨酰亮氨酸甲酯等对映异构体、结果表明：部分固定相对氨基酸衍生物对映异构体有拆分效果；大部分固定相对二茂铁基丙氨酸衍生物对映异构体有较好拆分效果；所有固定相对由（D，D）-及（L，L）-亮氨酰亮氨酸衍生物构成的外消旋体均有良好的拆分效果，分离系数最高达1.79。本文对部分化合物对映异构体的拆分机制进行了初步探讨。     

新型手性固定相DNBP用于有机磷化合物对映异构体的拆分

利用高效液相色谱手性固定相直接分离对映异构体是近十年才发展起来的新型方法,目前正在得到越来越广泛的应用。作者曾利用L-氨基酸-叔丁酰胺类(TBVS和TBILS)以及β-环糊精类(β-CD)手性固定相直接拆分了一些含磷手性中心及一些含碳、磷两手性中心的化合物对映体,取得了一定的结     

高效液相色谱手性固定相的研究 IV. (L,L)-二肽叔丁酰胺型手性固定相拆分α-氨基烃基膦酸衍生物对映异构体

本文制备了十种新型(L,L)-二肽叔丁酰胺型键合硅胶手性固定相, 并将其用于高效液相色谱拆分外消旋α-氨基烃基膦酸衍生物。实验结果表明拆分效果良好。本文就固定相及α-氨基烃基膦酸衍生物的结构对拆分效果的影响进行了,讨论并对拆分机制进地了初步探讨。     

高效液相色谱手性固定相的研究 IV. (L,L)-二肽叔丁酰胺型手性固定相拆分α-氨基烃基膦酸衍生物对映异构体

本文制备了十种新型(L,L)-二肽叔丁酰胺型键合硅胶手性固定相, 并将其用于高效液相色谱拆分外消旋α-氨基烃基膦酸衍生物。实验结果表明拆分效果良好。本文就固定相及α-氨基烃基膦酸衍生物的结构对拆分效果的影响进行了,讨论并对拆分机制进地了初步探讨。     

手性有机磷农药对映体在衍生化环糊精类手性固定相上的分离

正相色谱条件下,首次在两种新型衍生化β-环糊精键合硅胶手性固定相上,对系列2-(噻唑基)-α-氨基膦酸酯化合物进行了有效的手性拆分研究,对映异构体选择性α达1.812,Rs高达4.072,为该类化合物的制备型拆分提供了一条行之有效的方法.探讨了化合物结构、流动相组成及流速对拆分的影响及其相应的手性识别机理.     

高效液相色谱手性固定相的研究 Ⅳ.(L,L)-二肽叔丁酰胺型手性固定相拆分α-氨基烃基膦酸衍生物对映异构体

本文制备了十种新型(L,L)-二肽叔丁酰胺型键合硅胶手性固定相,并将其用于高效液相色谱拆分外消旋α-氨基烃基膦酸衍生物。实验结果表明拆分效果良好。本文就固定相及α-氨基烃基膦酸衍生物的结构对拆分效果的影响进行了讨论,并对拆分机制进行了初步探讨。     

Enantiomeric separation of acidic compounds of pharmaceutical interest by capillary electrochromatography employing glycopeptide antibiotic stationary phases

Enantiomeric separation of some selected acidic compounds of pharmaceutical interest belonging to the group of non-steroidal anti-inflammatory drugs were separated by capillary electrochromatography employing silica based glycopeptide antibiotic stationary phases, namely vancomycin or a teicoplanin derivatives (Hepta-Tyr). The vancomycin stationary phase allowed to achieve the chiral resolution of some racemic studied compounds only using mobile phases containing ammonium formate at a relatively low pH 2.5-3.5 and acetonitrile. Employing the teicoplanin derivative stationary phase, good enantiomeric resolution was achieved eluting with mobile phases containing sodium phosphate pH 6-acetonitrile. Enantiomers were moved to the detector because a relatively high reversed electroosmotic flow (due to the positive charge of the stationary phase) and to the electrophoretic mobility of analytes.     

Evaluation of smectic biphenylcarboxylate ester liquid-crystalline polysiloxane stationary phases for capillary column gas chromatography

Mesomorphic biphenylcarboxylate esters were coupled via flexible aliphatic hydrocarbon spacers to a polysiloxane backbone. The influence of spacer length, percent mesomorphic substitution, and crosslinking of the stationary phase on liquid-crystalline transition temperatures and on chromatographic performance was investigated. Unique selectivity and good efficiency over a wide temperature range for gum and cross-linked liquid-crystalline phases were demonstrated by the separation of various isomeric polycyclic aromatic compounds.     

Beta-cyclodextrin chiral stationary phases for liquid chromatography. Effect of the spacer arm on chiral recognition

Cyclodextrins (CDs) can be bound on silica to prepare chiral stationary phases (CSPs) for liquid chromatography. The cyclodextrin ring is connected to a spacer previously bonded on the silica surface. Three different CD-CSPs were prepared with three different spacers. (i) A dimethylethoxysilane with a linear 6 carbon chain produced a monomeric layer. The bonded CD units can move and rotate freely. (ii) The corresponding trimethoxysilane produced a polymeric layer. The bonded CD units were not located at the same distance of the silica surface, but they could still move and rotate freely. (iii) The third spacer contained a cyclohexyl ring that may introduce some conformational rigidity in the CD connection to silica. The three CSPs prepared contained a CD surface coverage of about 0.3 micromol/m(2) which is approximately half of the maximum theoretical CD coverage. The first spacer was the most efficient to bond CDs with an average value of 1.7 spacers per CD ring, whereas 5.5 spacers per CD ring were needed with the two other spacers. The chiral recognition capabilities of the three phases were compared using 14 racemic compounds. No pronounced differences were noted, but the CSP prepared with the dimethylethoxysilane monomeric spacer seems to be the most efficient for chiral recognition.     

Separation of butyltin and phenyltin species by ion-exchange chromatography with complexing mobile phases

Summary Butyltin and phenyltin species have been separated by ion-exchange chromatography using silica-based and polymer-based columns. Mobile phases consisted of methanol-water mixtures containing polyfunctional carboxylic acids, which can act as complexing agents for organotin species. The best results were achieved with a system based on a methanol mobile phase containing malic and oxalic acids and a polymer-based column, which allowed the separation of tri- and diorganotin compounds and some resolution between monobutyltin and monophenyltin.     

Chiral separation of glycidyl selenide and glycidyl sulfide racemates on cellulose-based chiral stationary phases

In recent years, a growing interest has been paid to glycidyl selenide and glycidyl sulfide racemic compounds for their importance in the life science field. In this study, cellulose-based chiral stationary phases are employed for the separation of glycerin selenium and glycerin sulfur racemates. Most analytes obtain satisfactory separation. In order to optimize the resolution of racemates, mixtures of n-hexane with different alcohols are used as mobile phases. The structural features of these racemic compounds affecting chiral discrimination are discussed in detail. The results in this study suggest that the chiral recognition mechanism for these racemic compounds involve two factors: (a) the substitution residue on a nonchiral atom can play a direct or indirect effect during chiral discrimination and (b) the competition between hydrogen-bonding and pi-pi interaction exists for compounds containing both the hydroxyl and aromatic group at the same time. The two interactions play an opposite role in the chiral discrimination process.     

Effects of the dynamic modification of stationary phases by sorbates in gas chromatography: The possibility of separating enantiomers in achiral systems

It is shown that the gas chromatographic separation of enantiomers on columns with achiral nonpolar stationary phases is principally possible as a result of the dynamic modification of stationary phases by sorbates under analysis. It is found that a number of key characteristic features is intrinsic to such separation: it can be only partial, it does not occur for all chromatographic columns, and it is observed only for some compounds and only within narrow ranges of quantities of sorbates that are close to the limits of mass overload of chromatographic systems. These characteristic features are illustrated by the examples of separating (1R,5R)-(+)- and (1S,5S)-(?)-α-pinenes on a WCOT column with an RTX-5 phase. The main characteristic feature of the separation of enantiomers as a result of the dynamic modification of stationary phases is the nonconformity of peaks in chromatograms with two individual enantiomers, compared to other ways and means for their separation; the first eluting peak belongs to the enantiomer that predominates in a mixture irrespective of its configuration, while the second peak corresponds to the racemic mixture of enantiomers; i.e., the ratio of peak areas in chromatograms does not correspond to the actual ratio of enantiomers in samples under analysis and is strongly distorted as a result of their incomplete separation. It is concluded that the separation of racemic mixtures in achiral systems is fundamentally impossible under any conditions, and this is one of the key criteria of the validity of the considered concept as a whole.     

Enantiomeric separation of new phytoalexin analogs with cyclofructan chiral stationary phases in normal‐phase mode

For the first time, three different derivatized cyclofructan chiral stationary phases were used for the direct high‐performance liquid chromatographic enantiomeric separation of 11 new racemic analogs of a natural indole phytoalexin. This class of compounds is known to have significant antiproliferative activity and other potentially useful pharmacological properties. The effect of various experimental factors was investigated to optimize the separations in the normal‐phase mode. It was found that the nature of polar modifier and additive in the mobile phase have significant impact on the enantioseparations. Better chiral recognition of analyzed compounds was achieved on (R)‐naphthylethyl carbamate cyclofructan 6 than on isopropyl carbamate cyclofructan 6 and dimethylphenyl carbamate cyclofructan 7. The thermodynamic parameters showed that the chiral separation was enthalpy controlled in all cases.     

Coexistence of nematic and chiral nematic phases of an achiral liquid crystal trimer possessing an octafluorobiphenyl unit

We prepared some achiral flexible liquid crystal oligomers possessing an octafluorobiphenyl unit and investigated their phase transition properties using polarising optical microscopy and differential scanning calorimetry. All the compounds showed nematic phases. The trimer with even-numbered spacers was found to exhibit coexistence of the nematic regions and the chiral nematic regions with opposite twist senses of a sample contained in a homogeneous aligned cell during a cooling process, whilst that with odd-numbered spacers did not. We discuss how the even-numbered trimer produces the helical state.     

Separation of chiral furan derivatives by liquid chromatography using cyclodextrin-based chiral stationary phases

The enantiomeric separation of a set of 30 new chiral furan derivatives has been achieved on native and derivatized beta-cyclodextrin stationary phases using high performance liquid chromatography (HPLC). The hydroxypropyl-beta-cyclodextrin (Cyclobond RSP), the 2,3-dimethyl-beta-cyclodextrin (Cyclobond DM), and the acetyl-beta-cyclodextrin (Cyclobond AC) stationary phases are the most effective chiral stationary phases (CSPs) for the separation of these racemates in the reverse phase mode. No enantioseparations have been observed on the native beta-cyclodextrin chiral stationary phase (Cyclobond I 2000) and only a few separations have been attained on the S-naphthylethyl carbamate beta-cyclodextrin (Cyclobond SN) and 3,5-dimethylphenyl carbamate beta-cyclodextrin (Cyclobond DMP) chiral stationary phases in the reverse phase mode. The polar organic and the normal phase mode on these CSPs are not effective for separation of these compounds. The characteristics of the analytes, including steric bulk, hydrogen bonding ability, and geometry, play an important role in the chiral recognition process. The pH affects the enantioseparation of compounds with ionizable groups and the addition of 0.5% methyl tert-butyl ether to the mobile phase significantly enhances the separation efficiency for some highly retained compounds.     

Chiral HPLC and physical characterisation of orthoconic antiferroelectric liquid crystals

New orthoconic antiferroelectric liquid crystalline materials were synthesised and characterised in their racemic forms and as (S) enantiomers. The materials possess oligo-methylene spacers of different lengths in semi-fluorinated achiral chains and lateral substitution by fluorine at two different positions of the molecular core. For comparison purposes, analogical materials without fluorine lateral substitutions were also prepared. Polysaccharide chiral stationary phases based on two different chiral selectors were used for the separation of the enantiomers of the individual racemic mixtures by high-performance liquid chromatography. A baseline separation of (S) and (R) enantiomers was obtained for four of the six studied liquid crystalline materials. Two of the materials were partially separated under the optimised separation conditions. The elution order of the individual enantiomers in the racemic mixtures was successfully assigned, as pure (S) enantiomers of all the studied materials were available. Both the position of the fluorine atom within the molecular core and the size of the achiral moiety had significant effects on the separation of the individual enantiomers of the studied compounds. Moreover, it was also found that the structure of the chiral stationary phase selector significantly influenced the enantiomeric resolution.