Preparation and chiral recognition in HPLC of cellulose 3,5-dichlorophenylcarbamates immobilized onto silica gel

The 3,5-dichlorophenylcarbamates (2) of cellulose bearing a small amount of 3-(triethoxysilyl)propyl residues were synthesized by a one-pot process and immobilized onto a silica gel through intermolecular polycondensation of the triethoxysilyl groups. The obtained cellulose derivatives were characterized by (1) H NMR and elemental analysis (EA), and their recognition abilities were evaluated by high-performance liquid chromatography (HPLC). The cellulose derivatives containing about 1-5% of the 3-(triethoxysilyl)propyl residue were efficiently immobilized with a high chiral recognition ability. The immobilized chiral packing materials (CPMs) could be used with the eluents containing chloroform and tetrahydrofuran (THF), which cannot be used with the conventional coated-type chiral packing materials. By using these eluents, the chiral recognition for many racemates was improved.     

含磷手性化合物在多聚糖类手性固定相上的手性分离

在纤维素 三(3,5 二甲基苯基氨基甲酸酯)(ChiralcelOD)和直链淀粉 三(3,5 二甲基苯基氨基甲酸酯)(ChiralpakAD H)手性固定相上,采用高效液相色谱正相条件,分离了系列含磷手性化合物。考察了流动相中有机改性剂的种类及浓度对手性分离的影响;研究了化合物的结构与保留及对映体选择性的关系;并探讨了手性识别机理。     

Direct enantiomeric separations of tris(2-phenylpyridine) iridium (III) complexes on polysaccharide derivative-based chiral stationary phases

A convenient method is presented for the first time for the direct separation of enantiomers of a tris(2-phenylpyridine) iridium (III) and an analog substituted with long alkoxy chains on polysaccharide derivative-based chiral stationary phases by HPLC. Tris(2-phenylpyridine) iridium (III) was separated on the immobilized amylose 3,5-dimethylphenylcarbamate (Chiralpak IA) using hexane/CHCl3/CH2Cl2 (75:20:5) as an eluent, and the analog could be separated on the coated cellulose 3,5-dimethyl-phenylcarbamate (Chiralcel OD) and cellulose 4-methylbenzoate (Chiralcel OJ) using hexane/2-propanol (96:4) as the eluent. CD spectra of the eluted HPLC fractions were also recorded, and the observed mirror image patterns confirm their enantioseparations.     

Improved preparation of chiral stationary phases via immobilization of polysaccharide derivative‐based selectors using diisocyanates

The classical method for the preparation of immobilized polysaccharide‐based chiral stationary phases (CSPs) with a diisocyanate was improved. Cellulose or amylose was directly coated onto 3‐aminopropyl silica gel after it was dissolved in a mixture of N,N‐dimethylacetamide, LiCl, and pyridine, then immobilized onto silica gel with a diisocyanate, and finally allowed to react with an excess of corresponding isocyanate. Four polysaccharide derivatives, 3,5‐dimethylphenylcarbamate and 3,5‐dichlorophenylcarbamate of cellulose, and 3,5‐dimethylphenylcarbamate and 5‐chloro‐2‐methylphenylcarbamate of amylose, were immobilized onto silica gel utilizing this method. Compared with the classical diisocyanate method, the improved procedure avoided the derivatization and regeneration of 6‐hydroxyl groups of cellulose and amylose, and thus showed an advantage for simple and economical preparation. The relationships among the amount of diisocyanate used, immobilization efficiency, and enantioseparation on the cellulose‐based CSPs were investigated. Also, the solvent durability of the obtained CSPs was examined with eluents containing chloroform or THF. By utilizing these eluents, the chiral recognition abilities of the obtained CSPs for some of the tested racemates were improved.     

Immobilized polysaccharide derivatives: chiral packing materials for efficient HPLC resolution

Polysaccharide-based chiral packing materials (CPMs) for high-performance liquid chromatography have frequently been used not only to determine the enantiomeric excess of chiral compounds but also to preparatively resolve a wide range of racemates. However, these CPMs can be used with only a limited number of solvents as mobile phases because some organic solvents, such as tetrahydrofuran, chloroform, and so on, dissolve or swell the polysaccharide derivatives coated on a support, e.g., silica gel, and destroy their packed columns. The limitation of mobile phase selection is sometimes a serious problem for the efficient analytical and preparative resolution of enantiomers. This defect can be resolved by the immobilization of the polysaccharide derivatives onto silica gel. Efficient immobilizations have been attained through the radical copolymerization of the polysaccharide derivatives bearing small amounts of polymerizable residues and also through the polycondensation of the polysaccharide derivatives containing a few percent of 3-(triethoxysilyl)propyl residue.     

Immobilization of 3,5‐dimethylphenylcarbamates of cellulose and amylose onto silica gel using (3‐glycidoxypropyl)triethoxysilane as linker

The 3,5‐dimethylphenylcarbamates of cellulose and amylose were effectively immobilized onto plain silica gels as chiral packing materials (CPMs) for HPLC by means of intermolecular polycondensation of triethoxysilyl groups introduced with (3‐glycidoxypropyl)triethoxysilane. The immobilization and chiral recognition abilities of the obtained CPMs prepared with different amounts of (3‐glycidoxypropyl)triethoxysilane were investigated. In addition, the solvent compatibilities of the immobilized‐type CPMs were examined with eluents containing chloroform and THF. When these eluents were used, for most of the tested racemates, the chiral resolving abilities of the obtained CPMs were improved.     

Synthesis and chiral recognition of novel amylose derivatives containing regioselectively benzoate and phenylcarbamate groups

A new class of regioselectively substituted amylose derivatives bearing three different substituents at 2-, 3- and 6-positions, and two different substituents at 2-position and 3-, 6-positions were synthesized by a sequential process based on the esterification of 2-position of a glucose unit. Their chiral recognition abilities were evaluated as chiral stationary phases (CSPs) for high-performance liquid chromatography (HPLC). Each derivative had its own characteristic recognition ability depending on the arrangement of side chains at the three positions. Among the derivatives, amylose 2-(4-t-butylbenzoate) and amylose 2-(4-chlorobenzoate) series exhibited high chiral recognition. Some racemates can be efficiently separated on these derivatives as well as on the amylose tris-3,5-dimethylphenylcarbamate, which is commercially available as Chiralpak AD and one of the most powerful CSPs. The structures of the amylose derivatives were also investigated by circular dichroism spectroscopy.     

Some aspects of the preparative separation of enantiomers on chiral stationary phases

Summary In preparative column liquid chromatography, it is necessary to work with conditions of mass overload to obtain high throughput per unit time. The influence of sample mass and of eluent composition on the separation of R,S-1-(1-naphthylethyl)propylamide on chiral 3,5-dinitrobenzoylphenylglycine-silica (Pirkle type stationary phase) was investigated. At a sample load of 200μg of racemate per gram of stationary phase, the column becomes overloaded. At higher sample loads the peaks become triangular; therefore the first peak is always pure up to loads of 10mg g⁻¹, although resolution is low. The purity of the second peak depends on sample mass, but not on the strength (polarity) of the mobile phase. This is due to the effect that peak width, as well as resolution, decrease as the polarity of the eluent increases. In certain cases the polarimeter, used as a detector, can give more information on peak purity than the UV detector.     

非均匀取代淀粉衍生物手性固定相的制备及其手性识别能力

通过区域选择性方法制备了两种新型淀粉衍生物,分别为淀粉2-苯甲酸酯-3-(4-甲基苯基氨基甲酸酯)-6-(3,5-二氯苯基氨基甲酸酯)和淀粉2-苯甲酸酯-3-(3,5-二氯苯基氨基甲酸酯)-6-(4-甲基苯基氨基甲酸酯),将二者分别涂覆于氨丙基硅胶后用作液相色谱手性固定相。研究表明:所制备的手性固定相显示出特异的手性识别能力,其手性识别能力明显高于均匀取代淀粉衍生物——淀粉三(3,5-二氯苯基氨基甲酸酯),取代基的性质及在葡萄糖单元上的位置对手性固定相的手性识别能力有较大的影响。一些未在商品化的手性柱Chiralpak AD上得到有效分离的手性化合物在所制备的固定相上得到了更好的分离。所测试的8对对映体在淀粉2-苯甲酸酯-3-(4-甲基苯基氨基甲酸酯)-6-(3,5-二氯苯基氨基甲酸酯)固定相上均得到了分离,因而此固定相的手性识别能力较强,具有潜在的应用价值。     

Synthesis and enantioseparation behaviors of novel immobilized 3,5‐dimethylphenylcarbamoylated polysaccharide chiral stationary phases

Two new polysaccharide‐derived chiral selectors, namely, 6‐azido‐6‐deoxy‐3,5‐dimethylphenylcarbamoylated amylose and 6‐azido‐6‐deoxy‐3,5‐dimethylphenyl carbamoylated cellulose, were synthesized under homogeneous conditions and immobilized onto aminized silica gel by the Staudinger reaction, resulting in two new immobilized polysaccharide chiral stationary phases (CSPs). Their enantioseparation performances were investigated under normal‐phase mode by HPLC. Among 17 analytes, baseline separations of 12 pairs of enantiomers are achieved on the immobilized cellulose CSP, which demonstrates that this new cellulose material exhibits almost the same enantioseparation performance as the coated cellulose CSP. In addition, the amylose‐derived CSP presents limited enantiorecognition ability but certain complementarity with the immobilized and coated cellulose‐based materials. Neither metolachlor nor paclitaxel side chain acids are separated on two cellulose‐derived CSPs, but effective separations are obtained on the immobilized amylose column.     

Preparation and evaluation of a new synthetic polymeric chiral stationary phase for HPLC based on the trans-9,10-dihydro-9,10-ethanoanthracene-(11S,12S)-11,12-dicarboxylic acid bis-4-vinylphenylamide monomer

A new synthetic polymeric chiral stationary phase for liquid chromatography was prepared via free-radical-initiated polymerization of trans-9,10-dihydro-9,10-ethanoanthracene-(11S,12S)-11,12-dicarboxylic acid bis-4-vinylphenylamide. The new polymeric chiral stationary phase (CSP) showed enantioselectivity for many chiral compounds in multiple mobile phases. High stability and sample capacities were observed on this polymeric chiral stationary phase. Mobile phase components and additives affected chiral separation greatly. This new synthetic chiral stationary phase is complementary to two other related commercially available CSPs: the P-CAP and P-CAP-DP columns. Interactions between the chiral stationary phase and analytes that lead to retention and chiral recognition include hydrogen bonding, dipolar, and π–π interactions. Repulsive (steric) interactions also contribute to chiral recognition. Figure LC chromatograms showing the analytical (blue) and preparative (red) separations of N-(3,5-dinitrobenzoylleucine) enantiomers on a new synthetic polymeric chiral stationary phase     

A chiral porous organic cage for molecular recognition using gas chromatography

Molecular organic cages as shape-persistent organic molecules with permanent and accessible cavities have attracted a lot of interest because of their importance as host-guest systems. Herein, we report a chiral porous organic cage (POC) CC9 diluted with a polysiloxane OV-1701 to fabricate a CC9-coated capillary column, which was used for the high-resolution gas chromatographic separation of organic compounds, including positional isomers and racemates. On the CC9-coated capillary column, a large number of racemic compounds such as chiral alcohols, esters, ethers and epoxides can be resolved without derivatization. By comparing the chiral recognition ability of the CC9-coated column with the commercially available β-DEX 120 column and the POC CC3-R coated column recently reported by our group, the CC9-coated column offered good resolution during the separation of some racemates, that were not separated using the β-DEX 120 column or POC CC3-R coated column. Therefore, the CC9-coated column can be complementary to the β-DEX 120 column and CC3-R coated column. The results indicated that the CC9-coated column exhibited great potential for application in the separation of positional isomers and enantiomers with great selectivity, high resolution and good reproducibility.     

新型键合型纤维素类手性固定相的制备及安息香分离

采用六亚甲基二异氰酸酯作为键合试剂,制备了键合型纤维素3,5-二甲基苯基氨基甲酸酯手性固定相。分别往正己烷/乙醇或正己烷/异丙醇中添加四氢呋喃和二氯甲烷,系统地考察了四氢呋喃和二氯甲烷的含量对安息香外消旋体拆分的影响。实验结果表明,安息香两对映体的容量因子随二者含量的增加而降低,但分离效果变化不大,分离因子均在1.2以上。所制备的CSP在采用含有高浓度四氢呋喃(23%)、二氯甲烷的流动相进行手性分离时仍具有良好的稳定性。与涂敷型固定相相比,流动相选择范围更广。     

The preparative chromatographic enantioseparation of a racemic morphanthridine analog on a chiral stationary phase

Summary The preparative chromatographic enantioseparation of a chiral morphoanthridine analog has been performed on an analytical column using amylose-tris(3,5-dimethylphenylcarbamate) as chiral stationary phase. The racemate (100 mg) was resolved to baseline within 15 min. This paper describes the development of the method, estimation of the capacity of the chiral stationary phase and discussed the potential of the chromatography if performed under preparative conditions. From the results and calculations presented it seems likely that the resolution of 70 tons year⁻¹ could easily be achieved on 30 kg of stationary phase with a mobile-phase consumption of only 720 L day⁻¹.     

键合型聚丙烯酰胺衍生物手性固定相的制备与手性识别性能

高效液相色谱(HPLC)被广泛认为是分离制备光学纯单一对映体的最有效方法。在高效液相色谱手性拆分中,手性固定相(CSP)的性能直接影响到色谱柱的手性分离能力。在众多手性固定相中,键合型手性固定相具有溶剂耐受性好,分离模式灵活等优点,已经发展成为一类重要的手性固定相。本文通过两步化学反应合成了新型的光学活性丙烯酰胺衍生物--(S)-1-丙烯酰-2-(N-苯基甲酰胺基)吡咯烷((S)-APACP),采用核磁共振氢谱表征了(S)-APACP的化学结构;通过3步化学反应制备了键合型聚丙烯酰胺衍生物手性固定相,采用热重分析法表征了聚合物的键合量,采用HPLC评价了键合型手性固定相的识别能力,分析了影响其手性识别能力的因素。研究结果表明,APACP聚合物成功地键合到硅胶表面制备了具有良好溶剂耐受性的键合型手性固定相,其聚合物键合量为10.2%~11.8%,该键合型手性固定相对若干种对映体显示了较好的手性识别能力。     

Comparative studies of immobilized chiral stationary phases based on polysaccharide derivatives for enantiomeric separation of 15 azole compounds

Immobilized polysaccharide‐based columns showed excellent enantioselectivity in normal phase separation mode. In this work, enantioseparation abilities of four immobilized polysaccharide‐derived chiral stationary phases (Chiralpak IA, Chiralpak IB, Chiralpak IC, and Chiralpak ID) toward 15 azole compounds were evaluated. Separation was carried out using n‐hexane as mobile phase with ethanol, 1‐propanol, 1‐butanol, and 2‐propanol as modifiers. And twelve compounds have achieved baseline separation with the resolutions ranging between 2.05 and 21.73. The enantioseparation on the four polysaccharide‐based chiral columns using different alcohol modifiers was compared. In general, the best separation performance was identified as Chiralpak IC, which was able to resolve 11 compounds to baseline and two partially under the screening conditions. Separation on Chiralpak IB was not satisfactory, because only four compounds were baseline separated.     

Study of the enantiomeric separation of the anticholinergic drugs on two immobilized polysaccharide‐based chiral stationary phases by HPLC and the possible chiral recognition mechanisms

In this work, the enantiomeric separation of ten anticholinergic drugs was first examined on two derivative polysaccharide chiral stationary phases (CSPs), i.e., Chiralpak ID and Chiralpak IA in the normal phase mode. Except for scopolamine hydrobromide, the remaining nine analytes could be completely separated with good resolutions using both columns under the optimized mobile phase conditions. And the enantiomeric discrimination ability of the studied CSPs towards nine analytes was in the order of Chiralpak ID > Chiralpak IA. The influences of organic modifier types, alcohol content, and base/acid additives on the enantiomeric separation were evaluated and optimized. According to the experimental results, the effect of the structures of analytes on enantiomeric separation was discussed. Additionally, the chiral recognition mechanisms were proposed based on the thermodynamic analysis of the experimental data.     

高效液相色谱-串联质谱法结合多糖衍生物手性固定相拆分氰戊菊酯

建立了以多糖衍生物为手性固定相的高效液相色谱-串联质谱(HPLC-MS/MS)直接拆分氰戊菊酯对映体的方法。在反相液相色谱条件下,考察了手性固定相的种类、流动相组成、柱温、流速对氰戊菊酯4个立体异构体分离的影响。同时,利用热力学方法对氰戊菊酯的立体异构体与固定相之间的色谱保留和分离的热力学机理进行了探讨。结果表明:采用Lux Cellulose-3(纤维素-三(4-甲基苯甲酸酯))手性色谱柱,在以流动相为乙腈-水(5 mmol/L甲酸铵)=(55:45,V:V)流速0.4 mL/min,柱温30℃的条件下,可在14 mins内实现氰戊菊酯4个立体异构体的基线分离。拓展了HPLC-MS/MS在菊酯类手性农药对映体分离及检测上的应用。     

Development and validation of a chiral HPLC method for rapid screening of allylic alcohol asymmetric epoxidation processes

A simple and rapid HPLC method has been developed using a polysaccharide chiral stationary phase (Chiralpak AD-H) for the resolution of glycidyl tosylate enantiomers. These compounds were obtained by asymmetric epoxidation of allyl alcohol with chiral titanium-tartrate complexes as catalyst after in situ derivatization of the intermediate glycidols. Separations were achieved using two types of mobile phase: a normal-phase (n-hexane), and a polar-phase (methanol or acetonitrile). The influence of the type and concentration of organic modifier in the mobile phase (ethanol or 2-propanol), the flow rate and the column temperature was investigated. In normal-phase mode, the optimized conditions were: n-hexane/ethanol 70/30 (v/v) at a flow rate of 1.2 mL min⁻¹ and 40 °C. In polar-phase mode, the optimized conditions were: methanol at a flow rate of 0.8 mL min⁻¹ and 20 °C. In both cases, analysis time was ≤11 min and the chiral resolution was ≥2. Nevertheless, due to the better Rs obtained in normal-phase mode, only this method was validated to avoid peaks overlapping in real samples. This method was found to be linear in the 5-300 μg mL⁻¹ range (R² > 0.999) with an LOD of 1.5 μg mL⁻¹ for both glycidyl tosylate enantiomers. Repeatability and intermediate precision at three different concentrations levels were below 0.5 and 7.2% R.S.D. for retention time and area, respectively. This method was applied successfully for the determination of glycidyl tosylate enantiomers after in situ derivatization of glycidols obtained in allylic alcohol asymmetric epoxidation processes with chiral titanium-tartrate complexes as catalysts.     

Influence of the structure of organic phosphonate compounds on chiral separation on a pirkle type chiral stationary phase

Summary The enantiomers of eightO,O-dialkyl-2-benzyloxycarbonyl-aminoarylmethyl-phosphonates are directly separated on anN-(3,5-dinitrobenzoyl)leucine (DNBleu) column. The influence of the mobile phase composition and the column temperature on the retention and the enantioselectivity are investigated. The influence of the length and steric hindrance of alkoxyl groups of the phosphonate ester and the nature of the substituentp-Cl and pH on the benzene ring which is attached to the chiral carbon atom on chiral separation are discussed also.