Liquid Chromatographic Separation of Novel 4-Amino-Flavanes Series Diastereomers on a Polysaccharide-Type Chiral Stationary Phase

Enantiomeric separation of flavanone on Chiralpak® IA column and determination of the chiral mechanism

Thirteen flavanone racemates were successfully separated using a Chiralpak® IA column and isopropanol-hexane (50:50, v/v). The mobile phase flow rate and detection wavelength were 0.5 mL/min and 254 nm. The retention times values ranged from 5.50 and 56.45 min. The values of the retention, separation, and resolution factors ranged from 0.63 to 21.67, 1.12 to 2.45, and 0.13 to 11.94. The docking binding energies ranged from -6.2 to -8.2 kcal/mol, showing enthalpy-determined host-guest complex formation. The molecular docking results and the experimental data were agreed well. The results showed that S-enantiomers had stronger bindings with chiral selectors compared to R-enantiomers. Consequently, the R-enantiomers eluted first followed by S-enantiomers. The reported method is highly useful to determine the enantiomeric composition of the reported flavanone in any sample.

Enantioseparation and molecular docking study of selected chiral pharmaceuticals on a commercialized phenylcarbamate-β-cyclodextrin column using polar organic mode

The chiral separation capability of Chiral-CD-Ph column, containing phenylcarbamate-β-cyclodextrin as the chiral selector in polar organic mode was investigated. A total of twenty-five compounds with different structures and acid-base properties were evaluated, and twenty of them were separated using acetonitrile or methanol as eluent. The effects of various chromatographic parameters, such as the type and proportion of organic modifier, flow rate, and column temperature were analyzed in detail in relation to chromatographic performance. A U-shape retention curve was observed when a mixture of acetonitrile and methanol was used as the eluent, indicating different types of interactions in different solvent mixtures. Van 't Hoff analysis was used for calculation of thermodynamic parameters which revealed that the enantioseparation is mainly enthalpy controlled; however, entropic control was also observed. The enantiomer recognition ability at the atomic level was also investigated through a molecular docking study, which revealed surface binding in polar organic mode instead of inclusion complexation. Our work proves that the phenylcarbamate-β-cyclodextrin-based chiral stationary phase can be effectively used in polar organic mode for the chiral separation of structurally diverse compounds. Furthermore, it is important to note that our study demonstrated that surface binding is responsible for the formation of supramolecular complexes in certain cyclodextrin derivatives.

Chiral Separation of 3,4-dihydropyrimidin-2(1H)-ones and 3,4-di -hydropyrimidin- 2(1H)-thiones Enantiomers by HPLC on Chiralcel®OD-H

Objective:

Ten racemic 3,4-dihydropyrimidin-2(1H)-ones and 3,4-dihydropyrimidin- 2(1H)-thiones were separated by liquid chromatography on Chiralcel®OD-H column containing cellulose tris(3, 5-dimethylphenylcarbamate).

Methods:

The enantioseparation was carried out using Chiralcel®OD-H polysaccharide-type chiral stationary phase to resolve such enantiomers under normal-phase mode.

Results:

Complete separations of the 3,4-dihydropyrimidin-2(1H)-ones and 3,4-dihydropyrimidin- 2(1H)-thiones derivatives with good resolution (RS= 1.04-2.80) were achieved within a short time (10-15 min).

Conclusion:

An optimal baseline separation (Rs> 1.5) was achieved using Chiralcel®OD-H under normal-phase mode. Structure-retention relationships have also been discussed.

Eluent Tolerance and Enantioseparation Recovery of Chiral Packing Materials Based on Chitosan Bis(Phenylcarbamate)-(n-Octyl Urea)s for High Performance Liquid Chromatography

The goal of the present work was to study the influence of the swelling of chitosan derivatives on the enantioseparation and the separation performance recovery of chiral stationary phases (CSPs) based on these derivatives. Therefore, six chitosan bis(phenylcarbamate)-(n-octyl urea)s were synthesized, which were coated on macroporous 3-aminopropyl silica gel affording new CSPs. Most of the CSPs demonstrated strong enantioseparation capability for the tested chiral compounds. The swelling capacity of the chitosan bis(phenylcarbamate)-(n-octyl urea)s in ethyl acetate, acetone and tetrahydrofuran (THF) was evaluated. Among the chitosan derivatives, the chitosan bis(3,5-dichlorophenylcarbamate)-(n-octyl urea) polymer showed the highest swelling capacity in ethyl acetate and THF. The polymer-based CSPs could be utilized with pure ethyl acetate and a normal phase containing 70% THF, but was damaged by pure THF. On the other hand, the separation performance of the damaged CSP could be recovered after it was allowed to stand for a period of time. The observations are important for the development and application of polysaccharide derivative-based CSPs.