Enantioseparation of paroxetine intermediate on an amylose-derived chiral stationary phase by supercritical fluid chromatography

Separation of chiral and achiral impurities in paroxetine hydrochloride in a single run using supercritical fluid chromatography with a polysaccharide stationary phase

Separating paroxetine hydrochloride and its impurities using conventional reversed-phase liquid chromatography (RPLC) is challenging due to their highly similar structures. In the present study, a rapid, simple, sensitive and environmentally friendly method was developed for the determination of chiral and achiral impurities in raw materials of paroxetine hydrochloride using chiral supercritical fluid chromatography (SFC). The impacts of chiral stationary phases (CSPs), mobile phases, column temperature and back pressure on the retention and separation of analytes were comprehensively evaluated. After method optimization, a satisfying result was obtained on a cellulose tris-(3-chloro-4-methylphenylcarbamate) stationary phase in 4.0 min using 70% CO₂ and 20 mM ammonium acetate in 30% methanol as the mobile phase. Molecular docking was further performed to understand the interactions between the analytes and CSP. The results suggested that hydrogen bonding and π-π interactions were the dominant interactions. The affinity given by the software was in good agreement with the elution order and free energy (△G) values obtained from van't Hoff equations. The results of molecular docking also provide insights into the different retentions of N-methylparoxetine at different temperatures. The results of method validation revealed that the method was sensitive with a limit of detection of approximately 0.05 μg·mL^-1 (corresponding to approximately 0.005% paroxetine hydrochloride in the sample solution). The relative standard deviations (RSDs) of precision and intra-assay precision were all less than 2.0%, and the recoveries of the method were 93.8~105.3% with RSDs less than 3.0%. The chiral and achiral RPLC methods included in the Chinese pharmacopoeia and the SFC method proposed in this study were simultaneously used to determine the impurity content in the raw materials of paroxetine hydrochloride. The results showed that impurities that cannot be detected by the reference method can be accurately quantified using the SFC method. In addition, the SFC method has advantages in terms of throughput, analysis cost and simplicity. This study can provide a reference for further research of impurities in paroxetine hydrochloride and promote the application of chiral SFC in the rapid separation of structurally similar compounds.

Enantiomeric Separation of Indole-3-Propanamide Derivatives by Using Supercritical Fluid Chromatography on a Polysaccharide-Based Chiral Stationary Phase

Thirteen pairs of I3P enantiomers were screened using nine polysaccharide chiral stationary phases and three different mobile phases. The purification strategy for 13 pairs of I3P enantiomers were designed and optimized considering enantiomeric purity and enrichment of isomers. Out of 13 I3P derivatives which were screened using supercritical fluid chromatography, 10 derivatives displayed excellent baseline separation using a Lux Cellulose-4 column and their resolution from higher to lower order of I3P-11, 13, 4, 12, 2, 1, 9, 3, 7 and 8 derivatives whereas in case of Lux Cellulose-2 column, the moderate separation was achieved as compared to Cellulose-4 in the order I3P-5, 6 and 10 derivatives. Excellent enantiomeric separations and retentions for all 13 I3P enantiomer derivatives were obtained in Cellulose-4 and Cellulose-2 columns in presences of methanol as organic modifier without any additives except in the case of I3P 12 enantiomer. The absolute stereochemical assignment of the purified isomers was determined through an optical rotation study. Among the series of I3P derivatives, I3P-5 showed potent antioxidant activity against catalase with an IC50 value of 13.78 μM. Further molecular docking, MM/GBSA and molecular dynamics studies revealed that the I3P-5 derivatives effectively bind to catalase with a docking score of -5.41 kcal/mol. Which validated chiral docking and indicated great potential for enantiomeric separation in drug discovery and present studies (R)-enantiomer preferentially depicts good binding capacity with catalase.

High-performance liquid chromatographic and subcritical fluid chromatographic separation of α-arylated ß-carboline, N-alkylated tetrahydroisoquinolines and their bioisosteres on polysaccharide-based chiral stationary phases

New, pharmacologically interesting chiral amino compounds, namely, stereoisomers of α-hydroxynaphthyl-ß-carboline, benz[d]azepine and benz[c]azepine analogs as well as N-α-hydroxynaphthylbenzyl-substituted isoquinolines were enantioseparated by high-performance liquid chromatographic and subcritical fluid chromatographic methods on polysaccharide-based chiral stationary phases. Separation of the stereoisomers was optimized in both subcritical fluid chromatography and normal phase liquid chromatographic modes by investigating the effects of the composition of the bulk solvent, temperature, and the structures of the analytes and selectors. Both normal phase liquid chromatography and subcritical fluid chromatography exhibited satisfactory performance, albeit with somewhat different effectiveness in the separation of the stereoisomers studied. The optimized methods offer the possibility to apply preparative-scale separations thereby enabling further pharmacological investigations of the enantiomers.

Chiral high-performance liquid and supercritical fluid chromatographic enantioseparations of limonene-based bicyclic aminoalcohols and aminodiols on polysaccharide-based chiral stationary phases

Enantioseparation of limonene-based bicyclic 1,3-aminoalcohols and 1,3,5- and 1,3,6-aminodiols was performed by normal-phase high-performance liquid chromatographic and supercritical fluid chromatographic (SFC) methods on polysaccharide-based chiral stationary phases. The effects of the composition of the mobile phase, the column temperature and the structures of the analytes and chiral selectors on retention and selectivity were investigated by normal-phase LC and SFC technique. Thermodynamic parameters derived from selectivity-temperature-dependence studies were found to be dependent on the chromatographic method applied, the nature of the chiral selector and the structural details of the analytes. Enantiorecognition in most cases was enthalpically driven but an unusual temperature behavior was also observed: decreased retention times were accompanied by improved separation factors with increasing temperature, i.e. some entropically driven separations were also observed. The elution sequence was determined in all cases. The separation of the stereoisomers was optimized in both chromatographic modalities.

Enantiomeric separation of six chiral pesticides that contain chiral sulfur/phosphorus atoms by supercritical fluid chromatography

Six chiral pesticides containing chiral sulfur/phosphorus atoms were separated by supercritical fluid chromatography with supercritical CO₂ as the main mobile phase component. The effect of the chiral stationary phase, different type and concentration of modifiers, column temperature, and backpressure on the separation efficiency was investigated to obtain the appropriate separation condition. Five chiral pesticides (isofenphos-methyl, isocarbophos, flufiprole, fipronil, and ethiprole) were baseline separated under experimental conditions, while isofenphos only obtained partial separation. The Chiralpak AD-3 column showed a better chiral separation ability than others for chiral pesticides containing chiral sulfur/phosphorus atoms. When different modifiers at the same concentration were used, the retention factor of pesticides except flufiprole decreased in the order of isopropanol, ethanol, methanol; meanwhile, the retention factor of flufiprole increased in the order of isopropanol, ethanol, methanol. For a given modifier, the retention factor and resolution decreased on the whole with the increase of its concentration. The enantiomer separation of five chiral pesticides was an "enthalpy-driven" process, and the separation factor decreased as the temperature increased. The backpressure of the mobile phase had little effect on the separation factor and resolution.

Density dependence of retention factors of trans-stilbene oxide for chiral separation by supercritical fluid chromatography

Retention factors for two enantiomers of trans-stilbene oxide, k₁ and k₂, were measured with a chiral AD-H column using two syringe pumps to feed CO₂ and methanol as a co-solvent at various temperatures, pressures and co-solvent mole fractions to determine the effects of these operating conditions on the retention factors. The retention factors k₁ and k₂ are for the (R,R)- and (S,S)-forms, respectively. When the isothermal compressibilities of a mixture of CO₂ and MeOH were lower than 0.01, far from the critical locus of the CO₂ and methanol mixture, both retention factors were well expressed with the solvent density and temperature with an average absolute relative deviation of 1-2%. In the vicinity of the critical locus, however, where the isothermal compressibilities were much larger than 0.01, the relationship between retention factor and density was complicated. Both retention factors were proportional to the isothermal compressibility, irrespective of methanol mole fraction at each temperature.

Chiral selectors in CE: recent developments and applications

This review article provides an overview of the recent advances in enantioanalysis by use of electrophoretic techniques. Due to the big number of publications in the subject mentioned above, this article is focused on chiral method developments and applications published from 2008 until 2011, and it demonstrates chiral selectors used in CE. Numerous chiral selectors have been used over the years, and these include the cyclic and the linear oligo- and polysaccharides, the branched polysaccharides, the polymeric and monomeric surfactants, the macrocyclic and other antibiotics, and the crown ethers. Different dual-selector systems are also presented in this article, and the results are compared with those obtained by use of a single chiral selector. Finally, several pharmaceutical and biomedical applications based on chiral recognition are summarized.

Metabolite analysis by supercritical fluid chromatography

Owing to its favorable properties, such as low viscosity and high diffusivity, a supercritical fluid can be used as the mobile phase in chromatography. Supercritical fluid chromatography (SFC) can provide high-speed and high-resolution separation. Since supercritical carbon dioxide (SCCO2), which is generally used as the mobile phase in SFC, is automatically emitted at room temperature, SFC is most commonly used as a preparative method. However, SFC can also be used to perform high-precision biomolecular analysis, especially for hydrophobic metabolites, because of the low polarity of SCCO2. The use of a mass spectrometer with SFC can widen the scope of application of SFC to bioanalysis. In this review, we summarize practical application of SFC as a tool for the analysis of metabolites in real biological samples.