Effect of (+) or (−) camphorsulfonic acid additives to the mobile phase on enantioseparations of some basic drugs on a Chiralcel OD column

Use of chiral ionic liquid as additive for synergistic enantioseparation of basic drugs in capillary electrophoresis

This work presents a synergistic system for enantioseparation in capillary electrophoresis (CE) with a chiral ionic liquid (CIL) based on D-10-camphorsulfonic acid as additive and carboxymethyl-β-cyclodextrin (CM-β-CD) as the chiral selector. The proposed method showed excellent enantioseparation performance towards sixteen chiral drugs. In contrast to the single CM-β-CD system, the notably improved resolution (Rs) and selectivity factor (α) of model drugs were observed in synergistic system. Several key parameters such as CIL concentration, CM-β-CD concentration, buffer pH and separation voltage were investigated, after which Statistical Product and Service Solutions (SPSS) was used to prove the potential synergistic effect. The nuclear magnetic resonance (NMR) results further demonstrated the function of the CIL and the superiority of synergistic system. Finally, chiral impurity determination of chlorpheniramine maleate sample was successfully carried out using the established method.

Study of Different Chiral Columns for the Enantiomeric Separation of Azoles Using Supercritical Fluid Chromatography

The enantiomeric separation of antifungal compounds is an arduous task in pharmaceutical and biomedical fields due to the different properties that each diastereoisomer presents. The enantioseparation of a group of fungicides (sulconazole, bifonazole, triadimefon and triadimenol) using supercritical fluid chromatography was achieved in this work. For this goal, four different chiral columns based on polysaccharide derivatives, as well as the effect of different chromatographic parameters such as temperature, type and percentage of organic modifier (methanol, ethanol and isopropanol), were thoroughly investigated. The inversion of the elution order of enantiomers as a result of a change in the stationary phase or organic modifier was also evaluated by employing a circular dichroism detector. The best separation conditions, in terms of the enantioresolution and analysis time, were obtained with the Lux® Cellulose-2 column using isopropanol as the organic modifier.

Chemical characterization, absolute configuration and optical purity of (1S)-(+)- and (1R)-(-)-10-camphorsulfonic acid

Comprehensive chemical characterization for two isomers of camphorsulfonic acid (CSA), occasionally used in the manufacture of active pharmaceutical ingredients (APIs), was performed by nuclear magnetic resonance (NMR) spectroscopy, high-resolution mass spectroscopy in negative electrospray ionization mode and gas chromatography/mass spectrometry (GC/MS) in electron ionization mode. Electronic circular dichroism (ECD) spectra together with quantum chemical calculations using time-dependent density functional theory (TD-DFT) were used to assign the stereochemistry for CSA for the first time and these assignments were then confirmed by single-crystal X-ray diffraction. As crystals were grown under the same conditions of high supersaturation using a mixed solvent without water removal, the crystal structures of the two enantiomers contained one ordered molecule of water in the asymmetric unit. The crystals of the (+)-enantiomer have a 1S,4R configuration and the H atom of the sulfonic acid group combines with the water molecule to form a hydronium ion, namely, hydronium (1S,4R)-(7,7-dimethyl-2-oxobicyclo[2.2.1]heptan-1-yl)methanesulfonate, H₃O⁺·C₁₀H₁₅O₄S^-. The crystals of the (-)-enantiomer have a 1R,4S configuration. The determination of the optical purity of CSA using NMR spectroscopy with a chiral solvating agent, (1R,2R)-1,2-diphenylethane-1,2-diamine, and GC/MS with a chiral column has been well explored. The results showed that the examined samples of these two isomers of CSA proved to be enantiomerically pure. In particular, for (1R)-(-)-10-camphorsulfonic acid, this is, to our knowledge, the first description on its spectral characterization in a scientific context.

Direct chiral resolution of metalaxyl and metabolite metalaxyl acid in aged mobile phases: the role of trace water

The separation of chiral transformation products greatly complements the understanding of the stereochemistry of chiral pollutants. In this study, direct enantiomeric resolution of metalaxyl and its main degradation product metalaxyl acid, often co-occurring in the environment, was carried out in normal-phase high-performance liquid chromatography with a Chiralcel OJ-H column. (R)-Metalaxyl acid and (S)-metalaxyl, which were almost parallel bonding to the chiral stationary phase, tended to separate, started to overlap, coeluted, and separated again with subtle changes of the mobile phase consisting of n-hexane, 2-propanol, acetic acid, and trace water. Their competition above hampered an acceptable direct separation in fresh mobile phases. Aged mobile phases with a storage period of 3-5 days, however, significantly improved their separation, in which trace water from moisture air diffusion was found to play a major role. Trace water differentially affected peak width and retention times and then induced enhanced peak separation, confirmed by deliberate addition of water to fresh mobile phases. Furthermore, none of the studied factors, involving temperature, concomitant analytes, and trace water, could cause changes of the configuration of the chiral stationary phase. Simultaneous enantiomeric separation of both compounds was achieved in aged or fresh mobile phases with adventitious or added water and gave satisfactory peak separation, all with Rs values of more than 1.20 in environmental samples.