Applications of the Chiralpak AD and Chiralcel OD chiral columns in the enantiomeric separation of several dioxolane compounds by supercritical fluid chromatography

Analytical and preparative enantioseparations in supercritical fluid chromatography using different brands of immobilized cellulose tris (3,5-dichlorophenylcarbamate) columns: Some differences

The aim of this study was to determine the impact of the origin and the manufacturing processes of the chiral stationary phases (CSPs) on their chromatographic behaviors. Hence, four chiral stationary phases based on immobilized tris (3,5-dichlorophenylcarbamate) derivative of cellulose supplied by four different manufacturers were evaluated. A set of twenty-nine compounds, including commercially available and in-house synthesized compounds, with a broad range of lipophilicity and polarity was chosen. Three main parameters were evaluated on all stationary phases: retention factor, selectivity and loading capacity. This work highlighted that the retention factor strongly varied according to the manufacturer. Regardless of the characteristic of the tested compounds i.e. neutral, acidic or basic, there was a trend in retention ability of the four chiral stationary phases: retention was increasing from CHIRAL ART Cellulose-SC, REFLECT I-Cellulose C, Chiralpak IC to Lux i-Cellulose-5. On the contrary, selectivity did not follow the same trend as retention. The difference in selectivity between each column towards one compound was quite low while the difference in resolution depended on the nature of the compounds investigated and was significant in certain cases. Finally, the four different columns presented similar and high loading capacity.

Chiral separation and a molecular modeling study of eight azole antifungals on the cellulose tris(3,5-dichlorophenylcarbamate) chiral stationary phase

Four immobilized polysaccharide-based chiral stationary phases have been examined for their enantioselectivity on azole analytes using normal phase liquid chromatography.

Resolution of ketoconazole enantiomers by high-performance liquid chromatography and inclusion complex formation between selector and enantiomers

The analytical resolution of ketoconazole (KTZ) enantiomers was performed by high-performance liquid chromatography with sulphobutylether-β-cyclodextrin (SBE-β-CD) as a chiral mobile phase additive (chiral selector). Some important factors affecting the resolution of KTZ enantiomers were investigated. In addition, the molecular interaction between KTZ and SBE-β-CD was studied using the UV absorption spectrum and HPLC for an understanding of the resolution process. The results show that the type and concentration of the chiral mobile phase additive, the pH of the mobile phase and the volume fraction of methanol (φMeOH) in the mobile phase all have a clear influence on the resolution of KTZ enantiomers. Under optimal conditions, namely the use of 0.5 mmol L

Evaluation of sulfated maltodextrin as a novel anionic chiral selector for the enantioseparation of basic chiral drugs by capillary electrophoresis

Introducing a new class of chiral selectors is an interesting work and this issue is still one of the hot topics in separation science and chirality. In this study, for the first time, sulfated maltodextrin (MD) was synthesized as a new anionic chiral selector and then it was successfully applied for the enantioseparation of five basic drugs (amlodipine, hydroxyzine, fluoxetine, tolterodine, and tramadol) as model chiral compounds using CE. This chiral selector has two recognition sites: a helical structure and a sulfated group which contribute to three corresponding driving forces; inclusion complexation, electrostatic interaction, and hydrogen binding. Under the optimized condition (buffer solution: 50 mM phosphate (pH 3.0) and 2% w/v sulfated MD; applied voltage: 18 kV; temperature: 20°C), baseline enantioseparation was observed for all mentioned chiral drugs. When instead of sulfated MD neutral MD was used under the same condition, no enantioseparation was observed which means the resolution power of sulfated MD is higher than neutral MD due to the electrostatic interaction between sulfated groups and protonated chiral drugs. Also, the countercurrent mobility of negatively charged MD (sulfated MD) allows more interactions between the chiral selector and chiral drugs and this in turn results in a successful resolution for the enantiomers. Furthermore, a higher concentration of neutral MD (approximately five times) is necessary to achieve the equivalent resolution compared with the negatively charged MD.

Maltodextrins as chiral selectors in CE: molecular structure effect of basic chiral compounds on the enantioseparation

Prediction of chiral separation for a compound using a chiral selector is an interesting and debatable work. For this purpose, in this study 23 chiral basic drugs with different chemical structures were selected as model solutes and the influence of their chemical structures on the enantioseparation in the presence of maltodextrin (MD) as chiral selector was investigated. For chiral separation, a 100-mM phosphate buffer solution (pH 3.0) containing 10% (w/v) MD with dextrose equivalent (DE) of 4-7 as chiral selector at the temperature of 25°C and voltage of 20 kV was used. Under this condition, baseline separation was achieved for nine chiral compounds and partial separation was obtained for another six chiral compounds while no enantioseparation was obtained for the remaining eight compounds. The results showed that the existence of at least two aromatic rings or cycloalkanes and an oxygen or nitrogen atom or -CN group directly bonded to the chiral center are necessary for baseline separation. With the obtained results in this study, chiral separation of a chiral compound can be estimated with MD-modified capillary electrophoresis before analysis. This prediction will minimize the number of preliminary experiments required to resolve enantiomers and will save time and cost.

Enantiomeric separation of chiral sulfoxides by supercritical fluid chromatography

The application of supercritical fluid chromatography (SFC) to the enantiomeric separation of several chiral sulfoxides belonging to the family of the substituted benzimidazoles, including omeprazole, lansoprazole, pantoprazole, rabeprazole, oxfendazole and ricobendazole, is presented in this work. The column employed was Chiralpak AD and the effect of different chromatographic conditions was studied. The results obtained showed that all the compounds can be enantiomerically resolved using SFC, with resolutions higher than 2 and analysis times that in most cases were lower than 10 min. Alcohol type modifiers provided the best results, with ricobendazole, oxfendazole, and omeprazole showing the highest retentions and resolutions. Study of the temperature effect revealed that, in general, the isoelution temperature was above the temperatures assayed, except in the cases of omeprazole, lansoprazole, and oxfendazole with ethanol as modifier and pantoprazole with acetonitrile. Enthalpy-entropy compensation could also be demonstrated for the retention of the first and second eluted enantiomers as well as for the selectivity, with compensation temperatures of 25 degrees C, 45 degrees C, and 83 degrees C, respectively. Reversal of elution on change of the organic modifier was only observed for omeprazole using 2-propanol.

Chiral separation strategy in polar organic solvent chromatography and performance comparison with normal-phase liquid and supercritical-fluid chromatography

A strategy, including a rapid screening and several optimisation steps, for the separation of chiral molecules of pharmaceutical interest by polar organic solvent chromatography (POSC), using four polysaccharide-based stationary phases, is proposed and compared with previously reported strategies in normal-phase (NPLC) and supercritical fluid chromatography (SFC). In a first part of this paper, different examples demonstrate the effectiveness of the POSC strategy for fast method development. Optimisation is based on the use of experimental design to map the experimental domain in an efficient way. In the second part, the best screening results, obtained after performance of earlier defined chromatographic screening strategies in NPLC and SFC, are compared to those obtained in POSC. The three techniques show complementary separation results and allowed baseline separation of 23 of 25 compounds. POSC is found to be a very interesting separation mode compared to NPLC, because of the many fast (< 10 min) baseline separations obtained.

Study of the enantiomeric separation of oxfendazole and cetirizine using subcritical fluid chromatography on an amylose-based column

The enantiomeric separation of cetirizine and oxfendazole on a Chiralpak AD column using subcritical fluid chromatography has been studied in this work. The enantioseparation of cetirizine was only possible when 2-propanol was used as a modifier, obtaining better results in presence of the additives triethylamine (TEA) and trifluoroacetic acid (TFAA). On the contrary, 2-propanol provided the lowest enantioresolutions for oxfendazole, in this case the best results in terms of high resolution and short analysis time were obtained with ethanol. The study of the temperature effect revealed that in the case of cetirizine using 2-propanol, and oxfendazole using methanol, the separation was enthalpy-driven and the isoelution temperature was above the working range. Using ethanol or 2-propanol, the results showed that the oxfendazole enantioseparation was entropically driven and the isoelution temperatures were below the range studied.

Supercritical fluid chromatography tandem-column method development in pharmaceutical sciences for a mixture of four stereoisomers

A tandem-column method using Chiralpak AD-H and Chiralcel OD-H columns was achieved for baseline separation of a mixture of chiral pharmaceutical compounds (i.e., four stereoisomers) via supercritical fluid chromatography (SFC) with a mobile phase consisting of 90% liquid carbon dioxide and 10% ethanol:isopropanol (50:50 v/v). On the contrary, this mixture (mixture A) could not be baseline separated by SFC conditions explored with individual Chiralpak AD-H and Chiralcel OD-H columns. The effects of various mobile phases on elution order, capacity factor, selectivity, and resolution were determined with mixture A on the individual aforementioned columns to develop the tandem-column method.

Sub- and Supercritical Chiral Separation of Racemic Compounds on Columns with Stationary Phases Having Different Functional Groups

Separation of the enantiomers of each of three different racemates, neutral rac-alpha-tetralol, acidic rac-2-phenylpropionic acid, and basic rac-1-phenylethylamine, using subcritical and supercritical fluid chromatography with two different chiral stationary phases, heptakis(2,3,6-tri-O-methyl)-beta-cyclodextrin (Sumichiral OA-7500 column) and tris(3,5-dimethylphenylcarbamate) of amylose (Chiralpak AD-H column), was compared. The elution order of the enantiomers of the three racemates was determined, and the effects of the type of alcohol modifier, column oven temperature, mobile phase composition, flow rate, and pressure were examined. The most appropriate column oven temperature depended on both the type of alcohol modifier and the compound analyzed. Lower alcohol content improved the peak separation of both rac-alpha-tetralol on the Sumichiral OA-7500 column and rac-1-phenylethylamine on the Chiralpak AD-H column, while the same phenomenon was not observed with either rac-alpha-tetralol or rac-2-phenylpropionic acid on the Chiralpak AD-H column. Decreasing outlet pressure improved the peak separation obtained with rac-2-phenylpropionic acid, but had little effect on either rac-alpha-tetralol or rac-1-phenylethylamine.

Chiral separation of omeprazole and several related benzimidazoles using supercritical fluid chromatography

A study of the enantiomeric separation of omeprazole and several related benzimidazoles, using supercritical fluid chromatography (SFC), on the amylose based column Chiralpak AD is presented in this work. The effect of the organic modifier as well as temperature on the retention and enantioresolution was investigated. Alcohol-type modifiers provided the best results, allowing the enantiomeric separation of all the compounds studied with resolutions that were in most cases higher than 2, and analysis times lower than 10 minutes. An investigation of the temperature effect revealed that the isoelution temperature was below the working temperature range in only two cases, and hence it was better to work at the highest temperature permitted.

Separation of triadimefon and triadimenol enantiomers and diastereoisomers by supercritical fluid chromatography

The enantiomeric separation of triadimenol and triadimefon on a Chiralpak AD column using supercritical fluid chromatography, was studied in this work. The effect of different modifiers (methanol, ethanol and 2-propanol) was tested, with methanol and ethanol providing the best results for the enantiomeric separation of the two compounds. The enantioseparation of a mixture of triadimenol and triadimefon (six stereoisomers) was achieved in only 15 min using a gradient of ethanol, 200 bar, 35 degrees C and a flow-rate of 2 ml/min. The separation of triadimenol diastereoisomers on different achiral columns (diol, silica and ODS) was also investigated. In this case, the type of organic modifier to be used depended on the stationary phase, the Spherex Diol being the column that gave the best separation. Using this column, resolutions higher than 3 were obtained in analysis times of 5 min with any of the modifiers checked.

Separation of antifungal chiral drugs by SFC and HPLC: a comparative study

The enantiomeric separation of several compounds, including an antifungal drug and several of its precursors, using HPLC and SFC is described in this work. The columns employed were based on polysaccharide derivatives and the results show that most of the separations obtained by SFC are better, in terms of high resolution and short analysis time, than those obtained by HPLC. Only one compound could not be resolved using SFC but, in this case, HPLC provided baseline resolution.

Separation of stereoisomers of several furan derivatives by capillary gas chromatography-mass spectrometry, supercritical fluid chromatography, and liquid chromatography using chiral stationary phases

The direct separation of several stereoisomers (enantiomers and geometrical isomers) of furan derivatives, important intermediates for the synthesis of physiologically active natural products, was achieved using capillary gas chromatography/mass spectrometry with a per-O-methyl-beta-cyclodextrin, supercritical fluid chromatography and high-performance liquid chromatography with a tris(3,5-dimethylphenylcarbamate) of cellulose or amylose for the chiral stational phases, respectively. The temperature dependence of the peak resolution (Rs) and the retention factor (k) over the range of 110-130 degrees was studied using crotyl furfuryl ether in gas chromatography. Successive increases in the Rs value and of the difference between the k value of the E-isomer and the k value of the Z-isomer were observed when the gradient temperature was decreased. The per-O-methyl-beta-cyclodextrin column was suitable for use with volatile furan ethers whose molecular masses are between 150 and 180. In conclusion, the separation of thermally unstable furan derivatives was accomplished using supercritical fluid chromatography and high-performance liquid chromatography.