Integration of supercritical fluid chromatography into drug discovery as a routine support tool

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.

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.

Comparison of dimethylated and methylchlorinated amylose stationary phases, coated and covalently immobilized on silica, for the separation of some chiral compounds in supercritical fluid chromatography

The chromatographic properties of a new coated amylose tris(3-chloro-5-methylphenylcarbamate) were evaluated in supercritical fluid chromatography for the separation of enantiomers of chiral 1-aryl-5-aryl-pyrrolidin-2-one derivatives, potential anticancer agents, and some commercial drugs. The mobile phase consisted of CO₂-modifier mixtures with 30% of either methanol or ethanol, the flow rate was 3 mL/min. The column oven temperature was 40 °C and the outlet pressure was 15 MPa, in order to limit the compressibility of the CO₂, thus limiting density variation along the column. The obtained results were then compared to those observed toward 3 other stationary phases: the coated amylose tris(3,5-dimethylphenylcarbamate), the immobilized amylose tris(3,5-dimethylphenylcarbamate) and the coated amylose tris(5-chloro-2-methylphenylcarbamate). It was shown that the new coated amylose tris(3-chloro-5-methylphenylcarbamate) was the most retentive column whatever the studied compounds, particularly for thalidomide and omeprazole with retention factors up to 73.3 and 29.5for the second enantiomer, respectively. Concerning the enantioselectivity, even most of the compounds are separated on all the four columns, the coated amylose tris(3-chloro-5-methylphenylcarbamate) allows the best resolution for most of the ten studied analytes (except omeprazole for which the resolution values are equal to 7.8 and 9.7 on the coated amylose tris(3-chloro-5-methylphenylcarbamate) and amylose tris(3,5-dimethylphenylcarbamate), respectively). Acting in complementary ways, the two chlorinated stationary phases permitted the complete separation of enantiomers of nine compounds out of the ten.

Ramifications and Insights on the Role of Water in Chiral Sub/Supercritical Fluid Chromatography

More than 40 cosolvents have been used with carbon dioxide to alter its solvation strength. Among the most interesting systems is the subcritical/supercritical CO₂/alkanol eluents. Using small amounts of water in CO₂/MeOH is known to be beneficial in chiral subcritical/supercritical chromatography. However, the ramifications of introducing water as a cosolvent component is not entirely understood. In this work, we demonstrate important aspects of the CO₂/MeOH/H₂O system on nine chiral stationary phases with very different surface chemistries, encompassing derivatized polysaccharides, macrocyclic glycopeptides, iso-butylmercaptoquinine, isopropyl macrocyclic oligosaccharides, and π-electron acceptor/π-electron donor phases. A hydrophilicity scale has been shown to be useful in predicting if a given chiral column chemistry would show a significant enhancement in separation efficiency in the presence of water in the CO₂/MeOH system. We demonstrate up to 8-fold enhancements in plate counts of chiral separations with a concomitant decrease in retention times, as predicted by the qualitative test. The same chiral analysis can now be completed in almost a third of the time with the addition of small amounts of water, thereby decreasing organic solvent consumption by a considerable amount. Hydrophobic stationary phases show a minimal increase in efficiency and decrease in analysis times and optimized separations show much larger reduced plate heights, compared to more hydrophilic stationary phases. Furthermore, the presence of water can alter the nature of the adsorption isotherm under nonlinear conditions. Small amounts of water can be used to tune nonlinear tailing peaks into fronting ones, significantly improving preparative enantiomeric separations.

Chaotropic Effects in Sub/Supercritical Fluid Chromatography via Ammonium Hydroxide in Water-Rich Modifiers: Enabling Separation of Peptides and Highly Polar Pharmaceuticals at the Preparative Scale

Chromatographic separation, analysis and characterization of complex highly polar analyte mixtures can often be very challenging using conventional separation approaches. Analysis and purification of hydrophilic compounds have been dominated by liquid chromatography (LC) and ion-exchange chromatography (IC), with sub/supercritical fluid chromatography (SFC) moving toward these new applications beyond traditional chiral separations. However, the low polarity of supercritical carbon dioxide (CO₂) has limited the use of SFC for separation and purification in the bioanalytical space, especially at the preparative scale. Reaction mixtures of highly polar species are strongly retained even using polar additives in alcohol modifier/CO₂ based eluents. Herein, we overcome these problems by introducing chaotropic effects in SFC separations using a nontraditional mobile phase mixture consisting of ammonium hydroxide combined with high water concentration in the alcohol modifier and carbon dioxide. The separation mechanism was here elucidated based on extensive IC-CD (IC couple to conductivity detection) analysis of cyclic peptides subjected to the SFC conditions, indicating the in situ formation of a bicarbonate counterion (HCO₃^-). In contrast to other salts, HCO₃^- was found to play a crucial role acting as a chaotropic agent that disrupts undesired H-bonding interactions, which was demonstrated by size-exclusion chromatography coupled with differential hydrogen-deuterium exchange-mass spectrometry experiments (SEC-HDX-MS). In addition, the use of NH₄OH in water-rich MeOH modifiers was compared to other commonly used basic additives (diethylamine, triethylamine, and isobutylamine) showing unmatched chromatographic and MS detection performance in terms of peak shape, retention, selectivity, and ionization as well as a completely different selectivity and retention behavior. Moreover, relative to ammonium formate and ammonium acetate in water-rich methanol modifier, the ammonium hydroxide in water additive showed better chromatographic performance with enhanced sensitivity. Further optimization of NH₄OH and H₂O levels in conjunction with MeOH/CO₂ served to furnish a generic modifier (0.2% NH₄OH, 5% H₂O in MeOH) that enables the widespread transition of SFC to domains that were previously considered out of its scope. This approach is extensively applied to the separation, analysis, and purification of multicomponent reaction mixtures of closely related polar pharmaceuticals using readily available SFC instrumentation. The examples described here cover a broad spectrum of bioanalytical and pharmaceutical applications including analytical and preparative chromatography of organohalogenated species, nucleobases, nucleosides, nucleotides, sulfonamides, and cyclic peptides among other highly polar species.

Evaluation of polysaccharide-based chiral stationary phases in modern SFC-MS/MS for enantioselective bioanalysis

Aim: The applicability of polysaccharide-based chiral stationary phases in modern supercritical fluid chromatography (SFC)-MS/MS for chiral bioanalysis was evaluated. Materials & methods: Ten popular polysaccharide-based chiral stationary phases (CSPs) were tested using a set of 23 drugs against three cosolvents. The effect of temperature and backpressure on separation was examined. Results: The recommended order of CSPs for screening was determined. Methanol with 0.1% NH₄OH is proven to be the first choice of cosolvent. Temperature of 40°C and backpressure of 10 or 15 MPa are recommended starting conditions. Phospholipid elution profiles on the polysaccharide-based CSPs were reported for the first time under SFC conditions. Conclusion: A simplified screening protocol with straightforward method optimization approaches was generated for SFC chiral assay development in a reasonable time frame with a high success rate.

Separation of stereoisomers of 7-oxa-bicyclo[2.2.1]heptene sulfonate (OBHS), a Selective Estrogen Receptor Modulator (SERM), via chiral stationary phases using SFC/UV and SFC/MS

The enantiomeric separation of a racemate of 7-oxa-bicyclo[2.2.1]heptene sulfonate (OBHS) derivatives, a Selective Estrogen Receptor Modulator (SERM), was obtained using supercritical fluid chromatography in tandem with UV and mass spectrometry (SFC/UV and SFC/MS, respectively). Supercritical CO₂ modified with methanol or isopropyl alcohol was used with isopropylamine (IPAm), trimethylamine (TEA), or trifluoroacetic acid (TFA) as an additive to obtain the enantiomers separations. Both Chiralpak IC and IA were evaluated for the separation of enantiomers. Results showed enantiomers separation can be achieved in less than 5 min with a resolution greater than 1 and 0.9, respectively, for the different OBHS derivatives (compounds A and B) using supercritical CO₂ modified with 40% isopropyl alcohol containing 0.25% IPAm and IC column applying isocratic conditions. Similar conditions were used with the semi-preparative Chiralpak IC column to isolate more than 50 mg of each enantiomer. SFC/MS and SFC/UV results showed pure enantiomers were isolated. Method development via SFC was much simpler than those reported in the literature using HPLC.

Preliminary kinetic evaluation of an immobilized polysaccharide sub-2μm column using a low dispersion supercritical fluid chromatograph

The performance of a 3×50mm, 1.6μm d_p column with an immobilized polysaccharide stationary phase (ChiralPak IA-U) was evaluated for efficiency, and pressure drop, with respect to flow rate and modifier concentration using supercritical fluid chromatography (SFC). This appears to be the first such report using such a column in SFC. A unique low dispersion (ultra-high performance) SFC was used for the evaluation. The minimum reduced plate height of 2.78, indicates that the maximum efficiency was similar to or better than coated polysaccharide columns. Selectivity was different from ChiralPak AD, with the same chiral selector, as reported by many others. At high flows and high methanol concentrations, pump pressures sometimes approached 600bar. With 5% methanol, pressure vs. flow rate was non-linear suggesting turbulent flow in the connector tubing. The optimum flow rate (F_opt) at 40% methanol was ≈0.8mL/min, where the column efficiency was highest. At 5% methanol, F_opt increased to ≈1.6mL/min, but efficiency degraded noticeably. The differences in F_opt suggests that the solute diffusion coefficients are a strong function of modifier concentration. Several sub-1min separations, including a 7.5s separation, are presented.

Kinetic performance of a 50mm long 1.8μm chiral column in supercritical fluid chromatography

Reduced plate heights (hr) of <2 were observed for the first time during the chiral separation of enantiomers, on sub-2μm particles with supercritical fluid chromatography (SFC). The enantiomers of trans-stilbene oxide, were separated on a 4.6×50mm, 1.8μm R,R-Whelk-O1 column, with hr as low as 1.93. The plumbing of a commercial SFC instrument was modified to create a low dispersion version. Without the modification performance was considerably worse. vanDeemter like plots of reduced plate height vs. flow rate, for trans-stilbene oxide, indicate that the optimum flow varied with% modifier. On a 4.6×250mm, 5μm R,R- Whelk-O1 column, the optimum flow was >4mL/min for 5% methanol in CO2, decreasing to <2mL/min for 40% methanol (more than a factor of 2). For a 4.6×50mm column packed with 1.8μm particles the optimum appeared to be near, or >5mL/min with 2.5%, 5%, and 10% methanol, decreasing to between 3 and 3.5mL/min at 40% methanol. This is the first time such shifts have been characterized. Since the solutes were the same in all cases, the differences are likely due to changes in solute diffusion coefficients caused by changes in modifier concentration, and pressure. Pump pressure requirements sometimes exceeded 500bar. It is shown that a 5mL/min flow rate is inadequate for use with 1.8μm particles in a 4.6mm ID column format. Instead, it is suggested to decrease the ID of the column to 3mm, where the optimum flow rates are on the order of 2mL/min with decreased tubing variance. Nevertheless, a number of sub-1min chromatograms are presented.

Cardiovascular drug determination in bioanalysis: an update

The great impact of cardiovascular diseases in human health has led to the development of a huge number of drugs and therapies to improve the treatment of these diseases. Cardiovascular drug analysis in biological fluids constitutes an important challenge for analytical scientists. There is a clear need for reliable methods to carry out both qualitative and quantitative analysis in a short time of analysis. Different problems such as drug monitoring, analysis of metabolites, study of drugs interactions, drugs residues or degradation products, chiral separation, and screening and confirmation of drugs of abuse in doping control must be solved. New trends in sample preparation, instrumental and column technology advances in LC and innovations in MS are described in this work.

Greener Solvent Usage for Discovery Chemistry Analysis and Purification

The concept of green chemistry has been implemented in chemical manufacturing and process chemistry over the past 15 years. Only recently has the concept been introduced to smaller volume activities such as medicinal and analytical chemistry. This chapter discusses green chemistry approaches suitable for discovery chemistry analysis and purification. Topics covered include use of supercritical fluid chromatography (SFC) for analysis and purification to reduce solvent usage, optimizing analytical LC methods to minimize solvent usage, optimization of reverse phase purifications, use of greener solvents for flash purification, and an evaluation of flash SFC for discovery chemistry purifications. Approaches that have been successful in numerous pharmaceutical medicinal chemistry laboratories will be presented.

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.