Using multiple HPLC chromatographic modes and various chiral columns in the context of an automated screening system, a potential separation was initially identified for the methyl ester of evacetrapib and its stereoisomers using an immobilized polysaccharide-based HPLC column. The bonded nature of this column, the Chiralpak(®) IC, allows for enhanced separation development with a diverse solvent range not amenable to standard coated chiral stationary phases. The ternary eluent system ultimately identified provided isomer resolutions not obtainable via the more established hexane/alcohol or polar organic chromatographic modes. A systematic separation development process is described, first for the resolution of the isomers, and later incorporating five potential impurities. A robust separation system was eventually developed that effectively resolves all compounds within a reasonable analysis time.

Mitosis inhibitor (R)-litronesib (LY2523355) is a 1,3,4-thiadiazoline-bearing phenyl and N-(2-ethylamino)ethanesulfonamido-methyl substituents on tetrahedral C5. Chiral instability has been observed at pH 6 and above with the rate of racemization increasing with pH. A positively charged trigonal intermediate is inferred from the fact that p-methoxy substituent on the phenyl accelerated racemization, whereas a p-trifluoromethyl substituent had the opposite effect. Racemization is proposed to occur through a relay mechanism involving intramolecular deprotonation of the sulfonamide by the side chain amino group and attack of the sulfonamide anion on C5, cleaving the C5S bond, to form an aziridine; heterolytic dissociation of the aziridine yields an ylide. This pathway is supported by (1) a crystal structure providing evidence for a hydrogen bond between the sulfonamide NH and the amino group, (2) effects of substituents on the rate of racemization, and (3) computational studies. This racemization mechanism results from neighboring group effects in this densely functionalized molecule. Of particular novelty is the involvement of the side-chain secondary amino group, which overcomes the weak acidity of the sulfonamide by anchimeric assistance.

Using HPLC chiral separation screening, various columns representing the polysaccharide, macrocyclic antibiotic and brush classes were assessed in multiple chromatographic modes for the separation of evacetrapib, a potential cardiovascular drug, from its enantiomer, two diastereomers and several impurities. Screening data consistently pointed to the brush-type Whelk-O 1 chiral column as most promising for this task. A systematic separation optimization process is outlined using the (S,S) Whelk-O 1 chiral column, first for the resolution of the isomers, and later including six potential impurities. A relatively complex yet rugged separation system was eventually identified that effectively resolves all compounds within a reasonable analysis time, and should serve as an adequate tool for evacetrapib bulk drug enantiopurity measurement.

Chiral separation screening has become a widely accepted approach for the rapid identification of an appropriate chiral stationary phase for use in more focused enantioseparation optimization. A set of extended screens encompassing various chromatographic modes using high performance liquid chromatography (HPLC) and supercritical fluid chromatography (SFC) is presented. These multimodal screens are tailored to meet the specific and changing needs of customers as distributed along the drug development process within a typical pharmaceutical development setting. In addition, a systematic column testing and regeneration approach is presented and emphasized for maintaining the reliability of column and screen data. Comprehensive screening systems created to serve such an expansive customer base, actively supported with manufacturer-recommended column suitability and regeneration procedures, are not well represented in the literature.

An HPLC chiral separation flow scheme was developed for identification of suitable enantioseparation conditions for small molecules. This flow scheme employs various chiral stationary phases (CSPs) and separation modes with the aim of improving efficiency by leading the scientist toward a reliable enantioseparation through a reduced number of experiments. In cases where a partial chiral separation is achieved with a particular CSP, guidance in the flow scheme is provided to improve resolution. Using prior knowledge, literature references, and data from 60 nonproprietary compounds analyzed in this study, the flow scheme was developed with separation mode (solvent compatibility) versatility in mind.

A novel, potent series of indole analogs were recently developed as MR antagonists, culminating in 14. This compound represents the first MR antagonist in this class of molecules, exhibiting picomolar binding affinity and in vivo blood pressure lowering at pharmaceutically relevant doses.

This study demonstrates the increased versatility of the Chiralcel OJ-H stationary phase when using various alcohol/acetonitrile mobile phases. This chiral stationary phase has traditionally been employed in the normal phase mode and more recently with neat alcohols as eluents. Selected isomeric human mineralocorticoid receptor (hMR) antagonist pharmaceutical candidates and synthetic intermediates were separated using the Chiralcel OJ-H HPLC column with novel polar cosolvent eluent systems. The capacity factors, resolution, and selectivity of the chiral separations were assessed while varying the alcohol/acetonitrile composition and alcohol identity. The mixed polar eluents provide separations that are nearly always superior to both the traditional hexane-rich and single-alcohol "polar organic" eluents for the compounds tested in this article.

Seven macrocyclic antibiotics were evaluated as chiral selectors for the enantiomeric separation of 11 dansyl amino acids using narrow-bore high-performance liquid chromatography (HPLC). The macrocyclic antibiotics were incorporated as mobile phase additives to determine the enantioselective effects on the chiral analytes. The resolution and capacity factor (k') of each analyte were assessed while varying the structure of macrocyclic antibiotic and the mobile phase buffer pH. The selectivity of the chiral selectors was measured as a function of changes in these parameters. All 11 dansyl amino acids were separated by at least one of the chiral selectors. Three-dimensional computer modeling of the more effective chiral selectors illustrated the importance of macrocyclic antibiotic structure concerning stereospecific analyte interaction.

Chiral preparative chromatography is a technology increasingly used in the pharmaceutical industry to deliver enantiomerically pure drug candidates. A strategy for rapid screening of conditions on polysaccharide chiral stationary phases (CSPs) has been developed with an emphasis on preparative applications. Sample solubility is a major limiting factor in preparative chromatography. Most reported analytical chiral separations on polysaccharide CSPs are with eluent systems consisting of mainly hexane and small amounts of alcohol as a modifier. The intelligent chiral resolution system (ICRS) was developed to emphasize polar solvents as the first choice for eluent systems. Examples of this approach, and details on the screening procedure are presented. Using the system, chiral preparative procedures can be developed for most compounds in approximately 3 hours.

The macrocyclic antibiotic LY333328 has been evaluated as a chiral selector for the enantioseparation of nine dansylated amino acids. This macrocyclic glycopeptide was used as a chiral mobile phase additive (CMPA) in conjunction with narrow bore high-performance liquid chromatography (HPLC). The key mobile phase parameters of LY333328 concentration and buffer pH were varied, along with variations in stationary phases consisting of C8, phenyl, cyano, and silica. After observing and plotting changes in retention and resolution based on corresponding variation in these parameters, a better understanding of the behavior of this chiral selector was obtained. The pKa values of the dansyl amino acid analytes and LY333328 were measured and used to gain a better understanding of the microenvironment in which these enantioseparations occur. Optimized conditions resulted in the baseline separation of eight of nine dansyl amino acids.

A new macrocyclic antibiotic, LY307599, has been evaluated as a chiral selector for the separation of the enantiomers of flurbiprofen using capillary electrophoresis (CE). The effect of varying separation buffer parameters such as buffer strength, pH, LY307599 concentration and methanol concentration were assessed. Using the optimized CE conditions, the separation of flurbiprofen enantiomers can be achieved using LY307599 as a chiral selector.

Abstract A thorough analysis of a new commercially available pepsin chiral stationary phase (CSP) has been completed using seproxetine (S-norfluoxetine) hydrochloride bulk drug substance and R-norfluoxetine hydrochloride as the test analytes. Chromatographic properties of this new Ultron ES-Pepsin column were investigated by varying key mobile phase parameters (pH, flow rate, buffer strength and organic concentration), column temperature and sample loading. After observing and plotting changes in retention, resolution and theoretical plates based on corresponding variation in these parameters, it is possible to choose conditions for the separation that are optimum and robust. The subsequent method validation demonstrated acceptable precision, linearity, recovery, selectivity, limit of detection and ruggedness for the determination of R-norfluoxetine in seproxetine hydrochloride bulk drug substance.