On the solvent versatility in immobilized amylose tris(3,5-dimethylphenylcarbamate) chiral stationary phase in high performance liquid chromatography: Application to the asymmetric cyclopropanation of olefins

Common screening approaches for efficient analytical method development in LC and SFC on columns packed with immobilized polysaccharide-derived chiral stationary phases

Owing to their remarkable enantioselectivity, versatility, and stability, immobilized polysaccharide-based chiral stationary phases (CSPs) have been successfully integrated into the tool box of many research and industry groups for the separation of enantiomers or stereoisomers by liquid and supercritical fluid chromatography. Due to the structurally diverse range of compounds available, efficient method development for chiral separations utilizing such CSPs is a challenging subject. In this chapter, we will discuss simplified screening protocols and straightforward approaches to achieve chiral separations in HPLC and SFC using the column series CHIRALPAK™ IA, IB, IC, and ID in reasonable time frame and with limited experimental work and a high success rate.

Chiral separations by HPLC on immobilized polysaccharide chiral stationary phases

Immobilized polysaccharide chiral stationary phases (CSPs) are a new development in chiral chromatography with increasing importance for the resolution of racemic compounds. These CSPs can be used with solvents traditionally applied for the classical coated polysaccharide CSPs as well as solvents that were "forbidden" for the coated phases such as tetrahydrofuran, chloroform, dichloromethane, acetone, 1,4-dioxane, ethylacetate, and certain ethers. However, these forbidden solvents may be required for the determination of the chiral recognition mechanism. Therefore, the immobilized CSPs are effective for the evaluation of chiral recognition mechanisms. Furthermore, immobilized chiral columns are also useful for monitoring the progress of stereospecific synthetic reactions which are normally performed in such solvents. The present chapter describes the detailed experimental protocol of a chiral resolution on immobilized polysaccharides CSPs by HPLC.

Chiral recognition ability and solvent versatility of bonded amylose tris(3,5-dimethylphenylcarbamate) chiral stationary phase: enantioselective liquid chromatographic resolution of racemic N-alkylated barbiturates and thalidomide analogs

The chiral recognition ability and solvent versatility of a new chiral stationary phase containing amylose 3,5-dimethylphenylcarabamate immobilized onto silica gel (CHIRALPAK IA) is investigated. Thus, the direct enantioselective separation of a set of racemic N-alkylated barbiturates and 3-alkylated analogs of thalidomide was conducted using different nonstandard solvents as eluent and diluent, respectively in high-performance liquid chromatography (HPLC). The separation, resolution, and elution order of the investigated compounds were compared on both immobilized and coated amylose tris(3,5-dimethylphenylcarbamate) chiral stationary phases (Chiralpak IA and Chiralpak AD, respectively) using a mixture of n-hexane/2-propanol (90:10 v/v) as mobile phase with different flow-rates and fixed UV detection at 254 nm. The effect of the immobilization of the amylose tris(3,5-dimethylphenylcarbamate) chiral stationary phase on silica (Chiralpak IA) on the chiral recognition ability was noted as the bonded phase (Chiralpak IA) was superior in chiral recognition and possesses a higher resolving power in most of the reported cases than the coated one (Chiralpak AD). A few racemates were not or poorly resolved on the immobilized Chiralpak IA or the coated Chiralpak AD when using standard solvents were most efficiently resolved on the immobilized Chiralpak IA upon using nonstandard solvents. Furthermore, the immobilized phase withstands the nonstandard (prohibited) HPLC solvents such as dichloromethane, ethyl acetate, tetrahydrofuran, methyl-tert-butyl ether, and others when used as eluents or as a dissolving agent for the analyte itself. The direct analysis of a real sample extracted from plasma using DCM on Chiralpak IA is also shown.

Preparative HPLC separation of bambuterol enantiomers and stereoselective inhibition of human cholinesterases

We separated and characterized the enantiomers of bambuterol (5-[-(tert-butylamino)-1-hydroxyethyl]-m-phenylene-bis(dimethylcarbamate) hydrochloride), which is used in racemic form as a prodrug of terbutaline, a beta(2)-adrenoceptor agonist. The enantioseparation was attempted on several chiral HPLC columns, and the most effective separation was achieved on the amylose-based Chiralpak AD column. Since in vivo conversion of bambuterol into terbutaline involves hydrolysis by butyrylcholinesterase (EC 3.1.1.8), we studied the reaction of enantiomers with eight human BChE variants. Both enantiomers inhibited all studied BChE variants; however, the rate of inhibition with the (R)-enantiomer was about five times faster than with the (S)-enantiomer. (R)-bambuterol inhibition rate constants for homozygous usual (UU), fluoride-resistant (FF) or atypical (AA) variant ranged from 6.4 to 0.11 min(-1)microM(-1). The inhibition rates for heterozygotes were between the respective constants for the corresponding homozygotes.

Analytical and semipreparative high performance liquid chromatography separation of stereoisomers of novel 3,4-dihydropyrimidin-4(3H)-one derivatives on the immobilised amylose-based Chiralpak IA chiral stationary phase

Direct HPLC separation of stereoisomers of three novel 5-methyl-2-(alkylthio)-6-(2,6-difluorophenylalkyl)-3,4-dihydropyrimidin-4(3H)-ones endowed with antiviral and potential antiproliferative and morphological differentiation activity against melanoma cells was performed by using the new immobilised amylose-based Chiralpak IA chiral stationary phase. Stereoselective conditions were achieved using normal phase eluents containing "non-standard" solvents such as ethyl acetate, methyl tertbutyl ether, or dichloromethane. In order to study the chiroptical properties of single stereoisomers, mg-scale separations were performed on analytical and semipreparative size Chiralpak IA columns in combination with ethyl acetate-based eluents.

Impact of immobilized polysaccharide chiral stationary phases on enantiomeric separations

Immobilized polysaccharide-based chiral stationary phases (CSPs) are gaining importance in the resolution of racemic compounds due to their stable nature on working with normal solvents and those prohibited for use with coated phases (tetrahydrofuran, chloroform, dichloromethane, acetone, 1,4-dioxane, ethyl acetate, and certain other ethers). This review discusses the use of immobilized polysaccharide CSPs in the chiral resolution of various racemates by liquid chromatography. The discussion includes immobilization methodologies, enantioselectivities, efficiencies, and a comparison of chiral recognition capabilities of coated vs. immobilized CSPs. Some applications of immobilized CSPs to the chiral resolution of racemic compounds are also presented.

Direct HPLC enantioseparation of chiral aptazepine derivatives on coated and immobilized polysaccharide-based chiral stationary phases

The direct HPLC enantioseparation of Mianserin and a series of aptazepine derivatives is accomplished on polysaccharide-based chiral stationary phases (CSPs). The resolutions are performed on the coated-type Chiralcel OD and Chiralpak AD CSPs and on the first commercially available immobilized-type Chiralpak IA CSP, in normal-phase and polar-organic modes. The complete separation of enantiomers of all racemates investigated was successfully achieved under at least one of CSP/eluent combinations employed. Pure alcohols such ethanol or 2-propanol, with a fixed percentage of DEA added, serve as valuable alternatives to the more common n-hexane-based normal-phase eluents in resolution of Mianserin on the AD CSP. In order to study the chiroptical properties of aptazepine derivatives, chromatographic resolutions are carried out at semipreparative scale using Chiralpak AD and Chiralpak IA as CSPs. Nonconventional dichloromethane-based eluents have permitted to expand the chiral resolving ability of the immobilized Chiralpak IA CSP and to perform mg-scale enantioseparations with an analytical-size column. Assignment of the absolute configuration of the separated enantiomers is empirically established by comparing their chiroptical data with those of structurally related Mianserin.

Immobilized versus coated amylose tris(3,5-dimethylphenylcarbamate) chiral stationary phases for the enantioselective separation of cyclopropane derivatives by liquid chromatography

The solvent versatility of Chiralpak IA, a new chiral stationary phase (CSP) containing amylose tris(3,5-dimethylphenylcarabamate) immobilized onto silica gel, is investigated for the enantioselective separation of a set of cyclopropane derivatives using ethyl acetate or dichloromethane (DCM) as non-standard mobile phase eluent and diluent, respectively in high-performance liquid chromatography (HPLC). A comparison of the separation of cyclopropanes on both immobilized and coated amylose tris(3,5-dimethylphenylcarbamate) chiral stationary phases (Chiralpak IA and Chiralpak AD, respectively) in HPLC using a mixture of n-hexane/2-propanol (90/10 and 99/1, v/v) as mobile phase with a flow rate of 0.5 ml/min and UV detection at 254 nm, is demonstrated. The optimized method of separation is used for an online HPLC monitoring for the Rh(II)-catalyzed asymmetric intermolecular cyclopropanations in dichloromethane. Direct analysis techniques without further purification, workup or removal of dichloromethane were summarized. The method provides an easy and direct determination of the enantiomeric excess of the cyclopropanes and selectivity of the catalyst used without any further work up.