Determination of the enantiomeric purity of 5,6- and 6,7-dihydroxy-2-aminotetralins by chiral HPLC

5,6- and 6,7-Dihydroxy-2-aminotetralin (ADTN), racemic dopamine receptor agonists, were resolved into their enantiomers by a new chiral HPLC assay. The separation was performed on a Crownpack CR column, which contains an 18-crown-6-type chiral crown ether as a chiral selector. The chiral recognition is based on the compiexation of the protonated primary amino group and the oxygen atoms inside the cavity of the crown ether. The amino group is attached to the chiral centre and therefore these compounds could be resolved. Mobile phase was perchloric acid pH 2.0 and the detection was UV at 200 nm. Resolution factors were 3.1 for 5,6-ADTN and 1.1 for 6,7-ADTN resulting in very low limits of quantitation (<0.1%) of the enantiomer present as impurity. Data on the validation of the assay and on the stability of the column are also reported. © 1993 Wiley-Liss, Inc.     

Determination of the enantiomeric purity of dihydroxy- and dimethoxy-2-aminotetralins by high-performance capillary electrophoresis with cyclodextrins as chiral selector

A chiral separation of 5,6- and 6,7-dihydroxy-2-aminotetralin and of the corresponding dimethoxy analogues can be achieved by high-performance capillary electrophoresis using cyclodextrins as chiral selector. The selectivity of a number of native and derivatized cyclodextrins was screened and hydroxylalkyl-β-cyclodextrins turned out to be the most effective. Optimization of hydroxyethylcyclodextrin and hydroxypropylcyclodextrin concentration for each compound led to baseline separation (resolution factors from 1.7 to 2.3) resulting in a detection limit of 0.1% for the enantiomer present as impurity. Modifiers of the electroendosmotic flow, such as hydroxypropylcellulose and hexadecyltrimethylammoniun bromide, must be added to the background electrolyte to obtain such results. © 1995 Wiley-Liss, Inc.     

Preparative HPLC separation of methoxytetralins, ligands for melatonin receptors, containing two chiral centers with polysaccharide chiral stationary phases. Determination of enantiomeric purity

Preparative chromatography was used to obtain approximately 200 mg of each of the four individual isomers of the three methoxytetrahydronaphthalenic derivatives, new agonist and antagonist ligands for melatonin receptors to be tested for binding. The mobile and stationary phases were chosen to achieve best resolution in shorter runtime. Enantiomeric purity was verified and quantified using normal and reversed phase methodology on cellulose CSPs. Enantiomer elution order was analysed and discussed. Limit of detection (LOD) and limit of quantification (LOQ) were calculated.     

Direct enantiospecific HPLC bioanalysis of (R,S)-atenolol on a chiral stationary phase

The simultaneous determination of the enantiomers of the β₁-selective adrenergic antagonist atenolol in human plasma and urine is described. After an alkaline preextraction atenolol is extracted from biological material at pH 12.3 using dichloromethane/propan-2-ol. The separation of the underivatized enantiomers is achieved by high-performance liquid chromatography on a chiral stationary phase (Chiralcel OD, cellulose tris-3, 5-dimethylphenylcarbamate, coated on silica gel) with fluorimetric detection. (?)-(S)-Pindolol is used as an internal standard. The detection limits of 5 ng/ml enantiomer in plasma and 50 ng/ml enantiomer in urine are sufficient for pharmacokinetic studies after therapeutic doses. © 1993 Wiley-Liss, Inc.     

Chromatographic resolution of the chiral isomers of several beta-blockers over cellulose tris(3,5-dimethylphenylcarbamate) chiral stationary phase.

The optical resolution of seven beta-blockers which have in common the N-isopropyl-3-aryloxy-2-hydroxypropylamine moiety was carried out by HPLC using the cellulose tris(3,5-dimethylphenylcarbamate) chiral stationary phase to quantitatively characterize the enantioselectivity of these compounds. The capacity factors and separation factors at different column temperature were determined with some qualitative trends derived. A compensation effect was observed for these compounds where there exists an approximately linear relationship between the enantiomeric differences in enthalpic and entropic energies.     

Polar organic chiral separation of propranolol and analogues using a β-cyclodextrin bonded stationary phase

A β-cyclodextrin bonded stationary phase was employed for the enantioresolution of propranolol and several analogues in conjunction with various polar organic mobile phases. The effects of structural alterations in the non-polar regions of the analytes were found to exert profound changes upon chiral resolution and capacity values, indicating that features which cannot hydrogen-bond with the cyclodextrin molecule still play an important role in this chiral recognition process. This was linked to a repulsive steric effect facilitating the necessary conditions for chiral resolution. The degree of ionization of the analytes and the type and concentration of organic modifier used were also seen to influence the analytes¹ enantio-selectivity and capacity values. © 1996 Wiley-Liss, Inc.     

Diphenylethanediamine (DPEDA) as chiral selector: VII. Efficient HPLC resolution of a series of underivatized diarylcarbinols on a chiral stationary phase based on C5-amide-bonded N-3,5-dinitrobenzoyl-DPEDA

Fast and efficient baseline separation of asymmetrically substituted diarylmethanols and 1,1-diarylethanols was achieved on an endcapped, amide-linked N-3,5-dinitrobenzoylated, (R, R)-1,2-diphenyl-1,2-ethanediamine-derived chiral stationary phase (CSP). Optimal enantioselectivities on this CSP were obtained using 1% 2-propanol in n-heptane as the mobile phase. Enantiorecognition was found to be governed by π-basicity and the substitution pattern of the aromatic substituents. © 1996 Wiley-Liss, Inc.     

Interactions of chiral molecules with an (r)-n-(3,5-dinitrobenzoyl) phenylglycine HPLC stationary phase

Forty different chiral molecules were studied by liquid chromatography with a Pirkle-type, (R)-N-(3,5-dinitrobenzoyl) phenylglycine (DNBPG), chiral stationary phase column. The dramatic effect of a small molecular change on chiral recognition was demonstrated using DL-amino acid derivatives. The inductive effect on chiral recognition was also studied using trifluoro-, trichloro-, dichloro-, monochloroacetyl, and acetyl derivatives of four different chiral amines. The study of the enantiomer separation of 11 different crown ethers of 2,2′-binaphthyldiyl showed that the rigidity of the chiral center can be an additional parameter in chiral recognition for the DNBPG phase but not for a β-cyclodextrin bonded chiral phase. It is apparent from this study that steric effects, inductive effects, and molecular rigidity play important roles in chiral recognition with DNBPG chiral stationary phases.     

Preparative enantiomeric separation of new selective CB2 receptor agonists by liquid chromatography on polysaccharide-based chiral stationary phases: determination of enantiomeric purity and assignment of absolute stereochemistry by X-ray structure analysis

The development of high-performance liquid chromatography (HPLC) methods using derivatized amylose chiral stationary phases has permitted preparative enantioseparations of substituted 4-oxo-1,4-dihydroquinoline-3-carboxamide derivatives with satisfactory yields. These compounds constitute new potent selective agonists of the cannabinoid CB(2) receptor. Analytical enantioseparation methods using UV detection were validated to determine the enantiomeric purity of these compounds. Linear calibration curves in the range from 0.18 to 0.40 mM were obtained; repeatability, limits of detection (LOD), and quantification (LOQ) were determined: LOD varied, for the various solutes, from 0.5 to 1.2 μM. All the separated compounds were prepared with high enantiomeric purities superior to 99.3% Absolute configuration of the enantiomers was unequivocally established by single crystal X-ray diffraction method and correlated to the chiroptical properties of isolated enantiomers.     

(Z)-1,1-dichloro-2-(4-benzyloxyphenyl)-2,3-bis(4-methoxyphenyl)cyclopropane: The synthesis and enantiomeric separation of an antitumor agent

(Z)-1,1-Dichloro-2-(4-benzyloxyphenyl)-2,3-bis(4-methoxyphenyl)cyclopropane ( 5 ), a potential antitumor agent designed to treat breast cancer, was prepared in three steps. A stereospecific palladium-catalyzed cross coupling reaction which provided the intermediate (Z)-triaryl alkene 4 was a crucial step in the synthesis. Makosza phase transfer reaction on 4 gave the enantiomeric (Z)-dichlorocyclopropane derivatives 5 which were resolved by semipreparative HPLC on a chiral stationary phase consisting of amylose tris-3,5-dimethylphenyl carbamate coated on silica gel. © 1994 Wiley-Liss, Inc.     

Separation of nicotine and nornicotine enantiomers via normal phase HPLC on derivatized cellulose chiral stationary phases

This paper describes the enantiorecognition of (±)nicotine and (±)nornicotine by high-performance liquid chromatography using two derivatized cellulose chiral stationary phases (CSPs) operated in the normal phase mode. It was found that different substituents linked to the cellulose backbone significantly influence the chiral selectivity of the derivatized CSP. The results showed that, in general, the tris(4-methylbenzoyl) cellulose CSP (Chiralcel OJ) surpasses tris(3,5-dimethylphenyl carbamoyl) cellulose CSP (Chiralcel OD). On the former column, the resolution (±)nicotine and (±)nornicotine enantiomers depended largely on mobile phase compositions. For the separation of the nicotine enantiomers, the addition of trifluoroacetic acid to a 95:5 hexane/alcohol mobile phase greatly improved the enantioresolution, probably due to enhanced hydrogen bonding interactions between the protonated analytes and the CSP. For (±)nornicotine separation, a reduction in the concentration of alcohol in the mobile phase was more effective than the addition of trifluoroacetic acid. Possible solute-mobile phase-stationary phase interactions are discussed to explain how different additives in the mobile phase and different substituents on the cellulose glucose units of the CSPs affect the separation of both pairs of enantiomers. Chirality 10:364–369, 1998. Published 1998 Wiley-Liss, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

HPLC enantioseparation on cellulose tris(3,5-dimethylphenylcarbamate) as a chiral stationary phase: Influences of pore size of silica gel,coating amount,coating solvent,and column temperature on chiral discrimination

Cellulose tris(3,5-dimethylphenylcarbamate) (CDMPC) was coated on large-pore silica gels and used as a chiral stationary phase (CSP) for high-performance liquid chromatographic separation of enantiomers. The influences of pore size of silica gel, coating amount of CDMPC, coating solvent, and column temperature on chiral discrimination were investigated. CSPs prepared with a large-pore silica gel having a small surface area showed higher chiral recognition. The amount of CDMPC adsorbed on the silica gel influenced the chiral recognition of some racemates. Loading capacity of racemates increased with an increase of the amount of CDMPC supported on the silica gel, and a CSP coated with 45% CDMPC by weight can be used for both analytical and semi-preparative scale separations. The CDMPC, coated using acetone as the coating solvent, exhibited, in many cases, higher enantioselectivity than that obtained with tetrahydrofuran F as the coating solvent. © 1996 Wiley-Liss, Inc.     

Structural features affecting chiral resolution of cannabimimetic enantiomers by amylose 3,5-dimethylphenylcarbamate chiral stationary phase

The effect of structural features of six pairs of enantiomers of cannabimimetic compounds on their chromatographic resolution on an amylose tris(3,5-dimethylphenylcarbamate) chiral stationary phase was studied using various compositions of n-hexane with 2-propanol and ethanol. Structural analysis by molecular mechanics was also performed to verify that the 3D conformation within this family of compounds was preserved with substitution. The homologous enantiomeric pairs showed better resolution when there was an additional OH group near the chiral centers (position 7 on the cannabinoid structure). Better resolution was observed also for the enantiomeric pair that had the smaller alkyl side chain. These differences indicated that the additional OH group contributed to a better discrimination of the enantiomers by the chiral sites of the stationary phase and that the bulkier alkyl side chain reduced it. The chromatographic resolution of two enantiomeric pairs of nonclassical cannabinoids HU-249 and HU-250, HU-255 and HU-256, was compared both in ethanol and 2-propanol. Both enantiomeric pairs showed relatively high resolution and selectivity, but the rigid benzofuran analogs (HU-249 and HU-250) exhibited better resolution using 2-propanol, in spite of the flexibility of the open chain analog (HU-255 and HU-256) and its additional OH group. The elution order of all the cannabinoids was (+)/(?) using both solvents. Unusual solvent effects were displayed by one enantiomeric pair, Δ⁶-THC, which was resolved easily using 2-propanol, but whose elution order reversed with 1% ethanol in the mobile phase. Partial separation was obtained at 5% ethanol [elution order (+)/(?)] and full separation was obtained at 0.5% ethanol [elution order (?)/(+)]. © 1995 Wiley-Liss, Inc.     

Direct chromatographic resolution of racemic cyclohexylaminoglutethimide and its acetylated metabolite using cellulose-based chiral stationary phase

Racemic cyclohexylaminoglutethimide (±ChAG) and its acetylated metabolite (±ChAG) were resolved by a direct chromatographic method using a Chiracel OD column without derivatization. Maximum resolutions (R) of 4.89 and 0.74 were obtained for the enantiomers of cyclohexylaminoglutethimide and its acetylated metabolite, respectively.     

Development and validation of a gradient reversed-phase high-performance liquid chromatographic assay for S(−-2-(N-propyl-N-2-thienylethylamino)-5-hydroxytetralin (N-0923) from a transdermal delivery system

A gradient reversed-phase HPLC method for potency determination of N-0923 (10 mg0 from a transdermal delivery system (TDS), was developed and validated with single point calibration yusing internal standard quantitation. N-0923 and the internal standard, N-0434, are eluted from a reversed-phase C₁₈ column using a gradient which contains 0.1 M triethylamine-0.04 M citrate buffer, pH 5.9, water, and acetonitrile with UV detection at 272 nm. N-0923 is isolated from the transdermal delivery system by extraction with n-heptane followed by extraction of the resulting organic phase with 0.1 M citric acid containing the internal standard. The method weas free from matrix interferences in both untreated and forced degraded placebo delivery systems. Acceptable linearity and quantitative recovery form spiked placebo delivery systems over the range 50–150% of nominal label claim were demonstrated. Within-day assay precision from individual samples of active transdermal dlivery systems (n = 10) was 5.6% R.S.D. The detection limit was at least 0.1 μg/ml which is equivalent to 0.05% of the working standard concentration. Replicate injection precision at this level was 0.08% R.S.D. (n =4). Analysis of thermally stressed active and placebo delivery systems with this HPLC method and photodiode-array detection showed that the chromatography was stability-indicating as demonstrated by the absence of measurable interferences from principal degradation products of either the N-0923 or the delivery system excipients.     

Chiral separation of tryptophan enantiomers by liquid chromatography with BSA-silica stationary phase

The separation of tryptophan enantiomers was carried out with medium-pressure liquid chromatography using BSA (bovine serum albumin)-bonded silica as a chiral stationary phase. The influence of various experimental factors such as pH and ionic strength of mobile phase, separation temperature, and the presence of organic additives on the resolution was studied. In order to expand this system to preparative scale, the loadability of sample and the stability of stationary phase for repeated use were also examined. The separation of tryptophan enantiomers was successful with this system. The data indicated that a higher separation factor (α) was obtained at a higher pH and lower temperature and ionic strength in mobile phase. Addition of organic additives (acetonitrile and 2-propanol) in mobile phase contributed to reduce the retention time of L-tryptophan. About 30% of the separation factor was reduced after 80 days of repeated use.     

Preparation of chiral statonary phase from an α-amino phosphonate

A chiral statonary phase (CSP) derived from an N-(3,5-dinitrobenzoyl)-α-aminobenzylphosphonate has been prepared and evaluated for its utility in the direct separation of enantiomers. This CSP, 2, is structurally related to earlier N-(3,5-dinitrobenzoyl)-α-acids acid-derived phases (e.g., CSP 1), but the mode of attachment to the support is different. In scope; CSP 2 is qualitaively similar to CSP 1. However, it differs quantitatively from CSP 1, showing either greater or lesser selectivity for different pairs of enantiomers.     

Enzymatic and chromatographic chiral discrimination of racemic (thio)glycidyl esters: Part II. Optical resolution of racemic (thio)glycidyl esters on modified cellulose chiral stationary phases

Chiral chromatography on cellulose tris(3,5-dimethylphenyl carbamate) (Chiralcel OD) and cellulose tribenzoate (Chiralcel OB) coated stationary phases has been successfully used for the optical resolution of rac-(thio)glycidyl esters (acetate, propionate, butyrate). Glycidyl esters could sufficiently be resolved on the OD column whereas for the thio analogues baseline resolution is obtained on CSP OB using hexane/2-propanol mobile phases. The separation factor (α) and resolution (R_S) depend on column temperature, eluent composition, and flow rate, respectively. Best results were obtained for the butyrates and at low temperatures in general. © 1993 Wiley-Liss, Inc.     

Resolution of terfenadine enantiomers by beta-cyclodextrin chiral stationary phase high-performance liquid chromatography.

Enantiomers of terfenadine were resolved by high-performance liquid chromatography (HPLC) using a chiral stationary phase (CSP) column packed with beta-cyclodextrin (beta-CD) covalently bound to silica. Separation was achieved in both the reverse phase and normal phase modes. Resolution of enantiomers was confirmed by ultraviolet-visible absorption, circular dichroism, and mass spectral analysis.     

The influence of solute structure,temperature, and eluent composition on the chiral separation of 21 aminotetralins on a cellulose tris-3,5-dimethylcarbamate stationary phase in high-performance liquid chromatography

In the present study 21 different chiral aminotetralins were used to investigate the mechanism behind their enantiomeric resolution (R_s) on a commercially available high-performance liquid chromatography (HPLC) cellulose tris-3,5-dimethylcarbamate stationary phase. The differences in the chemical structures of the aminotetralins used were never directly located on the chiral carbon. Their chromatographic behavior was studied for two eluent compositions at six different temperatures. Hydrogen bonding and π? π interactions are two possible solute–chiral stationary phase (CSP) interactions. Differences between the enantiomers in their spatial arrangement of positions involved in solute–CSP interactions were the major forces behind enantiomeric separation. Lowering the temperature increased the R_s for the aminotetralins having π-electrons not directly bonded to that part of the molecule where the hydrogen bonding with the CSP is located. Primary amines and secondary amines, with a sufficiently short N-alkyl substituent, showed a decrease of R_s with lower temperatures, all other aminotetralins yielding an increase of R_s with lower temperatures. © 1992 Wiley-Liss, Inc.