Amylose-based Stationary Phase Research Articles

Insight into GEBR-32a: Chiral Resolution, Absolute Configuration and Enantiopreference in PDE4D Inhibition.

Alzheimer’s disease is the most common type of dementia, affecting millions of people worldwide. One of its main consequences is memory loss, which is related to downstream effectors of cyclic adenosine monophosphate (cAMP). A well-established strategy to avoid cAMP degradation is the inhibition of phosphodiesterase (PDE). In recent years, GEBR-32a has been shown to possess selective inhibitory properties against PDE type 4 family members, resulting in an improvement in spatial memory processes without the typical side effects that are usually correlated with this mechanism of action. In this work, we performed the HPLC chiral resolution and absolute configuration assignment of GEBR-32a. We developed an efficient analytical and semipreparative chromatographic method exploiting an amylose-based stationary phase, we studied the chiroptical properties of both enantiomers and we assigned their absolute configuration by 1H-NMR (nuclear magnetic resonance). Lastly, we measured the IC50 values of both enantiomers against both the PDE4D catalytic domain and the long PDE4D3 isoform. Results strongly support the notion that GEBR-32a inhibits the PDE4D enzyme by interacting with both the catalytic pocket and the regulatory domains.

Liquid Chromatographic Separation and Thermodynamic Investigation of Ethyl Nipecotate Enantiomers on Immobilized Amylose-Based Chiral Stationary Phase.

Ethyl nipecotate enantiomers are widely used as chiral building blocks in the synthesis of drug substances. An efficient and economic chiral high-performance liquid chromatographic method for determination of enantiomeric purity of ethyl nipecotate is developed and validated. Chiral separation was achieved on immobilized amylose-based stationary phase using a mixture of n-hexane: ethanol: diethylamine (80:20:0.1, v/v/v) as mobile phase. Resolution between R-(-)-ethyl nipecotate (REN) and S-(+)-ethyl nipecotate (SEN) peaks was found to be 3.59. The detector response of SEN exhibited an excellent linearity over the concentration range of 4.5-120μgmL-1. The limit of detection and limit of quantification for SEN were 0.016 and 0.045μg and REN were 0.015 and 0.043μg, respectively. The influence of column oven temperatures on chiral retention and separation was studied in the range of 25°C to 50°C; the thermodynamic parameters ΔH°, ΔS° and ΔG° were evaluated from van't Hoff plots and used to explain the strength of interaction between analyte and stationary phase.

A Validated LC Method for the Determination of Enantiomeric Purity of Clopidogrel Intermediate Using Amylose-Based Stationary Phase

A simple chiral liquid chromatographic method for the enantiomeric purity of methyl (2S)-(2-chlorophenyl)-(2-(thiophen-2-yl)ethylamino) acetate—a clopidogrel intermediate—is proposed. Chromatographic separations are carried out isocratically on a chiral amylose-based column (ChiralPAK AD-H) using a mobile phase consisting of hexane/isopropanol/diethylamine, 90/10/0.1, v/v/v. Under the optimum conditions, the resolution between the two isomers was found to be more than 4.5. The method was developed and validated in terms of linearity, precision and accuracy, limit of detection (LOD) and quantitation (LOQ) and robustness. The proposed approach has been successfully applied to bulk samples for evaluating enantiomeric purity.

Evaluation of differences between Chiralpak IA and Chiralpak AD-RH amylose-based chiral stationary phases in reversed-phase high-performance liquid chromatography.

Polysaccharide-based chiral stationary phases can be used for the enantioselective separation of a wide range of structurally different compounds. These phases are available with chiral selectors coated or immobilized on silica gel support. The means of attachment of the chiral selector to the carrier can influence the separation performance of these stationary phases. This paper deals with evaluation of differences in the separation abilities of coated Chiralpak AD-RH versus immobilized Chiralpak IA amylose-based stationary phases in the reversed-phase mode of high-performance liquid chromatography. A set of chiral analytes was separated under acidic and basic conditions. Differences were observed in the enantioseparation potential of the tested phases. The linear-free energy relationship and additional evaluation of ionic interactions were used to ascertain whether the interactions that participate in retention and enantioseparation are affected by the means of preparation of these phases. All the interactions covered by the linear-free energy relationship were significant for the studied phases and their absolute values were almost always higher for the coated phase. Ionic interactions were found to be more important on the immobilized stationary phase but did not contribute to any improvement in the enantioselective separation performance.

A Validated Chiral LC Method for Enantiomeric Separation of Nebivolol Stereoisomers in Bulk Drugs and Dosage Forms on Amylose-Based Stationary Phase

A novel and reproducible isocratic normal phase liquid chromatographic method was developed for the quantitative determination of 10 stereoisomers of Nebivolol in pharmaceutical bulk drugs and dosage forms. The method was developed using an amylose-based chiral stationary phase, Chiralpak AD-3 (250 × 4.6 mm, 3 μm) column with mobile phase containing n-hexane-ethanol-isopropanol-diethanolamine in the ratio 42:45:13:0.1 (v/v/v/v). The eluted compounds were monitored at 280 nm. Ten stereoisomers of Nebivolol were well separated with resolution >2.0 for all pair of components. The developed method was validated as per International Conference on Harmonization (ICH) guidelines with respect to specificity, linearity (R(2) value >0.999), limit of detection, limit of quantification, accuracy (recovery range 95.8-103.2%), precision (relative standard deviation, RSD, <2.5%) and robustness. Nebivolol sample solutions were found to be stable when characterized over a period of 48 h. Forced degradation studies were also performed to demonstrate the stability-indicating power of the developed HPLC method. The method was found to be rugged and robust.

Development of HPLC/fluorescence detection method for chiral resolution of dansylated benzimidazoles derivatives

The development of high performance liquid chromatography method on amylose-based stationary phase (Chiralpak AD) with n-hexane-2-propanol (90:10, v/v) as mobile phase allowed the enantioseparation of non-dansylated and dansylated benzimidazole derivatives, prepared from potent-AMPK activators, to be achieved. Using both fluorescence and ultraviolet detection, limits of detection and quantification were determined. Fluorescence detection seems to be the most appropriate technique since the first enantiomer of dansylated benzimidazole 8 eluted with a limit of quantification of 2.25 nm. The quantification limit was improved 10-fold by fluorescence detection compared with a previous report describing mass spectrometry detection. Linearity and repeatability parameters were validated. These lower limits obtained by fluorescence detection, associated with good resolution observed for the dansylated derivatives, make this chiral methodology convenient for the use of these fluorescent potent-AMPK activators as probes to elucidate their cellular localization and their mechanism of action.

ENANTIOMERIC LC SEPARATION OF METOLAZONE ON AMYLOSE BASED SORBENT

A simple, rapid and robust LC method was developed and validated for the enantiomeric separation of metolazone. The enantiomers of metolazone were resolved on a Chiralpak AD-H (amylose based stationary phase) column using a mobile phase consisting of Hexane: 2-propanol: Methanol: Acetic acid (80:10:10:0.2, v/v) at a flow rate of 1.0 mLmin -1. The resolution between the enantiomers was found to be not less than 3.0 in optimized method. The presence of acetic acid in the mobile phase played an important role, in enhancing chromatographic efficiency and resolution between the enantiomers. The developed method was extensively validated and proved to be robust. The calibration curve for enantiomers showed excellent linearity over the concentration range of 5mgmL-1 to 50mgmL-1. The limit of detection and limit of quantification for enantiomers were 0.05 and 0.16 mgmL-1, respectively. The proposed method was found to be suitable and accurate for quantitative determination of enantiomers in bulk drug substance.

Enantioseparation of Secnidazole by High-Performance Liquid Chromatography Using Amylose-Based Stationary Phase

The secnidazole, a drug used in hepatic amebiasis, giardiasis and bacterial vaginosis, was enantioseparated on a semi-preparative scale by high performance liquid chromatography (HPLC), using chiral stationary phase (CSP) containing amylose tris (3, 5-dimethylphenyl) carbamate on silica gel (Chiralpak® AD). The experiments were carried out under normal phase conditions and the separation method exhibited very high selectivity and resolutions. The chromatographic parameters and the effects of column temperature on the retention time and selectivity were evaluated. Thermodynamic parameters were obtained from van't Hoff plots, and the elution order of the enantiomers was determined by circular dichorism. The enantiomers of secnidazole were separated under overloaded conditions with a good performance.

VALIDATED CHIRAL LC METHOD FOR DEXRABEPRAZOLE ON REVERSE PHASE AMYLOSE BASED STATIONARY PHASE

A simple, rapid and robust LC method was developed and validated for the enantiomeric separation of dexrabeprazole in bulk drug and formulation. The enantiomers of dexrabeprazole were resolved on a Chiralpak AD-RH (amylose based stationary phase) column using a mobile phase consisting of water: acetonitrile (50:50, v/v) at a flow rate of 0.5 ml min -1. The resolution between the enantiomers was found to be more than 1.5 in optimized method. The developed method was extensively validated and proved to be robust. The calibration curve for (S)-enantiomer showed excellent linearity over the concentration range of 0.05 µg ml-1 (LOQ) to 1 µg ml-1. The limit of detection and limit of quantification for (S)-enantiomer were 0.015 µg ml -1 and 0.05 µg ml-1, respectively. The percentage recovery of the (S)-enantiomer ranged between 97 to 101 % in bulk drug samples of dexrabeprazole. The proposed method was found to be suitable and accurate for quantitative determination of (S)-enantiomer in bulk drug substance.

Chiral Separation of Tenatoprazole and Several Related Benzimidazoles by Normal Phase LC Using Amylose-Based Stationary Phase

Simple and efficient analytical LC methods using amylose-based stationary phase Chiralpak AS-H were developed for direct enantioseparation of tenatoprazole and several related benzimidazoles. The chromatographic experiments were performed in the normal phase mode with n-hexane–ethanol–triethylamine (TEA) as mobile phase. The effects of the mobile phase additive, concentration of organic modifiers and column temperature were studied for the enantioseparation. The thermodynamic parameters were also calculated from the van’t Hoff plots. It was found that the enantioseparations were all enthalpy driven. The enantiomers of all compounds were resolved (R s > 3.3) within 14 min using n-hexane–ethanol–TEA (20:80:0.1%, v/v/v) as mobile phase with a flow rate of 0.4 mL min−1 at 40 °C. The optimized method was validated for determination of the enantiomers of tenatoprazole in terms of linearity, precision and accuracy according to ICH guidelines and applied to the assay of tenantoprazole bulk drugs. The proposed method was shown to be accurate and suitable for the quantitative determination of tenatoprazole enantiomers.

Development and Validation of Chiral LC Method for the Enantiomeric Separation of Duloxetine on Amylose Based Stationary Phase

A simple, rapid, and robust liquid chromatography method was developed and validated for the enantiomeric separation of duloxetine in bulk drug substance. The enantiomers of duloxetine were resolved on a Chiralpak AD-H (amylose based stationary phase) column using a mobile phase consisting of n-hexane-ethanol-diethyl amine (80:20:0.2, v/v/v) at a flow rate of 1.0 mL/min. The resolution between the enantiomers was found to be not less than 2.8 in optimized method. The presence of diethyl amine in the mobile phase played an important role in enhancing chromatographic efficiency and resolution between the enantiomers. The developed method was extensively validated and proved to be robust. The calibration curve for (R)-enantiomer showed excellent linearity over the concentration range of 750 ng/mL (LOQ) to 7500 ng/mL. The limit of detection and quantitation for (R)-enantiomer were 250 and 750 ng/mL, respectively. The percentage recovery of the (R)-enantiomer ranged between 98.3% to 101.05% in bulk drug samples of duloxetine. The proposed method was found to be suitable and accurate for quantitative determination of (R)-enantiomer in bulk drug substance.

Enantiomeric LC Separation of Epinephrine on Amylose based sorbent

A simple, rapid, and robust chiral HPLC method has been developed and validated for separation of the enantiomers of epinephrine, l-1-(3,4-dihydroxyphenyl)-2-(methylamino)ethanol, an antihypertensive drug, in the bulk drug. The enantiomers were resolved on an amylose-based stationary phase with n-hexane–2-propanol–methanol–trifluoroacetic acid–diethylamine 90:05:05:0.2:0.2 (v/v) as mobile phase at a flow rate of 1.0 mL min−1. In the optimized method resolution between the enantiomers was not less than 3.0. The trifluoroacetic acid and diethylamine in the mobile phase were important for enhancing chromatographic efficiency and hence the resolution of the enantiomers. The method was extensively validated and proved to be robust. The calibration plot for the d enantiomer was highly linear over the concentration range 100–2,000 μg mL−1. The limits of detection and quantification for the d enantiomer were 0.15 and 0.45 μg mL−1, respectively. Recovery of the d enantiomer from bulk drug samples of epinephrine ranged between 99.5 and 101.5%. Epinephrine sample solution was stable for up to 48 h. The method was suitable for accurate quantitative determination of the d enantiomer in the bulk drug substance

Preparative enantiomeric separation of potent AMP-activated protein kinase activator by HPLC on amylose-based chiral stationary phase: Determination of enantiomeric purity and assignment of absolute configuration

The development of high performance liquid chromatography method on amylose-based stationary phases (Chiralpak AD) has permitted to achieve the preparative enantioseparation of one benzimidazole derivative, potent-AMP-kinase (AMPK) activator with satisfactory yields. Analytical enantioseparation method was optimized and validated to determine the enantiomeric purity. Using the UV detection, repeatability, limits of detection (LD) and quantification (LQ) were determined. Single-crystal X-ray analysis was successful to determine the absolute configuration of the individual enantiomers. A relation between the retention order and the absolute configuration of the enantiomers was established.

A Validated Chiral LC Method for the Enantiomeric Separation of Repaglinide on Amylose Based Stationary Phase

A simple, isocratic, normal phase chiral HPLC method was developed and validated for the enantiomeric separation of repaglinide, (S)-(+)-2-ethoxy-4-N [1-(2-piperidinophenyl)-3-methyl-1-butyl] aminocarbonylmethyl] benzoic acid, an antidiabetic in bulk drug substance. The enantiomers of repaglinide were resolved on a ChiralPak AD-H (amylose based stationary phase) column using a mobile phase consisting of n-hexane: 2-propanol:trifluoroacetic acid (95:5:0.2 v/v/v) at a flow rate of 1.0 mL min−1. The resolution between the enantiomers was found to be not >3.5 in optimized method. The presence of trifluoroacetic acid in the mobile phase played an important role, in enhancing chromatographic efficiency and resolution between the enantiomers. The developed method was extensively validated and proved to be robust. The calibration curve for (R)-enantiomer showed excellent linearity over the concentration range of 900 ng mL−1 (LOQ) to 6,000 ng mL−1. The limit of detection and limit of quantification for (R)-enantiomer were 300 and 900 ng mL−1, respectively. The percentage recovery of the (R)-enantiomer ranged between 98.3 and 101.05% in bulk drug samples of repaglinide. Repaglinide sample solution and mobile phase were found to be stable up to 48 h. The developed method was found to be enantioselective, accurate, precise and suitable for quantitative determination of (R)-enantiomer in bulk drug substance.

Screening approach for chiral separation of pharmaceuticals: IV. Polar organic solvent chromatography

The aim of this work is to determine generic screening conditions and an initial simple separation strategy allowing the rapid separation of drug enantiomers in polar organic solvent chromatography (POSC). Four cellulose/amylose-based stationary phases were investigated in detail using two mobile phase basis solvents commonly applied in this mode, i.e. acetonitrile and methanol. Polar mode is interesting for use in purification of enantiomers. In a first step, the parameters potentially influencing the separation, such as addition of an alcohol to the polar organic solvent or the type of mobile phase additive(s), were examined by means of experimental designs. Afterwards, the factors found most important are investigated in more detail. Results showed that the cellulose- and amylose-based stationary phases have very broad and complementary enantiorecognition abilities in the POSC mode. The type of organic solvent for the mobile phase appeared to have a dramatic influence on the quality of the separation. Based on the results, a screening strategy was proposed. Enantioseparation was observed in more than 85% of the tested compounds and analysis times of last eluted peak were usually below 10 min.

A validated chiral LC method for the enantioselective analysis of Levetiracetam and its enantiomer R-α-ethyl-2-oxo-pyrrolidine acetamide on amylose-based stationary phase

A new, simple chiral HPLC method was developed for the enantiomeric separation of Levetiracetam, [( S)-α-ethyl-2-oxo-pyrrolidine acetamide], an antiepileptic drug in pharmaceutical formulations and in bulk materials. Enantiomeric separation was achieved on a chiralpak AD-H column using a mobile phase consisting of hexane and isopropanol in the ratio (90:10, v/v) at a flow rate of 1.0 ml/min. The resolution between the enantiomers was found to be not less than 7 in the optimized method. Interestingly, unwanted enantiomer, namely R-α-ethyl-2-oxo-pyrrolidine acetamide (( R)-enantiomer), was eluted prior to its mirror image in the developed method. The developed method was found to be selective in the presence of related impurities of Levetiracetam, namely N-(1-carbamoyl-propyl)-4-chloro-butyramide (Imp-1) and 1-ethyl-2-oxo-1-pyrrolidine acetic acid (Imp-2), and also under exposed conditions of UV light and 60 °C. The limit of detection (LOD) and limit of quantification (LOQ) of ( R)-enantiomer were found to be 900 and 2250 ng/ml, respectively, for 10 μl injection volume. The method precision for ( R)-enantiomer at limit of quantification level was within 8% R.S.D. Calibration curve for ( R)-enantiomer was linear over the studied ranges (2250–9000 ng) with correlation coefficient greater than 0998. The active pharmaceutical ingredient was extracted from its finished dosage form (tablet) using isopropanol. The percentage recoveries of ( R)-enantiomer were ranged from 94.2 to 102.6 and from 93.5 to 104.1 in spiked bulk and formulation samples of Levetiracetam, respectively. Levetiracetam sample solution and mobile phase are found to be stable for at least 48 h. The developed method was found to be rugged and robust. The proposed method was found to be suitable and accurate for the quantitative determination of ( R)-enantiomer in bulk drugs and commercial formulations. Chiralcel OD-H column can also be used as an alternative column for the above purpose.