Three column intermittent simulated moving bed chromatography: 3. Cascade operation for center-cut separations.

A general design methodology for chromatographic three fraction separation by application of the three column intermittent simulated moving bed (3C-ISMB) cascade is proposed and experimentally validated by studying the purification of an intermediately retained stereoisomer of nadolol, from an equimolar mixture of its four stereoisomers. The theoretical part shows that the 3C-ISMB cascade can be easily designed by applying Triangle Theory. Moreover, a re-scaling approach for the second stage is proposed so as to account for the fact that the feed flow rates to stage 2 are generally higher as compared to stage 1 due to dilution in the latter. Scaling the columns of the second stage accordingly enables to run both stages under optimal conditions with respect to switching time and step ratio, which is an important advantage as compared to integrated ternary processes. The experimental part starts with studying the linear adsorption behavior of nadolol in heptane/ethanol/DEA on Chiralpak AD for varying ratios of heptane and ethanol. Based on that, a solvent composition of Hept/EtOH/DEA 30/70/0.3 (v/v/v) is selected and the competitive multi-component Langmuir isotherm of the quaternary mixture is determined by frontal analysis. The resulting isotherm parameters are used to design several first stage experiments aiming at removal of the most retained component. The resulting ternary intermediate product is reprocessed in several second stage experiments studying various configurations. Finally, the dilution of the intermediate product with Hept/DEA yielding a solvent composition of Hept/EtOH/DEA 60/40/0.3 (v/v/v) is examined showing that the resulting increase in retention is beneficial for final product purities. Moreover, the reduction in viscosity compensates for the dilution as it enables higher flow rates. Dilution of the intermediate product is hence the best option, yielding highest overall cascade productivity (2.10gl(-1)h(-1)) and highest product purity (97.8%) requiring a specific solvent consumption of 12l/g of product.

Preparation of 2R, 3S, 2'R-nadolol enantiomer using S-(-)-menthyl chloroformate as a chiral derivatizing reagent.

Stereoisomers of nadolol were derivatized with S-(-)-menthyl chloroformate((-)-MCF) forming their diastereomers, RSR-nadolol-(-)-MCF, SRS-nadolol-(-)-MCF, RRS-nadolol-(-)-MCF and SSRnadolol-(-)-MCF. Diastereomeric mixture were then chromatographically resolved by preparative HPLC (JAIGEL-ODS-BP-L, 500 × 25 mm column) eluted with methanol-water (84:16, v/v) at flow rate 2.5 mL/min. RSR-nadolol-(-)-MCF diastereomer was hydrolyzed with 5% LiOH at 80°C for 48 h, and the decomposed mixture was further purified by semi-preparative HPLC. The purity and final yield of RSR-nadolol were 99.97% and 12.95%, respectively.

Optimized separation of beta-blockers with multiple chiral centers using capillary electrochromatography-mass spectrometry.

This work focuses on the simultaneous analysis of beta-blockers with multiple stereogenic centers using capillary electrochromatography-mass spectrometry (CEC-MS) with a vancomycin stationary phase. The critical mobile phase variables (composition of organic solvents, acid/base ratios) as well as column temperature and electric field strength, effecting enantioresolution and analysis time were first optimized sequentially. Next, to achieve global optimum a multivariate D-optimal design was used. Although multivariate approach did not improve enantioresolution any further, analysis time was significantly reduced. Under optimum CEC-MS conditions, all stereoisomers were resolved with resolution in the range 1.0-3.1 in less than 60 min with an average signal-to-noise (S/N) greater than 1000. The developed CEC-MS method has the potential to emerge as a screening method for analysis of multiple chiral compounds using a single protocol using the same column and mobile phase conditions, thus reducing the operation time and cost.

Adsorption of beta blockers to environmental surfaces.

Beta-adrenergic blocking agents (beta blockers) are widely used pharmaceuticals which have been detected in the environment. Predicting the transport and ultimate fate of beta blockers in the environment requires understanding their adsorption to soils and sediments, something for which little information is currently available. The objective of this work was to examine the adsorption of three beta blockers, propranolol, metoprolol and nadolol, to a natural alluvial material, as well as to six minerals present as components of the alluvial material. Batch adsorption experiments indicate that, for most of the minerals studied, compound hydrophobicity is an important predictor of adsorption, with propranolol,the most hydrophobic compound studied, adsorbing to the greatest extent. Results further suggest that, for the minerals studied, electrostatic effects are not a good predictor of adsorption; adsorption extent was not well-predicted by either surface zeta potential or by the difference between experiment pH and point of zero charge, despite the cationic nature af the three beta blockers at experiment pH values. Experiments were conducted to examine the effect of an anionic surfactant, sodium dodecyl benzene sulfonate (SDBS), on adsorption. Results indicate that SDBS significantly increases the adsorption of propranolol to two different sorbents. This result is potentially important because surfactants such as SDBS are likely to be present in wastewater effluents with beta blockers and could influence their mobility in the environment.

G-protein-coupled receptor chromatographic stationary phases. 2. Ligand-induced conformational mobility in an immobilized beta2-adrenergic receptor.

Membranes from a HEK-293 cell line expressing the beta(2)-adrenergic receptor (beta(2)-AR) have been immobilized on an artificial membrane liquid chromatographic stationary phase. The resulting phase was packed into a glass column (1.8 x 0.5 (i.d.) cm) and used in on-line chromatographic system. Frontal displacement affinity chromatography was used to determine the dissociation constants (K(d)) of CGP 12177A (552.6 nM) and (S)-propranolol (84.3 nM). Zonal displacement chromatography using CGP 12177A as the marker and racemic mixtures of the antagonists nadolol and propranolol demonstrated that the immobilized beta(2)-AR retained its ability to specifically bind these compounds. Similar experiments with (R)- and (S)-propranolol demonstrated that the immobilized receptor retained its enantioselectivity as (S)-propranolol displaced the CGP 12177 marker to a great extent that the (R)-enantiomer. The addition of the agonist butoxamine to the mobile phase increased the retention of the CGP-12177A as did the addition of the agonist fenoterol. These results indicate that the immobilized beta(2)-AR retained its ability to undergo ligand-induced conformational changes. The data from this study suggest that the immobilized beta(2)-AR can be used to screen for ligand binding interactions in both the resting and active states of the receptor.

Chiral separation and modeling of the three-chiral-center beta-blocker drug nadolol by simulated moving bed chromatography.

Nadolol, a beta-blocker used in the management of hypertension and angina pectoris, has three chiral centers and is currently marketed as an equal mixture of its four stereoisomers. Resolution of three of the four stereoisomers of nadolol was obtained previously by HPLC, with a complete separation of the most active enantiomer (RSR)-nadolol, on a column packed with perphenyl carbamoylated beta-cyclodextrin (beta-CD) immobilized onto silica gel. In this study, continuous separation of the target enantiomer of (RSR)-nadolol from its racemic mixture (which is a ternary mixture in the chromatographic system) was studied by non-linear SMB chromatography. Different regions of (2, 3) and (1, 2) complete separation regime were determined in the (m2, m3) region and the effect of non-linearity such as overall feed concentration and component composition on the separation performances was investigated. A direct simulation approach has been proposed to simulate the SMB separation performance for the pseudo-binary mixture of nadolol. The simulation was conducted on the basis of a shortcut method constituted only of the weak-key and strong-key components. The performance of the cyclic steady-state behavior of the SMB unit was predicted reasonably well. It was also discussed quantitatively that the complete separation region obtained from the shortcut method is a subset of the true complete separation region and the optimal separation conditions obtained differed slightly from the "true" separation.

Polymeric alkenoxy amino acid surfactants: II. Chiral separations of beta-blockers with multiple stereogenic centers.

Two amino acid-based (leucine and isoleucine) alkenoxy micelle polymers were employed in this study for the separation of multichiral center-bearing beta-blockers, nadolol and labetalol. These polymers include polysodium N-undecenoxy carbonyl-L-leucinate (poly-L-SUCL) and polysodium N-undecenoxy carbonyl-L-isoleucinate (poly-L-SUCIL). Detailed synthesis and characterization were reported in our previous paper [26]. It was found that poly-L-SUCIL gives better chiral separation than poly-L-SUCL for both nadolol and labetalol isomers. The use of 50-100 mM poly-L-SUCIL as a single chiral selector provided separation of four and three isomers of labetalol and nadolol, respectively. Further optimization in separation of both enantiomeric pairs of nadolol and labetalol was achieved by evaluation of type and concentration of organic solvents, capillary temperature as well type and concentration of cyclodextrins. A synergistic approach, using a combination of poly-L-SUCIL and sulfated beta-CD (S-beta-CD) was evaluated and it showed dramatic separation for enantiomeric pairs of nadolol. On the other hand for labetalol enantiomers, separation was slightly decreased or remain unaffected using the dual chiral selector system. Finally, simultaneous separation of both nadolol and labetalol enantiomers was achieved in a single run using 25 mM poly-L-SUCIL and 5% w/v of S-beta-CD in less then 35 min highlighting the importance of high-throughput chiral analysis.

Nadolol: high-pressure liquid chromatographic methods for assay, racemate composition and related compounds.

High-pressure liquid chromatographic (HPLC) methods have been developed for the determination of drug content, racemate A and related compounds in nadolol raw materials. The method for drug content and related substances resolved seven related compounds and several unknown impurities from the drug. The minimum quantifiable levels were 0.05% or less for four of the seven related compounds and 0.3% or less for the remainder. Total impurities in eight raw material samples ranged from 0.06 to 0.96% and assay levels ranged from 98.7 to 101.0%. The method was adapted for the determination of nadolol racemate A by a change in mobile phase composition. One raw material sample contained less than 40% of racemate A. Two samples which had a granular appearance were variable in racemate A content. The methods were adapted for the determination of drug and racemate A in nadolol tablets. Drug content in three tablet samples was between 96.2 and 98.4% and racemate A content was about 52%.