Curt Pettersson

Separation of enantiomeric amines by ion-pair chromatography

A high-performance liquid chromatographic method for the separation of optical isomers (enantiomers) of amines is described. It is based on ion-pair chromatography with a chiral counter ion in a system with an organic mobile phase and an adsorbing stationary phase. The method has been applied to enantiomers of 1-aryloxy-3-isopropylamine-2-propanol derivatives (alprenolol, metoprolol, propranolol) which are completely resolved with (+)-10-camphorsulphonate as the counter ion. Studies of the influence of the counter-ion structure and the mobile phase composition are presented.

Separation of enantiomers using cellulase (CBH I) silica as a chiral stationary phase

A new chiral stationary phase for high-performance liquid chromatography based on a glycoprotein (celllulase, CBH I) isolated from a culture filtrate of a fungus, Trichoderma reesei, was prepared. Chiral acidic and basic drugs were resolved into their enantiomers on this phase. Compared with other similar chiral phases, high enantioselectivity was obtained for β-blocking agents despite low capacity factors. As much as 200 nmol of propranolol in a single injection could be separated into its enantiomers on an analytical column (250 × 5.0 mm I.D.) without loss of resolution. No significant decrease in enantioselectivity was observed after daily use of the phase during a period of 4 months with varying mobile phase compositions. The retention and enantioselectivity of amines increased with increasing pH of the mobile phase, whereas the opposite effect was observed for acids. Addition of organic solvents to the mobile phase both decreased the retention and increased the enantioselectivity for the analytes.

Hydrogen bonding descriptors in the prediction of human in vivo intestinal permeability

Hydrogen bonding has been identified as an important parameter for describing drug permeability. Recently, we derived models for predicting intestinal permeability using the hydrogen bonding descriptors polar surface area (PSA) and number of hydrogen bond donors (HBD), and a lipophilicity descriptor [J. Med. Chem. 41 (1998) 4939]. We have now explored other types of hydrogen bonding descriptors to see if these improve the models. Both an experimental hydrogen bonding descriptor, deltalogP, and calculated descriptors, based either on semiempirical calculations or on experimentally derived hydrogen bond strength values of small molecules, were used. Principal component analyses (PCA) were performed in order to characterize the different parameters, using both a drug data set and a data set of small non-drug-like molecules for which deltalogP-values had been published. For a set of diverse drug molecules, for which human intestinal permeability data was available, a PLS-analysis was performed to study the correlation of permeability to the different hydrogen bonding parameters. No correlation could be identified between deltalogP and human intestinal permeability in this data set. However, the combination of a hydrogen bond donor descriptor, a general hydrogen bonding descriptor and a lipophilicity descriptor enabled the prediction of human intestinal permeability, whereas hydrogen bond acceptor descriptors were found to be less important. The obtained models successfully predicted the intestinal permeability values of two external data sets.

Chromatographic separation of enantiomers of acids with quinine as chiral counter ion

Abstract A study of the separation of enantiomers of carboxylic and sulphonic acids as diastereomeric ion pairs with quinine as the chiral counter ion is presented. Different modified silica adsorbents have been used as stationary phases in order to regulate retention and stereoselectivity. The retention can also be controlled by the concentration of quinine and the acid in the mobile phase as well as by the relative amounts of the solvent components dichloromethane, hexane and pentanol. Stable and reproducible chromatographic systems are obtained with a low content of water (80 ppm) in the mobile phase.

Chiral resolution of carboxylic and sulphonic acids by ion-pair chromatography

Abstract Enantiomers (optical isomers) of carboxylic and sulphonic acids have been separated in a chromatographic system having a chiral counter ion in an organic solvent as mobile phase and a surface-modified, polar silica (LiChrosorb DIOL) as adsorbing stationary phase. Separation factors of 1.3–1.5 for the enantiomers of 10-camphorsulphonic acid and moderately hydrophobic carboxylic acids have been obtained with quinine as chiral counter ion. With UV-absorbing counter ions, such as quinine and quinidine, even non-UV-absorbing acids give a response in the UV detector. The detector response and the stereoselectivity can be regulated by polar additives, e.g ., 1-pentanol, and it will also depend on the anion in the mobile phase. The influence of solute and counter ion structure on the stereoselectivity is discussed. Applications of the chromatographic systems to practical problems are presented.

Chiral stationary phases based on intact and fragmented cellobiohydrolase I immobilized on silica

Abstract Cellobiohydrolase I (CBH I) was enzymatically degraded into two fragments which were immobilized on silica. Each fragment was shown to contain at least CBH I was immobilized via its carboxylic groups onto aminopropyl silica and via its amino groups to aldehyde silica. The CBH I-aminopropyl silica separ

Separation of enantiomers using α-chymotrypsin-silica as a chiral stationary phase

Abstract Direct separations of enantiomeric acids and N-substituted amino acids using α-chymotrypsin adsorbed or covalently immobilized on silica as the chiral stationary phase are presented. Phosphate buffer was used as the mobile phase. α-Chymotrypsin covalently bound to an aldehyde-activated silica resulted in a stable phase as opposed to α-chymotrypsin adsorbed on silica. The covalently bound stationary phase maintained the chiral discrimination ability even after more than 4000 column volumes of mobile phase had passed through the column. An increase in the amount of α-chymotrypsin from 110 to 140 mg/g silica was found to affect the retention by a factor of two without significantly influencing the enantioselectivity. The effect of pH, ionic strength and charged modifiers was studied in order to find optimum conditions for chiral separations. The chiral resolution could be optimized by adjusting the pH and by addition of octanesulphonate to the mobile phase.

Influence of enantiomeric purity of a chiral selector on stereoselectivity

Abstract A complete separation and determination of (R)- and (S)-propranolol is possible even when the chiral counter ion in the mobile phase, benzoxyca

Development of a chiral non-aqueous capillary electrophoretic system using the partial filling technique with UV and mass spectrometric detection.

A chiral non-aqueous CE system with UV and mass spectrometric detection has been developed. The enantioseparation was promoted by diastereomeric complex (ion-pair) formation between the amines (e.g. salbutamol, atenolol) and the chiral selector, (-)-2,3:4,6-di-O-isopropylidene-2-keto-L-gulonic acid [(-)-DIKGA]. Different solvent mixtures were studied, as well as different concentrations of (-)-DIKGA and ammonium acetate in the background electrolyte. A partial filling technique was developed with a selector plug composed of (-)-DIKGA and ammonium acetate in a solvent mixture of methanol and 2-propanol. The separated enantiomers of pronethalol were detected by a Q-TOF MS system equipped with a sheath-flow electrospray ionization interface.

Non-aqueous capillary electrophoretic separation of enantiomeric amines with (−)-2,3:4,6-di-O-isopropylidene-2-keto-l-gulonic acid as chiral counter ion

(-)-2,3:4,6-Di-O-isopropylidene-2-keto-L-gulonic acid [(-)-DIKGA] has been introduced as a chiral counter ion in non-aqueous capillary electrophoresis. High enantioresolutions (R(s)> or =3) were obtained for amines, e.g., pronethalol, labetalol and bambuterol. Methanol containing NaOH and (-)-DIKGA was used as the background electrolyte. The counter ion concentration and the nature of the injection medium were found to affect the chiral separation. Covalent coating of the fused-silica capillary reduced the electro-osmotic flow resulting in improved enantioresolutions.