Chiral Liquid Chromatography

1 Introduction.- 1 Molecular asymmetry.- 1.1 Chirality.- 1.2 Chiroptical properties.- 1.3 Asymmetric centres.- 1.4 Twisted structures.- 1.4.1 Cumulenes.- 1.4.2 Spiro compounds.- 1.5 Hindered rotation.- 1.5.1 Atropisomers.- 1.5.2 Ansa compounds.- 1.6 Molecular overcrowding.- References.- 2 The importance of enantiomer separations.- 2.1 Introduction.- 2.2 Enantiomers versus racemates: questions of efficacy and safety.- 2.3 Enantiomers versus racemates: questions of pharmacokinetics.- 2.4 Experimental considerations for investigation of pure enantiomers.- 2.5 Conclusion.- References.- 3 Chiral liquid chromatography: past and present.- 3.1 Historical perspectives.- 3.2 Three-point rule.- 3.3 Development of commercially-available or easily accessible direct chiral resolution methods.- 3.3.1 Chiral ligand exchange chromatography.- 3.3.2 Synthetic multiple-interaction CSPs.- 3.3.3 Protein CSPs.- 3.3.4 Cyclodextrin CSPs.- 3.3.5 Cellulose CSPs.- 3.3.6 Synthetic polymer CSPs.- 3.3.7 Chiral ion-pair chromatography.- 3.3.8 Other direct chiral resolution methods.- 3.4 Present status of chiral liquid chromatography.- References.- 2 Chiral Derivatization.- 4 Chiral derivatization.- 4.1 Introduction.- 4.2 Diastereomer formation.- 4.3 Reagents.- 4.3.1 Acylating reagents.- 4.3.2 Amine reagents.- 4.3.3 Isocyanates and activated carbamates.- 4.3.4 Isothiocyanates.- 4.3.5 Chloroformates.- 4.3.6 Reagents based on o-phthalaldehyde and chiral thiols.- 4.3.7 Other reagents.- 4.4 Separation mechanisms.- 4.5 Detection.- 4.6 Applications.- 4.6.1 Resolution of l-isopropyl-amino-2-propanols (?-blockers).- Acknowledgements.- References.- 3 Direct Chiral Resolution.- 5 Chiral ligand exchange chromatography.- 5.1 Introduction.- 5.2 Immobilized metal coordinating ligands.- 5.3 Metal coordinating ligands as mobile phase additives.- 5.4 Ligand exchange mechanism.- 5.5 Enantiomeric resolution of d and l amino acids.- 5.5.1 Free amino acids.- 5.5.2 Dansyl amino acids.- 5.5.3 Imino acids.- 5.6 Parameters affecting ligand exchange.- 5.6.1 Metal ion.- 5.6.2 Metal to ligand ratio.- 5.6.3 Concentration of metal complex.- 5.6.4 Eluent pH.- 5.6.5 Elution order.- 5.6.6 Organic modifier.- 5.6.7 Stereoselectivity.- 5.7 Conclusion.- References.- 6 Synthetic multiple-interaction chiral bonded phases.- 6.1 Introduction.- 6.2 Survey of multiple-interaction CSPs.- 6.2.1 Historical development.- 6.2.2 Survey.- 6.2.3 Preparation of CSPs.- 6.2.4 General chromatographic considerations.- 6.3 Resolutions of enantiomeric solutes.- 6.3.1 Survey.- 6.3.2 Derivatization of solutes.- 6.3.3 Limitations.- 6.4 Special applications.- 6.4.1 Preparative separations.- 6.4.2 Enantiomeric trace analysis.- 6.4.3 Elution order and configuration.- 6.5 Conclusion.- References.- 7 Immobilized proteins as HPLC chiral stationary phases.- 7.1 Introduction.- 7.2 The AGP-CSP.- 7.2.1 Preparation of the CSP.- 7.2.2 Solute selectivity.- 7.2.3 Mobile phase effects.- 7.2.4 Effect of pH.- 7.2.5 Effect of mobile phase modifiers.- 7.2.6 Applications of the AGP-CSP to pharmacological studies.- 7.3 The bovine serum albumin (BSA) CSP.- 7.3.1 Preparation of the CSP.- 7.3.2 Solute selectivity.- 7.3.3 Mobile phase effects.- 7.3.4 Effect of pH.- 7.3.5 Effect of buffer concentration.- 7.3.6 Effect of mobile phase modifiers.- 7.3.7 Applications of BSA-CSP to pharmacological studies.- 7.4 Chiral phases based on enzymes and other biological polymers.- 7.4.1 Immobilized ovomucoid.- 7.4.2 Immobilized ?-chymotrypsin.- 7.5 Conclusion.- References.- 8 Cyclodextrin inclusion complexation.- 8.1 Structure of cyclodextrin.- 8.2 Mechanism of chiral separation.- 8.3 Inclusion complexes.- 8.4 Examples of chiral separations.- 8.4.1 ?-Cyclodextrin column.- 8.4.2 ?-Cyclodextrin column.- 8.4.3 ?-Acetylated cylcodextrin.- 8.4.4 Aromatic and alkyl groups and their behaviour with cyclodextrin.- 8.5 Choosing conditions for separation.- 8.5.1 Mobile phase effects.- 8.5.2 Salt and pH effects.- 8.5.3 Effect of temperature.- 8.5.4 Effect of flow rate.- 8.6 Care and use of cyclodextrin columns.- 8.7 Advantages and disadvantages.- 8.8 Use of cyclodextrins in mobile phase.- References.- 9 Binding to cellulose derivatives.- 9.1 Cellulose.- 9.2 Cellulose triacetate.- 9.3 Cellulose derivatives.- 9.3.1 Applications.- 9.3.2 Practical considerations.- 9.4 Derivatives of other polysaccharides.- References.- 10 Binding to synthetic polymers.- 10.1 Introduction.- 10.2 Helical polymethacrylates.- 10.2.1 Applications of poly(triphenylmethyl methacrylate).- 10.2.2 Practical considerations.- 10.3 Polyacrylamides and polymethylacrylamides.- 10.4 Other synthetic polymer CSPs.- References.- 11 Ion-pairing.- 11.1 Introduction.- 11.2 Retention principles.- 11.3 Desired properties of chiral counter-ions.- 11.3.1 Acid-base character of counter-ions.- 11.3.2 Kind and nature of counter-ions.- 11.3.3 Presence of functional groups suitable for tertiary interaction.- 11.3.4 Enantiomeric purity of chiral counter-ions.- 11.3.5 Other important properties of chiral counter-ions.- 11.4 Availability of chiral counter-ions.- 11.5 Separation variables.- 11.5.1 Influence of mobile-phase composition.- 11.5.2 Stationary-phase selection.- 11.5.3 Influence of concentration of chiral counter-ion and of mobile-phase additive on retention.- 11.5.4 Influence of optical antipode selection of chiral counter-ion on selectivity of separation.- 11.5.5 Influence of column temperature and flow rate.- 11.6 Problems of diastereomeric complex formation using chiral counter-ions: advantages and limitations.- 11.7 Combination of ion-pair chromatography and inclusion complex formation.- References.- 12 Other direct chiral resolution methods.- 12.1 Introduction.- 12.2 Minor variations on more common methods.- 12.3 More unusual direct chiral resolution methods.- References.- 4 Strategy for Development of LC Enantiomeric Determination Methods.- 13 Consideration of other techniques.- 13.1 Introduction.- 13.2 Measurement of optical rotation.- 13.3 Nuclear magnetic resonance spectroscopy.- 13.4 Gas chromatography.- 13.5 Other chromatographic techniques.- 13.6 Radioimmunoassays.- References.- 14 Choice of chiral LC systems.- 14.1 Reference to known examples.- 14.2 Relative merits of LC enantioseparation methods.- 14.2.1 Direct v. indirect methods.- 14.2.2 Chiral stationary phases v. mobile-phase additives.- 14.2.3 Choice of chiral stationary phase.- 14.3 Method development.- 14.4 More complex enantiomer separation problems.- 14.4.1 Preparative enantiomer separations.- 14.4.2 Sensitivity.- 14.4.3 Limited time for method development.- 14.4.4 Determination of trace enantiomers in the presence of excess of the antipode.- 14.4.5 Other typical enantiomer separation problems.- References.- 15 Optimization.- 15.1 Introduction.- 15.2 Optimization methods.- 15.2.1 Chromatographic response surface mapping.- 15.2.2 Modified sequential simplex approach.- 15.3 Comparison of methods for oxamniquine and its metabolic precursor.- 15.4 Conclusion.- References.- 5 Future Trends and Requirements.- 16 Future trends and requirements.- 16.1 Introduction.- 16.2 Hardware.- 16.2.1 Detectors.- 16.2.2 Miniaturization.- 16.2.3 Multicolumn systems.- 16.3 Trends in the development of new chiral packings.- 16.3.1 Recognition mechanisms.- 16.3.2 New types of chiral stationary phases.- 16.3.3 Use of computer-assisted modelling.- 16.3.4 Conclusions.- 16.4 Preparative liquid chromatography.- 16.4.1 Preparative chiral separations.- 16.4.2 Preparative diastereoisomer separations.- 16.4.3 Packings for preparative chiral HPLC.- References.