University of Bath PHD Resolution of enantiomers using cyclodextrins in NMR and HPLC Cooper, Andrew Donovan Award date: 1991 Awarding institution: University of Bath Link to publication Alternative formats If you require this document in an alternative format, please contact: [email protected] General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Download date: 06. Oct. 2021 Resolution of Enantiomers using Cyclodextrins in NMR and HPLC Submitted by Andrew Donovan Cooper, B.Sc., GRSC, for the degree of Ph.D. of the University of Bath 1991 COPYRIGHT Attention is drawn to the fact that copyright of this thesis rests with its author. This copy of the thesis has been supplied on condition that anyone who consults it is understood to recognise that its copyright rests with its author and that no quotation from the thesis and no information from it may be published without the prior written consent of the author. This thesis may be made available for consultation within the Univerity Library and may be photocopied or lent to other libraries for the purposes of consultation Signed: f t # Date: 1 UMI Number: U547969 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. Dissertation Publishing UMI U547969 Published by ProQuest LLC 2013. Copyright in the Dissertation held by the Author. Microform Edition © ProQuest LLC. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code. ProQuest LLC 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 SoSS-R I Acknowledgements Thanks are due, first and foremost, to my supervisors - Dr Alan F Casy and Dr Terence M Jefferies of the School of Pharmacy and Pharmacology, University of Bath, and Dr. Geoff R Bedford of ICI Pharmaceuticals, Alderley Park, for their help, encouragement and advice throughout the course of this work. The support of the technical staff of the School of Pharmacy and Pharmacology is gratefully acknowledged. In particular, thanks are due to Kevin Smith, Don Perry and Richard Sadler for assistance with chromatographic studies, and to Dave Wood and Harry Hartell for assistance with NMR studies. Help and advice received during the period spent in the laboratories of ICI Pharmaceuticals, Alderley Park is acknowledged. Particular thanks are due to Rick Gaskell, Brian Wright, David Greatbanks and Rod Pickford in this respect. The invaluable contribution of ICI Research Engineering Laboratory in building a valve-switching unit is also acknowledged. The support of a number of suppliers of chromatographic equipment is acknowledged. Thanks are due to SGE Ltd. (Milton Keynes) and Phase Separations Ltd. (Deeside) for the gift of HPLC columns; to Hamilton (Reno, Nevada, USA) for the gift of HPLC column packing material; to LDC Analytical (Stone, Staffs) for the loan of a Promis 2 autosampler; to Applied Chromatography Systems Ltd. (Macclesfield, Cheshire) for the loan of a Chiramonitor detector; to Perkin-Elmer Ltd. (Beaconsfield, Bucks.) for the loan of a photo-diode array detector; and to Technicol (Stockport, Greater Manchester) and Wacker Chemie GMBH (Munich, Germany) for the gift of cyclodextrins. Second-hand HPLC columns were donated by Dr. Roger J. Simmonds of Upjohn Ltd. (Crawley, West Sussex), to whom I am indebted. The financial support of the UK Science and Engineering Research Council and of ICI Pharmaceuticals Ltd. is also acknowledged. 2 Summary The interaction of B-cyclodextrin with a number of pharmaceutical and other racemates has been investigated in three ways: (i) by HPLC using 13-cyclodextrin-containing eluents, (ii) by HPLC using a B-cyclodextrin stationary phase (Cyclobond I) and (iii) in NMR experiments. Previously unreported chiral discriminations have been achieved in numerous cases by each technique, namely 24 cases using B-cyclodextrin eluents, 20 examples using Cyclobond I, and 35 cases in NMR. The application of B-cyclodextrin-containing mobile phases in HPLC to the semi-preparative resolution of pharmaceutical racemates has been investigated. An on-line solid-phase extraction recovery system was designed, which allowed recovery of resolved enantiomers free from mobile phase additives. Optical purities of 88% or greater were achieved in the four cases investigated, at throughputs of 1-5mg racemate per hour. The potential applicability of this technique to other chiral separations has been discussed. The influence of mobile phase composition and stationary phase type on resolution of enantiomers using B-cyclodextrin eluents have been investigated with the aim of facilitating the optimisation of both analytical and semi-preparative chiral separations. Correlations between observed chiral discriminations in the three techniques were sought, with a view to using NMR or Cyclobond experiments for the rapid evaluation of whether a given racemate would be likely to be resolvable using B-cyclodextrin-containing HPLC eluents. Potentially useful empirical correlations were found, although the theoretical basis for these was not strong. NMR experiments were used to investigate the stability and structure of B-cyclodextrin complexes. A theory was developed which allowed in some cases the determination of the stability of the diastereomeric complexes from measurements on a racemate. 3 Contents Page Chapter 1 - Introduction 1.1 Chirality and pharmaceutical development 8 1.2 Chromatographic chiral separations 19 1.3 Cyclodextrins 33 Chapter 2 - Experimental 2.1 Materials 47 2.2 Analytical HPLC studies 63 2.3 Semi-preparative resolution of trimeprazine enantiomers 67 2.4 Semi-preparative resolution of thromboxane antagonist enantiomers 72 2.5 Semi-preparative resolution of brompheniramine enantiomers 75 2.6 Determination of the solubility of beta-cyclodextrin in some aqueous-organic solvent mixtures 78 2.7 NMR experiments 79 Chapter 3 - Results: Analytical HPLC studies 3.1 Introduction 83 3.2 Tetrahydroisoquinolines 99 3.3 Phenothiazines 101 3.4 Mandelic acids and related compounds 103 3.5 Thromboxane antagonists 104 3.6 Other compounds 110 4 3.7 Determination of beta-cyclodextrin complex formation constants by HPLC 113 3.8 Application of advanced detection techniques to chromatographic studies using cyclodextrin-containing eluents 117 3.9 Use of derivatised cyclodextrins as mobile phase additives 121 Chapter 4 - Results: Semi-preparative resolution of enantiomers using B-cyclodextrin-containing mobile phases 4.1 Introduction 127 4.2 Trimeprazine 133 4.3 Thromboxane antagonists 155 4.4 Brompheniramine 170 Chapter 5 - Results: 1H-NMR studies on the interaction of racemic substrates with cyclodextrins 5.1 Introduction 180 5.2 Tetrahydroisoquinolines 192 5.3 Phenothiazines 198 5.4 Mandelic acids and related compounds 202 5.5 Thromboxane antagonists 210 Chapter 6 - Discussion and Conclusions: Prediction and optimisation of semi-preparative HPLC chiral separation using cyclodextrin-containing eluents 6.1 Introduction 221 6.2 Correlation between NMR and HPLC data 226 5 6.3 NMR determination of complex stability, stoichiometry and structure 245 6.4 Optimisation of semi-preparative separations using cyclodextrin-containing eluents 247 Appendix 1 - Simultaneous determination of cyclodextrin-substrate complex formation constants for two enantiomers in racemic mixture by NMR 263 References 265 6 Chapter 1 Introduction 7 1.1 Chirality and pharmaceutical development In recent years, it has become increasingly clear that chirality has important implications in pharmaceutical development. Hitherto, many chiral drug compounds have been developed and marketed as racemates. However, recent advances in chiral synthesis and chromatog­ raphic resolution of enantiomers have opened up the possibility of single enantiomer pharmaceutical products. Research into the pharmacokinetic and pharmacodynamic properties of enantiomers has shown that there may be major advantages in terms of drug efficacy and safety in following this course. Regulatory authorities have indicated that legislation may soon compel investigation of individual enantiomers in any new drug submission. 1.1.1 Fundamentals of optical isomerism The phenomenon of optical isomerism was first discovered by Pasteur (Pasteur (1948)). He found that on crystallisation of sodium and ammonium salts of synthetic tartaric acid, two types of crystal were formed which were non-superimposable mirror-images of each other. Mechanical separation of the crystals enabled the examination of their properties. Their melting points, refractive indices, solubilities, etc. were found to be identical.