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University of Bath PHD Synthetic studies on the norditerpenoid alkaloid methyllycaconitine from delphinium, a potent nicotinic acetylcholine receptor antagonist Coates, Philippa Anne Award date: 1996 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: 09. Oct. 2021 SYNTHETIC STUDIES ON THE NORDITERPENOID ALKALOID METHYLLYCACONITINE FROM DELPHINIUM; A POTENT NICOTINIC ACETYLCHOLINE RECEPTOR ANTAGONIST submitted by Philippa Anne Coates for the degree of PhD of the University of Bath 1996 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 recognize that its copyright rests with its author and that no quotation from the thesis and no information derived from it may be published without the prior written consent of the author. RESTRICTIONS ON USE This thesis may be made available for consultation within the University Library and may be photocopied or lent to other libraries for the purposes of consultation. Signed: I UMI Number: U601788 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 U601788 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 Abstract In this thesis, the exploration of the roles of the unusual acyl group of the toxic norditerpenoid alkaloid MLA, a highly potent novel competitive nicotinic acetylcholine receptor antagonist which is uniquely selective for the a-bungarotoxin binding site in both insects and vertebrates, is described. Chapter 1 is a review of the literature relating to the history, occurrence, and biological action of MLA and other norditerpenoid alkaloids. The optimization of the extraction of crude norditerpenoid alkaloids from the seeds of Garden Hybrid Delphinium is described in Chapter 2. Vacuum liquid chromatography led to the isolation of pure MLA and delpheline. Characterization of these natural alkaloids and of semi-synthetic derivatives, including lycoctonine, obtained from the saponification of MLA, and esters of lycoctonine, using spectral techniques, helped to establish unambiguously stereochemistry of the methyl substituent on the succinimide of MLA. Chapter 3 describes the development of sensitive high performance liquid chromatography assay for the routine monitoring of MLA levels in plant extracts and semi-synthetic alkaloid samples, prior to biological testing. In Chapter 4, the design of a series of small molecule analogues of MLA, and the preparation of acylated cholines and homocholines, from isatoic anhydride, are described. The incorporation of the succinimide ring found in MLA into these anthranilate esters, by fusion with methylsuccinic anhydride, is also described. Future work is to include synthesis of further esters of substituted anthranilic acid and esterification of lycoctonine with alternative aromatic and aliphatic acid chlorides, in order to explore further the pharmacophore of MLA. II The norditerpenoid alkaloid natural products and the esters of substituted anthranilic acid have been assayed for nicotinic potency in competition binding assays to rat brain membranes and for inhibitory effects on binding of 3H-a- bungarotoxin to cockroach head homogenate, in order to explore the structural features of MLA required for activity. Dedication This thesis is dedicated to my family, namely, my parents Philip and Anne Coates, my sister Elizabeth, her husband Ian, their daughter Olivia, my brother Robert, my brother David, and his wife Stacy, all who have given me continual encouragement and love throughout the years of my research. Ill Acknowledgements First and foremost, I would like to thank Professor Barry V. L. Potter, Dr. Ian S. Blagbrough, and Dr. Michael G. Rowan for their excellent supervision. Second, I would like to thank Dr. Terence Lewis and colleagues at Zeneca Agrochemicals (Jealott's Hill), Dr. David Pearson and Dr. Fergus Earley, for financial support and many helpful suggestions. Third, I would like to thank Dr. Susan Wonnacott, Dr. Sarah Branch, Dr. Richard Kinsman, and Dr. Noel Thomas for their input and interest in this research project. Thanks also to Dr. Xavier Doisy, Dr. Geraldine Grangier, Dr. David Hardick, David Callis, and William Trigg for their useful discussions. In addition, I would like to thank David Wood, Roland Hartell, Gary Cooper, and Paul Needham for help with regards to NMR spectra, HPLC and computer support. Also, thanks to the people I have worked alongside in the laboratory and the office, including Dr. Mark Ashton, Dr. Changsheng Liu, Dr. Simon Fortt, Dr. David Jenkins, Dr. Dethard Lampe, Dr. Stephen Mills, Dr. Eduardo Moya, Dr. Nick Noble, Dr. Andrew Riley, Dr. Stephen Taylor, Dr. Stephen Walford, Abi Ashamu, Victoria Bailey, Simon Carrington, and Soulla Diogenous for their support. Finally, thanks to other members of the School of Pharmacy, especially Dr. Elena de Angelis, Dr. John Lord (and his wife Catrin), Dr. Joanne Peart, Susan Alston, and Caron Challinor, to other members of the University of Bath whose paths I feel fortunate to have crossed, in particular, Dr. Mark Hagger, Dr. Claire Swaffield, Dr. Guy Nason, Jonathan Foweraker, and Sarah Wild, as well as many other members of Wine Tasting Society, and to other people that I have known in Bath, notably Sonia Leigh and Charlotte Marrison, for their friendship. IV Abbreviations °c degrees Celsius AIBN a,a'-azobisisobutyronltrile Ac acetyl 'Am isoamyl / isopentyl aq aqueous bp boiling point Bu butyl 'Bu isobutyl nBuLi nbutyl *Bu tert-butyl / tertiary butyl Bz benzoyl Cl chemical ionisation COSY correlated spectroscopy CSA (+)-10-camphorsulfonic acid 2D two dimensional DCC A/,AkJicyclohexylcarbodiimide DDQ 2,3-dichloro-5,6-dicyano-1,4-benzoquinone DIBAL diisobutylaluminium hydride DMAP 4-(/V,Aklimethylamino)pyridine DME 1,2-dimethoxyethane (glyme) DMF A/,AFdimethylformamide DMSO dimethylsulfoxide El electron impact Et ethyl FAB fast atom bombardment GC gas chromatography h hours HPLC high performance liquid chromatography Hz Hertz IC50 50% inhibitory concentration IR infrared J coupling constant V Ki inhibitory concentration LDA lithium isopropylamide LHMDS lithium 1,1,1,3,3,3-hexamethyldisilazide M molar M+. molecular radical cation MCPBA mefa-chloroperbenzoic acid Me methyl MH+ protonated molecular ion min minutes MOM methoxymethyl mp melting point Ms mesyl /methanesulfonyl MS mass spectroscopy MW relative molecular weight m/z mass by charge n normal (or straight-chain) NBS A/-bromosuccinimide NMR nuclear magnetic resonance nOe nuclear Overhauser effect PCC pyridinium chlorochromate Ph phenyl ppm parts per million Pr propyl jPr isopropyl pTSA para-toluenesulfonic acid rt room temperature THF tetrahydrofuran THP tetrahydropyranyl TLC thin layer chromatography TMS tetramethylsilane UV ultraviolet VA/ volume by volume WA/ weight by volume VI CONTENTS Title I Abstract n Dedication m Acknowledgements iv Abbreviations v Contents vn Chapter 1 INTRODUCTION 1 1.1 METHYLLYCACONITINE 1 1.1.1 Structure and Isolation 1 1.1.2 Biological Activity 1 1.2 AIMS OF THESE STUDIES 5 1.3 DELPHINIUM AND ACONITUM 6 1.3.1 Plant Classification and Nomenclature 6 1.3.2 General 7 1.3.3 Hybridization 7 1.3.4 Toxicity 8 1.3.5 Insecticidal Activity 9 1.3.6 Folk Medicine 10 1.4 DITERPENOID ALKALOIDS 12 1.4.1 Nature and Definition of an Alkaloid 12 1.4.2 Definition of a Diterpenold Alkaloid 12 1.4.3 Biosynthesis of C19- and C20-Dlterpenoid Alkaloids 13 VII 1.4.4 C10-Dlterpenoid Alkaloids 15 1.4.4.1 Occurrence 15 1.4.4.2 Structure 15 1.4.4.3 Types 16 1.4.4.4 Nomenclature 19 1.4.4.5 MLA and other aromatic esters of Lycoctonine-Type 19 Diterpenoid Alkaloids 1.4.5 C2o-Diterpenoid Alkaloids 21 1.4.5.1 Occurrence 21 1.4.5.2 Types 24 1.5 SYNTHETIC STUDIES OF Cig-DITERPENOID ALKALOIDS 26 Chapter 2 NATURAL PRODUCTS ISOLATION, 46 CHARACTERIZATION AND SEMISYNTHESIS 2.1 AIMS 46 2.2 RESULTS AND DISCUSSION 47 2.2.1 Optimization of the Extraction of Garden Hybrid 47 Delphinium Seeds 2.2.2 Purification of Crude Alkaloldal Material 50 2.2.3 NMR Assignment of Delphellne 52 2.2.4 X-Ray Structure of Delphellne 65