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Investigations into Calabar beans (the dried ripe seeds of Physostigma venenosum ) and their alkaloidal components compose a classical scientific journey throughout some one-and-a-half centuries and not only represent a fascinating aspect of the history of medicine but which is, moreover, still ongoing at the forefront of chemical and medical discovery. Those in particular involving its major such component, l -physostigmine, have led to an understanding of some of the fundamental mechanisms occurring in physiology, pharmacology and biochemistry and, either actually or potentially (by providing a template and thereby acting as a "lead compound") have provided a useful treatment for a variety of neurological disorders associated with irregularities in cholinergic transmission in which augmentation of cholinergic activity has proved to be beneficial. The aquatic leguminous vine, Physostigma venenosum, is widely distributed throughout the coastal regions of equatorial West Africa and having a colourful history - by virtue of their former use as an ordeal poison in trials for suspected witchcraft and to effect folkloric ritualistic executions in the Efik society of Old Calabar (now part of present-day south-eastern Nigeria) - are its dried ripe seeds (Calabar beans). The major toxic component of these is l -physostigmine which is also known as eserine and is, as yet, the only alkaloid which has also been isolated from a microbial source (along with l -N(8)-norphysostigmine), is the first alkaloid that was found to contain a 1,2,3,3a,8,8a-hexahydropyrrolo[2,3- b ]indole tricyclic ring system and is the first natural product that was found to contain a carbamyl group. Furthermore, it is the first alkaloid that was proven to exert its pharmacological activity through the inhibition of an enzyme, is one of the first examples whereby the mechanism of action of a drug could be defined at the molecular level relatively simply, played a crucial role in the Nobel Prize-winning discovery of the mechanism of neurohumoral transmission, and has, either directly or by acting as a "lead compound", afforded products for the treatment of a wide range of disorders associated with deficiencies in cholinergic transmission. Several other alkaloids have also been isolated from the Calabar bean. For some of these, structures have been established - using spectroscopic and spectrometric techniques and l -physostigmine as a model reference compound, syntheses effected and pharmacology investigated.

Table of Contents

Chronology.-  Abbreviations.- Preface and acknowledgements.- 1. Introduction.- 2. l-Physostigmine (eserine).- 3. l-Physovenine.- 4. l-Eseramine.- 5. l-N(8)-Norphysostigmine.- 6. l-Geneserine.- 7. 1H-, 13C- and 15N-Nuclear magnetic resonance spectra of the alkaloids of the Calabar bean.- 8. Other alkaloids of, as yet, unknown structures that have been isolated, or allegedly so, from the Calabar bean.- 9. Non-alkaloidal components of the Calabar bean.- 10. Biological activities of the alkaloids of the Calabar bean.- 11. Notes.- 12. References.- 13. Index.

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One of the most exciting and interesting aspects of the study of natural products is the "field work" involving ethnological and ethnobotanical studies and which, where apposite, have been alluded to in the present treatise Many texts on alkaloids are limited to chemical aspects, whereas the somewhat unique and therapeutically significant biological activities of the Calabar bean's alkaloids (particularly l-physostigmine) has led to a detailed and through presentation of these facets in the present treatise Throughout this present study, along with a detailed account of what has been done, investigations of what remains to be done have been high-lighted and approaches to effecting this are suggested, including the interpretations of already - published data

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One of the most exciting and interesting aspects of the study of natural products is the "field work" involving ethnological and ethnobotanical studies and which, where apposite, have been alluded to in the present treatiseMany texts on alkaloids are limited to chemical aspects, whereas the somewhat unique and therapeutically significant biological activities of the Calabar bean's alkaloids (particularly l -physostigmine) has led to a detailed and through presentation of these facets in the present treatise Throughout this present study, along with a detailed account of what has been done, investigations of what remains to be done have been high-lighted and approaches to effecting this are suggested, including the interpretations of already - published data

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