Alkaloids constitute one of the widest classes of natural products, being synthesized practically by all phyla of both marine and terrestrial organisms, at any evolutionary level. The extraordinary variety (and often complexity) of alkaloid structures and biological properties have long intrigued natural product chemists (for structure determination and biosynthetic studies), analytical chemists, and synthetic organic chemists. Toxicologists, pharmacologists and pharmaceutical companies have used and will certainly continue to use alkaloids as biological tools and/or as lead compounds for development of new drugs. When we started our project of a handbook on alkaloid science, we were faced with an impressive number of papers describing the structures and activities of alkaloids, and also with an intense review activity, published in excellent book series or in single books covering specific classes of alkaloids. Consequently, we decided to organize our handbook to present the different aspects of alkaloid science (e.g. the structure and pharmacology of bioactive alkaloids; recent advances in isolation, synthesis, and biosynthesis) in a single volume, aiming to provide representative examples of more recent and promising results as well as of future prospects in alkaloid science.
Obviously, the present handbook cannot be regarded as a comprehensive presentation of alkaloid research, but we feel that the diversity of topics treated, ranging from bitterness to the anticancer activity of alkaloids, can provide a good idea of the variety of active research in this field. In particular, Section I describes the structures and biological activities of selected classes of alkaloids. Almost half of the chapters focus their attention on terrestrial alkaloids (Chapters 1–5). The other half (Chapters 7–11) describe recent results in the field of marine alkaloids, while Chapter 6 is focused on neurotoxic alkaloids produced by cyanobacteria, microorganisms living in both marine and terrestrial environments. The particular emphasis on marine alkaloids undoubtedly reflects our long-standing research activity on marine metabolites, but it is also a result of the impressive amount of work carried out in the last few decades on marine natural product chemistry.
Section II (Chapters 12–15) gives an account of modern techniques used for the detection and structural elucidation of alkaloids, while Section III is divided into two parts: different methodologies for the synthesis of alkaloids and accounts of modern biosynthetic studies Finally, we should point out that even today the term alkaloid is ambiguous (a discussion on the definition of alkaloid is presented in Chapter 4). The initial definition of Winterstein and Trier (1910) ("nitrogen-containing basic compounds of plant or animal origin") has obviously been superseded. The most recent definition of alkaloid can be attributed to S. W. Pelletier (1984): "compound containing nitrogen at a negative oxidation level characterized by a limited distribution in Nature". In the preparation of this handbook we have decided to follow this last definition and, thus, to include "borderline" compounds such as capsaicins and nonribosomal polypeptides. We cannot conclude without thanking all the authors who have made their expert contributions to the realization of this volume, which we hope will stimulate further interest in one of the most fascinating branches of natural product chemistry.
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