Though definitions may vary from source to source, the term alkaloid generally refers to members of a large set of naturally occurring, slightly basic (i.e., alkaline) nitrogen-containing organic compounds. Generally excluded from this group are amino acids, peptides, proteins, N-containing carbohydrates, and nitrogenous bases used in the construction of nucleotides. Though a small number are produced by animals or microorganisms, the vast majority of alkaloids are plant-produced compounds possessing a remarkably diverse range of structural features, from simple cycloaliphatic amines to highly complex polycyclic N-heterocycles. Some representative alkaloids are shown in Fig. 7.1. Alkaloid-containing plants and their extracts have been used by humans for thousands of years, mainly on the basis of their stimulant, therapeutic, or poisonous properties. References to plants containing compounds such as morphine (from opium poppies), strychnine (from seeds of the Strychnos nux-vomica tree), ephedrine (from the plant Ephedra chinensis), and coniine (from the poison hemlock plant) may be found in some of our earliest known writings. Today, it has been estimated that the health care of over 5 billion people worldwide benefits from the use of plant-based medicinal agents, many of which are alkaloids. With that in mind, it is worth noting concerns that deforestation, environmental damage, large-scale development, and unregulated harvesting programs may ultimately lead to the extinction of hundreds of known medicinal plants and perhaps even more whose medicinal properties have yet to be discovered, thereby endangering the prospects for future discoveries of new curative agents for the benefit of all humankind. As a scientific field, alkaloid chemistry itself dates back to the early 1800s with the first isolation of pure crystalline morphine from opium. This milestone achievement allowed the delivery of accurate, therapeutic doses of a drug that was immensely valuable for the relief of pain but which could also lead to fatal overdoses when administered from simple extracts of variable composition and strength. The subsequent rapid development of increasingly sophisticated techniques for the isolation and purification of the active components (often alkaloids) from many other medicinal plants essentially spawned the field of organic chemistry.