Alkaloids: A Brief Overview of Botanical and Pharmacological Properties

The classical definition of alkaloids describes this class of secondary metabolites as chemical structures containing nitrogen as part of a heterocyclic, with alkaline character, characterized by complex structure and limited distribution, mainly in the plant kingdom. The modern history of alkaloids starts in the early nineteenth century as figured by two milestone dates, 1803 when Derosne described the isolation of a mixture containing narcotin and morphine from opium, and 1819 when the chemist Meissner delivered an operative definition of the term alkaloid. They have been observed with sporadic distribution in bacteria, fungi, Pteridophytae and Gymnophytae, while they are mainly represented in higher plants and within Angiosperms, particularly in selected families, such as Annonaceae, Lauraceae, Loganaceae, Menispermaceae, Papaveraceae, Ranuncolaceae, Rubiaceae, Rutaceae, Solanaceae and others. Frequently, a plant activates selectively a metabolic pathway that produces a mixture of multiple but structure-related alkaloids. Sometimes, dozens may be with a restricted number representing the majority of the total content. The latter parameter could change significantly as a result of a plethora of many factors, including the plant organ, seasonal variations, phenological status and others. As general rules, the alkaloids are segregated in the form of salt inside cell vacuole or sometimes in laticifer, mainly through the superficial tissues, supporting the hypothesis of their biological involvement in plant-environment interactions.