Plant Alkaloids: Structures and Bioactive Properties

Alkaloids are nitrogen-containing natural products found in bacteria, fungi, animals, and plants with complex and diverse structures. The widespread distribution of alkaloids along with their wide array of structures makes their classification often difficult. However, for their study, alkaloids can be classified depending on their chemical structure, biochemical origin, and/or natural origin. Alkaloids can be derived from several biosynthetic pathways, such as the shikimate pathway; the ornithine, lysine, and nicotinic acid pathway; the histidine and purine pathway; and the terpenoid and polyketide pathway. Traditionally, plant alkaloids have played a pivotal role in folk medicines since ancient times as purgatives, antitussives, sedatives, and treatments for a wide variety of ailments. Currently, several alkaloids have served as models for modern drugs, and there are several alkaloids used in pharmacology, such as codeine, brucine, morphine, ephedrine, and quinine. Herein, this work is a comprehensive revision from the Web of Knowledge and Scopus databases on the recent information (2010–2019) regarding plant-derived alkaloids, their structural classification and bioactive properties.