Abstract
Phytochemicals belonging to the group of alkaloids are signature specialized metabolites endowed with countless biological activities. Plants are armored with these naturally produced nitrogenous compounds to combat numerous challenging environmental stress conditions. Traditional and modern healthcare systems have harnessed the potential of these organic compounds for the treatment of many ailments. Various chemical entities (functional groups) attached to the central moiety are responsible for their diverse range of biological properties. The development of the characterization of these plant metabolites and the enzymes involved in their biosynthesis is of an utmost priority to deliver enhanced advantages in terms of biological properties and productivity. Further, the incorporation of whole/partial metabolic pathways in the heterologous system and/or the overexpression of biosynthetic steps in homologous systems have both become alternative and lucrative methods over chemical synthesis in recent times. Moreover, in-depth research on alkaloid biosynthetic pathways has revealed numerous chemical modifications that occur during alkaloidal conversions. These chemical reactions involve glycosylation, acylation, reduction, oxidation, and methylation steps, and they are usually responsible for conferring the biological activities possessed by alkaloids. In this review, we aim to discuss the alkaloidal group of plant specialized metabolites and their brief classification covering major categories. We also emphasize the diversity in the basic structures of plant alkaloids arising through enzymatically catalyzed structural modifications in certain plant species, as well as their emerging diverse biological activities. The role of alkaloids in plant defense and their mechanisms of action are also briefly discussed. Moreover, the commercial utilization of plant alkaloids in the marketplace displaying various applications has been enumerated.
Highlights
Plants possess a diverse array of metabolic products arising from both primary and secondary metabolisms
Vincamine is synthesized in leaves of V. minor when 16-methoxy tabersonine undergoes epoxidation in the presence of tabersonine 3-oxidase (T3O), which after rearrangement forms an eburnamine-vincamine like skeleton that further transforms into vincamine [90]
The availability of precursors, enzymes required for catalysis, and chemical modifications in alkaloidal transformations have given rise to structural diversity in alkaloids
Summary
Plants possess a diverse array of metabolic products arising from both primary and secondary metabolisms. Specialized metabolites are derived from the primary metabolism and are present only in prominent tissues required for specific functions [1]. Alkaloids are naturally occurring specialized metabolites with nitrogen as a characteristic element present in their chemical structures. Alkaloids occur with different chemical structures and attached functional entities, displaying wide-reaching biological properties. The compounds synthesized in different plant tissues have been extensively studied for their biosynthesis and biological activities [5]. Pharmaceutical industries have utilized these naturally occurring compounds to develop formulations for better therapeutic potentials. These alkaloids show activities ranging from medicinal to acute toxicity, such as in the case of poppy alkaloids, depending upon the dosage of compounds [6]. The role of alkaloids in plant defense and their commercial importance have been described in the latter sections
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