**Abstract**

Natural products are in the form of primary and secondary metabolites and are isolated chemical compounds or substances from living organisms. Terpenes, Phenolic compounds, and Nitrogen-containing compounds are secondary metabolites. The biosyntheses of secondary metabolites are derived from primary metabolism pathways, which consist of a tricarboxylic acid cycle (TCA), methylerythritol phosphate pathway (MEP), mevalonic and shikimic acid pathway. This chapter provides an overview of the diversity of secondary metabolites in plants, their multiple biological functions, and multi-faceted cultural history.

**Keywords:** natural products, biosynthesis, metabolites, phytochemicals, terpenes, phenolic compounds, nitrogen-containing compounds

### **1. Introduction**

Natural products are lead compounds, which are frequently produced by plants and microbes as their secondary metabolites, and securing large quantities of such compounds for industrial and clinical applications has been a persisting problem [1]. Natural products (chemical compounds or substances) are isolated from living organisms [2]. Biogenesis belief that complex living things come only from other living things and also the production of new living organisms or organelles using reproduction. Chemistry of natural product is produced by the pathway of primary or secondary metabolism [3]. Metabolism is used to describe all chemical reactions which include maintaining the living state of cells of an organism [4]. Metabolism can be in form of catabolism or anabolism. Metabolites are a product of metabolism and restricted to small molecules [5].

Plants produce natural products with highly diverse structures; these products are called "secondary metabolites" in contrast to the "primary metabolites", which are essential for plant reproduction, and growth. The leaf, stem, root, or bark of the plant has plant secondary metabolites that have been produced, for example Alkaloids, Tannins, Flavonoids, and Phenolic compounds [6]. Most food, spices and herbs are indigenous plants has these secondary metabolites [7]. Plant secondary metabolites are exclusively produced by more than 30,000 different plants. They serve as defense compounds against pathogens and herbivores, as flower pigments that attract pollinators. Natural products have a strong impact on human culture and are used throughout human history as pigments, condiments, and pharmaceuticals [8].

This chapter therefore provides an overview of the biosynthesis of natural products, their multiple biological functions and multi-faceted cultural history.
