**1. Introduction**

Secondary metabolites in plants are commonly used to describe metabolic pathways that produce molecules or metabolites that can provide for normal growth or are only needed under certain conditions. In contrast, primary metabolites traditionally describe key household maintenance functions, such as energy production or the production of essential metabolites and macromolecules. These differences may be somewhat misleading; however, as is now known, secondary metabolites compounds plays a very important role in the biology of various organisms. In fact, it is clear that evolution would not selectively maintain the complex pathways that make up secondary metabolites if there were no competing advantages for the developing organism.

This logic, coupled with the fact that the biological function of the majority of plant and microbial secondary metabolites is poorly understood, has led to an alternative description of plant metabolites as "natural products" [1], though that description also carries some limitations. Nature produces a tremendous array of secondary metabolites or natural products, with the most diversity seen in microorganisms and plants [2]. It is a great resource for mankind and many examples of microbial or plant metabolisms are exploited by man, for example, antibiotics and pharmaceuticals. However, we have only scratched the surface, especially since there are various natural metabolites that have applications in the field of biomedicine. It is the basis of many natural product discovery projects, for example, attempts to use metagenomics to study marine microbial diversity [3]. In contrast to these attempts to explore metabolic diversity in new key locations, plant metabolic diversity has been exploited by humans throughout history, initially using plant extracts and more recently through scientific activity to identify metabolites with specific functions and then use these products directly or as traces for therapeutic compounds [4].
