ABSTRACT
One characteristic of the higher plants is their ability to synthesize an enormous variety of organic molecules known as “secondary metabolites.” These molecules are widely used with an important economic impact (Balandrin et al., 1985). Therefore, chemical and biotechnological strategies have been used for the production of these compounds. However, many of these organic molecules have complex structures and sometimes can be chiral, which are difcult, expensive, or even impossible to synthesize (Yeoman and Yeoman, 1996). But, why are they called secondary metabolites? In a living plant, there are a coordinated series of enzyme facilitated chemical reactions known as metabolism. These partial reactions are organized together to form metabolic pathways for the synthesis and utilization of molecular species such as sugars, amino acids, fatty acids, nucleotides, and the polymers derived from them (polysaccharides, proteins, lipids, RNA, DNA, etc.). This collection of processes is known as primary metabolism and the compounds involved, which are essential for the survival of the plant, are described as “primary metabolites.” In addition, all plants also use other metabolic pathways, producing compounds, which initially might not be of any obvious use to the organism. These are “secondary metabolites,” and the reactions involved in their biosynthesis and utilization constitute the secondary metabolism. However, the dividing line between primary and secondary metabolism is not so distinct, because many of the intermediates in primary metabolism are also intermediates of the secondary metabolism. In fact, the overlapping role of many
20.1 Introduction .......................................................................................................................... 471 20.2 Functions of Secondary Metabolites .................................................................................... 472 20.3 Rosmarinic Acid: Presence in the Plant Kingdom ............................................................... 472 20.4 Rosmarinic Acid: Biosynthesis ............................................................................................. 473 20.5 Rosmarinic Acid: Role in Plants ........................................................................................... 473 20.6 Rosmarinic Acid: Pharmacology .......................................................................................... 475 20.7 Biotechnological Approaches to RA Production .................................................................. 475
20.7.1 Traditional Strategies to Improve RA Biosynthesis ................................................. 477 20.7.2 Metabolic Engineering ............................................................................................. 478
20.8 Conclusions ........................................................................................................................... 478 Abbreviations ................................................................................................................................. 479 References ...................................................................................................................................... 479
compounds ensures a close interconnection between primary and secondary metabolism because many of the small molecules generated in the primary metabolism are building blocks for all the secondary metabolic pathways (Figure 20.1).
