Disorders of Primary Metabolites in Response to Drought May Increase the Synthesis of Natural Products for Medicinal Purposes: South American Herbs - a Case Study

The use of plants for healing diseases is one of the oldest medical practices and there are several studies showing that botany and medicine are related. Recent researches have shown that around 25% of new chemical entities and 42% of anticancer drugs marketed worldwide from 1981 to 2006 are obtained from natural products and their derivatives. One-third of the botanical biodiversity of the planet is in South American tropical ecosystems (Neotropical). Over the centuries, plants have been used by indigenous people for curing diseases. This strong tradition has been a great challenge for the scientific community in order to validate the folkloric medicinal use of herbs. In this way, a very few Neotropical pharmaceutical products have reached the market in industrialized countries, even though they have a considerable plant diversity. Plants synthesize several organic compounds which are not related to their growth and development and are called secondary metabolites or natural products that are derived from central or primary metabolism. Because plants are sessile organisms, they have to respond quickly to environmental changes in order to escape and survive under unfavorable conditions. Drought is one of the most worldwide serious impediments for crop yields producing adverse negative effects on plant growth, by impacting leaves and roots growth, stomatal conductance, photosynthetic rate and biomass gain. The three major classes of secondary metabolites are produced from pathways of different primary metabolites, including glycolysis, tricarboxilic acid cycle, aliphatic amino acids, pentose phosphate pathway, shikimate pathway and aromatic amino acids. This review compiles the metabolic changes occurring at primary metabolite level and total biosynthesis of natural products with potential for the development of new drugs in response to drought.