More than 80, 000 of the 250, 000 species of flowering plants have been reported to be used by human civilizations for medicinal purposes. Fossil records date human use of plants as medicines at least to the Middle Paleolithic age some 60,000 years ago. The World Health Organization (WHO) estimated that as much as 80 per cent of the worlds population relies on traditional forms of medicine, chiefly plants. The tropical rain forest plants are biologically and chemically diverse resource as they synthesize a wide spectrum of organic molecules as defense agents against diseases, pests and predators. They have been shown to be the source of chemicals of diverse structures with promising biological activities and perhaps the most valuable source of therapeutic agents due to their rich biodiversity.
Tropical rain forests have been called the ‘world's largest pharmacy’, because over one quarter of natural medicines have been discovered within them; additionally, about 70% of the drugs used today are models of natural products. Plants have always been a rich source of natural products and historically provided many major new drugs. Natural products or natural product-derived compounds signify great structural variety, which is not usually found in synthetic compounds.
Of the 1184 new chemical entities reported through 1981 to 2006, 60% were derived from or based on natural products. Twenty-five percent of all prescription medications are made using the various types of secondary metabolites from living organisms, mainly plants. One hundred twenty-one prescription drugs are made from higher plants. This does not include antibiotics from microorganisms. Among the world’s 25 best-selling pharmaceutical agents, 12 are natural product-derived , and natural products are playing key role in drug discovery programs of the pharmaceutical industry and various research organization. Half of these plant-based medicines come from the tropics, and 74% of these came from native folklore.
Seventy percent of the plants identified as having anti-cancer characteristics by the US National Cancer Institute are found only in the tropical rain forests. Quinine, the first known antimalarial, comes from a Neotropical tree, and Curare, used as a poison for arrow tips by indigenous peoples in the Neotropics, is also useful for heart conditions. As new medical discoveries are being made all the time obviously, the tropical rain forests and their resources such as natural products find place in every part of our life. Plants have evolved and adapted over millions of years to withstand bacteria, insects, fungi and weather to produce unique, structurally diverse secondary metabolites. Therefore, natural products play a leading role in the research of leads for the development of drugs for treating human diseases .
The investigation of biological and chemical properties of natural products for the past two centuries has not only produced drugs for the treatment of several diseases, but has instigated the development of synthetic organic chemistry, and the arrival of medicinal chemistry as a major route to discover efficacious and novel therapeutic agents. Structural alteration of natural compounds or synthesis of novel compounds, based on designs following a natural compound scaffolding; have offered us a lot of vital new drugs in the fields of medicine, agriculture, and food spheres.
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