CHAPTER TWO
2.1 LITERATURE REVIEW
Natural products are a source of new chemical diversity and are the choice of today’s world. The sources of natural product are plants, animals and microorganisms. Among them plant and its products are more reliable for its renewability and therefore, considered as catalyst for human welfare. Still, they are the primarily required materials for health care system in some parts of the world. Therefore, in the past few decades, there is a growing research interest in plants as a therapeutic agent.
The therapeutic potential of plant products can be traced back to over five thousand years ago as there is evidence of its use in the treatment of diseases and for revitalizing body systems in Indian, Egyptian, Chinese, Greek and Roman civilizations (Mahesh and Satish, 2008). Also India is one of the megadiversity hot spots with rich heritage of traditional knowledge of folk medicines. Therefore in India, plants of therapeutic potential are widely used by all sections of people both as folk medicines in different indigenous systems of medicine like Siddha, Ayurveda and Unani and also as processed product of pharmaceutical industry (Srinivasan et al., 2007). India has about 4.5 million plant species and among them estimated only 250,000- 500,000 plant species, have been investigated phytochemically for biological or pharmacological activity. Still a large number of higher plants as a source for new therapeutics are to be explored.
The potential for developing phytomedicine into various health care products appears rewarding, both from the perspective of economy and safety. Friedman et al., (2007) and Serafinao et al., (2008) noted that many plant extracts are quite effective than the synthetic ones with no or insignificant side effects and very little scientific research on their biological activity has been worked out. Furthermore, the growth of multidrug resistant microbial strains which are limiting the effectiveness of synthetic drugs led to an awareness among the common people against the use of synthetic product (Sundsford, 2004; Edith et al., 2005; Hancock 2005; Isturiz, 2008). This factor forced the scientists to develop methods of bioprocesses for the production and extraction of compounds from natural renewable sources for their potential application in food, cosmetics and pharmaceuticals industry with antimicrobial, antioxidant, anti-inflammatory and antidiabetic activity (Velioglu et al., 1998; Oreopoulou and Tzia, 2007). Nayak and Pereira (2006) proposed that the therapeutic properties of plant extracts have far more to offer in future as a novel discovery Thus, use of phytochemicals as major bioactive compounds with multidimensional benefits are gaining momentum.
Phenolics the important secondary metabolites from M.oleifera and J. curcas:
M.oleifera and J. curcas metabolites represent an important source of sugars, minerals, organic acids, dietary fibre, as well as bioactive compounds like phenols, alkaloids and flavanoids which are synthesized as secondary metabolites and are constitutive, existing in healthy plants in their biologically active forms, but others occur as inactive precursors and are activated in response to tissue damage or pathogen attack (Osbourne 1996; Dahanukar et al., 2000). These secondary metabolites produced by M.oleifera and J. curcas are with wide range of chemical, physical and biological activities. The majority of bioactive compounds belong to a number of families, each of which has particular structural characteristics.
There are four major pathways for synthesis of secondary metabolites or bioactive compounds: (1) Shikimic acid pathway, (2) Malonic acid pathway, (3) Mevalonic acid pathway and (4) Non-mevalonate (MEP) pathway (Tiaz and Zeiger, 2006). Alkaloids are produced by aromatic amino acids (shikimic acid pathway) and by aliphatic amino acids (tricarboxylic acid cycle). Phenolic compounds are synthesized through shikimic acid pathway and malonic acid pathway. Through mevalonic acid pathway and MEP pathway terpenes are produced. Of these, the bioactive compounds mostly found in M.oleifera and J. curcas are phenolics and polyphenols (Shi et al., 2005) which are secondary metabolites and a much diversified group. Subclasses in this group of compounds which have been found to have antimicrobial activity include phenols, phenolic acids, quinones, flavones, flavonoids, flavonols, tannins and coumarins. This group includes metabolites derived from the condensation of acetate units (tepernoids) those produced by the modification of aromatic amino acids (phenylpropanoids and coumarins), flavonoids, isoflavonoids and tannins. Phenolics are involved in many physiological activities such as stimulation of phagocytic cells, host-mediated tumor activity. They are soluble in water, alcohol and acetone and gives precipitates with proteins (Basri and Fan, 2005). There are evidences that phenolics were traditionally used for protection of inflamed surfaces of the mouth and treatment of wounds, hemorrhoids and diarrhoea (Ogunleye and Ibitoye, 2003). They are also found to stimulate macrophages, which are antiinfective (Dewick, 2002; Spatafora and Tringali, 2012).
