Secondary Metabolites of Medicinal Plants. Bharat Singh

Secondary Metabolites of Medicinal Plants - Bharat Singh


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      Print ISBN: 978-3-527-34732-2

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      Traditional system of medicine is also known as indigenous medicine system used to maintain our health and to diagnose and treat several complaints based on theories, beliefs, and family experiences. The indigenous system of medicine has been in practice since the last thousands of years; contributions from community practitioners have maintained their popularity at a global level (Sofowora 1982). The traditional knowledge of plants could be attributed to acceptability, affordability, pleasant feeling, and affectivity against any type of disease as compared with modern medicine (Giday et al. 2003; Tolossa et al. 2013). In the case of traditional medicine, the knowledge is transferred from the elders to the younger generation verbally or by just showing the growing plants in the open fields. Several studies have revealed that transfer of medicinal knowledge of plants to the coming generations is adversely affected by development of modern medicine. The interest of younger generation to traditional knowledge is diminishing day by day (Yineger and Yewhalaw 2007). The wide acceptance of indigenous medicine and limited approach to modern healthcare facilities could be considered as main reasons for the continuation of the traditional practices. The documentation of traditional knowledge can be used to support human healthcare system to maintain healthy lives. The documented information will be used in future course of studies to validate biological and pharmacological activities as exhibited by medicinal plants; therefore it is an urgent need of modern time to enhance the affordability and acceptability of plants in rural and modern healthcare systems (Demie et al. 2018).

      The terpenoids constitute the largest class of natural products, and many interesting products are extensively applied in the industrial sector as flavors, fragrances, and spices and are also used in perfumery and cosmetics. Many terpenoids have biological activities and are also used for medical purposes. In higher plants, the conventional acetate–mevalonic acid pathway operates mainly in the cytosol and mitochondria and synthesizes sterols, sesquiterpenes, and ubiquinones mainly. In the plastid, the non-mevalonic acid pathway takes place and synthesizes hemi-, mono-, sesqui-, and diterpenes along with carotenoids and phytol tail of chlorophyll. The monoterpenes are widely distributed natural products found in herbs, spices, citrus, conifers, and most flowers and fruits. These are C10, short chain compounds, normally found in combination with sesquiterpenes, that play many significant roles, viz. antimicrobial, insect repellant, and pollinator attractants (Davis 2010). Iridoids are characterized by skeletons – in which a six-membered ring, containing an oxygen atom, is combined to an iridane skeleton – and are found in plants combined with sugar as glycosides. The iridoids are classified as iridoid glycosides (aucubin, harpagoside), nonglycosylated iridoids (loganin), secoiridoids (gentiopicroside), and bisiridoids, developed by dimerization of iridoids and secoiridoids (Ludwiczuk et al. 2017). Sesquiterpenes (C15) are less volatile than monoterpenes but have more potential for stereochemical diversities and odors and possess anti-inflammatory and antimicrobial properties (Buckle, 2015). The seed maintenance and bud dormancy are regulated by abscisic acid (sesquiterpene), and it also responded positively to water stress by modifying the properties of cell membrane (Berli et al. 2010). Triterpenoids are widely distributed in plants often accumulated in their glycosylated form. Saponins comprise hydrophobic triterpenoid aglycones called sapogenin and one or more hydrophilic sugar moieties. The triterpenoids possess antimicrobial and anti-inflammatory activities (Vincken et al. 2007).

      The quinones are a group of compounds occur in several plant species and are synthesized via the shikimate or polyketide pathways (Scott Obach and Kalgutkar 2010). The benzoquinones, naphthoquinones, and anthraquinones are found in higher plant species. Till today, nearly 600 quinones have been identified from various plant families, viz. Rubiaceae (Harborne 1982). These compounds are cyclic α,β-diketones, which can be converted by reduction into hydroquinones (Morrison and Boyd 1973). The oxidized form of conjugated quinones are colorful (yellow color) like p-benzoquinone, while


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