Phytochemicals secondary metabolites

The point has been made in many of these chapters that methodological and scientific development over recent years is such that very considerable advances will be made over the next decade indeed, one suspects that such is the pace of advance that the information presented in this volume will before too long be considered dated. This is to be welcomed and, in our opinion, is greatly preferable to the former situation, in which texts on natural toxicants/phytochemicals/secondary metabolites often contained much the same general coverage over many years. 

Phytochemicals are biologically-active, non-nutritive secondary metabolites which provide plants with colour, flavour and natural toxicity to pests. The classification of this huge range of compounds is still a matter of debate, but they fall into three main groups ... 

The discovery that, in industrialised societies, diets deficient in fruits and vegetables can effectively double the risk of developing many different types of cancer has focused renewed attention on the beneficial properties of these foods (Block e/a/., 1992 Patterson ef a/., 1990 Southon and Faulks, 2002). As we have seen, plant foods are rich in micronutrients, but they also contain an immense variety of biologically active secondary metabolites providing colour, flavour and natural toxicity to pests and sometimes humans (Johnson et ah, 1994). The chemistry and classification of such substances is still a matter for much research and debate, but this has not prevented attempts to isolate and exploit substances that have variously been termed protective factors , phytoprotectants , phytochemicals and nutraceuticals . Phytochemical compounds include ... 

Another field of research is the possibility offered by phytochemicals in protecting plants against diseases and pathogens (fungus, bacteria and nematodes). Numerous studies have suggested that plant-pathogen interactions are partially mediated via plant secondary metabolite production, despite the inconsistency revealed by some works on the ability of particular compounds to provide resistance to a specific pathogen. 

Tomas-Barberan, F.A., Capillary electrophoresis a new technique in the analysis of plant secondary metabolites, Phytochem. Anal., 6, 177, 1995. 

Verpoorte R, Contin A, Memelink J (2002) Biotechnology for the production of plant secondary metabolites. Phytochem Rev 1 13-25... 

Phytochemical studies of these species led to the isolation and structural characterization, by NMR and MS analysis, of many secondary metabolites, mainly flavonoids, and expecially flavonol glycosides, clerodane diterpenes, and triterpenes having the lupane, ursane, and oleanane skeletons. Particularly flavonoids and their glycosides have a chemotaxonomic interest in the genus and in general in the Chrysobalanaceae family. 

In the course of our phytochemical work we studied seven Licania species all belonging to Venezuelan flora, collected in Puerto Ayacucho, Estado Amazonas and in the Parque Nacional Henry Pittieri, Maracay, Estado Aragua. A number of new and known secondary metabolites, mainly flavonoids, especially flavonol glycosides, sterols, and triterpenes having the lupane, ursane, and oleanane skeleton were isolated and characterized. The last part of this chapter deals also with the isolation of clerodane diterpenes from the methanol extract of L. intrapetiolaris by Oberlies et al., 2001 [4]. All the Licania species investigated up to now are reported in Table 1. 

In the remaining sections of this chapter, brief details of the experimental approaches to our separate projects on the discovery of novel plant-derived cancer chemotherapeutic agents and cancer chemopreventives will be provided in turn, with emphasis of the phytochemical aspects. A number of novel bioactive plant secondary metabolites will be presented that have been isolated via activity-guided fractionation techniques in our recent work on these two projects. 

There is a huge variety of plant defensive secondary metabolites that has been the subject of major phytochemical [1-6] or pharmacological and toxicological [7-12] compilations. This structural complexity is very briefly reviewed below before considering those plant bioactives with signal transduction targets. The major groups are the phenolics, the terpenoids and the alkaloids as well as bioactives structurally related to... 

The polyphenolics, ubiquitous phytochemicals in the plant kingdom, are important aromatic secondary metabolites of plants. Diverse combinations of polyphenolics are found in plant-based materials. Polyphenolics are important because they are responsible for the color and flavor of fresh and processed products. Some have strong antioxidant and anticancer activities. They are routinely consumed in the human diet in significant quantities. 

Polyphenolic phytochemicals are ubiquitous in the plant kingdom. These important aromatic secondary metabolites of plants are consumed in significant amounts in daily life. Their occurrence among plant-based materials is frequently varied. They contribute to sensory qualities such as color, flavor, and taste of plant-based materials. The composition of polyphenolic phytochemicals is influenced by maturity, cultivar (Lee and Jaworski, 1987), cultural practices, geographic origin, climatic... 

Yazaki K, Sugiyama A, Morita M, Shitan N. 2008. Secondary transport as an efficient membrane transport mechanism for plant secondary metabolites. Phytochem Rev 7 513-524. 

The intimate relationship of endophytes with plants can raise questions about the validity of assumptions that a secondary metabolite is a tme phytochemical rather than biosynthesized by the endophyte(s) associated with the plant. 

Flavones and flavonols are relevant phytochemicals in food products, spices and medicinal plants. They are secondary metabolites belonging to the polyphenols group, and have in common the general structure of two aromatic rings and often more than three phenolic hydroxyls. Flavones and flavonols often show high antioxidant activity in vitro, and they complex metal ions and scavenge free radicals. They have a planar structure that allows intermolecular interactions and stacking in... 

Since the discovery of qinghaosu, systematic phytochemical studies on A. annua have been also conducted. Different A. annua materials including the leaves, stems/ flowers, roots, and seeds as well as the endophytes inside A. annua have been employed for phytochemical investigations. Up to the time of this writing, more than 150 natural products were reported to belong to different chemical structure types. Herein, we try to give a summary of these secondary metabolites isolated from A. annua to date. 

In summary, 150 secondary metabolites, besides those common compositions of the plant, have been found and isolated from A. annua, including compounds isolated from endophytes inside A. annua. To date, all phytochemical studies in relation to A. annua have led to 60 sesquiterpenes 16 mono-, di-, and ttiterpenes 46 flavonoids 7 coumarins 9 miscellaneous components and 13 endophyte-produced natural products. 

Gershenzon, J. (1984) Changes in the levels of plant secondary metabolites under water and nutrient stress, in Recent Advances in Phytochemistry. 18. Phytochemical Adaptations to Stress (eds B.N. Timmermann, C. Steelink and F.A. Loewus). Plenum, New York, pp. 273-320. 

Suzuki M, Vairappan CS. Halogenated secondary metabolites from Japanese species of the red algal genus Laurencia (Rhodomela-ceae, Ceramiales). Curr. Topic. Phytochem. 2005 7 1-34. 

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