Phytochemicals types

Although it is comparatively easy to explain the fact that some alkaloids inhibit AChE because of their molecular features, it is not easy to correlate chemical structure and activity for some other phytochemical types for which AChE inhibition has recently been reported. 

Recent work identifying Plagiochila retrorsa Gottsche from collections made in the Azores and Madeira establishes a significant range extension for a taxon, known under several other names, which occurs in the southern Appalachian Mountains and in Costa Rica. Rycroft et al. (2001) described morphological and phytochemical characteristics of representative specimens of this liverwort. Phytochemically, P. retrorsa belongs to the 9,10-dihydrophenanthrene chemotype species (major stmctural type is that of compounds 449 and 450). 

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 ... 

The types and quantities of phytochemicals present in foods may have very little bearing on the nutritional quality of these foods and their contribution to human health. This is because ... 

The different types or classes of phytochemicals can have multiple influences on the GIT (Kitts, 1994). For example, caffeine stimulates the motor, hormonal and secretory functions (Boekmaefa/., 1999). Although many phytochemicals reduce nutrient quality or availability, traditional herbal medicines have exploited some of these characteristics to improve health. Moreover, some of the systemic responses attributed to certain phytochemicals (beneficial or detrimental) can be explained by their influences on the GIT (Carbonaro et al., 2001). To date, the most of the information about phytochemicals is focused on the reductions in the functional capacities of the GIT (the bad), or the toxic properties (the ugly). There are also numerous examples of phytochemicals that can be used to obtain desirable GIT characteristics (the... 

In recent years, numerous papers have been published about one of the most important groups of phytochemicals, the polyphenols (Manach and others 2004). These compounds, which possess an array of healthy properties, but also some disadvantages that will be discussed in this chapter, are present in a variety of plants used in both human and animal diets. However, the structure of this type of compound means that they can be oxidized by several pro-oxidant agents. The objective of this chapter is to describe the main enzymatic agents responsible for the degradation of polyphenols. In order to understand the mechanisms of degradation that will be described in the following sections, a brief summary of the main properties of the polyphenols is required. 

Dembinska-Kiec A, Mykkanen O, Kiec-Wilk B and Mykkanen H. 2008. Antioxidant phytochemicals against type 2 diabetes. Br J Nut 99 ES109-ES117. 

As has been explained in previous chapters, the antioxidant capacity of fruits and vegetables is a function of the amounts and types of phytochemicals that are present in the fresh tissues. However, the individual contribution to the total antioxidant capacity varies widely. Various studies have demonstrated that phenols and flavonoids contribute to a higher extent than ascorbic acid, carotenoids, and others to the antioxidant capacity of fmits and vegetables (Robles-Sanchez and others 2007). It has been observed that a given content of vitamin E in fruits contributes significantly more to the antioxidant capacity than the same content of ascorbic acid. 

Cui, J.-F., Eneroth, P., Bruhn, J. G., Arihara, S., and Yoshikawa, K. (1998). Alkaline cleavage of gypenosides and characterization of dammarane-type aglycones by gas chromatography-mass spectrometry. Phytochem. Anal. 9, 128-133. 

When a racemic substance is hydrogenated or when the reduction leads to the production of centers of asymmetry, the phytochemical reduction will take at first a completely or partially asymmetric course. Examples of such asymmetric reactions are the conversions of pure racemic valeraldehyde, acetaldol, furoin and furil, diacetyl and acetyl-methylcarbinol to optically active alcohols. Occasionally meso forms also arise, as for example in the case off glycols (p. 84). The reasons for the stereochemical specificity of these reactions have not been clarified. This type of phenomenon has frequently been observed in the related intramolecular dismutation of keto aldehydes, especially if enzyme materials of differing origins are used. 

The phytochemical reducibility of quinones was first demonstrated in the case of p-xyloquinone. This compound is worthy of interest since it is very easily formed from diacetyl by purely chemical means through a type of aldol condensation followed by ring closure. It is reduced to p-xylohydroquinone by fermenting yeast. Benzoquinone, thymoquinone and a-naphthoquinone similarly yield the corresponding hydroquinones. Tetrabromo-o-quinone and anthraquinone proved resistant to attack, while phenanthraquinone could be reduced phyto-chemically to phenanthrahydroquinone in poor yield (9%). Phytochemical reduction can also be accomplished in the dicyclic terpene series. According to unpublished experiments by Neuberg and Peiser, 2,3-dihy-... 

The phytochemical study consisted of fractionating plant extracts leading to the isolation of various novel and known derivatives. The choice of appropriate separation methods was crucial for this type of research the extracts may be very complex, thus separation of one single component... 

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