Coumarins, plant

Phytochemistry Aboveground parts contain essential oil, phenols, ketones, flavonoids, alkaloids, and coumarins (Plant Resources of the USSR 1993). 

Expression or cold pressing is a process in which the oil glands within the peels of citrus fruits are mechanically crushed to release their content. There are several different processes used for the isolation of citrus oils however, there are four major currently used processes. Those are Pellatrice and Sfumatrice—most often used in Italy—and the Brown Peel Shaver as well as the EMC extractor, which are used predominantly in North and South America. For more details see for example Lawrence 1995. All these processes lead to products that are not entirely volatile because they may contain coumarins, plant pigments, and so on however, they are nevertheless acknowledged as essential oils by the International Organization for Standardization (ISO), the different pharmacopoeias, and so on. 

A special group of 8-lactones formally derived from the hydrox-ycinnamic acids are coumarins with a skeleton of 2//-benzopyran-2-one, which is also called chromen-2-one or 5,6-benzo-2-pyrone (8-99). More than 1000 coumarins are found in nature, but only the basic member of the homologous series of coumarins performs as an aromatic compound this is called coumarin. Plant materials also contain a number of non-volatile coumarins substituted with hydroxyl and methoxyl groups and their glycosides. These and other coumarins, generally taking on the role of phytoalexins, such as iso-coumarins, furanocoumarins and pyranocoumarins, are described in Section 10.3.2.5.2. Some isocoumarins are intensely sweet (such as phyllodulcin) or bitter substances (such as 6-methoxymellein),... 

Phytoalexins are low molecular weight compounds produced in plants as a defense mechanism against microorganisms. They do, however, exhibit toxicity to humans and other animals in addition to microbes (30). Coumarins, glycoalkaloids, isocoumarins, isoflavonoids, linear furanocoumarins, stilbenes, and terpenes aU. fall into the category of phytoalexins (31). Because phytoalexins are natural components of plants, and because their concentration may increase as a response to production and management stimuli, it is useful to recogni2e the possible effects of phytoalexins in the human diet. 

Structure and properties of plant coumarins 98KPS250, 98KPS384. 

Lactones. Physiologically active lactones such as parasorbic acid, coumarin, scopoletin, and protoanemonin occur in many plant families (Figure 2). The lactones may perform a regulatory function in the plant, and have been shown to inhibit germination and to repress root growth [reviewed in detail by Hemberg 61), Evenari 36,37), and Borner 12)]. 

Coumarin, the lactone of o-hydroxycinnamic acid, and some of its derivatives have been isolated from many plant species 31). Thimann and Bonner 141) attributed the growth-inhibiting effects of coumarin to its action on enzyme sulfhydryl groups. Inhibitory effects of coumarin on Avena coleoptiles and pea stem sections could be overcome by 2,3-dimercaptopropanol (BAL). Coumarin has also been reported to disrupt mitosis 29,30). 

Chelidonic acid has been found to exist in the free state in many plants (122). A concentration as high as 10 2 M, calculated on a fresh-weight basis, has been measured. Leopold et al. (89) found that chelidonic acid functioned as a growth inhibitor in the pea straight-growth test. Some inhibition was obtained at 10 5 M and 50% inhibition was measured at 10 4 M. Growth was promoted in the presence of IAA. This action is similar to that noted for coumarin and other unsaturated lactones. As with lactones, the inhibitory effect of chelidonic acid could be relieved by pretreatment of the tissue with BAL. 

The cyclopenta[c]coumarin derivative (12), which occurs with sesquiterpenes in liverworts, has been synthesised in both racemic and enantiomeric forms by lactonisadon and further manipulation of the cyclopentenylbenzene derivative (11) <96SYN863>. Liverworts have been used to illustrate the value of direct nmr analysis of CDCI3 plant extracts <96CC2187>. 

The availability of North American specimens of Glehnia made it possible to compare coumarin and acetylene profiles of this widely disjunct system (Hiraoka et al., 2002). Analysis of plant material collected from four widely separated sites, that is, northern California, central Oregon, northern Washington, and northeastern Queen Charlotte Islands, British Columbia, revealed a profile characterized by low levels of furanocoumarins and a comparatively high level of panaxynol. The results are similar to those that characterize the southern Japanese form. The North American... 

E) coumarins, (F) quinones, (G) flavonoids, (H) tannins, (I) alkaloids, (J) terpenoids and steroids and (K) miscellaneous and unknowns. Although many of these compounds are secondary products of plant metabolism, several are also degradation products which occur in the presence of microbial enzymes. 

Arcmatic compounds phenols, phenolic acids, cinnamic acid derivatives, coumarins, flavonoids, quinones, and tannins, all of which are aromatic compounds, comprise the largest group of secondary plant products. They are often referred to as "phenolics" and have been identified as allelopathic agents in more instances than all of the other classes of compounds combined 5). 

Plant metabolism can be separated into primary pathways that are found in all cells and deal with manipulating a uniform group of basic compounds, and secondary pathways that occur in specialized cells and produce a wide variety of unique compounds. The primary pathways deal with the metabolism of carbohydrates, lipids, proteins, and nucleic acids and act through the many-step reactions of glycolysis, the tricarboxylic acid cycle, the pentose phosphate shunt, and lipid, protein, and nucleic acid biosynthesis. In contrast, the secondary metabolites (e.g., terpenes, alkaloids, phenylpropanoids, lignin, flavonoids, coumarins, and related compounds) are produced by the shikimic, malonic, and mevalonic acid pathways, and the methylerythritol phosphate pathway (Fig. 3.1). This chapter concentrates on the synthesis and metabolism of phenolic compounds and on how the activities of these pathways and the compounds produced affect product quality. 

Shikimates, which include phenylalanine, tyrosine, tryptophan, and their derivatives, are represented by many aromatic natural products, including hydroquinones found inbrownalgae such as Sargassum (Segawaand Shirahama 1987). Flavonoids are a structural class of shikimates found in plants, including isoflavonoids or neo-flavonoids, as is the y-pyrone (coumarin) core structure (Knaggs 2003). 

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