Simple plant phenols

Simple plant phenols are monomeric monohydroxy- to polyhydroxyphenolic compounds. In the plant kingdom a great number of these substances is present, and in the majority of cases their biochemical function is not yet known. As already mentioned, they participate particularly in secondary metabolism. They are formed as products of metabolic transformations 

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Fig. 2.4 Some common simple plant phenolic adds, cinnamic acid derivatives on the right and benzoic acid derivatives on the left, where H equals hydrogen, OH equals hydroxy, and OMe equals methoxy...

Food and plant phenolics are commonly detected using DAD detectors (Tan and others 2008). Photodiode array detection allows collection of the entire UV spectrum during the elution of a chromatographic peak, which makes it possible to identify a phenolic compound by its spectra. Simple phenols, phenolic acids, flavanones, benzophenones, isoflavones, and flavan-3-ols have maximum absorbance at 280 nm, hydroxycinnamic acids at 320 nm, flavonols, flavones, and dihydroflavonols at 365 nm, and anthocyanins at 520 nm (Ibern-G6mez and others 2002 Merken Hand Beecher 2000). Hydrolyzable tannins show a characteristic shoulder at 300 nm, suitable for identifying them (Arapitsas and others 2007). For stilbenes, maximum absorbance of trans-forms are at 306 nm and at 285 nm for cA-forms (Lamuela-Raventos and others 1995). 

Precursors of phenylpropanoids are synthesized from two basic pathways the shikimic acid pathway and the malonic pathway (see Fig. 3.1). The shikimic acid pathway produces most plant phenolics, whereas the malonic pathway, which is an important source of phenolics in fungi and bacteria, is less significant in higher plants. The shikimate pathway converts simple carbohydrate precursors into the amino acids phenylalanine and tyrosine. The synthesis of an intermediate in this pathway, shikimic acid, is blocked by the broad-spectrum herbicide glyphosate (i.e., Roundup). Because animals do not possess this synthetic pathway, they have no way to synthesize the three aromatic amino acids (i.e., phenylalanine, tyrosine, and tryptophan), which are therefore essential nutrients in animal diets. 

It has been noted that the chemical diversity of plant phenolics is as vast as the plant diversity itself. Most plant phenolics are derived directly from the shikimic acid (simple benzoic acids), shikimate (phenylpropanoid) pathway, or a combination of shikimate and acetate (phenylpropanoid-acetate) pathways. Products of each of these pathways undergo additional structural elaborations that result in a vast array of plant phenolics such as simple benzoic acid and ciimamic acid derivatives, monolig-nols, lignans and lignin, phenylpropenes, coumarins, stilbenes, flavonoids, anthocyanidins, and isollavonoids. 

Pedersen, M. and DaSilva, E.J., 1973. Simple brominated phenols in the bluegreen alga Calothrix brevissima West. Plants, 115 83—86. 

A straightforward classification attempts to divide the broad category of phenolics into simple phenols and polyphenols, based exclusively on the number of phenol subunits present, but many plant phenolic compounds are polymerized into larger molecules. Thus, the term plant phenolics encompasses simple phenols, phenolic acids, coumarins, flavonoids, stilbenes, hydrolyzable and condensed tannins, lignans, and hgnins [4]. 

Polyphenols are a widespread group of secondary metabolites found in plants derived from phenylalanine and tyrosine, and they are characterized by the presence of several phenol groups (i.e., aromatic rings with hydroxyls) [1]. Plant phenolics include simple phenols, phenolic acids (benzoic and cinnamic acid derivatives), coumarins, flavonoids, stilbenes, hydrolysable and condensed tannins, lignans, and lignins [2, 3]. 

The chemical nature of plant phenolics varies from simple molecules (phenolic acids) to complex polyphenols such as flavonoids, anthocyanins, and highly polymerized substances that include varying proportions of phenolic acids, phenyl propanoids, anthocyanins, and tannins, among others [3,16-18],... 

At the phylogenetic level of the plants, it appears to catalyze the formation of intermediates in biosynthetic systems which produce the flower pigments and related flavonoids, the lacs and lacquers, the simple and polymeric tannins and their esters, the phenolic alkaloids, the quinones, tropolones and simple plant melanins, and the lignins. At higher phylogenetic levels the phenolase complex catalyzes intermediate phases in the... 

Phenolic compounds that act as antioxidants are widespread in the plant kingdom. Plant phenolics can be classified as simple phenolics, phenolic acids, hydroxycin-namic acid derivatives, and flavonoids. In addition to the basic hydroxylated aromatic ring structure of these compounds, plant phenolics are often associated with sugars and organic acids. The consumption of natural plant phenolics have been estimated to be up to 1 g per day. Overall, the presence of phenolics in the diet has been positively... 

Simple phenols are scarce and, in general, they are found as heterosides in plants. Phenolic acids are grouped into benzoic acid derivatives and cinnamic acid derivatives. The most relevant extracted phenols used in cosmetics are arbutin, vanillin and salicylic alcohol or saligenin. 

As a group, the MlC-causing bacteria may use almost any available organic carbon molecules, from simple alcohols or sugars to phenols to wood or various other complex pcJymers as food (heterotrophs), or they may fix CO9 (autotropha) as do plants. Some use inorganic elements or ions (e.g., NH or NO, CH, H, S, Fe, Mu, etc.), as sources of... 

As recently as 1970, only about 30 naturally occurring organohalogen compounds were known. It was simply assumed that chloroform, halogenated phenols, chlorinated aromatic compounds called PCBs, and other such substances found in the environment were industrial pollutants. Now, only a third of a century later, the situation js quite different. More than 5000 organohalogen compounds have been found to occur naturally, and tens of thousands more surely exist. From a simple compound like chloromethane to an extremely complex one like vancomycin, a remarkably diverse range of organohalogen compounds exists in plants, bacteria, and animals. Many even have valuable physiological activity. Vancomycin, for instance, is a powerful antibiotic produced by the bacterium Amycolatopsis orientalis and used clinically to treat methicillin-resistant Staphylococcus aureus (MRSA). 

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