Phenolic compounds and their derivatives

Essential Oils, Natural Phenolic Compounds and their Derivatives... 

The composition of coal tar varies with the carbonization method but consists, largely, of mononuclear and polynuclear aromatic compounds and their derivatives. Coke oven tars are relatively low in aliphatic and phenolic content while low-temperature tars have much higher contents of both. 

A hydrolysis step is involved in the pulp industry in order to concentrate the cellulose from wood. This uses large-scale processes whereby a liquid fraction, the lignocellulose, is formed as a by-product in the process, and contains high levels of phenolic components and their derivatives. These compounds also constitute an environmental problem due to their possible introduction into rivers, lakes, and/or seas. Chlorophenols from the cellulose bleaching process have traditionally attracted most of the interest in the analysis of industrial waste because of their high toxicity. 

Antioxidants from Cereais, Oiiseeds, and Rotated Sources Seeds rich in oils are also abundant sources of various types of antioxidative compounds. Among these carotenoids, phenolic acids, and their derivatives, flavonoids, phytic acid, lignans, and tocopherols are predominantly found depending on the plant genera and species. Reviews by Wanasundara et al. (110) and Shukla et al. (111) discuss antioxidants of oilseeds and their products in detail. 

High-performance liquid chromatography (HPLC) is the method for detection, identification and also quantification of flavonoids, phenolic acids and their derivatives. With this method, the sample is applied and eluted through a chromatographic column under specific conditions designed for optimum separation and resolution so that each compound or group of compound passes through the column with a... 

Dihydric Phenols (Catechols) and their Derivatives (i) 1,2-Dihydroxy Compounds... 

The phenolic constituents and their derivatives were tested for their inhibitory effects on the beef heart cyclic AMP phosphodiesterase. Almost all of the phenolic compounds isolated from the mulberry tree showed significant inhibitory activities (174). 

A wide variety of stationary phases have been used to separate substituted monocyclic phenols and phenolic acid compounds and their derivates by thin-layer chromatography (TLC). In particular, the composition of phenolic acids and flavonoids in leaves, roots, and fruits of several plants and in natural products has been extensively studied by the two-dimensional TLC by using cellulose or silica gel plates in one direction and silanized silica gel in the second direction. Quantitative determinations of flavonoids components of plant extracts were widely performed. 

A molar equivalent of hydrogen peroxide to monomer and horseradish peroxidase is a well-known redox system that catalyzes the free radical polymerization of phenol, anilines, and their derivatives [6-14]. Horseradish peroxidase-mediated polymerization of styrene and methyl methacrylate, with a monomer (styrene or methyl methacrylate) to hydrogen peroxide ratio of 40 1, did not occur in the absence of 2,4-pentanedione. Therefore, it is likely that this compound is involved in the initiation of free radical formation. A reasonable hypothesis for the horseradish peroxidase-catalyzed polymerization of vinyl monomers is that the enzyme is oxidized by hydrogen peroxide and passes from its native state through two catalytically active forms (Ez and Ezz). Each of these active forms oxidizes the initiator (b-diketone, 2,4-pentanedione) while the enzyme returns to the native form. The Ezz state of enzyme is oxidized by hydrogen peroxide to produce inactive enzyme, Ezzz, which spontaneously reverts to the native form of enzyme. The free radicals produced from the initiator generate radicals in the vinyl monomer to form polymer (Fig. 2). 

Simple phenolic compounds include (1) the phenylpropanoids, trans-cinnamic acid, p-coumaric acid and their derivatives (2) the phenylpropanoid lactones called coumarins (Fig. 3.4) and (3) benzoic acid derivatives in which two carbons have been cleaved from the three carbon side chain (Fig. 3.2). More complex molecules are elaborated by additions to these basic carbon skeletons. For example, the addition of quinic acid to caffeic acid produces chlorogenic acid, which accumulates in cut lettuce and contributes to tissue browning (Fig. 3.5). 

The behavior of phenolic compounds derived from decaying plant residues, or released from degrading humic substances, is dictated by the physico-chemical processes of adsorption and desorption. Equilibria between these processes determine the concentration of phenolic compounds in the soil solution and consequently the bioactivity, movement, and persistence of these substances in the soil. Surface interactions between phenolic compounds and colloidal matrices may promote their polymerization (25, 26) or protect them from microbial degradation and mineralization. 

Berchemia zeyheri (Rhamnaceae), a tree native to southern Africa which is prized for its beautiful wood, known as pink ivory or red ivory. The complexity of the phenolic compounds present in heartwood extracts prompted their analysis as permethylated derivatives. Stereochemical features were determined by using both NMR and circular dichroism spectroscopy of the parent compounds and their degradation products. These methods were used successfully to obtain a full stereochemical description of the zeyherin epimers 374 and 375, ° which were first isolated in 1971 but not fully characterized at that time. Subsequent work has led to the discovery of further auronol dimers and novel heterodimers with flavanone or isoflavanone constituents as summarized in Table 16.15. ° ° °... 

Boric acid has the particular ability to form stable complexes with compounds that present cis-hydroxyl groups (cis-diol groups) [117]. Several compounds, such as sugars and their derivatives and some phenolics (o-diphenols) have these cis-diol groups and therefore can form stable complexes with B [117]. 

The reagent is particularly suitable for the determination of amines and phenols and their derivatives, and also for unsaturated compounds. Temperature has a marked effect on the rate and on the extent of bromi-nation. It is necessary to know or to determine what bromo compound is being formed. 

An HPLC method using a 90-min binary gradient with (a) acidified water, pH 2.4, and (b) acetonitrile on an Adsorbosphere C]8, 3-/zl cartridge (Alltech) was also developed for pheno-lics in barley (127). Seven phenolic compounds, including vanillic acid, p-coumaric acid, ferulic acid, and their derivatives, were separated by HPLC after alkaline hydrolysis in order to evaluate the role of bound phenolic acids in their antioxidant activity in beer. In this method, cis and trans isomers of p-coumaric and ferulic acids are quantified by HPLC, although cls-p-coumaric acid was not well separated from its trans isomer in this analysis. 

The ability of compounds with a quinonic structure to form donor-acceptor interactions and CT complexes is useful in regioselective halogenation of phenol (or naphthols and their derivatives). 

In association with well-known health benefits related to the consumption of fruit- and vegetable-rich diets, research on the protective effects of plant-derived phenolic compounds (polyphenols) has developed notably in recent years. In particular, their antioxidant properties have been the objective of extensive research. However these phenolics are the target of an array of chemical reactions that, if confirmed to occur in vivo, would contribute to their health promoting effects. It is now emerging that both parent compounds and their metabolites produced after ingestion can regulate cell and tissue functions by both antioxidant and nonantioxidant mechanisms. This volume provides the latest evidence supporting these concepts. 

Ag20. Protection of the basic nitrogen as an amide moiety was also found to decrease the side reactions involving oxidation at nitrogen. By combining these various tactics, it is now possible to obtain good yields of compounds related to 306 via oxidative cyclizations of phenols and their derivatives. 

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