Polyphenols structural types

ABSTRACT More than 200 naturally occurring oligostilbenes isolated from plant kingdom are grouped into I-V structural types. They are a special kind of polyphenolic natural products with multi-faceted bioactivities. This article will review their classification, distribution, spectral characteristics, biological activities (anti-fungal, antibacterial, antioxidant, anti-inflammatory and anticarcinogenic activities, etc.) and mimetic biosynthesis. 

Further examples of this type of polyphenolic structure in which molecular complexity and size are increased by oxidative coupling of two or more glucose derivatives (45-49) by formation of new C-0 bonds have been described, 0-62... 

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. 

Because of the easily oxidizable structure of the polyphenols previously described, many studies have been published about the enzymatic degradation of these antioxidant compounds. This chapter exhaustively reviews the main publications concerning the degradation of this type of antioxidant compound by several enzymes. 

The most prominent wood adhesives used over the last quarter of a century have been aminoplast and polyphenolic types (2). In the United States, polyphenolic adhesives continue to be predominantly used for production of weather-resistant wood products, such as structural plywoods and flake boards (3). Phenolic resin prices have increased over the past decade, generally paralleling phenol prices. This increase has occurred in part due to a continuing erosion of United States phenol manufacturing capacity and the corresponding increase in availability of phenol from other countries. Any significant increase in the price of oil (the source of phenol) itself or interruption in supply will only compound the problem and raise phenol prices even higher. 

It is possible to prepare R. vernicifera laccase which is reversibly depleted in the type 2 copper. This is a great aid in understanding the role of type 2 copper in the mechanism. Type 2-depleted laccase may exist with the type 3 site in the oxidized or reduced form. The spectral features of the blue type 1 copper change with change in the oxidation state of the type 3 copper. This intersite structural interaction may relate to the electron-transfer pathway between type 1 and type 3 copper.1337 The type 2 site has been implicated in the binding of polyphenolic substrates.959... 

The chalcone synthase (CHS) (EC 2.3.1.74) superfamily of type III Polyketide synthases (PKSs) are pivotal enzymes in the biosynthesis of plant polyphenols. They are structurally and mechanistically different from the modular type I and the dissociated type II PKSs of bacterial origin the simple homodimer of 4CM-5 kDa proteins performs a complete series of decarboxylation, condensation, cyclization,... 

More recently, there has been a renewed recognition of the potential of bark-derived polyphenols for adhesives as a result of improved understanding of the chemical structure of these materials (, 5), new types of formulations (5), and the fact that tannins are being commercially used in adhesives in South Africa (7), thus serving as a prototype for utilization in other parts of the world. In order to properly assess the current developments in this field, this overview will provide a historical perspective on adhesives based on tannins as well as a summary of the extraction techniques and chemical structures. Finally, areas where additional work could be fruitful will be suggested. 

More than 5000 different phytochemicals have been identified, but it is believed that thousands more have yet to be discovered (Liu, 2003). Based on their structural characteristics, they may be classified into several groups including polyphenols, terpenoids, and alkaloids (Manach et ah, 2009). As evidence continues to emerge linking phytochemicals to health promotion and disease prevention, there is increased interest in extraction, isolation, and analysis of these compounds from a variety of plant sources. These procedures have been optimized for several different types of phytochemicals and are used in the discovery of compounds from new sources. 

A different type of polypeptide has been made by polymerizing tyrosine and its derivatives with peroxidase, laccase, or bilirubin oxidase [19, 63], The resulting polymers do not have the a-peptide structure, but consist of polyphenols with mixtures of phenylene and oxyphenylene units. Tyranosinase is also known to oxidize tyrosine, which can lead to polymerization reactions to form melanin [64]. 

Free radicals are ubiquitous. They are found in living plants and for practical purposes are essential to all life. They also exist in plant material that is dried. These types of free radicals are called persistent free radicals and are normally associated with free radicals present in the structural biomass of the plant (polyphenols, carbohydrates, and lignin). The tobacco precursors of free radicals found in the particulate phase of cigarette mainstream smoke (MSS) are also long-lived, persistent free radicals but arise from the thermolysis of the tobacco biomass to form numerous types of phenolic and quinoidal free radicals [Wooten et al. (27A120)]. Short-lived free radicals are also present in the vapor phase... 

It is now well-established that some enzyme families, including various peroxidases and laccases, catalyze the polymerization of vinyl monomers and other redox active species such as phenol-type structures. Vinyl polymerization by these redox catalysts has recently been reviewed 93). These catalysts have been used to prepare polyanilines 94) and polyphenols 95,96). A few examples of related research are included in this book. For example. Smith et al (57) described a novel reaction catalyzed by horseradish peroxidase (HRP). In the presence of HRP and oxygen, D-glucuronic acid was polymerized to a high molecular weight (60,000) polyether. However, the authors have not yet illucidated the polyether structure. Two other oxidative biotransformations were discussed above i) the sono-enzymatic polymerization of catechol via laccase 31), and ii) the oxidation of aryl silanes via aromatic dioxygenases 30). 

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