Synthesis of polysaccharides

Ring-opening polymerization has played an important role in systematic approaches to the chemical synthesis of polysaccharides and the clarification of their biomedically interesting characteristics in relation to their own molecular structures. The early... 

The polymer 21 contains a reactive olefinic linkage in its repeating unit, and can be modified chemically in various manners. In particular, it is expected that the polymer can be used as a versatile precursor for the chemical synthesis of polysaccharide... 

Hence polysaccharides have been viewed as a potential renewable source of nanosized reinforcement. Being naturally found in a semicrystalline state, aqueous acids can be employed to hydrolyze the amorphous sections of the polymer. As a result the crystalline sections of these polysaccharides are released, resulting in individual monocrystalline nanoparticles [13]. The concept of reinforced polymer materials with polysaccharide nanofillers has known rapid advances leading to development of a new class of materials called Bionanocomposites, which successfully integrates the two concepts of biocomposites and nanometer sized materials. The first part of the chapter deals with the synthesis of polysaccharide nanoparticles and their performance as reinforcing agents in bionanocomposites. 

Scheme 2. Various conditions and steps involving general synthesis of polysaccharide nanoparticles...

We must give first an outline of the non-metal pathways which we observe in all cells. We start here because we know nothing about their abiotic chemistry but assume that cellular life arose from it. We shall assume that the basic requirement of all metabolism is the energised and catalysed synthesis of polysaccharides, lipids, proteins and nucleic acids. These are polymers (see Table 4.5), formed from monomers, all of which could have always arisen when energy was applied to the... 

One of the recent fundamental advances in carbohydrate chemistry has been enzymic synthesis in vtiro this has now been realized with dextran8 and with levan.8 However, since phosphate sugars are not involved in the enzymic syntheses of these two bacterial polysaccharides, it is obvious that phosphorylation is just one process for the natural synthesis of polysaccharides. 

J. F. Robyt, Mechanism in the glucansucrase synthesis of polysaccharides and oligosaccharides from sucrose, Adv. Carbohydr. Chem. Biochem., 51 (1995) 133-168. 

The overall process can be divided into several stages activation (or initiation), binding to a macromolecule, elongation, movement of the elongating molecule, termination and post-synthetic modification. Analogous processes occur in the synthesis of polysaccharides and peptides (Chapters 6 and 20. See Table 6.2). 

The chemical synthesis of polysaccharides which involves the generation of many glycosidic bonds to form one molecule has been reviewed recently... 

From the standpoint of synthesis of polysaccharides, the most significant aspect of a polymerization mechanism is whether or not it involves regio- and stereo-selective control. However, the structural and stereochemical problems with polysaccharide synthesis are generally simpler than those that obtain with a racemic, unsymmetrical monomer, such as (R, S)-propylene oxide. For example, a variable percentage of head-to-head and tail-to-tail sequences is found in... 

The involvement of glycolipid and glycoprotein intermediates in the synthesis of polysaccharides from glycosyl-nucleotides in plants is considered to be a likely possibility. Such intermediates could act as specific primers, or acceptor substrates, for the formation of polysaccharides. Furthermore, subunits of complex heteropolysaccharides could be assembled on such intermediates, and later incorporated into polysaccharides, or directly cross-linked into the cell wall. Evidence of the involvement of such intermediates in the synthesis of polysaccharides in a number of organisms is presented in Sections XII,3,b and XII,3,c. 

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