Sugar, reactions polymerization

Plants and animals synthesize a number of polymers (e.g., polysaccharides, proteins, nucleic acids) by reactions that almost always require a catalyst. The catalysts present in living systems are usually proteins and are called enzymes. Reactions catalyzed by enzymes are called enzymatic reactions, polymerizations catalyzed by enzymes are enzymatic polymerizations. Humans benefit from naturally occurring polymers in many ways. Our plant and animal foodstuffs consist of these polymers as well as nonpolymeric materials (e.g., sugar, vitamins, minerals). We use the polysaccharide cellulose (wood) to build homes and other structures and to produce paper. 

Previous efforts for attaching sugar moieties onto preformed polymers relied on the nucleophilic substitution reaction of aminated sugars with polymeric activated carbonyl compounds. Polymeric backbones containing active carbonyl compounds such as carboxylic acid, acid chloride, carbonate, N-hydroxysuccinimide ester and anhydride react readily with aminated sugar under mild reaction conditions to afford glycopolymers via an amide linkage (Scheme 1.11). 

FIGURE 1.9 (a) Amino acids build proteins by connecting the n-carboxyl C atom of one amino acid to the n-amino N atom of the next amino acid in line, (b) Polysaccharides are built by combining the C-1 of one sugar to the C-4 O of the next sugar in the polymer, (c) Nucleic acids are polymers of nucleotides linked by bonds between the 3 -OH of the ribose ring of one nucleotide to the 5 -P04 of its neighboring nucleotide. All three of these polymerization processes involve bond formations accompanied by the elimination of water (dehydration synthesis reactions). 

Allcock, H, R., and Scopelianos, A. G., Sjmthesis of sugar-substituted cyclic and polymeric phosphazenes, and their oxidation, reduction, and acetylation reactions. Macromolecules. 36. 715, 1983. 

Monosaccharides are probably involved in the browning reactions that occur during the roasting of coffee. Caramelization involving the sugars alone, and Maillard reactions, between sugars and free amino acids, produce polymeric yellow to dark brown substances, known as melanoidins. These melanoidins can be extracted into hot water, separated and characterized.105... 

In the presence of bases, monomeric as well as polymeric sugars are converted into various carboxylates salts [14]. The reaction proceeds through a retro-Michael dehydration step to form an unsaturated aldehyde, followed by rehydration of the aldehyde function and isomerization to acid (Fig. 2.3). The same reaction is also responsible for a stepwise depolymerization of polymeric sugar to carboxylate... 

The initial products of the reactions between sugars and proteins may enter a cascade of reactions yielding fluorescence, browning, and polymerization of proteins ("cross-linking"). The brown pigments, so-called melanoidins, are polymers whose composition has not yet been established completely. Melanoidins bind calcium and may thus interfere with de- and remineralization in caries. 

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