Monosaccharides trioses

Monosaccharides are those carbohydrates that cannot be hydrolyzed into simpler carbohydrates They may be classified as trioses, tetroses, pentoses, hex-oses, or heptoses, depending upon the number of carbon atoms and as aldoses or ketoses depending upon whether they have an aldehyde or ketone group. Examples are listed in Table 13-1. 

Depending on the number of carbon atoms present, monosaccharides are classihed as triose, tetrose, pentose or hexose, containing three, four, five or six carbon atoms, respectively. Glucose is a hexose as it contains six carbon atoms. Sometimes, monosaccharides are classified more precisely to denote the functional group as well as the number of carbon atoms. For example, glucose can be classified as an aldohexose, as it contains six carbon atoms as well as an aldehyde group. 

FIGURE 7-1 Representative monosaccharides, (a) Two trioses, an aldose and a ketose. The carbonyl group in each is shaded, (b) Two common hexoses. (c) The pentose components of nucleic acids. D-Ribose is a component of ribonucleic acid (RNA), and 2-deoxy-o-ribose is a component of deoxyribonucleic acid (DNA). 

Monosaccharides, also called simple sugars, are classified by the number of carbon atoms (triose, tetrose, pentose, and so on) and by the nature of the carbonyl group (aldose or ketose). 

The resulting furfurals then can undergo a series of complicated polymerization reactions. Hodge (8) reported that these reactions include hydrolytic fission, fission of 2-ketoses, dehydration of triose, dismutation of biose, trioses, and tetroses, self- and cross-condensations of aldehydes and ketones, reversion of aldoses and ketoses to various oligosaccharides, dimerization of monosaccharides, cyclodehydration of aldoses followed by polymerization, and finally, the enolization and dehydration of formed oligosaccharides. 

Drawing Monosaccharide Structures The Fischer Projection. From the stereochemical point of view, monosaccharides are considered to be derived from the two trioses, D- and L-glyceraldehyde (see Fig. III-l). These two parent compounds differ only in the steric arrangement of the atoms about the central asymmetric carbon they are mirror images (enantiomorphs, optical antipodes) of one another. 

Triose (Section 27.2) A monosaccharide containing three carbons. 

Monosaccharides carbohydrates that cannot be hydrolyzed (split, with the addition of HjO) into simpler carbohydrates. Typically, they contain 3,4,5, or 6 carbons (trioses, tetroses, pentoses, hexoses). Glucose (fig. 3.1) as well as fructose and galactose are examples of hexoses. 

There are many publications and comprehensive handbooks on the thin-layer chromatography (TLC) of carbohydrates (e.g., Refs. 1 and 2). The reason is their great importance in life science and the great diversity of cases monosaccharide, disaccharide, trisaccharide, oligosaccharide, polysaccharide, aldose, ke-tose, triose, tetrose, pentose, hexose, as well as reducing and nonreducing sugars. In addition, when extracted from natural products or produced by fermentation, carbohydrates are accompanied by many impurities. That is why separation methods are used predominantly for their analysis. 

Carbohydrates form a class of compounds of carbon with hydrogen and oxygen. The name comes from the chemical formulas of these compounds, which can be written C (H20) suggesting a hydrate of carbon. Simple sugars, or monosaccharides, are carbohydrates with the chemical formula C H2 0 . Sugars with three, four, five, and six carbon atoms are called trioses, tetroses, pentoses, and hexoses, respectively. 

Lower monosaccharides, i.e., aldo- and keto-bioses, -trioses, and -tetroses, do not exist naturally in a free state. Glyceroaldehyde and hydroxyacetone in phospho-rylated forms are the products of alcoholic fermentation and glycolytic sequence. Erythrose and erythrulose also appear in phosphorylated forms in the pentose cycle of glucose, while ketopentose-ribulose can be found as its phosphate ester (Table 5.1). 

Monosaccharides are identified by their carbonyl functional group (aldehyde or ketone) and by the number of carbon atoms they contain. The simplest monosaccharides are the two trioses glyceraldehyde (an aldotriose) and dihydroxyacetone (aketotriose). Four-, five-, six-, and seven-carbon-containing monosaccharides are called tet-roses, pentoses, hexoses, and heptoses, respectively. Structures of some monosaccharides are shown in Figure 9-1. All monosaccharides, with the exception of dihydroxyacetone, contain at least one asymmetrical or chiral carbon atom, and therefore two or more stereoisomers are... 

Monosaccharides bearing an aldehyde are known as aldoses, whereas those bearing a ketone are known as ketoses. Sugars bearing three, four, five and six carbon atoms are known as trioses, tetroses, pentoses and hexoses, respectively. 

The forms of glucose in aqueous solution are quite complex and small proportions exist as furanose structures. These arise from the reaction between the OH group at C-4 and the aldehyde group in aldoses. The five-membered ring system is quite stable but pyranose forms are favoured over furanose forms by most monosaccharides notable exceptions are the ketohexose fructose and the aldopentose ribose. Too much strain would be involved in reducing bond angles to produce smaller rings, so trioses and tetroses do not form intermolecular cyclic systems. 

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