Monosaccharides pentoses

L. Hough and A. C. Richardson, The monosaccharides Pentoses, hexoses and higher sugars, in D. J. Coffey, (Ed.), Rodd s Chemistry of Carbon Compounds, Vol. IF, Elsevier, Amsterdam, 1967, pp. 67-595. Chapter 23. 

Contents History Classification Monosaccharides Pentoses (5-Carbon Sugars)... 

Table 20.4 Some Important Monosaccharides Pentoses (five carbon atoms) ...

The simple sugars or monosaccharides are polyhydroxy aldehydes or ketones, and belong to Solubility Group II. They are termed tetroses, pentoses, hexoses. etc. according to the number of carbon atoms in the long chain constituting the molecule, and aldoses or ketoses if they are aldehydes or ketones. Most of the monosaccharides that occur in nature are pentoses and hexoses. 

Enantiomerically pure tetroses, pentoses, and hexoses have been synthesized by the following reaction sequence (A.W.M. Lee, 1982 S.Y. Ko, 1983), which is useful as a repetitive two-carbon hotnologi-.ation in total syntheses of higher monosaccharides and other polyhydroxy compounds (1) Wittig reaction of a protected hydroxy aldehyde with (triphenylphosphor-... 

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. 

Monosaccharides have the formula (CH2 0) , where n is between 3 and 6. Of the 70 or so monosaccharides that are known, 20 occur in nature. The most important naturally occurring monosaccharides contain five carbons (pentoses) or six carbons (hexoses). Structures of ribose, an important pentose, and a-glucose, a hexose that is the most common monosaccharide, are shown in Figure 13-14. As shown in the figure, it is customary to number the carbon atoms in a monosaccharide, beginning with the HCOH group adjacent to the ether linkage. 

Supplement 1941 1-161 Derivatives. Methyl alcohol, 273. Ethyl alcohol, 292. Ethyl ether, 314. Glycerol, 502. Carbonyl Compounds Aldehydes, Ketones, Ketencs and Derivatives. Formaldehyde, 558. Acetaldehyde, 635. Acetone, 635. Ketene, 724. Hydroxy-Carbonyl Compounds Aldehyde-Alcohols, Ketone-Alcohols, Monosaccharides and Derivatives. Glycolaldehyde, 817. Aldol, 824. Pentoses, 858. Hexoses, 878. 

Figure 9.12 Deoxy derivatives. These contain one less oxygen atom than the monosaccharide from which they are derived. 2-Deoxyribose is a most important deoxy pentose and is a major constituent of deoxyribonucleic acid (DNA). Deoxy hexoses are widely distributed among plants, animals and microorganisms especially as components of complex polysaccharides. Examples are rhamnose (6-deoxymannose), a component of bacterial cell walls, and fucose (6-deoxygalactose), which is often found in glycoproteins and is an important constituent of human blood group substances.

In addition to the common pathways, glycolysis and the TCA cycle, the liver is involved with the pentose phosphate pathway regulation of blood glucose concentration via glycogen turnover and gluconeogenesis interconversion of monosaccharides lipid syntheses lipoprotein formation ketogenesis bile acid and bile salt formation phase I and phase II reactions for detoxification of waste compounds haem synthesis and degradation synthesis of non-essential amino acids and urea synthesis. 

A probable pathway for the degradation of hemicelluloses via free-radical intermediates has been proposed by Fengel and Wegener (1989) and is shown in Figure 5.1. Hemicellulose polymers are depolymerized to form oligosaccharides and monosaccharides, which are dehydrated to form furfural (pentoses) and hydroxymethyl furfural (hexoses). 

Carbohydrates Ceiiuiose Starch 1 Hemiceiiuiose Lignin J ( monosaccharides "j ( hexoses "j Cx(H20)y < oligosaccharides > pentoses > [ chitin J ( glucosamine J (C2H20)4 unsaturated aromatic alcohols —> polyhydroxy carboxylic aoids HPOy, GO2, CH4, glucose, fructose, galactose, arabinose, ribose, xylose... 

Tables V-LVII detail H and F shift and coupling information, and Tables LVIII to LXXI incorporate the C-n.m.r. data. The data within this compilation are arranged according to the following outline hexoses prior to pentoses, followed by anhydro sugars, sugar acids and lactones, amino sugars (and their synthetic, A -containing precursors), mono-, di-, and tri-deoxy sugars, branched derivatives, ketoses, polyfluorinated monosaccharides, and, finally, difluorinated amino sugars. Within this compilation, and even within each table, pyranoid derivatives are listed prior to their furanoid counterparts, hexoses prior to pentoses, functionalized prior to deoxy compounds the arrangement within each sub-table is made alphabetically.

The basic structural unit of carbohydrates is the monosaccharide. Molecules in this class contain just one sugar moiety ahexose, pentose, or whatever. Monosaccharides are the building blocks of more complex carbohydrates in mnch the same sense that amino acids are the building blocks for proteins and nncleotides are the building blocks for nucleic acids. 

Pentose a monosaccharide containing five carbon atoms. 

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