The Monosaccharides

A review on the physiological importance of trioses and related substances has appeared.12 

Preparation. Fischer and Baer employed the glycol cleavage of l,2 5,6-di-0-isopropylidene-D-mannitol, followed by acid hydrolysis, to provide d-glyceraldehyde.13 A most convenient preparation is that of Perlin,14 who oxidized D-fructose with a limited proportion of lead tetraacetate, and hydrolyzed the resulting derivative. D-Glyceraldehyde 3-phosphate has been synthesized.15 

DL-Glyceraldehyde, known, in contrast to the optically active forms, as a crystalline material (dimer, mp 142°), has been resolved by condensation with (d Xtro)-a-(2-hydroxy-1 -naphthyl jbenzylamine.16 

The oxidation of glycerol in the presence of Acetobacter xylinum gives the ketotriose 2, which can be separated as its insoluble sodium hydrogensulfite addition compound, and then, recovered on acidification. The dimer, mp 82°, is obtained on crystallization from ethanol but, on standing, higher-melting products are deposited from the mother liquor.17 The 1-phosphate has been synthesized.18 

Occurrence and preparation. The tetrose (4) participates as D-erythrose 4-phosphate in the pentose phosphate pathway of carbohydrate metabolism.11 D-Erythrose can be prepared using a method of degradation from the pentose, D-arabinose,19 or from D-glucose.20 Synthesis of the 4-phosphate has been reported.21 

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Carbohydrates may be divided into monosaccharides, disaccharides and polysaccharides. The monosaccharides under certain conditions react as polyhydroxy-aldehydes or polyhydroxy-ketones two important representatives are glucose CjHjjO (an aldose) and fructose (laevulose) CgHuO, (a ketose). Upon hydrolysis di- and polysaccharides 3deld ultimately monosaccharides. Common disaccharides are sucrose, lactose and maltose (all of molecular formula C,2H2. 0,), whilst starch, dextrin and cellulose, (CjHjoOj), in which n > 4, are typical polysaccharides. 

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. 

Of all the monosaccharides d (+) glucose is the best known most important and most abundant Its formation from carbon dioxide water and sunlight is the central theme of photosynthesis Carbohydrate formation by photosynthesis is estimated to be on the order of 10 tons per year a source of stored energy utilized directly or indi rectly by all higher forms of life on the planet Glucose was isolated from raisins m 1747 and by hydrolysis of starch m 1811 Its structure was determined in work culmi nating m 1900 by Emil Fischer... 

Sugar is destroyed by pH extremes, and inadequate pH control can cause significant sucrose losses in sugar mills. Sucrose is one of the most acid-labile disaccharides known (27), and its hydrolysis to invert is readily catalyzed by heat and low pH prolonged exposure converts the monosaccharides to hydroxymethyl furfural, which has appHcations for synthesis of glycols, ethers, polymers, and pharmaceuticals (16,30). The molecular mechanism that occurs during acid hydrolysis operates, albeit slowly, as high as pH 8.5 (18). 

Dextrose (D-glucose) is by far the most abundant sugar in nature. It occurs either in the monosaccharide form (free state) or in a polymeric form of anhydrodextrose units. As a monosaccharide, dextrose is present in substantial quantities in honey, fmits, and berries. As a polymer, dextrose occurs in starch, cellulose (qv), and glycogen. Sucrose is a disaccharide of dextrose and fmctose. 

FIGURE 7.21 Amylose and amylopectin are the two forms of starch. Note that the linear linkages are o (1 4), but the branches in amylopectin are o (1 6). Branches in polysaccharides can involve any of the hydroxyl groups on the monosaccharide components. Amylopectin is a highly branched structure, with branches occurring every 12 to 30 residues. 

Amino sugars, such as o-glucosamine, have an OH group leplaced by an -NH2. The N-acetyl amide derived from o-glucosamine is the monosaccharide unit from which chitm, the hard crust that protects insects and shellfish, is made. Still otheramino sugars are found in antibiotics such as streptomycin and gentamicin. 

Disaccharides, which are dimers farmed when two monosaccharide units combine with the elimination of H20. The monosaccharides may be the same (two glucose units in maltose) or different (a glucose and fructose unit in sucrose). 

Many are neutral glucans, being composed of the monosaccharide component... 

The group formed by detaching one hydrogen atom from each of two (or three) carbon atoms of a monosaccharide is named by replacing the terminal -e of the monosaccharide name by -diyl (or -triyl ), preceded by the appropriate locants. 

Symbols for the common monosaccharide residues and derivatives are listed in Table 2. They are generally derived from the corresponding trivial names. Abbreviations for substituents (see 2-Carb-1.16.2), preceded by locants, follow the monosaccharide abbreviations directly. 

The hyphens may be omitted, except that separating the configurational symbol and the three-letter symbol for the monosaccharide. 

The reversible reactions are initiated by an equilibrium between neutral and ionized forms of the monosaccharides (see Fig. 6). The oxyanion at the anomeric carbon weakens the ring C-O bond and allows mutarotation and isomerization via an acyclic enediol intermediate. This reaction is responsible for the sometimes reported occurrence of D-mannose in alkaline mixtures of sucrose and invert sugar, the three reducing sugars are in equilibrium via the enediol intermediate. The mechanism of isomerization, known as the Lobry de Bruyn-... 

The aerial part of sage was successively extracted with water, potassium oxalate, DMSO and KOH, and gave rise to different fractions with bioactivity. Partial purification of the water extract gave rise to a polydisperse fraction called A, that based on the monosaccharide composition, IR, and NMR, was thought to be composed of arabinogalactans associated with the highly ramified rhamnogalacturonans core. Fracfion B, exfracfed wifh oxalate, was... 

Wood chips can also be utilized as such to produce bioethanol. The cellulose and hemicellulose material is hydrolyzed in the presence of acids (H2SO4, HCl, or HCOOH) or enzymes to yield glucose and other monosaccharides [16]. Lignin is separated by filtration as a solid residue and the monosaccharides are fermented to ethanol, which, in turn, is separated from water and catalyst by distillation. Ethanol can be used not only as energy source but also as a platform component to make various chemicals, such as ethene and polyethene. Today green acetaldehyde and acetic acid from wood-derived bioethanol is manufactured by SEKAB Ab, at the Ornskoldsvik Biorefinery of the Future industrial park. 

The monosaccharides include glucose, the blood sugar and ribose, an important constiment of nucleotides and nucleic acids. 

Ethylene dithioacetals and diethyl dithioacetals have been investigated for a number of monosaccharides. The c.d. spectra show one, or two, c.d. band(s) of low intensity between 235 and 250 nm, and a third band of low intensity that peaks below 220 nm. These workers found no overall relationship between the configurational pattern of the monosaccharide and the sign of these bands. However, there does appear to be a correlation between the configurations of C-2, C-3 and C-4 and the sign of the c.d. band that peaks below 220 nm. 

Whereas humans can obtain energy from sucrose, insects obtain energy from trehalose, whose line structure follows. Identify the monosaccharides from which trehalose is constructed. 

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