Glucose aldohexose

Problem 22.11 The C -epimeric aldohexoses glucose and mannose give the same osazone as fructose. Write equations and explain the configurational significance. M... 

Fischer found osazone formation to be useful not only in identifying carbohydrates, but also—and this was much more intportant—in determining their configurations. For example, the two diastereomeric aldohexoses (+)-glucose and... 

The term glycosylation (more rarely, glucosylation) has been used almost universally to reflect the nonenzymatic adduct of the aldohexose glucose... 

For the epimerization of aldohexoses (glucose and mannose), minute amounts of fructose are produced as the sole by-product. In the case of the aldo-... 

Hexoses.—CgH Og.—Out of twenty-four possible hexoses, only four are capable of utilisation by higher animals. These are the aldohexoses, glucose, mannose, and galactose, and the ketohexose fructose. All are D-sugars, being related structurally to d-glycerose. 

Important monosaccharides are the aldohexoses, glucose and galactose, and the ketohexose, fructose. 

Like aldopentoses aldohexoses such as d glucose are capable of forming two fura... 

The aldohexoses are allose altrose glucose mannose gulose idose galactose and talose The mnemonic All altruists gladly make gum m gallon tanks is helpful m writing the correct Fischer projection for each one... 

Classify each of the following sugars. (For example, glucose is an aldohexose. (a) CH2OH (b) CH2OH (c CHO... 

Six of the 18 aldohexoses, namely, D-glucose, d- and L-mannose, D-galac-tose, D-allose, and L-altrose have been found in bacterial polysaccharides. 

From a structural point of view, the carbohydrate template can have either furan or pyran rings although in some cases open chain structures can be formed. A large variety of aldopentoses (e.g. d- and L-arabinose, D-ribose, D-xylose), aldohexoses (e.g. D-glucose, D-mannose, D-galactose) as well as ketohexoses (e.g. D-fructose, L-sorbose) can be used as scaffolds. 

Van t Hoff had predicted, in 1874, that there should exist 16 normal straight-chain optically isomeric aldohexoses (8,13). It was the awesome challenge to substantiate this prediction that Fischer accepted in the mid-1880s, and that was met by his classical contribution in 1891 entitled, On the Configuration of Glucose and Related Compounds (4). 

Figure 9.5 Cyclic, hemiacetal structures of D-glucose. The reaction between an alcohol and aldehyde group within an aldohexose results in the formation of a hemiacetal. The only stable ring structures are five- or six-membered. Ketohexoses and pentoses also exist as ring structures due to similar internal reactions.

The carbonyl group in glucose and ribose is an aldehyde such compounds are termed aldoses. Fructose, by contrast, has a ketone group and is therefore classified as a ketose. Glucose could also be termed an aldohexose and fructose a ketohexose, whereas ribose would be an aldopentose, names which indicate both the number of carbons and the nature of the carbonyl group. Another aspeet of nomenclature is the use of the suffix -ulose to indicate a ketose. Fructose could thus be referred to as a hexulose, though we are more likely to see this suffix in the names of specific sugars, e.g. ribulose is a ketose isomer of the aldose ribose. 

It follows that, when we dissolve a sugar such as glucose or ribose in water, we create a mixture of various equilibrating structures. The relative proportions of pyranose and furanose forms, and of their respective anomers for the eight aldohexoses, are shown in Table 12.1. In each case, the proportion of non-cyclic form is very small (<1%). 

The most important natural monosaccharide, D-glucose, is an aliphatic aldehyde with six C atoms, five of which carry a hydroxyl group (1). Since C atoms 2 to 5 represent chiral centers (see p. 8), there are 15 further isomeric aldohexoses in addition to D-glucose, although only a few of these are important in nature (see p.38). Most natural monosaccharides have the same configuration at C-5 as D-glyceraldehyde-they belong to the D series. 

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