Ketoses common names

As indicated previously, primary and secondary amines can also react with carbonyl compounds to form a mixture of compounds containing small molecules and polymers. The small molecule compounds obtained from an aldose and an amine have the common name Amadori products because the Amadori rearrangement is involved in their formation. The compounds generated from ketoses and amines are known as Heyns products (although the differentiation Amadori/Heyns is not always considered). The mechanism for the reaction of primary amines with a reducing sugar can be formulated as follows ... 

The nomenclature of carbohydrates usually includes the suffix -ose. Monosaccharides may also be identified according to the nature of the carbonyl functional group (aldose or ketose), the number of carbons in the molecule (tri-, tetr-, pent- ose) or a combination of these two. Monosaccharides also have common names such as ribose, glucose, galactose, and fructose (four of the most common monosaccharides found in nature). 

Figure 24-2 o-Ketoses (up to the ketohexoses), their signs of rotation, and their common names. 

An intramolecular ether (commonly called an intramolecular anhydride), formally arising by elimination of water from two hydroxy groups of a single molecule of a monosaccharide (aldose or ketose) or monosaccharide derivative, is named by attaching the (detachable) prefix anhydro- preceded by a pair of locants identifying the two hydroxy groups involved. 

In clinical chemistry however, these systems have not been differentiated as yet. Since the oxidation of an alcohol corresponds to the reduction of a ketose or an aldose, the designations ketose reductase and aldose reductase, respectively, were suggested (H4, W14). In this paper however, the enzyme or enzyme system will be named polyol or sorbitol dehydrogenase (SDH), although the latter expression does not characterize exacdy the enzyme s function in a general biochemical sense. But sorbitol or fructose have been commonly used as substrates in clinical chemical investigations. 

Notice that glucose is an aldehyde and fructose is a ketone. Polyhydroxy aldehydes like glucose are called aldoses. Polyhydroxyke-tanes like fructose are called ketoses. Carbohydrates are also named for the number of carbons they possess triose, tetrose, pentose, hexose, heptose, and so on. The names are commonly combined making glucose an aldohevose... 

In 1937, the true structure of the rearranged product was reported by Kuhn and Weygand. Amadori s stable isomers were shown to be unbranched A-substituted l-amino-l-deoxy-2-ketoses. Therefore, in a strict sense, the reaction named by Kuhn and Weygand the Amadori rearrangement is the complete conversion of a Af-substituted aldosylamine to a iV-substituted l-amino-l-deoxy-2-ketose. On this basis, simple enolization of an aldosylamine or ketosylamine to the intermediate 1,2-enolic form common to both should not be construed as the Amadori rearrangement. Also, the recently demonstrated conversion of a ketosylamine to a 2-amino-2-deoxyaldose does not come under the definition in spite of an obvious similarity to the Amadori rearrangement. 

As the name implies, carbohydrates are characterized by a nominal (CH20) composition. Next to proteins, carbohydrates combined into polysaccharides are generally the most abundant (Table 8.6) and widely distributed biopol5miers in living organisms. (However, there are some plankton in which the lipid concentration exceeds that of carbohydrates (Wakeham et al, 1997).) The fundamental monomeric rmits of most carbohydrates are five- (pentose) and six-(hexose) carbon sugars, of which there are roughly ten common forms (Fig. 8.9). These structural units usually occur as either aldoses or ketoses, in which either the first (aldose) or second (ketose) carbon... 

The ketoses are classified as 2-ketoses, 3-ketoses, etc., following the carbonyl position on the chain. The 2 of 2-ketoses, a common natural structure, can be removed. The suffix ose is replaced by ulose in the parent name. Likewise, fructose is a 2-hexulose, or more simply, a hexulose. For the complete name, it is preceded by the configuration descriptor. The systematic name of fructose 4.37 would be D-araZ>Z o-2-hexulose. In the case of 2-ketoses, there is no possible ambiguity for the configuration of pyranoses and furanoses. The nomenclature is copied from that of aldoses as, for example, /3-D-fructopyranose 4.38. Methyl glycoside 4.39 of sialic acid is called methyl 5-acetamido-3,5-dideoxy-D-gZycera-a -D-gaZacfo-2-nonulopyranosidonic acid. 

Of common occurrence in biochemistry are the D forms of the aldoses, namely glucose (the most important), mannose and galactose, and the ketose called fructose. 

Most aldoses and ketoses are unbranched compounds with an oxygen functional group at each carbon atom. However, a few structural variations occur in some uncommon monosaccharides. Most of these compounds are named using the more common monosaccharides as the parent. Most ketoses have the carbonyl carbon atom at C-2 and can isomerize to aldoses (Section 26.4). However, a 3-keto isomer of ribose exists. A more common structural variation is substitution of one or more hydroxyl groups by hydrogen. The most important example of such a deoxy sugar is 2-deoxyribose, which is present (in cyclic form) in DNA. 

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