Aldoses heptoses

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. 

II. Reaction of Aldoses with Dicarbonyl Compounds 1. Hexoses and Heptoses... 

Monosaccharides with four, five, six, and seven carbon atoms in their backbones are called, respectively, tetroses, pentoses, hexoses, and heptoses. There are aldoses and ketoses of each of these chain lengths ... 

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... 

Sugars, ketoses Anthrone Bright purple (pentoses) orange-yellow (heptoses) blue fluorescence (aldoses) 110... 

As we have seen, sugars with aldehyde groups are called aldoses, and those with ketone groups are called ketoses. The number of carbon atoms in the sugar generally ranges from three to seven, designated by the terms triose (three carbons), tetrose (four carbons), pentose (five carbons), hexose (six carbons), and heptose (seven carbons). 

Qassified into triose, tetrose, pentose, hexose and heptose depending upon the number of carbon atoms. They may be either aldoses or ketoses depending upon whether they contain a (potential) free aldehyde (OH) or ketone (C=0) group, respectively. 

The trivial names of the aldoses can be used as prefixes to determine the stereochemistry for other chiral compounds. However, in this case, the -ose suffix is omitted and the prefix is written in italics (Figure 2.8). In this respect, it should be mentioned that the chiral centers can be separated by one or more nonchiral centers. If the number of chiral centers exceeds four (e.g., in heptose, octose, nonose, etc. derivatives), a multiple configurational prefix is added to the stem name (Figure 2.9). In this case, the first four chiral centers are selected, followed by the remaining ones. However, the name of the compound starts with the prefix of the chiral center with the highest location. In the case of ketoses, if the carbonyl group is not at C-2, then its location should also be given in the name. 

The reported yields in these ketose preparations range from less than 10% to around 50%. Nevertheless, this is the method of choice for preparing certain ketoses, especially where the starting aldose can be sacrificed. For some unknown reason, the best yields have consistently been obtained in the formation of D- Zwco-heptulose from D-j/Zj/cero-D-j/aZo-heptose. The procedure of Pratt, Richtmyer, and Hudson for preparation of this substance is given here. 

In summary, it can be said that, in homogeneous alkaline solution, either methanolic or aqueous, an equilibrium is established between the aldose, nitromethane, and deoxynitroalditols, and that, for successful addition, this equilibrium must be displaced in favor of the alditols, either through precipitation of their sodium salts from methanolic solution, or by direct crystallization from aqueous solution. Because of these requirements, the method is not so widely applicable as the cyanohydrin synthesis, but, for selected sugars, such as n-gZgcero-D-ZaZo-heptose and o-erythro-i -manno-octose, its simplicity and the satisfactory yields obtained make it the method of choice. 

It was found that carbazole and phloroglucinol are unsuitable for determining the heptose content of sugar mixtures because of interference from other sugars similar interference is encountered with resorcinol. With orcinol, cysteine, and diphenylamine, however, specific reactions can be obtained at selected wavelengths. Ketoheptoses (and keto sugars in general) react under milder acid conditions than the aldoses, and this property can be used for identification purposes. In the orcinol test, for... 

Finally, further examples of unsaturated 1-nitroalditols have been described, and have been utilized in standard syntheses of 2-deoxy-aldoses by this means, 2-deoxy-D-rtho-hexose,174 2-deoxy-D-manno-heptose,175 2-deoxy-D-gaiacto-heptose,176 and 2,6-dideoxy-L-manno-heptose177 have been prepared. The reaction of ammonia with 3,4,5,6-tetra-0-acetyl-l,2-dideoxy-l-nitro-L-arabino-hex-l-enitol has been further examined, and found to proceed stereospecifically to give... 

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