The D Family of Aldoses

Fig. 1. The family of D-aldoses derive from D-glyceraldehyde by chain extension at the carbonyl carbon atom.

To continue forming the family of D-aldoses, we must add another carbon atom (bonded to H and OH) just below the carbonyl of either tetrose. Because there are two D-aldotetroses to begin with, and there are two ways to place the new OH (right or left), there are now four D-aldopentoses D-ribose, D-arabinose, D-xylose, and D-lyxose. Each aldopentose now has three stereogenic centers, so there are 2 = 8 possible stereoisomers, or four pairs of enantiomers. The D-enantiomer of each pair is shown in Figure 27.4. 

The family of D-aldoses having three to six carbon atoms... 

Most monosaccharides are aldoses, and almost all natural monosaccharides belong to the D series. The family of d aldoses is shown in I Figure 7.8. D-glyceraldehyde, the smallest monosaccharide with a chiral carbon, is the standard on which the whole series is based. Notice that the bottom chiral carbon in each compound is directed to the right. The 2" formula tells us there must be 2 trioses, 4 tetroses, 8 pentoses, and 16 hexoses. Half of those are the d compounds shown in Figure 7.8. The other half (not shown) are the enantiomers or l compounds. 

Figure 24.6 summarizes the family of d ketoses that have between three and six carbon atoms. This family tree is constructed in much the same way as the family tree of aldoses, beginning with dihydroxyacetone as the parent. However, because the carbonyl group is at C2 rather than C1, ketoses have one less chirality center than aldoses of the same molecular formula. As a result, there are only four D ketohexoses, rather than eight. The most common naturally occurring ketose is D-fructose. Each compound in Figure 24.6 has a corresponding l enantiomer that is not shown. 

FIGURE 1.3 The family tree of D-aldoses with the trivial and abbreviated names. 

Tri-O-acetal-D-glucal (1) is the best known and most useful member of the family of cychc 1,2-unsaturated aldose derivatives called glycals . These compounds are of major significance in synthesis - to a large extent because of the wide range of biologically important compounds that can be obtained from them by addition... 

Aldotetrose B must be D-threose because the alditol derived from it (o-threitol) is optically active (the alditol from D-erythrose, the other possible D-aldotetrose, would be meso). Due to rotational symmetry, however, the alditol from B (D-threitol) would produce only two NMR signals. Compounds A-F are thus in the family of aldoses stemming from D-threose. Since reduction of aldopentose A produces an optically inactive alditol, A must be D-xylose. The two diastereomeric aldohexoses C and D produced from A by a Kiliani-Fischer synthesis must therefore be D-idose and D-gulose, respectively. E and F are the alditols derived from C and D, respectively. Alditol E would produce only three C NMR signals due to rotational symmetry while F would produce six signals. 

Aldose sugars make up a large part of the carbohydrate family, but the ones that are really worth knowing are part of the D-family. The simplest of these D-sugars is the triose glyceraldehyde. From there you have 2 tetroses, 4 pentoses, and 8 hexoses. Each of these aldose sugars has an enantiomer. 

Wood-degrading fungi produce a family of pyranose oxidases (EC 1.1.3.10), enzymes catalyzing the oxidation at C-2 of several aldoses. A simple and convenient conversion of D-glucose into D-arabino-hexos-2-ulose involves the use of a pyranose-2-oxidase isolated from Polyporus obtusus, which was purified and immobilized on activated CH-Sepharose 4B.446... 

The D family of aldoses. All these sugars occur naturally except for threose, lyxose, allose, and gulose. 

Use Figure 23-3 (the d family of aldoses) to name the following aldoses. 

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