D-Ketose

FIGURE 7.3 The Structure and stereochemical relationships of D-ketoses having three to six carbons. The configuration in each case is determined by the highest numbered asymmetric carbon (shown in gray). In each row, the new asymmetric carbon is shown in red. 

Figure 9.4 Stereoisomers of the D-ketoses. There will be an equal number of isomers in the l series of ketoses.

FIGURE 7-3 Aldoses and ketoses. The series of (a) D-aldoses and (b) D-ketoses having from three to six carbon atoms, shown as projection formulas. The carbon atoms in red are chiral centers. 

Configurational relationships of the D-ketoses. The most important sugars are starred. 

FIGURE 1.4 The family tree of D-ketoses with the trivial and derived names. 

The family of D-ketoses, shown in Figure 27.5, is formed from dihydroxyacetone by adding a new carbon (bonded to H and OH) between C2 and C3. Having a carbonyl group at C2 decreases the number of stereogenic centers in these monosaccharides, so that there are only four D-ketohexoses. The most common naturally occurring ketose is D-fructose. 

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

Dihydroxyacetone is the simplest ketose. The stereochemical relation between d-ketoses containing as many as six carbon atoms are shown in Figure 11.3. Note that ketoses have one fewer asymmetric center than do aldoses with the same number of carbons. d-Fructose is the most abundant ketohexose. 

Figure 11.3. d -Ketoses containing three- four, five, and six carbon atoms. The keto group is shown in blue. The asymmetric center farthest from the keto group, which determines the d designation, is shown in red. 

On the basis of these results, Hakomori and coworkers53,54 proposed a l-deoxy-l-(N-peptidyl)-D-ketose structure for the linkage of the peptide and carbohydrate components of UGP I, II, and III this kind of structure is identical with that of the product of the Amadori rearrangement of glycosylamines. 

D-Aldoses are thus converted into D-ketoses. The reaction is analogous to the ketol isomerization described on page 1061. 

Construct an array analogous to Figure 16.1 for the D-ketoses as high as the hexoses. Dihydroxyacetone should be at the head, in place of glyceraldehyde. 

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. 

A family tree of the D ketoses that have between three and... 

The (3S,4R) configured probes were prepared by enzymatic routes based on the stereospecific formation of a C-C bond catalyzed by either TK with Li-HPA as donor or by fructose-6-phosphate aldolase (FSA) Ref. [41]. The advantage of FSA for the synthesis of these probes is that acceptor substrates were commercially available, whereas a-hydroxylated TK acceptor substrates had to be prepared first by chemical routes [40, 41]. In particularly, the recently engineered FSA(A129S) variant that was optimized for dihydroxyacetone (DHA) as the donor substrate was found to be a powerful biocatalyst, leading to D-ketose analogs 16a and 16b with 67% and 77% yields, respectively. TK reactions furnished the same products but with lower yields only (37% and 47% respectively) (Scheme 15.17). 

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