Glyceraldehyde stereochemistry

The overall stereochemisfry of monosaccharides is classified as D or L based on a comparison to glyceraldehyde stereochemistry. 

I-Oialkoxy carbonyl compounds are a special class of chiral alkoxy carbonyl compounds because they combine the structural features, and, therefore, also the stereochemical behavior, of 7-alkoxy and /i-alkoxy carbonyl compounds. Prediction of the stereochemical outcome of nucleophilic additions to these substrates is very difficult and often impossible. As exemplified with isopropylidene glyceraldehyde (Table 15), one of the most widely investigated a,/J-di-alkoxy carbonyl compoundsI0S, the predominant formation of the syn-diastereomer 2 may be attributed to the formation of the a-chelate 1 A. The opposite stereochemistry can be rationalized by assuming the Felkin-Anh-type transition state IB. Formation of the /(-chelate 1C, which stabilizes the Felkin-Anh transition state, also leads to the predominant formation of the atm -diastereomeric reaction product. 

The configurations of other componds were related to glyceraldehydes through reactions of known stereochemistry. 

The configuration of (-)-glyceraldehyde was related through reactions of known stereochemistry to (+)-tartaric acid. 

Each of these compounds has a prefix d- with the name. As we saw in Section 3.4.10, this indicates that the configuration at the highest numbered chiral centre is the same as that in D-(R)-(4-)-glyceraldehyde the alternative stereochemistry would be related to... 

Compatibility of asymmetric epoxidation with acetals, ketals, ethers, and esters has led to extensive use of allylic alcohols containing these groups in the synthesis of polyoxygenated natural products. One such synthetic approach is illustrated by the asymmetric epoxidation of 15, an allylic alcohol derived from (S)-glyceraldehyde acetonide [59,62]. In the epoxy alcohol (16) obtained from 15, each carbon of the five-carbon chain is oxygenated, and all stereochemistry has been controlled. The structural relationship of 16 to the pentoses is evident, and methods leading to these carbohydrates have been described [59,62a]. 

Almost all the naturally occurring amino acids have the (S) configuration. They are called L-amino acids because their stereochemistry resembles that of L- (— )-glyceraldehyde. 

Similar considerations suggest that only one basic group is involved in aldolase catalysis.136 When l,3-dihydroxy-2-propanone 1-phosphate is incubated with aldolase, a stereospecific exchange with solvent occurs (see p. 135). This exchange shows that carbanion formation precedes condensation with glyceraldehyde 3-phosphate (see also, Ref. 158), and it is found that the new carbon-carbon bond is formed with the same stereochemistry as the departed hydrogen.40 This... 

Although TA from yeast is commercially available, it has rarely been used in organic synthesis applications, and no detailed study of substrate specificity has yet been performed. This is presumably due to high enzyme cost and also since the reaction equilibrium is near unity, resulting in the formation of a 50 50 mixture of products. In addition the stereochemistry accessible by TA catalysis matches that of FruA DHAP-dependent aldolase and the latter is a more convenient system to work with. In one application, TA was used in the synthesis D-fructose from starch.113 The aldol moiety was transferred from Fru 6-P to D-glyceraldehyde in the final step of this multi-enzyme synthesis of D-fructose (Scheme 5.60). This process was developed because the authors could not identify a phosphatase that was specific for fructose 6-phosphate and TA offered an elegant method to bypass the need for phosphatase treatment. 

The monosaccharides with the same stereochemistry as L-glyceraldehyde at the most distant asymmetric carbon will form the L-series of aldoses. 

The D/L labeling is unrelated to (+)/(-) it does not indicate which enantiomer is dextrorotatory and which is levorotatory. Rather, it says that tlie compound s stereochemistry is related to that of the dextrorotatory or levorotatory enantiomer of glyceraldehyde. Nine of the nineteen L-amino acids commonly found in proteins are dextrorotatory (at a wavelength of 589 nm), and D-fructose is also referred to as levulose because it is levorotatory-. 

There are three trioses - a ketose (dihydroxyacetone), and the two enantiomeric forms of glyceraldehyde. In the carbohydrate field the R,S system of designating stereochemistry of a chiral centre, used elsewhere in organic chemistry, becomes very cumbersome, and Fischer s original conventions, as modified by Rosanolf are still used. 

Glyceraldehyde, of which 107 and 109 arc protected forms, is the only three-carbon sugar. There are two four-carbon sugars erythrose 111 and threose 113. Both exist in hemiacetal (furanose) and open chain forms and both are chiral but their symmetry properties differ. The tetrols formed by reduction of the aldehydes are me so erythritol 112 and C2 symmetric threitol 114 having the same stereochemistry as tartaric acid 35. Threose or threitol can be oxidised to tartaric acid. These sugars are the origin of the terms erythro and three sometimes used to describe such diastereomeric relationships. 

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