Aldotetrose

Glyceraldehyde can be considered to be the simplest chiral carbohydrate It is an aldotriose and because it contains one chirality center exists in two stereoisomeric forms the D and l enantiomers Moving up the scale m complexity next come the aldotetroses Examining their structures illustrates the application of the Fischer system to compounds that contain more than one chirality center... 

The aldotetroses are the four stereoisomers of 2 3 4 trihydroxybutanal Fischer pro jections are constructed by orienting the molecule m an eclipsed conformation with the aldehyde group at the top The four carbon atoms define the mam chain of the Fischer projection and are arranged vertically Horizontal bonds are directed outward vertical bonds back... 

Molecular models of the four stereoiso meric aldotetroses may be viewed on Learning By Modeling... 

The particular aldotetrose just shown is called d erythrose The prefix d tells us that the configuration at the highest numbered chirality center is analogous to that of d (+) glyceraldehyde Its mirror image is l erythrose... 

Which aldotetrose is the structure shown Is it D erythrose D threose L erythrose or L threose (Be careful The conformation given is not the same as that used to generate a Fischer projection)... 

As shown for the aldotetroses an aldose belongs to the d or the l series accord mg to the configuration of the chirality center farthest removed from the aldehyde func tion Individual names such as erythrose and threose specify the particular arrangement of chirality centers within the molecule relative to each other Optical activities cannot be determined directly from the d and l prefixes As if furns ouf bofh d eryfhrose and D fhreose are levorofafory buf d glyceraldehyde is dexfrorofafory... 

An analogous pattern of configurations can be seen m the aldopentoses when they are arranged m the order ribose arabinose xylose lyxose (RAXL is an easily remem bered nonsense word that gives the correct sequence) This pattern is discernible even m the aldotetroses erythrose and threose... 

Problem 25.5 Redraw the following aldotetrose as a Fischer projection, and assign R or S configuration to each chirality center ... 

Aldotetroses are four-carbon sugars with two chirality centers and an aldehyde carbonyl group. Thus, there are 22 = 4 possible stereoisomeric aldotetroses, or two d,l pairs of enantiomers named erythrose and threose. 

Fischer projections of the tour-, five-, and six-carbon d alcloses are shown in Figure 25.3. Starting with D-glyceraldehyde, we can imagine constructing the two d aldotetroses by inserting a new chirality center just below the aldehyde carbon. Each of the two d aldotetroses then leads to two d aldopentoses (four total), and... 

Diels and Stephan173 treated the benzoate of 3-hydroxy-2-butanone with bromine, and obtained crystalline 1-bromo- and 1,1-dibromo- derivatives. With dilute alkali, these formed 4-deoxy-DL-gZycero-tetrulose and 4-deoxy-DL-erythrosone respectively. Both compounds gave with phenylhydrazine 4-deoxy-DL-erythrose phenylosazone, which had previously been prepared from the corresponding aldotetrose.174... 

V. 3-C-(Hydroxymethyl)tetroses 1. 8-C-(IIydroxymethyl)-T>-glycero-aldotetrose (Apiose)... 

In addition, LDHs are able to concentrate selectively and organize organic molecules [198-200] For example, Pitsch et al. reported that glycolalde-hyde phosphate intercalated in LDHs from highly dilute aqueous solution can condense to racemic aldotetrose-2,4-diphosphates and aldolhexose-2,4,6-triphosphates [200], which has led to speculation about the possible role of LDHs in chemical evolution and the origins of fife. 

II. Transformation of Monomeric Saccharides 1. Aldopentoses, Aldotetroses, and Aldotrioses... 

Transaldolase, which catalyzes reactions with d-erythrose 4-phosphate and D-fructose 6-phosphate as substrates. As in the case of fructose-1,6-bisphosphate aldolase, this enzyme uses a e-amino side-chain to form a Schiff base intermediate. In this case, however, the triose phosphate moiety is not released but is transferred to the other aldose (in this case, the aldotetrose). 

Little work has been done with the aldotetroses these could lose two molecules of water per molecule to form 34. Compound 33 could form a furanone after ring closure, but, because the con-... 

Problem 22.20 Two Ruff degradations of an aldohexose give an aldotetrose that is oxidized by HNO, to /n o-tartaric acid. What can be the family configuration of the aldohexose ... 

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