Ribose 3-Pentulose, erythro

In contrast, much information is available about five-carbon sugars. The most widely studied D-pentoses, D-ribose and 2-deoxy-D-erythro-pentose, are discussed in Section VII (see p. 86). The aldopentoses can form either furanose or pyranose rings, and both structures are known, although not in the same crystal. Crystallographic data have not been obtained for either of the 2-pentuloses D-erythro- and D-threo-2-pentulose ( D-ribulose and D-xylulose ), as they are syrupy. 

Decarboxylation must lead to incorporation of a proton from the solvent. The oxidative decarboxylation of 6-O-phosphono-D-gluconate gives D-erythro-pentulose-1 (S)-t 5-phosphate (with inversion of configuration).45 The R-isomer can be obtained46 from D-ribose 5-phosphate by using D-ribose 5-phosphate ketol isomerase (E.C. 5.3.1.6). 

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