3- Deoxyglyculosonic acids

A number of 3-deoxyglyculosonic acids have been identified. These substances are acid-labile and are decomposed on hydrolysis with acid under normal conditions, and have therefore often escaped detection in the past. The simplest member of this class, 3-deoxy-L- /yccro-pentulosonic acid (26), occurs as terminal groups in the capsular polysaccharide from Klebsiella K38. Pyranosidic 3-deoxy-D-r/ircohexulosonic acid is a component of the Vibrio parahaemolyticus 07 and 012 LPS. The same acid, as )3-py-ranosyl groups, is also present in the extracellular polysaccharide from Azo-tobacter vinelandii. ... 

Warren,13 the KDO moieties usually give a TBA response equivalent to that obtained after acid hydrolysis. Apparently, both the ketosidic and aglyconic linkages of KDO are cleaved during such treatment, so that KDO reacts essentially as the free 3-deoxyglyculosonic acid. Due to partial destruction of KDO by acid,23-25 the color yield is less than optimal (see Fig. 5b, d). 

An analogous approach to 3-deoxyglyculosonic acids would be realized were an ylide 149 (R= C02Et X= NR 2) available. Nevertheless, this problem was solved in an original way. The condensation of 2,4-O-ethylidene-D-erythrose with the sodium salt of ethyl (diethyl-... 

Further development of this method will possibly provide a most convenient synthesis of 3-deoxyglyculosonic acids, and, especially, sialic acids, as the configuration of the final product has already been fixed in the enamino lactone of type 165b, in contradistinction to the analogous enamino lactones (for example, 144), which are formed as a mixture of epimers. 

The Wittig reaction with ylide 149 (R = COaEt X = OEt) was also applied to certain aldehydo-aldoses by Samokhvalov and coworkers15 in order to find more convenient paths to 3-deoxyglyculosonic and sialic acids. This ylide was generated in situ from the corresponding phosphonium salts by means of sodium ethoxide in ethanol at —20°. Such an approach was first attempted15(a) by starting from 2,3 4,5-di-O-isopropylidene-aWe/u/do-D-arabinose, and the expected ethyl 3-deoxy-2-0-ethyl-4,5 6,7-di-0-isopropylidene-D-arafoino-hept-2-en-onate (161) was formed in about 70% yield. 

---