Pyranoside derivatives of 3-deoxyald-2-ulosonic acids

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Abstract
At pH 11.5 in 0.2M-sodium tetraborate solution and in the presence of Ni2+, 2-O-benzyl-D-arabinose reacts with oxaloacetic acid to give a 50–60% yield of 5-O-benzyl-3-deoxyoct-2-ulosonic acids (mixed D-gluco- and D-manno-isomers). The methyl esters of these were separated and the α-methyl glycoside of the D-manno-isomer was prepared. The conformation of the compounds was established by n.m.r. spectroscopy at 250 MHz. It was observed that esterification of the carboxy-group greatly increases the stability of the glycosidic bond of 3deoxy-D-manno-octulosonic acid while the benzyl substituent in position 5 exerts only a weak stabilising effect. 2-O-Benzyl-D-glyceraldehyde, when treated with oxaloacetic acid in the presence of Ni2+ at pH 7 in the absence of borate, yields 5-O-benzyl-3-deoxyhex-2-ulosonic acids, the predominant D-erythro-isomer being isolated as its methyl ester.