Methyl /,-arabino pyranose

In 1934, Hudson and his group observed that treatment of a number of methyl D-aldohexopyranoside tetraacetates gave the a-D-aldohexopyranose pentaacetates on acetolysis with sulfuric acid as catalyst. Three years later, they observed that methyl jS-D-arabinopyranoside 2,3,4-triacetate gives 56% of alde%do-D-arabinose hexaacetate and 11% of /3-D-arabino-pyranose 1,2,3,4-tetraacetate the optical rotation of the mixture decreased steadily during the reaction. However, for the a-D-arabinoside, the rotation rose very sharply during the first minute and then fell more slowly. At the end of the reaction, the products were essentially those from the jS-D-glycoside at the point of maximum rotation, a 14% yield of methyl jS-D-arabinopyranoside was isolated, showing that anomerization can occur under these conditions, followed by subsequent acetolysis to the peracetate. 

The isomeric forms of hexulosonic acids present in aqueous and other solutions have been studied by C n.m.r. methods. L-xy/o-Hexulosonic acid and its methyl ester exist predominantly in the a-pyranose form, whereas the D-arabino-isomers show a- and j3-pyranose and ot- and /3-furanose forms. The methyl ester favours the pyranoses in water and the furanoses in DMSO. D-xy/o-Hex-5-ulosonic acid showed both furanoses and the acyclic form, while this latter... 

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