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A facile synthesis of 2-O-(α-d-mannopyranosyl)-α-d-mannopyranosides

✍ Scribed by Reiko T. Lee; Yuan C. Lee

Publisher
Elsevier Science
Year
1995
Tongue
English
Weight
333 KB
Volume
271
Category
Article
ISSN
0008-6215

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✦ Synopsis

During the preparation of simple mannopyranosides using the Koenigs-Knorr type reaction, we observed that a significant amount of disaccharide glycoside was produced when the alcohol was used in amounts less than equivalent of 2,3,4,6-tetra-O-acetyl-c~-D-mannopyranosyl bromide ("acetobromomannose"). The disaccharide product turned out to be almost exclusively of one isomeric structure, i.e., that of a-D-Man-(1 --* 2)-a-o-Man.

Mannose was converted to acetobromomannose according to the method of Kartha and Jennings [1], which proceeded smoothly, and TLC indicated the presence of essentially a single product. Subsequent repeated evaporation with toluene produced a brown syrup, which was used in the glycoside formation without crystallization. Helferich and Zimer [2] reported formation of 1,3,4,6-tetra-O-acetyl-/3-D-glucopyranose and -galactopyranose from their respective acetobromo derivatives by a controlled hydrolysis. It appears that in their reactions the acetyl group at the 2-position migrated to the 1-OH. Deferrari et al. [3] extended the procedure to mannose to obtain 1,3,4,6-tetra-O-acetyl-fl-o-mannopyranose. In our reactions, however, the 2-O-deacetylated derivative must have been generated without the loss of the bromine atom, since we obtained the a-o-Man-(l~2)-a-D-Man disaccharide exclusively as the per-O-acetylated glycoside and not as its 1-acetate. Also, in our reaction negligible amounts of trisaccharides or higher saccharides were produced. Therefore, we suspect that partial and specific

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