Tungstate complexes of aldoses and ketoses of the lyxo series. Multinuclear NMR evidence for chelation by one or two oxygen atoms borne by the side chain of the furanose ring
✍ Scribed by Stella Chapelle; Jean-François Verchère
- Publisher
- Elsevier Science
- Year
- 1995
- Tongue
- English
- Weight
- 614 KB
- Volume
- 277
- Category
- Article
- ISSN
- 0008-6215
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✦ Synopsis
The formation of tungstate complexes of aldoses and ketoses with lyxo configuration was studied in aqueous solution by ~3C and ~83W NMR spectroscopy. Two series of complexes were structurally characterized, in which the sugars adopt the furanose form and chelate a ditungstate group at a tetradentate site. All sugars form a major complex (type L for lyxo) similar to the molybdate species, in which the sites of chelation, O-1,2,3,5 for aldoses or 0-2,3,4,6 for ketoses, involve the anomeric oxygen atom and the side chain atom 0-5 or 0-6. A second type of complex was identified (type M for manno), in which the sites of chelation are 0-2,3,5,6 for D-mannose (tungstate species only) and 0-3,4,6,7 for D-manno-heptulose (tungstate and molybdate complexes). The overall equilibrium constants for the formation of the complexes are reported and show that ketoses form stronger complexes than aldoses.