Proton NMR Spectra of Peracetylated D-Galactopyranose Derivatives in the Presence of Lanthanide Shift Reagents

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Abstract
Proton NMR spectra of the peracetylated derivatives of D-galactopyranoses and some of their aryl glycosides and glycosyl bromides were measured at 100 MHz in the presence of a shift reagent, tris(2,2-dimethyl-6,6,7,7,8,8,8-heptafluoro-3,5-octanedionato)-europium. Bound chemical shifts to lower fields were determined mainly by first-order analysis for all the methine, methylene, and acetyl protons in these compounds. Comparison of the shift data for these sugars of the galactopyranose series with those for the corresponding sugars of the glucopyranose series showed that the signals of H-4 in the former and H-2 (α-anomers) and H-6 (H-6′) in the latter were most markedly shifted by the addition of the reagent. The highest values of the bound chemical shifts of the acetyl protons and the differences in values between H-6 and H-6′ were further observed to be lower in the former sugars than in the latter sugars. These shift patterns, characteristic of the sugars of the galactopyranose series, were found to be more marked in their β-anomers. Based on these results, the preferred coordination structures for the complexes between these sugars and the reagent were inferred, and their stereochemical significance is discussed.

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