Novel Chemical Shift Changes of Carbohydrates Induced by Lanthanide Shift Reagents: Some Experimental Optimizations

Abstract

The 1H n.m.r. spectra of 1,2:5,6-di-O-isopropylidene-α-D-glucofuranose (4), of 1,2:5,6-di-O-isopropylidene-α-D-allofuranose (5), and of their 3-O-acetyl derivatives 6 and 7, respectively have been separately measured in the presence of varying concentrations of the tris {dipivaloylmethane} derivatives of europium (1), thulium (2), and praseodymium (3). For these derivatives, both europium (1) and thulium (2) induce shifts to low field whereas praseodymium (3) produces high field shifts; for any individual proton the magnitude of the induced shift is shown to be linearly proportional to the amount of added reagent and is best followed by addition of volume aliquots of a dilute solution of the lanthanide. It is shown that simplistic rationales concerning the relationship between the magnitudes of induced shifts and the geometry of the substrate system can be entirely misleading; the D-gluco -derivative 4 is particularly noteworthy in this regard. Since the magnitudes of the induced shifts are temperature dependent it is important to report the temperature at which experiments are performed. For 1 the induced shifts are ca. 2.2 times larger for carbon tetrachloride solutions than for deuterochloroform solutions when operating under otherwise identical conditions.