Selective HOESY experiments for stereochemical determinations

Abstract

Heteronuclear Overhauser effect spectroscopy (HOESY) is a powerful method for tracking geometrical proximities between two heteronuclei (for instance, (1)H and (13)C, as this will be the case here). The method is based on cross-relaxation arising from dipolar interactions. Sensitivity permitting, it is applied in the 2D mode yielding all spatial correlations in a single experiment. Whenever sensitivity is not sufficient, it can be applied in the one-dimensional mode by selectively inverting one particular proton. In that case, it yields, from the carbon-13 spectrum, remote spatial correlations. The method has been employed here for the discrimination between two possible E or Z isomers in a medium-size molecule.

Carbon-13 Heteronuclear Longitudinal Spin Relaxation for Geometrical (and Stereochemical) Determinations in Small or Medium Size Molecules

“…These determinations make use of relayed proton-proton-carbon cross-relaxation.Another good example of what can be gained from HOESY experiments is provided by the work of Ancian et al53 about the preferential conformation of uridine in water. Through the TOCSY-HOESY experiment above described, these authors were able to show unambiguously that the torsion angle of the uracil group around the glycosidic bond lies in a range corresponding to the anti-form of the pyrimidine base with respect to the furanose ring.The discrimination between E and Z isomers of the compound shown in figure 11 constitutes a further example of the interest of selective HOESY experiments55 .…”