NMR structure determination of saccharose and raffinose by means of homo- and heteronuclear dipolar couplings

Residual dipolar couplings have dramatically improved the accuracy and prec ision of high-resolution NMR structures during the last years. This was fir st demonstrated for proteins. In this article, we describe, with raffinose and saccharose as examples, that dipolar couplings improve the precision of structures of carbohydrates for which usually very few structural paramete rs are available. The relative orientation as well as the dynamics of the m onosaccharide moieties with respect to each other can be determined with th e help of C-13,H-1 and H-1,H-1 dipolar couplings, which can easily be measu red. Significant differences between the solution and the X-ray crystal str ucture exist. These results indicate that residual dipolar-coupling data ma y provide a more complete and dynamic model of carbohydrates in particular, and small molecules in general.