Measurement of 1H-1H Residual Dipolar Coupling Constants for Structural Studies of Medium Size Molecules

Residual dipolar coupling constants (RDCs) are being increasingly applied to elucidate the configuration and conformation of small organic molecules, peptides and oligosaccharides. In this paper we describe a set of robust 1D NMR methods for accurate and precise measurement of proton–proton RDCs of small and medium size molecules. The performance of these techniques is not impeded by the presence of overlapping and broad 1H multiplets that are typically observed for such molecules in weakly aligned media. The use of these techniques provides access to a large pool of proton–proton RDCs opening new avenues for the solution structure elucidation of medium size molecules by NMR. The techniques are illustrated on the determination of the alignment tensor of the reducing monosaccharide ring of cellobiose and the determination of the relative configuration of sodium cholate. Configuration and conformation: New methods for accurate and precise measurements of 1H–1H residual dipolar coupling constants D of medium‐size molecules with unresolved 1H spectra are presented. The picture shows a selection, from a crowded 1H spectrum, of H4α signals of cellobiose, which enable the measurement of DH4α,H2α and lead to an improved definition of the alignment tensor.