Characterization of Stereochemistry and Molecular Conformation Using Solid-State NMR Tensors

A solid-state NMR technique is described for establishing stereochemistry using the natural product terrein as a model compound. This method involves comparison of experimental (13)C tensor principal values with ab initio computed values for all possible computer-generated stereoisomers. In terrein the relative stereochemistry is confirmed by NMR to be 2R*,3S with high statistical probability (>99.5%). The proposed approach also simultaneously verifies the molecular conformation of the two hydroxy groups in terrein established by X-ray data. It is sufficient to use only shift tensor values at carbons 2 and 3, the stereocenters, to characterize both the stereochemistry and molecular conformations. The solid-state NMR method appears to be especially useful for determining relative stereochemistry of compounds or their derivatives that are difficult to crystallize.