On the structure and spectroscopic properties of two 13-hydroxylupanine epimers

In solution, both epimers occur in conformational equilibrium with considerable domination of the C-boat conformer (85-90%). This conformation is stabilized by the other type of intermolecular hydrogen bonds in comparison with that operating in the solid. Intermolecular deuterium bonds between 13α- and/or 13β-hydroxylupanine molecules and the solvent CDCl3 molecules as well as the N16⋯H-O association have been found to play a crucial role.