Crystal and molecular structure of secoisolariciresinol

The R,R-2,3-bis[(4-hydroxy-3-methoxyphenyl)methyl]-1,4-butandiol lignan sec oisolariciresinol (1) is a constituent of Gymnosperms used in the treatment of benign prostatic hyperplasya. The results of crystallographic and ab in itio theoretical studies are reported and discussed. In the crystal, the mo lecule of (1) assumes a clustered conformation, characterized by the facing of the two phenyl rings. This geometry is stabilized by the formation of a network of hydrogen bonds. Theoretical calculations indicate that: i) the intramolecular hydrogen bond O1-H1...O1' is the major factor dictating the facing of the two phenyl groups, while intermolecular hydrogen bonds and cr ystal packing have smaller effects; ii) the 1-4O...O non-bonded interaction s in the vanillyl groups are important in determining the most stable confo rmation; iii) calculations with two explicit water molecules in the model g ive a good simulation of the local effects of a water solvent and indicate that (1) probably assumes a clustered conformation also in polar solvents.