The (-)-gossypol-2,4-pentanedione (1:2) inclusion complex

Abstract

(−)-Gossypol and 2,4-pentanedione form an inclusion complex in a one-to-two molar ratio. The compound crystallizes in the tetragonal P41212 space group and has unit cell dimensions of a=b = 10.9966(7) A and c = 60.213(4) A. Both solvent molecules are in the enol form and occupy two distinct cavities within the structure. The first cavity is formed between pairs of gossypol naphthalene rings and contains a pair of symmetry-related solvent molecules that each accept a hydrogen bond from one of the surrounding gossypol molecules. The four molecules together form a wedge-shaped assembly that is repeated throughout the cell. The assemblies stack to form columns, and adjacent columns are aligned parallel to form layers. Neighboring layers are oriented at 90° angles, which accounts for the fourfold symmetry of the space group. The second solvent cavity is located in isolated pockets that form between the layers. These solvent molecules also accept hydrogen bonds from the surrounding gossypol molecules. Although many gossypol solvates have been reported, this structure is unusual in a number of features. It is the first report of a chiral non-conglomerate gossypol solvate. It is also the only known chiral gossypol inclusion complex to not lose appreciable amounts of solvent when removed from its mother liquor.