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Title: 6,6'-Dimethoxygossypol: molecular structure, crystal polymorphism, and solvate formation

item ZELAYA, CARLOS - University Of New Orleans
item STEVENS, EDWIN - University Of New Orleans
item Dowd, Michael

Submitted to: Structural Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/30/2009
Publication Date: 11/21/2009
Citation: Zelaya, C.A., Stevens, E.D., Dowd, M.K. 2009. Structural Chemistry. 6,6'-Dimethoxygossypol: molecular structure, crystal polymorphism, and solvate formation. 21:113-122.

Interpretive Summary: Low temperature x-ray diffraction was used to study the structure of four new solid-state forms of dimethoxygossypol, a natural product of the cotton plant. The x-ray diffraction patterns indicated that two of the forms are polymorphs and two of the forms are solvates. The results will be of interest to scientists working to develop products based on gossypol unusual ability to form inclusion complexes.

Technical Abstract: 6,6´-Dimethoxygossypol (DMG) is a naturally produced derivative of gossypol that is found in relatively high concentration in some Gossypium barbadense cotton varieties. Like gossypol, DMG forms an equimolar solvate with acetic acid, but it was not clear if, like gossypol, the compound would form clathrates with other solvents. Four new structures of DMG are reported in this work that includes two polymorphic and two solvated forms. The polymorphs include two monoclinic structures with P21/c and C2/c space groups. Packing of the DMG molecules in the P21/c structure is similar to packing of the gossypol molecules in the P1 polymorph of gossypol. The DMG molecules in the C2/c polymorph pack in a new highly-ordered arrangement not previously observed among these compounds. Solvates were formed with cyclohexanone and water; both with DMG-to-solvent ratios of 1:1. Both solvated forms are triclinic with P-1 space groups. The DMG molecules of DMG-cyclohexanone (1:1) assemble in a manner that is similar to the gossypol molecules of gossypol-cyclohexanone (1:1), and the DMG molecules of DMG-water (1:1) pack in a manner that is similar to the DMG molecules of DMG-acetic acid (1:1) as well as gossypol molecules in gossypol solvates formed with acetic acid and methanol. Although DMG is not as versatile of a host compound as gossypol, it still forms solvates under many conditions. Consequently, some care is needed to be sure that one understands exactly which form is present when the compound is isolated.