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United States Department of Agriculture

Agricultural Research Service

Title: Crystal and Molecular Structure of An Isomeric Gossypol-Acetic Acid Clathrate

Authors
item Dowd, Michael
item Thomas, Leonard - IOWA STATE UNIVERSITY
item Calhoun, Millard - TEXAS AG EXPERIMENT STAT

Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 2, 1999
Publication Date: N/A

Interpretive Summary: Research conducted by scientists at the USDA, ARS, SRRC in New Orleans, LA indicates that a crystalline form of gossypol can be used to separate the two isomers into separate crystals. In many cases, it is difficult to separate the biologically active form from the inactive forms. This is believed to be the case for gossypol, a compound from cottonseed that is responsible for the toxicity of cottonseed products but also has male anti-fertility, anti-viral, and anti-cancer properties. The compound exists in two isomeric forms, and preliminary studies suggest that the important physiological properties are associated with only one of the forms. Preparing samples of the individual gossypol isomers has been a difficult problem. Previous methods were time consuming, multi-step procedures that produced product in low yield. Samples can now be prepared by selecting individual crystals, determining the isomeric form of each crystal, and combining the crystals of each form. These samples are needed for medicinal research, and the results will be of particular interest to researchers working toward understanding gossypol's anti-cancer and male anti-fertility properties.

Technical Abstract: Single crystals of gossypol with three molecules of acetic acid (gossypol triacetic acid) were grown from solutions of gossypol acetic acid and acetone. The crystals were unstable in air but could be stabilized for x-ray diffraction analysis by coating the crystal surfaces with a thin layer of mineral oil. The gossypol triacetic acid complex (C30H30O8/3C2H4O2) forms an orthorhombic crystal system with P212121 (Z = 4) symmetry. Unit cell dimensions were a = 9.0208(7) A b = 17.4884(10) A and c = 24.358 (2) A yielding a volume of 3842.7(5) A3and a density of 1.2077(2) g/cm3 As with all previously reported crystals of gossypol, the gossypol molecules were of the aldehyde tautomer, and the two planar naphthalene rings were approximately perpendicular. Acetic acid molecules were found to lie in channels within the gossypol matrix. As indicated by the symmetry of the P212121 space group, individual crystals contained only one gossypol isomer. However, both isomers crystallized from the acetone solution. The ability to grow large, non-racemic, crystals leads to a simple procedure for separating small quantities of the individual gossypol isomers.

Last Modified: 7/27/2014
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