Submitted to: Proceedings of American Chemical Society National Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 2/15/2005
Publication Date: 3/13/2005
Citation: Dowd, M.K., Stevens, E.D. 2005. Crystal and molecular structures of gossypol-cycloheptanone (1:2) and gossypol-cyclooctanone (1:2) (abstract). 2005 229th American Chemical Society National Meeting, March 13-17, 2005, San Diego, CA. p. 67.
Technical Abstract: Gossypol is a polyphenolic terpenoid that is found in many tissues of the cotton plant. The compound is unusual in that it forms inclusion complexes with many small molecular weight molecules. In this work, the structures of gossypol inclusion compounds formed with cycloheptanone and cyclooctanone were solved by x-ray diffraction at -120 degrees C. Both structures crystallize in monoclinic systems with C2/c space groups. Unit cell dimensions are a =15.610(2) Å, b = 14.142(2) Å, c = 18.440(3) Å, and beta = 107.961(2)degrees for the cycloheptanone complex; and a = 15.634(2) Å, b = 13.380(2) Å, c = 20.607(3) Å, and beta = 109.666(4)degrees for the cyclooctanone complex. The structures were solved to R1 values (on the observed data) of 0.0436 and 0.0764, respectively. The cyclooctanone structure exhibited disorder among the gossypol isopropyl moieties, with the methyl groups pointed both outward (58% occupancy) and inward (42% occupancy). The asymmetric unit of each structure consists of one-half gossypol molecule and one ketone molecule (i.e., the gossypol-to-ketone molar ratio is 1:2). Hydrogen bonds are formed between the cycloketone carbonyl oxygen atom and the gossypol C-1 and C-1' hydroxyl hydrogen atoms. A second intermolecular hydrogen bond is present between the terminal O-3 and O-4 hydroxyl groups of adjacent gossypol molecules. These hydrogen bonds tie the gossypol molecules into chains that run parallel to the a-axis. Neighboring chains align to form layers. Each layer is composed of gossypol molecules of the same enantiomer, with adjacent layers composed of the opposite enantiomer. The guest molecules reside between the layers, interacting with the gossypol and ketone molecules of the adjacent layer through van der Waals contacts. The structures represent a new family of gossypol inclusion compounds.