Total and Percent Atropisomers of Gossypol and Gossypol-6-methyl Ether in Seeds from Pima Cottons and Accessions of Gossypium barbadense L

Gossypol occurs naturally in the seed, foliage, and roots of the cotton plant ( Gossypium ) as atropisomers due to restricted rotation around the binaphthyl bond. The atropisomers differ in their biological activities. (-)-(R)-Gossypol is more toxic and exhibits significantly greater anticancer activity than the (+)-(S)-atropisomer. Most commercial Upland ( Gossypium hirsutum ) cottonseeds have an (R)- to (S)-gossypol ratio of approximately 2:3, but some Pima ( Gossypium barbadense ) seeds have an excess of (R)-gossypol. There is no known source of cottonseed with an (R)- to (S)-gossypol ratio of greater than approximately 70:30. Cottonseed with a high percentage of (R)-gossypol would be of value to the pharmaceutical industry. It was theorized that G. barbadense cotton might be a source of this desirable high (R)-gossypol seed trait. There are 671 different accessions of G. barbadense in the U.S. Cotton Germplasm Collection, few of which had been characterized with respect to their (R)- to (S)-gossypol ratio. This work completed that analysis and found considerable variation in the atropisomer ratio. Approximately half of the accessions have an excess of (R)-gossypol, and 52 accessions have essentially a 1:1 ratio. The highest percentage of (R)-gossypol was found in accessions GB26 (68.2%) and GB283 (67.3%). Surprisingly, five accessions had 5% or less of (R)-gossypol: GB516 (5.0%), GB761 (4.5%), GB577 (4.3%), GB719 (3.7%), and GB476 (2.3%). These accessions may be useful in a breeding program to reduce (R)-gossypol in Pima seed, which is a concern to the dairy industry because of the toxicity and male antifertility activity of this atropisomer. Also, GB710 was devoid of gossypol.