Isolation of 6-methoxy gossypol and 6,6'-dimethoxy gossypol from Gossypium barbadense Sea Island cotton.

6-methoxy gossypol and 6,6'-dimethoxy gossypol were isolated from the seeds and root bark of a St. Vincent Sea Island variety of cotton (AZK-267, GRIN# PI 528406). Crude mixtures of gossypol and the methoxy compounds were obtained by extraction of the tissue with acetone and precipitation with acetic acid. After recrystallization, the preparations were treated with 3-amino-1-propanol to form gossypol Schiff's bases, which were separated by preparative reverse phase chromatography. The separated Schiff's bases were then hydrolyzed with acid, extracted into diethyl ether, concentrated, and precipitated with acetic acid. From the above procedure, both methoxy gossypol compounds were obtained as 1:1 molar acetic acid solvates. Each compound was prepared in sufficient amounts to determine its physical properties and begin testing for bioactivity. Light absorbance differed significantly for the di-3-amino-1-propanol derivatives of gossypol and the methoxy gossypol compounds at 254 nm. Relative response factors were developed, which can be used for determining or correcting analytical measurements of these methylated gossypol forms.