Stereoselective interaction between gossypol and rat plasma

Gossypol, a potential male oral contraceptive, is chiral and chemically reactive. The present study was done to learn more about the stereoselective activity of this drug. The isomers were equipotent in hemolyzing erythrocytes in protein-free buffer while (+) gossypol was a more potent hemolysin than (-) in plasma. Both isomers disappeared from buffer at the same rate while (-) disappeared from plasma much faster than (+). Treating plasma with aspirin or DNFB to react with the free amino groups on the protein, slowed the disappearance of (-) gossypol. We conclude that (-) gossypol binds to free amino groups on protein and this stereoselective protein binding may account for some of the pharmacokinetic or pharmacodynamic difference between the two isomers of gossypol.