Binding of gossypol derivatives to human serum albumin

In light of our previous finding that gossypol competes effectively with bilirubin for the high affinity bilirubin binding site on human serum albumin, a study of the binding to albumin of four gossypol derivatives was undertaken. The derivatives are compounds in which the aldehyde groups of gossypol are converted to nitriles and the periphenolic groups are acylated with acetyl, propionyl, butyryl, or valeryl groups. These periacylated gossylic nitriles bind to the high affinity bilirubin binding site on human serum albumin, but with dissociation constants approximately 30 times greater than that of gossypol. The gossypol derivatives also bind to another site on albumin, but with dissociation constants approximately 6 times greater than those for the bilirubin site. This second site has been identified as the major drug binding site in domain III.