Extraction of daunorubicin and doxorubicin and their hydroxyl metabolites: self-association in aqueous solution.

The extraction of daunorubicin and doxorubicin and their hydroxyl metabolites daunorubicinol and doxorubicinol was studied using chloroform-1-pentanol (9:1) as the organic phase. Because of differences in acid dissociation constants, the pH for optimum extraction varied from 8.0 to 8.6 for the different compounds. Self-association in the aqueous phase significantly influenced the distribution ratio. Constants for the formation of dimers and tetramers in aqueous solutions were about 10(4.5) and 10(12), respectively.