The condensation of doxorubicin (I) with Fmoc-beta-alanyl-L-leucyl-L-alanyl-L-leucine (II) by means of HATU and DIEA in DMF gives the protected adduct (III), which is treated with piperidine in DMF to yield the deprotected adduct (IV). Finally, this compound is condensed with succinic anhydride (V) in the same solvent and treated with NaOH or NaHCO3 to afford the target sodium salt.