Synthesis of carboxyacyl derivatives of phosphatidylethanolamine and use as an efficient method for conjugation of protein to liposomes.

Carboxyacyl derivatives of phosphatidylethanolamine with different chain length were synthesized. These compounds were generally prepared by conversion of an appropriate dicarboxylic acid to its anhydride with dicyclohexylcarbodiimide, then reaction with phosphatidylethanolamine (PE) and triethylamine, followed by acidification. These derivatives, when incorporated into liposomes, were highly efficient in conjugating protein to liposomes. Liposomes with PE amide derivative incorporated were activated with water-soluble carbodiimide, and subsequently reacted with protein. The protein to lipid coupling efficiency was shown to be dependent on the chain length of the derivative, and the optimum coupling efficiency was achieved with PE amide of 1,12-dodecanedicarboxylic acid. Up to 60% covalent coupling efficiency of mouse IgG to liposomes was demonstrated with little non-covalent binding. This method will be of great importance in the liposome-targeting field.