Synthesis of multiacyl poly(ethylene glycol) for the conjugation of cytochrome c to phospholipid vesicle

To conjugate water-soluble macromolecules on the surface of phospholipid ve sicles, we synthesized a poly(ethylene glycol) (PEG)-lipid having four acyl chains using a lysine (Lys)-type monodendron structure. One end of the dia mino-PEG was amidified with Lys, and then two amino groups of the Lys moiet y were amidified with two Lys derivatives which had been acylated with two stearoyl groups. The other end of the PEG was activated with a triazine gro up or a pyridyldithio group. The hydrate of the lipid mixture of dipalmitoy lphosphatidylcholine, cholesterol, dipalmitoylphosphatidylglycerol, and the PEG-lipid at a molar ratio of 5/5/1/0.3 was extruded in order to prepare t he phospholipid vesicles with the average diameter of 270 +/- 20 nm. The co upling ratio of cytochrome c with the PEG-lipid was monitored by HPLC, dete cting the pyridyl 2-thione liberated from the pyridyldithio group and deter mining it to be 26% on the basis of the incorporated PEG-lipid.