Heterobifunctional PEGs: efficient synthetic strategies and useful conjugation methodologies.

The desire to develop nanoparticle and liposomal formulations as drug carriers capitalizing on active transport mechanisms requires constant development of novel heterobifunctional polyethyleneglycol (PEG) constructs. Such constructs should be capable of sequentially reacting with extracellular binding ligands and structural components of nanoparticles and/or liposomes. This paper describes two syntheses of heterobifunctional PEGs useful for tethering small molecule ligands to synthetic lysine-bearing polymers.