A New N-Acetylgalactosamine Containing Peptide as a Targeting Vehicle for Mammalian Hepatocytes Via Asialoglycoprotein Receptor Endocytosis

Galactoside-containing cluster ligands have high affinity for asialoglycoprotein receptors (ASGP-r), which are found in abundance in mammalian parenchymal liver cells. These ligands may be conjugated with a therapeutic drug to improve the efficiency of delivery to diseased liver cells. This report describes a new synthetic route towards clustering glycopeptides containing N-acetyl-D-galactosamine (GalNAc). The building block Fmoc-α-(ah-Ac3GalNAc)-Lglutamate allowed access to the target compound YEEE(α-ah-GalNAc)3, a structural mimic of YEE(ah-GalNAc)3, via solid phase peptide synthesis (SPPS). Fatty acid, poly-lysine, fluorescein and biotin conjugates further demonstrate the facility of the described method. Using fluorescein labeling and 131I labeling, in vitro and in vivo assays confirmed that YEEE(a-ah-GalNAc)3 possesses both specificity and affinity to the liver, similar to the agent YEE(ah-GalNAc)3, which targets liver lesions. The synthesis described in this report represents a considerable improvement in synthesizing a ligand for ASGP-r by simplifying both the preparation of the starting material and the procedure for conjugating the galactosidase cluster to drugs.