The peptide (TSP) 4 is an efficient substrate for GalNAc transferase 1 . To localize the active site of GalNAc transferase. Biotin-(TSP)4-Lys(ASA)-G was prepared by on-line solid phase synthesis using Fmoc strategy The new protecting group, 1-(4,4-dimethyl-2,6-dioxocyclohexy-1-ylidene)ethyl (Dde) was used as a temporary protecting group for N -lysine The bi-derivatized peptide was characterized by mass spectrometry and FTIR spectrometry. This strategy can be generalized to other bi-denvatized peptides synthesized for ligand-receptor studies