To a solution of peptide (0.03 mmol), bifunctional EBX reagent 1b (0.033 mmol, 1.1 equiv.) in DMF (1.5 mL), DIPEA (10 μL, 0.060 mmol, 2 equiv.) was added into the solution (concentration: 20 mM) and the mixture was stirred for 20 min without protection of atmosphere or light. For the isolation, the crude was subjected to Prep-HPLC without dilution, followed by lyophilization.