benzyl(S)-11-Benzyl-1-(9H-fluoren-9-yl)-3,6,9,12,15-pentaoxo-2,18-dioxa-4,7,10,13,16-pentaazaicosan-20-oic acid (150 mg，0.2 mmol), methanol (8mL), and DMF (1mL) were added to the single-mouth bottle, and then Pd/C (45mg, 5%) was added for hydrogenation reaction for 2 hours. After filtration, 1.8 mL of diethylamine was added to the filtrate, and the mixture was stirred at room temperature for 2 hours. The crude product is obtained by reducing pressure concentration. Finally, (S)-11-Benzyl-1-(9H-fluoren-9-yl)-3,6,9,12,15-pentaoxo-2,18-dioxa-4,7,10,13,16-pentaazaicosan-20-oic acid was obtained after purification.
