A solution of 4-(aminomethyl)-1-(tert-butoxycarbonyl)piperidine (5.72 g) in CH2Cl2 (150 mL) was treated with Et3N (3.51 g), N-(9-fluorenylmethyloxycarbonyl)glycine (7.93 g, 26.7 mmol), EDCI (3.80 g) and HOBt (4.33 g). After the reaction mixture was stirred at room temperature for 5 h, the mixture was washed with water (100 mL×3) and brine (100 mL×2), dried over anhydrous sodium sulfate, filtered, and concentrated. Recrystallization from CH3CN/CH3OH (150 mL/1 mL) at 0° C. afforded 1-(tert-Butoxycarbonyl)-4-[{N-(9-fluorenylmethyloxycarbonyl)glycyl}aminomethyl]piperidine (5.75 g, 44%) as pale yellow crystals.
