3-Aminohexahydro-2-oxo-1H-azepine-1-acetic acid (which can be prepared by the procedure of Thorsett, E. D. et al. J. Med. Chem. 1986, 29, 251-260; 9.3 g, 50 mmol) was added to a solution of sodium hydrogen carbonate (5 g, 60 mmol) in water (100 mL). A solution of 1-[[(9H-fluoren-9-ylmethoxy)carbonyl]oxy-2,5-pyrrolidinedione (Fmoc-OSu; 18.6 g, 55 mmol) in tetrahydrofuran (110 mL) was added. The solution was stirred at room temperature overnight and then ether (200 mL) was added. The layers were separated and the organic layer was back-extracted with saturated sodium hydrogen carbonate-water (1:1; 60 mL). The combined aqueous layers were acidified with 1 M HCl (110 mL). The solid was filtered off, washed with water (4×20 mL), and dried in vacuo to give 3-[[(9H-fluoren-9-ylmethoxy)carbonyl]amino]hexahydro-2-oxo-1H-azepine-1-acetic acid (20.1 g, 98%) as a white solid, mp 118° C. (dec.)
