To a solution of compound 3 (1.46 g, 2.86 mmol, 1 eq.) in DCM (20 mL), TFA (4 mL) was added. The mixture was stirred at room temperature for 2 h and the complete removal of tert-butyl group was monitored by HPLC. Afterwards, the mixture was dried in vacuo to offer the crude product for the next step. To a solution of the resulting crude product in anhydrous DMF (50 mL), tert-butyl (6bromohexyl)carbamate (1.20 g, 4.29 mmol, 1.5 eq.) and K2CO3 (0.790 g, 5.72 mmol, 2 eq.) were added.