was added followed by DMAP (0.107 g 0.874 mmol 0.2 eq.) and 4-methyl morpholine (0.885 g 8.75 mmol 2 eq.). The mixture was left to react at room temperature for 5.0 h. The reaction solution was further treated with 18 mL of TFA for 30 min at room temperature to remove the Boc protecting group. The crude product was obtained by double precipitation from cold diethyl ether and dry dried under vacuum. (0.93 g, 3.7 mmol, 93%). The yield of the obtained product is 93 % (0.93 g).