To a solution of compound 5a (59.83 mg, 0.22 mmol, 1 eq.), in 1.5 mL DMF, HATU (81.74 mg, 0.22 mmol, 1 eq.), HOAT (29.26 mg, 0.22 mmol, 1 eq.) were added and the solution was stirred at r.t. for 5 min. Compound 1 (100 mg, 0.215 mmol, 1 eq.) was added and the pH of the reaction mixture was adjusted to >9 by addition of DIPEA (~ 3 eq.). The mixture was stirred at r.t. until no presence of the starting materials was detected by LC-MS (acidic method). Water was added and the mixture was extracted with ethyl acetate (×3). The combined organic phases were washed with brine (×2), dried over MgSO 4 and evaporated under reduced pressure to give the corresponding crude which was purified by HPLC using a gradient of 20% to 95% v/v acetonitrile in 0.01% aqueous solution of ammonia over 10 min to yield the final compound (72.8 mg, yield: 51%