The resulting mixture was stirred at r.t. for 5 min. Compound 3 (10 mg, 0.028 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. The solvent was evaporated under reduced pressure to give the corresponding crude which was purified by HPLC using a gradient of 5% to 95% v/v acetonitrile with 0.01% aqueous solution of formic acid over 15 min to yield the final compound as a yellow solid. Yield: 25 mg, 0.026 mmol (95% To a solution of the Boc-deprotected carboxylic acid derivative of compound 6b (obtained as described in ref. ) (23.88 mg, 0.028 mmol, 1 eq.) in DMF dry (0.5 mL), HATU (10.64 mg, 0.028 mmol, 1 eq.) and HOAT (3.81 mg, 0.028 mmol, 1 eq.) were added. The solution was stirred for 5 min, compound 3 (10 mg, 0.028 mmol, 1 eq.) was added and the pH of the reaction was adjusted to >9 with DIPEA. The mixture was stirred at r.t. until no presence of the starting materials was detected by LC-MS. 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 with 0.01% aqueous solution of ammonia over 10 min to yield the final compound as a white solid (24 mg, yield: 84%). ¹H-NMR (500 MHz, CDCl 3 ) δ 8.70 (s, 0. 58.8, 57.0, 56.9, 48.9, 43.2, 41.9, 38.4, 38.3, 36.5, 35.4, 35.3, 31.5, 26.4, 22.7, 15.