To a 50-mL round-bottom flask purged and maintained with an inert atmosphere of nitrogen and containing a solution of 2-[(12R)-3-[(4-[[(tert-butoxy)carbonyl]amino]cyclohexyl)oxy]-8-thia-4,6-diazatricyclo[7.4.0.0[2,7]]trideca-1-(9),2(7),3,5-tetraen-12-yl]acetic acid (98 mg, 0.21 mmol, 1.00 equiv) in 4 mL of DMF was added NH4Cl (68 mg, 1.27 mmol, 6.00 equiv), EDCI (61 mg, 0.32 mmol, 1.50 equiv), 4-dimethylaminopyridine (39 mg, 0.32 mmol, 1.50 equiv) and HOBt (43 mg, 0.32 mmol, 1.50 equiv) successively. The resulting solution was stirred overnight at room temperature and quenched with water and extracted with 3×50 mL of ethyl acetate. The combined organic layers were washed with brine, dried over anhydrous sodium sulfate and concentrated under vacuum. The residue was applied onto a silica gel column with ethyl acetate/petroleum ether (2:1) to give tert-butyl N-(4-[[(12R)-12-(carbamoylmethyl)-8-thia-4,6-diazatricyclo[7.4.0.0[2,7]]trideca-1(9),2(7),3,5-tetraen-3-yl]oxy]cyclohexyl)carbamate (72 mg, 74%) as a white solid.
