To 2-(4-amino-phenyl)-1-cyclobutyl-6-ethylsulfanyl-1H-indole-3-carbonitrile (230.0 mg, 0.66 mmol) was combined with p-nitrophenyl chloroformate (266 mg, 1.32 mmol), DCE (3.0 mL), and pyridine (104.7 mg, 1.32 mmol) and stirred at room temperature for 2 h. (R)-1-Cyclopropylethanol (115.0, 1.34 mmol) was added and mixture was heated at 80° C. for 2 h. The reaction mixture was diluted with EtOAc and washed with sat. aq. K2CO3 (2×15 mL), water, and brine. The organic layer was dried, concentrated and purified on silica gel (EtOAc/hexane 10%)) to provide (R)-[4-(3-cyano-1-cyclobutyl-6-ethylsulfanyl-1H-indol-2-yl)-phenyl]-carbamic acid 1-cyclopropyl-ethyl ester (209 mg, 69%) as a white solid.
