100 mg (0.16 mmol) of phenyl [5-cyano-1-[(2,4-dimethoxyphenyl)sulphonyl]-3-(2-ethoxypyridin-3-yl)-2-oxo-2,3-dihydro-1H-indol-3-yl]carbamate (prepared according to Example 1, process steps 1a) to 1f)) were initially charged in 8 ml of anhydrous tetrahydrofuran (dried over molecular sieve), and 65.8 mg (0.24 mmol) of tert-butyl 4-piperidin-4-ylpiperazine-1-carboxylate were added. The mixture was then stirred at room temperature overnight. The progress of the reaction was monitored by TLC (silica gel, CH2Cl2/MeOH 9:1) and LCMS (RP, mobile phases acetonitrile/water and 0.01% TFA). The solvent was removed under reduced pressure, and the residue was taken up in dichloromethane and extracted with 2 N aqueous sodium hydroxide solution (1×). The combined organic phases were dried over magnesium sulphate and filtered, and the solvent was removed under reduced pressure. The crude mixture was purified by column chromatography (5 g NP-SiO2 cartridge, Chromabond) using dichloromethane/methanol in a ratio of 98:2 as mobile phase. This gave 55.3 mg (0.07 mmol, 43%) of the desired product, which was directly used in the next reaction step for Boc deprotection.
