A solution of racemic (2′S, 3S, 4′R)-6-chloro-4′-[5-chloro-2-(1-ethyl-1-hydroxycarbonyl-propoxy)-phenyl]-2′-(5-fluoro-2-methyl-phenyl) spiro[3H-indole-3,3′-piperidine]-2,6′(1H)-dione (30 mg, 0.05 mmol) and CDI (20 mg, 0.12 mmol) in DMF (1 mL) was heated at 60° C. for 2 h. Then to this solution was added a mixture of methanesulfonamide (28 mg, 0.3 mmol) and NaH (12 mg, 60%, 0.3 mmol) in DMF (1 mL), which had been stirred for 2 h at room temperature. After the resulting mixture was stirred at room temperature for 1 h, it was poured into water and the aqueous solution was acidified to “pH” 1-2 by addition of concentrated HCl solution. The aqueous phase was extracted with EtOAc twice, The combined organic phases were dried over anhydrous Na2SO4, concentrated and the residue was purified by flash column to give the title compound as a white solid (10 mg).
