(S)—N-(5-Amino-1-hydroxymethyl-pentyl)-4-cyano-N-isobutyl-benzenesulfonamide (6) obtained in the previous reaction was dissolved in 50 mL CH2Cl2. BOP (1.2 eq), and triethylamine (5 eq) were added. After 10 minutes, (S)-2-methoxycarbonylamino-3,3-diphenyl-propionic acid (1 eq) was added and the mixture was stirred at RT for 3 hours. LCMS indicated a complete reaction. The reaction mixture was washed with sat. NaHCO3. The aqueous phase was washed again with 100 mL CH2Cl2. The combined organic layers where dried with MgSO4, filtered over dicalite and evaporated to dryness. The residue was purified by column chromatography with CH2Cl2-MeOH(NH3) (97:3). The appropriate fraction was evaporated to dryness. (1.31 g, 84% yield over 2 steps)
