6-formyl-benzo[b]thiophene-2-carboxylic acid (1-isobutoxy-ethoxy) amide (Scheme 7) (220 mg, 0.68 mmol) and (S)-2-(4-Aminomethyl-benzylamino)-3-phenyl-propionic acid cyclopentyl ester (263 mg, 0.75 mmol) were dissolved in DCE (10 mL) under an atmosphere of N2. Sodium triacetoxyborohydride (430 mg, 2.04 mmol) and acetic acid (50 μL) were added and the reaction stirred at r.t for 3 h. Sodium hydrogen carbonate (20 mL) was added and the reaction mixture extracted with dichloromethane (3×50 mL). The organic layers were combined and concentrated. The residue was purified by column chromatography (50%-100% EtOAc/heptane) to give the protected compound (80 mg, 21%). m/z 658 [M++H]+
