(S)-{[4-(tert-Butoxycarbonylamino-methyl)-cyclohexylmethyl]-amino}-phenyl-acetic acid tert-butyl ester (290 mg, 0.9 mmol) and 6-formyl-benzo[b]thiophene-2-carboxylic acid (1-isobutoxy-ethoxy) amide (Scheme 7) (255 mg, 0.8 mmol) were stirred in DCE (8 ml) for 30 min. Acetic acid (4 ul, 0.08 mmol) and sodium triacetoxyborohydride (504 mg, 2.4 mmol) were added and the reaction mixture was stirred at r.t. for 1 h30. DCM (5 ml) and a saturated solution of NaHCO3 (10 ml) were added and phases were separated. The aqueous phase was extracted with EtOAc (15 ml). The organics were dried over magnesium sulfate, filtered and concentrated under vacuum. The crude product (543 mg) was purified on column chromatography (5 to 10% MeOH in DCM) to yield the expected pure product (172 mg, 34% yield). LCMS purity 100%, m/z 638 [M++H]+.
