To (S)-[(3-Amino-benzyl)-tert-butoxycarbonyl-amino]-phenyl-acetic acid cyclopentyl ester (0.317 g, 0.75 mmol) was added 6-Formyl-benzo[b]thiophene-2-carboxylic acid (1-isobutoxy-ethoxy)-amide (Scheme 7) (0.210 g, 0.65 mmol) in DCE (8 ml). 2 drops of glacial acetic acid were added, and then sodium triacetoxyborohydride (0.170 g, 0.8 mmol). The mixture was stirred for 2 h and then poured into DCM (150 ml). The solution was washed with saturated sodium bicarbonate (50 ml), then dried (MgSO4), concentrated and purified by flash column chromatography to yield the desired product as a pale yellow foam (0.346 g, 73% yield). 1H NMR (300 MHz, CDCl3), δ: 8.35-8.43 (1H, m), 7.56-8.05 (2H, m), 7.01-7.41 (8H, m), 6.90-7.01 (1H, m), 6.42 (1H, dd, J=2.6, 7.9 Hz), 5.25-5.31 (1H, m), 5.12 (1H, q, J=5.2 Hz), 4.40 (1H, d, J 5.4 Hz), 4.00 (1H, dd, J=3.1, 15.8 Hz), 3.60-3.70 (1H, m), 3.35-3.40 (1H, m), 1.33-1.94 (21H, m), 0.98 (3H, d, J=6.6 Hz), 0.97 (3H, d, J=6.6 Hz)
