Triethylamine (21 μL), 1-hydroxybenzotriazole (9 mg) and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (28 mg) were added to a solution of N-tert-butoxycarbonyl-4-[2-(tert-butoxycarbonylamino)ethyl]-L-Proline (48 mg) and trans-4-((R)-2-hydroxy-4-phenylbutyrylamino)-L-proline 3-quinolylamide (Compound D101 (H), 56 mg) in dichloromethane (3 mL) at 0° C. The mixture was stirred at room temperature overnight. The reaction mixture was diluted with chloroform and washed with saturated sodium hydrogen carbonate and brine. The organic layer was dried over anhydrous sodium sulfate and evaporated in vacuo. The residue was purified by preparative silica gel thin layer chromatography (chloroform:methanol=12:1, v/v) to give the title compound (47 mg) as a colorless foam: 1H NMR (400 MHz, CDCl3) δ 1.40 (s, 9H), 1.48 (s, 9H), 1.71 (m, 2H), 1.99 (m, 1H), 2.13-2.51 (m, 6H), 2.75 (m, 2H), 3.16 (m, 2H), 3.63 (m, 1H), 3.73 (m, 1H), 3.87 (m, 1H), 3.90 (m, 1H), 4.38 (m, 1H), 4.53 (m, 1H), 4.80 (m, 1H), 4.82 (m, 1H), 5.50 (m, 1H), 7.15-7.64 (m, 9H), 7.68 (m, 1H), and 8.54 (m, 2H).
