To a stirred solution of L-prolin-N-(2-(tert-butyloxycarbonylaminomethyl)-5-chlorobenzyl)amide (0.026 g, 0.07 mmol), (2R,3R)-3-[3-(tert-butoxycarbonyl)phenyl]-2-hydroxy-3-pyridin-2-ylpropanoic acid from step 6 (20 mg, 0.058 mmol), and HOBT hydrate (12 mg, 0.087 mmol) in DMF (1 mL) was added EDC (0.017 g, 0.087 mmol). Diisopropylethylamine (0.0122 mL, 0.07 mmol) was added and the mixture was stirred at ambient temperature for 3 days, at which time HPLC analysis indicated complete consumption of the proline starting material. The DMF was removed under reduced pressure and the residue was partitioned between EtOAc (50 mL) and 10% aqueous Na2CO3 (20 mL). The EtOAc layer was separated, dried over anhydrous MgSO4, and filtered. The filtrate solvent was removed under reduced pressure and the residue was purified by preparative HPLC on a Waters PrepPak using 10% to 100% CH3CN:H2O with 0.1% TFA as eluant over 60 min. The product-containing fractions were combined and the acetonitrile was removed under reduced pressure. The remaining aqueous solution was basicified with saturated aqueous NaHCO3, extracted with 4×20 mL CH2Cl2, dried over Na2SO4 and filtered. The filtrate solvent was removed under reduced pressure to give 1-((2R,3R)-3-(3-tert-butyloxycarbonylphenyl)-3-(2-pyridyl)-2-hydroxypropanoyl)-N-(2-tert-butyloxycarbonylaminomethyl-5-chlorobenzyl)-L-prolinamide an oil (0.018 g, 45%). HPLC RT=2.54 min, method B; LC-MS M+H=693, 695.
