To a solution of R-mandelic acid (60 mg, 0.39 mmol), N-[5-chloro-2-(1H-tetraazol-1-yl)benzyl]-L-prolinamide (Example 26, Step B, 120 mg, 0.39 mmol, HPLC RT=2.25 min, method A), and HOBt hydrate (60 mg, 0.39 mmol) in DMF (3 mL) was added EDC (98 mg, 0.51 mmol). Diisopropylethylamine was then added slowly in portions (˜0.05 mL total) to bring the pH of the solution to 6–7 as measured on wetted E. Merck pH indicator strips. The mixture was stirred at ambient temperature for 18 h, and the solvent was removed under reduced pressure. The residue was partitioned between EtOAc (50 mL) and saturated aqueous NaHCO3 (10 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 pressurized silica gel column chromatography using EtOAc as eluant. Product-containing fractions were combined and the solvent was removed under reduced pressure to give the title compound as an amorphous solid (TLC Rf=0.6 (EtOAc); HPLC RT=2.82 min, method A; LCMS m/z=441).
