To a solution of (R)-3-[N-(5′-chloro-2′-fluorobiphenyl-4-ylmethyl)-N′-(3-methoxyisoxazole-5-carbonyl)hydrazino]-2-hydroxypropionic acid (40.0 mg, 0.1 mmol) in acetone (1.0 mL, 14 mmol) was added bromomethyl acetate (16.9 μL, 172 μmol) followed by Et3N (24.0 μL, 172 μmol), and resulting mixture was stirred for 90 minutes. The reaction was quenched with AcOH (19.6 μL, 345 μmol) and the mixture was concentrated. The residue was dissolved in AcOH (3 mL), filtered, and purified by reverse phase preparative HPLC. The desired fractions were combined and lyophilized. The solid was dissolved in AcOH (1.5 mL), filtered, and purified by reverse phase preparative HPLC to yield the title compound (14.3 mg, purity 97.8%) as a TFA salt. MS m/z [M+H]+ calc'd for C24H23ClFN3O8, 536.12. found 536.2.
