A solution of (2R,4S)-4-amino-5-biphenyl-4-yl-2-methyl-pentanoic acid benzyl ester hydrochloride (100 mg, 0.287 mmol) and acetic acid (3S,4S)-4-acetoxy-2,5-dioxo-tetrahydro-furan-3-yl ester (0.431 mmol) in 1:1 methylene chloride/pyridine (1.4 mL) is stirred at room temperature for 24 hours. The solvents are removed under reduced pressure and obtained residue is used directly in the subsequent hydrolysis reaction. Next, a solution of the benzyl ester in ethyl acetate is hydrogenated at 1 atm over 10% Pd/C for 18 hours. Methanol is added and the catalyst is filtered through Celite. The Solvent is removed under reduced pressure and the residue is purified by preparative HPLC using a gradient of 10-100% MeCN/water (0.1% TFA). The proper fractions are lyophilized to furnish (2R,4S)-5-biphenyl-4-yl-4-((2S,3S)-2,3-diacetoxy-3-carboxy-propionylamino)-2-methyl-pentanoic acid. HPLC Retention time 0.95 minutes (condition A); MS 500.3 (M+1); 1H NMR (400 MHz, DMSO-d6) δ ppm 1.09 (d, J=7.20Hz, 3H), 1.45 (m, 1H), 1.82 (m, 1H), 2.39 (m, 1H), 2.70 (d, J=6.82Hz, 2H), 4.01 (m, 1H), 5.38 (m, 2H), 7.19 (d, J=8.21Hz, 2H), 7.34 (t, 1H), 7.45 (t, 2H), 7.53 (d, J=8.21Hz, 2H), 7.64 (d, J=7.20Hz, 2H), 8.00 (d, J=8.72Hz, 1H).
