Isopropyl Acetate → (2r,4s)-5-Biphenyl-4-yl-4-tert-butoxycarbonylamino-2-methylpentanoic acid potassium salt

100 mg (R)-5-Biphenyl-4-yl-4-tert-butoxycarbonylamino-2-methylenepentanoic acid potassium salt (2-a, R1=Boc, R2=H, R3=CO2K) (prepared according to procedure in Example 42) is added to isopropyl acetate (1 ml). 5% Rhodium on carbon (10 mg) is then added. Hydrogen gas at ambient pressure is applied to the mixture. The mixture is stirred at ambient temperature and pressure overnight. The mixture is then filtered over Celite and washed with isopropyl acetate (2×1 ml). The mixture is then concentrated in vacuo to give (2R,4S)-5-biphenyl-4-yl-4-tert-butoxycarbonylamino-2-methylpentanoic acid potassium salt (1-a, R1=Boc, R2=H, R3=CO2K) and (2S,4S)-5-biphenyl-4-yl-4-tert-butoxycarbonylamino-2-methylpentanoic acid potassium salt (1-b, R1=Boc, R2=H, R3=CO2K). Spectroscopic data as in Example 42, Method 1.