20 mg (R)-5-Biphenyl-4-yl-4-tert-butoxycarbonylamino-2-methylenepentanoic acid (2-a, R1=Boc, R2=H, R3=CO2H) is added to ethanol (400 μl). 10% Palladium on carbon (2 mg, 50% water wet, Degussa type E101 NE/W) 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 ethanol (2×0.5 ml). The mixture is then concentrated in vacuo to give (2R,4S)-5-biphenyl-4-yl-4-tert-butoxycarbonylamino-2-methylpentanoic acid (1-a, R1=Boc, R2=H, R3=CO2H) and (2S,4S)-5-biphenyl-4-yl-4-tert-butoxycarbonylamino-2-methylpentanoic acid (1-b, R1=Boc, R2=H, R3=CO2H). 1H NMR (CDCl3): 1.11-1.16, 1.21 and 1.33, 1.39-1.53, 1.70-1.92, 2.32-2.81, 3.72-3.97, 4.44-4.50, 6.41 and 6.56, 7.16-7.49, 10.84.
