Ethanol → (2R,4S)-2-methyl-4-((2-methylpropan-2-yl)oxycarbonylamino)-5-(4-phenylphenyl)pentanoic acid

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Reaction Conditions

Reaction Steps

10 g (2R,4S)-5-biphenyl-4-yl-4-tert-butoxycarbonylamino-2-methylpentanoic acid (3-a, R1=BOC, R2=R3=H) are added to ethanol (100 ml). The mixture is heated to 65° C. 2 ml of concentrated sulphuric acid is then added over 0.5 h. The mixture is then stirred overnight. The ethanol is removed and heptane added. Further azeotropic distillations are performed using heptane to remove any residual ethanol. The solvent is removed in vacuo to afford (2R,4S)-4-amino-5-biphenyl-4-yl-2-methylpentanoic acid ethyl ester hydrogen sulphate (3-a, R1=R2=H, R3=Et). 1H NMR (DMSO): 1.12 (6H), 1.56 (1H), 1.87 (1H), 2.67 (1H), 2.78 (1H), 2.98 (1H), 3.76 (2H), 7.34 (3H), 7.47 (2H), 7.64 (4H), 8.57 m/z (ES+) 312 ([MH]+, 100.

Provenance & Evidence