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

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Reaction Steps

10 g (2S,4S)-4-amino-5-biphenyl-4-yl-2-methylpentanoic acid ethyl ester hydrochloride (3-a, R1=R2=H, R3=Et) in isopropyl acetate (50 ml) is added to a mixture of pivaloyl chloride (4.1 ml) in isopropyl acetate (50 ml). The mixture is then stirred for 40 min at room temperature. Triethylamine (10.3 ml) in isopropyl acetate (30 ml) is then added over a period of 1 h. The resulting mixture is stirred for 16 h. Citric acid (7.5 g) dissolved in water (30 ml) is added and the phases are separated. The organic phase is washed twice with water (30 ml) and concentrated in vacuo to give (2R,4S)-5-Biphenyl-4-yl-4-(2,2-dimethylpropionylamino)-2-methylpentanoic acid ethyl ester (3-a, R1=Piv, R2=H, R3=Et). 1H NMR (DMSO): 1.05 (9H), 1.09 (3H), 1.15 (3H), 1.54 (1H), 1.78 (1H), 2.48 (1H), 2.72 (2H), 3.97 (1H), 4.00 (2H), 7.15 (1H), 7.25 (2H), 7.34 (1H), 7.45 (2H), 7.55 (2H), 7.62 (2H).

Provenance & Evidence