Methyl iodide → Valsartan Impurity 92

Participants

Reaction Steps

2 g (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-a, R1=Boc, R2=H, R3=CO2H), ratio of diastereomers of 80:20 ratio, respectively, prepared according to Example 3 in WO/2008/031567, is added to 2.55 g caesium carbonate. Dimethylformamide (4 ml) is then added. Methyl iodide (0.55 ml) is then added and the mixture is stirred for 16 h at room temperature. Water (10 ml) and isopropyl acetate (10 ml) are added. The phases are separated. The aqueous phase is washed with isopropyl acetate (2×10 ml). The combined organic phases are washed with 20% aqueous sodium chloride solution (15 ml) and then dried (MgSO4). The mixture is concentrated under reduced pressure to afford (2R,4S)-5-biphenyl-4-yl-4-tert-butoxycarbonylamino-2-methylpentanoic acid methyl ester (1-a, R1=Boc, R2=H, R3=CO2Me) and (2S,4S)-5-biphenyl-4-yl-4-tert-butoxycarbonylamino-2-methylpentanoic acid methyl ester (1-a, R1=Boc, R2=H, R3=CO2Me) as an 80:20 mixture of diastereomers, respectively. 1H NMR (CDCl3): 1.17-1.20, 1.25-1.26, 1.41, 1.46-1.63, 1.76-1.85, 1.92-1.99, 2.51-2.59, 2.61-2.71, 2.76-2.85, 3.70, 3.83-3.99, 4.09-4.40, 7.25-7.28, 7.33-7.37, 7.43-7.47, 7.53-7.55, 7.59-7.61. Ratio of diastereomers 80:20 (1-a, R1=Boc, R2=H, R3=CO2Me:1-b, R1=Boc, R2=H, R3=CO2Me) by integration of signals at 1.76-1.85 (1-b, R1=Boc, R2=H, R3=CO2Me) and 1.92-1.99 (1-a, R1=Boc, R2=H, R3=CO2Me).

Provenance & Evidence