Acetic Acid → 4-[(2S)-(2-amino-2-cyanoethyl)]-3-fluorobenzonitrile

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A solution of 4-{2-cyano-2-[(diphenylmethylene)amino]ethyl}-3-fluorobenzonitrile from step 2 (24.5 g) in tetrahydrofuran (190 ml) is treated with water (45 ml) then with acetic acid (90 ml) and let stir for 24 h at 40° C. Approximately 75% of the volatiles were then removed under reduced pressure. The residual solution is diluted with water (100 ml) and 1 N hydrochloric acid (25 ml), extracted with 2 portions (100 ml each) of diethyl ether then was made basic with 8N potassium hydroxide and aqueous potassium phosphate until pH 9-10 was reached. The aminonitrile was extracted with three portions (300 ml each) of ethyl acetate. The pooled organic layers were washed with brine, dried over sodium sulfate and concentrated under reduced pressure. The orange product gum was dissolved in ethanol (20 ml) and diluted with hexanes (20 ml). Aliquots of 500 mg were injected on chiralcel AD column using 50% ethanol:50% hexanes isocratic conditions. The faster nitrile is the wrong enantiomer (Rt=19 min) while after evaporation and coupling (step 4) the slower enantiomer (t=24 min) will lead to the potent diastereomer of the (2S)—N-[(1S)-1-cyano-2-(4-cyano-2-fluorophenyl)ethyl]-4-fluoro-4-methyl-2-({1(S)-2,2,2-trifluoro-1-[4′-(methylsulfonyl)biphenyl-4-yl]ethyl}amino) pentanamide that is assumed to be of S configuration.

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