Sodium borohydride → (3S)-N-[N-[3-[[(t-Butyloxy)carbonyl]amino]-2-hydroxy-4-phenylbutyl]-L-phenylalanyl]-L-leucine, t-butyl ester

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A solution of (3S)-N-[N-[3-[[(t-butyloxy)carbonyl]amino]-2-oxo-4-phenylbutyl]-L-phenylalanyl]-L-leucine, t-butyl ester (1.46 g, 2.45 mmol) in 15 ml of methanol was cooled to 0° C. Sodium borohydride (93 mg, 2.45 mmol) was added in portions over 5 minutes. After 15 minutes, the solvent was evaporated. The residue was taken up into ethyl acetate (100 ml), washed with water, dried (sodium sulfate) and evaporated to give 1.14 g of a slightly yellow gum. This material was combined with 1.73 g of material similarly prepared. The combined material (2.87 g) was purified by flash chromatography on 215 g of Merck silica gel (230-400 mesh), eluting with hexane-ethyl acetate (1.5:1), to give 2.11 g of the title compound as a colorless oil; TLC: Rf =0.19, 1.25:1 hexane-ethyl acetate.

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