Ammonium Chloride → Benzyl 2(S)-tert-butoxycarbonylamino-4(R)-hydroxy-5-nitropentanoate

Participants

Reaction Conditions

Reaction Steps

A solution of 11.3 g (30.8 mmol) of benzyl 2(S)-tert-butoxycarbonylamino-5-nitro-4-oxopentanoate in 300 ml of tetrahydrofuran is cooled to −78° C., 30.8 ml of a 1M solution of L-Selectrideo in tetrahydrofuran are added dropwise, and the mixture is stirred at −78° C. for 1 h. After warming to RT, a saturated ammonium chloride solution is cautiously added to the solution. The reaction solution is concentrated, and the residue is taken up in water and ethyl acetate. The aqueous phase is extracted three times with ethyl acetate. The combined organic phases are dried over sodium sulfate and evaporated. The crude product is prepurified on silica gel 60 (mobile phase: cyclohexane/ethyl acetate 10/1), and the collected fractions are concentrated and stirred with cyclohexane/ethyl acetate 5/1. The remaining crystals are collected by suction filtration and dried. 2.34 g (21% of theory) of the desired diastereomer are obtained. Chromatographic separation of the mother liquor on Lichrospher Diol 10 μm (mobile phase: ethanol/isohexane 5/95) results in a further 0.8 g (6.7% of theory) of the product.

Provenance & Evidence