4-Methylmorpholine → N-[(1,1-Dimethylethoxy)carbonyl]-L-alanyl-L-proline phenylmethyl ester

Participants

Reaction Steps

A solution of t-butoxycarbonyl-L-alanine (2.48 g., 13.1 mmole) in 23 ml. of dry chloroform at -15° (ice-salt bath) is treated with N-methylmorpholine (1.47 ml., 13.1 mmole) followed by isobutyl chloroformate (1.8 ml., 13.1 mmole) to give a precipitate. After 15 minutes, L-proline, phenylmethyl ester, hydrochloride salt (3.18 g., 13.1 mmole) and N-methylmorpholine (1.47 ml., 13.1 mmole) are added. Gas evolution ensues and the mixture is kept below -10° for one hour, then allowed to warm to room temperature, and stirred overnight under argon. The mixture is diluted with ethyl acetate, filtered, and the filtrate evaporated to dryness. The residue is taken up in ethyl acetate and washed successively with 5% potassium bisulfate, saturated sodium bicarbonate, saturated sodium chloride, dried (Na2SO4) and evaporated. The residue is purified by flash chromatography on silica gel (210 g.) eluting with ethyl acetate/hexane (1:2) to give t-butoxycarbonyl-L-alanyl-L-proline, phenylmethyl ester (4.37 g.) as a colorless oil; Rf (ethyl acetate/hexane, 1:1) is 0.47.

Provenance & Evidence