Ethyl Acetate → N~2~-[(2S)-1-Ethoxy-1-oxo-4-phenylbutan-2-yl]-N~6~-(trifluoroacetyl)-L-lysine

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Reaction Steps

10 g of crude N2-[1-ethoxycarbonyl-3-phenylpropyl]-N6-trifluoroacetyl-L-lysine rich in 1S-isomer (the molar ratio of the 1S- to the 1R-isomer was 80:20) was suspended in 10-fold volume mixed solutions of 80 ml of ethyl acetate and 20 ml of n-hexane. 1.46 g (0.5 eq.) of oxalic acid monohydrate was added, and the reaction mixture was stirred at room temperature for 24 hrs. The reaction mixture was filtered, and the filtrate was concentrated to dryness under reduced pressure at a temperature lower than 40° C. The filtered cake was dissolved in 80 ml water, and 1N sodium hydroxide solution was added to adjust the pH value to 4.0 to 6.0. The solution was cooled to 0 to 5° C., and stirred for 3 hrs. After filteration, and the solid was dried in vacuum at a temperature lower than 40° C. to give 5.8 g of pure N2-[1-(S)-ethoxycarbonyl-3-phenylpropyl]-N6-trifluoroacetyl-L-lysine. The yield is 58%, and the molar ratio of the 1S- to the 1R-isomer is 99.0:1.0.

Provenance & Evidence